Thrust mechanism
Origin of most of the thrust in subsonic engines: the fan bearings.
The fan blades accelerate the air backwards, and Sir Isaac pulls the fan blades forward, dragging the aircraft along with them.
In a rocket/turbojet/ramjet, it's the combustion chamber pressure, pushing on the closed front end of the chamber, reduced by viscous forces as the exhaust streams along the nozzle, and in some cases a turbine.
Thrust from shuttle engine again: about 400,000lb. The chamber pressure quoted is about 2800 psi, the throat of the exit of the chamber is roughly 24 inches across (about 430 square inches), which would give 1,200,000lb: so the price of stabilizing (by slowing and expanding) the flow out of the nozzle seems to be 800,000lb of thrust. The nozzle is thus pulled off the engine with 800,000lb of force, while the combustion chamber is pushed up into the engine by 1,200,000lb, giving a net 400,000lb. This suggests that the link between the chamber and the nozzle need to be tougher than that between the engine and its mount. I think that makes sense. Rocket scientists?
Last edited by awblain; 1st Jul 2009 at 21:26.