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VI. Helicopters A. B. C. D. E.
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions 12/09/09
A. B. C. D.
Controls Stabilizer Controls Vibrations Power Systems
Author: Harry L. Whitehead
1
Helicopters History
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
1483, DaVinci – Developed “Helix” – Kind of aerial screw – Shows basic understanding that the atmosphere can support weight but no provisions for torque on fuselage
12/09/09
Author: Harry L. Whitehead
2
Helicopters History
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
1800s, Forlanini (Italy) – Used steam engine – Counter-rotating “butterfly” wings – Could ascend (without pilot) to 40 feet for about 20 minutes
12/09/09
Author: Harry L. Whitehead
3
Helicopters History
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
1907, Cornu (France) – First piloted helicopter – Flew for few seconds – Used internal combustion engine – No controls but well balanced
12/09/09
Author: Harry L. Whitehead
4
Helicopters History
1909, Igor Sikorsky (Russia) – Small counter-rotating coaxial rotors – First use of airfoil shaped rotors
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
5
Helicopters History
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
1920s, Petroczy & Von Karmon (Austria) – Counter-rotating, coaxial, airfoil rotors – 3 40HP engines – No controls, just made to lift straight up
12/09/09
Author: Harry L. Whitehead
6
Helicopters History
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
1923, de Bothezat (U.S.) – 4 rotors – Complicated power transmission system – Low power – Several flights of 1 minute @ 6 feet
12/09/09
Author: Harry L. Whitehead
7
Helicopters History
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
1923, de la Cierva (Spain) – Developed Autogyro – Solved some control problems by allowing rotors to Flap
12/09/09
Author: Harry L. Whitehead
8
Helicopters History
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
1936, Focke-Wulfe (Germany) – FW-61 established endurance & speed records – Mostly flown by Hannah Reich – Flown inside stadium for most of records
12/09/09
Author: Harry L. Whitehead
9
Helicopters History
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
1939, Sikorsky (U.S.) – Developed VS-300 – Broke all FW-61 records – Used 3-bladed main rotor, vertical 2bladed tail rotor & 2 horizontal 2-bladed outrigger rotors for stability and control
12/09/09
Author: Harry L. Whitehead
10
Helicopters Configurations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Autogyros – Developed by de la Cierva – Uses free-spinning main rotor with airplane-like engine/prop for forward motion – No power to main rotor, spins from air action = can’t hover or ascend vertically
12/09/09
Author: Harry L. Whitehead
11
Helicopters Configurations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Dual Rotor – 2 counter rotating main rotors • No tail rotor needed • May be separate or coaxial – Used extensively through history, today few (Boeing, Kaman)
12/09/09
Author: Harry L. Whitehead
12
Helicopters Configurations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Single Rotor – Most used design – 1 main rotor for lift and control – Tail rotor for anti-torque • FAA calls it “Auxiliary Rotor” • More precisely known as “Anti-torque Rotor”
12/09/09
Author: Harry L. Whitehead
13
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Helicopters Hughes Helicopter ConfigurationsH-17 Skycrane
1952
Single Rotor
Function: transport Crew: 2 Engines: 1 * G.E. J35 Rotor Span: 130ft Length: Height: 30ft Disc Area: Empty Weight: Max.Weight: 46000lb Speed: Ceiling: Range: 65km Load: 25000lbs Hot Cycle Blades
12/09/09
Controls Stabilizer Controls Vibrations Power Systems
Author: Harry L. Whitehead
14
Helicopters Configurations
Tilt Rotor – Bell V-22 – Engines and main rotors (“PropRotors”) mounted on wingtips • Rotate so rotor is horizontal (on top) to takeoff and land like helicopter • Rotate so rotor is vertical to act like prop for high speed forward flight Author: Harry L. Whitehead 12/09/09
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
15
Helicopters Types of Rotors
General
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– All must change blade angle or Pitch for control actions – Called “Feathering” – Is rotation around the span axis of the blade
12/09/09
Author: Harry L. Whitehead
16
Helicopters Types of Rotors
General
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Some also: • Flap or Teeter
12/09/09
Author: Harry L. Whitehead
17
Helicopters Types of Rotors
General
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Some also: • Lead/Lag (Hunt or Drag)
12/09/09
Author: Harry L. Whitehead
18
Helicopters Types of Rotors
Semi-Rigid Rotor
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– 2-bladed – Blades Feather and entire rotor Teeters – No Hunting action allowed – Very popular in early Bell designs (and others)
12/09/09
Author: Harry L. Whitehead
19
Helicopters Types of Rotors
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Semi-Rigid – Bell 206
12/09/09
Author: Harry L. Whitehead
20
Helicopters Types of Rotors
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Fully Articulated Rotor – 3 or more blades – Blades can Feather, individually Flap, and Hunt –Hunting limited by mechanical Dampers
12/09/09
Author: Harry L. Whitehead
21
Helicopters Types of Rotors
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Fully Articulated – Is most complicated but smoothest in flight – Problem: Ground Resonance potential
12/09/09
Author: Harry L. Whitehead
22
Helicopters Types of Rotors
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Fully Articulated – Hughes 500 (McDonnellDouglas, Boeing)
12/09/09
Author: Harry L. Whitehead
23
Helicopters Types of Rotors
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Fully Articulated – Sikorsky S58
12/09/09
Author: Harry L. Whitehead
24
Helicopters Types of Rotors
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Fully Articulated – AStar 350 12/09/09
Author: Harry L. Whitehead
25
Helicopters Types of Rotors
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Rigid – 2 or more blades – Blades Feather but all other forces absorbed by bending of the blades – Strongest and most maneuverable but needs composites to withstand fatigue
12/09/09
Author: Harry L. Whitehead
26
Helicopters Forces on the Rotors
Static Forces
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Gravity pulls down and blades can bend relatively low • Called Droop – All need some kind of Droop (Static) Stop to prevent too low and possible Tail Boom strike • Especially for Fully Articulated at low RPM 12/09/09
27
Helicopters Forces on the Rotors
Turning Forces
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Centrifugal Force tries to hold the blades straight out but lift tries to bend up – Result is Coning • Upward bending into Cone shape • More lift = more Coning
12/09/09
Author: Harry L. Whitehead
28
Helicopters Forces on the Rotors
Torque
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– From Newton’s 3rd Law – Main rotor turns in one direction = fuselage tries to turn opposite (Torque) – Is directly proportional to power applied to M/R 12/09/09
Author: Harry L. Whitehead
29
Helicopters Forces on the Rotors
Torque – Compensated for by Tail Rotor thrust
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
What happens if Tail Rotor fails during flight?
12/09/09
Author: Harry L. Whitehead
30
Helicopters Forces on the Rotors
Torque – Compensated for by Tail Rotor thrust or counter-rotating M/Rs
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
31
Helicopters Forces on the Rotors
Torque – Problem: Tail Rotor causes “Translating Tendency” or “Drift” • Is movement of entire helicopter in direction of T/R thrust (to right in U.S.) • Compensated by slight tilt of M/R mast to left
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
32
Helicopters Forces on the Rotors
Gyroscopic Precession
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Any rotating body (M/R) acts like a Gyroscope and exhibits 2 characteristics: • Rigidity • Precession – Rigidity resists the change from it’s position in relation to space, not the Earth – Precession is the fact that the effect of any upsetting force applied to the body is felt 90o later in direction of rotation • Affects the design and rigging of the M/R 12/09/09
Author: Harry L. Whitehead
33
Helicopters Forces on the Rotors
Gyroscopic Precession – For flight = need to tilt “Rotor Disk” in direction of desired flight • Changes lift & thrust vectors toward that direction = movement of helicopter – To accomplish = need to make pitch change 90o earlier
12/09/09
Desired
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
directio
n of flig
ht
34
Helicopters Forces on the Rotors
Gyroscopic Precession – For flight = need to tilt “Rotor Disk” in direction of desired flight • Changes lift & thrust vectors toward that direction = movement of helicopter – To accomplish = need to make pitch change 90o earlier
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
35
Helicopters Forces on the Rotors
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
36
Helicopters Forces on the Rotors
Ground Effect
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Increased lift within ½ rotor diameter of ground – “Cushion of Air” – Comes from change in angle of attack near ground because relative wind changes
12/09/09
Author: Harry L. Whitehead
37
Ground Effect
Helicopters Forces on the Rotors
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
– Out of Ground Effect (OGE) • Rotor wash is free to accelerate straight down = given Controls angle of attack and lift and large tip vortex Stabilizer Controls
Vibrations Power Systems
Rotation Downwash Angle of Attack Relative Wind
12/09/09
Author: Harry L. Whitehead
38
Ground Effect
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Power Systems
Helicopters Forces on the Rotors
– In Ground Effect (IGE) • Rotor wash is forced to move outward as well as down = Controls reduced down vector = increased angle of attack Stabilizer + Controls Vibrations smaller tip vortex
Rotation Downwash Angle of Attack Relative Wind
12/09/09
Author: Harry L. Whitehead
39
Helicopters Forces on the Rotors
Flight Forces
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Same as airplane: • Lift up • Weight (Gravity) down • Thrust forward and up • Drag back and down 12/09/09
Author: Harry L. Whitehead
40
Helicopters Forces on the Rotors
Flight Forces
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– In hover: • Lift and Thrust both act up • Weight and Drag act down
12/09/09
Author: Harry L. Whitehead
41
Helicopters Forces on the Rotors
Flight Forces – Forward Flight: • Thrust vector tilted in desired direction = overall loss of upward lift = need more power applied • Similar to airplane in turn
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
42
Helicopters Flight Conditions
Dissymmetry of Lift
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– At a hover with no wind the rotor blades are all traveling at the same speed in relation to the air around them
12/09/09
Author: Harry L. Whitehead
43
Helicopters Flight Conditions
Dissymmetry of Lift – Any relative air motion (wind or flight) = blade going into wind (Advancing Blade) travels faster than Retreating Blade • Think in terms of Airspeed
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
100 mph
44
Helicopters Flight Conditions
Dissymmetry of Lift – Faster airfoil = more lift on Advancing side (and less lift on Retreating side) – Lift not equal = Dissymmetry of Lift – Without compensation = roll to left (and gets more severe with speed increase)
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
45
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Dissymmetry of Lift – Compensated for by allowing the blades to Flap or the rotor to Teeter • Advancing blade Flaps (Teeters) up = decrease in angle of attack due to upward vector of Relative Wind 12/09/09
Author: Harry L. Whitehead
46
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Dissymmetry of Lift – Compensated for by allowing the blades to Flap or the rotor to Teeter • Retreating blade Flaps (Teeters) down = increase in angle of attack due to Relative Wind change Author: Harry L. Whitehead 12/09/09
47
Helicopters Flight Conditions
Coriolis Effect
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Caused by Flapping or Teetering up – Blade flaps up = Center of Mass moves closer to axis of rotation = RPM increases
12/09/09
Author: Harry L. Whitehead
48
Helicopters Flight Conditions
Coriolis Effect – The inertia of the rotor stays constant so as the Axis of Rotation is reduced the Speed of Rotation must increase – Is same as skater in spin with arms out then speeds up when arms are moved in to sides 12/09/09
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
49
Helicopters Flight Conditions
Coriolis Effect – Creates force to accelerate the blade (Hunting action) – Fully Articulated head allows limited Hunting action • Uses hydraulic or composite dampers to minimize movement
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
50
Helicopters Flight Conditions
Coriolis Effect – Semi-Rigid usually uses “UnderSlung Rotor Head” • Teetering Axis is above Feathering Axis (“Delta Hinge” arrangement) = as teeters it also swings to high side
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
51
Helicopters Flight Conditions
Coriolis Effect – Semi-Rigid usually uses “UnderSlung Rotor Head” • Center of Mass of the Rotor then stays basically in line with driveshaft/ mast
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
52
Helicopters Flight Conditions
Translational Lift
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Increased lift during the translation to forward flight from a hover – Occurs between 16 and 24 knots airspeed • Feel vibration and definite increase in lift (that point is called “Effective Translational Lift”) 12/09/09
Author: Harry L. Whitehead
53
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Translational Lift – At hover and below 15 knots, the ground is forcing the rotor downwash outward and creating some turbulence around rotor blades
12/09/09
Author: Harry L. Whitehead
54
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Translational Lift
– At hover and below 15 knots, the ground is forcing the rotor downwash outward and creating some turbulence around rotor blades –Above 15 kts, the blades “bite” into undisturbed air = more efficient = less Author: Harry L.power Whiteheadneeded 55 12/09/09
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Translational Lift – Above about 50 knots, drag starts to increase greatly and we need more power to further accelerate
12/09/09
Author: Harry L. Whitehead
56
Helicopters Flight Conditions
Transverse Flow Effect
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– At slow airspeeds (less than 20 kts.) = air through rear of rotor is accelerated downward longer than air at front = decrease in angle of attack in rear
12/09/09
Author: Harry L. Whitehead
57
Helicopters Flight Conditions
Transverse Flow Effect
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Effect felt 90o later = drift to right – Pilot must compensate with some left Cyclic to keep going in a straight line
12/09/09
Author: Harry L. Whitehead
58
Helicopters Flight Conditions
Transverse Flow Effect
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– As airspeed increases = entire rotor has basically undisturbed airflow = no Transverse Flow Effect is felt
12/09/09
Author: Harry L. Whitehead
59
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Autorotations – Flight with no engine power applied to the main rotors – Air is normally drawn down through rotors but if have engine failure = aircraft drops and wind goes up through rotors = keeps them rotating at near normal RPM
12/09/09
Author: Harry L. Whitehead
60
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Autorotations – When engine fails, pilot lowers Collective stick to bottom = sets in minimal angle on all blades and adjusts Cyclic to certain forward airspeed
12/09/09
Author: Harry L. Whitehead
61
Helicopters Flight Conditions
Autorotations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– With Relative Wind from underneath and forward: • Lift and Drag vectors are changed so Resultant is forward of Axis of Rotation = tries to accelerate rotor and is called Autorotative Force 12/09/09
Author: Harry L. Whitehead
62
Helicopters Flight Conditions
Autorotations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– With Relative Wind from underneath and forward: • Occurs in middle 25 – 75% of rotor • Is called the Autorotative (Autorotation) Region 12/09/09
Author: Harry L. Whitehead
63
Helicopters Flight Conditions
Autorotations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– With Relative Wind from underneath and forward: • In outer 30% of rotor = blade twist makes the angle of attack low and the speed makes the drag high • Resultant is behind the Axis of Rotation 12/09/09
Author: Harry L. Whitehead
64
Helicopters Flight Conditions
Autorotations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– With Relative Wind from underneath and forward: • Is a Decelerating force (AntiAutorotative Force) and is called the Driven (or Propeller) Region
12/09/09
Author: Harry L. Whitehead
65
Helicopters Flight Conditions
Autorotations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– With Relative Wind from underneath and forward: • Inner 25% has an angle of attack higher than the Critical Angle of the airfoil = Stall Region and also creates an AntiAutorotative Force 12/09/09
Author: Harry L. Whitehead
66
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Autorotations – At some forward airspeed these forces combine to stabilize the RPM (achieve equilibrium) – RPM means Inertia = energy available to use when near the ground • This Autorotation RPM is critical rigging adjustment Author: Harry L. Whitehead 67 12/09/09
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Autorotations – At about 50 feet above the ground, the pilot pulls back on the Cyclic to flare the aircraft (pulls the nose up some = reduced airspeed) • = momentary increase in airflow and higher RPM (= more inertia)
12/09/09
Author: Harry L. Whitehead
68
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Autorotations – At about 10 feet above the ground, the pilot pulls up on the Collective and starts to use that energy in the rotor to cushion the landing
12/09/09
Author: Harry L. Whitehead
69
Helicopters Flight Conditions
Autorotations – Also leads manufacturers to publish “HeightVelocity Diagram” in Flight Manual – Also known as the “Dead Man’s Curve” – If fly in shaded area combinations of Height (Altitude) and Velocity = can’t successfully Autorotate Author: 12/09/09
Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
70
Helicopters Flight Conditions
Retreating Blade Stall
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– As we move forward = Retreating Blade flaps down to compensate for Dissymmetry of Lift by increasing the angle of attack – At some high forward airspeed (especially if the rotor RPM is allowed to get low) a portion of the airfoil (rotor disk) will exceed the Critical Angle of Attack and Stall
12/09/09
Author: Harry L. Whitehead
71
Helicopters Flight Conditions
Retreating Blade Stall – Generally occurs at the 7 – 9 o’clock position (looking down on the rotor = left rear of rotor) = vibrations + nose pitches up • gyroscopic precession = loss of lift in rear of rotor
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
72
Helicopters Flight Conditions
Retreating Blade Stall – Nose pitch up = excessive angle of attack in front (stall) = loss of lift on left and roll to left
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
73
Helicopters Flight Conditions
Vortex Ring State (Settling With Power)
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– If descending at 300 fpm or more + less than 10 mph forward airspeed + 20 to 100% power applied = can descend inside rotor downwash 12/09/09
Author: Harry L. Whitehead
74
Helicopters Flight Conditions
Vortex Ring State (Settling With Power) – Blades produce tip vortices (like any airfoil) + upward flow of air in middle of rotor (from descent) = Vortex across entire rotor = loss of lift and increased descent rate
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
75
Helicopters Flight Conditions
Vortex Ring State (Settling With Power) – Increasing power to control descent rate = increases problem by increasing the amount of vortex created – Must accelerate out of it or descend below it (if there’s enough altitude)
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
76
Helicopters Flight Conditions
Vortex Ring State (Settling With Power)
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
77
Helicopters Flight Conditions
Ground Resonance
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
http://www.chinookhelicopter.com/Fundamentals_of_Flight/Ground_Resonance /Ground_Resonance.html 12/09/09
Author: Harry L. Whitehead
78
Helicopters Controls
Axes of Flight
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Same as airplane: Longitudinal Axis = Roll, Lateral Axis = Pitch, Vertical Axis = Yaw
12/09/09
Author: Harry L. Whitehead
79
Helicopters Controls
Flight Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– 3 basic controls: Cyclic, Collective, Pedals
12/09/09
Author: Harry L. Whitehead
80
Helicopters Controls
Flight Controls
– 3 basic controls: Cyclic, Collective, Pedals – Cyclic: • Controls Pitch and Roll • Tilts rotor disk in desired direction of movement • Is primary airspeed and flight path control (pitch & roll)
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
81
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Axes of Flight
– Cyclic: • Uses Swashplate to do job – Is device with rotating component and stationary component – Connected by double-row ball bearing – Lower (stationary) part connected to Cyclic stick via push-pull tubes and/or hydraulics – Upper (rotating) part connected to main blades and rotates with them Author: Harry L. Whitehead 12/09/09
82
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Axes of Flight – Cyclic: • Uses Swashplate to do job – Pilot pushes Cyclic stick in direction of desired movement – Swashplate is tilted to change M/R blade pitch a different amount depending on where it is in rotation » The pitch changes cyclically as it rotates » Direction of tilt is designed to take Gyroscopic Precession into account » May or may not tilt same as rotor disk action
Helicopters Controls
Axes of Flight – Cyclic: • Example system: Huey (Bell UH-1)
12/09/09
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Lateral tubes Fore & Aft tubes
Author: Harry L. Whitehead
84
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Axes of Flight – Collective: • Changes the pitch of all blades the same amount at the same time (collectively) • Controls the overall lift generated by the rotors 12/09/09
Author: Harry L. Whitehead
85
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Axes of Flight – Collective: • Uses the Swashplate to do the job by raising or lowering it to change the pitch on all blades
12/09/09
Author: Harry L. Whitehead
86
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Axes of Flight – Collective: • Collective stick also has engine throttle(s) – Motorcycle style rotating throttle except must rotate away from you to increase – Turbines usually governed so open throttle Harrygovernor L. Whitehead keep RPM steady87 12/09/09 wide openAuthor: and let
Helicopters Controls
Axes of Flight
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Collective: • Example system: Hughes (Schweizer) 269
12/09/09
Author: Harry L. Whitehead
88
Helicopters Controls
Axes of Flight
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Pedals: • Control Yaw by controlling the thrust of the Tail Rotor (on single-rotor helicopters) and driven by main transmission so will still work if engine quits – Dual rotors = differential cyclic control by pedals – Coaxial rotors = rudder in rotor downwash • Push left pedal to yaw to the left, right pedal to yaw to the right – Left pedal increases T/R thrust • Needed especially during slow and high power conditions (I.e. and landing) Author:takeoff Harry L. Whitehead 89 12/09/09
Helicopters Controls
Axes of Flight
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Tail Rotor Types: • Semi-rigid – Most common until recently – Usually 2-bladed – Has same Dissymmetry of Lift problems as M/ R so will teeter usually (some let blades flap)
12/09/09
Author: Harry L. Whitehead
90
Helicopters Controls
Axes of Flight
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Tail Rotor Types: • Semi-rigid – Most common until recently – Usually 2-bladed – Has same Dissymmetry of Lift problems as M/ R so will teeter usually (some let blades flap) – Most use Offset Hinges so pitch is physically changed as rotor teeters = minimal actual teetering action 12/09/09
Author: Harry L. Whitehead
91
Helicopters Controls
Axes of Flight
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Tail Rotor Types: • Fenestron – French design – Enclosed multi-bladed variable-pitch fan – Safer and quieter
12/09/09
Author: Harry L. Whitehead
92
Helicopters Controls
Axes of Flight
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Tail Rotor Types: • NOTAR – Developed by Hughes Helicopters (then McDonnell-Douglas now Boeing) – Uses fan inside tail boom with exhaust out side of boom through variable vent connected to pedals – Also uses Coanda Effect from rotor downwash » Air flowing over the curved surface “sticks” to that surface and creates lift sideways93 Author: Harry L. Whitehead 12/09/09
Helicopters Controls
Miscellaneous
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Stabilizer surfaces • Fixed Horizontal – Creates download on tail to keep fuselage more level during high speed flight • Synchronized Elevator – Connected to Cyclic – Changes pitch to change tail down load for various flight speeds • Fixed Vertical – For directional stability 94 12/09/09
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Miscellaneous – Hydraulics • For larger or heavier M/R systems • Mostly use Irreversible type systems to overcome flight loads and dampen vibrations in sticks 12/09/09
Author: Harry L. Whitehead
95
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Miscellaneous
– Example system: Author: 12/09/09 • Bell 206
Harry L. Whitehead
96
Helicopters Controls
Stabilizer Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Are inherently unstable – As rotor lift/thrust vector tilts away from vertical = creates vector to pull away from center – = negative stability
12/09/09
Author: Harry L. Whitehead
97
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
•Compensations •Bell Stabilizer Bar –Bar below M/R @ 90o to blade span –Acts like gyroscope and uses Rigidity in Space characteristic to try and keep rotor and aircraft in one attitude –Worked too well so needs damper to limit it’s Author: Harry L.hydraulic Whitehead 98 12/09/09 effectiveness and allow reasonable maneuverability
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Compensations – Offset Flapping Hinge • On fully-articulated rotor heads and on some tail rotors • Hinge moved a distance from rotor’s rotation axis = acts like lever provide restoring force Author: to Harry L. Whitehead 99 12/09/09
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Compensations • Stabilization Augmentation System (SAS) – Like simple autopilot – One- or two-axis – Only to aid stability, not true autopilot 12/09/09
Author: Harry L. Whitehead
100
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Large number of moving and rotating parts = susceptible to vibrations – Vibrations = abnormal wear, premature part failure, and uncomfortable ride for people – Must minimize vibes
12/09/09
Author: Harry L. Whitehead
101
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Types • Low Frequency – Feel as “beat” in structure and may be able to almost count the beats – Comes from Main Rotor
12/09/09
Author: Harry L. Whitehead
102
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Types • Low Frequency –Vertical vibe »Up & down motion »Caused by blades being Out-of-Track
12/09/09
Author: Harry L. Whitehead
103
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Types • Low Frequency –Lateral vibe »Side-to-side motion »Comes from blades being out of balance or spaced unequally
12/09/09
Author: Harry L. Whitehead
104
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Types • High Frequency – Felt as “buzz” in structure – Comes from cooling fan, engine and/or accessories, gearboxes, or (most commonly) Tail Rotor – May only notice if some part of body goes to sleep » Feet = Tail Rotor (through pedals) » Butt = others 12/09/09
Author: Harry L. Whitehead
105
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Measurement of vibes • Feel – Adjust until feels OK (at minimum level)
12/09/09
Author: Harry L. Whitehead
106
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Measurement of vibes • Electronic – Use accelerometers to measure rate and strength accurately – Use Strobe light or “Clock” to locate – Use above as coordinates on chart to determine exactly where and how much weight to add or remove – Can use to troubleshoot (narrow down vibe rate and look at those components operating at that rate) 12/09/09
Author: Harry L. Whitehead
107
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Correction of vibes (M/R & T/R) • If out of balance condition – May require Static or Dynamic procedures (or both depending on helicopter) – Some require Static balancing after assembly » Put on balance stand and adjust until no movement when released » T/R done like propeller (knife-edge stand) » M/R done on special stand with Bullseye level 12/09/09
Author: Harry L. Whitehead
108
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Vibrations
– Correction of vibes (M/R & T/R) • If out of balance condition » M/R also may require Blade Sweep to be adjusted (for chordwise balance) » = stretch string between blades and adjust until blades are exactly 180o apart (adjust by “sweeping” blades forward or aft as necessary) Author: Harry L. Whitehead 109 12/09/09
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Vibrations
– Correction of vibes (M/R & T/R) • If out of balance condition – Dynamic balancing done during operations on ground and in air – Uses Electronic gear to measure rate and strength and charts to show adjustments • Some M/Rs don’t need dynamic after static but 110 12/09/09 all T/Rs do Author: Harry L. Whitehead
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Example: Chadwick-Helmuth Vibrex® system 12/09/09
Author: Harry L. Whitehead
111
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Vibrations – Measurement of vibes • Example chart: – T/R balance
12/09/09
Author: Harry L. Whitehead
112
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Vibrations – Measurement of vibes • Example chart: – T/R balance
12/09/09
Author: Harry L. Whitehead
113
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Vibrations – Measurement of vibes • Example chart: – M/R balance
12/09/09
Author: Harry L. Whitehead
114
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Vibrations – Measurement of vibes • Example chart: – M/R balance
12/09/09
Author: Harry L. Whitehead
115
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Correction of vibes (M/R & T/R) • If out of Track condition – Track = path Blade tips follow during rotation – In-Track = all tips follow same path (or Cone the same amount) and = minimal vertical vibes – All M/Rs need to be checked and adjusted and some T/Rs
12/09/09
Author: Harry L. Whitehead
116
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Correction of vibes (M/R & T/R) • If out of Track condition – Ground check » Use marking stick or Flag » Marking Stick uses crayon or grease pencil on end of long stick and carefully raise to bottom of blades to make mark on lowest one (adjust until marks all blades)
12/09/09
Author: Harry L. Whitehead
117
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Correction of vibes (M/R & T/R) • If out of Track condition – Ground check » Flag is strip of canvas suspended between F shaped pole + put crayon mark on blade tips (different color on each blade) then move Flag so just touches each blade to get a colored mark » Use colors to determine which blade needs adjustment 12/09/09
Author: Harry L. Whitehead
118
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Flag Tracking
Flag Tracking
12/09/09
Author: Harry L. Whitehead
119
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Correction of vibes (M/R & T/R) • If out of Track condition – Ground check » All are adjusted by changing the length of the Pitch Links (controls Angle of Incidence of blades) » Link between Swashplate and M/R blade » Increase angle = more lift = blade flies higher » Each manufacturer usually has standard adjustments (I.e. 1/6 turn = ½” blade movement) Author: Harry L. Whitehead 120 » Limitation: can’t check in flight 12/09/09
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Vibrations – Correction of vibes (M/R & T/R) • If out of Track condition – Ground & Flight » Use spotlight or strobe » Spotlight uses colored reflectors attached to blade » Light shows colored streaks and can see “altitude” Author: Harry L. Whitehead 121 12/09/09 difference between them
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Correction of vibes (M/R & T/R) • If out of Track condition – Ground & Flight » Strobe is keyed by pickup on swashplate » Flashes once for each blade » Has reflectors on each blade with different angled “Target” line » Flashes ‘stop’ targets at one location and can easily see difference and which blade to adjust 12/09/09
Author: Harry L. Whitehead
122
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Correction of vibes (M/R & T/R) • If out of Track condition – Ground & Flight » For ground and hover adjustment = use Pitch Links » For in-flight adjustment = most blades have trailing edge fixed trim tabs to allow limited bending
12/09/09
Author: Harry L. Whitehead
123
Helicopters Controls
Power Systems & Other Components
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Powerplants • Reciprocating – See all types: Horizontal and Vertically mounted Opposed engines & some Radials 12/09/09
Author: Harry L. Whitehead
124
Helicopters Controls
Power Systems & Other Components
– Powerplants • Reciprocating – Verticals and Radials usually are Dry-sump with M/R Transmission (GearBox) mounted on top Harry L. Whitehead and using same Author: oil supply 12/09/09
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
125
Helicopters Controls
Power Systems & Other Components – Powerplants • Reciprocating – Verticals and Radials usually are Dry-sump with M/R Transmission (GearBox) mounted on top and using same oil supply
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Bell 47
126
Helicopters Controls
Power Systems & Other Components
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Powerplants • Reciprocating – Horizontals usually use some form of Belt Drive » Multiple V-belts or one wide “timing” belt 12/09/09
Author: Harry L. Whitehead
127
Helicopters Controls
Power Systems & Other Components – Powerplants • Reciprocating – None have propeller for cooling air blast and “fly wheel” for starting – All use some form of Cooling Fan driven by engine to blow air across cylinders – All are generally hard to start (no fly wheel to help process keep going) Author: Harry L. Whitehead 12/09/09
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
128
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Power Systems & Other Components
– Powerplants • Reciprocating Instruments – Since M/R is essentially a Variable-pitch Propeller = all use both Tachometer (RPM) and Manifold Pressure gauges for power measurement – Engines must be operated at relatively constant RPM (to allow enough Lift & Thrust) and usually very near the manufacturer’s Overspeed limit 12/09/09
Author: Harry L. Whitehead
129
Helicopters Controls
Power Systems & Other Components
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Powerplants • Reciprocating – Usually uses Correlated Throttle and Collective » Pull up on collective = more blade pitch = more lift/thrust generated = more drag » Need more engine power to keep RPM constant » Correlation increases throttle automatically as Collective is pulled up (may not do Author: Harry L. Whitehead 12/09/09 entire job, though)
130
Bell 47
Helicopters Controls
Power Systems & Other Components
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Powerplants • Reciprocating – Usually uses Correlated Throttle and Collective » Pull up on collective = more blade pitch = more lift/thrust generated = more drag » Need more engine power to keep RPM constant » Correlation increases throttle automatically as Collective is pulled up (may not do Author: Harry L. Whitehead 12/09/09 entire job, though)
131
Helicopters Controls
Power Systems & Other Components
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Powerplants
• Turbines – Are ideal powerplants as operate most efficiently at constant RPM and have very high power to weight ratio 12/09/09
Author: Harry L. Whitehead
132
Helicopters Controls
Power Systems & Other Components
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Powerplants
• Turbines – Are TurboShaft engines » All output power is converted to rotating shaft power (Torque) » Torque sent to Transmission to drive Main & Tail Rotors and other necessary components 12/09/09
Author: Harry L. Whitehead
133
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Power Systems & Other Components
– Powerplants • Turbines – Are TurboShaft engines » Two basic types: Direct Shaft & Free Turbine » Direct Shaft has PTO shaft connected to all Compressor and Turbine section stages » Are very hard to start as must turn all engine + Main and Tail rotors 12/09/09
Author: Harry L. Whitehead
134
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Power Systems & Other Components
– Powerplants • Turbines – Are TurboShaft engines » Two basic types: Direct Shaft & Free Turbine » Free Turbine has some Turbine stages which only supply PTO power » Easier to start as rotors not mechanically connected to main part of engine 12/09/09
Author: Harry L. Whitehead
135
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Power Systems & Other Components
– Powerplants • Turbines – Are TurboShaft engines » Measure power output with Tachometers, Torquemeters, and Turbine Temperature gauges » Tachs measure RPM in % (due to high actual RPM) » Free Turbine versions need to measure both main engine (N1) and Power Turbine (N2) and have separate gauges136 Author:usually Harry L. Whitehead 12/09/09
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Power Systems & Other Components
– Powerplants • Turbines – Are TurboShaft engines » Torquemeters measure power being absorbed by M/Rs » Similar to MAP gauge on recips » Measures in % or in Pounds of Torque
12/09/09
Author: Harry L. Whitehead
137
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Power Systems & Other Components
– Powerplants • Turbines – Are TurboShaft engines » Turbine Temps very important as are directly proportional to how hard the engine’s working and critical during the start cycle » May be TIT, ITT, TOT, or EGT system (manufacturer’s choice) » CAN NOT exceed max. limit or will damage section components 138 Author:Turbine Harry L. Whitehead 12/09/09
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Power Systems & Other Components
– Transmissions • For speed and/or directional change of rotating shaft(s) • May be Rack & Pinion or Planetary Gear systems • Uses engine oil or has own supply
12/09/09
Author: Harry L. Whitehead
139
Helicopters Controls
Power Systems & Other Components
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Transmissions • For speed and/or directional change of rotating shaft(s) • May be Rack & Pinion or Planetary Gear systems Schweizer (Hughes) 269 Transmission: Rack (Ring Gear) and Author: Harry L. Whitehead 140 12/09/09 Pinion
Bell 47 Transmission: Planetary system
12/09/09
Author: Harry L. Whitehead
141
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Power Systems & Other Components
– Transmissions • Engine drives M/R Transmission which in turn drives the T/R, Hydraulic pumps, Electrical Generator, Cooling Fans (if appropriate for the aircraft), and Rotor Tach sending unit connected to (usually) Dual Tach (Rotor and Engine RPM Author: Harry L. Whitehead 142 12/09/09 on same gauge)
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Power Systems & Other Components
– Clutch • USED TO RELIEVE THE ENGINE LOAD DURING STARTING • May be Manual, Electrical, or Centrifugal • Manual and Electrical pull Idler Pulley against Belt(s) to tighten them and connect engine with Transmission
12/09/09
Author: Harry L. Whitehead
143
Helicopters Controls
Power Systems & Other Components – Clutch • Centrifugal uses hinged Shoes pushed against a Drum by Centrifugal Force – Shoes on arms attached to engine crankshaft – Drum attached to Transmission Author: Harry L. Whitehead 12/09/09
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
144
Helicopters Controls
Power Systems & Other Components
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Freewheeling Unit • FOR AUTOROTATION PURPOSES • Disconnects M/R from engine if engine turns slower than M/ R • Usually either Roller or Sprag style 12/09/09
Author: Harry L. Whitehead
145
Helicopters Controls
Power Systems & Other Components
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Freewheeling Unit • FOR AUTOROTATION PURPOSES • Disconnects M/R from engine if engine turns slower than M/ R • Usually either Roller or Sprag style 12/09/09
Author: Harry L. Whitehead
146
12/09/09
Author: Harry L. Whitehead
147
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions 12/09/09
A. B. C. D.
Controls Stabilizer Controls Vibrations Power Systems
Author: Harry L. Whitehead
1
Helicopters History
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
1483, DaVinci – Developed “Helix” – Kind of aerial screw – Shows basic understanding that the atmosphere can support weight but no provisions for torque on fuselage
12/09/09
Author: Harry L. Whitehead
2
Helicopters History
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
1800s, Forlanini (Italy) – Used steam engine – Counter-rotating “butterfly” wings – Could ascend (without pilot) to 40 feet for about 20 minutes
12/09/09
Author: Harry L. Whitehead
3
Helicopters History
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
1907, Cornu (France) – First piloted helicopter – Flew for few seconds – Used internal combustion engine – No controls but well balanced
12/09/09
Author: Harry L. Whitehead
4
Helicopters History
1909, Igor Sikorsky (Russia) – Small counter-rotating coaxial rotors – First use of airfoil shaped rotors
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
5
Helicopters History
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
1920s, Petroczy & Von Karmon (Austria) – Counter-rotating, coaxial, airfoil rotors – 3 40HP engines – No controls, just made to lift straight up
12/09/09
Author: Harry L. Whitehead
6
Helicopters History
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
1923, de Bothezat (U.S.) – 4 rotors – Complicated power transmission system – Low power – Several flights of 1 minute @ 6 feet
12/09/09
Author: Harry L. Whitehead
7
Helicopters History
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
1923, de la Cierva (Spain) – Developed Autogyro – Solved some control problems by allowing rotors to Flap
12/09/09
Author: Harry L. Whitehead
8
Helicopters History
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
1936, Focke-Wulfe (Germany) – FW-61 established endurance & speed records – Mostly flown by Hannah Reich – Flown inside stadium for most of records
12/09/09
Author: Harry L. Whitehead
9
Helicopters History
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
1939, Sikorsky (U.S.) – Developed VS-300 – Broke all FW-61 records – Used 3-bladed main rotor, vertical 2bladed tail rotor & 2 horizontal 2-bladed outrigger rotors for stability and control
12/09/09
Author: Harry L. Whitehead
10
Helicopters Configurations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Autogyros – Developed by de la Cierva – Uses free-spinning main rotor with airplane-like engine/prop for forward motion – No power to main rotor, spins from air action = can’t hover or ascend vertically
12/09/09
Author: Harry L. Whitehead
11
Helicopters Configurations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Dual Rotor – 2 counter rotating main rotors • No tail rotor needed • May be separate or coaxial – Used extensively through history, today few (Boeing, Kaman)
12/09/09
Author: Harry L. Whitehead
12
Helicopters Configurations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Single Rotor – Most used design – 1 main rotor for lift and control – Tail rotor for anti-torque • FAA calls it “Auxiliary Rotor” • More precisely known as “Anti-torque Rotor”
12/09/09
Author: Harry L. Whitehead
13
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Helicopters Hughes Helicopter ConfigurationsH-17 Skycrane
1952
Single Rotor
Function: transport Crew: 2 Engines: 1 * G.E. J35 Rotor Span: 130ft Length: Height: 30ft Disc Area: Empty Weight: Max.Weight: 46000lb Speed: Ceiling: Range: 65km Load: 25000lbs Hot Cycle Blades
12/09/09
Controls Stabilizer Controls Vibrations Power Systems
Author: Harry L. Whitehead
14
Helicopters Configurations
Tilt Rotor – Bell V-22 – Engines and main rotors (“PropRotors”) mounted on wingtips • Rotate so rotor is horizontal (on top) to takeoff and land like helicopter • Rotate so rotor is vertical to act like prop for high speed forward flight Author: Harry L. Whitehead 12/09/09
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
15
Helicopters Types of Rotors
General
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– All must change blade angle or Pitch for control actions – Called “Feathering” – Is rotation around the span axis of the blade
12/09/09
Author: Harry L. Whitehead
16
Helicopters Types of Rotors
General
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Some also: • Flap or Teeter
12/09/09
Author: Harry L. Whitehead
17
Helicopters Types of Rotors
General
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Some also: • Lead/Lag (Hunt or Drag)
12/09/09
Author: Harry L. Whitehead
18
Helicopters Types of Rotors
Semi-Rigid Rotor
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– 2-bladed – Blades Feather and entire rotor Teeters – No Hunting action allowed – Very popular in early Bell designs (and others)
12/09/09
Author: Harry L. Whitehead
19
Helicopters Types of Rotors
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Semi-Rigid – Bell 206
12/09/09
Author: Harry L. Whitehead
20
Helicopters Types of Rotors
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Fully Articulated Rotor – 3 or more blades – Blades can Feather, individually Flap, and Hunt –Hunting limited by mechanical Dampers
12/09/09
Author: Harry L. Whitehead
21
Helicopters Types of Rotors
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Fully Articulated – Is most complicated but smoothest in flight – Problem: Ground Resonance potential
12/09/09
Author: Harry L. Whitehead
22
Helicopters Types of Rotors
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Fully Articulated – Hughes 500 (McDonnellDouglas, Boeing)
12/09/09
Author: Harry L. Whitehead
23
Helicopters Types of Rotors
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Fully Articulated – Sikorsky S58
12/09/09
Author: Harry L. Whitehead
24
Helicopters Types of Rotors
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Fully Articulated – AStar 350 12/09/09
Author: Harry L. Whitehead
25
Helicopters Types of Rotors
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Rigid – 2 or more blades – Blades Feather but all other forces absorbed by bending of the blades – Strongest and most maneuverable but needs composites to withstand fatigue
12/09/09
Author: Harry L. Whitehead
26
Helicopters Forces on the Rotors
Static Forces
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Gravity pulls down and blades can bend relatively low • Called Droop – All need some kind of Droop (Static) Stop to prevent too low and possible Tail Boom strike • Especially for Fully Articulated at low RPM 12/09/09
27
Helicopters Forces on the Rotors
Turning Forces
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Centrifugal Force tries to hold the blades straight out but lift tries to bend up – Result is Coning • Upward bending into Cone shape • More lift = more Coning
12/09/09
Author: Harry L. Whitehead
28
Helicopters Forces on the Rotors
Torque
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– From Newton’s 3rd Law – Main rotor turns in one direction = fuselage tries to turn opposite (Torque) – Is directly proportional to power applied to M/R 12/09/09
Author: Harry L. Whitehead
29
Helicopters Forces on the Rotors
Torque – Compensated for by Tail Rotor thrust
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
What happens if Tail Rotor fails during flight?
12/09/09
Author: Harry L. Whitehead
30
Helicopters Forces on the Rotors
Torque – Compensated for by Tail Rotor thrust or counter-rotating M/Rs
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
31
Helicopters Forces on the Rotors
Torque – Problem: Tail Rotor causes “Translating Tendency” or “Drift” • Is movement of entire helicopter in direction of T/R thrust (to right in U.S.) • Compensated by slight tilt of M/R mast to left
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
32
Helicopters Forces on the Rotors
Gyroscopic Precession
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Any rotating body (M/R) acts like a Gyroscope and exhibits 2 characteristics: • Rigidity • Precession – Rigidity resists the change from it’s position in relation to space, not the Earth – Precession is the fact that the effect of any upsetting force applied to the body is felt 90o later in direction of rotation • Affects the design and rigging of the M/R 12/09/09
Author: Harry L. Whitehead
33
Helicopters Forces on the Rotors
Gyroscopic Precession – For flight = need to tilt “Rotor Disk” in direction of desired flight • Changes lift & thrust vectors toward that direction = movement of helicopter – To accomplish = need to make pitch change 90o earlier
12/09/09
Desired
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
directio
n of flig
ht
34
Helicopters Forces on the Rotors
Gyroscopic Precession – For flight = need to tilt “Rotor Disk” in direction of desired flight • Changes lift & thrust vectors toward that direction = movement of helicopter – To accomplish = need to make pitch change 90o earlier
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
35
Helicopters Forces on the Rotors
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
36
Helicopters Forces on the Rotors
Ground Effect
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Increased lift within ½ rotor diameter of ground – “Cushion of Air” – Comes from change in angle of attack near ground because relative wind changes
12/09/09
Author: Harry L. Whitehead
37
Ground Effect
Helicopters Forces on the Rotors
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
– Out of Ground Effect (OGE) • Rotor wash is free to accelerate straight down = given Controls angle of attack and lift and large tip vortex Stabilizer Controls
Vibrations Power Systems
Rotation Downwash Angle of Attack Relative Wind
12/09/09
Author: Harry L. Whitehead
38
Ground Effect
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Power Systems
Helicopters Forces on the Rotors
– In Ground Effect (IGE) • Rotor wash is forced to move outward as well as down = Controls reduced down vector = increased angle of attack Stabilizer + Controls Vibrations smaller tip vortex
Rotation Downwash Angle of Attack Relative Wind
12/09/09
Author: Harry L. Whitehead
39
Helicopters Forces on the Rotors
Flight Forces
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Same as airplane: • Lift up • Weight (Gravity) down • Thrust forward and up • Drag back and down 12/09/09
Author: Harry L. Whitehead
40
Helicopters Forces on the Rotors
Flight Forces
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– In hover: • Lift and Thrust both act up • Weight and Drag act down
12/09/09
Author: Harry L. Whitehead
41
Helicopters Forces on the Rotors
Flight Forces – Forward Flight: • Thrust vector tilted in desired direction = overall loss of upward lift = need more power applied • Similar to airplane in turn
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
42
Helicopters Flight Conditions
Dissymmetry of Lift
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– At a hover with no wind the rotor blades are all traveling at the same speed in relation to the air around them
12/09/09
Author: Harry L. Whitehead
43
Helicopters Flight Conditions
Dissymmetry of Lift – Any relative air motion (wind or flight) = blade going into wind (Advancing Blade) travels faster than Retreating Blade • Think in terms of Airspeed
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
100 mph
44
Helicopters Flight Conditions
Dissymmetry of Lift – Faster airfoil = more lift on Advancing side (and less lift on Retreating side) – Lift not equal = Dissymmetry of Lift – Without compensation = roll to left (and gets more severe with speed increase)
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
45
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Dissymmetry of Lift – Compensated for by allowing the blades to Flap or the rotor to Teeter • Advancing blade Flaps (Teeters) up = decrease in angle of attack due to upward vector of Relative Wind 12/09/09
Author: Harry L. Whitehead
46
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Dissymmetry of Lift – Compensated for by allowing the blades to Flap or the rotor to Teeter • Retreating blade Flaps (Teeters) down = increase in angle of attack due to Relative Wind change Author: Harry L. Whitehead 12/09/09
47
Helicopters Flight Conditions
Coriolis Effect
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Caused by Flapping or Teetering up – Blade flaps up = Center of Mass moves closer to axis of rotation = RPM increases
12/09/09
Author: Harry L. Whitehead
48
Helicopters Flight Conditions
Coriolis Effect – The inertia of the rotor stays constant so as the Axis of Rotation is reduced the Speed of Rotation must increase – Is same as skater in spin with arms out then speeds up when arms are moved in to sides 12/09/09
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
49
Helicopters Flight Conditions
Coriolis Effect – Creates force to accelerate the blade (Hunting action) – Fully Articulated head allows limited Hunting action • Uses hydraulic or composite dampers to minimize movement
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
50
Helicopters Flight Conditions
Coriolis Effect – Semi-Rigid usually uses “UnderSlung Rotor Head” • Teetering Axis is above Feathering Axis (“Delta Hinge” arrangement) = as teeters it also swings to high side
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
51
Helicopters Flight Conditions
Coriolis Effect – Semi-Rigid usually uses “UnderSlung Rotor Head” • Center of Mass of the Rotor then stays basically in line with driveshaft/ mast
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
52
Helicopters Flight Conditions
Translational Lift
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Increased lift during the translation to forward flight from a hover – Occurs between 16 and 24 knots airspeed • Feel vibration and definite increase in lift (that point is called “Effective Translational Lift”) 12/09/09
Author: Harry L. Whitehead
53
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Translational Lift – At hover and below 15 knots, the ground is forcing the rotor downwash outward and creating some turbulence around rotor blades
12/09/09
Author: Harry L. Whitehead
54
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Translational Lift
– At hover and below 15 knots, the ground is forcing the rotor downwash outward and creating some turbulence around rotor blades –Above 15 kts, the blades “bite” into undisturbed air = more efficient = less Author: Harry L.power Whiteheadneeded 55 12/09/09
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Translational Lift – Above about 50 knots, drag starts to increase greatly and we need more power to further accelerate
12/09/09
Author: Harry L. Whitehead
56
Helicopters Flight Conditions
Transverse Flow Effect
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– At slow airspeeds (less than 20 kts.) = air through rear of rotor is accelerated downward longer than air at front = decrease in angle of attack in rear
12/09/09
Author: Harry L. Whitehead
57
Helicopters Flight Conditions
Transverse Flow Effect
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Effect felt 90o later = drift to right – Pilot must compensate with some left Cyclic to keep going in a straight line
12/09/09
Author: Harry L. Whitehead
58
Helicopters Flight Conditions
Transverse Flow Effect
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– As airspeed increases = entire rotor has basically undisturbed airflow = no Transverse Flow Effect is felt
12/09/09
Author: Harry L. Whitehead
59
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Autorotations – Flight with no engine power applied to the main rotors – Air is normally drawn down through rotors but if have engine failure = aircraft drops and wind goes up through rotors = keeps them rotating at near normal RPM
12/09/09
Author: Harry L. Whitehead
60
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Autorotations – When engine fails, pilot lowers Collective stick to bottom = sets in minimal angle on all blades and adjusts Cyclic to certain forward airspeed
12/09/09
Author: Harry L. Whitehead
61
Helicopters Flight Conditions
Autorotations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– With Relative Wind from underneath and forward: • Lift and Drag vectors are changed so Resultant is forward of Axis of Rotation = tries to accelerate rotor and is called Autorotative Force 12/09/09
Author: Harry L. Whitehead
62
Helicopters Flight Conditions
Autorotations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– With Relative Wind from underneath and forward: • Occurs in middle 25 – 75% of rotor • Is called the Autorotative (Autorotation) Region 12/09/09
Author: Harry L. Whitehead
63
Helicopters Flight Conditions
Autorotations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– With Relative Wind from underneath and forward: • In outer 30% of rotor = blade twist makes the angle of attack low and the speed makes the drag high • Resultant is behind the Axis of Rotation 12/09/09
Author: Harry L. Whitehead
64
Helicopters Flight Conditions
Autorotations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– With Relative Wind from underneath and forward: • Is a Decelerating force (AntiAutorotative Force) and is called the Driven (or Propeller) Region
12/09/09
Author: Harry L. Whitehead
65
Helicopters Flight Conditions
Autorotations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– With Relative Wind from underneath and forward: • Inner 25% has an angle of attack higher than the Critical Angle of the airfoil = Stall Region and also creates an AntiAutorotative Force 12/09/09
Author: Harry L. Whitehead
66
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Autorotations – At some forward airspeed these forces combine to stabilize the RPM (achieve equilibrium) – RPM means Inertia = energy available to use when near the ground • This Autorotation RPM is critical rigging adjustment Author: Harry L. Whitehead 67 12/09/09
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Autorotations – At about 50 feet above the ground, the pilot pulls back on the Cyclic to flare the aircraft (pulls the nose up some = reduced airspeed) • = momentary increase in airflow and higher RPM (= more inertia)
12/09/09
Author: Harry L. Whitehead
68
Helicopters Flight Conditions
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Autorotations – At about 10 feet above the ground, the pilot pulls up on the Collective and starts to use that energy in the rotor to cushion the landing
12/09/09
Author: Harry L. Whitehead
69
Helicopters Flight Conditions
Autorotations – Also leads manufacturers to publish “HeightVelocity Diagram” in Flight Manual – Also known as the “Dead Man’s Curve” – If fly in shaded area combinations of Height (Altitude) and Velocity = can’t successfully Autorotate Author: 12/09/09
Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
70
Helicopters Flight Conditions
Retreating Blade Stall
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– As we move forward = Retreating Blade flaps down to compensate for Dissymmetry of Lift by increasing the angle of attack – At some high forward airspeed (especially if the rotor RPM is allowed to get low) a portion of the airfoil (rotor disk) will exceed the Critical Angle of Attack and Stall
12/09/09
Author: Harry L. Whitehead
71
Helicopters Flight Conditions
Retreating Blade Stall – Generally occurs at the 7 – 9 o’clock position (looking down on the rotor = left rear of rotor) = vibrations + nose pitches up • gyroscopic precession = loss of lift in rear of rotor
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
72
Helicopters Flight Conditions
Retreating Blade Stall – Nose pitch up = excessive angle of attack in front (stall) = loss of lift on left and roll to left
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
73
Helicopters Flight Conditions
Vortex Ring State (Settling With Power)
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– If descending at 300 fpm or more + less than 10 mph forward airspeed + 20 to 100% power applied = can descend inside rotor downwash 12/09/09
Author: Harry L. Whitehead
74
Helicopters Flight Conditions
Vortex Ring State (Settling With Power) – Blades produce tip vortices (like any airfoil) + upward flow of air in middle of rotor (from descent) = Vortex across entire rotor = loss of lift and increased descent rate
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
75
Helicopters Flight Conditions
Vortex Ring State (Settling With Power) – Increasing power to control descent rate = increases problem by increasing the amount of vortex created – Must accelerate out of it or descend below it (if there’s enough altitude)
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
76
Helicopters Flight Conditions
Vortex Ring State (Settling With Power)
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
77
Helicopters Flight Conditions
Ground Resonance
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
http://www.chinookhelicopter.com/Fundamentals_of_Flight/Ground_Resonance /Ground_Resonance.html 12/09/09
Author: Harry L. Whitehead
78
Helicopters Controls
Axes of Flight
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Same as airplane: Longitudinal Axis = Roll, Lateral Axis = Pitch, Vertical Axis = Yaw
12/09/09
Author: Harry L. Whitehead
79
Helicopters Controls
Flight Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– 3 basic controls: Cyclic, Collective, Pedals
12/09/09
Author: Harry L. Whitehead
80
Helicopters Controls
Flight Controls
– 3 basic controls: Cyclic, Collective, Pedals – Cyclic: • Controls Pitch and Roll • Tilts rotor disk in desired direction of movement • Is primary airspeed and flight path control (pitch & roll)
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
81
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Axes of Flight
– Cyclic: • Uses Swashplate to do job – Is device with rotating component and stationary component – Connected by double-row ball bearing – Lower (stationary) part connected to Cyclic stick via push-pull tubes and/or hydraulics – Upper (rotating) part connected to main blades and rotates with them Author: Harry L. Whitehead 12/09/09
82
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Axes of Flight – Cyclic: • Uses Swashplate to do job – Pilot pushes Cyclic stick in direction of desired movement – Swashplate is tilted to change M/R blade pitch a different amount depending on where it is in rotation » The pitch changes cyclically as it rotates » Direction of tilt is designed to take Gyroscopic Precession into account » May or may not tilt same as rotor disk action
Helicopters Controls
Axes of Flight – Cyclic: • Example system: Huey (Bell UH-1)
12/09/09
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Lateral tubes Fore & Aft tubes
Author: Harry L. Whitehead
84
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Axes of Flight – Collective: • Changes the pitch of all blades the same amount at the same time (collectively) • Controls the overall lift generated by the rotors 12/09/09
Author: Harry L. Whitehead
85
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Axes of Flight – Collective: • Uses the Swashplate to do the job by raising or lowering it to change the pitch on all blades
12/09/09
Author: Harry L. Whitehead
86
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Axes of Flight – Collective: • Collective stick also has engine throttle(s) – Motorcycle style rotating throttle except must rotate away from you to increase – Turbines usually governed so open throttle Harrygovernor L. Whitehead keep RPM steady87 12/09/09 wide openAuthor: and let
Helicopters Controls
Axes of Flight
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Collective: • Example system: Hughes (Schweizer) 269
12/09/09
Author: Harry L. Whitehead
88
Helicopters Controls
Axes of Flight
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Pedals: • Control Yaw by controlling the thrust of the Tail Rotor (on single-rotor helicopters) and driven by main transmission so will still work if engine quits – Dual rotors = differential cyclic control by pedals – Coaxial rotors = rudder in rotor downwash • Push left pedal to yaw to the left, right pedal to yaw to the right – Left pedal increases T/R thrust • Needed especially during slow and high power conditions (I.e. and landing) Author:takeoff Harry L. Whitehead 89 12/09/09
Helicopters Controls
Axes of Flight
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Tail Rotor Types: • Semi-rigid – Most common until recently – Usually 2-bladed – Has same Dissymmetry of Lift problems as M/ R so will teeter usually (some let blades flap)
12/09/09
Author: Harry L. Whitehead
90
Helicopters Controls
Axes of Flight
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Tail Rotor Types: • Semi-rigid – Most common until recently – Usually 2-bladed – Has same Dissymmetry of Lift problems as M/ R so will teeter usually (some let blades flap) – Most use Offset Hinges so pitch is physically changed as rotor teeters = minimal actual teetering action 12/09/09
Author: Harry L. Whitehead
91
Helicopters Controls
Axes of Flight
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Tail Rotor Types: • Fenestron – French design – Enclosed multi-bladed variable-pitch fan – Safer and quieter
12/09/09
Author: Harry L. Whitehead
92
Helicopters Controls
Axes of Flight
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Tail Rotor Types: • NOTAR – Developed by Hughes Helicopters (then McDonnell-Douglas now Boeing) – Uses fan inside tail boom with exhaust out side of boom through variable vent connected to pedals – Also uses Coanda Effect from rotor downwash » Air flowing over the curved surface “sticks” to that surface and creates lift sideways93 Author: Harry L. Whitehead 12/09/09
Helicopters Controls
Miscellaneous
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Stabilizer surfaces • Fixed Horizontal – Creates download on tail to keep fuselage more level during high speed flight • Synchronized Elevator – Connected to Cyclic – Changes pitch to change tail down load for various flight speeds • Fixed Vertical – For directional stability 94 12/09/09
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Miscellaneous – Hydraulics • For larger or heavier M/R systems • Mostly use Irreversible type systems to overcome flight loads and dampen vibrations in sticks 12/09/09
Author: Harry L. Whitehead
95
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Miscellaneous
– Example system: Author: 12/09/09 • Bell 206
Harry L. Whitehead
96
Helicopters Controls
Stabilizer Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Are inherently unstable – As rotor lift/thrust vector tilts away from vertical = creates vector to pull away from center – = negative stability
12/09/09
Author: Harry L. Whitehead
97
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
•Compensations •Bell Stabilizer Bar –Bar below M/R @ 90o to blade span –Acts like gyroscope and uses Rigidity in Space characteristic to try and keep rotor and aircraft in one attitude –Worked too well so needs damper to limit it’s Author: Harry L.hydraulic Whitehead 98 12/09/09 effectiveness and allow reasonable maneuverability
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Compensations – Offset Flapping Hinge • On fully-articulated rotor heads and on some tail rotors • Hinge moved a distance from rotor’s rotation axis = acts like lever provide restoring force Author: to Harry L. Whitehead 99 12/09/09
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Compensations • Stabilization Augmentation System (SAS) – Like simple autopilot – One- or two-axis – Only to aid stability, not true autopilot 12/09/09
Author: Harry L. Whitehead
100
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Large number of moving and rotating parts = susceptible to vibrations – Vibrations = abnormal wear, premature part failure, and uncomfortable ride for people – Must minimize vibes
12/09/09
Author: Harry L. Whitehead
101
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Types • Low Frequency – Feel as “beat” in structure and may be able to almost count the beats – Comes from Main Rotor
12/09/09
Author: Harry L. Whitehead
102
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Types • Low Frequency –Vertical vibe »Up & down motion »Caused by blades being Out-of-Track
12/09/09
Author: Harry L. Whitehead
103
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Types • Low Frequency –Lateral vibe »Side-to-side motion »Comes from blades being out of balance or spaced unequally
12/09/09
Author: Harry L. Whitehead
104
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Types • High Frequency – Felt as “buzz” in structure – Comes from cooling fan, engine and/or accessories, gearboxes, or (most commonly) Tail Rotor – May only notice if some part of body goes to sleep » Feet = Tail Rotor (through pedals) » Butt = others 12/09/09
Author: Harry L. Whitehead
105
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Measurement of vibes • Feel – Adjust until feels OK (at minimum level)
12/09/09
Author: Harry L. Whitehead
106
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Measurement of vibes • Electronic – Use accelerometers to measure rate and strength accurately – Use Strobe light or “Clock” to locate – Use above as coordinates on chart to determine exactly where and how much weight to add or remove – Can use to troubleshoot (narrow down vibe rate and look at those components operating at that rate) 12/09/09
Author: Harry L. Whitehead
107
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Correction of vibes (M/R & T/R) • If out of balance condition – May require Static or Dynamic procedures (or both depending on helicopter) – Some require Static balancing after assembly » Put on balance stand and adjust until no movement when released » T/R done like propeller (knife-edge stand) » M/R done on special stand with Bullseye level 12/09/09
Author: Harry L. Whitehead
108
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Vibrations
– Correction of vibes (M/R & T/R) • If out of balance condition » M/R also may require Blade Sweep to be adjusted (for chordwise balance) » = stretch string between blades and adjust until blades are exactly 180o apart (adjust by “sweeping” blades forward or aft as necessary) Author: Harry L. Whitehead 109 12/09/09
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Vibrations
– Correction of vibes (M/R & T/R) • If out of balance condition – Dynamic balancing done during operations on ground and in air – Uses Electronic gear to measure rate and strength and charts to show adjustments • Some M/Rs don’t need dynamic after static but 110 12/09/09 all T/Rs do Author: Harry L. Whitehead
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Example: Chadwick-Helmuth Vibrex® system 12/09/09
Author: Harry L. Whitehead
111
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Vibrations – Measurement of vibes • Example chart: – T/R balance
12/09/09
Author: Harry L. Whitehead
112
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Vibrations – Measurement of vibes • Example chart: – T/R balance
12/09/09
Author: Harry L. Whitehead
113
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Vibrations – Measurement of vibes • Example chart: – M/R balance
12/09/09
Author: Harry L. Whitehead
114
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Vibrations – Measurement of vibes • Example chart: – M/R balance
12/09/09
Author: Harry L. Whitehead
115
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Correction of vibes (M/R & T/R) • If out of Track condition – Track = path Blade tips follow during rotation – In-Track = all tips follow same path (or Cone the same amount) and = minimal vertical vibes – All M/Rs need to be checked and adjusted and some T/Rs
12/09/09
Author: Harry L. Whitehead
116
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Correction of vibes (M/R & T/R) • If out of Track condition – Ground check » Use marking stick or Flag » Marking Stick uses crayon or grease pencil on end of long stick and carefully raise to bottom of blades to make mark on lowest one (adjust until marks all blades)
12/09/09
Author: Harry L. Whitehead
117
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Correction of vibes (M/R & T/R) • If out of Track condition – Ground check » Flag is strip of canvas suspended between F shaped pole + put crayon mark on blade tips (different color on each blade) then move Flag so just touches each blade to get a colored mark » Use colors to determine which blade needs adjustment 12/09/09
Author: Harry L. Whitehead
118
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Flag Tracking
Flag Tracking
12/09/09
Author: Harry L. Whitehead
119
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Correction of vibes (M/R & T/R) • If out of Track condition – Ground check » All are adjusted by changing the length of the Pitch Links (controls Angle of Incidence of blades) » Link between Swashplate and M/R blade » Increase angle = more lift = blade flies higher » Each manufacturer usually has standard adjustments (I.e. 1/6 turn = ½” blade movement) Author: Harry L. Whitehead 120 » Limitation: can’t check in flight 12/09/09
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Vibrations – Correction of vibes (M/R & T/R) • If out of Track condition – Ground & Flight » Use spotlight or strobe » Spotlight uses colored reflectors attached to blade » Light shows colored streaks and can see “altitude” Author: Harry L. Whitehead 121 12/09/09 difference between them
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Correction of vibes (M/R & T/R) • If out of Track condition – Ground & Flight » Strobe is keyed by pickup on swashplate » Flashes once for each blade » Has reflectors on each blade with different angled “Target” line » Flashes ‘stop’ targets at one location and can easily see difference and which blade to adjust 12/09/09
Author: Harry L. Whitehead
122
Helicopters Controls
Vibrations
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Correction of vibes (M/R & T/R) • If out of Track condition – Ground & Flight » For ground and hover adjustment = use Pitch Links » For in-flight adjustment = most blades have trailing edge fixed trim tabs to allow limited bending
12/09/09
Author: Harry L. Whitehead
123
Helicopters Controls
Power Systems & Other Components
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Powerplants • Reciprocating – See all types: Horizontal and Vertically mounted Opposed engines & some Radials 12/09/09
Author: Harry L. Whitehead
124
Helicopters Controls
Power Systems & Other Components
– Powerplants • Reciprocating – Verticals and Radials usually are Dry-sump with M/R Transmission (GearBox) mounted on top Harry L. Whitehead and using same Author: oil supply 12/09/09
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
125
Helicopters Controls
Power Systems & Other Components – Powerplants • Reciprocating – Verticals and Radials usually are Dry-sump with M/R Transmission (GearBox) mounted on top and using same oil supply
12/09/09
Author: Harry L. Whitehead
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Bell 47
126
Helicopters Controls
Power Systems & Other Components
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Powerplants • Reciprocating – Horizontals usually use some form of Belt Drive » Multiple V-belts or one wide “timing” belt 12/09/09
Author: Harry L. Whitehead
127
Helicopters Controls
Power Systems & Other Components – Powerplants • Reciprocating – None have propeller for cooling air blast and “fly wheel” for starting – All use some form of Cooling Fan driven by engine to blow air across cylinders – All are generally hard to start (no fly wheel to help process keep going) Author: Harry L. Whitehead 12/09/09
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
128
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Power Systems & Other Components
– Powerplants • Reciprocating Instruments – Since M/R is essentially a Variable-pitch Propeller = all use both Tachometer (RPM) and Manifold Pressure gauges for power measurement – Engines must be operated at relatively constant RPM (to allow enough Lift & Thrust) and usually very near the manufacturer’s Overspeed limit 12/09/09
Author: Harry L. Whitehead
129
Helicopters Controls
Power Systems & Other Components
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Powerplants • Reciprocating – Usually uses Correlated Throttle and Collective » Pull up on collective = more blade pitch = more lift/thrust generated = more drag » Need more engine power to keep RPM constant » Correlation increases throttle automatically as Collective is pulled up (may not do Author: Harry L. Whitehead 12/09/09 entire job, though)
130
Bell 47
Helicopters Controls
Power Systems & Other Components
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Powerplants • Reciprocating – Usually uses Correlated Throttle and Collective » Pull up on collective = more blade pitch = more lift/thrust generated = more drag » Need more engine power to keep RPM constant » Correlation increases throttle automatically as Collective is pulled up (may not do Author: Harry L. Whitehead 12/09/09 entire job, though)
131
Helicopters Controls
Power Systems & Other Components
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Powerplants
• Turbines – Are ideal powerplants as operate most efficiently at constant RPM and have very high power to weight ratio 12/09/09
Author: Harry L. Whitehead
132
Helicopters Controls
Power Systems & Other Components
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Powerplants
• Turbines – Are TurboShaft engines » All output power is converted to rotating shaft power (Torque) » Torque sent to Transmission to drive Main & Tail Rotors and other necessary components 12/09/09
Author: Harry L. Whitehead
133
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Power Systems & Other Components
– Powerplants • Turbines – Are TurboShaft engines » Two basic types: Direct Shaft & Free Turbine » Direct Shaft has PTO shaft connected to all Compressor and Turbine section stages » Are very hard to start as must turn all engine + Main and Tail rotors 12/09/09
Author: Harry L. Whitehead
134
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Power Systems & Other Components
– Powerplants • Turbines – Are TurboShaft engines » Two basic types: Direct Shaft & Free Turbine » Free Turbine has some Turbine stages which only supply PTO power » Easier to start as rotors not mechanically connected to main part of engine 12/09/09
Author: Harry L. Whitehead
135
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Power Systems & Other Components
– Powerplants • Turbines – Are TurboShaft engines » Measure power output with Tachometers, Torquemeters, and Turbine Temperature gauges » Tachs measure RPM in % (due to high actual RPM) » Free Turbine versions need to measure both main engine (N1) and Power Turbine (N2) and have separate gauges136 Author:usually Harry L. Whitehead 12/09/09
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Power Systems & Other Components
– Powerplants • Turbines – Are TurboShaft engines » Torquemeters measure power being absorbed by M/Rs » Similar to MAP gauge on recips » Measures in % or in Pounds of Torque
12/09/09
Author: Harry L. Whitehead
137
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Power Systems & Other Components
– Powerplants • Turbines – Are TurboShaft engines » Turbine Temps very important as are directly proportional to how hard the engine’s working and critical during the start cycle » May be TIT, ITT, TOT, or EGT system (manufacturer’s choice) » CAN NOT exceed max. limit or will damage section components 138 Author:Turbine Harry L. Whitehead 12/09/09
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Power Systems & Other Components
– Transmissions • For speed and/or directional change of rotating shaft(s) • May be Rack & Pinion or Planetary Gear systems • Uses engine oil or has own supply
12/09/09
Author: Harry L. Whitehead
139
Helicopters Controls
Power Systems & Other Components
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Transmissions • For speed and/or directional change of rotating shaft(s) • May be Rack & Pinion or Planetary Gear systems Schweizer (Hughes) 269 Transmission: Rack (Ring Gear) and Author: Harry L. Whitehead 140 12/09/09 Pinion
Bell 47 Transmission: Planetary system
12/09/09
Author: Harry L. Whitehead
141
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Power Systems & Other Components
– Transmissions • Engine drives M/R Transmission which in turn drives the T/R, Hydraulic pumps, Electrical Generator, Cooling Fans (if appropriate for the aircraft), and Rotor Tach sending unit connected to (usually) Dual Tach (Rotor and Engine RPM Author: Harry L. Whitehead 142 12/09/09 on same gauge)
Helicopters Controls
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
Power Systems & Other Components
– Clutch • USED TO RELIEVE THE ENGINE LOAD DURING STARTING • May be Manual, Electrical, or Centrifugal • Manual and Electrical pull Idler Pulley against Belt(s) to tighten them and connect engine with Transmission
12/09/09
Author: Harry L. Whitehead
143
Helicopters Controls
Power Systems & Other Components – Clutch • Centrifugal uses hinged Shoes pushed against a Drum by Centrifugal Force – Shoes on arms attached to engine crankshaft – Drum attached to Transmission Author: Harry L. Whitehead 12/09/09
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
144
Helicopters Controls
Power Systems & Other Components
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Freewheeling Unit • FOR AUTOROTATION PURPOSES • Disconnects M/R from engine if engine turns slower than M/ R • Usually either Roller or Sprag style 12/09/09
Author: Harry L. Whitehead
145
Helicopters Controls
Power Systems & Other Components
History Configurations Types of Rotor Systems Forces Acting on the Rotor Flight Conditions
Controls Stabilizer Controls Vibrations Power Systems
– Freewheeling Unit • FOR AUTOROTATION PURPOSES • Disconnects M/R from engine if engine turns slower than M/ R • Usually either Roller or Sprag style 12/09/09
Author: Harry L. Whitehead
146
12/09/09
Author: Harry L. Whitehead
147
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