Eagler's Nest
Airframes => Single Seaters => XL => Topic started by: Maxray on February 02, 2019, 04:04:27 AM
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Hi guys,
Can anyone tell me how they were able to glue the bottom surface of
the nose sheeting? Mine bows outward and the rubber bands and sticks to not hold
the surface against the nose pieces. Help!!!
Thanks again guys!
Max~
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Here's how I did my leading edges:
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rfeenstra's solution is one several builders have used with success. If something like that will not hold the ply in contact with the nose ribs, you may have to make plywood forms that will press the nose ply firmly against the nose rib. Many builders of aluminum wings use a plywood form to hold wing skins over ribs for riveting. Cut the plywood form using your nose rib template to create a concave form that exactly matches your wing. Make one for each rib station and pull it against the nose ribs with a strong bungee or nylon strap.
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Here is a photo of a wing skin fixture.
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If you are making foam nose ribs with a hot wire, the scrap should be a perfect fit
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Thank you guys!!!! All great solutions!! Genius, all!!!
I will post pics..
Max
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Here's how I did my leading edges:
I used this method as well with a strap at each nose rib location, and light staples along the spar caps in between the straps.
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One hint. Make sure your ply is well humidified. I glued my ply on in the winter with low humidity. Looked great until summer with high humidity. The ply expanded and caused dimples between the ribs. In the winter (with the heat on again), the wood dries out and the dimples go away. This happens even though the wood was well sealed with spar varnish.
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Great reminder! I soak my plywood on the tub, warm water with towels holding them down.
For 45 minutes. Makes the plywood very pliable!
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Is it possible your plywood is too pliable when you put it over the nose ribs? If so, soak it again and roll it up while wet. Let it dry while in a roll. When dry, unroll and try an install.
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I am going to Epoxy the soaked .125" Birch ply to just the bottom of the front spar.
clamping the sheet to the spar, with "C" Clamps, using a piece of scrap 1" x 2" x 5' .
to apply even pressure. (My sheets are 20" x 60".)
Since the sheet will only be wet, to within 2" of the edge, There should be no problem with adhesion.
I use a number of scrap 1"x 2" x 5', along with ratchet straps to let this epoxy cure, and the sheet to become shaped to the ribs.
** no other glue joints yet **
Once this bottom epoxy has cured, I will loosen the straps, then apply Epoxy to the leading rib edges, (now dried) and top of the spar. Again with the straps & Scraps, until this has cured.
Move to next sheet, and repeat.
Gluing the bottom of the spar, will allow for precise fitting,
and the straps will help the dampened sheet to conform to the ribs
This way, there's no fighting with the sheet to keep it aligned.
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When we built the original Treehugger LEU wings, we made sure all the nose ribs were exactly alike by routing against a metal master template and drum sanding carefully. They all stacked up perfectly. We fixtured the wing structure with the leading edge up, trailing edge down and worked to get it as straight as possible. Then glued all the ribs on, ensuring each rib was square to the spar. When we put on the plywood leading edge skin we worked hard to get the skin to contact all the nose ribs thoroughly. Used bungees, rubber bands, ratchet straps, outer nose-shaped forms, wedges and weights to ensure full contact. Unfortunately, after a bit of time in our humid weather, the nose developed some "divots" and hollow spots. Apparently no detriment to the flying qualities, but ugly.
Due to an unfortunate landing in a tree, Treehugger's wings were damaged. After a couple years, we decided to rebuild the airplane and install the Verner 3 cyl engine.
The wings were completely stripped of fabric and the nose skin removed. Damage to the structure was repaired. We had new nose ribs made by a friend on his company's CNC router, which were all perfect. We decided to install the plan's specified nose ribs, and then put in "outline" nose ribs between each of the plan's ribs. By "outline" I mean they were the outer shape of the nose ribs, but not much meat in the interior of each nose rib, just enough to hold the nose outline.
They were attached as before. Then we started thinking of what may cause the plywood to distort after installation. One reason for distortion was the manner of installation - the forcing of the plywood to each nose rib to get full contact.
If you think about it, the nose ribs, no matter how hard you try, will not all line up perfectly straight with each other when installed on the wing spar. Maybe only a few thousandths of error, but not perfect. And, plywood will bend easily in one direction (simple bend), but not in more than one direction (compound bend). Trying to bend and force the plywood to each of the ribs results in a compound bend and causes strains in the plywood which will eventually show up.
What we did is not to try to force the plywood to contact all the edge surface of all the ribs. We considered that with nominal force to hold the skin to the ribs that there would be some poor contact area between the skin and the ribs, but the plywood would not be forced into a compound bend. To address the poor contact issue, we decided to use a thick structural mix of epoxy (West System) and milled glass or milled cotton fiber, with the consistency of toothpaste. This was applied to each nose rib in a fairly thick bead. The plywood was moistened with plain epoxy in all the rib contact areas (none of this contact area was varnished), then the plywood was carefully positioned on the wing leading edge, taking care not to "smudge" or displace the bead of thick epoxy to ensure that we had all ribs/plywood contact areas full of the structural mix. We used various methods to gently hold the plywood to the ribs, but none were forced.
They came out great. The wings were covered, and have survived two summers here in Ky., very hot/humid, and a visit to Oshkosh last summer with no dimpling or distortion of the leading edge.
You may want to consider this technique as you start your leading edge work.
Hope this helps.
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Tom H wrote:< What we did is not to try to force the plywood to contact all the edge surface of all the ribs. We considered that with nominal force to hold the skin to the ribs that there would be some poor contact area between the skin and the ribs, but the plywood would not be forced into a compound bend.>
This is what I was trying to explain, with the use of the 1"x 2". Eyeballing their straightness, and adjusting the straps accordingly.
Once again, I am not building a L.E.from plans, or a kit, and I appreciate the input.
But it is, along the similar design lines. So things I do may not be in accordance
with plans built Eagles. Hopefully I will meet Part 103 weights. And so far all looks well.
When I fabricated my L.Edge ribs, I too made sure they were exactly alike. But not having a CNC, I placed the bottom edges of all the ribs on my tablesaw and clamped them together, from the inside edge, much the same as when sawing the slot in their noses, prior to sanding them on the beltsander. I was very concerned to get them all the same on the outside edge. The inside edge wasn't too much of a concern to me..
My spars are laminated 3/16" White Ash. Much stronger than Spruce, and just a tad heavier. But I know they are without flaws, or knots or internal stresses found in lumber not laminated.
I have access thru the spar web, so each of my 1/4" ply ribs can be checked with
a mirror, and a paste of epoxy can be added with a syringe, if needed, to fill
any gaps in the interior.
To quote a phrase from the car forums,"YMMV" (Your mileage may vary)
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Tom,
I was thinking along the same lines but was not sure how to make a mix of epoxy and filler. The gaps are not much and thus will be the way I go.
Thank you. My nose pieces were laser cut so they are all the exact same dimensions. I hot cut the Styrofoam fillers to a laser cut template.
I like the idea of not forcing the ply skins. I will use a mix of all the great holding suggestions here.
Thanks again guys!
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Here are some prior thoughts on the plywood dimples...
https://www.eaglersnest.com/forum/index.php?topic=758.0 (https://www.eaglersnest.com/forum/index.php?topic=758.0)
(https://media.giphy.com/media/l2YWl620FrxrhASR2/giphy.gif)
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Hi I recommend to staple and glue the bottom on first . that is after fitting the wood to the wing part then put glue on the nose ribs and pull the wood around the leading edge and use straps (Ratchet) Then glue the top of the wing spar and staple it . Leonard
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I will do that Boss! Thank you! I want to but a shirt and hat!!
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Hi Guys
if it turns out that you have dimples in your leading edge skins cut a one half nose rib (top half) and force it in through the lighting holes in the spar and move it to the dimple and it will take the dip out . in most cases. Leonard
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I got my Tee shirt and hat yesterday!
Thank you Leonard!
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Left wing ready for covering! The wife sanded everything and put two coats of spar varnish on it. Going in the wing rack today.
I have a bout two weeks work to finish the right wing.