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foam/Polystyrene wings

looking for advice on building a Polystyrene wing

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Adrian Day16/03/2013 21:45:56
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351 forum posts
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have made a foam/Polystyrene wire cutter..today and wanting to make a simple light weight model wing ... can anyone tell me if this Polystyrene would be any good for this application ??? Polystyrene from Wickes .... be grateful for your help
Regards Adrian

David Gilder16/03/2013 22:10:42
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Adrian.

Its not virgin bead but I have used this with my hotwire for fuselages and it is good enough.

it will need a very gentle sanding after but should be good enough (as long as your veneering the wing!)

Davewink

Adrian Day16/03/2013 22:41:19
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351 forum posts
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thank you Dave for your fast reply
sounds good to me... if its worked for someone else it may just work for me

its just going to be used in 600mm lengths and going to have 4x4mm spruce spar... then coated with a 1 mm balsa veneer .. ... do you think that will be strong enough ?

thanks for the advice again.. what grade sand paper??
Regards Adrian

David Gilder16/03/2013 23:18:29
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1859 forum posts
673 photos

Adrian, The foam itself doesn't have any stuctural strength. it is the veneer that makes it strong!

Regarding the spars, I would be tempted to go for spar top and bottom if your only going for 4mm!

Apart from that, It all sounds fine.

Let us all know how you get on!

laugh

Adrian Day17/03/2013 00:52:22
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351 forum posts
101 photos

i have some 6x6 if that would be any better? i have a lot of 4x4 and 6x6 that i can use.. what would you suggest
was only going with the 4x4 for lightness that's the only reason i was going to use it but if you think thicker would be better will go with that??

will keep you posted on how it goes 
thanks again
Adrian

Edited By Adrian Day on 17/03/2013 00:56:30

David Gilder17/03/2013 01:16:27
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1859 forum posts
673 photos

Adrian,

It really depends on what style of model really as to how much strength the wings need.

Guessing from the wingspan, you looking to make a parkflyer / 3d hack so the model will be thrown around a bit as apposed to a glider that has less loading on the wings.

Thats the only reason I suggest a slightly thicker spar top and bottom,

Are you having the wigs detachable individually or are you planning to make them into a 1 piece wing? This also has a bearing on the spars. If your using a joining spar through the fuselage and into the wings then you will already have extra strength built in from this near to the root and could get away with 1 full length spar top and a 1/2 length bottom spar from end of joining tube to nearer tip.

Its mainly trial and error and initially depends on the type of flying the model is expected to have to endure!!

Sorry if this complicates things!

Oh. It is possible with foam veneered wings of smaller size, depending on whats needed, to not even need a spar!!surprisecrying

Steve Hargreaves - Moderator17/03/2013 18:06:38
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All the foam wings of my experience (Wot 4s etc) don't have any spar at all....just the veneer covering (usually obechi). They are what is called a "stressed skin" structure.....

For 600mm span I'm sure just a layer of 1/32 balsa will be more than adequate....

How do you intend to fix the balsa to the foam? I'm sure I can remember reading about people using slightly thinned Copydex glue to fix the wing skins....

dbflyer17/03/2013 18:33:09
51 forum posts
1 photos

You don't need any spars in a foam wing of 600mm half span.

Adrian Day17/03/2013 23:37:31
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351 forum posts
101 photos

hello all sorry just got online been a busy day ...
Steve I was told to try using building PVA on them but i dont know just yet what to try ... never done them before been looking it up on you tube but not found anything that explains in enough detail.

David the model is a small light weight own design based around a model called the wasp but i have designed the tail and wings made some changes to the fuselage fitted a motor servos inside just have the wings to make.. going to make it a little 4 ch. mini sport. its going to have 1200mm span joined in the middle in the normal way.. its not going to be fast as working on the model coming in under 1lb auw on around 90w motor .. ...steve does this sound right ??? i know you know this area

thank you db Don't know to much about adding spars to foam wings i guessed it would depend on the thickness of the wing..

more input is welcome on this issue

regards Adrian


David Gilder18/03/2013 00:22:52
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1859 forum posts
673 photos

Hey Adrian.

Personally I would be inclined on a span of 1200mm to include a full length top spar.

2 ways to do this...

1. On your cutting templates, put in a spar cut out so when you hotwire the foam, you cut out the spar recess as you go.

or

2. Once the foam is cut out, using a very sharp blade and a steel rule, carfully cut out the spar rccess.

Personally I would go with option 1, as you will get a more consistant depth along the core for the spar!

Other than that, I understand that most people use latex glue for the sheeting! coat both the core and the balsa, allow to dry overnight, then line up and weigh down for another day to ensure a good adhesion.

a point to note, when you cut out the foam cores, keep the outer waste parts as you can use these to place the core in when gluing the balsa skins on without causing warping!

Hope that helps

Dave

Toni Reynaud18/03/2013 07:32:08
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424 forum posts
58 photos

A few more thoughts..........

On my Hercules and Hurricane, I used a single spar of 3mm x 10 mm hard balsa on the top of the wings. I cut the slot using a hot wire, made from a piece of the same wire as the bowand bent to just a smidgeon smaller than 3mm wide and 10mm deep. Use with a straightedge to cut the slot.

The wings were covered in brown paper using thinned PVA. However many years ago I used to use obeche veneer stuck on with Copydex, as you have heard. Thinned about 30% with water, cover wing and wood and allow 20 minutes to dry, and it acts like contact glue - make sure it's all lined up correctly before touching together! Nowadays some people are using Gorilla glue, but it has to go onto the wood VERY thinly, as it foams up quite a lot as it dries.

More clues here .

Have fun. Polystyrene is great for cheap and relatively quick and easy planes.

Steve Hargreaves - Moderator18/03/2013 09:53:40
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I have heard that PVA takes an age to dry when used in this sort of application...simply because its water based & the water takes an age to dry out...if ever!! How about this glue for sticking your wing skins in place!!! Coloured blue so you can see where you've been.....

What sort of model is it Adrian? High wing floater type or something a bit more sporty? If it weighs 1lb & you have 90watts from the motor then you have....90 watts per pound as your power to weight ratio.....certainly adequate for sport flying....wink 2

PatMc18/03/2013 11:00:25
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4427 forum posts
538 photos

Adrian,
IMO a veneered foam sports model wing of 1200mm doesn't need any spars unless it uses very thin section & is going to be subjected to extreme G forces but this is unlikey with a sports design. I've made a lot of foam wings using obeche or balsa skins wings & only ever used spars in a few 100" & larger competition thermal glider wings. These gliders had thin sections & the strain they had to take under tow is much greater than any powered aerobatic model wings would normaly endure.

Here's an article from a 1974 RCM&E that has some still useful tips on veneered foam construction. From experience I would only use the rolled LE on thick wings with a blunt LE section. Normaly I'd use 1/4" balsa LE & suitable thickness TE glued on after the wing panels had been veneered then plane & sand them to section.

BTW if you want a lightweight wing & don't mind an open structure look you could veneer only the front 1/3 and about 1/4" of the TE with 1/16" balsa. Then glue strips of 1/16" x 3/16" between in the place that ribs would normaly take on an open structure. This will give a light strong wing that looks like a conventional open structure when it's been covered & again no need for spars.

kc18/03/2013 12:19:06
6568 forum posts
173 photos

Some points not already mentioned

Centre joint in veneered wings is always fibreglassed or other similar if no spar is used.

The hot wire must not 'drag' or lag through the foam, very steady speed is needed to avoid a wrong profile. 2 person job - calling out the sections in order to synchronise speed.

Foam used in around 50 inch span models is 1 pound per cubic foot.

Adrian Day20/03/2013 00:56:54
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351 forum posts
101 photos

wow a lot to take in!
thank you all for your comments a lot to reply to, will get back to you all some time later today ... as just about to hit the hay .. been a long day .. made a power supply today for the foam cutter and tested it .. its a little cool for my liking but it cuts at a slow speed but clean .. will get back to you all soon thanks again Kind regards
Adrian

chris basson20/03/2013 09:51:58
168 forum posts
7 photos
Hi Adrian!
What have you used for your power supply? I'm planning to try some foam cutting, initially for a flying wing glider...

Another Question I have is, if there are imperfections in the wing when they are cut is it possible to fill them prior to skinning & is it okay to fiberglass straight onto the foam surface? If so will this be as strong as veneer or am I more likely to need a spar?

Chris
Adrian Day20/03/2013 20:33:06
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351 forum posts
101 photos

hi chris
the power supply is a computer power supply use the red and black wires as they are 12v the yellow is 5v and to start it you join the green wire to the black on the multi block that goes into the mother board... dont cut any others for some reason they dont work.. just the only thing i have found is that it only just works one 24" wire... i have also used a car battery charger that seems to work better and you can have a 30" wire .. so a little better

the second question
i cant answer i think that will be a god question for the other better wing builders.. i think from building car parts you can do it .. but not 100% sure

Regards Adrian

bren ocallaghan04/07/2013 16:49:57
1 forum posts

www.craftfoam.co.uk Is a very effective and versatile material for this sort of modelling as it allows you to be flexible with your build. Been on the site and they give out some good nifty hints and tips too which I wouldn't have thought of, but can be surprisingly effective!!

Bob Cotsford04/07/2013 21:45:13
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8628 forum posts
483 photos

Looks like what's commonly called blue/pink foam to me Bren, extruded foam has actually been around for a few decades now and is usually sourced from builders merchants.

Erfolg04/07/2013 22:24:46
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11780 forum posts
1340 photos

I am not convinced that spars are needed on even large wings, say 100" span.

George Stringwell, in his book Thermal Soaring, described how others inserted ply blades,these are used to distribute forces into a foam veneer wing.

Although it was or is common with IC modellers to use a bandage and resin to re-enforce the joint, at the centre. It is certainly not essential. Again the methods that were common with Thermal Soarers, can be easily be used to make a far neater joint. In some opinions far neater.

Edited By Erfolg on 04/07/2013 22:26:04

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