Propulsion System Classification Questions and Answers

Answer: C

Correct answer: Only three

The first three pairings are sound. The fourth is not: a ramjet has no compressor and depends entirely on ram compression, so it develops no useful thrust at rest and must be accelerated to roughly Mach 2 by some other means. That single limitation is why ramjets appear on missiles boosted by a rocket, and never as a vehicle’s only engine.

Answer: D

Correct answer: Only three

The first three are right, including that overall efficiency is the product. The fourth attaches the wrong dependence to propulsive efficiency: pressure ratio and turbine entry temperature govern the *thermal* efficiency, how well the fuel energy becomes kinetic energy in the gas. Propulsive efficiency depends only on how that jet velocity compares with the flight velocity.

Answer: A

The other three all take their oxidiser from the atmosphere and stop producing thrust where there is none. A rocket carries its own, which costs a great deal of mass but makes it the only type that works outside the atmosphere at all.

Answer: B

The other three all use a compressor driven by a turbine to raise the pressure. A ramjet relies on forward speed alone, which makes it mechanically simple but leaves it producing no thrust whatever until the aircraft is already moving fast.

Answer: C

The other three deliver essentially all of their output as jet momentum from the nozzle. A turboprop extracts nearly all the available energy to the shaft, leaving only a small residual jet thrust that is usually counted as a bonus.

Answer: D

The other three all govern how much of the fuel energy becomes kinetic energy in the gas. The velocity ratio determines propulsive efficiency instead, which is a separate factor that multiplies with thermal efficiency to give the overall figure.

Answer: A

The other three are the recognised consequences of moving more air more slowly. Specific thrust falls rather than rises, which is exactly why a high bypass engine must be physically larger to produce the same total thrust.

Answer: B

At that cruise Mach number the high bypass turbofan has by far the best propulsive efficiency and the lowest jet noise. A turbojet would burn far more fuel, a turboprop cannot reach the speed, and a ramjet produces no thrust at rest at all.

Answer: C

Propulsive efficiency would indeed approach unity, but an efficiency of one applied to zero thrust is useless. The practical cycle settles on a jet velocity somewhat above flight speed, trading some efficiency for the thrust the aircraft actually needs.

Answer: D

Slowing hypersonic flow to subsonic speed would raise the temperature beyond any material's limit, so combustion must occur in supersonic flow. The fuel has milliseconds to mix and burn, which is the problem that has kept the concept experimental.