Oswald Efficiency Factors for Gliders

[John D. Newell, Jr.]

Hello,

I wanted to know if anyone had accurate values for the Oswald Efficiency
Factors for modern full size gliders such as the ASK-21 and ASW-27,
Ventus 2, DG 800S etc.? I presume the values would be between 0.9 and
0.99, but I would like to know some specific values if possible. Any
other applied aerodynamic data specific to modern gliders would be
helpful as well.

thanks, John Newell email: new...@njc.org

[Judah Milgram]

John D. Newell, Jr. wrote:

> I wanted to know if anyone had accurate values for the Oswald Efficiency
> Factors for modern full size gliders such as the ASK-21 and ASW-27,
> Ventus 2, DG 800S etc.? I presume the values would be between 0.9 and
> 0.99, but I would like to know some specific values if possible. Any
> other applied aerodynamic data specific to modern gliders would be
> helpful as well.

Hi -

As for the general question, there's an excellent book on the subject,
"Grundlagen fuer den Entwurf von Segelflugzeugen", (Fundamentals of
Sailplane Design) which I am presently translating into English. It
should be available in about six months; I'll put you on my
announcement list.

As for the efficiency factor, I'll have to look in some old
OSTIV papers for this. "Grundlagen" has some specific info on wing
design in terms of the induced drag increment, but not the efficiency
factor per se. Although it can be backed out, I suppose.

Thinking about designing a sailplane?

regards,

Judah

--
Judah Milgram mil...@eng.umd.edu (301)422-4626
finger milg...@eng.umd.edu for address, pgp key etc.
or: http://www.glue.umd.edu/~milgram/

[John Lowry]

Dear John D., Judah, and All:
Assuming the usual quadratic drag polar (that is, CD is quadratic in CL),
along with knowledge of best glide speed and angle (where the product of
air speed and delta_t, for a fixed vertical interval, is maximum), along
with gross weight and wing geometry (area and aspect ratio), it's easy
algebra to back-engineer BOTH parasite drag coefficient CD0 AND airplane
efficiency factor e.
The details are in our publication FFF#1, Instant Drag Polar. Contact me
if interested (jlo...@mcn.net).
John.

--
John T. Lowry, PhD
Flight Physics; Box 20919; Billings MT 59104
voice: 406-248-2606
Author, Computing Airplane Performance with
the Bootstrap Approach

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