Re: Translational lift in helicopters

[John Denker <jsd@MONMOUTH.COM>]

At 02:30 AM 8/20/99 -0400, Bob Yeend wrote:
> The reason a helicopter experiences it has to do with lift on an
> airfoil being proportional to the square of the velocity of air over the
> wing.

The effect you describe is real, but it is unrelated to the effect I was
referring to.

We evidently are using the same term to refer to two different phenomena.

I refer to W. Z. Stepniewski and C. N. Keys, _Rotary Wing Aerodynamics_
Volume II figure 3.25 which shows the hover ceiling IGE (in ground effect)
and OGE (out of ground effect).  The ceiling IGE is about 4000 feet higher
that OGE.

The velocity-squared effect you describe has nothing to do with ground
effect, and therefore cannot explain the data in figure 3.25.


3.22 which shows the power required for level flight as a function of
forward airspeed.  It shows a pronounced minimum at 80 Ktas;  the power for
0 Ktas (i.e. HOGE -- hover out of ground effect) is twice the minimum power.