Author Topic: Stopping wing twist during flight. (Read 1678 times)

Chris Wilson · « **on:** November 10, 2010, 07:59:27 PM »

As the title says, what is the best construction method to prevent wing twist in flight?

I like the look of ribs angled away from the usual 90 degrees and pattered in a 'W'' shape, and hard covered wings but is there anything else to this?

Cheers. (I have seem what I think was a SV11 build article and it looked the goods here.)

Chris Wilson · « **Reply #1 on:** November 10, 2010, 08:19:24 PM »

Quote from: Ty Marcucci on November 10, 2010, 08:11:23 PM

A Warren truss or eggcrate type wing will resist warping in flight. Used in free flight and in some stunters. Some times called Geodetic.

Thanks for the reply Ty and I agree but what exactly do you warren truss? Everything?

Main spar, ribs, shear webbing - the lot? And eggbox I have seen as a fantastically strong construction method but its not easy to shape a wing.

Cheers.

Steve Helmick · « **Reply #2 on:** November 10, 2010, 09:03:14 PM »

Like Ty, I'm an olde free flighter. IMHO, the fancy diagonals are more decoration than fuctional. The D-box or C-tube is far stiffer in torsion, IF you use sheer webs to "close the tube". The reason is, that the diagonals are long, shallow (thin part of the wing, generally), and angles are less than ideal in most cases. Cap strips are a very good thing, making ribs into T-sections or I-beams.

The one place where diagonals really do a lot of good is inside the D-box/C-tube. They're deep, they're short, and they can be pretty close to forming an equilateral triangle...more resistant to flexing. Further, the weight (not much) ahead of the high point helps resist flutter, tho it's not a significant problem with 18%+ thick wings going something under 100kph.

Steve

Chris Wilson · « **Reply #3 on:** November 10, 2010, 09:45:52 PM »

Quote from: Ty Marcucci on November 10, 2010, 08:40:37 PM

Go to Building Techniques ans see Randys wing.

Do you have a link back for that mate?

Steve Helmick · « **Reply #4 on:** November 10, 2010, 10:07:26 PM »

This orta work...

Steve

http://stunthanger.com/smf/index.php?topic=19131.0

John Sunderland · « **Reply #5 on:** November 10, 2010, 11:01:21 PM »

Another way to stiffen up a D tube wing is to sheet over the TE rather than butting up to it. Its a pain to taper and sand but can be done while jigged up and to me its worth the extra effort. In combo with the shear webs half way out each panel this wing in silk span is plenty stiff with a medium thick wing. I built a molded LE lost foam Nobler wing standard configuration and it flexes like mad.

Bob Reeves · « **Reply #6 on:** November 12, 2010, 10:43:19 AM »

Just sheet the outboard rib bay top and bottom on each wing tip. This along with sheer webs about half way out on the leading edge and inside the trailing edge sheeting will produce a pretty stiff wing. Granted this is a small wing but.. It only has one sheer web in the outboard bay trailing edge and you cannot twist it without breaking something.

Chris Wilson · « **Reply #7 on:** November 14, 2010, 02:41:38 PM »

Quote from: Bob Reeves on November 12, 2010, 10:43:19 AM

Just sheet the outboard rib bay top and bottom on each wing tip. This along with sheer webs about half way out on the leading edge and inside the trailing edge sheeting will produce a pretty stiff wing. Granted this is a small wing but.. It only has one sheer web in the outboard bay trailing edge and you cannot twist it without breaking something.

Ah, so closing off the ends or boxing them in is a key here! Makes sense to me, thanks Bob.

Randy Powell · « **Reply #8 on:** November 15, 2010, 11:59:38 AM »

If you look at that thread, note that both the main spar and the trailing edge have sheer web, closing the box. Makes a big difference. The long, fairly narrow ribs are enormously stiffened by the cap strips making a "T" section. This is also quite light.

Russell Shaffer · « **Reply #9 on:** November 15, 2010, 12:56:26 PM »

My latest build has sheer webs on the spars and the TE. It was quite floppy even with the LE sheeting and after I put in the sheer webs, it was "wow, I sure hope it was straight when I glued it!". It made a huge difference in stiffness and I'm really glad it was still in the jig when the webs were installed.

jim gilmore · « **Reply #10 on:** November 15, 2010, 02:26:17 PM »

Has anybody tried using a very thin shear web with holes in then ?
Say only an outline of maybe 3/32 to 1/18 inch ?

Randy Powell · « **Reply #11 on:** November 15, 2010, 04:05:52 PM »

Jim,

I've built them with all kinds of variations. Spar caps with Warren truss layout, vertical supports only and a 1/16" vertical sheer web. The last works the best by far.

Andrew Tinsley · « **Reply #12 on:** November 26, 2010, 02:13:37 PM »

Hi all,
I have had some hand me down aircraft and a couple that I bought (wanted the engines!). They were all covered with various heatshrink covering. No matter what the wing construction (D box, Detroiter etc), they all had lots of wing twist. Stripping off this plastic rubbish and recovering in ultra thin mylar and silk, plus a couple of coats of shrinking dope, gave VERY much stiffer wings!
The fancy plastic coverings may look nice, but they DO NOT add stiffness!

Regards,

Andrew.

Steve Fitton · « **Reply #13 on:** November 29, 2010, 07:23:22 AM »

Use foam wings. All twist/flex problems solved, plus you have a very accurate warp free wing. If its fully sheeted you have an easy job sanding on it for the finish as well.

don Burke · « **Reply #14 on:** November 29, 2010, 04:48:48 PM »

Quote from: jim gilmore on November 15, 2010, 02:26:17 PM

Has anybody tried using a very thin shear web with holes in then ?
Say only an outline of maybe 3/32 to 1/18 inch ?

The idea of a web is to make the bay something other than a rectangle with no support in the corners. A thin full web or diagonal stut accomplishes that.

Chris Wilson · « **Reply #15 on:** December 01, 2010, 03:20:33 PM »

Quote from: jim gilmore on November 15, 2010, 02:26:17 PM

Has anybody tried using a very thin shear web with holes in then ?
Say only an outline of maybe 3/32 to 1/18 inch ?

Yep, Supermarine Spitfires built during WWII has shear webbing with holes punched out in their centres.

The design engineers quickly realized that the very centre of the webs have zero stresses on it and so it was not contributing anything to the airframe structure.

But if you are want to copy this into a model then I urge to you to look at the amount weight saved by those tiny holes when compared to the amount of work in doing so - you may conclude that it just isn't worth the effort!

Chris Wilson · « **Reply #16 on:** December 01, 2010, 03:31:30 PM »

I have recently had a chance to look at a Yatsenko model with fibreglass/ carbon fibre shell wings and that makes a mockery out of any stiffness problem.

Pity they are so expensive to purchase because I would buy one in flash otherwise!

Mark Scarborough · « **Reply #17 on:** December 02, 2010, 09:00:53 AM »

Quote from: Russell Shaffer on November 15, 2010, 12:56:26 PM

My latest build has sheer webs on the spars and the TE. It was quite floppy even with the LE sheeting and after I put in the sheer webs, it was "wow, I sure hope it was straight when I glued it!". It made a huge difference in stiffness and I'm really glad it was still in the jig when the webs were installed.

Russ,
yep, thats a very valid observation. Pat taught me a trick about that, when you build the wing, only put the shear webs in every other bay until the wing is done. Then you can check it for straight as sometimes sheeting the wing leading edges can input a bit of twist, if needed put a touch of twist in it to straighten it back out, THEN glue in the other alternating shear webs, thus locking the wing totally straight

Russell Shaffer · « **Reply #18 on:** December 02, 2010, 10:00:44 AM »

Mark, that is a great idea. Trouble is, I'm seeing so many good ideas that I'll never remember them.

Mark Scarborough · « **Reply #19 on:** December 02, 2010, 12:29:13 PM »

you need to build faster, then you will remember them

Russell Shaffer · « **Reply #20 on:** December 02, 2010, 03:47:38 PM »

Mark, if I went any faster I WOULD have trouble. I tacked the wing into place and stood back to admire my handywork. That's when I realized that the plane was upside down and I had a plane that Leo would approve of. I fixed it.