Fundamentals of Propulsion Flashcards
What is propulsion?
a means of creating force leading to movement
What does a propulsion system consist of?
a source of mechanical power and a propulsor
How can propulsive systems be classified?
*air-breathing
>the need for an atmosphere
*non air-breathing
>no need for atmosphere
What are some examples of air-breathing systems?
*steam/piston engines
*jet engines
*high-speed engines
What are some examples of non-air-breathing systems?
*chemical rockets
*electric- electromagnetic
*experimental future systems
What are examples of propulsors?
*propellor
*nozzle/fan
*nozzle
What are examples of the fuel/propellent?
*liquid
*solid
*nuclear
What has the development of propulsive systems been dictated by?
speed and power
What does doubling the speed do to the power?
causes the power to increase 8 fold
What is the propulsive force?
thrust
How does (almost) every propulsion system generate thrust?
by accelerating a mass of gas in the direction opposite to the direction of intended motion
How does an air-breathing propulsive system work?
mass of air enters the propulsive system and is expelled by the system with a higher momentum
How does a non-air-breathing system work?
a mass of gas/plasma is expelled by the system
What is the propulsive efficiency?
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
What does propulsive efficiency measure?
the effectiveness with which the propulsive duct is being used for propelling the aircraft
If velocity(out) > velocity(in) to get high net thrust, what happens to the efficiency?
low propulsive efficiency
If velocity out is roughly equal to velocity in, what happens to propulsive efficiency and thrust?
high efficiency
low net thrust
What is specific impulse?
the thrust with respect to the amount of propellant per unit time
What is the relationship between thrust specific fuel consumption and specific impulse?
inversely proportional, they address the same performance of the propulsive system
When is specific impulse mostly used?
in the case of rockets and space propulsion
Why is specific impulse important?
*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
