Propulsion System Classification Questions and Answers

Answer: A

Both statements are true and the second is the dominant mechanism. Falling temperature partly offsets it by improving the cycle, so the observed lapse is gentler than a simple density scaling would predict but unmistakably present.

Answer: B

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: all propulsion works by Newton’s third law on some accelerated fluid, and an air breathing engine takes its oxygen from the atmosphere. Statement 3 is inverted - a rocket’s thrust *rises* with altitude, because \( F = \dot{m}V_e + (p_e-p_a)A_e \) and the falling ambient pressure increases the pressure term. Only an air breather loses thrust with altitude, and it does so because the air thins.

Answer: C

Correct answer: 1 and 2 only

Statements 1 and 2 correctly separate the two efficiencies: thermal efficiency is a cycle matter governed by pressure ratio and turbine entry temperature, and propulsive efficiency is a matching matter governed by the ratio of jet to flight velocity. Statement 3 repeats the sum-versus-product error - overall efficiency is the product, so it is always smaller than either factor.

Answer: D

The first two are correct. Lower specific thrust means far more air must be processed for the same total thrust, so the engine grows rather than shrinks, which is exactly what nacelle diameters have done over the decades.

Answer: A

Correct answer: 1 and 2 only

Statements 1 and 2 are correct. Statement 3 is the recurring ramjet error: with no compressor there is no pressure rise at rest, so the cycle cannot operate and no thrust is produced. A ramjet must be brought to high subsonic or supersonic speed by a booster before it will run at all.

Answer: B

The four differ chiefly in how much air they accelerate and by how much, which is what sets the flight regime each suits. Only the last dispenses with the atmosphere altogether, at the cost of carrying its oxidiser with it.

Answer: C

Correct answer: A-1, B-2, C-3, D-4

Four definitions, and the trap is the pair that both begin with thrust. Specific thrust is thrust per unit air mass flow, which sizes the engine. Thrust specific fuel consumption is fuel flow per unit thrust, which is the inverse-looking quantity that measures economy. Bypass ratio is bypass flow over core flow, and overall efficiency is the product of thermal and propulsive efficiency.

Answer: D

Correct answer: A-1, B-2, C-3, D-4

The four engines line up in ascending order of speed, which makes the match straightforward: a reciprocating engine and propeller for light aircraft at low speed and power, a turboprop for regional work up to about four hundred knots where the tip speed limit begins to bite, a high bypass turbofan for long range high subsonic cruise, and a scramjet for sustained hypersonic flight.

Answer: A

Knowing which lever moves which efficiency is what makes a design argument coherent. Raising turbine entry temperature does nothing for propulsive efficiency, and lowering jet velocity does nothing for the thermodynamics of the core.

Answer: B

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