Wing building tips

[jrbirdman47]

It has been noted that there isn't much in the way of building tips, videos, etc for the wings. I have seen YouTube videos for fuselage and tail, but not much for wings. I can't video, (And I'm almost finished building 4 wings), but I did take a lot of pictures while constructing the wings and will post them here as tips and techniques and invite y'all to do the same. It's a daunting task that can be intimidating and I hope this helps those who are starting their wing build.

The first pic: Remember to place a .8mm plywood shim under the front spar to allow the leading edge skin to butt flush against the rib on bottom.

Second pic: I clamped the front spar against a 1 X 2 stip on the edge of the bench to keep it rigid and straight. Photo shows the 1/8" plywood shim between the spar and edge strip, opposite the clamping cam, to account for the wing and strut attach pads.

[jrbirdman47]

"Racking" the wing.

I didn't get a picture, but this is very important! First I used a carpenters square to draw a line vertically from the center of the wing attach fitting holes on both the forward and rear spars. (My thinking was that these two holes had to be perfectly aligned to mount a square wing) Then I used a  sheet rock square with the short side against the forward spar and exactly on the lines on both spars to get everything square. ( I went through several squares at Lowes until I found one that really was square) Once this is done you can lock the spars down in place and begin glueing ribs to spars.

[jrbirdman47]

Don't forget to apply downward force to the top of each rib to completely seat it before clamping/ glueing them. Some ribs may sit perfectly before applying glue, and then try to raise up in the slightest when lubricated by the epoxy. You should have about .8mm protruding above the spar to account for the thickness of the leading edge skin.

[jrbirdman47]

Racking the wing, part 2:

First photo shows a piece of scrap 2 X 4 screwed to the bench behind the rear spar. With the wing spars and ribs in place, I applied moderate pressure forward to seat the ribs against the forward spar, then screwed the block in place. I did this in two places, about a third of the way down the spar each.

Second pic shows how the spar is clamped to the 2 X 4. I applied downward pressure to seat the spar in the ribs and then tightened the screw.

Note the liberal use of freezer paper under all glue joints to keep epoxy from glueing the wing to the bench. I highly recommend freezer paper!

[jrbirdman47]

Aligning the rib trailing edge:

For most of the ribs, if the trailing edges aren't spaced at exactly 15 inches, it's no big deal. But for 3 places you should strive for the trailing edge of the rib to be exactly 90 degrees from the rear spar. Those being the end ribs, and the rib making up the inboard aileron well.

Start by jigging those ribs to 90 degrees from the back of the rear spar when you glue them to the rear spar. Once cured, they will likely have a slight "set" to one side or the other which you can fix when installing the wing trailing edge.

The end ribs should be straight for aesthetic reasons, and can easily be glued straight using a straight edge along the full length of the outside of the rib. But the ribs forming the aileron well will be what you base the aileron end ribs on, so if they are slightly angled, the aileron end ribs will be also.

What so important? Because you will drill the aileron hinge pin hole based 90 degrees to that rib and if it is off, the axis of the hinge pin will be off as well. Extend that axis line 6 1/2 feet, (The length of the aileron), and you can see how it will cause binding when moving the aileron.

To make a smooth, easy moving aileron you must drill both aileron pin holes exactly aligned to each other.

The photos show how I handled this. When preparing to glue the wing trailing edge on I again measured the rear spar to rib end angle and used a wood block screwed to the bench to nudge the rib into perfect alignment. Once the ribs were all where they should be, I glued the trailing edge in place.

[jrbirdman47]

Now that you have those ribs perfectly plumb and square, you can jig the aileron end rib in place and drill the pin hole completely through using the aileron hinge block as a guide. In the picture, the right hand aileron, inboard rib is being drilled after clamping it to the wing rib with 1/2" spacers between them.

[jrbirdman47]

Want to make that leading edge skin, (.8mm plywood), easy to bend around the leading edge ribs? I took all the plywood to be used and rolled it up and slid it into a 10" diameter cardboard concrete form as soon as I started on the wing. (A shipping tube could be used too, I just had one laying around). By the time I was ready to use the plywood it had taken the set and was easy to glue around the leading edge ribs.

[Chuck in Indiana]

Nice. Thanks for this.. 

[jrbirdman47]

Starting the ailerons:

I jigged the aileron end ribs to the rib next door at the spacing I wanted first and prepared to drill the hinge pin hole. To ensure correct alignment I inserted a 3/8 tube, (What to do with the left over scrap from the tail?), into the hinge block and compared it to the rear spar for parallel both horizontally and vertically.

First picture shows looking horizontally toward the rear spar.

Second shows looking downward. The pencil line on the table is parallel to the rear spar.

Once I was satisfied, I drilled the hole through the rib which forms the aileron well using the hinge block for a guide.

[jrbirdman47]

Glueing the aileron spar in:

I thought the aileron spar would center on the hinge/ hinge block. It did not, and doing so would have made the spar curve back toward the ends.

First picture shows 10.5 inches from trailing edge to the rear of the aileron spar where it attaches to the ribs.

Second picture shows that same 10.5 inches measured at the hinge block for proper spar placement.

Third picture shows actual spar placement on the hinge block. Note it is slightly forward of center.

[jrbirdman47]

Making "False Ribs":

The lightest way I could think to help stiffen the leading edge skins, (Both aileron and wing), was to add styrofoam false ribs. Cutting them to shape was done using a hot wire stretched across the wood ribs. The wire can be purchased, but if you or the spouse has an old hair dryer, the wire inside those is perfect for such things, but trust me, you want to get permission to destroy said dryer first. Once you have the wire, build a frame of appropriate size. I built one with a 15 inch spacing for normal rib spacing, and an additional spreader for the outboard 19 inch spacing. Then just use a battery charger to heat the wire and run it across the wood ribs to shape the foam. I used the 2 amp setting and it works well. I also tried the little 12 volt batteries and had good results.

[jrbirdman47]

Building the aileron well:

This is for those of you using the Iron Design plans to construct ribs:

I decided to use aluminum flashing to cover the aileron well and learned that it is very important to get the plywood as close to perfectly straight as possible. This was accomplished by marking the distance from the rear spar for top and bottom surfaces. As long as the plywood is at the mark your trailing edge will be plenty straight enough. Holding the plywood in place is tough, and this is one of the few places where I did use staples. I tried it without and..... Just nope. Clamping is difficult because the top and bottom surfaces are so far from parallel.

First pic shows trailing edge of plywood at the mark.

Second shows entire well assembly stapled/ clamped in place.

 

[Chuck in Indiana]

Beautifully done.. thanks again.

[jgreen]

What are the thoughts on installing the aileron diagonals with or without thin ply gussets?  I am at that point building an XL wing with T88.

[jrbirdman47]

Definitely with the gussets. They add considerable strength. Because the aileron is actuated from one end it has quite a twisting moment when deflected into the slipstream, so I figure every little bit helps.