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Help with Blow Back When Using Collective p95 - Chapter 12
Jojo
Topic Author
Jojo created the topic: Help with Blow Back When Using Collective p95 - Chapter 12
"Principles of Helicopter Flight 2nd Edition P 95 last paragraph...
"In similar fashion, blow forward will result when the collective lever is lowered (and CL is evenly reduced), often experienced when lowering the lever firmly at the start of an autorotation".
I get that the Rotor Disc will Tilt forward in a "Blow Forward" but not sure of the physics behind it?
If someone could help me understand I would be greatly appreciative. These are my study notes so far on blow back so you can see how I have been working through things - if I have anything wrong or have left out an important step please let me know.
Blow back = Rearward tilt of disc during transition to forward flight.
ADVANCING BLADE
Vr (Rotational Velocity) + Airflow due to forward flight = Greater on Advancing Blade.
Dynamic Pressure (1/2pV2) is more on Advancing Blade
Collective Up = Both blades increase AoA (CL)
Increased AoA * higher Dynamic Pressure = Lift greater on Advancing Blade = Disc higher at nose and lower at rear = Blow Back
RETREATING BLADE
Vr (Rotational Velocity) – Airflow due to forward flight = Less on Retreating Blade.
Dynamic Pressure (1/2pV2) is less on Retreating Blade
Collective Up = Both blades increase AoA (CL)
Increased AoA * lower dynamic pressure = Lift lower on Retreating Blade = Disc higher at nose and lower at rear = Blow Back
