Performance Metrics

Question 1

List 5 examples of performance metrics

Answer 1

Polytropic efficiency
Propulsive efficiency
Overall efficiency
Specific fuel consumption
Specific thrust

Question 2

What is the relationship between compressor efficiency and pressure ratio?

Answer 2

It is found that the compressor efficiency tends to decrease as the pressure ratio for which a compressor is designed increases

Question 3

What’s the definition of polytropic efficiency?

Answer 3

The isentropic efficiency for an elemental stage in a process such that it is constant through the whole process

Question 4

What’s the definition of propulsive efficiency?

Answer 4

The ratio of thrust power to the sum of thrust power and jet kinetic power

Question 5

What do you want for high propulsive efficiency?

Answer 5

Jet velocity must be higher than the aircraft velocity (but not too much higher)

Question 6

What is the efficiency of energy conversion?

Answer 6

A measure of how much kinetic energy is gained by the engine jet relative to the energy contained in the fuel

Question 7

What is the definition of overall efficiency?

Answer 7

The ratio of the work done in overcoming drag to the energy supplied by the fuel

Question 8

What is the definition of specific fuel consumption (SFC)?

Answer 8

Fuel consumption per unit thrust

Question 9

What is the definition of specific thrust?

Answer 9

The thrust per unit mass of air flow