Propellers Flashcards
(27 cards)
Define blade face
- Flatter side of the blade that faces relative airflow
- Side facing the pilot in cockpit
Define blade back
The cambered side if the blade that faces the direction of flight
Define blade angle
- Angle between plane of rotation and the chord line
- Varies along the length of the blade - greater at the propeller root and decreases at the propeller tip.
Blade angle = helix angle + AoA
Define helix angle
- Angle between plane of rotation and RAF
- AKA “pitch angle” or “angle of advance
Define angle of attack
- Angle between the relative airflow and the chord line.
Define helix
- The spiral or screw like path that the tips of the propeller blades trace as the propeller rotates and moves forward.
Define helical twist
Define blade face
The flatter side of the blade that faces the relative airflow. Faces the pilot in the cockpit.
Define blade back
The camber side of the blade that faces the direction of flight.
Define blade angle
The angle between the plane of rotation and the chord line
Blade angle = helix angle + angle of attack
Define helix angle
The angle between the plane of rotation and the RAF
AKA pitch angle or angle of advance
Define angle of attack
Angle between RAF and the chordline
Define helix
The spiral or screw-like path that the tips of the propeller blades trace in the air as the propeller rotates and move forward.
Define helical twist
The twist in the propeller blade where the blade angle changes from the blade’s root to its tip.
TAS variation and AoA
High TAS/Small AoA
Low TAS/High AoA
RPM variation and AoA
Low RPM/Small AoA
High RPM/High AoA
Most effective blade section
The middle
What is windmilling flight?
- When propeller is being driven by the airflow
- Engine fails, loss of engine torque, decrease in propeller RPM
- Propeller will reach fine pitch stop
- Negative AoA, so the TR acts in the opposite direction compared to normal flight
What is feathering?
- Function of CSU
- Increase blade angle pass the coarse pitch stop
- No net propeller torque
- Propeller will stay stationary
What is reverse thrust?
- Decrease blade angle passed the fine pitch stop to a negative blade angle (-20 degrees AoA)
- Reduces landing distance
- Risk of propeller overspeed is power is applied
- Once propeller is in reverse, the CSU will not change the blade angle
Centrifugal Twisting Moment (CTM)
- Centripetel force must be applied towards the propeller hub to keep the blades rotating around it.
- Broken down into two forces
1. Force acting parallel to the span of the blade
2. Force acting perpendicular to the span - Due to the propeller’s twist, the perpendicular forces are not aligned = centrifugal twisting moment
- CTM is more pronounced with wider blades
Aerodynamic twisting moment (ATM)
- Occurs when TR is not acting inline with the pitch changing axis
- ATM acts to coarsen the blade
- CTM is greater than ATM and they oppose each other in flight
In windmilling flight, what does ATM do?
- Acts to fine the blade
- Since ATM and CTM are now acting inline the same direction, there is a risk of over speeding the propeller
Asymmetric blade effect
- Tendency of an aircraft to yaw during takeoff, particularly during high power/low speed flight.
- Due to the plane of rotation of the propeller being tilted back during takeoff off
- Down going blade experiences faster RAF and greater AoA, resulting in more thrust being produced
- In a clockwise rotating propeller, the thrust line is to the right, causing yaw to the left
