C25 - Propellers Flashcards
Define Propeller Disc?
The circular area where the blades rotate.
How is a Blade attached to the Hub of a Propeller System?
At the Blade Root.
Define Blade Chord Line?
Imaginary straight line from the Leading to Trailing Edge of the Blade.
Define Blade Angle?
Angle between Plane of Rotation and Chord Line
True of False. The Blade Angle decreases from the Hub to the Tip?
True.
What percentage is the Blade Angle measured between the Hub and Tip?
75%.
Define Blade Angle of Attack?
Between the Relative Airflow and the Blade’s Chord Line.
Define Helix Angle?
Between the Plane of Rotation and the Relative Airflow.
What is the sum of the Blade Angle?
Helix Angle + Angles of Attack.
Define Geometric Pitch?
The distance a Propeller would travel forward in one revolution.
Define Effective Pitch?
The actual distance a Propeller would travel forward in one revolution.
What is known as the difference between Geometric and Effective Pitch?
Slip.
What are small pitch angles known as?
Fine Pitch.
What are larger pitch angles known as?
Coarse Pitch.
What is the term and angle for the largest positive angle of a Blade (2)?
- Fully Coarse / Feathered.
- 90°.
What is the term and angle for the smallest positive angle of a Blade (2)?
- Fully Fine.
- 0°.
Name four types of Propeller Systems?
- Fixed-Pitch.
- Two-Pitch.
- Adjustable Pitch.
- Constant Speed.
What are the two forces acting on a Blade?
- Thrust.
- Torque.
What two factors are linked to the direction of the Relative Airflow on a Blade?
- Rotational Speed of the Propeller (RPM).
- Inflow into the Propeller (TAS).
With regards to Blade Angle of Attack, what happens when the Speed of an Aircraft reduces?
Blade AoA increases.
With regards to Blade Angle of Attack, what happens when the Speed of an Aircraft increases?
Blade AoA decreases.
With regards to Blade Angle of Attack, what happens when RPM is increased?
Blade AoA increases.
What happens at low RPM on a Propeller Blade?
Negative Blade Angle of Attack.
What happens at Negative Blade Angle of Attack?
The Aircraft experiences an increase in Drag.
How is the Blade’s Angle of Attack kept constant?
The Blade is twisted by design.
With Variable Pitch Propellers, what Pitch is selected during Take-off?
Fine Pitch.
With Variable Pitch Propellers, what Pitch is selected as TAS increases during flight?
Coarsen Pitch.
If an Engine Failure occurs, what condition is Propeller said to be in?
Windmilling.
The Drag from a failed Propeller can be minimised by setting the Blades head-on to the Relative Airflow. This position is known as?
Feathered.
Name one benefit of Windmilling after an Engine Failure?
It can assist in an Engine Restart in flight.
How can reserve thrust be produced on a Blade?
Beyond Fully Fine Pitch (0°).
What RPM does a Fan rotate at?
2700 RPM.
What Relative Airflow speed can a Fan Tip experience?
780kt.
