Foam instead of Balsa?

[FiddleSticks]

Hi all,

 

Just wondering how practical it would be to build a balsa plane from foam instead? Went to Hobbycraft today and their balsa selection wasn't great but they got a bloody great pile of foam board - £4 per sheet or 4 for £12. Grabbed the 4 obviously lol. Plenty of little cheap designs on youtube etc for foam planes but i was just wondering if it's practical for the balsa designs that can often be larger. I don't think there's another balsa supplier around here and hobbycrafts prices were horrible!

 

Thanks,

 

FS

[Michael Barclay]

9 minutes ago, FiddleSticks said:

Hi all,

 

Just wondering how practical it would be to build a balsa plane from foam instead? Went to Hobbycraft today and their balsa selection wasn't great but they got a bloody great pile of foam board - £4 per sheet or 4 for £12. Grabbed the 4 obviously lol. Plenty of little cheap designs on youtube etc for foam planes but i was just wondering if it's practical for the balsa designs that can often be larger. I don't think there's another balsa supplier around here and hobbycrafts prices were horrible!

 

Thanks,

 

FS

It's possible to build from many materials. Just think outside the box and be prepared to experiment and sometimes fail.

[Eric Robson]

Tony Nijhus 72" Sunderland made from Hobbycraft foam board and B and Q 3mm depron. Plan was for balsa construction. Modified formers to allow for the thicker covering materials. Currently building a Me 109f details on this forum 

[Michael Barclay]

3 minutes ago, Eric Robson said:

Tony Nijhus 72" Sunderland made from Hobbycraft foam board and B and Q 3mm depron. Plan was for balsa construction. Modified formers to allow for the thicker covering materials. Currently building a Me 109f details on this forum 

Lovely job Eric. Have you flown it off water?

Edited October 27, 2023 by Michael Barclay

[Lipo Man]

The Flitetest “master series” can be built from hobbycraft foamboard. It’s heavier than the stuff they use in the USA so planes usually come out a bit tail heavy. Easily fixed - just use a slightly bigger motor and battery to get a little extra weight in the nose. Their P47 would be a good place to start - flies really well, and plans are free online. You need to remove the paper from one side of the foamboard for the curved pieces - a warm iron unsticks the paper. 

[Eric Robson]

48 minutes ago, Michael Barclay said:

Lovely job Eric. Have you flown it off water?

No Michael, to keep the weight down I have not even painted the white parts. It did get wet once when a shower caught me by surprise. It takes off easily from damp grass and has plenty of power so it could take possibly glassing on the hull but there are no lakes locally that would allow flying from

[martin collins 1]

One of our club members is building a Tony Nijhus Hawker Hurricane using Foamboard and depron, more or less following the original design but with mostly the alternative materials. Some structural areas retain wood for spars and motor mounting/retracts etc.

[SIMON CRAGG]

I started building from Foamboard at the start of the pandemic, and have gradually refined and modified how I use it.

 

So far from the Flite Test stable;

 

Versa

F22

Vulcan

Viggen

 

and at present a larger (40") Thunderbob.

 

They have all flown brilliantly, and the F22 is my go to model: RAPTOR    4S 1500    23.1OZ    64MM        60A    40.0A / 622W 

 

All are 5mm Foamboard apart from the Thunderbob which is mainly 10mm.

 

Brilliant material, which can be turned into great models. The F22 was £11.00!

[Mike Chantler]

I built an F86 from an old Ron Collins plan. I was a bit shocked by the price of the balsa so I replaced it all one-for-one with XPS foam sheet and sections, plus some 6mm carbon/foam sandwich in place of liteply formers. Took me quite a while to learn how to use and finish it as a) it dings really easily during construction, and some of the foam glues stay really rubbery which means they don't sand. Next time will cover in brown paper before glassing, and keep the glue very thin and use the stuff that dries hard.

 

[Glenn Philbrick]

Im thinking of building a couple of small electric foam models to get through the winter. What foam is considered easy to use, what adhesives are used and can they be cut with a laser printer? Lastly is there a thread about how to do it anywhere? 

Thanks.

[Graham Davies 3]

Lots and lots of stuff on here from various members who are really pushing the boundaries with what is possible using various foam products. I'm currently building a 1/6 scale Mk1 spitfire with flaps and retracts using the black laminate flooring underlay from B&Q. £28 for a massive pack. I have used the white Diall stuff too in both 3mm and 6mm. I don't use much foamboard now as it is heavier and the paper doesn't add a lot if you think carefully about the structure. 

 

For glue, UHU Por is good, used thinly and as a contact adhesive. I also use aliphatic resin, but it takes a lot longer to go off compared to using it on wood. Hot melt glue is also hand in certain situations, but is heavy.

 

The Flitetest website is a good place to start as it gives you lots of techniques and ideas. However, I never liked the 'lobster tail' appearance of the models so use different techniques that for me give better results. The materials are soft, so be careful handling them, and think about covering. I have used laminating film (not easy to apply to foam as you can't use too much heat, and need light pressure), brown paper and PVA which woks well, particularly when using a coat or two of water based varnish to give it a tougher 'shell', and the spitfire will be glass clothed using water based EZ coat.

 

Models are generally lighter, but you need to think carefully about the structure or they either end up weak in key areas (undercarriage!) or heavy. Eric, Martin Collins1 and others (including myself) I am sure would happily share the ideas they have used.

 

Here's a few of my foam squadron as an appetiser...

 

Graham

 

[martin collins 1]

My first Foamboard/depron build has a thread on here, you may find it helpful, my preffered glue is the Gorilla clear stuff which is foam safe, it takes longer to dry but dries hard.  Free plans to build the 109 are linked in the thread.

 

Edited October 28, 2023 by martin collins 1

[Glenn Philbrick]

Thanks for the replies, just what I need to get going.

[Simon Chaddock]

FiddleSticks

There are some differencins required to change from balsa to foam, not least is that foam is 1/10 the density, several times weaker in tension and compression and more flexible but to a degree this can be compensated by increasing the thickness used.

Obviously the really high stress parts can be reinforced with wood or carbon but this does assume you can identify where foam and with what thickness would be adequate.

It can pay to select a design that naturally has thick wings and a suffidiently bulky fuselage, like a Sunderland.

I have found even EDFs can be made of thin sheet foam particulary those of the 50's era with big wing root inlets that provide support to the high stress wing root area.

This Hawker Hunter (its the protoype) is made entirely from 5 mm B&Q laminate underlay foam. The nose cone is printed but otherwise there is no balsa or carbon anywhere, even in the wings.

It is not covered in any way. The bare foam is just carefully filled, sanded and painted with a water based acylic paint. Once dry the acrylic is fully shower proof.

The airframe is so light it only needs a 50 mm EDF and a 3s 1800mAh LiPo to fly very nicely. Easy to hand launch and belly land however a direct conversion of a balsa equvalent it is not.

ps Not a good idea to paint a RC plane pale sky blue overall even if the original was!  😉 

 

     

Edited October 28, 2023 by Simon Chaddock

[Michael Barclay]

21 hours ago, Eric Robson said:

No Michael, to keep the weight down I have not even painted the white parts. It did get wet once when a shower caught me by surprise. It takes off easily from damp grass and has plenty of power so it could take possibly glassing on the hull but there are no lakes locally that would allow flying from

That's a shame, Eric. Looks like it belongs on water. I built a Heinkel HE5 in Depron which flies beautifully off grass, but I did glass it, and will fly off water when the field floods. Best of luck. It’s still a nice build.

[Robin Colbourne]

There's a thread about the Paper Aviation Ezee Peezee, which was a 1990s  76"-ish span trainer typer model built largely from foamboard here Paper Aviation Ezee Peezee

 

Outerzone has a plan for an Ugly Stick -type model from cardboard, although it should adapt to foamboard too. 

Card Stick

[Fly Boy 3]

Hi all, when you build from foam, or depron etc, do you actual replace all balsa items such as for as, ribs, with these other materials or take a different approach. The wings for example will they need ribs etc, I have numerous plans of balsa models that could be converted, if only I know how lol.

 

[Eric Robson]

This is the way I have built my latest foam board and depron model. On some I just use a ply or balsa main sparand foam board second  spars. I have used depron and ply ribs the ply at the undercarriage mount point. It is 65" span and weighs 6.5lb ready to fly .

[Simon Chaddock]

Oldmanflying

The thing you have to remember is foam is about 1/5 the weight of balsa but it is also rather more flexible so it not a "like for like" substitution.

Ribs and fuselage formers can be thicker to compensate for  a lack of stiffness. Foam can make a good substitution a balsa skin as it can be quite a bit thicker yet still be lighter. The result is a surface better able to resist buckling better than the thin balsa.

 

The problem is a balsa plan will not tell you what thickness foam to use and where foam will not work. In Eric's example above he has used balsa in specific locations.

 

My own preference is to use thicker foam skins over foam ribs or formers so no further wood reinforcement is necessary except at motor or undercarriage mounts.   

 

[SIMON CRAGG]

Thunderbob is made from 5 and 10mm foamboard. Two ply joiners on wing and 1/8 carbon spar under tail which is rock solid. Brilliant stuff, it does take some getting used to though. I have now built 8 foamboard models and the fun for the £ cannot be beaten IMHO!.

[Nigel Heather]

13 hours ago, SIMON CRAGG said:

Thunderbob is made from 5 and 10mm foamboard. Two ply joiners on wing and 1/8 carbon spar under tail which is rock solid. Brilliant stuff, it does take some getting used to though. I have now built 8 foamboard models and the fun for the £ cannot be beaten IMHO!.

Hi Simon,

 

When you say you used foamboard are you talking about the stuff with paper lining either side or the stiff without paper (like depron)

[Simon Chaddock]

Hi Nigel

Foam board with paper on needs a rather different form of construction. Such foam board is pretty stiff with the paper on so either the paper has to be removed on one side to allow limited curvature or the construction has to be all flat surfaces. "Flight Test" have specialised in designing and selling a big range of designs and kits using their own specified foam board.

 

A Depron type sheet foam with no paper is of course lighter but more flexible than foam board so construction has to take the flexibility into account but can include an element of curved or even double curved surfaces. As a result the construction is more complex more akin to a conventional balsa type construction.

 

I use Depron foam sheet and tend to specialise in designs that require double curved surfaces that if necessary are achieved by using many narrow shaped planks. 

A properly supported double curved skin is considerably more rigid than a flat surface when using the same material but it does take longer to do.

Probably my most extreme example of this type on construction.

A scale EDF in 3mm sheet foam. Relatively simple flying surfaces but the body is a 3mm skin over 23 Depron 'ring' formers.

 

There is no internal structure other than to support the battery, ESC, servos and radio.

[SIMON CRAGG]

Nigel

 

Thunderbob was made of the type of foamboard that has a thin paper covering each side.

 

I got it from Amazon, free post.

[SIMON CRAGG]

Flite Test Voggen 5mm Foamboard

 

 

[Flyboy3]

Exellent information lads.  Thanks