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Old Dec 11, 2012, 02:41 PM
slebetman is online now
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Question

Advise on wing twist for rubber powered wing


I've gotten into rubber powered free flight recently and have found myself enjoying it a lot. In fact, I currently have more free flight projects than RC. So I thought I'd take a stab at designing a penut size flying wing.

Here's a CG calculator link to my basic design: http://fwcg.3dzone.dk/?wing_span=14&...ow_mac_lines=0

I tried entering the values into the Pankin twist formula but ended up with non-sensical results (gave me 2000+ degrees of twist). So I thought I'd do the next best thing: ask other people's opinions.

I don't necessarily need precise calculations. Just want to poll you guys about what amount of twist feels about right for my wing design. TLAR would do just fine. My gut tells me that I'd want around 6 to 8 degrees.

So, what do guys think?
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Old Dec 11, 2012, 03:44 PM
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I guessed at some numbers but this is what my spreadsheet gives for 5% static margin at 12 mph:

Best glide 3 degrees twist and 8 grams

Minimum sinking speed 6 degrees twist and 10 grams

--Norm
Old Dec 12, 2012, 04:13 AM
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Thanks Norm, I guess you're better at guessing input values than I am. Must have messed up something. My airfoils are just hand drawn approximations of typical thick Horten style airfoil so I don't have exact coefficient values. So I just guessed them and I guess my guessing didn't work.

I think I'll start with 5 degree twist for now and just build a prototype. Then modify my plans based on test flight experience.

Not sure if I should start a build thread here or the free flight forum. The free flight forum looks very quiet lately.
Old Dec 12, 2012, 02:44 PM
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I assumed a flat plate at such small dimension so put in 0 for both ZLA and cm. It would be better to know the actual airfoil data but if you're hand drawing them it's hard to know. Also I think I typed in the weight numbers backwards. Maximum duration at minimum sinking speed is most influenced by span loading so 8 grams at 12 mph.

Best distance will be at a higher speed so slightly more weight, about 10 g.

The 12 mph guess was because I assumed that you would be flying indoors. Allowable weight goes up as the square of the speed so a little faster can carry a lot more weight.
Old Dec 13, 2012, 09:46 AM
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Quote:
Originally Posted by slebetman View Post
Thanks Norm, I guess you're better at guessing input values than I am. Must have messed up something. My airfoils are just hand drawn approximations of typical thick Horten style airfoil so I don't have exact coefficient values. So I just guessed them and I guess my guessing didn't work.

I think I'll start with 5 degree twist for now and just build a prototype. Then modify my plans based on test flight experience.

Not sure if I should start a build thread here or the free flight forum. The free flight forum looks very quiet lately.
It's a wing.build it on here.
Stuart


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