By Eric Ahlstrom

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The Pilot Escape System or PES

Star Aerospace, LLC. is designing a new technology Unlimited racer. The project sponsor has required an ejection system be installed. The system must provide a means to save the pilot from the majority of foreseeable accidents at a reasonable cost and weight. The system also has to be small enough for two to fit in a 3,500 lb. racer. Based on these requirements, we have decided on a custom application of the SKS-94. Originally produced by Zvesda in Russia, the system is now imported to a US manufacturer and fitted with American pyrotechnics. FAA certification of the charges and the chute pack is close to ten years, allowing virtually zero maintenance.

Designed for light aerobatic aircraft, the PES is not really a cut down ejection seat. It is more of an assembly of only the technologies needed for low to mid altitude subsonic ejection, with each part sized to create an effective and light weight package. Although the PES is a different type of system than a full ejection seat, it may be useful for comparison to look at what parts of a full military fighter seat we are leaving behind:

• Canopy jettison: Thick, bullet resistant canopies are the norm in military aircraft, and must be jettisoned or fractured with charges before ejection. Most air racers use a separate windshield for bird strike protection and a thin overhead canopy to save weight. This allows a PES to punch right through the canopy without external charges. This can save a precious quarter to half a second of ejection time as well as prevent any canopy to seat conflicts.

• Sequencing: Many military aircraft are multiple seat and require ejections to proceed in a specific order and with a delay between ejections to prevent seat vs. seat and seat vs. canopy impacts. Air racers are single seat and need no such delays. In the case of a two seat racer, like ours, divergent ejection paths can allow simultaneous ejection with zero delay.

• Survival pack: Military pilots eject in harsh and remote environments, so the seat must carry a survival pack and survival equipment on the pilot. This ranges in weight from 15 to 50 lb. and adds to the weight the seat must eject and the parachute has to handle. Air racing needs none of this.

• Seat rockets: Needed for zero altitude, zero airspeed ejection. Important in STOVL aircraft to get away from an engine failure in low altitude hover, its utility to an air racer is limited. Almost all escape decision points in air racers have historically occurred with significant forward airspeed and 50 feet of altitude.

• Emergency oxygen: Needed for high altitude ejection to keep the pilot alive above the breathable atmosphere. Air racing emergencies virtually all occur at low altitude and even Bob Hannah’s 10+ G loss-of-trim-tab excursion didn’t put Voodoo high enough to need oxygen if he had bailed out.

• Pilot protection and restraint: At dynamic pressures above 400 KEAS (500 mph at Reno) and high Mach, the aerodynamic loads require a pilot’s body to be shielded and restrained while the seat decelerates to maximum parachute speed. Air racers are limited by propellers to low enough dynamic pressures for pilots to survive without shielding.

• Aerodynamic stabilizers: Likewise, high speed ejection requires the seat be aerodynamically stable as the rockets fly the seat to a higher altitude. Stabilizing booms extend from supersonic rated seats to align the seat straight and level. Below 300 KEAS, this is not necessary.

• Electronics: Needed to sense speed, altitude, Mach number; sequence the canopy and select a host of functions to keep the pilot alive. Multiple seat fighters also have to sequence which seat goes first and when so that one ejection does not hinder the other. The wider the ejection envelope, the more functions the seat has to select at the proper time and in the proper order. With a limited escape window and divergent paths for multiple seats, a PES for air racers can be made simpler and cheaper.

Pictured below is a "live fire" test of the SKS-94 from a modified Su-31. The extension boom and the clearance it provides from the tail section are clearly illustrated. The ejecting pilot is being pulled up and back on his parachute with an actual gain in altitude. Excess gas pressure from the extending boom can be seem venting above the rear pilot’s head. It is remarkable that the technology allows the aircraft to keep flying; the seat and pilot were prevented from striking the airframe during and after ejection. Although this test was performed under straight and level conditions, it illustrates some of the potential for air racing, aerobatic, and agricultural aircraft.

For the sports and light airplanes, there was developed the SKS-94, the crew emergency escape system. For the first time, the SKS-94 implemented a new escape method, which provided/or maximum escape intensification with minimum weight penalty.

For initial tests, the canopies were removed. The test pictured used a real test pilot, illustrating the confidence that Zvesda personnel have in their systems! At less than 24" wide, the seat system is quite compact and can be fitted to even the tight confines of an aerobatic aircraft. At less than 50 lb., the weight impact is within the practical envelope for small air racers, as well as aerobatic and agricultural aircraft. For an Unlimited, it’s a non issue. For through the canopy ejection, canopy breakers are added to the top of the seat.

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Accident dramatizations have been included to help the reader understand what a pilot goes through during a potentially fatal emergency. Most of the accidents listed in these articles resulted in major or fatal injuries to the pilot. It is the opinion of the author that some, perhaps most of these injuries could have been prevented with the pilot extraction system technology described.