Adrian Day Posted March 16, 2013 Share Posted March 16, 2013 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 Quote Link to comment Share on other sites More sharing options...
David Gilder Posted March 16, 2013 Share Posted March 16, 2013 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!) Dave Quote Link to comment Share on other sites More sharing options...
Adrian Day Posted March 16, 2013 Author Share Posted March 16, 2013 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 Quote Link to comment Share on other sites More sharing options...
David Gilder Posted March 16, 2013 Share Posted March 16, 2013 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! Quote Link to comment Share on other sites More sharing options...
Adrian Day Posted March 17, 2013 Author Share Posted March 17, 2013 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 Quote Link to comment Share on other sites More sharing options...
David Gilder Posted March 17, 2013 Share Posted March 17, 2013 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!! Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted March 17, 2013 Share Posted March 17, 2013 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.... Quote Link to comment Share on other sites More sharing options...
dbflyer Posted March 17, 2013 Share Posted March 17, 2013 You don't need any spars in a foam wing of 600mm half span. Quote Link to comment Share on other sites More sharing options...
Adrian Day Posted March 17, 2013 Author Share Posted March 17, 2013 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 Quote Link to comment Share on other sites More sharing options...
David Gilder Posted March 18, 2013 Share Posted March 18, 2013 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 Quote Link to comment Share on other sites More sharing options...
Toni Reynaud Posted March 18, 2013 Share Posted March 18, 2013 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. Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted March 18, 2013 Share Posted March 18, 2013 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.... Quote Link to comment Share on other sites More sharing options...
PatMc Posted March 18, 2013 Share Posted March 18, 2013 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. Quote Link to comment Share on other sites More sharing options...
kc Posted March 18, 2013 Share Posted March 18, 2013 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. Quote Link to comment Share on other sites More sharing options...
Adrian Day Posted March 20, 2013 Author Share Posted March 20, 2013 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 Quote Link to comment Share on other sites More sharing options...
chris basson Posted March 20, 2013 Share Posted March 20, 2013 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 Quote Link to comment Share on other sites More sharing options...
Adrian Day Posted March 20, 2013 Author Share Posted March 20, 2013 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 Quote Link to comment Share on other sites More sharing options...
bren ocallaghan Posted July 4, 2013 Share Posted July 4, 2013 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!! Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted July 4, 2013 Share Posted July 4, 2013 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. Quote Link to comment Share on other sites More sharing options...
Erfolg Posted July 4, 2013 Share Posted July 4, 2013 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 Quote Link to comment Share on other sites More sharing options...
Shaunie Posted July 4, 2013 Share Posted July 4, 2013 In my first modelling career 20 years ago there were loads of models with foam wings, obechi veneers and no spars. One I built was the Masterline Vandal about 54" span and I put a Super Tigre 61K on the front with a tuned pipe, the wing strength was never an issue (2" bandage at the root). I built my own foam cutter from 20mm steel conduit bent into a hacksaw frame shape, PCB fibreglass insulator one end and used 0.8mm stainless m.i.g welding wire as the element. One improvement I never got around to making was putting a pulley at one end and then having a strong spring to set the wire tension. The reason I wanted to do that was to keep tension constant as the wire heated up (the wire temperature tends to increase as the wire goes into the foam) which tends to either make the wire sag or go extremely tight when the wire cools down when switched off. It got lost in a house move unfortunately and I never got round to building another one. Shaunie. Quote Link to comment Share on other sites More sharing options...
Olly P Posted July 10, 2014 Share Posted July 10, 2014 I know I am resurrecting an old thread, but seemed to be worthwhile. I have found a supplier of Foam on ebay, but he has various densities, from 10-12g./ltr, 15g/ltr, 20g/ltr, 25g/ltr and 30g/ltr. I think the lightest grade should be sufficient as the majority of the strength will come from the spars and 1.5mm (1/16) skinning that I'll be putting on. Has anyone got any experience with the various grades/densities of the foam? Thanks Olly Quote Link to comment Share on other sites More sharing options...
Steve Dunning Posted July 10, 2014 Share Posted July 10, 2014 If you look at the UKCAA section, you will know that I have been producing foam wings for many years. I sometimes get asked if I have any obeche veneer for sale. I tell them that I cannot remember the last time I used veneer. As for foam suppliers, I obtain mine from Custompac in Castleford, using the 10kg/cu.m density, the lightest they produce. As foam is produced using steam, the blocks need to be left for a while, un-packed, to allow any moisture to evaporate off. I square the blocks off (level along the large side) to ensure they are true before cutting. As I use a Step 4 CNC machine, this is easy to achieve. With this system, no templates are required. Getting back to the original question, after cutting I use 1/16th balsa, This gives a superb finish and is stronger than veneer. The skins are applied under vacuum on a veneering table used by carpenters to apply veneer. I hope that gives you an insight Olly, hope you have success with your wing cutting. Steve D Elation Model Products Quote Link to comment Share on other sites More sharing options...
TigerOC Posted July 11, 2014 Share Posted July 11, 2014 I have made a few glider wings recently which are 60". Ordinary polystyrene is much lighter than XPS and cuts well. I surface fill the wing with the very light weight filler and then sheet with 1/32 balsa using polyurethane glue in a vacuum bag (domestic). I finish the wing with 0.6oz fibreglass cloth using WBPU and re-enforce the wing joint with extra layers of the same glass cloth. The last wing I made I weighed through the process and applying this fibreglass layer using WBPU added a mere 18g. The whole wing weighed only 355g before covering. I have found the standard covering adds huge weight (200g) and am now spraying the wings which gives a better finish and is lighter. These wings are very strong and show little or no flex in use. Rob Edited By TigerOC on 11/07/2014 09:04:49 Quote Link to comment Share on other sites More sharing options...
Olly P Posted July 11, 2014 Share Posted July 11, 2014 Thanks guys. Having checked wing sizes, the stuff on eBay will be a little small, so I'm now lookng at custompac as recommended above. next is to do the CAD work to allow me to make templates....that'll be a while away... Quote Link to comment Share on other sites More sharing options...
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