As had been stated earlier, many US manufacturers designed their own seats in the early days of jet combat aircraft. In 1964, there were some 25 companies with ejection seat capability, among them: North American (now part of Rockwell International), which produced a high-speed ejection seat for its A-3 Vigilante and a low-speed seat for its OV-10 Bronco; while Stanley Aviation is known for its encapsulated escape system for the B-58 Hustler.
During the early days of ejection seat development, Lockheed developed a downward-firing seat for use on the XF-104 Starfighter, first flown in February 1954. This method of escape was, naturally, configured for high speed/altitude operations, in order to clear the pilot of the F-104's high T-tail. However, as most ejections occurred at low speed and low (if not zero) height, this concept was abandoned in favour of a conventional upwards-ejecting seat of Lockheed design. Later export models were equipped with Martin-Baker seats.
Boeing's B-52 Stratofortress also features downwards-ejecting seats for some rear crew members. While fine for escape at high altitude, with typical 'gallows humour', the USAF refer to their use at low level as 'self burial'.
Today, in the US, there are only two ejection scat manufacturers: Universal Propulsion (building the Stencel scat for the AV-8B Harrier II but with little R&D capability) and McDonncll Douglas Aerospace, with its Advanced Concept Ejection Scat (ACES II) system in use with many US-built aircraft.
The McDonnell Douglas capability arises, mainly, from its Douglas forebear, which began such work in 1945 and, by 1953, had developed the ESCAPAC seat for its A-4 Skyhawk. This seal was progressively developed through 15 models (/ero-zero capability coming around 1961) and fitted to 14 aircraft types, including the A-7 Corsair II, B-57 Canberra and S-3 Viking. The scat was also used by early versions of the A-10 and F-15, although both types are now equipped with ACES II seats.
The McDonnell Aircraft arm of the corporation was responsible for the development of the crew escape capsule used on the F-l 11 series of tactical fighters/bombers. Intended to allow aircrew a 'shirtsleeve' environment, the escape capsule — or crew module — is integrated into the aircraft to provide a pressurised cabin, extending to the forward portion of the wing glove. The side-by-side module does away with personal ejection seats, parachutes and survival equipment for the two crew members.
In the event of an emergency, at any point in the F-l I I's flight envelope, the crew module is separated from the aircraft and propelled by rocket motors to a height sufficient for the recovery. The module also has a zero-zero capability. Air Bag type shock absorbers are provided to cushion the module impact on either land or water. In the latter case, there is provision for underwater escape, self-righting buoyancy and occupant environmental hazard protection.
ACES II and beyond
The ACES II is currently the standard American built seat on some USAF combat aircraft, including the A-10 Thunderbolt II, B-1B Lancer, B-2 Advanced Technology Bomber, F-15 Eagle, F-l6 Fighting Falcon and the F-l 17A stealth fighter. It has also been selected for the F-22 Advanced Tactical Fighter and over 6,000 seats have been delivered. As of September 11, 1993, 301 successful ACES II ejections had occurred with a success rate (in USAF service) of 90.7%. Some 16 overseas customers of the F-l6 use the ACES II seat and, in Japan, the seat is built under licence for the F-15J Eagle.
Described as a 'rugged, lightweight, easy-to-maintain' ejection seat, ACES II was designed by the Douglas Aircraft Company element of McDonnell Douglas and is currently produced by Boeing who recently bought that part of the company. It provides optimum performance over an envelope from zero to 600kts (1,11 Ikm/h) and from zero to 50,000ft (15,240m) altitude. At low speeds, the parachute can be deployed within 1.8 seconds after initiating ejection (which, according to the manufacturer, is faster than the Russian K-36 seat).
The company's STAPAC gyro-controlled system controls a vernier rocket for positive pitch stabilisation of the seat during ejection at low speeds. For high altitudes, a Hemisflo drogue is used for stabilisation and deceleration after separation. The recovery parachute is deployed by mortar and is reefed to reduce the shock loads on the pilot. Sensors on the seat detect altitude and airspeed, sending the data to the recovery-sequencing subsystem, which then directs the operation of the seat according to the circumstances prevailing. For example, in a low-speed ejection, the drogue would not be deployed, while at high altitude, deployment of the parachute is delayed until a lower, safer altitude is reached.
Emergency oxygen supplies are carried for high-altitude ejections, while an automatic harness release mechanism separates the pilot from the seat when required. The seat can be equipped with canopy breakers for aircraft which may have to eject pilots through the canopy, while a URT-33C radio beacon is provided in the seat pan and, if selected, can begin transmission following seat-man separation.
Since January 1993, the company has been under a joint USAF/USN contract for a fourth generation escape system technologies demonstration programme to last five years. The objectives of the programme are to develop and demonstrate seat technologies which will allow ejection at speeds up to 787kts and automatically maintain seat stabilisation (by use of four rocket motors at each corner of the seat). Demonstration ejections were scheduled to begin during the third quarter of 1996.
(c) M J Gething 1994