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Determening wing twist

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Posted (edited)

I´m in the process of building new wings for my Kitfox 2 and i also want to replace my 6 gal aluminium tanks to new 13 gal fiberglass tanks from Kitfox. When ordering the tank they want me to specify the wing twist and i have looked in the manual for advice an found that placing a block that is 1 3/4" under the tip end of the front spar when setting up to build the wings will give the correct twist.

Also after reading on this forum it seems that this gives you 1 degree of twist in the wing....and after setting it up in my cad and making the measurements it seems to be right.

Does everyine else agree :), its kinda big investment in thoose tanks and i want to be sure that i get the correct twist.

 

 

 

Vinge_1.jpg

Edited by Peter_se

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Posted

I think my model 2 measured 1 1/2" when I was finished. The same exact measurement on both wings. It was set by the original builder when he built the wings. I used floating poly tanks so twist wasn't a concern when mounting them.

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Posted


I built my wings with 1/2 twist and I would do it again in a heartbeat.

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Posted

Just for information, the Kitfox IV has 0.5" twist.

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Posted

I did my bluefox wings at 3/4 twist. Was 1 1/2 twist but changed it. 

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Posted

Hmm...a lot if variations...would I be ok with going with the 1 deg I wonder...

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Posted

Personally I don't see why any twist is required. A rectangular wing planform stalls root first naturally and progresses out to the tips. Twist is generally to prevent tip stall, but can be for performance. On a kitfox I can't see twist helping performance much if at all.  I also have a Sonerai with rectangular wing and that one has no twist and stalls fine with no crazy wing drop.  Since I'm not building from scratch I won't be changing what I have, but if I were building from scratch I may just leave the twist out.

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Posted


The less you put in it the better it will perform.  I hate the 1.75" of twist that was in my avid, it left a lot on the table on both ends of the envelope.  I would not build a wing with more than .500" washout in it.

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Posted

My original model build manual specifies 3/4 inch of twist. My plane was built with 5/8" twist on both wings. I see no need for more twist than that. Did they really specify 1-1/2"? Seems extreme, especially since they started at 3/4" and ended up at 1/2". 

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Posted

Maybe I’m reading it wrong?

this is from my original manual

Wing twist.jpg

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Posted

I remembered it wrong. My original manual called for 2" twist. Most 1-3s are 1-3/4". Mine is 1-5/8 and draggy like a parachute. Model 4-1200 called for 1/2".

 

E6AD640D-B32E-44DF-8181-3803C094D1DC.jpeg

5DE8B91E-B711-490D-9EBB-83E3E468752A.jpeg

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Posted

There is a lot of discussion here about twist with the stated implication that twist increases the drag of the wing. I don't believe that's true, small amounts of twist do not result in increased drag, in fact the opposite may be true.

By shifting the center of lift closer to the wing root, there is less induced drag because there is less side flow wash out and less lost performance because that. In effect, wash out twist increases the apparent aspect ratio of the wing and probably helps cruise performance.

Also wing twist produces a much more stable aircraft in roll and vastly increases aileron effectiveness near the stall. A quick glance at most light sport accidents shows stall spin to be a big deal, so making your airplane more likely to drop a wing during the stall and lose control is not a good thing.

Somehow I think Dean Wilson knew what he was doing when he set the wash out where he did.

https://www.boldmethod.com/learn-to-fly/aircraft-systems/how-wing-washout-makes-your-airplane-and-wings-more-stable/

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Posted

Yes probably so, i have now ordered new tanks from Kitfox based on a 1 3/4" twist in the wings as per the manual.

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