Can you explain why the downward force of induced flow actually moves the resultant relative wind angle up?

That was a bar room description of an airfoils stall characteristics. Bernoulli’s principle refers to “any fluid.” Newtons 3rd law is the force acting on the underside of the airfoil.

Kurt

I’m always trying to review learn something more.

I am also a rated fixed wing pilot, land and sea. The actual separation of air flow over the airfoil happens at around 12 to 16 degrees between the relative wind and the airfoils cord line. I have practiced stall spin recovery’s over and over. Not recommended or required until the CFI training, but fun if your ship is classified in the utility or acrobatic categories, and you clear an area with plenty of altitude. It’s an E ticket ride. (5,000 AGL minimum)

I shared this power on “Blade Stall” at sea level question with a group of CFI’s locally and their response was this. Power on blade stall can occur at any altitude, even at sea level when pitch command inputs are larger than horse power available to maintain rotor RPM. Abrupt collective pitch inputs can drag down rotor RPMs. If there is insufficient power to maintain rotor RPMs, high pitch angle and low rotor RPM (STALL) can happen at any altitude. This has caused enough fatalities that the FAA has written the “Special SFAR 73″ in the FAR’s to address training requirements for pilots flying in the low inertia // low horsepower Robinson’s 22 and 44. Since excessive pitch and a lack of horsepower is the cause,, recovery is impossible,, and the result is a catastrophic boom chop. Common causes in training for getting into a low rotor RPM situation are rolling the throttle the wrong way, or “death” gripping the throttle.

Thanks for your help Ehud,,, I’ll read your article—– http://thehood.livejournal.com/42360.html

Kurt McKibben

The gist of it is that if you increase the blade pitch so that the angle of attack (angle between the chord of the rotor blade and the relative wind) increases then there exists a point where — just like in a fixed-wing aircraft — the air will separate from the airfoil.

At that point it has vortexes which prevent it from “reattaching” to the blade even if you lower collective pitch. (Note that I said “blade pitch” above because you can get a good stall region going with cyclic inputs alone if the conditions are right.)

Blade stall in its simplest form is the same for fixed-wing as it is for rotary wing. The angle of attack can get beyond the point where air will adhere to the surfaces. At that point there is a stall condition. In a fixed-wing a pilot can aim down and hope the resultant high velocity will get the airflow back on the airfoil. Sadly in a rotorcraft when we stall we have no airfoil and we have no ability to generate forward speed.

I hope that’s helpful… if not I hope to learn more by reading what all you people write

Regards,

Ehud
Tucson, AZ USA

Any help out there???

As always, great article.I always look forward to your articles.