Foam board Marutaka B25 Mitchell 71" span

[Eric Robson]

I started this model in April this year then the flying season started. I also had family coming to stay so the Mitchell was put away, Having just finished the Whirlwind and knowing that there is little hope of a test flight for a while the Mitchell build was restarted.

5mm foam board was substituted for 6.3mm balsa and the formers were adjusted to suit. This is the basic fuselage, instead of foam board for the upper and lower sides I has tried some of the Depron  look alike which B&Q sell it is easier than stripping the paper off the foam board.

[Eric Robson]

The wing is the same type that I have used on the other foam board models a flat bottom with no formers just spars from foam board and ply braces on the dihedral breaks.

The Mitchell has a Gull wing and supports were made for its assembly, unfortunately I accidently wiped out some of the build photos so these are all I have the 2nd picture is the stage I was at when it was put away

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[martin collins 1]

Great to see work on the B25 started again Eric, a B25 is on my list of foamboard models to do. I have an Aerotec International kit here which is a similar size, i will be using some of the parts for patterns for mine. Several other planes will get done before i get to this one though. Will watch yours with interest. 😊

[Ron Gray]

@Eric Robson the only foam board I can see at diy.com are the A4 sheets of 2mm?

[martin collins 1]

They sell several different types Ron, they do Vitrex in 5mm it is grey in colour and sold as an underlay, you need to look in that section. They also do depron sheets in the insulation section in 3,5 and 8mm this is white in colour. 

[Ace]

Ron, if you look for it at your local B&Q (diy.com) it usually gives the isle number?

Castleford W Yorks its isle 78

[Eric Robson]

Just a warning about the extruded polystyrene board from B and Q, it looks like depron but does not form as well, care has to be taken as it cracks easily. The 3mm is not too bad but it does not seem to have the grain that depron had, I tried a small piece to find out which way the grain was and it cracked  both ways cold, after gently warming it it went the way I wanted. The 6mm was used for the rudders and fuselage top in flat lengths and sanded to shape, this turned out ok but it is more reluctant to bending as I found out when my outside tap burst with the severe frost, it took a lot of heat to get it to go round the pipe which already had thick lagging on. 

[Eric Robson]

Covering almost done, The fins  are 6mm depron from B &Q after covering both sides with brown paper they are quite rigid. I covered one side and lightly ironed it then done the other side immediately,  then kept rotating till both sides were almost dry and after 12 hours the are still flat. On the 110 I did not do this and the fins distorted slightly.  

[Ron Gray]

Have you built with the grey Depron, just wondering if it’s any different from the white which I’m currently using (6mm sheets I bought 8 years ago!). 

[Eric Robson]

Hi Ron, 

The grey depron on the sides of the B25 is the last of the original depron Leeds model shop had in stock. I bought the last 3 sheets of 3mm some time ago, all the white had gone.

I don't know if it is psychological but it does not feel the same, I have been told it's only the colour that is different but it feels more rubbery than the white. The other thing is the white is easier to work with as the marking out is clearer.

Regarding working with the grey it forms just the same as the white, providing you get the grain right it forms cold ok, the fuselage on my 110 was wrapped with 3 mm depron no problem also my Seafury.

For some reason the early pictures won't upload but the 110 was clad in sections the joins on the top and bottom centre lines. 

[Eric Robson]

Ron, this is one of the photos of the Seafury build. I used a balsa frame work similar to a Brian Taylor build, foamboard formers and 3mm depron cladding.  You can see how well it forms round the lower side. It's messy when sanding ,black bits all over.

[Ron Gray]

Oh I don't know, the white is pretty messy when you sand that, I have to have a good wipe down before I'm allowed back into the house. At least with the black it wouldn't show as much! Anyway, I've just ordered 20 sheets of the 6mm (for our club build of the Hanky Planky) so I'll find out for myself how good (or bad) it is. As for marking, maybe a white pen? also do you prefer it to them Hobbycraft (paper faced) foam board?

Edited December 19, 2022 by Ron Gray

[Eric Robson]

Ron, I use both in a build I use the Hobbycraft board for wing bottom panels and formers I don't take the paper off and rough up the surface lightly where there is something glued to it. I have been using the American Maker foam for the wing upper surfaces, but it is hard to get a hold of now so when I run out of the sheets I have I will use depron or the B&Q  stuff.

On the grey depron a sharp pencil breaking the surface is a good way of marking, make sure there is no nicks on the surface in the vicinity of your mark, I found out the hard way

[Ron Gray]

Thanks Eric, I’m seriously thinking about building the Kestrel (Dec and Jan RCM&E) out of Depron although I may well cut my own foam wings (hot wire) rather than build them.

[Eric Robson]

How would you sheet the foam Ron?  I don't know if veneer is  easy to come by these days.   

[Ron Gray]

Laminating film directly on it!

[Eric Robson]

The only problem I see with that is the 8 wing attachment points, 

[Ron Gray]

Hard points epoxied into the foam

[Eric Robson]

I done hard points on a depron SE 5 and the struts went through the wings on a not too heavy landing, I laid strips of 1/16" ply  front to rear about 10mm wide to spread the load, it worked well lasted for ages.

[Ron Gray]

That sounds like a plan. I haven't really looked at it too much but I was thinking of 'pinning' the hard points with carbon rods running from the outer ribs on the mid section and the outer ones the same but one from the false TE and the other as a spar extension. Like I say I haven't yet got my thinking cap on! 

[Ron Gray]

Just been looking at my delivery of 6mm Depron (grey). Apart from the colour it seems to behave just like my white sheets, same sort of flex and cuts the same. I haven’t sanded any yet but looking good so far, just a shame that the sheets aren’t bigger (625x800). 
 

Wow that’s a shock, just went back on their website and the price has gone up from £48 that I paid yesterday to £60! Still cheap at £3 a sheet.

[Eric Robson]

Hi Ron, I would make the wing in one piece and use ply hooks on the main spar position with retaining bolts at the rear and quick links on the struts to attach to the fuselage. I am not keen on using tubes in foam for wing location, I tried it on an Aerotech P38 outer wing panels but after a while they became sloppy in the polystyrene foam. The Black Widow I have has built up wings and the outer panels are as firm as the day they were made. 

I think people are taking the pee at the moment with prices I looked on one site foe polystyrene foam ( it was a modellers site) and the were asking £94 for pure white foam 1200mm sq. 80mm thick. Another has the Seagull Mosquito at £950 just the same stock model as Kings Lynn MS have at £499 that kit was about £300 last year.

The 6mm Depron did behave in the same way on the grey and the white but the 3mm did seem different. 

[Ron Gray]

37 minutes ago, Eric Robson said:

I am not keen on using tubes in foam for wing location, I tried it on an Aerotech P38 outer wing panels but after a while they became sloppy in the polystyrene foam.

The plan is to use Phenolic tubing so the female part will be glued in place.

[Eric Robson]

I used aluminium 12mm telescoped with both epoxied in to the wings and ply facings on the ends

[James Green2]

I do quite like this B&Q foam board. I am just finishing up the HT on my Typhoon and it is made of 2 laminations of the 9mm sanded to a reasonable aerofoil shape. I used Copydex to join the sheets together as it seemed a bit wasteful to use POR. It seems strong enough now dry. The issue I have is finding any brown masking paper to cover it with. Tool Station are out of stock in my area. I have some lighter brown paper, but this has a ribbed pattern to it. The heavier stuff I have does not have gloss on one side. I guess I have to experiment. Thanks James.