"1/2 A" & "1/8 A" airplanes These are the small ones...more popular now than ever.

Sweet little P-51 airframe

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Old 05-06-2014, 07:59 PM
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MJD
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Default Sweet little P-51 airframe

The LHS had one of these for sale, airframe only, so I snagged it today. What a nice little light weight but stiff and strong molding job. A quick measurement shows it has about 100 square inches area. The wing is both spanwise and torsionally stiff and so is the vertical stab/rudder. The h-stab and elevator are flat foam with a bit of a skin, and in reality I think are probably plenty stiff and strong enough for Sure Start power levels (which would be sporty enough on this!). I'd do "something" with the h-stab and elevators for pushing it hard, and maybe a light glass skin over the fuse. But kudos for the "as-is" condition to the manufacturer, it's well done IMHO.

http://www.sonicmodell.com/en/produc...PSid=21&id=117
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Old 05-06-2014, 11:03 PM
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That's just about perfect..!
I'd like to see a Cox .049 in that.
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Old 05-06-2014, 11:36 PM
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They are painted foam plane types: EPO /EPP / EPS I wonder what foam safe clear coat to fuel proof can be used that wont nuke the paint as well?

Last edited by Pond Skipper; 05-06-2014 at 11:40 PM.
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Old 05-07-2014, 04:02 AM
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They're regular EPS foam, and with a nice light color coat and decals. So yeah, gotta figure out the fuel proofing. I'm not really a fan of pseudo-proofing with polyurethane or the like.

If I stiffen the h-stab then VA MKII power is feasible. I believe the wing is more than adequate if the weight is down.
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Old 05-07-2014, 05:51 AM
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My dilemna is how to treat the motor install neatly. The spinner is 40mm.. I don't wanna put a 1.5" spinner on a half-A. Maybe to form a new spinner and move the engine forward into the spinner cone a bit.
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Old 05-07-2014, 06:53 AM
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Yes can be done back in the day guys would spray raw foam perhaps a two step one to seal the existing paint without attacking it and then a fuel proof such as brush on epoxy.
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Old 05-07-2014, 07:00 AM
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Yeah, something like that will do. Laminating epoxy heated up as you brush it is one way - hair dryer (not heat gun unless you're vewwwy careful) held off from the surface as you brush makes sure you are only heating the thin film and not the bulk material. No issue with substrate with straight epoxy.

I think the VA .049 RC or an AME .061 would be amusing.
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Old 05-07-2014, 12:02 PM
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I soak the two part bottles in hot water to warm them up nice and runny.
With foam I would imagine its not worth the risk to use a heat gun / my heat gun is very hot made for stripping paint = P
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Old 05-08-2014, 09:21 AM
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The model already has paint or ink or some kind over the foam..?
I'd do a test and see if a mist coat of KlassKote clear applied with an airbrush attacks it. If not, just fog a final light coat on it and see how that holds up to the fuel spray. I'll bet a one oz mixing cup full of that paint would be enough if you dole it out carefully and with a miserly attitude.
Another approach would be to airbrush some thinned WBPU clear, let it fully cure for a few days basking in the sun to finish shrinking, THEN hit it will KlassKote clear
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Old 05-08-2014, 09:32 AM
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I had in mind one of the above approaches. Get this - I spent four hours yesterday evening doing nothing but tidying my workshop. I was holding the P-51 and thinking about "stuff", then took a step towards the bench. Caught my foot on something, started going over, grabbed the bench with one hand, and snapped the P-51 fuselage in two with the other as I stopped the fall. %#$@$^&, *$%^%^, #$%$, and several other terms of endearment were shouted loud enough to startle my wife one floor directly above.

I can fix it cleanly, but what an annoying little thing to happen - one of those "I know it's my fault, shuddup already!!" moments..
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Old 05-08-2014, 09:33 AM
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Oh yeah - yes, it has a really light sprayed finish with decals. Really nicely done.
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Old 05-08-2014, 10:55 AM
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Oh jeeze....that really sucks about the P-51.
The worst thing is to absent mindedly leave an Xacto laying out on a cluttered bench and do basically the same thing with your free hand.
At least this wasn't a model that you spent 100 hours building.
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Old 05-08-2014, 11:45 AM
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Quote:
Originally Posted by combatpigg View Post
Oh jeeze....that really sucks about the P-51.
The worst thing is to absent mindedly leave an Xacto laying out on a cluttered bench and do basically the same thing with your free hand.
At least this wasn't a model that you spent 100 hours building.
I have "found" my X-acto knife that way many times.. ;-)

Yeah if this was stick and tissue I would have sat down and cried. Or just set fire to it on the floor.

I felt better when I held the pieces together later on and saw they would glue together fairly cleanly. I'll get over it.

I am trying to remember the last time I put .5 oz cloth and epoxy on something (but nothing else over or with it). I can't recall if it transparent enough to go over the paint.decal finish. Thought I might put very light glass over the front of the fuse and maybe 8-10" of the wing root - for snottier .049's and longer life.
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Old 05-09-2014, 10:01 AM
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If you think you can reach inside the fuselage well enough to laminate cloth where you think you need it, that would look better. The wing could have a slit cut in the underside to bury a fiberglass kite tube, then patch the ditch with scrap foam. The ailerons and elevator could even be carefully dissected and have 1/32" plywood inserted if they are too flimsy.
Cloth on the exterior is going to look messy up close and I think you can totally avoid it.
I don't know exactly how to go about it, but if you attach the stock spinner to a 5x3 rubber prop it would give decent performance, the prop / spinner would last forever just as long as you did a clever job of it. I think Shoe Goop to attach the plastic spinner to an adapter made out of aluminum is the rough idea.
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Old 05-09-2014, 11:13 AM
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The fuselage is conveniently split down the center - so getting inside is no problem.

The wing is very stiff and at light flying weight I see no need for reinforcement. At most I'd inset something in the center 8-10". The aileron and rudder are plenty good as is. Only the h-stab and elevator need a bit of attention, but they are not far off the mark for regular power levels.

I might shoot the rudder and nose in red, that way I can blend in my butchering more easily.

A lightweight 1.5" aftermarket spinner would be fine too, like a nice light Brodak Al unit. Or use part of the foam spinner as the cowl and have a smaller spinner on the engine/prop. I'll figger something out.
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Old 05-10-2014, 08:34 AM
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Ha ha - progress!

I was puttering around in the workshop just now, and thought "live on the edge.." so I grabbed my trusty (?) can of Lustrekote clear, and bravely shot a 2" wide band across the tail end of one side of the fuse, laying it on a bit heavier at the very end and tapering off to a mist coat.

Only the very heavy (near sagging) part showed any bubbling, and this settled down again after a few minutes to flash off the solvents. The other areas were absolutely fine. Hooray!

The bare foam is not, predictably, this is just EPS. But the paint finish seems to be sufficient barrier to a light coat of Lustrekote. There are stripes on the bottom of the wing that are masked off bare foam.. I'll have to shoot PU there first I guess.

Again, I am convinced the wing is stiff enough for all but the worst 1/2A hijinx. This is a bird to build light, lighter, then lighter still, and I think an .049 and tank plus some micro gear will deliver on that account. I believe this is a perfect home for the VA MK II on its side, with a Fuji bladder tank (it fits). I'll trace the fuse profile on 1/8" ply, cut a nose plate, then sand off 1/8" from the left nose half. Easier to do than to describe.
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