Fundamentals of Propulsion

Question 1

What is propulsion?

Answer 1

a means of creating force leading to movement

Question 2

What does a propulsion system consist of?

Answer 2

a source of mechanical power and a propulsor

Question 3

How can propulsive systems be classified?

Answer 3

*air-breathing
>the need for an atmosphere
*non air-breathing
>no need for atmosphere

Question 4

What are some examples of air-breathing systems?

Answer 4

*steam/piston engines
*jet engines
*high-speed engines

Question 5

What are some examples of non-air-breathing systems?

Answer 5

*chemical rockets
*electric- electromagnetic
*experimental future systems

Question 6

What are examples of propulsors?

Answer 6

*propellor
*nozzle/fan
*nozzle

Question 7

What are examples of the fuel/propellent?

Answer 7

*liquid
*solid
*nuclear

Question 8

What has the development of propulsive systems been dictated by?

Answer 8

speed and power

Question 9

What does doubling the speed do to the power?

Answer 9

causes the power to increase 8 fold

Question 10

What is the propulsive force?

Answer 10

thrust

Question 11

How does (almost) every propulsion system generate thrust?

Answer 11

by accelerating a mass of gas in the direction opposite to the direction of intended motion

Question 12

How does an air-breathing propulsive system work?

Answer 12

mass of air enters the propulsive system and is expelled by the system with a higher momentum

Question 13

How does a non-air-breathing system work?

Answer 13

a mass of gas/plasma is expelled by the system

Question 14

What is the propulsive efficiency?

Answer 14

the ratio of the propulsive power to the sum of the same power and the kinetic energy per unit time left in the jet at the exit of the system

Question 15

What does propulsive efficiency measure?

Answer 15

the effectiveness with which the propulsive duct is being used for propelling the aircraft

Question 16

If velocity(out) > velocity(in) to get high net thrust, what happens to the efficiency?

Answer 16

low propulsive efficiency

Question 17

If velocity out is roughly equal to velocity in, what happens to propulsive efficiency and thrust?

Answer 17

high efficiency
low net thrust

Question 18

What is specific impulse?

Answer 18

the thrust with respect to the amount of propellant per unit time

Question 19

What is the relationship between thrust specific fuel consumption and specific impulse?

Answer 19

inversely proportional, they address the same performance of the propulsive system

Question 20

When is specific impulse mostly used?

Answer 20

in the case of rockets and space propulsion

Question 21

Why is specific impulse important?

Answer 21

*provides a convenient way to determine the thrust of a rocket once the weight flow rate through the nozzle is known
*it indicates the efficiency of the propulsive system, the engine with the higher value of specific impulse is more efficient because it produces more thrust for the same amount of propellant
*it provides an easy way to size the engine