Propellers Flashcards
Purpose of a propeller
To convert engine power into thrust
How does propeller produce thrust
Bernoullis theorem
Cold jet principle (newton’s third law)
Where does thrust act
Along the longitudinal axis of the aircraft
How does torque act in relation to a blade
At right angles to the propellers longitudinal axis
Describe centrifugal force in relation to propellers
The forces acting outwards, down thr longitudinal axis, pulling the blades out the hub
What’s the greatest force on a propeller
Centrifugal force
Describe thrust bending and why it happens
Thrust bending is when the tips of the blades bend forward when roating producing thrust. This is due to the lifting force and the flexibility of the blade that causes this forward arc
Describe torque bending
The reaction force opposing the blades moving through the air, opposite to their rotational path
Explain aerodynamic twisting moment
The moment that the blade courses the pitch due to the aerodynamic force applied infrastructure of the point of rotation
Define centrifugal twisting moment
The fining of pitch due to the weight force being in front of the point of rotation therefore the force reduces the blades angle
Name 6 parts of a blade
Butt Shank Face Back Leading edge Trailing edge
Define plane of rotation
Plane perpendicular to the shaft, as which the blades rotate
2 types of blade stations
Normal - measured from the centre of rotation, used to specify points on the blade
Master - used in maintenance to check blade angles, known point.
In relation to a angle of attack with a propeller, if the aircraft is moving faster the angle of attack is…
Smaller.
Rotational velocity and thrust are two main variables that impact AoA
Define geometric pitch
The distance measured in inches a propeller will move through a solid with no impacts over one revolution.
Define effective pitch
The actual distance measured in inches that a blade will move in one revolution
Define slip
The difference between geometric pitch and effective pitch. How efficient a propeller is. Most range from 75 to 85% efficient
What is torque reaction
Reaction force to the rotation of a propeller.
Define on speed
When a propeller is moving at the “correct”, set speed
Define windmilling
A propeller spinning in the wind, which can create drag
Outline feathering
When the blade is set extremely course to be in a position of lest air resistance. This setting also stops windmilling
Define reversing
When the propeller is in negative pitch, however the propeller still spins in the same direction. This is used to slow down, or move backwards when on the ground
5 Safety features in relation to propellers
Negative torque system, NTS De coupling Auto feathering Pitch lock Propeller brake
Outline a front spinner
An aerodynamic fairing that covers the prop hub and reduces drag
