By Eric Ahlstrom

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The Timing

Steve Hinton had plenty of time to know he was not going to make it, yet could not safely bail out. Egress from most air racers is slow and cumbersome even on the ground. In the air, during an emergency it can take the better part of a minute. After that the pilot still needs enough altitude to clear the airframe and open his chute safely. In almost all of the fatal and injury accidents described in these articles the pilots had time to realize they needed to get out, but did not have the altitude or time for a manual bail out.

Often, we have seen a pilot "stay with the airplane" simply because he has no other choice. Nothing brave or noble, they just know they can't get out. Egress is so restrictive in many air racers that the pilot is virtually bolted in (this was done in some experimental programs up until the late 50's). Many racers, especially in the Sports Class, use multiple canopy latches that are virtually impossible to open quickly in an emergency. Any powered pilot extraction technology depends on any restrictive structures above the pilot to be taken out by the egress system.

Manual egress in the pits can still be inconvenient, but when the pilot needs to bail out – he needs to bail out NOW! Opinions of the viability of extraction systems not withstanding, rapid manual egress should be demonstrated before any aircraft is allowed on course. Otherwise, we might as well leave the parachutes behind.

In all motor sports, there is a point between loss of control and crashing that the driver knows he is going to crash. Sometimes it’s only a split second, most of the time it’s much longer. The available decision time to leave the aircraft will vary with the pilot and the situation. Pumped up and focused down, a pilot can pull the handle in a few tenths of a second once the decision is made. G forces from tumbling that would pull the pilot’s arms away from the handles would also be sufficient to incapacitate most pilots. So we can expect that a conscious pilot will be able to pull a well placed handle. If we can equip him with a system that will separate him from the aircraft in a few more tenths of a second, then the window for escape comes down under a second and safe escape from low altitude accidents becomes possible.

If the air racers in the incidents dramatized in this article were equipped with an escape system that they could trust at low altitude, it would give them a second option to "riding it in". By lowering the altitude and decreasing the time required for a safe bail out, a pilot extraction system can reduce the chance of the infamous pilot-bails-out-aircraft-crashes-into-crowd scenario.

The Technology

First test flight with this big prop. Lifting off the stability is not good…
A shallow turn and you find the world flipping over and the aircraft
out of control. Time to bail. As you fight your way out of the cockpit you
can’t avoid the tail, and the slipstream blows you into it like a freight train…

(Mike Carrol: modified P-39, 1968)

In a high speed ejection, the pilot is vulnerable to impacting the airframe. Early ejection seats addressed this with increasingly powerful charges to blow the seat clear. This resulted in crippling G forces to the pilot. The modern, light weight, and cheap answer was to reduce the size of the charge and extend the seat on a vertical rail. Several modern fighters, like the F-16, use just such an extension rail to insure that the seat clears the tail without the need for excessive catapult force.

The next problem is insuring that the pilot has decelerated enough so that when the chute opens it won’t shred itself or the pilot due to excessive airspeed. High performance parachutes have been adapted to very wide opening speed envelopes through the use of aerodynamic sliders. Essentially a parachute within the parachute, the slider rides up the risers under aerodynamic load to limit the degree the parachute can open under excessive dynamic pressure. As the parachute decelerates, the slider is forced down the risers by canopy inflation. This allows an average weight pilot to eject at nearly 300 KEAS or 375 mph at Reno altitude. This is the cornering speed of a Silver Class winner and virtually no injury accident has occurred at this high of a speed.

This still sounds too slow for Gold Class Unlimiteds until we look at how propeller aircraft perform after an engine or airframe failure. The answer is not too well. With large props and much higher wetted area to weight ratios that modern jets, crippled air racers tend to decelerate very quickly, often losing half their speed in a matter of a few seconds. So 300 KEAS is fast enough for almost all historic air racing accidents.

The next issue is decelerating the pilot before he hits the ground. Virtually all air racing accident decision points have taken place with significant forward airspeed and some altitude. If a parachute is extended from the pilot on its own rocket, the altitude it needs to open is reduced from hundreds to tens of feet. The chute must then decelerate the pilot and arrest any remaining sink rate before he hits the ground. As little as 50 feet AGL at ejection can be sufficient if the pilot has more than 50 KEAS of airspeed. Most air racers stall well above this speed, so the energy to open the chute under low speed conditions is almost always present.

Sink rate increases the required altitude for saving the pilot. 200 mph straight down would raise the minimum altitude by several hundred feet. Fortunately, an emergency developing into this kind of situation without warning is almost unheard of in air racing

We now get a clearer picture of the minimum escape system for an air racer. A light weight, inexpensive combination of seat, extension catapult, and rocket assisted chute. We do have to be careful about getting too light.

There is a danger with lightweight seats that the variations in pilot weight will create too wide of a potential G load during catapult firing and parachute opening. The lightweight pilot has the advantage since the parachute is rated in dynamic pressure (KEAS) multiplied by the pilot’s weight. A lighter pilot will have a higher maximum parachute speed, will decelerate faster, and will have a lower sink rate once the chute is open. G load during ejection can be compensated for with ballast attached to the seat that does not go with the pilot and parachute.

The heavy pilot will have a lower G load coming out of the aircraft, but exerts more force on the chute system. He will have a lower maximum escape speed, and cannot survive ejection as low to the ground or with as high a sink rate as the lighter pilot. The differences are measured in feet, but sometimes a few feet are all we have.

Automatic Ejection ?

Howling along at nearly 500 mph, this aircraft is feeling GOOD!
As you plan your line to pass the leader you hear a sudden thump…

(Bob Hannah, Voodoo 1998)

Engine failure on a lift fan / vectored aft nozzle STOVL aircraft like the Yak-140 or the Lockheed-Martin JSF can cause a rapid attitude change that is beyond the pilot’s ability to sense and react to. Battle damage is capable of turning a modern fighter into a tumbling mass of disintegrating, high G hell. For these extreme situations, some military seats have been equipped to automatically eject the pilot if they sense an out of control condition.

We have seen in flight break ups and in flight loss of parts in air racing. When this happens, the pilot has a good chance of being incapacitated by the G load. Even if he is conscious, he may not be able to make an ejection decision. It is possible that sensors or lanyards attached to various parts of the airframe could initiate an auto eject, but which parts would be sensed and how?

An ejection system that can deploy fast enough to save a pilot at low altitude may not be able to cleanly separate from a tumbling or disintegrating air racer. There is also the problem of a transient like Hannah’s where the pilot recovered from what was virtually an out-of-the-envelope G load. Everyone asked on this subject agrees that it would not have been a good idea for Hannah to be ejected. Any highly robust system that is smart enough for all foreseeable cases currently entails more weight, cost, and most importantly, time. Time to deploy, time to arrest the sink rate, time and altitude that an air racer may not have. At this point in history with the technology we have in hand, we should probably put off implementing auto ejection for air racers.

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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.