Doublers

Stuka Stunt Main Forum · 11 of 11 known posts recovered

ed n · Jul 18, 2001 03:19 PM

Just wondering, anyone ever try making doublers out of formica? I'm thinking of trying this on a Twister, since I don't want to use the lite-ply ones which come with it. Seems it would make a pretty crush-proof nose. Any drawbacks? Too heavy? I know it's hard to cut, but I have the tools.

Ed N.

LNeumann · Jul 18, 2001 03:24 PM

#1 source

I have never tried it, but two thoughts come to mind: Heavy, and brittle. I don't like Lite Ply, either, as it crushes too easily. But if you extend the upper motor mount all the way to the wing, extend the lower one back, but not quite all the way )stagger them) and then use 1/16 Birch plywood, the plywood will be harder and the nose will be stiffer.

Leonard Neumann

ed n · Jul 18, 2001 05:43 PM

#2 source

I hadn't considered the brittleness; I guess it would crack from vibration.

Ed N.

Jim T. · Jul 18, 2001 06:51 PM

#3 source

If I were scratch building one, I'd do it like Leonard says. The Liteply doublers work fine, if you cut them out for the engine mount, i.e. mount the engine directly on the bearers or on a 1/8 inch aluminum pad (better)directly on the bearers.

Jim

Peabody · Jul 18, 2001 08:36 PM

#4 source

When I was brand new to cl (about 11 years ago), I crafted an aeroplane from copper plumbing tube and used foam wings and a ply tail. Real heavy! But it couldn't be broken, even if stepped upon! Barely flew.

Young John Sunderland has a whole bunch of nifty, new ideas on building noses! Sort of a svelt "Big Jim" deal. He gave a presentation at Brodak's event, and I hope he'll write something of stunt news.

The reality is that you'll have a lot more fun if you build something to FLY (read:light) rather than to crash.

Have fun

Peabody

Steve Helmick · Jul 18, 2001 09:03 PM

#5 source

I absolutely agree with Leonard and Mr. Peabody, and have said this before: The light models flew so much better, they actually lasted a lot longer than the heavy ones. I do have some doubts as to the necessity of extending the engine bearers TO the LE. Considering the actual flexing, I would think that a pair of plywood splines inlaid (say 1/16" x 1/2" perpendicular to the plywood doublers, and extended to the high point of the wing... curve them if needed...would do more good for less weight). There have been some threads on the wing/fuselage joint, maybe you can find them with the search function. Have to admit that I have had very little luck with the one here. Steve

LNeumann · Jul 18, 2001 09:42 PM

#6 source

If you want to keep it light while extending the engine bearers back, you can taper them to a point at the back. Start the taper right behind the engine and make a triangle section from that point back. The cutout in the fuselage must be done to match and that becomes a little harder.

Alternately, you can drill lightening holes in the maple engine bearers for the full length behind the engine. Or...
You can rout a groove in the bearers behind the engine. Anything to remove some of the material while extending them back to help reduce flexing and remove a "break point" (stress riser). The nose section is one of those places you want to make as "bullet proof" as possible without adding a lot of weight in doing so.

Leonard Neumann

The Kiwi · Jul 19, 2001 12:00 AM

RE: Doublers - balsa or ply, & some Etc.#7 source

LAST EDITED ON Jul-19-01 AT 00:04 AM (EST)

>Anything to remove some of the material while extending
>them (maple bearers) back to help reduce flexing and
>remove a "break point" (stress riser). The nose
>section is one of those places you want to make as
>"bullet proof" as possible without adding a lot of
>weight in doing so.
>
"Richard" Mathis (the built in censor here doesn't like his actual nickname, D-i-c-k) had much the same idea 35 years ago with his pair of large profile designs, Excalibur and Coyote. Instead of ply, he used 1/2" balsa. Improved the look of the nose without any loss of strength, stiffness, or vibration dampening.

Leonard and I have both pontificated around the online messaging areas about building a motor crutch before installing it in any plane, be it profile or built up. The idea is tied to making absolutely certain that the two bearers are totally parallel and flat. I started doing it with high-vibration old stuff and was rewarded with better power, higher performance.

The less vibration the airframe picked up from the engine, the more power the engine made available. The less crushing that is going on, the longer this improved power situation lasts. That's part of why both Rat Race and Speed use(d) magnesium pans - the fit of the engine to the mounts is/was superior.

There are several thicknesses of circuit board material available; single layer, double, and triple layers. I suppose someone could find a really thin variety and shape it as a doubler instead of just a mount pad under the engine lugs. It wouldn't be brittle the way formica would be, but heavy, yes -- it would be overkill in my book.

I combined Excalibur ideas with profile noses from some of my early Slow Combat stuff, before everyone started using aluminum motor mounts. Leonard disagrees, but I think Larry Cunningham has built Twisters my way. I've often built a "pocket" between bearers on profiles, for fuel tanks. These noses have one single plywood doubler, inboard, and no doubler on the outboard side at all.

The tanks have to be the type with vent tubes forward, and I add a balsa "tripler" on the inboard side. Once or twice, I layered some light glass cloth between the plywood and the balsa tripler, when using 1/32" plywood instead of the regular 1/16" thickness.

On a couple of stretched-out profiles, one based on a Buster wing, and another on a Magician wing, I widened the pocket by sawing off 1/8" each from the inner faces of the bearers, to make allowance for either deeper bodied tanks or more offset than I'd have had room for otherwise. It wasn't necessarily based on any concern about the weight of the nose, however.

I think I get a better engine run with profiles that have the tank recesses, whether it's a conventionally vented, or a Uniflow tank. George Aldrich's last stunter was a Bill Hopkins "Aldrich Special" that never had the engine on the inboard side the way Bill's kits were designed, but the fuel tank was mounted right in the middle of the profile fuselage, with just less than half sticking out on each side. No vibration problem.

It was one of his pinched-corner Nobler type tanks, conventionally (atmosphericly) vented, and the engine was a McGas 40. It was mounted dead-nuts centered on the engine's thrust line, no offsets at all. Speed upright and inverted was exactly the same, leastwise it seemed so, as close as I could tell with some two-lap timings with my stop watch. (Incidentally, for anyone with a yen to duplicate it, the finish was simple - clear SuperPoxy over natural balsa.)

mcm · Jul 19, 2001 01:17 AM

#8 source

Based on the last time I made a counter-top (about two months ago), I don't think the new materials that have largely replaced true formica would be too brittle. I think it is worth trying on a profile you don't care too much about. Weight would be heavier, but probably neglible. Finishing, though, might be pretty difficult. I think it's worth a try, but most modern materials seem to have a rougher overall finish than the formica I grew up with, and--even with sanding--might be difficult to get a paint to permanently adhere to. Still, I think it's worth a try, especially since the new materials are a heck of a lot easier to cut and trim than true formica was. I still normally use a router, but tin snips and file, or even several passes with a box knife, will work very well.
--Mitch

De Hill · Jul 19, 2001 08:39 AM

#9 source

I think that the late Doc Passen Produced some of his kits with formica doublers. how well did they work? Dunno.

ed n · Jul 19, 2001 11:22 AM

#10 source

>Based on the last time I made a counter-top (about two months
>ago), I don't think the new materials that have largely
>replaced true formica would be too brittle.

The material I have is actually made by Wilsonart, not Formica brand.

Regarding The Kiwi's comments on circuit board material, I have used strips of 1/16" G10 fiberglass under the engine flanges over 1/16" aircraft plywood doublers with good results, but the plywood still crushes slightly over time. The main problem is that cutting G10 fiberglass ruins saw blades quickly.

Ed N.