By Eric Ahlstrom

A Brief History of Seats

Ejection seats have been around in military aircraft for 50 years. Like parachutes and helmets, these lifesavers are considered just another piece of flight equipment for high performance jets. It wasn't always that way.

Late in WWI, parachutes became available for the first time. Crude by modern standards, the chute was a simple canopy, had no maneuvering risers and the pilot had to pull it out of the bag to get it to open. Even so, it was obvious to pilots that it could save a life if the plane was shot to pieces and the pilot had some altitude to jump. High ranking officers of both the British and German air forces originally denied their pilots access to parachutes, fearing that it would encourage them to bail out without facing combat.

By WWII, the parachute was standard equipment and the typical pilot went aloft with a dazzling array of survival and flight equipment. Goggles, oxygen mask, throat mike, heated flying suit, life vest, skull cap, parachute, etc. made the pilot into a walking collection of the highest technology available; to keep him alive to fly and fight and live to come home if he lost the battle that day.

Bailing out of a burning or out of control aircraft was no mean feat. If the pilot was lucky he had some altitude and enough control to pull the canopy back, get disconnected from the radio and oxygen, go inverted and pop the seat harness. Gravity separated the pilot from the airplane and simply pulling the ripcord enabled a drogue chute to extend and inflate the main chute. The pilot floated down to a softer landing than the aircraft was about to have.

Most pilots were not so lucky. Often the aircraft was on fire or some piece of the airframe had been shot off. The pilot needed to fight himself loose of the cockpit while the world tumbled around him in a dizzying gyration of G forces and chaos. Wounded or unconscious, a pilot had even worse chances. Damage to the canopy could prevent it from opening; pilots often got hung up on some part of the cockpit and couldn't climb out against the G forces; finally clear, many struck the airframe on the way out and were injured or killed. America’s highest scoring ace of the war, Major Richard Bong (40 kills), was lost on a test flight after the war when his parachute tangled on the tail of a P-80.

After the war, the jet age arrived. Aircraft speeds had increased and with them the possibility of a clean bail out became more remote. The solution was the ejection seat. An automatic device to blow the pilot clear of the airframe, protect him from the shock, deploy his parachute and carry his survival gear. The ejection seat was the final answer to saving the pilot when all else was lost.

It wasn't so simple, of course. Early ejection seats were nothing more than ballistic charges placed to blow the seat and pilot out of the cockpit. The pilot then had to manually open his chute and hopefully not get hit as the seat tumbled to earth nearby.

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The next step was adding rockets to the seat to provide some clearance from the airframe and extra altitude for the parachute to open. In the 50’s, rockets were so slow that they couldn't get a pilot clear of the tail, so some experimental seats fired down instead of up; hardly encouraging for low altitude ejection! A more energetic catapult was developed to get the pilot clear faster, but the resulting G forces caused worse injuries than a tail strike.

The solution was an extension rail to explosively extend the seat up beyond the height of the tail, then let the slower rockets fly the seat clear of the airframe. As STOVL jets like the Harrier were designed, seats capable of flying the pilot to a height safe for parachute opening were designed to go with them. So called "zero-zero" capability, these seats could (under optimum conditions) save a pilot who had no altitude and no airspeed for the parachute to open.

Separating the canopy from the aircraft became critical since an out of control aircraft could easily "fly" under the area the canopy was jettisoned to and blow the pilot right into a heavy piece of metal and Plexiglas. The final solution to this was to simply leave the canopy in place and install hard rails on top of the seat to punch the seat and pilot through the plexi. This is only an option on thinner, non bullet resistant canopies.

Modern seats

Today, ejection seats come in many forms reflecting the operating envelope of the aircraft and the survival needs of the pilot. At the top end for supersonic fighters are seats that sense the altitude, attitude and airspeed; tension pilot restraints, extend Mach fairings, aerodynamic stabilizers and maneuvering thrusters; sense and time each mechanism, all to protect the pilot and place the seat in the correct attitude for parachute deployment. Multi-seat aircraft have command ejection and sequencing features. These insure that if one crew member punches out, everyone goes with him. To prevent one ejection from interfering with another, the seats fire in a set sequence and delay. While preventing seat vs. seat problems, this takes time. Combined with the time for a bullet resistant canopy to clear the airframe, the time factor increases the minimum ejection altitude.

In some STOVL aircraft, automatic systems sense the condition of the airframe and eject the pilot before an unrecoverable attitude is reached. In some fighters, major airframe failures are tied to auto ejection systems. Emergency oxygen is provided and the parachute is deployed by rocket to reduce the altitude requirement for opening. With rocket assist, the parachute extends above the seat and pulls the pilot upwards out of the seat, preventing post ejection injury. The pilots survival pack is attached to the chute harness by a lanyard to hit the ground before he does; even deploying a life raft, dye marker and strobe/radio beacon automatically. The ejection seat had become a 200+ lb. independent flying machine costing over a quarter of a million dollars.

Inverted ejections

When the aircraft is inverted, it would make sense that we should have this rocket powered seat fly us upright and gain altitude before deploying the chute. Great in theory, this idea has proven difficult in practice since the altitude for the seat to turn from inverted to upright and arrest a severe sink rate exceeds the altitude it takes to deploy a parachute. It proved much easier to extend the parachute on a separate rocket, drastically reducing the free fall needed to open the chute. Finally, here was the ultimate drogue chute: a rocket that only had to accelerate the weight of the chute pack and unfold the canopy. The Russian company Zvesda leads in this technology and has begun co-producing advanced safety systems with the UPCO division of BF Goodrich.

composite photo of Vertical-Seeking Seat during testing, part of the cancelled Maximum Performance Ejection System. (US Navy Photo)

The world has witnessed several low and adverse attitude ejections in the last fifteen years in airshow accidents and seen ejection seats with rocket assisted parachutes save pilots from shattered and nearly inverted aircraft at less than 100 ft. Nose down attitude and a high sink rate are far more common ejection conditions and these have been addressed by the leading manufacturers over the infamous but uncommon inverted scenario. The key is getting the pilot separated from the aircraft and getting the chute open as soon as possible.

How does this apply to air racing?

State of the art ejection seats are heavy and expensive, weighing 150 to 230 lb. and costing $180k to $250k. Many early seats from retired fighters are on the surplus market; but their pyrotechnics are old and unstable and the seat technology is not considered safe for low altitude ejection. Air racing cannot support the costs or adapt to the weight of the new seats. Yet we also cringe at the thought of relying on outdated charges and high altitude technology for low level pylon racing emergencies. If we examine air racing as just another envelope to save a pilot from, a manufacturer could pick and choose the components of an ejection seat that we need and leave the rest behind.

Most of the bail out injuries and fatalities in air racing have occurred at low to medium altitude and airspeeds between 50 and 280 KEAS. The 500+ mph speeds of top Unlimiteds decay very rapidly during a typical mayday. Unlike jets, all air racers have props which act as speed breaks to slow the aircraft as soon as power is lost or pulled off. Further, air racers have much lower wing loadings and are much lighter than jets; this means they decelerate much faster than a jet without power. This lower airspeed is within the envelope of a high performance, rocket assisted parachute and high enough that true "zero-zero" capability is not needed. Airframe clearance is critical, so extending the seat on a rail is required. Canopies on all air racers are thin enough (less than 6mm) to allow the seat to blow through them. Finally, air racing pilots do not need survival packs or emergency oxygen, so we can decrease the weight and cost of our ideal racing ejection system even further.

What we end up with is a pilot escape system (PES) that consists of a height adjustable seat; a seat extension system to catapult the seat through the canopy and keep it clear of the airframe; a rocket powered parachute pack that extends the parachute clear and opens it; and a release mechanism that allows the pilot to be pulled off of the seat by the open parachute.

The system is a modified SKS-94 from the UPCO division of BF Goodrich. Originally manufactured by Zvezda in Russia, these systems have been tested and proven in high performance aerobatic and subsonic aircraft. They have been installed in the Sukhoi SU-31M aerobatic aircraft and tested with live pilots. The weight is 50 lb. and cost is currently $40k for a custom installation. Star Aerospace LLC is designing a new Unlimited and has been tasked by their sponsor to integrate a pilot safety system appropriate for air racing. Combining the weight and cost restrictions with the envelope of the majority of air racing injuries and fatalities, the SKS-94 may be the right system for air racing today.

Part two of this series will cover the specifics of applying pilot escape technology to air racers.

About the author:

Eric Ahlstrom is president of Star Aerospace LLC, an aerodynamics and aerospace systems consulting and manufacturing firm. He and several other ex Douglas and Boeing engineers are helping bring the peace dividend to air racing and general aviation. The principals have decades of experience in a wide variety of motorsports, including motorcycles, hydroplanes, drag racing, off road rally and circle track. Star Aerospace LLC markets a line of high performance modifications for general aviation aircraft and is constructing its own line of kit aircraft. An Unlimited racing program is in progress and details will be published when the design phase is complete. http://staraerospace.com

photo credits:

Black and white historical photos provided by:
The National Archives and Records Administration

Aces II ejection seat photo provided by: B.F. Goodrich Aerospace

Vertical-Seeking Seat test photo provided by: United States Navy