Ejection seat

In aircraft, an ejection seat is a system designed to rescue the pilot or other crew of an aircraft (usually military) in an emergency. In most designs, the seat is propelled out of the aircraft by an explosive charge or rocket motor, carrying the pilot with it. The concept of an ejectable escape capsule has also been tried. Once clear of the aircraft, the ejection seat deploys a parachute.

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. [ [http://www.ejection-history.org.uk/PROJECT/YEAR_Pages/1910s.htm#1916 Compressed Air Parachute Extraction System Patented] ]

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 and tested in 1943 for the Saab 21. The first test in the air was on a Saab 17 on 27 February 1944, [ [http://www.canit.se/~griffon/aviation/text/saabejec.htm Early Swedish ejection seats] ] and the first real use occurred in July 29 1946 after a mid-air collision between a J 21 and a J 22. [ [http://www.canit.se/~griffon/aviation/text/21saab.htm The Swedish military aviation - Saab J 21/A 21/A 21R] ] The Saab 21 was the first aircraft to have an ejection seat as standard equipment.

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" were also fitted with ejection seats.

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 U.S. ejectee. Martin-Baker 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 amount of 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 of rocket-powered ejection seats designed for use at supersonic speeds began in such planes as the F-106 Delta Dart. Six pilots have ejected at speeds exceeding 700 knots (805 mph) and the highest altitude a Martin-Baker seat was deployed at was 57,000 ft (from a Canberra bomber in 1958). Following an accident on 30 July 1966 in the attempted launch of a D-21 drone, two Lockheed A-12Crickmore, Paul F. "Lockheed's Blackbirds: A-12, YF-12 and SR-71", Wings of Fame, Volume 8, AIRtime Publishing Inc., Westport, Connecticut, 1997, ISBN 1-880588-23-4, page 90] crew members ejected at Mach 3.25 at an altitude of 80,000 ft. The pilot was recovered successfully, however the observer drowned after a water landing before he could be rescued. 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.

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 12–14 "g" (117–137 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.Fact|date=June 2008

The Russian K-36 ejector seat manufactured by NPP Zvezda is sometimes considered by many Fact|date=May 2008as 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 U.S. 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's new Joint Strike Fighter. The F-22 Raptor uses a variant of the ACES II ejection seat. The 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. [ [http://www.sirviper.com/index.php?page=div/mig29_crash The MiG-29 crash at Fairford Airbase] ]

The minimal ejection altitude for ACES II seat in inverted flight is about 140 feet above ground level at 150 KIAS. While the Russian counterpart - K-36DM has the minimal ejection altitude from inverted flight of 660 feet AGL. Also, to eject safely from MiG-29A on the ground (zero level) the speed must be at least 40 knots.

By April 2008, Martin-Baker ejection seats had saved 7240 lives. [ [http://www.martin-baker.com Martin Baker - Ejection seat and escape system technology] ] They give survivors a [http://www.martin-baker.com/Ejection-Tie-Club.aspx unique tie and lapel pin] . The total figure for all types of ejector seats is unknown, but must be considerably higher.

Egress Systems

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). perform both functions as 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.

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 inward 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 F-104 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.Fact|date=September 2008

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, while gravity and wind remove the hatch and arm the seat. The four seats on the forward upper deck (two of them, EWO and Gunner, facing the rear of the airplane) fire upwards as usual. Note that any such downward-firing system is of no use on or near the ground unless the aircraft is upside-down 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., the 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 crewman 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.

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.

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.

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 [http://www.clavius.org/techlltv.html 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, (STS-1 to STS-4), but the seats were disabled and then removed as the crew size was increased. [Dennis R. Jenkins: Space Shuttle - The History of Developing the National Space Transportation System, Dennis R. Jenkins Publishing 1999, Page 272, ISBN 0963397443]

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.

Sukhoi Su-31M is single engine aerobatic aircraft factory equipped with ejection seat Zvezda SKS-94.

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 – weighs almost four times the amount of an average passenger. Any ejection would have to be initiated by the flight crew, as civilians would lack the requisite training on how to use an ejection seat properly, and could be prone to 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.Fact|date=June 2008 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.

Some ultralight and single-engine general aviation aircraft such as the Cirrus SR-22 have been fitted with ballistically deployed parachutes recently. However, these systems cannot be considered "ejection" systems because the entire aircraft with occupants is suspended by the chute.

References

ee also

* Escape crew capsule

External links

* [http://www.ejectionsite.com/ The Ejection Site]
* [http://www.gdt-systems.com/ www.gdt-systems.com]
* [http://ejectionseat.com.ne.kr/ ejectionseat.com.ne.kr]
* [http://ejectionseat.com.ne.kr/esimul.htm Ejection seat simulator]
* [http://www.ejection-history.org.uk/ Ejection History]
* [http://www.martin-baker.com/Products/Ejection-Seats/Mk--10.aspx Picture and specifications of an ejection seat]
* [http://www.authorsden.com/visit/viewarticle.asp?AuthorID=77566&id=36725 A History of Military Aircraft Egress Systems by Kalikiano Kalei]