Propellers Flashcards
Propeller Manufacturers
Mcauley
Hartsell
MTU
Components of the Total Reaction
Propellor thrust
Propellor torque
Composite Propeller
Preferable as much lighter than metal or wood
Difficult to repair from foreign object damage (FOD)
Angle of Attack
The angle between its chord and the relative airflow
4 degrees is most efficient
Blade Angle
The angle between the chord line of the propeller and the plane of rotation
Blade angle = helix angle + angle of attack
Helix Angle
The angle between the plane of rotation and the relative airflow
Relationship Between RPM, TAS and AoA
Fixed pitch (blade angle remains constant):
For a given RPM, increased TAS will reduce the angle of attach and vice versa
For a given TAS, increased RPM increases the angle of attack and vice versa
Any angle of attack can be achieved with combinations of TAS and RPM
One RPM value will only have one TAS to achieve a certain AoA
As AoA decreases, thrust decreases as TAS increases
Thrust/Toque Ratio
Changes with the AoA
Best Thrust/Torque Ratio
Achieved using the most efficient AoA
Gives the greatest amount of propeller thrust for the smallest amount of propeller torque
Best value for money
Engine Torque
Acts to overcome propeller torque and enables the blades to rotate
Engine Torque Vs Propeller Torque
ET = PT: the blades rotate at a constant RPM (RPM constant)
ET > PT: RPM increases
ET < PT: RPM reduces
Fixed Pitch Propellers
Fixed blade angle
Efficient only at one TAS
Variable Pitch Propellers
Varies the blade angle to maintain an efficient angle of attack over a wide range of RPM and TAS
Also known as constant speed units (CSU)
Increased TAS on a Variable Pitch Propeller
Blade angle must be increased to maintain the AoA
Fine Pitch
Small blade angle
Good for acceleration (high RPM)
Suitable for takeoff and slow flight