JudgeSmails218
Well-known member
- Joined
- Mar 8, 2004
- Posts
- 108
Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
Two neat references:
An old one that started me off: (AC 61-13b FAA AC 61-13B Basic Helicopter Handbook )
http://www.hothelicopters.com/faa_ac_6113b.htm
The new, updated one: (FAA-H-8083-21 Rotorcraft Flying Handbook, PDF down-loadable)
http://www.faa.gov/library/manuals/aircraft/media/faa-h-8083-21.pdf
Helicopters aerodynamics are quite interesting, worth the read.
You can stall a helicopter in a whole bunch of ways. First, you can fly too fast. When you do, you stall the retreating blade and the aircraft rolls into the stalled blade. On American helos this is to the left.
Second, you can fly too slow. Hovering takes the most power, once you achieve "translational lift" the entire rotor system gets more efficient. If you slow below translational lift, the entire rotor stalls and you may not have the power or the altitude to fly out of it. Ground effect is very important in this regard as it takes way more power to hover out of ground effect than it does within ground effect.
Third, you can set up a descent that causes the rotor to fly through its own down-wash resulting in a stall.
Forth, you can fly through an airmass that is changing direction or speed (most commonly in the mountains, but could be anywhere like around buildings or other man-made structures).
Fifth, you can fly too fast sideways or backwards. Sideways causes the tailrotor to stall causing loss of directional control and flying backward causes a barn door effect with the aircraft fuselage that the flight controls may not be able to overcome.
There are probably more ways, but these are the quick 5 that I can think of.
Kuma
Why, thank you; you are too kind.This is it exactly. You are a smart smart smart man!
If you slow below translational lift, the entire rotor stalls and you may not have the power or the altitude to fly out of it.
Kuma
Kuma, a question. If the entire rotor system is stalled, what is providing lift in the hover? ETL is characterized by moving into undisturbed air, thereby increasing the efficiency of the rotor system. Moving from ETL back to a hover puts the rotor system back into disturbed air caused by its tip vortices. My understanding is these vortices obviously disrupt the smooth flow of air over the airfoil, thus reducing rotor efficiency, but not necessarily stalling the the entire disk.
Maybe I'm missing something, could you elaborate?
My statements are from the point of view of the pilot, not the aerospace engineer. I could talk at a cocktail party level of detail, but if you want me to start talking about blade element diagrams and taking the integral of the lift equation over the entire span at each position with respect to the rotational arc...I'm out.
Kuma