Multi-Tapered Wing Planform

[green66]

Hi all,

Re gliders, does anyone have data on, or know how to calculate or just roughly quantify, interference drag produced at the taper breaks of a multi-taper wing planform?

Every profile discontinuity causes some local vorticity, thus some change in momentum resulting in additional drag. With all the usage / hype of triple & quad-taper wings to obtain lift profiles near the elliptical optimum, I'm curious as to whether the total drag created at the taper breaks, esp if dihedral also changes at these locations, might offset the benefit of multiple tapers?

And with that, what is the benefit, from the lift distribution standpoint, of using multiple tapers instead of adjusting the taper ratio, airfoil, and twist along the span of a single-taper wing? Seems like adjusting twist and section parameters could achieve similar effect (not to mention bypassing the need to reinforce the structure at the taper breaks).

Any comments appreciated.

[Ollie]

The whole idea of the design is relative to all parts and all relations to each other.

Quote:
"Design Philosophy

by Don Stackhouse

"There have been some rather heated discussions lately on the R/C Soaring Exchange about the relative merits of computer analysis versus old cut-and-try methods in the aerodynamic design of wings. Similar threads have argued over the shape of the "ideal" planform, the "best" airfoil, the "optimum" aspect ratio, and the validity of modified airfoils or of blending from one root airfoil into a different tip airfoil. All this controversy reminds me of one of my favorite stories:

"The Four Blind Men and the Elephant (an old Hindu parable)

"One day four blind men encountered an elephant for the first time. They approached it cautiously, but with great curiosity. The first one grabbed hold of the trunk and declared "Aha! An elephant is just like a snake!" The second found an ear and replied "No, an elephant is exactly like a tent." The third bumped into a leg and decided the elephant was just like a tree, and the fourth caught the tail and maintained that the elephant was just like a rope. They all went home arguing, each steadfastly insisting that he was right and the other three were wrong.

"The flight of a model sailplane is a complex phenomenon, each portion of the model seeing its own unique set of conditions at any given time, yet still having an influence on all of the other parts of the model at the same time. In addition, we expect our models to perform well at a wide variety of operating points within the overall flight envelope. To help us achieve this aim we have available a large database of experimental data and theoretical analysis tools, plus the insight garnered from all of our own experiences and the experiences of others, and the results of actual tests of the model. The results depend on how well we use all of this information together to reach the final design.

"If we get hung-up on one parameter, or one design technique, or one phase of the design process, we automatically give ourselves a case of "tunnel vision". There is no single airfoil, aspect ratio, planform, tail size or type, etc., that is optimum at all flight conditions for even a single model, much less a variety of models."

[Sparky Paul]

Google on "planform & wing".
Lots of interesting... stuff..some useful.. :)
Here's one such:
http://ciurpita.tripod.com/rc/rcsd/drag/drag.html
And another: both model oriented..
http://www.geocities.com/jebbushell/garton2m/garton2m.htm
And for the absolute smoothest straighest wiggle-free wing fans.. :)
http://www.appliedfluids.com/UUST01.pdf

[Ollie]

Thanks, Paul!

[Purdue Aero Man]

With all the usage / hype of triple & quad-taper wings to obtain lift profiles near the elliptical optimum...


Elliptic loading is not optimal for every wing planform. Minimum induced drag occurs when the wing produces uniform downwash in the Trefftz Plane.

[Sail 'n Soar]

Elliptic loading is not optimal for every wing planform. Minimum induced drag occurs when the wing produces uniform downwash in the Trefftz Plane.


And that occures with an elliptic loading. Don't confuse planform with loading.

From an ancient Purdue aero man

[Sail 'n Soar]

Did a Gogle on Trefftz Plane. Boy, are we getting deap. With so many other errors and variations, the difference appears to be lost in the wash.