How ejection seats work
By Marshall Brain
http://www.JewishWorldReview.com | (MCT) It is one of the most dramatic things you will ever see. A multi-million dollar fighter jet is streaking toward the ground at hundreds of miles per hour. In another second the plane will explode into a million pieces when it craters into the earth. Then, at the last moment, you watch the pilot eject. If you are close enough, what you see is something that looks like a rocket powered chair carrying the pilot, and then a parachute opens to bring the pilot safely to the ground.
What has happened? From the pilot's perspective it is a small miracle - a miracle that has saved hundreds of lives over the years. From an engineer's perspective, it is the combination of technologies that tries to make the best of a bad situation. Every ejection seat system is different, but they all have a lot in common. So let's look at the technology that gives an ejection seat the power to rescue the pilot from certain death.
The first step is for the pilot to recognize that things are hopeless. The plane is going to crash and there is nothing that he or she can do about it. At this moment, the pilot reaches for the ejection handle. It might be alongside the seat or between the legs or above his head. Pulling the handle starts the ejection process.
The next step is to get rid of the canopy. The canopy is the clear shell that covers the cockpit, and it has to get out of the way. One system uses explosive bolts and small rockets. The bolts release the canopy and the rockets push the canopy up and out of the way. The other system uses a system of explosive cords attached to the canopy. The cords explode and completely shatter the canopy.
Now that the seat has a clear path out of the plane, it begins to do its job. The first phase of ejection uses a catapult gun. The seat slides along the rails of the catapult for several feet so that it is moving in the right direction.
Next, several rocket engines under the seat fire. These rocket engines need to solve a pressing problem during ejection, and that problem is known as the tail of the plane. As soon as the pilot and his seat get out into the slipstream, the wind is going to push the seat straight toward the tail of the plane. The rocket engine gets the seat moving fast enough so that it misses the tail.
This entire process - the canopy, catapult and rockets - all happens in about half a second. At this point the seat has done its job. So a motor fires to cut the pilot loose from the seat and the parachute system starts to deploy. This is a little tricky, because if the pilot is close to the ground moving slowly you want to do one thing. On the other hand, if the pilot is two miles up flying near the speed of sound, you want to do something else. The seat has sensors that let it detect its speed and altitude. Depending on the conditions, it may or may not use a drogue chute to slow the pilot down, and it may or may not delay the opening of the main parachute.
Once the parachute opens, the pilot floats to the ground. The ground might be right there if the pilot ejected a low altitude, or it might be two miles below. Or it might not be there are all if the pilot ejected over water, and the pilot has to get ready to swim.
As you might imagine, a ride in an ejection seat is not fun. The seat ejects the pilot into wind that is blowing at hundreds of miles per hour, and accelerates the pilot upward from zero to 250 miles per hour in about half a second. The G-forces on the pilot can be gigantic, and then he has to nail the landing. Still, it is better than dying instantly when the plane hits the ground and explodes.
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© 2007, How Stuff Works Inc. Distributed by McClatchy-Tribune Information Services.