Hal Repor (1).docx

LANDING GEAR Landing gear is the undercarriage of the aircraft or space craft which primarily supports the static and dynamic loads acting on the platform, also crucial in various phases of flight. The major purpose of using the landing gear is: 1. 2. 3. 4. 5.

To support static loads To dampen and withstand vertical loads To control horizontal component of velocity To taxi and steer the aircraft To withstand takeoff and landing loads

Landing design parameters vary with aircraft design as static and dynamic loads vary also the position of the cg also changes. Different types of wheel configurations: 1. Bicycle 2. Tricycle 3. Tail based Tricycle is used because there is ease of loading of cargo and the pilot has better visual reference on the ground. The carriage is located behind the cg. Tail based used where more prop clearance is required, this configuration might cause difficulty in loading, lesser visual reference on ground. The carriage is located ahead of cg. Types of landing gears: Telescopic: This configuration follows a cylinder in cylinder type arrangement the shock absorber is oleo pneumatic. The oil and nitrogen used act as damping agents. Articulate: This configuration consist a number of joints and joining members. There is a suspended lever which is attached to the wheel assembly the

direction bar dictates the direction of retraction and extension. This is generally used when the sink rates are lower and also the ground clearance. Semi articulate: This is similar to articulate but has lesser number of joints. Nitrogen is generally preferred in the shock absorber because the gas is thermodynamically inert has large molecular size and is non corrosive in nature. The shock absorber consists of a flutter valve which regulates the flow of fluid so that required reactive forces could be generated so that the impulsive loads can be dampened. The braking system of the landing gear consist of set of rotors and stators which on interacting with each other produce the required braking force. The rotor discs are made of carbon fibre. The ABS system prevents skidding by pressure fluctuation through suitable input from wheel accelometers and pressure transducers. The up lock and down lock mechanisms ensure proper locking of the gear when in fully extended and retracted position. Directional solenoid controls the opening and closing of the doors. The steering mechanism follows a rack and pinion type arrangement.

REAR LANDING GEAR OF LCA

HYDRAULICS Hydraulic systems are widely used in flight controls, braking, deployment of landing gear or we could wherever actuation ease is required hydraulics are used. Hydraulic systems generally work on Pascal’s law which states that pressure is transmitted equally in all directions through which large forces could be transmitted through application of less effort. They form a vital component in a power assisted control loop and have major advantages: 1. High power to weight ratio 2. Ability to hold a control position without fluctuation 3. Reliable and easy access for maintainence.

The major components of a hydraulic system are: 1. 2. 3. 4. 5. 6. 7.

Reservoir Non return valves and directional valves Pressure relief valves Accumulators Pumps Filters Actuators

Reservoir is the component where the hydraulic fluid is stored the fuel stored here is clean, pressurized and froth free. Strap type reservoirs are used in military aircraft. The non return and directional valves control the flow of hydraulic fluid in the loop so that required actuating effect takes place. When there is excess pressure development in the loop then the pressure relief valve reduces the excess pressure development.

Accumulators provide pressurized fluid when there is sudden requirement of actuation. They are nitrogen pressurized vessels containing a certain amount of fluid. Pumps are devices which pressurize the fluid; these are generally engine driven of electrically driven. Pumps can be piston or gear type. Filters ensure that no eroded material or debris mixes with the fluid and are responsible for keeping then fluid clean. Actuators are devices which convert the hydraulic input to mechanical output. They are generally double sided where on one side the pressurized fluid acts and on the other the used fluid is moved to the reservoir. The hydraulic fluid used in military aircraft are of MIL5606H standard since the fluid might heat up during operation the fluid must operate in a wide temperature range (-40 to 135*C)

POWER PLANT AND FUEL SYSTEM The power plant and fuel department is concerned with the choice of the power plant its design parameters like shape, size, thrust and performance parameters. Also the sizing of the fuel channel, LRU’S for transfer and storing fuel, fuel movement and dynamics are all studied in the group. The requirement of the fuel system is that in all altitude and attitudes the fuel rates and the amount of fuel supplied to the power plant must be same. Fuel is fed to the aircraft mainly through methods: 1. Gravity feed 2. Pressure feed (4000 lit of fuel can be fed in 8 min) Fuel feed system consists of a hydraulic pump or electrical pump (redundancy), a supply channel, filters, Lp lock, jet fuel starters. For inverted flights there is a special feed system. Since fuel is being consumed during flight the position of the cg shifts which affects the stability. Here the transfer system comes into play where fuel is mobilized from the main tanks to the tanks present in the wings. Fuel measurement system consists of probes which work on capacitive principles to measure the fuel levels. These probes may be positioned in different locations to get correct measurements in different attitudes. MFD display of the cockpit gives all vital information like fuel levels , EGT, oil temp & pressure, manifold pressure hence giving vital information on the health of the power plant and fuel feed system.

WING AND EMPANNAGE DESIGN Wings are the major lift producing component the geometric and structural parameters must be carefully planned. Wings are able to produce lift owing to their airfoil cross section where there is difference in pressures on the top and bottom surfaces hence generating the required lift. Geometric parameters like span, taper ratio, MAC, wing area have to carefully decided on as each have their own aerodynamic implications. A wing could be divided into three major regions: 1. Nose box 2. Torsion box 3. Rear box

Major structural members of the wing are: 1. 2. 3. 4.

Spars (front and rear spars) Stringers Skin Ribs

Due to large amount of aerodynamic loads (lift distribution span wise) acting the wings experience a bending moment at the root, these bending moments are taken by the spar. Special attachments in the wing fuselage interface resist the bending loads. There are special shear attachments which resist shear loading. Apart from these loads the wing also experiences torsional loads; the magnitude of these loads is determined by the eccentricity of the elastic line and the aerodynamic centre. The torsion box is carefully designed to resist these torsional loads.

Stringers are generally stiffening members they stiffen the skin so that they don’t buckle under load. Skin is the covering member of the wing mainly responsible for resisting shear stresses. Ribs are those members who maintain the airfoil shape of the wing also act as support brackets for taking concentrated loads. Wings generally employ thick airfoils because of height of attachment at the fuselage. (NACA 6 digit). Generally wings are designed to stall the root first so that we don’t lose aileron controllability. Wings can also be dihedral or anhedral whether we want our platform to be stable or maneuverable respectively. They can also be delta, swept back, and swept forward, to enhance aerodynamic performance. There are various devices which enhance flow over wings like nose droppers, strakes, slats & slots, fences, turbulators. Warning devices like breaker strips warn pilots from stalling. Skin pockets and holes in various elements of the wing are meant for weight reduction. These passages are also meant for hydraulic lines and fuel. Wings are auxiliary fuel tanks where fuel can stored and utilized, the fuel tanks are present between two ribs and are made leak proof by application of sealant. (PR1770). These tanks are also called dry bays. Wings also have control surfaces (ailerons, flaps, spoilers) which are of utmost importance in flight control; these surfaces require rotational freedom and are connected to hinges. The control surfaces are attached to wing by shroud riblets, actuators are placed in holding brackets.

The skin is attached to the wing by rivets or they are integrated, the latter design is generally followed.

COMPONENTS OF WING

DELTA DESIGN FOR A MILITARY AIRCRAFT

ENVIRNOMENTAL CONTROL SYSTEMS All modern day aircrafts operate at high speeds and altitudes, at such operating conditions the human physiology becomes adverse and survival becomes difficult. At high altitudes the temperature, density, vapour pressure all lower which needs to be considered by this group so that preventive measures can be taken. At high altitudes due to the low vapour and rarity of the atmosphere the oxygen present in air is not able to diffuse in the blood stream causing a condition called hypoxia this may affect consciousness and decision making. Conditions like bends; caused due to expansion of nitrogen may result in pain in joints, the skin can expand as a balloon and the blood may begin to boil as well. The loss in humidity can cause dry skin and irritation in nasal passages. Ozone present at these altitudes might also cause irritation. The ECS systems generally are of two types: 1. Air type (occupies lesser space) 2. Liquid type

The air type ECS system consists of: 1. 2. 3. 4. 5. 6. 7. 8.

Pressure tapping from the engine ( about 36 bar & 786*C) Pressure reduction valve Primary & secondary heat exchanger (finned type heat exchangers) Cold air unit Temprature control valve Pressurization system for the cockpit seal Radom pressurization unit (to prevent arcing) Humidity control system (centrifuge type)

The air ECS system works on the air cycle principle heat exchangers take heat from cockpit and dump heat to the surroundings, the expander cools the air

and compressor increases the pressure and temprature. Hence the required temperature and pressure and other environmental conditions can be maintained in the cabin. The OBOGS is an autonomous system which provides pure oxygen supply to meet all physiological conditions of the pilot it generally contains zeolite filters which filter all other components of air and supply unadulterated oxygen upto 98% pure.

A TYPICAL OBOGS SCHEMATIC

ARMAMENT AND EJECTION The armament and ejection group are responsible for positioning and accommodating stores (warheads) and integrating them in the aircraft. While the seat ejection is a safety feature which is common in all combat aircraft. The LCA aircraft has 9 hard points and 8 weapon stations, the out board has a capacity of 250kg, the middle board has a capacity of 800kg, the inboard has a capacity of 1200kg. It also has a belly attachment provision also a LDP bracket. The stores are attached to wing through an attachment interface called pylon. These pylons are meant to withstand the aerodynamic loads and the inertial loads of the stores. The pylon generally consists of; ERU (ejector release unit), PIB (pylon interface box), fairings, motorized valves, throttle, fuzzing unit. The ERU is a cartridge which on providing with an electric spark generates high pressure gases which release the stores. The PIB integrates the OAC with the store management system through a weapon bus so that easy selection, tracking, fusing and release of weapons are possible. The design considerations for the pylon are: 1. Light weight 2. Sleek design 3. Spacing 4. Flexibility 5. Necessary clearances 6. Fairings should be aerodynamic

The in board pylons have ERU 120, the middle board pylons have ERU 119 each having different dimensions of suspension tools. The outboard pylons are missile launchers and they do not have ERU’S. There are various types of warhead like BVRM’S (beyond visual range missiles), laser guided bombs, carpet bombs, glide bombs, 23mm cannon all can be integrated on the LCA. There are various radar systems which could be integrated; active, semi active, IR type radars. The stores could be arranged in mainly 3 configurations; single, side by side, tandem, triple type. The seat ejection system is a complicated system in which various design parameters like ejection speed & altitude, spin stabilization, ejection height all have to consider carefully. The ISS (intermediate seat selector) is a ejection protocol which has two modes of BOTH & SOLO in which the seat is ejected in a particular sequence. (rear within 0.17sec, 0.54sec front) A seat ejection system has a set of rocket motors which propels the seat along guide rails on pulling a cord in front of the seat, after moving out of the guide rail the rocket motors is turned off at a particular clearance distance, the drogue parachutes are deployed (spin stabilization), then the main parachute is deployed. The seat has a life support compartment which has all essentials for survival (knife, fluids, blankets, lighters, ropes).

ABOVE PICTURES SHOWING EJECTION SEAT & STORES OF LCA RESPECTIVELY.

FLIGHT CONTROL SYSTEM Flight controls group is responsible for designing the control system of the aircraft. The flight controls that are required for maintaining directional and attitude control. Data acquisition (vital flight parameters) is also a region of responsibility of the group. Flight controls are mainly three types: 1. Mechanical 2. Power assisted 3. Fly by wire Mechanical control systems consist of rods, brackets, tension rods, pulley system. The rods act as levers which reduces human effort in actuating the concerned control surface. Brackets are generally used for transfer load from one component to another. Lever ratio is an important parameter which determines the ease of operation of the concerned system. Mechanical systems are all subject to tension, compression, torsional and variable loads. In power assisted controls there is an actuator which moves the concerned control surface. These systems are used when aircraft travel at high speeds where the dynamic pressures are so high that human effort can’t deploy the surface. Also bigger aircrafts have bigger surfaces so greater the inertial loads. In FLY BY WIRE system there is a computer interface between the pilot input and the actuator the computer used in LCA is the qudraplex DFCC which has 4 channels of redundancy. The pilot signal is taken by the computer which gives command to the actuator. The two main components in this system are AFS (artificial feel system) which replicates the same resistance in stick movement (contains a stopper as well). The AFS consist of springs and dampers. The second component is the linear variable differential transducer which converts the mechanical movement of the stick into voltage. It works on the

principle of conductor motion in a magnetic field. This voltage is sent as input to the DFCC. The data acquisition mainly consists of measuring the; temperature, pressure, airspeed, attitude angles like angle of attack and angle of side slip. Temperature is measured through sensors which work on piezoelectric effect where a piezoelectric membrane produces voltage in corresponding change in temperature. The angle of attack and side slip angles are measured through rotary differential transducers. NSADP (nose air data probe) and side air data probe give the required data about equivalent airspeed, pressure and temperature. They generally employ the pitot method to carry out the measurements. De-icing system is also is present to prevent any malfunction due to ice formation. Various auxiliary systems like IMU (inertial measurement unit) measure the pitch, roll, yaw accelerations since they consist of accelometers and gyroscopes. It also consists of other systems like auto pilot, data recording unit (RS 422) which play a vital role in formation of the control loop.

TYPICAL FLY BY WIRE CONTROL LOOP

IRON BIRD TEST FACILITY The iron bird test facility is a state of the art facility in HAL ARDC complex where all hydraulics, flight response, and extensive simulation in various flight conditions are tested. Test pilots of HAL and the air force constantly test the LCA platform for its performance in various flight regimes and constantly tailor its control performance. The test rig in the facility tests the hydraulic system for actuation of the landing gear (airforce & navy), actuation system for control surfaces like ailerons, flaps LEVCONS. A real time cockpit with all MFU’S and a projector give the pilot a real time simulation and response in different flight envelopes. The test section test various other interfaces like the OAC (open architecture computer), ADC (air data computer), FDC (flight data computer), DFCC (digital flight control computer), also the BHEEM controller (this converts electric signals into pressure signals). The ETS or engineering test section can simulate failure conditions where adverse situation could be simulated.

PICTURE SHOWING TEST RIG

FUSELAGE (FRONT & REAR) The fuselage is a critical structural member which takes almost all loads acting on the aircraft; also it houses the intake, cargo and houses the LRU’S. The fuselage is divided into 38 stations for the LCA, the fuselage followed in today’s architecture is semi monocoque where the load is taken by the bulkhead (station) and is transferred through longitudinal members called longerons along with a skin. Alternate design choice could be monocoque. The rear fuselage (31 to 38) has provisions for mounting the LRU’s, has provision for mounting the engine and attaching the fin. The general structure of the rear fuselage is that the stations are mounted on shroud. The shroud along with polyamide coating is used for thermal insulation. The rear fuselage also has a dorsal spine which houses the ECS pipelines and the parachute assembly. The fuselage is joint mainly through rivets (where permanent joint is required) panels where accessibility of LRU’S is required are generally are fit with quick release fasteners called cam locks. The centre fuselage is major load carrying member where the wings are attached, intake is present, bracket for underbelly bomb and acts as an attachment between front and rear fuselage. This connection is made through 4 longerons. Front fuselage houses the pilot, avionics bay and radome. The major components of the front fuselage are the canopy and windscreen (acrylic sheet) the canopy systems have a locking system, counter poise, stowing bracket (for safety keys) and taxi rods.

The method of fixing the windscreen and canopy are similar but only variation is that the canopy has an extra surface to separate the DFCC and the cockpit.

MID SECTION FUSELAGE OF LCA