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Re: Attic ventilation from fans - to jet engines

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On May 17, 2006, at 12:06 PM, John Riley wrote:

Why don't the expanding gases exit through the front?
The compressor in the front of the engine acts like a sort of pump (It is a turbo-pump actually) forces oncoming air through the engine so that it only travels one way. Additional pressure is generated when the fuel is burned in the intake air, but the path of least resistance is out the exhaust. The turbine in the rear of the engine drives the compressor.

You can think of the engine as a device for accelerating air. It pushes air one way and the reaction to the push drives the airplane in the other direction. A propellor attached to a piston engine does the same thing and so does the turbo-fan on modern jet engines, which is a form of propellor. You get the same effect from a garden hose--the force accelerating out through the nozzle produces a reaction which you can feel as you hold the hose.

Rocket engines do the same thing, except that they don't burn fuel in air because they carry their own oxidizer but they generate thrust the same way by accelerating combustion products out the back with the reaction driving the rocket forward.
Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)   | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania 1864)

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