AS 03 - Propulsion Flashcards
Define Thrust in terms of energy
Fuel is fed to an engine, this chemical energy is changed into thermal energy then converted into mechanical work in propelling an aircraft against the drag.
What are the types of engines and the different type of propeller options?
Combustion and turbine engine
Fixed pitch and variable pitch propeller
Old and well-tried system, gives a small acceleration to a large amount of air and driven by a combustion or turbine engine describes what type of propulsion?
Engine/ propeller propulsion
What is a piston frequently referred to as? what is its product?
Referred to as a powerplant and its product is power.
PLAN/3000 gives what calculation?
The amount of power a combustion engine can produce.
The following equation explains what: T = m▲V?
The amount of thrust provided equals the rate at which momentum is given to the air
What’s the difference between turbo-prop and a turbo-jet/ fan means of propulsion?
A turbo-prop gives a large mass of air a small acceleration
A turbo-jet/ fan gives a small mass of air a large acceleration
What is the function of a propeller?
To convert the torque given by the engine’s power into a straight forward push or pull, called thrust, for forward speed.
How does a propeller operate? (Think motion and forces)
Moves forward in a corkscrew motion
Pushes air backward to create thrust
As it rotates, it produces lift and drag
Forces are designated as thrust and torque
The tip of the propeller spins faster than the base, how is uniform thrust maintained throughout most of the propeller diameter?
The propeller is “twisted” so that the angle of attack is less near the tip than the base.
Define pitch (WRT propellers)
It is the distance in feet a propeller travels forward in one revolution.
What are the main types of pitch?
Coarse and fine
What governs the pitch?
The angle at which the blade is set
What is the difference between coarse and fine pitch?
Coarse pitch: Blade set to a large angle, blade will travel a greater distance forward per revolution
Fine: Propeller will revolve around its own axis at a higher speed, enabling the engine to generate more power
What is the trade-off for a fixed pitch propeller?
The angle is set by the manufacturer, you either have better take-off or cruising performance.
“Engine and propeller always work at maximum efficiency” describes what pitch type?
Variable pitch
True or false
A variable pitch propeller is manually adjusted and the propeller revolves at different rates depending on pitch.
False, the pitch is automatically adjusted and the prop maintains a constant rpm, with different pitches.
What are the mechanisms for varying pitch?
Mechanical, hydraulic and electrical
What are some difficulties of making propellers work well at high speeds?
Rotational speeds: Prop moves through air faster than speed of sound well before the aircraft
Supersonic flow: (PPT doesn’t go into much detail about this one)
What kind of engine is used in the Dash 8?
Two Pratt & Whitney of Canada (PW120A)
Which engine type only has a small amount of exhaust gases used as jet thrust?
Turbo-prop, the engine exhaust gases are used to drive the compressor and engine. Afterwards, exhaust gases are used as jet thrust.
Describe the engine specs of a PW 120A and its propeller.
Each engine can produce 1800 SHP, with possible up trim to 2000 SHP in event of engine failure.
The propeller is a 13 ft diameter, four blade, constant speed, hydraulically controlled propeller.
Where is the propeller connected to in a “Free Turbine” system?
Connected to what is referred to as a power turbine which “floats” in the high pressure exhaust gases in the turbine section.
Review Questions
Name four common types of jet engines.
Ram-jet, turbo-jet, turbo-fan and engine/ propeller combination
Review Questions
Which type of engine gives a large mass of air a small acceleration?
Turbo-prop
Review Questions
What is the coarse pitch setting used for?
Cruise
What is the SHP of the PW-120A?
1800 SHP, can up trim to 2000 SHP in the event of an engine failure.
