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General control line discussion => Open Forum => Topic started by: Dwayne Donnelly on January 01, 2023, 06:18:18 AM
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I'm building a Brodak Ares and just weighed one of the 1/2X1/2 trailing edge pieces it weighs 29 grams that's 17lb per sq. foot, the leading edges don't look much better so looks like I'm replacing them. '' Anyone know what wood I should use, is contest grade to weak or not stiff enough?
Thanks H^^
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Dwayne,
Happy New Year! What you might do is weigh up all the ribs, spars, sheeting and use the heavy ones for the outboard wing, this will reduce tip weight. On the inboard side use the lightest close to the tip.
What do you plan on covering it with? I am wondering if polyspan is strong enough cord wise on I-Beamers to hold the structure from twisting or does it stretch like film coverings?
Best, DennisT
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What do you plan on covering it with? I am wondering if polyspan is strong enough cord wise on I-Beamers to hold the structure from twisting or does it stretch like film coverings?
Best, DennisT
I've found that the standard polyester covering we use over here (said to be just the same as Polyspan) imparts noticeably more rigidity than the heavyweight 'Modelspan' tissue I used to use with success on the few I-beamers I've built. I think Polyspan should be fine on an I-beam wing.
Regards
John
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I'm building a Brodak Ares and just weighed one of the 1/2X1/2 trailing edge pieces it weighs 29 grams that's 17lb per sq. foot, the leading edges don't look much better so looks like I'm replacing them. '' Anyone know what wood I should use, is contest grade to weak or not stiff enough?
Thanks H^^
I would check your math and be sure of the density, but I wouldn't be too concerned about it. You are not talking about a piece of wood that is all that large, and some will get carved and sanded away. The trailing edge needs to be pretty stuff and strong. See what the combined weight of all the wing components is and let that be your guide. If it all is beyond reason, find some 10 to 12 pound wood for the trailing edges and leading edges. They take a lot of abuse from handling and bumping into things.
HAPPY NEW YEAR!!
Dan McEntee
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Wing sheeting on the leading and trailing edges of a wing structure add tremendous strength. An I Beam doesn't have any sheeting to bolster the wing spars. Therefore the edges and spar itself need to be quite stiff to yield a rigid wing. Don't worry about weight much on these pieces. There isn't a lot of volume in wood here and you don't want anything soft and spongy.
Dave
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Therefore the edges and spar itself need to be quite stiff to yield a rigid wing. Don't worry about weight much on these pieces. There isn't a lot of volume in wood here and you don't want anything soft and spongy.
I imagine, then, that it wouldn't be the worst thing in the world to use basswood or spruce for the edges, and perhaps even the main spar itself, in place of balsa.
Steve
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I imagine, then, that it wouldn't be the worst thing in the world to use basswood or spruce for the edges, and perhaps even the main spar itself, in place of balsa.
Steve
Basswood would not be a good choice.
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I’ve built three I-beamers over the years. I use good wood, maybe 6-8 lb./ ft3. density at the LE and TE. The spar carries most of the loads. I do add .004 carbon sheet installed w/ thick CA to the forward surface of the TE and the upper and lower edges of the spar. Polyspan is my preferred covering – it adds tremendous stiffness.
BTW – The Ares has a small wing and needs to be built light if you want any performance out of it.
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I imagine, then, that it wouldn't be the worst thing in the world to use basswood or spruce for the edges, and perhaps even the main spar itself, in place of balsa.
Steve
I don't think I'd go that far. I chose something in the 10-12# balsa range for my Neptune. It has done well so far. You SHOULD watch your weight but you can do that with the sheet wood parts and mostly the finish. Also I used (and will use on my Atom) nylon hinges instead of cloth. You'd find it pretty hard to slot basswood or anything too much harder for hinges. The hinges are about my only departure from 1955 on these airplanes. I don't want to have to replace rotten cloth hinges in a few years as was the usual practice in those days. I think the difference between a stiff trailing edge (something close to 1/2" square x 48") and a soft one is just a few grams.....pick some lighter wheels and watch the glue. I'd love to silk them but again, there will be an extra few ounces of cloth and dope.
Dave
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Hmmm.
Using your numbers Dwayne, you could probably save around an ounce before you would get to the point that you know the wing would fold up on you.
Reinforcing with carbon strip is always high tech and zoot, but it isn't always light. You have to work to keep from overdoing the carbon and glue. Using enough CyA to get the carbon stuck down good isn't light, either. But almost certainly a carbon/wood composite is going to make the wing stiffer than even heavy wood if you put the carbon in the right places. Carbon on the spar caps to resist vertical bending. You might use some carbon on the inside face of the TE if you decide to go with low density wood there, but only run it out maybe half span? Carbon in that orientation isn't real efficient to resist vertical bending, but it is easy to build. It does act to resist internal drag loads, but then, that's what the covering on an I-beamer is supposed to do....
Dave
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Thank you for all the replies, I used the balsa density calculator http://www.nclra.org/Programs/BalsaDensity.php
I'm going to try and find some around 8-10lb if I can, if not I'll go with what I have put the heavy stuff on the outboard and hope I don't need tip weight.
Great replies, thank you so much.
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I have built probably around 5 I-Beams all of which were during the 60's. You need a stiff LE/TE with straight grain. Today I would use lighter wood and Carbon Fiber laminates. I covered most of mine with silk. Two were fully sheeted with 1/20.
Ken
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yikes, i will remove that post.
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Ya wanna good springy bit for the spar , and matched L E 's & T E's .
Over the edge of a bench & fingertip / deflection , test . even weight & grain .