Propellers characteristics Flashcards
What is the propeller?
a rotating wing generating lift and drag that accelerates the air backwards
What does the thrust generated by the propeller depend upon?
the forward speed due to the aircraft motion and the rotational speed of the propeller
What changes from root to tip of the propeller?
the angle of the relative airflow
What do the thrust and reaction force depend on?
the relative angle of attack
How do propellers produce thrust?
by realising a relatively small increase in speed to a high mass volume
What is the blade geometric pitch?
the angle between the aerofoil zero lift line and the plane of rotation
What is the solidity?
the fraction of the propeller disk area occupied by solid blades
What is the pitch?
the distance travelled by a blade element in one revolution
Why do modern propellers have variable pitch?
to accommodate different flight speeds
Where is the tangential velocity greatest in the propeller?
tangential velocity at root < tangential velocity at tip
How can negative thrust be avoided?
*varying the blade geometric pitch along the span
*varying the shape of the blade i.e the airfoil used at different sections
What blade profile is used to avoid excessive twist?
a blade profile that is thick with a high geometrical pitch near the tip and thin low geometrical pitch towards the tip
Where is the maximum power of a piston engine developed?
toward the maximum rotational speed of the engine
How is the power of the piston engine constrained?
by the mechanical and temperature consideration of the plant
Where is maximum efficiency found?
at the high end of the rotational speed range
