Ch. 2 Aerodynamics of Flight Flashcards
The inner 25% of the rotor blade is referred to as the _____ region.
This region operates above its maximum AOA, also referred to as _____, causing drag & slowing rotation of the blade.
Stall
Stall angle
AOA is usually _____ at higher airspeeds and _____ at lower airspeeds.
Lower; higher
The _____ region produces the forces needed to turn the blades during autorotation.
Driving
During autorotation in forward flight, all 3 regions of the blade move _____ (outboard/inboard) along the blade span on the retreating blade where AOA is _____ (higher/lower).
Outboard; higher
This is because inflow of air is going up through the rotor disk rather than down.
If the engine fails, the _____ unit automatically disengages the engine from the main rotor. Allowing the main rotor to rotate freely.
Freewheeling
The driven region of the rotor disk produces some lift, but that lift is offset by _____.
Drag
The overall result is a deceleration in the rotation of the blade.
_____ pitch must be increased in order to maintain altitude & airspeed while turning.
Collective
Collective pitch controls the AOI and along with other factors, determines the overall AOA in the rotor disk.
_____ + _____ = AOA
Resultant relative wind; chord line
AOA can change with no change in blade pitch angle or AOI.
What is the difference between centripetal & centrifugal force?
Centripetal force “pulls” or acts toward the center of rotation.
- a real force
Centrifugal force “pulls” or acts away from the center.
- considered a pseudo force
Total aerodynamic force (TAF) in the _____ region is inclined slightly forward of the axis of rotation.
Driving region
This forward incline produces a continual acceleration force during autorotation.
How do pilots avoid retreating blade stall?
By not exceeding the never-exceed speed (VNE)
Contacting the ground with skids during sideward flight will likely result in a _____.
Dynamic rollover
Why do transverse flow effect vibrations happen close to the same airspeed as ETL?
This is where the greatest lift differential exists between the front & rear portions of the rotor.
Just below ETL on takeoff & after passing through ETL on landing
- between airspeeds 12-15 knots
During vertical autorotation, the rotor disk is divided into what 3 regions?
Driven, driving, & stall
During translating tendency, the helicopter wants roll slightly to the _____ as it accelerates through approximately _____ knots.
Right; 20 knots
As the relative wind speed of the advancing blade increases, the blade _____ (gains/loses) lift & begins to flap _____ (up/down).
Gains; up
This upflap creates a downward flow of air & has the same effect as increasing the induced flow velocity, & decreasing the AOA.
Describe Ground Effect
Aka In Ground Effect (IGE)
Increased efficiency of the rotor disk caused by interference of the airflow when near the ground.
What changes the blade’s AOA differentially around the rotor disk & creates a differential lift?
Cyclic feathering
This controls the rotor disk attitude & is the means to control rearward tilt of the rotor (blowback).
What 4 conditions cause retreating blade stall?
- High airspeeds (exceeding VNE)
- High collective pitch angle
- Excessive forward cyclic
- Low Nr (rotor RPM)
3 highs, 1 low
Transverse flow effect _____ (increases/decreases) the AOA at the front disk area causing the blade to _____ (flap up/flap down).
Increase; flap up
A reduction in AOA at the aft causes the blade to flap down. Increasing the chance for blowback.
As induced flow increases, resultant relative wind becomes less _____ (horizontal/vertical). Causing AOA to _____ (increase/decrease).
Horizontal; decrease
Because AOA is determined by measuring the difference between the chord line & the resultant relative wind, as the resultant relative wind becomes more horizontal, AOA decreases.
While transitioning to forward flight around 16 to 24 knots, the helicopter goes through _____.
Effective translational lift (ETL)
The propeller region, or _____ region, consists of 30% of the blade radius.
Driven
How does Newton’s Third Law apply to flight?
The air deflected downward also produces an upward (lifting) reaction.