Propeller Flashcards
(17 cards)
What is a propeller?
A rotating propeller converts power from a piston engine into thrust. The propeller comprises 2 or more blades. On single-engine aircraft, equipped with Western-made engines, the propeller almost always rotates clockwise when viewed from the cockpit.
Blade angle
Angle between blade chord line and plane of rotation.
Fine Pitch
Propeller pitch with a lower blade angle.
Coarse pitch
Propeller pitch with a high blade angle.
Blade Angle of Attack
Angle between the blade chord line and the relative wind.
GEOMETRIC PITCH
Distance to advance at one revolution without the slippage.
Geometric pitch = Effective pitch + Slip.
Effective pitch
The actual distance at one revolution with slippage.
Effective pitch = Geometric pitch - Slip.
Propeller Efficiency
Is the ratio of thrust horsepower to brake horsepower. Varies from 50 to 87 percent, depending on propeller slippage.
PITCH DISTRIBUTION or propeller twist
A propeller tapers towards the tip and appears to twist. In effect, the airfoil section alters from the hub of the propeller to the tip and the blade angle decreases.
Types of Propellers
- Fixed pitch propeller
- Ground adjustable propeller
- Controllable Pitch
- Constant speed propeller.
FIXED PITCH propellers
Efficient at only one RPM and speed setting. At a constant RPM, a fixed pitch prop with increasing forward speed would result in a decrease of propeller angle of attack. At fast true airspeeds, a fixed pitch prop is very inefficient.
Cruise Propeller (Fixed pitch)
Fixed pitch prop with high pitch, therefore more drag. This results in lower RPM. Increased efficiency during cruising flight.
Climb Propeller (Fixed pitch)
Fixed pitch prop that has a lower pitch, therefore less drag. Results in the higher RPM by the engine. This increases performance during takeoffs and climbs.
Standard propeller
Compromise of both Climb and Cruise Propeller.
Disadvantage of cruise propeller
*It is most efficient only at a condition of cruise, but until reaching cruise speed, the AOA of the propeller blade is comparatively larger, therefore the propeller is less efficient.
*During take-off, the AOA of the propeller would be extremely large, resulting in poor acceleration, hence requiring a longer take-off run.
GROUND ADJUSTABLE PITCH PROPELLER
Mechanic can change the Pitch setting only on the ground when the aircraft is not flying, or engine is not running.
Spinner
The spinner covers and protects the propeller hub.
The Spinner’s shape helps air flow smoothly into and around the engine cowl for cooling purposes
