posted on Aug, 14 2008 @ 12:16 AM
I am absolutely stunned that none of you guys understand jet or rocket propulsion, it is junior grade physics.
The basic idea is that you have a chamber with a high pressure inside. Imagine something like a compressed scuba diving tank, or a propane bottle, or
maybe even a party balloon. This pressure might be measured in pounds per square inch, or some other suitable unit.
Now in a completely closed sealed container, this internal pressure pushes outwards equally in every direction. There is no external thrust generated
(obviously) because the internal pressure pushes outwards the same in every direction.
Now suppose suddenly you cut a hole in one end of this tank.. The internal pressure still pushes in every direction EXCEPT where the hole is. So the
internal foces OPPOSITE the hole push the tank in that direction.
If there is 100 psi in the tank, and a one square inch hole, there will be 100 lbs of thrust against the inside of the tank opposite where the hole
is. This is 100 lbs of unbalanced forces, and it acts INSIDE the tank. It needs no external air to push against.
A jet engine works exactly the same way. It is the forces innside the engine that push the engine in a forward direction. The gasses coming out the
back are just a release of pressure. Jet engines require external air for combustion. Rockets do not.
Getting back to rocket engines. A simple hole will not work very well, because all the gas pressure inside the engine will suddenly just empty out of
the hole, leaving no high pressure inside the engine. There would then be nothing to push against the front of the inside of the engine.
What is done is you fit a sonic nozzle to the engine. This is a convergent, divergent cone, the classic rocket nozzle shape. This creates a sonic
shock wave inside the narrowest part of the engine to keep a very high pressure buildup inside the engine. This higher internal pressure greatly
increases the thrust. The shape of this nozzle is critical to getting optimum thrust. But that thrust comes from the high pressure inside the
combustion chamber, not from the exhaust "pushing" against anything.
Hope that helps..
This is all pretty basic stuff. Surprised you guys have never heard it all before.