Ejection seat

External images
Hi-res cutaway of Martin Baker Mk 1 ejection seat
	Hi-res cutaway of Martin Baker Mk 1 ejection seat by Flight Global.

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 eject-able escape capsule has also been tried. Once clear of the aircraft, the ejection seat deploys a parachute. Ejection seats are common on certain types of military aircraft.

History

Martin-Baker WY6AM ejection seat

United States Air Force F-15 Eagle ejection seat test using a mannequin

An Aviation Structural Mechanic works on an ejection seat removed from the cockpit of an EA-6B Prowler aboard USS John C. Stennis.

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 layout for an ejection seat was first proposed by Romanian inventor Anastase Dragomir in the late 1920s. The design, featuring a parachuted cell (a dischargeable chair from an aircraft or other vehicle), was successfully tested on August 25, 1929 at the Paris-Orly Airport near Paris and in October 1929 at Băneasa, near Bucharest. Dragomir patented his "catapult-able cockpit" at the French Patent Office (patent no. 678566, of April 2, 1930, Nouveau système de montage des parachutes dans les appareils de locomotion aérienne).

The design was 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 13 January 1942 after his control surfaces iced up and became inoperable. The fighter, being used in tests of the Argus As 014 impulse jets for Fieseler Fi 103 missile development, had its regular HeS 8A turbojets removed, and was towed aloft from Rechlin, Germany by a pair of Bf 110C tugs in a heavy snow-shower. At 7,875 feet (2,400 m), Schenk found he had no control, jettisoned his towline, and ejected.^[2] The He 280, however, 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,^[3] and the first real use occurred in 29 July 1946 after a mid-air collision between a J 21 and a J 22.^[4]

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 and a few prototype aircraft 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 Sir James Martin and the British company Martin-Baker that was to prove crucial.

The first live flight test of the Martin-Baker system took place on 24 July 1946, when Bernard Lynch ejected from a Gloster Meteor Mk III. Shortly afterward, on 17 August 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. As aircraft speeds increased still further, this method proved inadequate to get the pilot sufficiently clear of the airframe. Increasing the amount of propellant risked damaging the occupant's spine, so experiments with rocket propulsion began. In 1958 the F-102 Delta Dagger was the first aircraft to be fitted with a rocket-propelled seat. Martin-Baker developed a similar design, using multiple rocket units feeding a single nozzle. The greater thrust from this configuration 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). The highest altitude at which a Martin-Baker seat was deployed 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 M-21^[5] crew members ejected at Mach 3.25 at an altitude of 80,000 ft (24,000 m) The pilot was recovered successfully, however the observer drowned after a water landing. 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 with the ground.

Pilot safety

The purpose of an ejection seat is pilot survival. 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 Soviet technology often goes up to 20–22 g (with SM-1 and KM-1 gunbarrel-type ejection seats). Compression fractures of vertebrae were (and are) a recurrent side effect of ejection, and are often a career-ending (if not fatal) injury for pilots and aviators.

Lt. (j.g.) William Belden ejects from an A-4E Skyhawk on the deck of the USS Shangri-La in the western Pacific circa 29 July 1970. The pilot was recovered by helicopter, unharmed; the Skyhawk was later recovered from carrier catwalk. (NH-90350)^[6]

The U.S. government selected the Martin-Baker seat for the U.S.A.'s new Joint Strike Fighter. The F-22 Raptor uses a variant of the ACES II ejection seat. The capabilities of the Zvezda K-36 were unintentionally 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.^[7]

The minimal ejection altitude for ACES II seat in inverted flight is about 140 feet (43 m) above ground level at 150 KIAS. While the Russian counterpart - K-36DM has the minimal ejection altitude from inverted flight of 660 feet (200 m) AGL. When an aircraft is equipped with the Zvezda K-36DM ejection seat and the pilot is wearing the КО-15 protective gear, he is able to eject at airspeeds from 0 to 1400 kph and altitudes of 0 to 25 km. The K-36DM ejection seat features drag chutes and a small shield that rises between the pilots legs to deflect air around the pilot.^[8]

As of August 2009, Martin-Baker ejection seats had saved 7289 lives.^[9] They give survivors a unique tie and lapel pin. The total figure for all types of ejector seats is unknown, but might be considerably higher.

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.

Capt. Christopher Stricklin ejects from his F-16 aircraft with an ACES II ejection seat on 14 September 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), perform both functions as a single action.

The ACES II ejection seat is used in most American-built fighters. 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 handle located between the pilot's knees, since the cockpit is too narrow for side-mounted handles.

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.

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. 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 - Miniature 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. This system was developed for the Hawker Siddeley Harrier family of VTOL aircraft as ejection may be necessary while the aircraft was in the hover, and jettisoning the canopy might result in the pilot and seat striking it.

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.^[10]

Drag Extraction is the lightest and simplest egress system available, and has been used on many experimental aircraft. 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.

Crewmember escape capsule from a B-58 Hustler

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 emergencies during low-altitude and/or low-speed flight, as well as ground mishaps. Before this capability, ejections could only be performed above minimum altitudes and airspeeds.

Zero-zero technology uses small rockets to propel the seat upward to an adequate altitude and a small explosive charge to open the parachute canopy quickly for a successful parachute descent, so that reliance on airspeed and altitude is no longer required for proper deployment of the parachute.

Other aircraft

The Kamov Ka-50, which entered service with Russian forces in 1995, was the first production 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. Prototype #9 (s/n 66-8834) of the AH-56 Cheyenne was fitted with downward firing ejection seats in 1970 after a fatal testing accident the previous year.

The Lunar Lander Research Vehicle (LLRV)/Training Vehicle (LLTV) used ejection seats; Neil Armstrong ejected on 6 May 1968; Joe Algranti & Stuart M. Present, later.

Early flights of the NASA's 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.^[11]

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.

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

Some ultralight, single-engine and glider general aviation aircraft such as the Cirrus SR-22 or Schempp-Hirth Discus 2c 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.

See also

• Escape crew capsule

References

External links

• The Ejection Site
• www.gdt-systems.com
• Ejection seat simulator
• Ejection History
• Picture and specifications of an ejection seat
• A History of Military Aircraft Egress Systems by Kalikiano Kalei