Building a wing from scratch (no plan)
 

I want to build a built up wing for this plane. I can cut the ribs from the template on the plan, but I need a game plan after that. Any ideas?

I tried but could not open the attachment, tho I should think it is doable. The way I would attack the job is to get a large sheet of white paper and mark a straight line down it with enough room above and below for the ribs at 90deg. Carefully mark a 90deg line near one end (a set of drafting triangles would be a great help here). Mark lines parallel to that one going out at the correct rib spacing. That is about all you need to assemble a straight true wing skeleton over it by pinning the lower spar along the first line and inserting the ribs over the parallel lines (still with wax paper or similar on top of the white paper). Leading and trailing edge material should follow logically.

Have fun!

Bedford

Welcome to the world of scratch building. That wing is doable. Look at my thread here Ugly Stik Wing, that is a build up wing off of a foam wing plan. I used a wing jig to build it.


I use freezer paper to layout my wing. I determine the wing span, rib spacing and wing chord. Then draw my spar location, then the ribs, leading edge and trailing edge. Just lines nothing else


If you look at your plan, it shows a CG range. I would locate the spar at the forward CG point. That calculates to be about 28%.To build a straight wing you have to make sure the ribs are all even with each other; TE same height on all ribs. To do this you can add a tab to the TE of the rib. The tab would hold the rib up and square to the building board and to the lower spar. Or you can use a balsa square positioned, on the layout plan, to hold all the ribs up. Just different ways to do this. Make sure ribs are glued square to the lower spar.


Glue in lower spar, upper spar, TE and LE. The order can vary.

The drawing shows that the designer wanted to emulate the look of a built up wing. Spacing looks reasonable, so that gives you the number of ribs. Sheeting layout looks reasonable too. A D-box wing should work well. Need to guesstimate material thickness for top and bottom spars.

Do you want to make it with the sheeting and cap strips? If so you'll want to put a full depth spar at the rear edge of the leading edge sheeting to form a nice strong and stiff "D" box structure.

You'll need to draw up your own plan for this to build over. You know it's a 33 inch span. So allowing half an inch on each tip for a wing tip of some sort let's call it a 32 inch span without any tips. So 16 inches per side.

I see a sheeted center area and 8 other cap strips. To copy that it means a root rib and nine other ribs. I'd use two ribs in the center. In fact an easy way to make a wing of this sort is to set up the root rib at the right angle and just make two panels then glue them together afterwards like a giant hand launch chuck glider. Then reinforce the center line joint with a 3/4 to 1 inch wide band of fiberglass tape and epoxy to form the load bearing function of the dihedral joint.

Given that the center sheet and cap strips suggest a total of 9 rib bays if you wish to copy that layout it means that you need to space the ribs at 16/9= 1 3/4" apart. More or less. I get 1.7778". Just fudge the center rib bay so the outer rib bays are all 1.75" long.

The wing area is listed at 242 square inches. That gives me a chord of 7.33" . If it's off by a touch sand something down to fit... :D With that in mind I'd suggest the rib and spar setup shown below. The full depth spar is also full span. You cut half depth notches in the upper half of the spar and "egg crate" notches in the lower half of the ribs. This forms the D box you want to have.

PS; I forgot to include on the sketch that the leading edge is 3/16 wide by 3/8 tall. It needs to be that tall due to the angle. But you'll carve much of it away.

Be sure to select soft light wood that curls easily for the leading edge sheet. For the trailing edge if you know what C grain looks like and have any use that for the split trailing edge pieces.

The slick thing with building like this is that when you lift up the wing it's almost ready for covering. Just a little shaping along the leading edge and it's done.

Here's a PDF of the wing rib with a scale included so you can check that it comes out correctly sized.

Just a note that I've done three wings built along these lines over the years. Each time it works out so neatly that I swear that I'll do more of them. It take a little longer to build up the lower sheet and cap strip assembly but once it's all done the actual laying down of the ribs and building up of the wing goes smoothly if you did all the prep work correctly.

Wow ! Thanks. Few questions for you though. The spars should be balsa? What thickness? The wing will be strong enough with no dihedral joiners, just the sheeted center with and glass?

If you notice on the plans, the foam core is built with a blunt T.E. and then you add T.E.stock from which you cut out the ailerons. How are the ailerons added on your wing?

Yes, balsa for a model of this size is fine. The size shown, which I didn't label, is that the spars are done from 1/8" sheet of a medium weight. The leading edge sheeting I mentioned as "soft" can be medium weight and strength as well. "Soft" is intended to refer more to the sheet's ability to easily take the curve.

The fiberglass and epoxy taping around the center section will do just fine for dihedral loads. It's the same method you would have used with the foam wing in any event.

I missed the notation about ailerons. And certainly an SST would have ailerons. Instead of bringing the lower TE sheet back and shaping it to a point as shown in the sketch do something more like shown below with the cap adjusted to the right point for the ailerons. Adjust the rib outline as needed to allow for this clipped construction. I don't know what the width of the ailerons are so this is more of a concept idea which you'll need to adjust to fit the right width ailerons.

Also now that I realize that this is an aileron and elevator controlled model I'd suggest that you don't need dihedral. As such you can build the wing all at once with the 33" span and add some wing tips and call it a day. So just make the spar longer and use a single rib in the middle and sheet across the center section to cover two rib bays.