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Bolt-on wings for Oly II - How would you do it?
Am to the point of planning my wing build now, but need a little advice for how to build bolt-on wings.
The wing will be mostly stock, although I am adding three 1/8th inch turbulator spars to the front, ahead of the spar. The wing will be build with spoilers, am planning on using HS81s to drive them directly, with extension leads attached to a Y-cord near the center. The real question is, how should the wing bolt on? The only one I have ever built this way had the wing in three sections, so one large bolt in the front with a smaller one towards the back of the wing. Because the OlyII wing is built in two sections, I can think of two ways to do this. 1) Use a nylon bolt on both sides, both right behind the spar, with a third one near the trailing edge on one side or the other. 2) Ditch the second bolt behind the spar, and just use two bolts, with the large front one one panel and the smaller one (near TE) on the other panel. Is either way better than the other? Or am I obsessing about something that would work either way? As for the bolt threads into the OlyII fuselage, am assuming that an epoxy laminated 1/4th x 1/2" spruce piece epoxied onto the fuselage, with some small bits of fiberglass reinforcement is way overkill... Thanks in advance. Mike K. |
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I like your bolt positioning. The major loads are carried by the spar but so many designs show the mounting being a dowel at the leading edge and a single bolt at the trailing edge. But all that means that since the spar carries most of the load all the wing loading then has to be transffered through the center section structure to get to the attachment points. Putting the main bolt or two directly at the spar avoids all this.
Anyway.... You can use the spruce or you can use my favourite, plywood. I like the plywood since the cross plies carry the threading better. Single or double, either will work fine. However maybe it's just me but I prefer the two smaller doubles as opposed to a larger single. If you use a single in the middle of a 1/2 inch wide cross beam there won't be a lot of wood left where the hole is drilled to take all the loading. If it's glued to a former than that's not a big deal. If it's on it's own then you're playing with fire. If you use the two bolt method then you can just use two separate blocks glued to the fuselage sides and not bother letting them go all the way across. It's still nice to add a former at the location of the blocks though. A former there would let you glue the screw blocks into a corner instead of relying on the bending loads of the blocks on the glue joint. It also provides more structure to transfer the loads into over more glue joint area. Always a good thing rather than a high load in a small glue joint area. The glue isn't the issue, it's the wood under it. I was writing up a description of how to join the loads from the wing mount blocks to the towhook without using any formers and gave up. Definetly alter the fuselage if required so that you have a strong former at the location of the screw block so the screw block(s) are tied into the former via a nice glue joint and the former carries the loads directly down to the towhook block or plate. It would not be innappropriate to make this one former out of plywood. There's a lot riding on this area of the model. During a heavy launch the towhook is trying to rip the mount out of the belly of the fuselage and the only thing holding it back is the wing spar. The rest of the stuff in between is probably screaming in pain if it's just balsawood. So it's best to give it a hand. One final thing. If you're trying to gild the lily by adding turbulator spars to support the covering better how about adding a fourth strip behind the high point? I'm assuming here that your present 3 strips are located with one at the high point and the other two equally spaced towards the leading edge. Adding a fourth located behind the high point would go a long way to supporting the inter-rib covering and avoiding the sharp high with a straight line behind it. Below is a sketch that shows what you probably have right now compared to adding a fourth spar. The real rib shape is shown in red and the covering segments between the ribs shown in black. You can see how much potential dip there is with only the high point spar and how much that is reduced with the addition of a fourth spar. Edit: The red didn't come through in the GIF conversion due to my settings but I think you'll get the idea.... |
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Last edited by BMatthews; Jan 29, 2006 at 05:02 PM.
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On my Oly II, I used two nylon bolts which had long unthreaded sections just below the heads... with the heads cut off. These were put into the wing leading edge sticking out forward, the unthreaded part into a bulkhead at the front of the wing opering.
The rear halves of the wing were seperately bolted to the fuselage. A horizontal 1/4" ply plate was threaded for the rear bolts. |
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Wing bolts
I've done the same thing however this is how I did it...
the end center sections are covered with 1/16" balsa so b4 I covered the forward portion ahead of the main spar approx 11/2 in front of the spar I installed a 1/16 " dam running parallel with the spar and even the the ribs. after putting on the top 1/16 " balsa sheeting I cut a hole in the corner approx 1/4 to 3/8" from the end plywood root rib/cap and the same distance from the spar. Now I mixed up a whole bunch of epoxy w/west systems 401 filler and I poured this mixture into the hole until it was full. Made sure that I got enough in there to fill the entire cavity. What your doing is building a hard point for your hold down screws. Directly below where the screws will enter the fuse I've install a 1/4 thick x 1 1/4' wide and the length that fits the fuse. Now I've cut a rectangle hole in the fuse and inserted this hold down into the rectangle on each side and sanded it flush with the fuse sides. This inside will have approx 1/4 triangle reinforcements and also from the top plate of this hold down to the top edge of the fuse will be filled with epxoy also. To do this you will have to assemble the wings together place saran wrap around the middle part of the wings so the epoxy mixture will not stick to it. Mix the expoxy with filler to just about whip cream consistency (sp) and put on top of the lower hard point so that it is even with top of the fuse. you might want to place 1/32 or 1/16 balsa on the sides of the 1/4 plywood so that the epoxy doesn't run out of each end. Install your wings with plenty of rubber bands. ensure that your wing is centered on the fuse. The center part of the Wing will squish down into the epoxy and create a selt centering jig for you. after it sets up you will have to drill the holes thru the hard point in the wing though the hard point in the fuse. After your holes are drilled tap the lower hard point for the screw that you will be using one on each side... done..........Whew........clear as mud right..... Best Regards, Wylie S. |
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Thread OP
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I'm leaning more towards three at the moment. Regards. Mike K. |
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Thread OP
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I've yet to get the fuse completed, but the idea of using more plywood for an extra former as a brace for the wing block is a good one. What would likely work well is to use the spruce running across, with a plywood former butted up against it, then all the way down to the bottom. This will greatly increase the glue area, and position the force to three pieces of the plywood fuselage. If I add some 1/4" triangle stock, or some small pieces of 2oz fiberglass cloth, even better. Ditching the spruce for laminated plywood pieces, maybe 3/4" wide instead (and 1/2" deep or so) might be even better. Not sure I have 1/4" ply, but I do have 1/8th". Laminate it with 2oz cloth in-between, I've pretty much over-engineered it, I think... LOL. Thanks again! Mike K. |
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