Aerodynamics Flashcards
What is inflow roll?
A roll to the side of the advancing blade.
Occurs when moving from a stationary hover to fwd flight once the disc has 10-20kts of airflow.
Due to the front of the disc having a greater horizontal component of airflow producing more lift and the aft of the disc having a greater vertical component of airflow producing less lift.
Gyroscopic precession means that the effect manifests 90 degrees later causing the lateral roll.
Compensated by the cyclic.
What causes Flapback?
A dissymmetry in lift due to adv blade experiencing a higher velocity of relative wind and the retreating side a lower velocity of relative wind. Phase lag means that the effect is felt 90 degrees later causing the disc to flapback. Over come by cyclic feathering.
Pitch angle
Angle between POR and Chord line
Induced Velocity
Speed of air being pushed downwards by the rotor
Induced flow
The mass of air being accelerated downwards by the rotor
Resultant airflow
Vertical (ind.Vel) and horizontal (blade rotation) components
AoA
Angle between RAF and Chordline
3 factors affecting AoA
Airspeed, blade pitch angle, Nr
Induced drag
Acts parallel to RaF, resultant of producing lift
Profile drag
Drag caused by air flowing around airfoil. Skin friction, shape, airspeed are 3 sources.
The coning angle is a result of which two forces
centrifugal (larger force) and lift forces
How is coning angle measured
Angle between rotor hub and tip path plane
What is momentum
Mass x Velocity
Flapping to equality
In fwd flight adv blade flaps up as raf increases causing AoA to decrease and lift to decrease slightly.
Retreating side flaps down as raf decreases, AoA increases and lift increases slightly
Use of both flapping and cyclic changes pitch to equalise lift
