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        Discussion Fun Build 5 (?) Design - 51" Span Lancaster in Pink Foam or (gasp!) Depron

#1 Steve85 Oct 16, 2011 09:30 AM

Fun Build 5 (?) Design - 51" Span Lancaster in Pink Foam or (gasp!) Depron
 
Hey Everyone,

I've been pretty scarce on these pages lately, mostly because we moved from Ottawa to Kingston this summer, and there's been a buttload of stuff to do. We're finally settling in, and although setting up my workshop hasn't yet floated to the top of the priority list, I think I finally have time for a little bit of hobbying.

John (jofrost) mentioned in the context of last year's Fun Build 4 that this year's theme might be multi-engined birds, so with that as inspiration, I've started thinking about what my entry might eventually be. I've wanted to try some of the foam-building techniques in Sparky's "Building with Foam" book for a while now, and foam seems like a lightweight way to build a smallish multi with a low enough wing loading so that it doesn't have to fly around a fighter speeds just to stay airborne. I don't know if John will allow foam in the next FB, but I'm going to give it a try.

In anticipation of FB 5 launching, and it having a multi-engined theme, I'm going to try designing and building a 1/24 scale foamie Lancaster for IPS motors. This scale puts the model at 51" wingspan, with 2.25 square feet of wing area, so I think that if I can keep the AUW to 22-23 ounces, I'll end up with a bird that should have scale flying characteristics, ie. slow and majestic. I honestly don't know if this can be done, but it'll sure be fun trying!

I Googled around to see if there were any plans available that might be useful, and as luck would have it, someone was selling a copy of the June 1987 Model Aviation article and plan of Dennis Norman's amazing 51" span rubber-powered Lancaster, so I snapped it up. Dennis' design is an engineering marvel, and the plan has a large number of formers for the fuselage, inner and outer nacelles. I'll be using them as cross-sections for my foam version. The wing uses cracked rib construction, however, so I'm going to be on my own in terms of finding a suitable airfoil.

So, on to the first of what I'm sure will be a million questions as I work up the design: can anyone suggest an airfoil for this model? I'm looking for a relatively thick airfoil (for scale appearance) that has good low speed lift and a gentle stall. Thanks in advance!

Steve

#2 Martin Irvine Oct 16, 2011 10:33 AM

Hi Steve:

A Clark Y or a NACA 2400 or 23000 series would be my choice. You can figure out the thickness from scale drawings and plug in the percentage. Do you have Profili? It will do ribs for a tapered wing quite well.

Martin

#3 Richard Woods Oct 17, 2011 04:55 AM

Quote:

Originally Posted by Martin Irvine (Post 19607951)
23000 series would be my choice.

Which is about as scale as you can get; what with the bomber itself using NACA 23018 at the root going to 23012 at the tip.

#4 Steve85 Oct 17, 2011 02:44 PM

Thanks, guys. I do have Profili, and I'll see if the NACA 23000 series is in its library tonight. I did a bit of Googling on the series, and as long as its characteristics scale down, it looks like the answer.

Steve

#5 DingoII Oct 17, 2011 03:10 PM

Steve,

If I may interfere here - I would stay away from 5-digit NACA airfoils, they have prety nasty behaviour in model scale. NACA 4-digit range is much better choice IMO, still I would prefer Eppler E205.

Looking forward to your build :)

Jan

#6 Martin Irvine Oct 17, 2011 10:39 PM

Well, I've had good luck with the 23012 airfoil in the 45-80" range.

Martin

#7 DingoII Oct 18, 2011 12:10 AM

No problem at all, I just happen to have a "red light" on 23xxx.

Jan

#8 LenBFP Oct 19, 2011 06:35 AM

Subscribed. :popcorn: I hope funbuild 5 is multi engine. This could be fun.

Len

#9 jhspring Oct 19, 2011 06:48 AM

Really looking forward to this one Steve. Subscribed. Jeff

#10 mrdj Oct 19, 2011 05:50 PM

Moving puts a big dent in model building. I finally have a basic desk in my new digs. Great subject, what markings will you use?

DJM

#11 Scaledown Oct 20, 2011 12:02 AM

I built a Halifax using IPS clones a few years back. Its got a reasonably low flying speed and handles flawlessly. I think I used a clark Y. Wing loading is of course the key to slow flight. Its all open framework except for the top and bottom fuselage which are curved 1/32 sheet, and a foam nose.

#12 Steve85 Oct 20, 2011 08:03 AM

Hey guys,

Thanks for all the interest and input! It turns out that Profili has the ability to generate a NACA airfoil just by inputting its numerical designation. The NACA 23012 tip airfoil was already in Profili's library, and I was able to quickly generate the NACA 23018 root airfoil using this handy feature.

I'm still doing a lot of reading to bone up on foam wing-building techniques, and have yet to decide if I'll cut a foam core with a hot wire, or use Depron and build up a wing like eflightray did for his magnificent Sunderland. I might even try an outer wing panel using each technique to get a better idea of their relative strengths and weights. I'm leaning toward a fiber glassed skin for hangar-rash resistance, but this may be a luxury the weight budget won't be able to afford. The fuselage will be pink (or blue) rigid foam insulation, either carved and sanded or hot wired, with a skin of 3/4 oz glass.

As for markings it's still early days, but it will definitely be a Bomber Command scheme, no doubt from an RCAF squadron in No. 6 Group, and possibly Lancaster Mk X KB726, code letters VR-A, in which P/O Andrew Mynarski won the Victoria Cross.

Ah, it's good to be back...:)

Steve

#13 Scaledown Oct 20, 2011 08:22 AM

Its really hard to make a bomber fly like a bomber and not a fighter unless you are ruthless with the weight saving. Fibreglassing isn't ruthless.
I built a wing recently that had a 2mm depron skin. I've even put an electric planer over depron to create 1mm depron (albeit for a small plane). I think the only thing lighter would be an open structure from balsa.

#14 Sopwith Mike Oct 20, 2011 09:12 AM

I'll second all that's been said about weight being the key to good performance. A 51" Lanc will never fly at scale speed, but you will have a lot of fun with the model.

I've just finished a 48" span depron BN Islander (designed to take to pieces and go in cabin baggage) which weighs 25 oz. Take off 4 or 5 oz for a one-piece model and dispense with the moulded cowls and 20 oz is a reasonable target for this size of plane.

I would strongly recommend a Clark Y or E205 over any other airfoil for this size and weight of model. In fact, have you considered using 6mm depron as a flat plate airfoil (curved over to mimic the top of Clark Y section). This gives a very light and strong wing but of course it will look non-scale from underneath.

A 3mm depron lower skin, 2 laminations of 6mm depron for the spar with a few 6mm ribs and a 3mm top surface will give you a very strong and rigid wing with enough room inside it to take aileron servos and power wires. If you can find 2mm depron, go for it.

I'm looking forward to seeing the model and hearing how it flies - best of luck!

#15 Steve85 Oct 21, 2011 12:52 PM

Hmmm, looks like I'll have to sharpen my pencil for the weight budget. Mike is right, a 1/24 scale Lancaster will never fly at scale speeds, because 200 mph translates to 12.5 km/h at that scale, and that would be well below the stall speed of anything I could build! I'll do some math over the weekend and see what I can allow for airframe weight.

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...;)

Steve


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