Wings

[jrbirdman47]

"Endeavor to persevere!"

[Brock]

Today was 'mounting day'.  It was time for the wings to meet the airframe.  Although my holes were all drilled to 1/4" I started with 3/16" bolts so the wing could quickly be put in place then I went back and through drilled some of the holes while installing 1/4" bolts that had been tapered to a bullet point.  After that I calibrated two digital levels (they needed it) and setup the wings dihedral at an initial 1.1 degrees on the front spars.  The 1.1 deg is what I calculated as an initial angle to give me something close to 3" dihedral.  Which turned out to be close as I later measured 2.5" with string sag.  I've no idea how much sag at this point.  The rear conduit struts didn't have the 5 deg angles so I just let them droop vertically to the floor as supports and adjusted them to give 2 degree washout.  Tomorrow I'll readjust the rigging and go about making the final rear struts then the front ones after that.  Very cool to see the big visual change, finally.

Speaking of 'big visuals' a box of wing covering showed up today.  I didn't realize how big the box would be.  Cool.

[Brock]

In my last post I mentioned that 1.1 degress on the main spare gave me 2.5" drop from tip to root.  Three inches is plans spec.  Then I got to thinking the other night, long after I should have been asleep, that 27' of string no matter how tight is going to sag.  So today I sighted from tip to tip along the string and sure enough, there is al least 1/2" sag.  So I'm calling 1.1 deg good.  The digital inclinometer seems easiest for me, the way i work anyway.

Today's goal was to make at least one strut.  I know I said (last post) i'd start with the rear struts but then I changed my mind.  Reason is, the front spar, if off a bit, can change the washout.  So I started with a front strut.  It worked out well.  Obviously, making the taper at the fulelage end was the most time consuming.  There still is a bit of work to do on the strut in the pictures below, but the hard work is done.

The green faring is a sample that I 3D printed for covering the struts and possibly some of the landing gear.  Depends how carried away I get.

[Chuck in Indiana]

Good idea doing the front first. It sets the dihedral, the rear sets the washout.

[pappyadkins]

Great job... BTW, on your 3D print... Love it, but have food for thought, what about your control cables up the rear strut?  Interested to see what you come up with... I've thought about similar idea... think I finally decided to go with an ultra light concept of 3d print myself, we'll see if what I came up with works... lol

[Brock]

It feels like real progress that now the wings are held on by struts of their final dimentions etc.  The Aluminum tubes all came out nice at 78-1/2".  Incedence on the left wing turned out to be 0.4 degrees more than the right wing.  Probably close enough but it challenged my thinking a bit.  Since the left wing has .4 deg more incidence what about the washout.  Should I make it 2 degrees from the root of each respective wing?  But that would put the left wing-tip with .4 degrees more angle of attack than the right tip.  I'll tell you what I did later if anyone is interested.  I'm hope'n it's not troublesome to trim out with the ailerons.

Also of note.  The dihedral came out at 1 and 1.4 degrees not 2 degrees as planned.  Hope it's not noticeable.  I'll be flying 1 degree tail low.  Also pictured is my make-shift wing support and the micro adjuster to get the height just right.

The metal ends of the struts took some thinking.  I made a few errors and had to start over.  I calculated I had enough metal for one more mistake/restart.  It didn't happen, and I have about 6" extra metal tubing left over.  Still to do is to weld-in 3/8" OD x 1/4" ID bushings in each tube, then finish the tack-welded rear tube angle slots.

[Brock]

Finally some progress using the 3D printed (LW-ASA) nose ribs.  I've been avoiding the nose ribs as once installed I can no longer set the wing on the leading edge but will have to  (mostly) lay it flat.  Still have about 40% of the sealing/varnish to do.  Notice the clamp-tabs printed onto the nose ribs.  The really helped out in gluing.  Tip & root ribs will take a bit more creativity to glue.  Perhaps staple the tab?

[Brock]

Since I have about 10 (five for each side) extra nose ribs I thought it might be good to add them in since some folks have mentioned some nose plywood 'buckling', as I re call.

Q.  What part of the wing seems to have more issues with the leading edge distortion/buckling?  Mostly inboard, middle, outboard of the strut attach?  Is it the full wing length evenly?

I've enough extra nose-ribs to basically double every other bay.  Else I could concentrate on inboard/outboard area.

Thanks.

[Chuck in Indiana]

Since I have about 10 (five for each side) extra nose ribs I thought it might be good to add them in since some folks have mentioned some nose plywood 'buckling', as I re call.

Q.  What part of the wing seems to have more issues with the leading edge distortion/buckling?  Mostly inboard, middle, outboard of the strut attach?  Is it the full wing length evenly?

I've enough extra nose-ribs to basically double every other bay.  Else I could concentrate on inboard/outboard area.

Thanks.

Bullet has some, all but 4 bays in the left wing, all but 2 in the right. Seems random. It doesn't seem to affect ol Bullet, but looks like crap.

[Brock]

Bullet has some, all but 4 bays in the left wing, all but 2 in the right. Seems random. It doesn't seem to affect ol Bullet, but looks like crap.

Thanks Chuck.  So I've decided to go ahead and double up on the nose ribs from the start instead of trying to fix a buckle after it happens.  It will cost me 10 3Dfoam ribs per wing at .5 oz each.  So I'll be adding at least just a bit more than 10 oz for both wings.  Probably closer to 16 oz when all done.  So what's another pound here or there.  Ahhh.

Here is another question for the collective.  I'll be installing the nose plywood in lengths of 45"+-. 
Q.  What has worked well for getting the inside varnished?  A monkey with long skinny arms?

My thinking is to glue down one side (top of wing first likely) then trying to put some varnish on things just before gluing the other (bottom) side.  Seems like it's going to be a circuis-act event.

[Chuck in Indiana]

Lay out the rib locations in pencil, varnish everything except that. Liberally apply glue to the rib locations plus a little overlap, clamp it up.

[Tom H]

The issue of the wing leading edge plywood "dimpling" has been discussed often since we built LEU Treehugger back in 2008.  We thought we could prevent them by making sure that the plywood leading edge was securely adhered to the full curved periphery of every rib.  To accomplish this we used ratchet straps, rubber bands, rope, wedges and anything we could think of to force the plywood to each rib.  Looked good at first, but eventually, dimples did form.  Since they showed up before the wings were fabric covered, we came up with a technique to use a three-part "rib", made from 2" foam board, that we inserted through the spar web lightening holes and then manipulated the three parts, covered in epoxy, to force the dimples out as best we could.  It helped, but the dimples were still there.
Several years later, when we were repairing and rebuilding the wings, we realized that, as careful as we were, that every rib (also, we did put add'l thin ribs between the "plans" ribs) may not in a perfect alignment with its neighboring rib.  As an example, one rib between two others may be barely offset in such a way that the plywood skin would not make perfect contact with the ribs entire curved surface.  The error may be very small, maybe less than 1/16".  We thought forcing the plywood to make the contact with all ribs may be trying to force the plywood into a compound curve, which plywood does not like to be forced into.
We decided to not try to force the plywood, and decided to adhere the plywood to the ribs with T88 epoxy thickened with milled glass (this if often used in composite construction for structural joints).  We primed the surfaces with pure T88 (after doing the prep that Chuck describes above), and then applied the thickened T88 (almost as thick as toothpaste, which would fill and stay in the small areas where the plywood may not contact the ribs) to the surfaces and installed the plywood.  We used only light to moderate force to ensure good contact.
The result after 10 years or so is very few minor "dimples".  We think our technique worked fairly well.
Hope our experience gives new builders some ideas to think through.

[Rick]

What glue are folks using for PLY to nose ribs? . . . Titebond or T-88

[Kamcoman77]

T-88. Ribs sanded into alignment using 2-ft long sanding board. Foam ribs between plywood ribs. Photo of my wing on Page 4.

[Rick]

Thank you. I used T-88 on everything else - except rib construction, and used 1/8" ribs between each 1/4" main rib. That 3' sanding board is a great tip! And I assume a long straight edge to confirm the sanding progress. Terrific, very glad I posted the question.