Propeller Basics Flashcards
What advantages does adding more blades to a prop have?
It allows the blades to be shorter so gives better ground clearance
Not as loud (because they are shorter)
Reduced vibration (because they are shorter)
What is Brake Horsepower?
The horsepower of an engine corrected for the inefifficencies of combustion, internal friction, and other factors. Example. A 200hp engine may actually only produce 180hp after these things are factored in.
What is Thrust Horsepower?
The brake horsepower, one transfered to the propeller and corrected for the ineficiencies of the prop. Thrust horsepower will always be lower than brake horsepower
What are the definitions of the following terms?
Propeller Efficiency
Geometric Pitch
Effective Pitch
Propeller Slip
What annoying effects do propellers have?
Torque
Slipstream
Gyroscopic Precession
Asymmetric Thrust (sometimes known as P-Factor)
What is torque in terms of a side effect of propellers on the AC?
Most props rotate clockwise (from the pilot’s perspective), which results in the aircraft wanting to rotate counter clockwise.
**On the exam, as in the picture below, make sure you understand which way the AC is facing before answering the question
What is a slipstream (AKA Propwash) in relations to the affect of propellers on an AC?
The airfoil of the propeller creates drag, which *causes the air to rotate in the direction of the propeller’s rotation as the air moves backward towards the AC.
This air spirals around the plane and hits the verticle stabalizer on the **left side*.
This will result in the nose yawing to the left
What counter measure do most AC manufacturers put in to offset for slipstream/propwash in cruise flight?
How does this counter measure affect flight characteristics outside of cruise?
The fin and rudder are installed at a slight angle to aling with the airflow, instead of with the axis of the aircraft. This makes the nose want to yaw a bit to the right to compensate for the slipstream making it want to go left.
In high airspeed, low power situations (power off descent) propwash will be less strong, so the countermeasure will overpower it and make the nose want to yaw to the right. In this case, a bit of left rudden may be neaded to compensate.
In a high power, low airspeed situation such as on takeoff roll, we don’t have enough airspeed hitting the countermeasure to offset the slipstream, so more right rudder! may be needed to keep the AC alinged.
What is the Gyroscopic Effect? (many exam questions about this)
Because it is spinning, a propeller is a gyroscope.
Procession is a gyroscopic force that originates from the moverment of the propeller. (not from the actual spinning, but from moving the spinning propeller).
Acording to this law of precession a force exerted on a spinning mass will cause a reaction 90° along the *direction of rotation
Because of the gyroscopic precession effect:
Pitching the nose causes yawing.
Yawing of the nose causes pitching
With conventional (tailwheel) landing gear, gyroscopic precession is exagerated on takeoff. Why? What effect does it have? (Common exam question)
Because you lift the tail as soon as you start moving forward.
The pilot exerting nose down pressure in oder to lift the tail causes the spinning prop to convert this force into a left yaw movement, which the pilot must counter by applying right rudder.
What is Asymmetric Thrust/P-Factor? (Common exam question, beward of perspective)
In level flight the thrust produced by the propeller is equal across the entire disc.
When we pitch the nose up, the pitch of the right descending blade increases. And the pitch on the left rising blade to decrease.
This causes left yaw.
How does a constant speed propeller work?
You set the RPM you want and the blade will automatically adjust themselves to keep it.
What is Coarse Pitch/High Pitch?
What is Fine Pitch/Low Pitch?
Refers to the high angle of attack of a propeller blade
Used in cruise and at high altitudes (lower RPM)
Refers to the low angle of attack of a propeller blade.
Used during takeoff and climb. (higher RPM)
**Think of using a kayak. When you are sitting still and need to get going, the angle of your paddle blades will take a thinner ‘bite’ out of the water. Once you get moving, you can decrease the angle of the paddles to get more thrust.
What is the difference between geometric pitch and effective pitch?
Propeller slip
