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Hollow moulded wings...anyone tried to make?

Old 03-20-2004, 12:11 AM
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Default Hollow moulded wings...anyone tried to make?

I've played around with foam cut /fibreglass wings (xc-sailplanes) with a measure of success,
but with the performance and weight of hollow moulded wings...seems like the next logical step.
However, cnc'ing a block of alluminium for a one-off mould seems (read = $$$) a bit much for personal pleasure.
Has anyone tried, or have links to, using the off-cut saddles from foam wings to act as the moulds.
My thoughts about it are: frame the saddles in 1/4 inch wood for rigidity. Glue and vacuum bag mylar
onto the "negative" or mould surfaces. Then the choice is up to you for what you want to make the wing skins from.
Hope these aren't the ramblings of an epoxybased psychotropic halucination. [sm=bananahead.gif]
Anyone???
Old 03-20-2004, 12:23 AM
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Default RE: Hollow moulded wings...anyone tried to make?

The cut off foam sections will need a lot of surfacing work, but what they really lack is a perimeter flange section, where you can attach the vacuum bag, when laminating your skins.

Best to construct a plug, or form that will duplicate your final wing and surround it with the form for a bagging flange, then build your upper and lower molds off that combination of surfaces.
Old 03-20-2004, 12:52 AM
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Default RE: Hollow moulded wings...anyone tried to make?

I think the better way to do an hollow core wing is to do a plug of your wing and make an epoxy female moulds of it, vacuum bagged the skins, glue internal structure and close the moulds. Open it and you will have always the same wing.
Marco Vergara.[img][/img]
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Old 03-20-2004, 10:38 AM
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Default RE: Hollow moulded wings...anyone tried to make?

!0 year old mold but, something like this still works.

54" span corsair wing I fly.
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Old 03-20-2004, 10:39 AM
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Default RE: Hollow moulded wings...anyone tried to make?

Finished wing
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Old 03-20-2004, 01:04 PM
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Default RE: Hollow moulded wings...anyone tried to make?

Geeze guys, those are great pics and some great advice.
Many thanks.
Mel...could you explain a little bit more about the perimeter flange.
Is that like a hinge? for the top and bottom?? or am I missing the point.
I am going to give my idea a try at least and will happily post pics of the
process,,,,,good or not.
thanx again.
Ray
Old 03-20-2004, 01:25 PM
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Default RE: Hollow moulded wings...anyone tried to make?

The perimeter flange is simply a flat extension around the plug, which allows the mold to have a similar flat area, where the vacuum bag can be easily attached.

This photo shows the vacuum seal tape in place, before applying PVA and primer, at the start of the laminating process.

If you aren't planning on bagging the laminates they will tend to be almost twice as heavy as you'd like. Heavy wings have a reduced performance capability.
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Old 03-21-2004, 05:46 PM
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Default RE: Hollow moulded wings...anyone tried to make?

ORIGINAL: Cloudbase

Geeze guys, those are great pics and some great advice.
Many thanks.
Mel...could you explain a little bit more about the perimeter flange.
Is that like a hinge? for the top and bottom?? or am I missing the point.
I am going to give my idea a try at least and will happily post pics of the
process,,,,,good or not.
thanx again.
Ray
You can just make a normal cored wing, and then just melt the foam out with acetone. This is a good method if you just want to make a single wing, although pointless if you are going to make many of them.

--Alex
Old 03-22-2004, 02:27 AM
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Default RE: Hollow moulded wings...anyone tried to make?

Ray here's alink to how I prototype my moulded wings:

http://www.rcgroups.com/forums/showt...threadid=93873

Sorry about all the other stuff there, it's a full constr. thread for a small electric ducted fan model. When I want to proof a new design I make up quick moulds by sandwiching blue foam in between 1" MDF which is cut about 1" larger all around (BTW, the blue foam is the planform of the wing minus a bit for a balsa LE plus 1/8" for a TE extension). Now drill clamping holes thru the whole lot to pass bolts thru later on when joining the upper and lower skins. Then I cut the foam core as per normal. Around the edges of the foam I glue 1/16" ply to stiffen things a bit. Next I laminate glass skins on a sheet of plate glass. What layup you use depends on the size of the wing, for a 60" span scale wing I might use 2 layers of 3oz glass. If you have the weave at 45deg it will bend inside the front curvature a bit better. When the glass skins are well and truly cured (I add black pigment to the epoxy and put it in the sun to cure) sand the exposed surface before you release it, and degrease it with acetone. Then release the skins and cut them to size and epoxy them into the saddles using the offcuts (ie wing shaped bits you would normally use) and some 1/4" thick sponge type foam, overlapping the edges by about 1/8" or so, which will be sanded flush afterwards. If you like you can give the ply edges and the MDF a coat of epoxy to seal them as well. BTW, don't vac bag these skins - by using the offcuts you introduce curvature in one plane only, vac bagging will introduce a wavy surface. Your mould is now done. Polish, wax and PVA it per normal moulds, and spray a coat of grey auto primer onto it's surface. I always layup over primer, as the epoxy sticks to the slightly porous primer much better than primer will ever stick to epoxy. It also fills any scratches etc that may be in the mould surface, so that your mould doesn't have to be mirror finish perfect.

Here's where I do things different to most. I don't vac bag my wing skins. I use the offcuts and some plastic freezer go-between stuff and some 1" sponge foam and clamp the upper and lower moulds together. The foam squashes down, the offcuts provide the form for the foam to squash against, and the plastic freezer stuff stops it all sticking together. I lay the glass into the mould, scrape the epoxy thru the weave with an old credit card, and place the balsa skins over it, with a few spots of masking tape to hold them in place. Assemble all the above stuff in the mould and use the holes around the edges of the mould to pass long 1/4" bolts and clamp the whole lot up real good. You don't need to try and squash the thing to death, but you'll feel when the foam has squashed almost completely.

Next day, pull it apart and sand & degrease the TE where the balsa skin stopped short by 1/4" and chamfer the balsa at the TE so that the upper and lower skins will join touching only at the TE. Here's another thing I do different. I use water based polyurethane floor sealer instead of epoxy for laminating the inner layer of glass. It's much lighter and cleaner to apply. It does need a day in the sun to fully harden, though (or a big oven at 40-50degC). Then you can add spars & stuff as per normal moudled wings and join them with a bead of filler along the TE and a few spots of filler at the LE (remember we're adding a balsa LE later, so the mould won't close up at the LE) to keep the skins the right distance apart.

Next day pull it all out of the mould, add the LE, shape it and wash off the PVA.

I can make one of these wings in about the same time it takes to make a normal foam wing and get it to the same finished stage, and I can make the second one much quicker!

I hope this helps!
Old 03-26-2004, 11:49 PM
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Default RE: Hollow moulded wings...anyone tried to make?

I just finished an experiment on this subject. I tee bar sanded a foam core for an 80" hotliner wing out of 4.5lb. last-a-foam. with root and tip templates made from Formica. Next I cut top and bottom skins out of 1/16 balsa. On a waxed formica table I laid down .014" mylar slightly larger than the wing planform. Mylar was waxed also. Next I put down one layer of 3oz. glass and squeeged Shell 862 with TETA hardnerinto the cloth. I laid on the balsa core and repeated with another layer of 3oz. glass. Next I laid the foam core down. On another table I did the same thing with the top skin except I put 2 mil. plastic (Menards, Home Depot) on the glass to separate it from the core. I next laid this on top of the core and bagged it all down. The next day i took off the top skin and hollowed out most of the core behind the D-box and left a little trailing edge foam. I sanded everything down to the final dimensions and bonded the together with about 3" - 5" of vacuum. The down side of this technique is you don't get the leaing edge under glass and you are limited to flat boom airfoils. The up side is it is CHEAP and FAST! If I were to do it agian I would put the plastic sheet between the core and the bottom skin also and not bond any foam in the wing. This wing came out heavier than I would have liked but it was fast, (no mold to build) and I now have a loading ramp for my pickup if it won't fly!
Old 03-30-2004, 05:56 PM
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Default RE: Hollow moulded wings...anyone tried to make?

That's a good start, Bruce! You can take it one step further, and wax a sheet of glass and layup the glass skin and vac bag the balsa skin to it. Next day peel it off and lay 3/4oz glass onto the foam core then the glassed balsa skin (glass outside of course) and bag it. The balsa will conform nicely and the glass gives a nice finish. You can even spray a coat of primer or colour coat onto the glass before laying up the glass/balsa skin. You'll need to add a basswood LE, or even just shape it from epoxy/microballoons.
Old 04-08-2004, 09:16 AM
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Default RE: Hollow moulded wings...anyone tried to make?

A while back we did a thread while actually building a hollow wing. The thread is 3 parts and pretty long, but you might get alot of what you are looking for out of it.

http://www.rcuniverse.com/forum/Comp...m_55779/tm.htm

Chris

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