Wing twist - hypotheticals

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Wing twist - hypotheticals

Postby samiam » Tue Mar 21, 2017 9:11 am

I wanted to pose some hypothetical questions about wing twist. This is based on Robbie's recent profile on the article posted on Sonex's website, which discusses how he stalled out for months out of fears of wing twist. I realize I have done a similar thing.

First off, I'm wondering how bad of a twist I could possibly get. I have the prepunched holes in the kit, the ribs are centered on the holes, and the leading edge is flush with the spar. The structure is level. I would think that it would be hard to introduce a significant amount of twist with this type of setup. Thoughts?

Secondly, let's say that I do goof up and introduce a small amount of twist into the surface. How big of a deal is this?

Thanks for your help, I'd like to get this thing riveted up soon!
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Re: Wing twist - hypotheticals

Postby Bryan Cotton » Tue Mar 21, 2017 11:10 am

Mike,
When all the skins are on the wing forms a box and it won't twist. You have a few opportunities along the way to ensure the wing is true.

First, before the placement of the first skin. I measured for level at either end and the middle. Make sure the skeleton is both true and secure. This prevents twist from happening. When you flip it over with one skin clecoed on, you can adjust the twist a lot still. View it as an opportunity or peril, or both. Once that second skin is on stop worrying about it. You have one last chance during the rivet sequence. You can still twist it with one skin riveted.

I think wing skinning is shown around page 50 of my thread. I really liked the horizontal skinning method. Bob Meyers had better wing supports which you can see on his website. They were shaped to cradle the airfoil. Still, mine worked ok.

You need enough paranoia to be careful, but not so much that you don't progress.

Igor Sikorsky once said that if you build an airplane straight it will fly straight. Build it crooked, it will fly crooked. It is that simple.
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Re: Wing twist - hypotheticals

Postby samiam » Tue Mar 21, 2017 12:54 pm

Thanks Bryan. I guess I just need to acknowledge that I am an amateur builder, and as such there is the chance that there could be a 1cm twist and that I just would have to live with it. I'm doing the best I can with leveling and squaring, and that's all I can do.

Thankfully the Sonex has neutral stability and light controls, so my constant adjustments for my crooked plane will be light :)
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Re: Wing twist - hypotheticals

Postby NWade » Tue Mar 21, 2017 2:00 pm

samiam wrote:Thanks Bryan. I guess I just need to acknowledge that I am an amateur builder, and as such there is the chance that there could be a 1cm twist and that I just would have to live with it


Eh, I found I worried a lot about twist until I was actually building the wing. Once I had it set firmly on blocks to keep it level on my table, things went pretty easily. I checked a few times throughout the process to ensure the root & tip of the wing were staying level, relative to each other - it was no sweat!

I did my first wing totally horizontal. I decided to try the other wing in the vertical position, squaring the spars and shimming the main spar at the tip to get them to be oriented the same (see lower right part of this photo). Once I had the first skin cleco'ed in place, I decided I liked working in the horizontal orientation better. Pushing against the wing skins could rock the whole assembly if I wasn't careful, and I didn't want any bumps to screw up the alignment. So I rotated it horizontal and blocked & shimmed it up to be level at root and tip.

Overall, I found the horizontal orientation easier to be precise with and keep consistent (gravity is helping, afterall, and you can use small wood blocks on either side of the main spar screwed into your table to hold the wing in-place). The vertical orientation is easier for squaring the spars and getting started; but I found that a wire-based plumb-bob in the tooling hole (as some builders and websites show) can be inaccurate based on friction and slight bends in the wire or how perpendicularly it sticks out of the tooling hole. Plus, very small shims under the spar can make a big impact on the twist. As a result, its a little trickier to get the wing twist-free in the vertical orientation IMHO. With the pre-drilled holes that come with the more-recent kits, the rib/spar squaring process should be a whole lot easier in either process (...yes, I'm jealous)!

Start with a flat table. Use a big/long level. If your level can't span the gap between main & rear spar, use a piece of angle aluminum or other strong material that won't flex and place your level on top of that. Get the readings the same at root & tip and you're ready to rock'n'roll! Lock things in position if you can, with wood blocks or straps or whatever works for you. Re-check your measurements every so-often. Try to have fun!

Enjoy,

--Noel
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Re: Wing twist - hypotheticals

Postby Bryan Cotton » Tue Mar 21, 2017 2:57 pm

I used steel rods through the rib tooling holes to check for level. Worked great.

You will really have to work hard to get a 1 CM twist, or hit the whisky hard. It's not that bad.
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Re: Wing twist - hypotheticals

Postby Sonex1517 » Tue Mar 21, 2017 6:23 pm

I am consistently amazed how many people found that article...

Since I did confess to obssessing about wing twist, I have to say it was unwarranted. I really believe it would be somewhat difficult to introduce a severe twist, provided you measure carefully and verify the ribs and spars are squared up.

Bryan's / Bob's method makes sense - vertical or horizontal should be ok if you take your time and check the alignment.

Just my two cents, worth much, much less.
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Re: Wing twist - hypotheticals

Postby samiam » Tue Mar 21, 2017 6:54 pm

Sonex1517 wrote:I am consistently amazed how many people found that article...

Since I did confess to obssessing about wing twist, I have to say it was unwarranted. I really believe it would be somewhat difficult to introduce a severe twist, provided you measure carefully and verify the ribs and spars are squared up.

Bryan's / Bob's method makes sense - vertical or horizontal should be ok if you take your time and check the alignment.

Just my two cents, worth much, much less.


It was a great article!

I suspect that I'm fretting about this too much. I think with the prepunched kit, if everything lines up AND is level, it would be pretty hard to have any major problem. It certainly isn't worth having my leveled wing sit in the garage for the past two months!
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Re: Wing twist - hypotheticals

Postby peter anson » Wed Mar 22, 2017 4:50 am

I built my wings vertical on cheap trestles, I clamped straight edges across the spars at each end and did nothing more than sight across the straight edges and use scraps of sheet material as shims to pack up the spars. It is surprisingly accurate and my Sonex flies well.

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Re: Wing twist - hypotheticals

Postby Direct C51 » Wed Mar 22, 2017 9:51 pm

samiam wrote:I suspect that I'm fretting aboutIt certainly isn't worth having my leveled wing sit in the garage for the past two months!


Analasys paralysis is certainly the enemy when trying to complete your airplane. I'm sure everyone has had some during their build. I find the later I get in my build, the less I tend to have. The Sonex wasn't designed for a professional machinist to build. It was designed for an amateur in their garage with common tools. You can't mess it up that badly. My advice, do your best to square it up and start drilling. You can always make your next airplane "perfect."
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