Shuttle verses aircraft?

Question

If jet aircraft have convergent exhaust nozzles to produce power. Why does the space shuttle have a divergent exhaust nozzle?

Answer 1

Well the shuttle isn't exactly divergent. It's convergent-divergent. Inside the nozzle it converges and compresses the exaust, and then diverges. You only see the divergent part so that's why most people think it's divergent.

The reason for the difference between the is because jets are designed to travel at very high speeds at relatively high pressure, while the shuttle reaches max q @ ~1000mph & 60000 feet. Most of the shuttle's operation is in high pressures, but at low velocities OR high velocities but high pressures. The convergent-divergent nozzle provides a good trade off between the two situations.

While convergent jet nozzles are designed for relatively high velocities at high pressures, in which case convergent designs are more efficient.

If you want more details just type in nozzle to wikipedia.

Answer 2

Because you are talking about two different processes - the expansion of incoming air with heat and adding combustion gases in the jet, where increasing the velocity increases the push. But the shuttle has rocket engines and constricting the flow would strongly interfere with the combustion - the engine cone is shaped to provide maximum forward force from the exploding fuel-oxidizer. The bowl shape provides increasing area as the combustion products expand. If the engine were cylinder shaped, besides not burning as well (shock waves in the engine) the engine would have to be much heavier to be stronger to resist the sideways forces.

Answer 3

They do hae divergent nozzles- around a central cone. Check out the cutaway picture in the link.