Flap settings for Dummies

wrote:
On 30 Mar, 03:30, Frank wrote:
Bill,

I like the 'neutral-force' idea, and I think I have actually felt that
a little bit on my Ventus. I'll keep looking at that. As for
building a drag meter, I looked through the articles you referenced
and beat a quick retreat. I would be much more likely to do serious
damage to my glider (and/or me) than I would be to do anything
positive! ;-)

Frank

The neutral-force force idea has been around for decades but there is
no particular reason to think that it gives the best glide angle for
the aircraft as a whole for a given speed - not least because it takes
no account of the fuselage drag .

It's an appalling idea because of it's simplicity, but I've seen no
support for it from glider designers - why put in the flap setting
detents instead of letting the lever float, if that is best?

The idea seems to be the flap is just there to "streamline" the rest of
the wing and doesn't provide any lift itself. Aerodynamicists never
mention this reason for having flaps, nor do they suggest using the
"trail" position, either. And, if you look at airfoil charts showing
pressure distributions, you will see there is a net force on the last
few inches of the airfoil, where the control surfaces are.

If you don't want to trust your handbook settings, you can make
comparison runs with another glider of the same performance. This is
much easier to do accurately than a complete flight test - no math, no
instrument calibration, no high tows, no smooth air or wind free
conditions needed.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org