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What is the weight of aileron cove/false spar material?
- Thread starter Marty57
- Start date
Gordon Misch
MEMBER
Toledo, Wa (KTDO)
Or Dakota Cub - I got some nice ones from them.
Marty57
PATRON
Nipomo, Ca
T.J.
I only have a break, no roller so not sure if I could fabricate out of aluminum.
I'm trying to figure out what part # from what vendor for the cove I need. Prices vary from $25 - $60, some list length and some don't. Univair seems to have the best price but not sure what part # to order; I need the J3 style, same as PA18? If I use the aluminum cove, do I need to use the brace shown below? Where do these go on the PA18 wing?
Marty57
I only have a break, no roller so not sure if I could fabricate out of aluminum.
I'm trying to figure out what part # from what vendor for the cove I need. Prices vary from $25 - $60, some list length and some don't. Univair seems to have the best price but not sure what part # to order; I need the J3 style, same as PA18? If I use the aluminum cove, do I need to use the brace shown below? Where do these go on the PA18 wing?
Marty57
Attachments
If you go metal get some .o25 2024T3, and make your own aluminum false spare. Piper used .020 beer can aluminum. I'm sure with a good brake you will have no problem with this simple fabrication. Make a simple slot bender to creat the cove or brake the rounded cove in 1/2" increments.. It will look round after you get it covered..
My hangar landlord is currently restoring a J3. He built his own false spar. To get the proper "cove", he took some 2x4's, and made a box out of them. Then he set the aluminum on top of this box. He then took a heavy galvanized pipe and set it on top of the 2x4 box frame. The pipe will go inside the box frame but very snug. He then took his scissor jack out of his spare tire kit from his Chevy pickup and set this under his bumper. he set the jack over the box frame/aluminum/pipe and jacked his truck up on the bumper. He basically forced the pipe into the wood frame. When it bottomed out, he lowered the jack down and took a hammer and pounded the pipe out of the frame and voila! He had the proper concave angle in his false spar. He is very clever and is an excellent IA. It took a little bit of working to get everything just right but they looked very nice. He went to a thicker aluminum too.
skywagon8a
MEMBER
SE Mass MA6
Marty57
Another alternative would be to make a reverse curve of about 1/8" in your reinforcement lip. Then when the fabric pulls it in it will end up being straight.
OR another alternative could be: after the fabric has tightened and distorted the cove and before the reinforcing tapes are attached to the edge, glue on and trim to shape a piece of balsa wood to give the straight edge that you desire.
If your ribs are a different dimension than Buggs ribs, will the aluminum cove which is available from any of the suppliers fit your ribs?
Another alternative would be to make a reverse curve of about 1/8" in your reinforcement lip. Then when the fabric pulls it in it will end up being straight.
OR another alternative could be: after the fabric has tightened and distorted the cove and before the reinforcing tapes are attached to the edge, glue on and trim to shape a piece of balsa wood to give the straight edge that you desire.
If your ribs are a different dimension than Buggs ribs, will the aluminum cove which is available from any of the suppliers fit your ribs?
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Gordon Misch
MEMBER
Toledo, Wa (KTDO)
Marty, another possibility would be to simply make the top and bottom stiffening legs out of aluminum and fasten them to the cove you already made. In that way you could duplicate the stiffening shape of the aluminum false spar, but wouldn't have to scrap the coves you already made and wouldn't have to sacrifice beautiful, essentially all-wood wings. The aluminum will be stiffer (higher elastic modulus) by a factor of 5 or more than the wood, ( http://www.engineeringtoolbox.com/young-modulus-d_417.html )so for a given size and shape of stiffening structure the aluminum will be much more effective. If you want a sketch of what I have in mind lemme know and I'll make a quick sketch to scan and email to you.
Marty57
PATRON
Nipomo, Ca
12 Geezer,
I was starting to think along the same lines. Basically an aluminum angle with the 15 degree bend on the edge so fabric won't catch. I could attach with what, pop rivets from the cove side? What were you thinking for dimensions? Something like 1" x 1" x .024 2024T3 or thicker? I can bend up to 3' with my break or use a friends break (HVAC contractor) to make 4' to match coves (or bend over a piece of wood for that matter). I can try it on my box to see how it works; more practice covering anyway. The wood coves are so easy to make; spread the glue and clamp in the form with c-clamps and a after epoxy dries and a perfect cove every time. I would like to see a sketch of what you have in mind. The cost to buy the cove looks like about $300, wood coves about $20. The $300 would be better spent on struts in my book.
Marty57
Marty57
I was starting to think along the same lines. Basically an aluminum angle with the 15 degree bend on the edge so fabric won't catch. I could attach with what, pop rivets from the cove side? What were you thinking for dimensions? Something like 1" x 1" x .024 2024T3 or thicker? I can bend up to 3' with my break or use a friends break (HVAC contractor) to make 4' to match coves (or bend over a piece of wood for that matter). I can try it on my box to see how it works; more practice covering anyway. The wood coves are so easy to make; spread the glue and clamp in the form with c-clamps and a after epoxy dries and a perfect cove every time. I would like to see a sketch of what you have in mind. The cost to buy the cove looks like about $300, wood coves about $20. The $300 would be better spent on struts in my book.
Marty57
Marty57
Gordon Misch
MEMBER
Toledo, Wa (KTDO)
I'll email you a sketch.
Edit: It's on the way. Dunno about fastening, maybe PK screws thru the wood, then into the metal? Or maybe pop rivets? Probably also glue. The shear between aluminum and wood is important to establish resistance against. So probably glue / pop-rivet?? Again, just one idea - - - Also, you'll get a lot more stiffness with a substantial break on the free edge of the aluminum - like maybe 1/4" or 3/8" or so wide, at 90 deg? My sketch just shows a small 15 deg break like you suggested. Anyway, with your test frame it will be easy to experiment and determine an optimum configuration. Let us know!!
Edit: It's on the way. Dunno about fastening, maybe PK screws thru the wood, then into the metal? Or maybe pop rivets? Probably also glue. The shear between aluminum and wood is important to establish resistance against. So probably glue / pop-rivet?? Again, just one idea - - - Also, you'll get a lot more stiffness with a substantial break on the free edge of the aluminum - like maybe 1/4" or 3/8" or so wide, at 90 deg? My sketch just shows a small 15 deg break like you suggested. Anyway, with your test frame it will be easy to experiment and determine an optimum configuration. Let us know!!
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Marty57
PATRON
Nipomo, Ca
Coves are made so I am trying a couple of things before giving up for metal. I stripped the text box tonight and glued on 1/8" ply to form a lip on both top and bottom. The box is a lot more solid this time. First time around I tried no lip on top edge and 1/16" ply on bottom only to establish a reference. I'll cover the box again in the morning to see how this works out. If I still have too much scalloping of the edge than I'll strip the box and try the aluminum. The test box makes this real easy to do.
Marty57
Test box with 1/8" lip top and bottom:
Marty57
Test box with 1/8" lip top and bottom:
Attachments
Piper didn't always do it the right way. .016 beer can metal.... supported between the ribs. carrying much of the flap and aileron load. If building experimental, go .025 2024T3. You can omit the intermediate support and have something to secure your flap and aileron hangers...
Marty57
PATRON
Nipomo, Ca
Bugs,
On my ailerons and flaps I glued a 1/16" strip of ply along the top of the ribs to bring them up to the level of the leading edge ply and the trailing edge ply so everything is the same height; no transition at all (learned this trick on the biplane builders site). I might add the same strip to to my wing ribs so the transition would only be 1/16". Another way to do this is to recess the 1/8" into the end ply of the rib so it is flush with the cap strip. That would be pretty easy to do. On my test box I am only testing the strength of the ply for scalloping so didn't feel it was necessary to recess for the test. I also added to the test box a "rib" going across the box. This rib is not for any strength or testing issues but I figured I can learn how to rib stitch with the box, install tapes, an inspection ring, etc. The amount of fabric you sent is enough for this second test and a third if necessary; sure is handy- thanks. I'll post after I get it covered; going to get started on that in a little while.
Narty57
On my ailerons and flaps I glued a 1/16" strip of ply along the top of the ribs to bring them up to the level of the leading edge ply and the trailing edge ply so everything is the same height; no transition at all (learned this trick on the biplane builders site). I might add the same strip to to my wing ribs so the transition would only be 1/16". Another way to do this is to recess the 1/8" into the end ply of the rib so it is flush with the cap strip. That would be pretty easy to do. On my test box I am only testing the strength of the ply for scalloping so didn't feel it was necessary to recess for the test. I also added to the test box a "rib" going across the box. This rib is not for any strength or testing issues but I figured I can learn how to rib stitch with the box, install tapes, an inspection ring, etc. The amount of fabric you sent is enough for this second test and a third if necessary; sure is handy- thanks. I'll post after I get it covered; going to get started on that in a little while.
Narty57
Marty57
PATRON
Nipomo, Ca
I covered the box with the 1/8" ply lips and it looks good. There is some slight scalloping; about 3/32" over a 16" span. The test box does have some differences from the wing that will make the wing stronger. On the test box the lip is glued on top of the cove's edge; on the wing it will inside the cove. This will allow the pressure to be against the edge of the 1/8" ply rather than the test box where the pressure is pulling against the glue joint. Second is a presumption I have regarding the fabric. On the test box the fabric is pulling from the rear spar to the cove;short distance with a lot of force. On the wing the pulling force will be from the leading edge to the cove; a much longer distance. In my thinking (correct me if I'm wrong) their won't be a great a force or pull against the cove over that great a distance. Is this line of thinking correct? I added the weight of the 1/8" lip to compare to the weight of the metal false spar. The wood is slightly heavier than the metal; .0625 oz higher per inch. Since I will be able to fasten with glue alone and no bracing is necessary I have to say it is a go for the wood cove. I know I have spent way too much time on this but it is resulting in about a $250 savings over metal false spars and, well, I like wood better. As you all can see, I don't give up very easy; that's why this is taking so darn long. The $250 is more savings to put toward the struts. I posted some pictures to show the amount of scalloping. The weird "rib" going across the box is there so I canlearn how to rib stitch. Now I can get something done!
Marty57
Second covering of test box:
Marty57
Second covering of test box:
Attachments
Gordon Misch
MEMBER
Toledo, Wa (KTDO)
Marty, I think if you let in the top of the rib so that the reinforcing strip is flush to the capstrip surface, as you mentioned previously, it will likely be even stiffer. I admire your perseverance!
Marty57
PATRON
Nipomo, Ca
Bugs,
I ran this by an engineer friend because I am just not sure. He suggested a strip of spruce across the span of the ribs before attaching the lip. He said this was common practice in the 30's and 40's to use wood coves. I sent him the pictures and my thoughts on the pressure and am awaiting his response. Piper has a brace between each rib to control this (at least on the original wings), I posted the drawing from your site earlier in this post. Did you use the brace in your wing? I can easily fabricate a brace if necessary. I was hoping someone would respond about the current use of the braces but no luck.
It is hard to imagine that the thin aluminum cove would resist the pressure better than the thick ply ........ lots to learn in this game.
Maert57
I ran this by an engineer friend because I am just not sure. He suggested a strip of spruce across the span of the ribs before attaching the lip. He said this was common practice in the 30's and 40's to use wood coves. I sent him the pictures and my thoughts on the pressure and am awaiting his response. Piper has a brace between each rib to control this (at least on the original wings), I posted the drawing from your site earlier in this post. Did you use the brace in your wing? I can easily fabricate a brace if necessary. I was hoping someone would respond about the current use of the braces but no luck.
It is hard to imagine that the thin aluminum cove would resist the pressure better than the thick ply ........ lots to learn in this game.
Maert57
Gordon Misch
MEMBER
Toledo, Wa (KTDO)
Boy, I'll say! I've been waging my own battles with my 12 today. FINALLY making some progress this eve (painting jury struts).
The thing about the aluminum is its stiffness, just as a property of the material. The elastic modulus numbers I gave earlier tell that story. Aluminum will deflect about 1/5 as much as fir (spruce is probably about the same as fir?) for a given cross section and force arrangement. So .025 aluminum will have about the same stiffness as 1/8 thick wood, given the same sizes otherwise. Also, the wood arrangement you have doesn't have a "cap strip" on the inboard side. If it did, it would be much stiffer. Compare to the cross section of an I-beam. I could run some actual calculations for you if you want.
Edit: Another difference between wood and aluminum is wood's tendency to take a "set" when exposed to a moderate load for an extended length of time. So the "dead load" for wood is somewhat less than its "live load" (transient load). Maybe you already know all this, but just in case not - - -
Re fabric tension, I don't think the size of the panel will make any difference. The shrinking process is going to shrink to a given tension based on the properties of the fabric, and that tension is all the cove sees. Could be wrong, but don't think so - - -.
One other idea to save some weight if you want to stick with wood. You could cut that stiffener such that it is wider in the middle between the ribs, where the maximum bending is taking place. Say 3/4" right at the rib and 1 1/2" in the center, just to grab some numbers out of the air.
Anyway, just a couple of ideas, probably worth what you paid for them! Maybe time for another coat of Stewarts on those struts now - - -
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Marty57
PATRON
Nipomo, Ca
12 Geezer,
What would the difference be with a 1/4" x 1/4" spruce strip glued to the underside of the lip (at the outermost edge)? If 1/8 and .025 have same numbers than the 15 degree bend must be the key. Can't see the big difference but then again I can't see lift and I trust those numbers! Make me a believer. I am not opposed to an aluminum angle but the only way to attach would be T88 epoxy and pop rivets. If that would work than I would go that rout. Does your 12 have the reinforcement piece between each rib like I posted earlier?
Marty57
What would the difference be with a 1/4" x 1/4" spruce strip glued to the underside of the lip (at the outermost edge)? If 1/8 and .025 have same numbers than the 15 degree bend must be the key. Can't see the big difference but then again I can't see lift and I trust those numbers! Make me a believer. I am not opposed to an aluminum angle but the only way to attach would be T88 epoxy and pop rivets. If that would work than I would go that rout. Does your 12 have the reinforcement piece between each rib like I posted earlier?
Marty57
Gordon Misch
MEMBER
Toledo, Wa (KTDO)
Yes, adding that 1/4 X 1/4 strip would stiffen it up considerably. The break on the edge of the metal does the same thing, and if it's a 90 deg break, more so. The key is to have material shaped such that the area distribution of the cross section is greatest at the edges, in the direction of bending. Think of a 2 X 4, bending flat and bending edgewise. Same cross section, just oriented differently. The contribution of a small element of area to bending resistance increases with the square of its distance from the bending center (neutral axis). A measure of this distribution of area is the "area moment of inertia" or "second area moment". Dunno how much you like math, but this wikipedia article gives a pretty good description (though a bit mathy). http://en.wikipedia.org/wiki/Second_moment_of_area The paragraph on "parallel axis theorem" applies to your 1/4 X 1/4 strip. Note the d^2 part of that formula.
Lemme know if this clarifies any?
Lemme know if this clarifies any?
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Marty57
PATRON
Nipomo, Ca
Yes, it's pretty clear. It would be real easy to add the spruce to the edge. I just need to decide how to do the lip, the ply or an aluminum angle. So' I'll start gluing up the coves to the ribs as I decide on the lip. I just need to "pull the trigger" and get moving. Thanks for the engineering lesson.
Marty57
Marty57
Gordon Misch
MEMBER
Toledo, Wa (KTDO)
I'm thinking you meant adding the 1/4 X 1/4 spruce to the free edge of the stiffening lip. That's where I was envisioning - Have fun!
Marty57
PATRON
Nipomo, Ca
I glued the cove in place today. It is still clamped but I am very happy how it came out. I still have the upper and lower lip to add and I have decided to add the aileron brace between each rib. I will be making the brace out of wood but follow the PA18 design. With the brace cutting the span between the ribs in half I feel that I can go back to a 1/16" ply lip top and bottom and a 1/4" x 1/4" spruce cap strip at the free edge. Cost for both wings will be under $40 compared to $300+ in aluminum. This really applies to the threads about scratch building vs some of the more advanced kits. This is the kind of thing that can really eat up time. I have spent a good bit of time over the past 2 week to get to this point so it takes a commitment. The second wing will be much quicker as the parts will be done with this wing. The second wing is hanging from the ceiling already; awaiting the flap and aileron and the work I am currently doing on the first wing. Feels good to put a long day in the shop again; it's been a tough couple of weeks.
Marty57
Marty57
