HugoW

Hi,

I'm in the middle of drawing a 1930's racer model. I have built a lot of planes before, some scale, but for this one I'm considering something weird; a scale copy of the original tube fuselage frame. Now I won't make it out of high tensile steel, but I'm considering ally tube to solder, or (carbon?)fibre tube to glue. Any idea's / thoughts / experience to share? It is just an idea, but I think it would be a nice scale feature.

All input is welcome,
Cheers,

Hugo

Lnewqban

Hugo,

Any tube that you use will have thin walls that will be impossible to weld.

Solder will be too weak, may be.

The joints of the struts and braces could be made out of welded metal and then inserted into the tubes (metal or fiber), to which they could be glued or soldered or riveted.

FlyerInOKC

My Feedback: (6)

What are the dimensions of the fuselage? Size can dictate viable materials.

BMatthews

There are some very thin wall stainless tubing sizes available. And silver brazing such tubes is a viable method for creating a larger scale model.

The usual K&S aluminium tubing is far too soft and weak an alloy to consider for any load bearing uses. And fiber tubing can't be bent where such a shape is required. If the original aircraft used only straight pieces then you could perhaps use fiber tubing or fiber rods.

The other issue is how to join such fiber tubes. Simply gluing then would produce weak joints at best. It may work for the flight loads but likely even anything but the lightest of landings would produce broken joints unless you can come up with some way of forming a load carrying socket or wrapping of some sort around the joints. But anything of that sort will form a rather nasty bulge.

Um.... I wonder if carbon or fiberglass tubing could be joined using a method similar to buiscuit joinery as used in wood working? What you'd do is to cut a slot in the longeron tube and a slot in the end of the uprights. Into this slot would go a biscuit shaped gusset of cross laminated carbon plate or something like G10 epoxy-glass board. The biscuit would form a load passing gusset which SHOULD produce a pretty good load bearing joint. For a scale of size I'd think that a 1/16 thick biscuit about 1/2 inch round should do the trick for tubes with around a 5/16 diameter. A slot of this sort in a 5/16 tube should not rob too much strength. Besides, you'd get some of the loss back from the biscuit being glued into the opening.

This biscuit thing just came to me as I typed the first portion. It would require some test joints made up and tried out to see if they can stand up. The key is to provide as much joint area as possible with a maximum of long fiber to long fiber contact. In wood working traditional joints such as half laps, mortise and tenon, fingernails and dovetails all seek to obtain this same larger amount of side grain to side grain contact. Joining carbon or glass fiber tubing has the same sort of requirements for a good load bearing joint. It also still does not give you a way of bending the tubing to form curved outlines.

If you try this idea out please let us now how the test joints do.

HugoW

Thanks for all the input. I think the biscuit idea is worth a try, and maybe the aluminium solder paste I bought a little while ago.

The plane is the Laird LC-DW 500 Super Solution (ah, that one! Yes, that one...):


I'd like to build one 1/5 scale (1/4 is preferred, but to big) and I have a PDF plan of the frame. And pics:







I have tons more info about the plane, but that is not relevant here. I may try some test joints, alloy tube with solder and biscuit trick would be an option too. Weight is an issue, though...

Hugo

LesUyeda

"maybe the aluminium solder paste I bought a little while ago."

Most of that variety of thing, is no more than epoxy, with a coloring, and fancy price.

Les

HugoW

True, but I used this on alloy exhausts and manifolds before. Doesn't seem like 2k to me.

http://www.durafixeasyweld.nl/index....n=home&lang=EN

Would you agree?

Hugo

FlyerInOKC

My Feedback: (6)

Sounds like J-B liquid weld in an aluminum color.

BMatthews

I do recall a paste which was a mix of aluminium powder and flux. It was intended to be beaded on over the cleaned metal and then heated with a torch until the powder melted and flowed. If that's the stuff then it may well be worth a test. If it's just a metal filled epoxy it likely won't work that well. At least not without some sort of reinforcing flange/gusset like thing to increase the glue area. But then it would have a lump around the joint again.

But as I suggested do not rely on K&S aluminium tubing. It's buttery soft and isn't the sort of stuff you want to rely on for the fuselage structure. You need to get some proper aircraft tubing such as 6061-T4 or -T6. Or some other suitable alloy that has some significant spring like ability to it.

kenh3497

At one point in time I had a BUNCH of aluminum tubing meant for use in hydraulic lines. It was capable of containing 10,000 PSI. I think the OD was 3/16, maybe 1/8???? The ID would thread to 4-40 perfectly. Sadly it all went to the scrap heap years ago. Maybe a search for a similar product would yield something you can use. It was in 10 foot lengths and you could pick it up from one end and it would support itself.

Good luck!!

Ken

box car

I get all my tubing from McMaster Carr. Order today have it in your hand the next day.

Ken

Boomerang1

My established ideas of building fabric covered, stringered aircraft were turned upside down by a
cheap ARF model. The method may make the purists puke but the advantages made me wonder
why hasn't this been done before?

Hugo is obviously going more 'authentic' than usual, the method I will now use goes the other
direction. I'm a believer that once it's covered & looks realistic it wouldn't worry me if I had built
it from Lego. Anyone interested? - John.

HugoW

Well, there are various reasons for various methods. I could carve the model from foam, smack some glass on and have a real nice model. But I'm a builder first, flyer second. I like the building process, and like a challenge. So you are right, once covered you will see little of it. But boy, did I have fun building it! Having the pics of the uncovered real plane and scale plane will look nice, too, and maybe add something on a scale competition.

BTW, that does not mean I'm not interested in the method you use, please enlighten us.

Last but not least, it is certainly not a fact I will go this route, yet. I've just worked out the details in CAD, and the weight of the frame will be fairly high. Since I will also be using a fabric / paint cover, and a heavy four stroke gasser, the weight sum does not look positive, now.

Cheers,

Hugo

saramos

Perhaps you could fashion cast jointers that fit inside the tubes. Mock it up with wood dowls that just fits the inside of the tubes. You can construct 1 of each geometry that is needed, tees, ells, etc.. Make silicone molds ,then cast them with a fairly dense urethane or even epoxy, adding chopped glass strands. Then glue it all with epoxy. I bet the joints would be quite durable.

Scott

Boomerang1

For a model like the Solution I'd start with a balsa/plywood box to carry the wing/tail/engine/undercarriage.
No need to make the box narrower at the bottom like the Solution's basic frame. The box provides all the rigging
angles for the important bits.

Then 'puff out' the box with white foam carving it & sanding it down like a big log. If weight's a factor I lightly
glue the foam on so I can remove it easily & hollow it out to a wall thickness of, say, half an inch leaving areas
touching the central box for support where required.

The trick is to make the foam a little smaller than the final shape, the difference is made up by stringers glued
onto the foam in the required, scale position. Once finished & sanded cover as normal.

Advantages? Much faster than adding little quarter formers, notching for stringers, adusting slots to make the
stringers straight - you know the story. The stringers are supported along their entire length so much, much
more resistant to bumping & breaking them. For the same reason the stringers don't get the 'starved horse'
look as the model ages.

Disadvantages? It may/may not be a little heavier. You may have to use a little imagination to fake the cockpit
interior as this will be a little smaller & look a little different. You may have a guilty concience about doing the job a
quicker, easier, more durable, less traditional way.

I know it works for me. - John.

HugoW

Interesting method, thanks for sharing. I just came across another one I like (though not very scale): Cut fuse formers like you would when making a build-up frame, but only the ones perpendicular to the length axle of the plane. Make them with, say, 4 inch spacing. Then make a stack; 4" foam, former, 4" foam, former, etc. Sand / cut off all foam that sticks outside the formers. Once done, glass the lot. When ready, disolve the foam with aceton (English?). This way you get a nice glass fuse, with formers glued in. No molds, so no reproduction, but I'm not planning to produce a series anyway.

Back to the frame, the idea does not look good now. Making fittings to the frame is difficult, and heavy. All in all, the weight becomes a real issue. And I would like it to fly when done...

Hugo

LesUyeda

" I just came across another one I like (though not very scale): "

Did some research on Byron once upon a time, and that was the method that he used to develop the male master for his female molds; and he claims to be very scale.

Les

flyintexan

My Feedback: (1)

Seen a friend use c.f. tubing and wood gussets (laser cut gussets) in combination with the original wood kit parts....not for scale, but for weight and rigidity. I must say, the method seems to have achieved both.



Good luck,
Mark