Jul 07, 2019, 02:58 PM
EP 3D Flyer
Quote:
 Originally Posted by Gluehand My intention with these experiments is to (try to) create a formula for an ultra "clean" wing, with a good self-stability without any "tabs" or extra features.....eventually I may even try to do away with the tip fins (playing around with dihedral). Reasons: Aesthetically....and the challenge in itself....
Your "ultra clean" wing is a wing without vertical surfaces? Similar to a Horten wing?

To me, the wing twist of a flying wing is like the decalage of a conventional plane. It gives the flying wing pitch stability, but at the same time creates drag.

You found the 8 degrees of twist is best for your flying wing. Does that mean that amount of twist gives your just-enough stability? More would make your wing less efficient; and less won't produce reliable flights?

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Jul 08, 2019, 05:46 AM
Registered User
Quote:
 Originally Posted by feda Your "ultra clean" wing is a wing without vertical surfaces? Similar to a Horten wing?
If possible without vertical surfaces.......or at least reduced to a minimum.......
Yes, something like a Horten wing....

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Quote:
 Originally Posted by feda To me, the wing twist of a flying wing is like the decalage of a conventional plane. It gives the flying wing pitch stability, but at the same time creates drag.
Yes, the twist is the decalage, and obviously it creates a certain drag, but not overly so when the twist/CG/airfoils are sorted out. That's the price of stability.

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Quote:
 Originally Posted by feda You found the 8 degrees of twist is best for your flying wing. Does that mean that amount of twist gives your just-enough stability? More would make your wing less efficient; and less won't produce reliable flights?
Initially we found that using a flat bottomed airfoil all the way out required an unrealistic amount of twist, and still the stability wasn't really satisfying.....pitch stability was critical, not least with speed variations....this felt like a dead end.

The first encouraging leap forward happened when we tried the combo with a flat bottomed root section gradually turning into a symmetrical section at the tip.
A great difference...!...this enabled us to work with more "sensible" twist angles.
However, lower twist angles still didn't provide the required pitch stability....at 6 and also 7° a flat and stable glide was possible to acheive with a smooth and slow launch in windless conditions, but with increasing speed due to e.g. a harder launch or a small headwind gust, the wing flipped over, nose up or nose down, with no self-recover....just "stopped flying"...
Too sensitive...!

At 8° all suddenly changed...! As the CG was sorted out, we could launch this wing briskly or soft, and when launching straight up, it recovered by itself turning into a flat and nice glide, finding its own speed, just like any properly trimmed model...! So with this configuration, I would say the stabiility wasn't "just enough"....it was great...

Out of curiousity we also weighted the wing down a bit, to emulate a future micro-rc-equipment. A somewhat shorter glide of course, but the stability remained...!

Of course we also cut a 9° wing, but all we experienced was more drag and no improvements whatsoever....i.e. we reverted to the 8° wing, calling it the "winner".......

Note, I don't claim to have "invented" anything unique.....the universe of variables is infinite, and I'm sure a similar result would be acheiveable with other airfoils, twist angles etc.
I guess we just found a "lucky" combination, useable as a platform for further experiments, and I'll stick to it for a while to see whether these learnings could find a practical use......somehow......

Below: The 8° "winner" of these tests.........not made to "concours de elegance" criteria......

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Last edited by Gluehand; Jul 08, 2019 at 06:26 AM.
Jul 21, 2019, 09:31 AM
Registered User
Hello,

I have yet to cover my "adjustable" wing mentioned above (why is the covering part always such a hump to get over...?), but hopefully soon....

In the meantime (I note there's a lot of "meantime" here...) a bit more on the "tailless" theme...
Browsing in the Swedish magazine "Hobbyfolk" 3/1949, I found an interesting description, deriving from no less than Emmanuel Fillon, on a 2m tailless glider, which instead of reflex tabs or twist, is based on a pair of trailing edge "slats" with an inverted Clark Y section....
Watch it below: