Ejections Seats

A Seminar Report On

EJECTION SEATS

Submitted To: -

Submitted By:-

Er. AMIT KAMBOJ Lecturer

Vijaydeep singh chauhan Roll no-1205358

Department of Applied Electronics &Instrumentation Engineering Seth Jai Prakash Mukand Lal Institute Of Engineering And Technology Radaur,Yamunanagar(135133) Affiliated to Kurukshetra University , Kurukshetra (An ISO 9000-2001 Certified Institute)

CONTENTS

• ACKNOWLEDGEMENT…………………………………………………1 • CERTIFICATE…………………………………………………………….2 • INTRODUCTION…………………………………………………………3 • HISTORY………………………………………………………………….4 • ESCAPE SYSTEM………………………………………………………...9 • AIR FORCE EJECTION SEATS………………………………………….10 • EVENT TIME SEQUENCE……………………………………………….13 • MODE ENVELOPES……………………………………………………...14 • EJECTION EVENTS……………………………………………………...16 • INTRODUCTION TO HOW EJECTION SEATS WORK………………..19 • MODES OF EJECTION……………………………………………………25 • TIMING AN EJECTION…………………………………………………...26 • EJECTION SEAT TERMS…………………………………………………29 • EJECTION SEAT IN OTHER AIRCRAFT………………………………..31 • FUTURE OF EJECTION SYSTEMS………………………………………32 • PILOT SAFETY…………………………………………………………….36 • SOURCES…………………………………………………………………..37

Acknowledgement There is always a sense of gratitude which one expresses to other for the help and timely services they render during all phases of life. I too would like to do it as I really wish to express my gratitude towards all those who have been helpful to me. Today after completing my seminar I feel a lot more relieved. I was very excited and bit nervous. I would never have completed it if the staff member of Instrumentation& Control Engineering Department had not helped me. I wish to express my humble thanks towards all of them. I am thankful to Er. AMIT KAMBOJ (Lecturer, Instrumentation Department) for providing me the opportunity to present a seminar in Instrumentation Deptt,jmit and especially for his invaluable guidance and frequent suggestions. Without him the seminar presentation would not have been possible.

VIJAYDEEP SINGH CHAUHAN 1205358

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CERTIFICATE This is to certify that the seminar report entitled “Ejection seats” submitted to Kurukshetra university, Kurukshetra in partial fulfillment of the requirement for the award of the degree of B.Tech ,is original work carried out by Mr.Vijaydeep singh chauhan with Roll no. 1205358 under my guidance. The matter embodied in this seminar report is genuine work done by the student & has not been submitted whether to this university or to any other university/ institute for the fulfillment of requirement of any course of study.

Signature of student

Er. R.S Chauhan

Er.Amit Kamboj

(Head of Department)

(Seminar Guide)

I&CE

Lect. I&CE Date:

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EJECTION SEATS "Aviation in itself is not inherently dangerous. But to an even greater degree than the sea, it is terribly unforgiving of any carelessness, incapacity, or neglect”.

INTRODUCTION

Emergency escape from aircraft has been of utmost importance to the United States Air Force since its inception. Regulations and policies to insure the safety and survival of crewmembers have been a major thrust of the entire safety program in the Air Force. The current sophisticated and advanced ejection seats with their increased performance capabilities attests to the goal of improving survivability of aircrews during escape from aircraft under adverse conditions throughout the flight envelope. Engineering sciences have made major contributions to individualizing the ejection seat operating mode to the specific circumstances of the ejection. Test personnel have rigorously demonstrated that these systems do work. Medical personnel have contributed to this effort by historically defining the limits within which the human can tolerate the forces of ejection

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History A bungee-assisted escape from an aircraft took place in 1910. In 1916 Everard Calthrop, an early inventor of parachutes, patented an ejector seat using compressed air[1]. The modern pattern for an ejection seat was invented in Germany in 1938 and perfected during World War II. Prior to this, the only means of escape from an incapacitated aircraft was to jump clear ("bail-out"), and in many cases this was difficult due to injury, the difficulty of egress from a confined space, g-forces, the airflow past the aircraft and other factors. The first ejection seats were developed independently during World War II by Heinkel and SAAB. Early models were powered by compressed air and the first aircraft to be fitted with such a system was the Heinkel He 280 prototype jet fighter in 1940. One of the He 280 test pilots, Helmut Schenk, became the first person to escape from a stricken aircraft with an ejection seat on January 13, 1942 after his control surfaces iced up and became inoperable. However the He 280 never reached production status. Thus, the first operational type to provide ejection seats for the crew was the Heinkel He 219 Uhu night fighter in 1942. In Sweden a version using compressed air was tested in 1941. A gunpowder ejection seat was developed by Bofors tested in 1943 for the Saab 21. The first test in the air was on a Saab 17 on 27 February 1944[2] and the first real use in July 29, 1946 after a mid-air collision between a J 21 and a J 22.[3] Saab 21 was the first aircraft to have ejection seat as standard. In late 1944, the Heinkel He 162 featured a new type of ejection seat, this time fired by an explosive cartridge. In this system the seat rode on wheels set between two pipes running up the back of the cockpit. When lowered into position, caps at the top of the seat fitted over the pipes to close them. Cartridges, basically identical to shotgun shells, were placed in the bottom of the pipes, facing upward. When fired the gases would fill the pipes, "popping" the caps off the end and thereby forcing the seat to ride up the pipes on its wheels, and out of the aircraft. By the

end of the war, the Do-335 Pfeil, Me-262 Schwalbe and Me-163 Komet also were fitted with ejection seats. 4 After World War II, the need for such systems became pressing, as aircraft speeds were getting ever higher, and it was not long before the sound barrier was broken. Manual escape at such speeds would be impossible. The United States Army Air Forces experimented with downward-ejecting systems operated by a spring, but it was the work of the British company Martin-Baker that was to prove crucial. The first live flight test of the Martin-Baker system took place on July 24, 1946, when Bernard Lynch ejected from a Gloster Meteor Mk III. Shortly afterwards, on August 17, 1946, 1st Sgt. Larry Lambert was the first live US ejectee. MartinBaker ejector seats were fitted to prototype and production aircraft from the late 1940s, and the first emergency use of such a seat occurred in 1949 during testing of the Armstrong-Whitworth AW.52 Flying Wing. Early seats used a solid propellant charge to eject the pilot and seat, by igniting the charge inside a telescoping tube attached to the seat. Effectively the seat was fired from the aircraft like a bullet from a gun. As jet speeds increased still further, this method proved inadequate to get the pilot sufficiently clear of the airframe and increasing the propellant risked damage to the occupant's spine, so experiments with rocket propulsion began. The F-102 Delta Dagger was the first aircraft to be fitted with a rocket propelled seat, in 1958. Martin-Baker developed a similar design, using multiple rocket units feeding a single nozzle. This had the advantage of being able to eject the pilot to a safe height even if the aircraft was on or very near the ground. In the early 1960s, deployment began of rocket-powered ejection seats designed for use at supersonic speeds, in such planes as the F-106 Delta Dart. Six pilots have ejected at speeds exceeding 700 knots (805mph) and the highest altitude a MartinBaker seat was deployed at was 57,000ft (from a Canberra in 1958). Following an accident in the attempted launch of a D-21 drone, two SR-71 crew members ejected at Mach 3.25 at an altitude of 80,000ft, the pilot successfully, however the observer was fatally injured. Despite these records, most ejections occur at fairly low speeds and altitudes, when the pilot can see that there is no hope of regaining aircraft control before impact on the ground.

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Egress Systems A warning applied on the cockpit side of all aircraft using an ejection seat system. Intended especially for the maintenance and emergency crews. A warning applied on the cockpit side of all aircraft using an ejection seat system. Intended especially for the maintenance and emergency crews. Capt. Christopher Stricklin ejects from his F-16 aircraft with an ACES II ejection seat, on September 14, 2003. Stricklin was not injured. Capt. Christopher Stricklin ejects from his F-16 aircraft with an ACES II ejection seat, on September 14, 2003. Stricklin was not injured. The "standard" ejection system operates in two stages. First, the entire canopy or hatch above the aviator is opened or jettisoned, and the seat and occupant are launched through the opening. In most earlier aircraft this required two separate actions by the aviator, while later egress system designs, such as the Advanced Concept Ejection Seat model 2 (ACES II) will perform both functions on a single action. The ACES II ejection seat is used in most of the United States Air Force's mainline fighters, including the A-10, F-15, and F-16. The A-10 uses connected firing handles that activate both the canopy jettison systems, followed by the seat ejection. The F-15 has the same connected system as the A-10 Seat. Both handles accomplish the same task, so pulling either one suffices. The F-16 has only one rubber handle located between the pilot's knees, since the cockpit is too narrow for side-mounted handles. Unlike the F-15 and A-10, however, the F-16 does NOT have canopy breaking systems installed. The angle of the ejection seat inside the aircraft is so extreme that a pilot's head would strike the canopy before any installed canopy breakers would. Also, the canopy is constructed of highly durable composite material which cannot be shattered by seat ejection. Non-standard egress systems include Downward Track (used for some crew positions in bomber aircraft, including the B-52 Stratofortress), Canopy Destruct (CD) and Through-Canopy Penetration (TCP), Drag Extraction, Encapsulated Seat and even Crew Capsule.

6 Early models of the F-104 Starfighter were equipped with a Downward Track ejection seat due to the hazard of the T-tail. In order to make this work, the pilot was equipped with "spurs" which were attached to cables that would pull the legs inwards so the pilot could be ejected. Following this development, a number of other egress systems began using leg-retractors as a way to prevent injuries to flailing legs, and to provide a more stable center of gravity. Some models of the F104 were equipped with upward-ejecting seats, which led to several fatal accidents when pilots trained on the downward-firing seats rolled inverted at low altitude and ejected. Similarly, two of the six ejection seats on the B-52 Stratofortress fire downward, through hatch openings on the bottom of the aircraft; The downward hatches are released from the aircraft by a thruster that unlocks the hatch, gravity and wind remove the hatch and arm the seat. The four seats on the forward upper deck fire upwards (two of them, EWO and Gunner, facing the rear of the airplane) as usual. Note that any such down-firing system is of no use on or near the ground unless the aircraft is upsidedown at the time of the ejection. Aircraft designed for low-level use sometimes have ejection seats which fire through the canopy, as waiting for the canopy to be ejected is too slow. Many aircraft types (e.g. BAe Hawk and the Harrier line of aircraft) use Canopy Destruct systems, which have an explosive cord (MDC - Mild Detonation Cord or FLSC -Flexible Linear Shaped Charge) embedded within the acrylic plastic of the canopy. The MDC is initiated when the eject handle is pulled, and shatters the canopy over the seat a few milliseconds before the seat is launched. Through-Canopy Penetration is similar to Canopy Destruct, but a sharp spike on the top of the seat, known as the "shell tooth," strikes the underside of the canopy and shatters it. The A-10 Thunderbolt II is equipped with canopy breakers on either side of its headrest in the event that the canopy fails to jettison. In ground emergencies, a ground crew or pilot can use a breaker knife attached to the inside of the canopy to shatter the transparency. The A-6 Intruder and EA-6 Prowler seats are capable of ejecting through the canopy, with canopy jettison a separate option if there is enough time. CD and TCP systems cannot be used with canopies made of flexible materials,

such as the Lexan polycarbonate canopy used on the F-16. 7 Soviet Yakovlev Yak-38 VTOL naval fighter planes were equipped with automatically activated ejection seats, mandated by the notorious unreliability of their vertical lifting powerplants. Drag Extraction is the lightest and simplest egress system available, and has been used on many experimental aircraft, and even the Space Shuttle. Halfway between simply "bailing out" and using explosive-eject systems, Drag Extraction uses the airflow past the aircraft (or spacecraft) to move the aviator out of the cockpit and away from the stricken craft on a guide rail. Some operate like a standard ejector seat, by jettisoning the canopy, then deploying a drag chute into the airflow. That chute pulls the occupant out of the aircraft, either with the seat or following release of the seat straps, who then rides off the end of a rail extending far enough out to help clear the structure. In the case of the Space Shuttle, the astronauts ride a long, curved rail, blown by the wind against their bodies, then deploy their chutes after free-falling to a safe altitude. Encapsulated Seat egress systems were developed for use in the B-58 Hustler and B-70 Valkyrie supersonic bombers. These seats were enclosed in an air-operated clamshell, which permitted the aircrew to escape at airspeeds high enough to cause bodily harm. These seats were designed to allow the pilot to control the plane even with the clamshell closed, and the capsule would float in case of water landings. Some aircraft designs, such as the General Dynamics F-111, do not have individual ejection seats, but instead, the entire section of the airframe containing the crew can be ejected as a single capsule. In this system, very powerful rockets are used, and multiple large parachutes are used to bring the capsule down, in a manner very similar to the Launch Escape System of the Apollo spacecraft. On landing, an airbag system is used to cushion the landing, and this also acts as a flotation device if the Crew Capsule lands in water. Zero-zero ejection seat A Zero-zero ejection seat is designed to safely extract upward and land its occupant from a grounded stationary position (i.e., zero altitude and zero airspeed), specifically from aircraft cockpits. The zero-zero capability was developed to help aircrews escape upward from unrecoverable emergency situations during low

altitude and/or low speed flight as well as ground mishaps. Before this capability, ejections had to be performed at minimum altitudes and airspeeds. 8 Zero-zero technology uses a small explosive charge to open the parachute canopy quickly, so that reliance on airspeed and altitude is no longer required for proper deployment of the parachute.

ESCAPE SYSTEMS Ejection Seat Operation With the advent of high-performance aircraft, the development of aircraft ejection seats became necessary due to speeds that precluded safe manual bailout. Strong windblast prevented clearing the aircraft and excessive G- forces immobilized aircrew members thus prohibiting escape. The modern ejection seat having undergone a series of refinements since its inception in l946 is today a highly automated system that requires the occupant to only initiate the firing mechanism to effect escape. Typically, the seat consists of a padded bucket, back, and headrest. The seat is mounted on rails which guide the seat on its initial trajectory. Most seats are propelled by rockets but the methods of restraint, seat separation, and chute deployment will vary according to the various types of ejection seats. Generally, escape is initiated by pulling a firing handle. In some seats a trigger within the handle then must be squeezed to initiate ejection. As the ejection seat travels up the rails, a leg restraint system activates. The development of rocket propulsion has produced the higher trajectory necessary to clear aircraft structures during high speed escape as well as escape during low speed and zero-zero (zero velocity and zero altitude) ejections. Seat stabilization gyros have been incorporated into recently developed ejection seats to cancel asymmetric forces producing rotation and tumbling (l).

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The Modern high technology ejection seat. (ACES I Air Force Ejection Seats The ejection seat for the T-37 is an individually activated ballistic seat rather than the rocket-powered seat of most other jet aircraft. It thus provides a rapid escape from the aircraft but with a limited escape envelope. The emergency minimum ejection altitudes for a T-37 with no sink rate, level bank, and pitch are: (l) With an Fl-B timer (l sec chute): 200 feet altitude and l20 knots indicated air speed (KIAS). (2) With an F-lB zero delay lanyard connected: l00 feet altitude and l20 KIAS. The seat should work at air speeds as high as 425 KIAS.

The T-37 seat accommodates a back-type parachute and is provided with an inertial reel shoulder harness, an automatic opening lap belt, and a seat separator (butt snapper). It can be manually adjusted up and down and has an emergency disconnect unit in the lower right side. This unit contains the communication lead and oxygen hose with quick disconnect fittings. The seat has a canopy piercer on 10

the top of the seat for through-the-canopy ejections. There are interconnected handgrips on either side of the seat. Within each handgrip is a trigger which is accessible only when the handgrips are in the full up position. Squeezing either trigger initiates canopy jettison and the seat fires 0.33 seconds later. After a 1second delay, a seat initiator fires the HGU-l2/A lap belt and the seat separator which provides an automatic and positive separation of the seat and the occupant. The lap belt lanyard (gold key) attached to the seat belt activates the parachute opening device, or pulls the D-handle via the zero-delay lanyard (2). The T-38 ejection seat contains an ejection rocket catapult, a calf guard, two leg braces, a shoulder harness inertia reel, automatic lap belt release, a head rest, a seat separator system, a drogue chute, a drogue gun with five initiators, and a seat adjusting unit. The seat height can be adjusted by an electrically operated actuator via a toggle switch. The inertial reel can be locked by a control lever. When the strap is free to reel in or out, it will lock at a minimum of 2Gs and a maximum of 3Gs but will return to free movement after relaxation of G forces. However, an excessive G load on the strap will lock the reel and it will remain locked until the crewmember resets the control lever. It also locks automatically during seat ejection. The calf guard is hinge mounted and attaches to the bottom front of the seat and is held in a stowed position. During ejection it is pulled downward into position automatically. There is a hand grip and trigger on both sides of the seat, either of which will activate the initiator and fire the rocket catapult for seat ejection. Pulling either trigger first fires the canopy ejection initiator causing canopy jettison. The inertial reel locks automatically and the seat catapult is activated which ejects the seat from the aircraft. Approximately 0.2 seconds after catapult firing, the drogue gun fires to deploy the drogue chute to stabilize the seat trajectory. At 0.65 seconds after the seat leaves the floor of the aircraft, the seat separator system is activated and that releases the lap belt and forces the occupant away from the seat with the parachute. The parachute deploys shortly thereafter. With this system, successful ejection is possible with 50 knots airspeed on the ground. After parachute deployment, the survival kit will automatically deploy in

approximately 4 seconds. If the survival kit is in the manual mode, it must be released manually with the handle on the right front center of the kit. The weight of the pilot influences the performance of this system. Tests conducted with mannequins weighing as much as 247 pounds were successful with this 11 system retaining its above 50 knots KIAS capability. Accelerative forces will vary according to the weight of the pilot, with pilots weighing in the 5th percentile experiencing l8-20 Gs and 95th percentile pilots experiencing l4-l6 Gs. Maximum recommended airspeed for ejection is 500 KIAS (2). The Martin-Baker seat was utilized in the F-4 and early A-10 aircraft. In 1967, as ejections from F-4s increased, it became apparent that a means to reduce spinal compression injuries caused by high onset rate of forces was needed. The Mark 5 seat was modified primarily through the addition of a rocket pack, lessening the ejection acceleration acting on the spine. It was designated the Mark 7 seat. Parachute deployment was aided by the use of a drogue chute. After the system had been in use for some time, failure of the F-4 forward canopy to jettison at high speeds indicated a need for additional force to insure positive jettison of the canopy. This was accomplished as well as incorporating three ejection sequences thus allowing the front seat to initiate dual ejection, aft seat initiated dual ejection, and aft seat single ejection (3). The Advanced Concept Ejection Seat (ACES II) is currently used in the A- l0, Fl5, F-l6, F-117A, B-lB, and B-2 aircraft and incorporates many of the advanced technology characteristics that have evolved in ejection seats. It has a zero-zero capability, deploying a useful chute with ejection on the ground at standstill. In low speed ejections, a gyro-controlled vernier rocket provides pitch stabilization. In high speed ejection conditions additional stabilization is provided by a drogue parachute. To achieve minimum-distance recovery in low-speed ejections, the recovery parachute is deployed as the seat leaves the cockpit. At high speeds, the drogue parachute is deployed immediately, quickly decelerating the seat and crewmember to a suitable speed for recovery parachute deployment. The use of multiple recovery modes permits the functions and timing of the recovery subsystem to be selected for each mode allowing optimum performance throughout the escape envelope. The recovery parachute and the drogue parachute subsystems are entirely independent. In the low-speed mode, Mode l, deployment of the recovery parachute is initiated as the seat and the crewmember are emerging from

the cockpit. Thus, the elapsed time from ejection initiation to parachute inflation is minimized for the critical low-speed, low-altitude ejection conditions. In the highspeed mode, Mode 2, the drogue parachute is needed to slow the seat and occupant prior to recovery parachute deployment. The drogue is not severed until after the recovery parachute has been deployed. 12 Mode 3 is used for high altitude ejection allowing the seat to descend or decelerate into the Mode 2 parameters prior to Mode 2 recovery being initiated. Mode selection is performed by the recovery sequencer in conjunction with an environmental sensing subsystem which determines airspeed and altitude conditions independent from aircraft systems

EVENT-TIME SEQUENCE

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Mode envelopes

Mode 1 operation

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Mode 2 operation

Mode 3 operation

ACES II functional breakdown 15

EJECTION EVENTS Pre-ejection The time interval from the initial need to leave the aircraft (e.g., aircraft damage, loss of controlled flight) until ejection is initiated is known as pre-ejection. During certain critical phases of flight, such as during takeoff and landing, this can be extremely short and not allow any preparation prior to ejection. However, in other situations, such as in- flight emergencies, this time may be sufficient for making changes to increase the probability of successful ejection. Speed can be reduced to lessen the effects of windblast and flailing. Harness straps can be tightened and body position can be adjusted to reduce injury from the forces encountered during ejection (3). The delay in making the decision to eject has been stressed in flying safety programs since accident data has revealed that over one-third of the aircrew fatally injured during ejection experienced the emergency at altitudes adequate for a successful ejection. This delay has been related to human factors and educational attempts to discourage fatal delays have been included in safety training (2).

Primary Acceleration Ejection forces are primarily in the upward direction. The object is to attain the greatest possible velocity over a specified period of time. The force which causes the seat to move upward ranges between l2 and 20 Gs. The incidence of spinal injury appears to increase markedly if the peak acceleration exceeds 25 Gs and if the rate of onset is greater than 300 Gs per second. Many factors will determine the actual value that an ejection seat will produce. The propulsion device will be affected by temperature, the total weight of the occupant-seat assembly, the aircraft velocity and relative airspeed at the time of ejection, and the altitude of ejection. The accelerative forces will also be influenced by the complex mechanical behavior of the pilot's body in its relationship to the seat as well as how various body parts relate to each other. The human body may be viewed as a fluid-filled body as it behaves in a dynamic fashion during the ejection sequence. Compression forces may be initially elastic but will often exceed the elastic limits and thus become "dynamic overshoots." These overshoots become important in addressing the injuries sustained during the ejection sequence. The line of seat thrust does not correspond to the long axis of the spine because the guide rails are tilted back at approximately l2 to 20 degrees. 16

The net effect is to produce a vector of forward acceleration necessitating adequate shoulder restraint and protection of the head. The rocket propelled seats have extended the duration of upward thrust and allowed a reduction in the rate of onset of the force to the body as compared to ballistic seats. The result has been an associated reduction in the incidence of spinal injury (l).

Forces of Windblast After the initial +Gz acceleration of the seat going up the rails, and differential plus and minus Gz acceleration of "gradual" entry into the airstream, the occupant-seat combination is rapidly decelerated due to ram air force from windblast. This force is termed the Q force and varies with the density of the air and is proportional to the surface area of the occupant- seat combination. Q forces are related to indicated airspeed rather than true airspeed. These forces increase with the square of the velocity thus producing the recommendation that pilots should reduce airspeed and increase altitude prior to ejection (3). Q forces have been divided into those produced by windblast, resulting in injuries such as petechial and subconjunctival hemorrhage, and those injuries produced by flailing of the head and extremities. Flail injuries are the result of the differential deceleration of the extremities in

relationship to the torso and seat. Flail injury occurs as a consequence of the extremities leaving their initial position, building up substantial acceleration, and then suddenly stopping. The sudden stop may produce a bone fracture, joint dislocation, or total disarticulation (l). Review of combat ejections in Southeast Asia revealed a strong correlation between high-speed ejection and flail injuries (3). Tumbling of the ejection seat and its occupant has been effectively reduced by use of stabilizer drogue chutes and gyro-controlled vernier rockets for positive pitch stabilization (4).

Parachute Descent and Landing This phase of the ejection sequence is critical to the outcome of the entire process of escape and yet 90 per cent of all non-fatal injuries associated with escape occur during landing. Although the techniques of landing by parachute are easily taught and simulated by jumps from training towers, the incidence of sprained or fractured ankles is estimated to be 50 per thousand descents (l). The correct procedures for parachute landing are taught aircrew during several phases of their training. Flight surgeons should become familiar with the proper procedures and use of equipment. Parachute opening shock can be severe if the drogue chute fails or the main parachute deploys prematurely. 17

High altitude escape is relatively rare, but if it occurs additional risk factors are present. Opening shock is increased due to increased velocities that increase terminal velocity to the point that damage to the parachute and injury to the crewmember usually results. Additional hazards include hypoxia and low temperatures. If the emergency oxygen supply in the emergency system malfunctions or the oxygen mask is lost during escape then hypoxia becomes a significant hazard. Protective flight clothing is usually adequate to prevent frostbite but the loss of gloves can impair usage of fingers required for subsequent survival activities (l). High-speed escape close to the ground presents the most difficult of ejection sequences. The initial thrust must be adequate to clear the rapidly moving tail section. The windblast will be high and time delays will be necessarily short to minimize loss of altitude before the main parachute deploys. The rocket seat, at high-speed low altitude ejection, has a lengthened initial impulse, allowing more time for the subsystems to operate, and slowing the seat to a safer velocity (3).

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INTRODUCTION TO HOW EJECTION SEAT WORKS U.S. Air Force Captain Scott O'Grady was helping to enforce the no-fly zone over northern Bosnia on June 2, 1995, when a Bosnian-Serb surface-to-air missile (SAM) struck his F-16. With the plane disintegrating around him, O'Grady reached down between his knees and grabbed the pull handle of his ejection seat. After a loud bang caused by the canopy separating, O'Grady was blasted into the air along with his seat. Soon after, his parachute deployed and, like 90 percent of pilots who are forced to eject from their aircraft, O'Grady survived the ejection from his F-16. Following six days of evading capture and eating insects for survival, O'Grady was rescued.

Photo courtesy U.S. Air Force Ejecting from an aircraft is rare, but pilots sometimes have to resort to pulling the ejection handle to save their lives.

Ejecting from an aircraft moving at speeds greater than the speed of sound (mach 1: 750 miles per hour / 1,207 kph) can be very dangerous. The force of ejecting at 19

those speeds can reach in excess of 20 Gs -- one G is the force of Earth's gravity. At 20 Gs, a pilot experiences a force equal to 20 times his or her body weight, which can cause severe injury and even death. Most military aircraft, NASA research aircraft and some small commercial airplanes are equipped with ejection seats to allow pilots to escape from damaged or malfunctioning airplanes. In this edition we will learn about the parts that make an ejection seat work, how the seat lifts a pilot out of a plane and about the physics involved in ejecting.

Physics of Ejecting Ejecting from an airplane is a violent sequence of events that places the human body under an extreme amount of force. The primary factors

involved in an aircraft ejection are the force and acceleration of the crewmember, according to Martin Herker, a former physics teacher. To determine the force exerted on the person being ejected, we have to look at Newton's second law of motion, which states that the acceleration of an object depends on the force acting upon it and the mass of the object.

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Newton's second law is represented as: Force = Mass x Acceleration (F=MA) Regarding a crewmember ejecting from a plane, M equals his or her body mass plus the mass of the seat. A is equal to the acceleration created by the catapult and the underseat rocket. Acceleration is measured in terms of G, or gravity forces. Ejecting from an aircraft is in the 5-G to 20-G range, depending on the type of ejection seat. As mentioned in the introduction, 1 G is equal to the force of Earth's gravity and determines how much we weigh. One G of acceleration is equal to 32 feet/second2 (9.8 m/s2). This

means that if you drop something off of a cliff, it will fall at a rate of 32 feet/second2. It's simple to determine the mass of the seat and the equipment attached to the seat. The pilot's mass is the largest variable. A 180-pound person normally feels 180 pounds of force being applied to him when standing still. In a 20-G impact, that same 180-pound person will feel 3,600 pounds of force being exerted. To learn more about force. "To determine the speed of the [ejection] seat at any point in time, one solves the Newton equation knowing the force applied and the mass of the seat/occupant system. The only other factors that are needed are the time of the force to be applied and the initial velocity present (if any)," writes Herker on his Web site describing the physics for understanding ejections. Herker provides this equation for determining the speed of the seat: Speed = Acceleration x Time + Initial speed V(f) = AT + V(i)

Initial speed refers to either the climb or the sink rate of the aircraft. It may also be determined by the initial step of the ejection process in a seat that combines an 21

explosive catapult and an underseat rocket. The seat speed must be high enough to allow separation of the seat and person from the aircraft as quickly as possible in order to clear the entire aircraft. The use of an ejection seat is always a last resort when an aircraft is damaged and the pilot has lost control. However, saving the lives of pilots is a higher priority than saving planes, and sometimes an ejection is required in order to save a life.

Bailing Out When a crewmember lifts the pull handle or yanks the face curtain down on the ejection seat, it sets off a chain of events that propels the canopy away from the plane and thrusts the crewmember safely out. Ejecting from a plane takes no more than four seconds from the time the ejection handle is

pulled. The exact amount of time depends on the seat model and the crewmember's body weight.

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This ACES II ejection seat has a middle pull handle used to activate the ejection sequence. Pulling the ejection handle on a seat sets off an explosive cartridge in the catapult gun, launching the ejection seat into the air. As the seat rides up the guide rails, a leg-restraint system is activated. These leg restraints are designed to protect the crewmember's legs from getting caught or harmed by debris during the ejection. An under seat rocket motor provides the force that lifts the crewmember to a safe height, and this force is not outside normal human physiological limitations, according to documents from Goodrich Corporation, a manufacturer of ejection seats used by the U.S. military and NASA.

Prior to the ejection system launching, the canopy has to be jettisoned to allow the crewmember to escape the cockpit. There are at least three ways that the canopy or ceiling of the airplane can be blown to allow the crewmember to escape: •

•

•

Lifting the canopy - Bolts that are filled with an explosive charge are detonated, detaching the canopy from the aircraft. Small rocket thrusters attached on the forward lip of the canopy push the transparency out of the way of the ejection path, according to Martin Herker, a former physics teacher who has written about ejection seats and maintains a Web site describing ejection seats. Shattering the canopy - To avoid the possibility of a crewmember colliding with a canopy during ejection, some egress systems are designed to shatter the canopy with an explosive. This is done by installing a detonating cord or an explosive charge around or across the canopy. When it explodes, the fragments of the canopy are moved out of the crewmember's path by the slipstream. Explosive hatches - Planes without canopies will have an explosive hatch. Explosive bolts are used to blow the hatch during an ejection.

The seat, parachute and survival pack are also ejected from the plane along with the crewmember. Many seats, like Goodrich's ACES II (Advanced Concept Ejection Seat, Model II), have a rocket motor fixed underneath the seat. After the seat and crewmember have cleared the cockpit, this rocket will lift the crewmember another 100 to 200 feet (30.5 to 61 m), depending on the crewmember's weight. 23

This added propulsion allows the crewmember to clear the tail of the plane. As of January 1998, there had been 463 ejections worldwide using the ACES II system, according to the U.S. Air Force. More than 90 percent of those ejections were successful. There were 42 fatalities.

Photo courtesy NASA

The parachutes opening on a Martin-Baker ejection seat during a test. The small parachute at the top is called the drogue parachute. Once out of the plane, a drogue gun in the seat fires a metal slug that pulls a small parachute, called a drogue parachute, out of the top of the chair. This slows the person's rate of descent and stabilizes the seat's altitude and trajectory. After a specified amount of time, an altitude sensor causes the drogue parachute to pull the main parachute from the pilot's chute pack. At this point, a seat-man-separator motor fires and the seat falls away from the crewmember. The person then falls back to Earth as with any parachute landing. 24

Modes of Ejection In the ACES II ejection seat produced by Goodrich Corporation, there are three possible ejection modes. The one used is determined by the aircraft's altitude and airspeed at the time of ejection. These two parameters are measured by the environmental sensor and recovery sequencer in the back of the ejection seat. The environmental sensor senses the airspeed and altitude of the seat and sends data to the recovery sequencer. When the ejection sequence begins, the seat travels up the guide rails and exposes pitot tubes. Pitot tubes, named for physicist Henri Pitot, are designed to measure air-pressure differences to determine the velocity of the air. Data about the air flow is sent to the sequencer, which then selects from the three modes of ejections: •

• •

Mode 1: low altitude, low speed - Mode 1 is for ejections at speeds of less than 250 knots (288 mph / 463 kph) and altitudes of less than 15,000 feet (4,572 meters). The drogue parachute doesn't deploy in mode 1. Mode 2: low altitude, high speed - Mode 2 is for ejections at speeds of more than 250 knots and altitudes of less than 15,000 feet. Mode 3: high altitude, any speed - Mode 3 is selected for any ejection at an altitude greater than 15,000 feet.

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Timing an Ejection • •

• • •

0 seconds - Pilot pulls cord; canopy is jettisoned or shattered; catapult initiates, sending seat up rails. 0.15 seconds - Seat clears ejection rails at 50 feet (15 m) per second and is clear of surrounding cockpit; rocket catapult ignites; vernier motor fires to counteract any pitch changes; yaw motor fires, inducing slight yaw to assure man-seat separation. (Burn time of all motors equals 0.10 seconds.) 0.50 seconds - Seat has lifted to about 100 to 200 feet (30.5 to 61 m) from ejection altitude. 0.52 seconds - Seat-man-separator motor fires; cartridge fires to release crewmember and his equipment from seat; drogue gun fires parachute. 2.5 to 4 seconds - Main parachute is fully deployed.

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Take a Seat

It's important for many types of aircraft to have an ejection seat in case the plane is damaged in battle or during testing and the pilot has to bail out to save his or her life. Ejection seats are one of the most complex pieces of equipment on any aircraft, and some consist of thousands of parts. The purpose of the ejection seat is simple: To lift the pilot straight out of the aircraft to a safe distance, then deploy a parachute to allow the pilot to land safely on the ground.

Photo courtesy U.S. Department of Defense

An ejection seat being removed from an F-15C Eagle To understand how an ejection seat works, you must first be familiar with the basic components in any ejection system. Everything has to perform properly in a split second and in a specific sequence to save a pilot's life. 27

If just one piece of critical equipment malfunctions, it could be fatal. Ejection seats are placed into the cockpit and usually attach to rails via a set of rollers on the edges of the seat. During an ejection, these rails guide the seat out of the aircraft at a predetermined angle of ascent. Like any seat, the ejection seat's

basic anatomy consists of the bucket, back and headrest. Everything else is built around these main components. Here are key devices of an ejection seat: • • • •

Catapult Rocket Restraints Parachute

In the event of an ejection, the catapult fires the seat up the rails, the rocket fires to propel the seat higher and the parachute opens to allow for a safe landing. In some models, the rocket and catapult are combined into one device. These seats also double as restraint systems for the crewmembers both during an ejection and during normal operation. Ejection seats are just one part of a larger system called the assisted egress system. "Egress" means "a way out" or "exit." Another part of the overall egress system is the plane's canopy, which has to be jettisoned prior to the ejection seat being launched from the aircraft. Not all planes have canopies. Those that don't will have escape hatches built into the roof of the plane. These hatches blow just before the ejection seat is activated, giving crewmembers an escape portal. Seats are activated through different methods. Some have pull handles on the sides or in the middle of the seat. Others are activated when a crew member pulls a face curtain down to cover and protect his or her face. In the next section, you will find out what happens once the seat is activated

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Ejection-seat Terms • • • •

Bucket - This is the lower part of the ejection seat that contains the survival equipment. Canopy - This is the clear cover that encapsulates the cockpit of some planes; it is often seen on military fighter jets. Catapult - Most ejections are initiated with this ballistic cartridge. Drogue parachute - This small parachute is deployed prior to the main parachute; it designed to slow the ejection seat after exiting the aircraft. A drogue parachute in an ACES II ejection seat has a 5-foot (1.5-m) diameter. Others may be less than 2 feet (0.6 m) in diameter. 29

• • •

• • •

• •

Egress system - This refers to the entire ejection system, including seat ejection, canopy jettisoning and emergency life-support equipment. Environmental sensor - This is an electronic device that tracks the airspeed and altitude of the seat. Face curtain - Attached to the top of some seats, pilots pull this curtain down to cover his or her face from debris. This curtain also holds the pilot's head still during ejection. Recovery sequencer - This is the electronic device that controls the sequence of events during ejection. Rocket catapult - This is a combination of a ballistic catapult and an under seat rocket unit. Under seat rocket - Some seats have a rocket attached underneath to provide additional lift after the catapult lifts the crewmember out of the cockpit. Vernier rocket - Attached to a gyroscope, this rocket is mounted to the bottom of the seat and controls the seat's pitch. Zero-zero ejection - This is an ejection on the ground when the aircraft is at zero altitude and zero airspeed.

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Ejection seats in other aircraft The Kamov Ka-50 was the first helicopter to be fitted with an ejection seat. The system is very similar to that of a conventional fixed-wing aircraft; the main rotors are equipped with explosive bolts and are designed to disintegrate moments before the seat rocket is fired. The Lunar Lander Research Vehicle (LLRV)/Training Vehicle (LLTV) used ejection seats; Neil Armstrong ejected on May 6, 1968; Joe Algranti & Stuart M. Present, later. Early flights of the US space shuttle were with a crew of two, both provided with ejector seats, but the seats were disabled and then removed as the crew size was increased.[citation needed] The Soviet shuttle "Buran" was planned to be fitted with K-36RB (K-36M-11F35) seats, but it was unmanned on its single flight; the seats were never installed. The only spacecraft ever flown with installed ejection seats are the Space Shuttle, the Soviet Vostok and American Gemini series. During the Vostok program, all the returning cosmonauts would eject as their capsule descended under parachutes at about 7,000 m (23,000 ft). This fact was kept secret for many years as the FAI rules at the time required that a pilot must land with the spacecraft for the purposes of FAI record books. Passenger planes are unlikely to ever receive ejection technology. A single ejection seat costs over ten times as much as a first-class ticket. Furthermore, the seat along with all its components weigh almost four times the amount of an average passenger. Any ejection would have to be initiated by the flight crew, as civilians would require training on how to use an ejection seat and could not be controlled enough to prevent them from inadvertently setting off the system. Even if an airline did manage to accomplish all this, there would still be the undeniable fact that an ejection would probably be fatal to children, those suffering from bone diseases, and the elderly. Furthermore, there is the problem of having a system which, in a few seconds or less, removes the entire roof of the aircraft, and the problem of firing off several hundred seats in such a way that they do not collide. 31

However, some ultralight and single-engine general aviation aircraft have been refitted with ballistically deployed parachutes recently. However these systems cannot be considered "ejection" systems because the entire aircraft with occupants is suspended by the chute.

FUTURE OF EJECTION SYSTEMS The ejection seat has evolved into a complicated system with subsystems. Seat improvement has improved the odds of survival, and expanded boundary limits for successful ejection. The ability of the seat to monitor environmental factors has allowed better control inputs, improving seat stability. The incidence of ejection injuries is reduced by employing a complex acceleration profile. The profile is impulsive and of high amplitude at the beginning and end of the acceleration period, while relatively smooth and of low amplitude during the interposed major time segment. The next generation of escape systems will use controllable propulsion systems to provide safe ejection over the expanded aircraft flight performance envelopes of advanced aircraft. Continued research will only enhance the capability of future ejection systems. Current research efforts are being directed toward solving the problems associated with high speed and high altitude ejections.

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Within the last 10 years, dramatic escapes from Russian fighter aircraft have captured the attention of military pilots and aviation enthusiasts around the world. The low-altitude ejection from a MiG-29 just prior to ground impact at the 1989 Paris Air Show and a pair of miraculous escapes from two exploding MiG-29s that had collided over Fairford, England, in 1993, vividly demonstrated the potential downside of flying high-performance, military aircraft. The pilots ejected successfully thanks to the K-36D ejection seat designed and built by the Zvezda Research, Development and Production Enterprise in Russia. The K-36D ejection seat and its associated life support equipment are designed, tested, and produced under the direction of Professor Guy Severin. Professor Severin, a member of the prestigious Russian Academy of Science, has devoted his life to developing and perfecting life-support and life-saving equipment for air and space systems. His achievements include the design of the cosmonaut seats, pressure suits, and the first extravehicular maneuvering unit for the Russian space program; aeronautical fire suppression equipment; and escape systems for fighters, bombers, VTOL aircraft, acrobatic aircraft, and the Russian Buran space shuttle. The K-36D ejection seat provides directional stability and crew protection features that significantly reduce the risk of injury during ejection, especially at the higher speeds associated with fighter aircraft operations in wartime. Successful K-36D operational ejections have occurred at speeds of 729 KEAS and Mach 2.6. The aerodynamic forces encountered at high speeds can cause severe neck, spine, and limb injuries. Our experience with Western ejection seats, which are aerodynamically unstable and have little or no limb restraint, indicates that the risk of major injury rises exponentially from about 350 KEAS to a high probability of fatal injury near the seat's structural limit, usually about 600 KEAS. The fact that the aerodynamic forces increase as the square of the velocity has made even incremental improvement of the performance envelope very difficult. Consequently, having an opportunity to test and evaluate an ejection seat with an envelope that Professor Severin claimed provides safe escape up to 755 KEAS, was one we couldn't pass up. Engineers and scientists from the Air Force Research Laboratory's (AFRL) Human Effectiveness Directorate and the US Navy's Air and Surface Warfare Centers first evaluated the K-36D ejection seat in 1993 as part of a foreign equipment comparative testing program sponsored by the Office of the Secretary of Defense. 33

Tests were conducted using Russian test facilities including a windblast facility a vertical ejection tower, a rocket-propelled sled, and a MiG-25 aircraft. The K-36D seat was ejected from the rocket sled at speeds as high as 730 KEAS and from the MiG-25 at speeds up to Mach 2.5 and altitudes up to 56,000 ft. Additional tests were then conducted at the Holloman AFB NM sled track to demonstrate performance at low speed and adverse attitudes. This program, which included 17 successive, successful tests, demonstrated that the performance of the K-36D seat at these test conditions was superior to ejection seats used in US aircraft.1 A number of features are responsible for the superior performance of the Russian seat. During ejection, telescoping booms are deployed from the seat to stabilize the attitude of the seat from the time it leaves the aircraft until the seat and its occupant decelerate to the speed where the recovery parachute is deployed and the occupant is separated from the seat. The K-36D seat also deploys a windblast deflector during ejections at airspeeds in excess of 430 KEAS. The windblast deflector improves the airflow around the seat and contributes to windblast protection. Leg lifting devices and arm and leg restraints are provided to prevent limb flail injuries due to windblast forces. The limb restraints do not require the crew to hook up as they enter the aircraft and do not restrict limb movement during normal flight operations. The successful results of the comparative-testing program led to a decision to adapt this technology in the development of an ejection seat suitable for use in American aircraft. AFRL contracted with Boeing North American (BNA) and their subcontractor Zvezda to engage in an advanced development effort to demonstrate a seat design that will meet US performance requirements. These requirements include: reducing the seat weight by more than 50 lb, accommodating a larger range of occupant weights and sizes, improving the performance of the seat under adverse attitudes with high descent rates, integrating US life support equipment, reducing life-cycle costs, and improving seat producibility and maintainability. The seat that has been developed to demonstrate the feasibility of meeting these requirements uses many of the operationally proven components of the K-36D seat including the stabilization booms, windblast flow deflector, and arm and leg restraints. The seat structure has been redesigned to reduce weight, increase the vertical adjustment range, and provide fore-aft tilt of the seat back. 34

The headrest/parachute container is smaller to improve the occupant's ability to "check six." The ejection catapult and rocket have been redesigned to control the seat acceleration for a wider range of occupant weights and sizes. Zvezda is meeting the challenge of providing improved performance for ejections from adverse attitudes with high descent rates by incorporating an electronic control system and a set of small, roll attitude control rockets. The control system uses data received from the aircraft to establish the best seat operating parameters for safe crew recovery. Zvezda was very proactive in their efforts to evaluate the effectiveness of the new seat design. They have developed a rocket-propelled sled with an aircraft forebody that can rapidly roll during the ejection. This facility is similar to the sled and for body that will be used to test the seat at Holloman AFB later this year. Zvezda has also developed a flying test bed to evaluate the performance of the seat at adverse roll attitudes. The testbed consists of a cockpit mounted on the tail of an An-12 transport. The cockpit can be rotated to specific roll angles prior to the ejection. At the time that this article was written, Zvezda had completed 21 successful tests using these facilities as well as the MiG-25 test aircraft used in the earlier comparative-testing program. Combining Russia's uniquely capable K-36D ejection seat and escape system design expertise with advanced US pyrotechnics, improved life support equipment, and electronic controls technologies offers the opportunity to provide US aircrews an affordable seat with unparalleled safe escape capability.

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Pilot safety The purpose of an ejection seat is pilot survival, not pilot comfort. Many pilots have suffered career-ending injuries while using ejection seats, including crushed vertebrae. The pilot typically experiences an acceleration of about 12 to 14 g (117 to 137 m/s²). Western seats usually impose lighter loads on the pilots; 1960s-70s era ex-Soviet technology often goes up to 20-22 g (with SM-1 and KM-1 gunbarrel type ejection seats). Career-ending injuries are quite common, partly because eastern military pilots usually continue to fly into their late 40s or early 50s and end (retire) their flying career afterward, while most western jet pilots retire from the military in their late 30s. Lt. William Belden ejects from an A-4 Skyhawk on the deck of the Shangri-La. Lt. William Belden ejects from an A-4 Skyhawk on the deck of the Shangri-La. The Russian K-36 ejector seat manufactured by NPP Zvezda is considered by many as the world's most advanced. It was studied at length by the US Navy and Airforce and IBP Aircraft opened up a factory in the US to manufacture it for the F-22 Raptor and the Joint Strike Fighter. The US Government however selected the Martin Baker seat from the UK in a political move for the new US fighters. The amazing capabilities of the K-36 were convincingly demonstrated at the Fairford Air Show on 24 July 1993 when the pilots of two MiG 29 fighters successfully ejected after a mid-air collision[4]. By January 2008, Martin-Baker ejection seats had saved 7219 lives[5]. They give survivors a unique necktie. The total figure for all types of ejector seats is unknown, but must be considerably higher.

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SOURCES • • • • •

WWW.WIKIPEDIA.COM WWW.GOOGLE.COM WWW.US.USMILITARY.ORG WWW.SCIENCE.HOWSTUFF.COM WWW.MARTIN-BAKER.COM

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