Simulation for Military Aircraft Ejection Seats

I’ve always been passionate about aircraft. When I served in the Air Force and took my pilot training, I learned a lot about how systems on military planes work. One of the most amazing components, to me, was the ejection seat, probably one of the most complex pieces of equipment on board.

image of parachute system

Drogue parachute system analysis with inset submodel of the critical area using nonlinear material properties. Courtesy CTC.

Even if the purpose of the seat is clear and simple — to provide the pilot a safe and immediate way out of the aircraft in case of accident — its job is a very tough one. The seat has to work in emergency conditions; it represents the last chance for a pilot to leave a severely damaged aircraft, maybe spiraling out of control. This system must be designed not to  fail despite the critical, varied and unpredictable conditions in which it will be used. That’s quite a challenge for designers! Let me give you an example.

A fire can occur when the plane is stationary on the runway, ready to take off, or flying at 50,000 feet at 600 knots — quite a range of conditions! In the first case, the goal of the ejection seat is to launch the pilot to a height that will allow the parachute to open properly and slow his fall while putting enough distance between the pilot and the aircraft, which is even more important if the plane explodes.

In the second case, the goals are to avoid a collision between the ejection seat and the aircraft’s tail (True: When you bail out, the tail behind you is traveling at the speed of sound toward you.) and then provide a very fast descent to a lower altitude so the pilot survives external extremes like temperature (down to -70 C), pressure (very low, which has a lot of bad effects on the body), and oxygen (not enough at 15,000+ feet).

How does the ejection process work? The seat is a pyrotechnic system, placed in the cockpit mounted on a  rail on a telescopic gun. When the pilot pulls the ejection handle, he starts the launch sequence:

  • The belts that keep him on the seat are automatically fastened; legs are kept in proper position by a restraint designed to protect limbs from getting caught or harmed by debris during ejection.
  • The ejection seat canopy is released. If the system fails, or if the aircraft is at ground level, an explosive reaction forces it to blow out.
  • The telescopic gun pushes the seat out of the cockpit, guided by the rails to avoid lateral collisions (For example, the plane could be in a spin).
  • A rocket pack pushes the seat high and away from the plane, at about 200 feet more than flying altitude (enough for the parachute to open even if used at ground level). The lift is not vertical, but it’s designed to push the pilot out with a specific angle of ascent to clear the aircraft’s tail.

A curiosity is that if the plane has a crew of two, the rear seat is ejected like the first (only 0.3 seconds prior — which is enough when you consider aircraft speed), and the two seats shoot out of the aircraft in opposite directions. If you are already in trouble (and clearly you are in deep trouble if you pulled the handle), it’s better to avoid another challenge like a mid-air collision with your crew.

Anyway, the pilot and his crew (along with all the equipment on the seat) must be prepared to handle 12 to 16 Gs of acceleration. The system must take care of the crew members until they reach the ground. This automated bailout is controlled by a microcomputer installed in the seat. It collects data about speed, height and acceleration from different sensors embedded in the seat, analyzes it, and makes split-second decisions, such as the timing of the complex parachute opening sequence.

When the seat is at a safe distance from the aircraft, a second rocket pack causes the seat to flip upside down, then a gun in the seat fires a metal slug that pulls a small parachute out of the top of the chair. This way, when parachute opens, the seat does not run into it. This small parachute is called an extractor; its goal is to open a second parachute, the stabilizer. This process is especially critical at high altitude, as it allows the seat to descend very fast but safely to an altitude where the pilot can easily survive.

In the meantime, the computer opens the emergency oxygen flow, turns on the transmitter, and sends an SOS message with GPS data. A barometric sensor checks the altitude and, when the right height is reached (set considering the highest mountains in the operation area), the final, main parachute opens and a last gun pushes the pilot away from the heavy seat, allowing him to land safely. If the ejection seat is activated at a very low altitude, all three parachutes open at the same time, and separation of the seats from the pilot and crew is immediate.

As you can see from my description, the ejection seat is a complex, integrated survival system made of electronic sensors,  actuators and explosive devices that must work in an exact sequence and adapt this sequence to external conditions. All of this is mounted on a structure that faces strong mechanical stresses and strains, protecting the pilot, safety equipment and parachute pack during a sudden emergency. And if just one piece of critical equipment malfunctions, it could be fatal.

By the way, did I mention that the entire sequence I’ve described, from the handle pull to the parachute opening, lasts no more than 4 seconds?

It was not always like this, of course. The ejection seat that was patented in Germany in 1939 worked via pressurized air. During the World War II, only 50 percent of bailouts were successful. Since those days, the system has evolved into a perfect mechanism that has saved more than 12,000 pilots’ lives.

It didn’t surprise me to discover the important role that simulation had in designing and testing such a complex system, increasing its reliability, easing synchronization of all the different parts, cutting the testing costs of new versions. Still curious? Check the article Up, Up and Away that further talks about  how simulation-driven innovation delivered a new ejection seat design for a military aircraft in less than 14 months.

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About Paolo Colombo

Paolo Colombo is the Aerospace & Defense Global Industry Director at ANSYS. He was born in Italy in 1970, joined the Air Force as student pilot in 1992 and, though his career took a different path, he is still regularly flying. From 1999 his passion for advanced technologies brought him to work with companies' managers and executives on emerging technologies in product engineering, rapid prototyping, additive manufacturing and engineering simulation. He joined ANSYS in 2010. Paolo holds a BSc and an MBA majoring in Innovation management.