Fun Build 5 (?) Design - 51" Span Lancaster in Pink Foam or (gasp!) Depron - Page 2 - RC Groups
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Oct 24, 2011, 05:24 PM
Registered User
Originally Posted by Steve85

I've had a look at some nice Depron scale models, including Mike's Canadair Scooper and the aforementioned Sunderland by eflightray, and can feel a pull towards the Dark Side of Depron. To date, I've only used it for lamination forms, but I think I'll seriously consider building at least the wings from the stuff, and perhaps even the fuselage as well. I know this is straying further and further from the traditional confines of previous Fun Builds, but it seems like too much fun to pass up. I've been looking for tutorials or how-to's on building scale models from Depron without much luck, though. If anyone knows where to point me, especially for techniques to build compound curved fuselages, I'd be grateful.

Oh, and I changed the title of my thread...

If you really want to wander far off the beaten path, here are a few threads to look at:
and this one
and here:

All show the "laser method" for building wings. The method is very light and accurate. You can sheet with either foam or balsa. In my hands at least, sheeting with $tree foam and covering with brown paper is light and strong.

Same thing with the heat formed foam fuselages but that needs a more complex setup and it took me a few tries to get it working well. The Laser method is much easier than it looks.

I'm also waiting for the start of Funbuild 5 and hoping for the multi engine theme............

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Oct 24, 2011, 05:48 PM
Slip the surly bonds...
Sopwith Mike's Avatar
And now you have really interested me in the project

I scanned a very good 3-view of the Avro Lincoln at the same scale as your Lancaster, bringing it to 60" span and have put it on the back burner while I finish one or two things. I also thought 4 x GWS A motors and a 20A(?) speed controller, running off a 2-cell 2000mAh LiPo. I've heard that 3 cells is too much for these little motors and don't want to get involved in anything more sophisticated for this model. I would guess a flying weight of 35 oz, wing are about 2.25 sq ft, so a very reasonable wing loading.

Depron is so easy to work with that models go together really quickly. I use UHU Por as a contact adhesive for all the internal joints but aliphatic glue for the joins that will see a sanding block. The UHU is just too rubbery to take sandpaper.

One major limitation of D is that the very nice surface which takes acrylic paint so well is easily damaged and of course when you sand it all the surface is removed. Iit's difficult to get a really sharp edge (at the wing TE for example) and I use balsa strip at both LE and TE to make the wing look a bit better.

There are some techniques for moulding D sheet. They involve formers and ovens. Enough said. It's easy to put a permanent curve in D sheet by rubbing it over the edge of a worktop, but putting a compound curve in is more difficult and tends to look "starve horse". I use pink foam block in all 3-d areas, sealing the foam with acrylic furniture varnish and often using very light glasscloth on high stress areas such as flying boat hulls (although tissue paper works just as well).

I will try using GWS micro mechanical retracts for the UC and a steerable tailwheel, but rudders would just be too much trouble. The canopy cries out for a moulding - if I get there first I'll send you one, but I very much doubt that I will!

It's a great project and I wish you all the best. Needless to say, I'm sugned up.

Oct 24, 2011, 07:58 PM
It's a Great Day to Fly
LenBFP's Avatar
Go to GGRN's home here and click on all threads started by GGRN. There is a wealth of videos on working with foam.

Oct 24, 2011, 11:28 PM
The "pro" in procrastination
Steve85's Avatar
Pat and Len,

Wow, what a wealth of ideas and techniques! It's going to take me a few days to go over them all, but the "laser" technique looks especially interesting. I went out and bought sheets of 6mm, 3mm and 2mm Depron over the weekend, and have started working with it to get more familiar with its properties. I've cut a set of 6mm ribs for an outer wing panel as an experiment (don't worry John (if you're following!) I won't be using this panel in the build!), but have realized it's quite difficult to cut 6mm Depron exactly perpendicular to the sheet surface using an X-Acto knife. Most of my ribs ended up with a slight bevel to their upper and lower edges, so I'll have to carefully sand them to a 90 degree angle. I had thought I'd try cutting the next set with my scroll saw, but the laser technique looks like it would solve the problem.

I like the fuselage thermo-forming idea, and it would work really well with the Lanc fuselage, I think. I may not need to go that elaborate, however, and will probably try a more conventional Depron inner structure with a 2 or 3mm skin.

Mike, your Lincoln sounds like a winner, and I'd welcome the opportunity to commiserate with you on a concurrent build! I've had good results with IPS A drives on 3s, especially with GWS 7x6 props. That combination draws about 2.25 amps, which the motors tolerate well, and produces almost 7 ounces of thrust at wide open throttle.

Oct 25, 2011, 04:28 AM
Slip the surly bonds...
Sopwith Mike's Avatar
Hi Steve,

Cutting D is quite different from balsa and I often have to resort to a sanding block to keep the edges right. We just are not used to holding the knife blade perpendicular, I suppose. I like the crisp sound of a new blade in D in the morning.

I find I have to sand off the sheen on the surface of sheet to get glue to stick properly.

I'm going to stick with the sheet sides/foam top method but some time I'll try the moulding method (when I have the house to myself for a few days, perhaps!)
Oct 26, 2011, 01:58 AM
It must have a machinegun
Scaledown's Avatar
If the compound curves are fairly gentle (as they are on most of the Lancaster fuselage) you can just use a separate piece of 3mm from former to former. The shape becomes a series of chords rather than a true curve, but when its painted matt you can hardly notice. Alternatively if you plan to skin it with brown paper or tissue you can use 6mm and sand it down at each joint.
I often mix and match depron and balsa, like using balsa ribs and spars and a depron skin.
Oct 26, 2011, 04:46 AM
Slip the surly bonds...
Sopwith Mike's Avatar
Originally Posted by Scaledown
I often mix and match depron and balsa, like using balsa ribs and spars and a depron skin.
For my two 48" Depron twins I used a 3-ply spar of 6mm D strips epoxied together, thinning out towards the tips to 2-ply then a single ply. The epoxy doubles the strength, the wing skins (glued with UHU Por) lock the whole thing solid. The Scooper had some anhedral at rest after a while, but the Islander is still looking good.

With four motors and more mass outboard I might use a balsa spar with bass strips in an I-beam set-up instead. Good thinking Scaledown.
Oct 27, 2011, 06:06 AM
It flew once before...
jofrost's Avatar
Originally Posted by Steve85
(don't worry John (if you're following!) I won't be using this panel in the build!), Steve

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