Propellors Flashcards
22.24.2 Define blade face.
Blade Face = The side that faces the pilot, painted black.
22.24.4 Describe the forces acting on a propeller blade; the rpm/airspeed relationship; and the
most effective blade sections.
Forces = See fig 12-5.
Relationship = See fig 12-6.
Most effective blade section is between 60-90% of the radius. Normally around 75%.
22.24.6 Explain how propeller pitch affects efficiency at different speeds.
See fig 12-8.
22.24.8 Explain the purpose of the constant-speed (variable pitch) propeller.
Efficiency is the purpose. Fixed pitch props are only efficient at one airspeed. Variable fixes this.
22.24.10 Describe in broad terms the operation of the constant speed unit (CSU) with changes
in power setting and airspeed.
If power setting increases the angle of attack reduces. The CSU will act to fine the propeller.
If Airspeed increases the Angle of attack will reduce. The CSU will act to coarsen the pitch.
In both cases if opposite occurs, then the CSU will act the opposite way.
22.24.12 Describe the correct procedure for handling manifold pressure and propeller controls.
MP should not be higher than recommended for RPM.
To increase power; Rich, Pitch, Power. 1. Increase Mixture, 2. Increase RPM, 3. Increase MP. To decrease Power, Pitch, Rich.
22.24.14 Describe the forces acting on a propeller when: (a) windmilling;
See fig 12-14.
22.24.14 Describe the forces acting on a propeller when: (b) feathered;
See fig 12-15.
22.24.14 Describe the forces acting on a propeller when: (c) in reverse thrust.
See fig 12-16.
22.24.16 Explain propeller centrifugal and aerodynamic twisting moments.
See fig 12-17 + 12-18.
22.24.18 Describe asymmetric blade effect.
The down going blade produces more thrust when the aircraft is in a climb, see fig 12-19. So clockwise spinning propeller, means the force will be precessed 90deg, which means the aircraft will yaw left.
22.24.20 Explain the terms power absorption and propeller solidity.
Power absorption = The ability of the propeller to convert engine power into thrust.
Propeller solidity = The ratio between a part of the propeller disc, vs. the circumference of the disc at the same radius.
22.24.2 Define blade angle.
Blade Angle = Angle between blade chord and plane of rotaion.
22.24.2 Define pitch (or helix) angle.
Pitch/Helix Angle/Angle of Advance = Angle between Relative airflow/resultant velocity vector and the plane of rotation.
22.24.2 Define helical twist.
Helical Twist = A propeller has a reduction in blade angle from hub to tip.
