YellowBlueBird

My first effort to build a wing using laser cut parts and a wing jig resulted in a bowed wing panel. The steel rod from the local big box store was not stiff enough. The rod appeared straight to start with. After taking the panel off of the jig it bowed down about an eight of an inch. What I am looking for is a 1/4 inch rod long enough to build a wing panel 40 inches from root to tip. Fiber glass arrows do not come in that length or at least not at the local sporting goods store.

The steel rod was soft enough to be shaped very easily. I am going to roll the rod over and reinsert it back into the wing and wait a few days and see if it helps straighten the wing panel.


Any info on using wing jigs will be helpful.

Jerry

ByLoudDesign

YBB, In my designs I design into every major component jigs. The jig is assembled using a lenght of steel or aluminum angle, this angle can stay in place if you like, be use to clamp the jig to the work surface. I use to have the builder glue a 1 x 2 to the bottom edge but once the jig is built on a GOOD FLAT surface it is a done deal! Look on my web site at the Do-24T build photos.

Weasel Keeper

My Feedback: (16)

If you try the big box store again in the hardware aisle with mailboxes and sign material, you can usually find a 1/4" fiberglass rod that is used as a reflector stake. They are orange or yellow and very rigid. In any case, the rod may need support at the middle to reduce sag.

BMatthews

I suspect that your mistakes were multiple.

First off the steel rod from the local hardware store is cold rolled mild steel. It's soft enough to bend easily and hold some of the bend. Using spring tempered rods would be better but you don't really want the rods to flex at all when in the jig.

How to get around this issue? Simple, you need to use multiple supports along the length of the rod. If you use longer carbon, fiberglass or spring steel rods you would still need to have multiple supports simply to avoid unwanted flex. Because the other materials will flex too. It's just that they will return to straight if given a chance. The trick is to support them over short enough distances to avoid them flexing in the first place. And that requires multiple supporting blocks along the length. If I were using a rod style building jig I'd shoot for no more than 6 to 8 inches between supports. 10 to 12 inches might be fine but I'm a bit of a fanatic when it comes to avoiding flex and the tighter spacing just avoids the issue so easily at such a small cost in time and inconvenience.

As you were building you likely pressed down on the parts to hold them in place. That pressure allowed the wing structure to flex the rods. And then when the glue cured/dried or when you pinned the wood down it locked the sag in place while the glue dried. I wish you luck with the straightening but it may require stronger measures.

If you used white or yellow carpenter's glue you might be able to soften up the glue with heat from steam to let the joints and the wood ease a little. If it's all CA'd together then you may not be as lucky.

Rodney

Like Mr. Mathews, I use a support about every 24 inches. I'm using 3/8 inch aluminum rods and have no problems with sag on 7 foot span wings. If using spaced supports you do have to make sure your table is flat for the full length or you will build in the unevenness of the table unless your measure and shim every support.

YellowBlueBird

BMatthews, you are right on all accounts. Pressure on the sheeting is most likely what caused the rod to bend. It held the bend and was easy to reshape. It does not stay straight any length of time.

Jerry

ARUP

Build onto the board. Just jig things as you go. Label the jigs and board for the opposite panel. I build l-o-n-g scale wooden sailplane wings that are as twisted (washout) as needed! All of my sailplanes fly 'straight' and never need aileron trim for maiden. I have a metal rod jig that I'll sell ya!

BMatthews

I had to scrap a wing that had built in curvature due to the sheeting. I've been a LOT more careful to avoid the same issue since.

Try some steam or even soak down the wing and put it in a warm environment with some curve in the opposite direction. At this point you have nothing to lose since it sounds like it's not useable in the present condition.

I'd suggest making up a temporary "oven" that is made from building insulation Styrofoam on all sides with a couple of incandescent lights inside as the heating elements. They'll get hot so be sure to support them off the foam to avoid melting the foam. But with a couple of 60 watt lights inside such a box it should get up to well over 100F inside. That and the wetted down wood should give you a reasonable chance of forcing the wing to warp the other way and come out straight.

Another thing you could try is to soak down the sheet wood with a strong ammonia. Not the sudsy wash day stuff. Some industrial strength basic ammonia. Prop the wing in a jig that holds it slightly over bent in the desired direction then swab down the sheeting with the pure ammonia. As the stuff on the wood dissipates hit it again with a generous application. Two or three times of this should let the ammonia soak well into the wood and soften it enough to stretch and compress as needed. After it dries so it's no longer wet or smelling of ammonia the wood will be back to it's normal strength. But keep it locked into the jig until then.

Over a the next few days some of the locked in tension might make it warp a little again or it may not. Hard to say.

If the wing uses webbing with the sheeting to form a "D" tube you will likely need to bust out the webbing. Or at least cut the majority away. That'll unlock the "D and allow the wing to take and hold the new shape. After you know it's stabilized straight then you can replace the D tube webbing.

YellowBlueBird

BMathews Thanks. Here is the plan. The D webbing has not been installed. The problem showed up before that step. Press the wing in the opposite direction for a day or so. Then insert new stiff rods and install the webbing and sheeting on the other side.

Calvinman

Hi YellowBlueBird,

I use drill rod or drill stock, it is a harder steel and is usually dead straight. That being said it is still easy to build a warp into a wing with a jig. I use my jig to get all the ribs spaced and perpindiculer and the spars in place and glued. After that I like to do my sheeting if possible on the building surface with the wing weighted down to keep everything straight. One eight of an inch of warp is not a big deal and can be removed in the manors mentioned above. I suffered the same fate and was able to straighten the wing thanks to the sage advice I received from this forum.

Calvi.

BMatthews

I'd suggest you do a little more than just press it the other way. At the very least get some steam on the wood to heat and moisturize the wood into softening up a little. And if that doesn't work I'd suggest ramping the effort up to using the ammonia.

Mind you the degree of the curve also plays a big part. How much is the amount of curve and over what sort of span? How much force does it take to bend it straight? If it's slight and takes only a little force to bend it back it's quite possible that you could very slightly over bend the wing the other way then install the webbing to lock the "D" and that it would then only spring back a little to straight. Or at least straight enough.

YellowBlueBird

The wing is now slightly over bent. Water and deflecting the wing 1/8" in the opposite direction resulted in just a slight over correction. The image shows the amount of deflection over 30 inches before treating with water and weights.This image shows what I think caused the rod to deflect in the first place. All of those magnets were attracted by the steel plate under the plans. Supports were placed under the rods after this image was made. A bit too late.

Thanks for all of the suggestions.
After solving the what rod to buy problem I will build the right wing panel.

Jerry

Calvinman

Hey Jerry, nice looking wing jig,

I can see where you might get some sag with those magnets hanging off the rods, I used to use collars with set screws(hand made!) but I lost the collars over my 15 year hiatas(sp) from RC. I did not want to go through the hassle of fabricating up another 50 or so of these and did not want to buy them at over a buck apiece. I posted asking what other people use and one fine gentleman told me he uses plastic tubing or hose that is just under on the inside diameter of the outside diameter of the wing jig rod. He slices up the tube into short lengths and then slices them open to enable slipping them over the rods to hold the ribs in place.

I use 4 pieces or shaft cut down to 3 or 4 inches long and squared up on the ends using a lathe to align my ribs over the plan and "lock" them in place with the pieces of tube, then move on down the line. I then glue in my spars, then remove my wing to sheet and weight it down on my building board. I learned to do this after building in a warp while sheeting

Here is a pic of the pieces of shaft I use to square up my ribs with.

Calvi

BMatthews

To be fair any rod or tube of any material will sag to some extent just due to gravity. Never mind any other factors that make things worse. Which is why I like the idea of a couple of extra supports mid way along the length.

For a wing of this sort I'd suggest a couple of mid span supports that can be moved. Then when the upper side sheeting is all done and you want to flip the wing and re-jig the ends to sheet the opposite side I'd suggest at that point that shims of double wedges be used to lightly but supportively fit under the rod at points where ribs can aid in supporting the wing while the final sheeting is installed.

YellowBlueBird

I have found a local tool supply shop with drill rod. The right size and length. It looks much better than the box store rods. On to the next wing panel.

BMatthews

Whoa there. Drill rod is supplied in the annealed state. From the supplier it's no more bend resistant than the mild steel you got from the hardware store. It's simply ground finished to a higher accuracy for size. So it's not going to gain you a darn thing for use in the jig.

And even if you get it heat treated in the long lengths it will still flex just as easily. It's just that it won't hold the bend. It'll spring back. So you will still want to consider tricks for supporting the rods at a couple of three spots in between the ends.

The only way to make the rods stiffer is to go up in size. Flexibility is based on the tensile and compressive moduli and the physical size. So to make the rods stiff enough to use without additional supports you either need to find a much stiffer material or you need to go up in diameter by quite a sizeable difference.

Calvinman

What BMathews says

YellowBlueBird

Thanks guys. I thought drill rod was already hardened. It just feels better than the stuff from the box store. When flexed it came back to original shape. Mid supports are defiantly in order. What about the so called shaft rod from Mcmaster-Carr? They have that for about 11 bucks for a suitable length. There are a lot of choices from McMaster-Carr. Many different alloys and type numbers that do not mean anything to me.

BMatthews

Shafting would, or at least SHOULD be heat treated to a springy sort of condition already. So I'd consider that a wise step for use in a jig of this sort.

I'd even go so far as to suggest you modify the jig to allow the use of different sizes of rod and buy something larger for the longer span projects. Perhaps something like 5/8 thick wall carbon tubing? Even if you had to combine two different sizes it would be a step up in the stiffness and support department. For example a nice straight piece of 3/4 carbon or Cr-Mo tube for just ahead of the main spar and a 1/2, 9/16 or 5/8 tube mid way between the spar and TE would be that little bit better than two pieces of the 9/16 by themselves.

Also consider that the stiffness of a rod or tube goes up by the fourth power of the diameter. So while the difference between 1/2 and 9/16's seems like very little it actually produces a very noticeable increase in stiffness. And the less deflection you have per lb of force the easier it is to keep the wing true during the build.

But of course using such large size rods or tubes will only work on thicker airfoils that have room for the holes in the ribs. But then thicker airfoils of that sort are typically the types that are best built with such a jig anyway. The thinner airfoils more often lend themselves to building on a flat board with simple packing where required.

All this is why I've never actually bothered with a wing jig that uses rods for rib alignment. The concept is a nice one. But I'm a stickler when it comes to details like unavoidable flexing. Instead I prefer to make up a "bed" that rests on the building board or bench for the whole span. Or in other cases I've used airfoils which I can build on a tilt with the trailing edge flat on the board and a support strip located up by the lower spar notch.