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Old Apr 11, 2014, 05:45 AM
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South Africa
Joined Feb 2010
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Question
Advanced wing design

Is there a simple way of making a 2 meter thin profile fast correx wing, i haven't had any success with my 1.7 meter wing i made, it came out perfect looked right, profile was fine, but when i flew it, it was very unstable in the air, perhaps it was related to weight, but i'm not sure. I still have the wing, landed safely with it, but would never use it again, perhaps it's a wing balance issue or the semi double spar i added ?

I'd rather like to use a thin spar than to taper a spar for i do not have equipment make a tapered spar, anything off the shelf i could use or an easy way to make a strong thin spar, then i was thinking tapering the wing it self at the TE as to make it more of a speed wing.
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Old Apr 12, 2014, 07:41 PM
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Australia, NSW, Gurley
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Go to your local golf club and ask if the have any old carbon golf club shafts or you could try arrow shafts.
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Old Apr 13, 2014, 04:25 AM
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South Africa
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Thanks Adrian but those golf clubs aren't uniform, thick at one end and thin on the other, i dunno perhaps you get some that is straight all the way however i don't think there is a 2 meter golf club, arrows will most likely not come in 2 meters length either.
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Old Apr 13, 2014, 08:29 AM
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Australia, NSW, Gurley
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Sorry mate thought you were looking for a tapered spar,wouldn't be hard to join them to get the right length.
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Old Apr 13, 2014, 01:14 PM
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South Africa
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No Heck tapered could work for sure, thanks i'll see if there are any shops selling them, perhaps a pawn shop would sell a few clubs for cheap... will go see. I doubt the golf shop would sell me cheap golf rods but i guess i could try and ask... again thanks....
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Old Apr 15, 2014, 05:54 PM
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LaGrange, GA
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Some folks have had success doubling up 4mm correx or making an I-beam structure out of it for spars. Don't know if it'd work for a 2m wing, but might be worth a try. Then you could cut the spar whatever shape or taper you wanted.
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Old Apr 20, 2014, 07:21 AM
Crash Test Dummy
Brunei, Brunei-Muara, Masin
Joined Nov 2013
130 Posts
Fishing rods use tapered carbon rods, you can buy them in all sorts of tapering diameters and usually in 600-700mm lengths.

Something like this: http://www.aliexpress.com/item/redwo...496924727.html - you can order however many segments to suit the length you need

I am a kite flyer, as well as an RC buff and always have a ton of carbon spars on hand. My biggest kite has a 1.8M x 6mm 2-piece carbon span, joined with a CA-glued ferrule (a piece of snug-fitting solid carbon rod inserted inside the tube) The loadings on that kite in 20knots of wind would be as great, or greater, than an RC wing and I haven't broken it yet.

For plane wings, a round tube is a PITA to fit, so you could use something like this: http://www.aliexpress.com/item/Crab-...847370996.html - 400mm x 3 x 3 with a 2mm hole - just buy some 2mm solid rod to ferrule it using CA. But I would just make up some 2-ply coroplast formers with the right diameter hole drilled through them and the carbon rod hot-glued in place.

But, with the advent of quads, there is a lot of large-diameter tube available too: http://www.aliexpress.com/item/Free-...702895408.html These puppies could make some seriously long and strong spars.
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Old May 05, 2014, 02:09 AM
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South Africa
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Thanks for the replies but getting carbon where i'm at seems to be a problem so i have to figure out a way doing it via what i have, which is light meranti type wood, i can cut a 2 meter piece of meranti and only use one doubler say 40cm long in the middle, would that be enough ?

i don't think a coro i beam will be strong enough.
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Old May 05, 2014, 05:03 AM
Crash Test Dummy
Brunei, Brunei-Muara, Masin
Joined Nov 2013
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We have Meranti here too - I played with it (I'm a woodworker), but it is heavy and if you cut it small enough to be light, is brittle.

Getting carbon tubes in SA is a problem? You make them there: http://grptubing.com/

I am making a 48" wing with 2mm coro as its only material, apart from a couple of pieces of polystyrene foam used as filler. It is traditonal spar/rib construction and hot glued together. It's taking longer than I thought as gluing it is proving a little problematic, but I am working through it. If it all goes to sh*t, I am out $2.50

The spar is a laminated piece of coro with spanwise and chordwise laminates - it's light and strong, but whether it is rigid enough in flight remains to be seen.

I should have it done in the next couple of days and will do some static deflection tests, I'll let you know if you want.
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Old May 11, 2014, 02:40 AM
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South Africa
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Thanks Mike,

i mailed to the place you posted, have yet to receive a response, guess with all these public holidays we've been having over here, response will take a while, but anyway, i can see them asking me an arm and half a leg for that carbon, that is why i'd like to get it doing the spad way.. ie CHEEP, so..... i guess i'm going to take the gamble and use a one piece 2 meter meranti spar and just use a 50cm doubler in the middle. i hope it works .... I think a coro spar would not be stiff enough, but i have never built one before so aren't the expert on that.
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Old May 17, 2014, 02:15 PM
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Ok i think i found the answer but am just not sure how to apply it. please help me out with this idea guys for it's the simplest shot i've got at strengthening this wing, ie it must work... Somehow ! !

After researching dozens of posts on the net i found that some of the foam flyer guys use packing tape or fiber reinforced tape to strengthen their wings, i'm very positive that this should work if i apply it correctly, question is:

how do i wrap it, should i perhaps build the wing and then afterwards wrap the tape spanswise from spar tip to spar tip (ie over the correx)

Or should i wrap the spar first spanwise with the tape a couple of times then add the spar to the correx wing sheets and then only fold over the correx sheets to make the wing, my thinking is if i wrap the tape over the spar first then only stick the spar onto the correx, it seems to me like the only think that the correx wingsheet will be sticking to is off course the tape wrapped spar.

And of course the tape is only sticking to the spar via its own adhesive, that is why i'm thinking perhaps putting the tape over the wing spanswise where the spar is located, but over the whole wing (ie correx sheet already folded and glued stationary onto the wooden spar.)

What do you guys think, it seems like the foam guys is having success using the tape, i definitely think it will add strength to the correx wing but how should i do it ?
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Old May 17, 2014, 09:16 PM
Crash Test Dummy
Brunei, Brunei-Muara, Masin
Joined Nov 2013
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I don't think tape would work on a coro wing. The way tape works with foam is by laminating a tough skin to the fragile foam which cuts down on the wing deforming. Coro already has a really tough skin - much tougher than reinforcing tape.

When we move house/country, I pack my fragile stuff in bubble-wrap, then wrap that in kitchen plastic film. The bubble wrap doesn't really do anything on its own - glasses will still break, it just adds a cushion. Adding kitchen film around that makes a really tough bubble that will withstand a lot of abuse - I have dropped a wine glass onto a tile floor wrapped this way and it just bounced. Adding tape to a foam wing is the same idea. Try it - get a piece of bubble wrap, wrap it round something (doesn't need to be fragile) and bang it - then add kitchen film and do it again, you will see what I mean

If you are trying to engineer lateral flex out of the wing, a rigid spar is the only answer. If you are trying to engineer chord-wise (don't know the right term) flex out of the wing, then ribs or some sort of reinforcing inside the corrugation is the answer.

I have a bunch of 3mm ply - I have played around with laminating pieces of that and it works great. As a ply, it's a bit crap - it's only 3 layers and the outer ones are more for show than strength, but it's light and easy to work.

You don't need to laminate the whole length of the spar - just at the joins. You need to cut so that the two outer surfaces of the ply have the grain going spanwise and the reinforcing/joining pieces 90 deg to that.

You only add reinforcement where you need it, therefore keeping the spar light. You can add some 'nocked' ribs to hold the spar in place - these can be made from laminated blocks of coro - I use 3x pieces of 2mm coro glued together, but you may not need them, depending on how your wing is constructed.

And the drawings aren't to scale, just to illustrate the idea Quick and dirty Sketchup...

So, no joy with the local carbon tubes?
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Old May 17, 2014, 09:24 PM
Crash Test Dummy
Brunei, Brunei-Muara, Masin
Joined Nov 2013
130 Posts
Just another thought - if you use ply, once you have laminated your joints, you can drill holes and insert a dowel or similar to strengthen the join - it can also act as something to tie things to or as a stabiliser for the spar, if you need it.

Obviously don't use a dowel that means the hole compromises the strength of the spar - you can use anything, it doesn't have to be a woodworking dowel - multiple bbq skewers works just as well to prevent twisting forces on your joints.

I would use epoxy. I know most people use 5 min epoxy, but I have a couple of litres of marine epoxy and find that works great, you just need to stabilise the joint while it dries and it gives you lots of time to work and wipe off, unlike 5-min

You can also laminate fabric to the ply using epoxy to act as reinforcement- use a polyester cloth with a tight weave - something sheer. I would thin the epoxy and paint it on just like doing fiberglassing, but much lighter.
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Old May 18, 2014, 02:34 AM
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South Africa
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Hi Immike thanks for the info, the design of the wing is really straight forward,

a single straight 2 meter spar with correx folded over,i understood what you said about the wing skin and that the tape won't work with the skin, however at some stage the corro skin will be stressed to a point where it will tear, so i feel the tape should at least add some strength, anyway besides using it on the skin the skin, i'm thinking of span wise wrapping the spar without using separate pieces ie, put the tape on the spar spanswise but wrapping it 4 to 6 times ie that would be 4 long 2 meter wraps without cutting the tape, sort of "lock in the spar" via the tape,

i have found that tape, even just the general normal packing tape is extremely tough to break as long as there is no tear in it it is practically impossible to try and break it by hand no matter how hard you pull.

I get that you are saying adding single layers on top and bottom of the correx skin, might not be the best way to do it, although i certainly think it would add some strength, but perhaps adding the tape directly to the spar as i just described by fully enclosing it spanwise in 6 or so long spanwise wraps, then folding the correx over the enclosed spar afterwards could work well.

Or spanwise wrap the whole wing afterwards at the area where the spar is located in the wing 6 times or so, it might not work pretty, but if enclosed in 6 or so wraps i feel that it could possibly work.

Nope, no luck with the carbon, those guys did not even bother to reply.

O thanks for the doubler advice, yes i only have a weak spot in the middle as the spar is tapered joined in the middle so i think then i will only add a doubler in the middle perhaps 50cm or so long, in conjunction with the wrapping method described above of fiberglass tape i feel it could work.
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Old May 18, 2014, 03:30 AM
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