Sr Telemaster Update

"rich" wrote

Fur will have the most advantageous weight to strength, and has good split resistance.

Next choice for me, would be poplar.

I once made a set of functional struts out of regular dowels with a balsa trailing edge sanded to a taper. It worked very well.

"Robert Reynolds" wrote>>

Yes, that would work well, but be VERY careful of the grain runout, as many dowel rods do not have the grain running very parallel with the rod. If that is the case, it could split and separate, very easily, with the wing and then the fuselage being returned to a "kit-like" form, very quickly.

Well, I was thinking of Fir with aluminum ends made from Alum tubing and sheet, but the wire control rods with the metal thingies would give the strength needed, and the balsa fairing for looks. Should be easy connect/disconnect too. Think I'll dummy up some samples and see what they look like. With the epoxy set overnight, I can get an engine hoist and lift up that wing now that it's joined and see about attachment points..

That's good advice, especially when you consider how you intend to attach the end fittings. I cut slots in my dowels and inserted brass sheet fittings. The brass was epoxied in place, then the end of the dowel was wrapped with thread and epoxied. I had to make sure the grain was straight or one of the sides would have flaked off. Now that I'm thinking about it, I recall making a smaller set of struts using a piece of threaded rod and a clevis for the end hardware.

You can buy airfoil shaped spruce sticks to use for struts. I had a ton of them from a buyout deal I made a few years ago, but I sold them all to a scale builder in Kansas City. I'd rather just make my own struts out of dowels, not that I do it very often anyway.

I just thought of another way to make functional struts. Make a strut out of a piece of 1/16" music wire with clevises soldered to the ends for attachment to the airplane. Sandwich the wire between two pieces of hard 1/8" x 1" balsa with a little groove carved along the length to accommodate the wire. Sand the balsa to an airfoil shape. You should be able to turn out a set in a couple of hours. You could paint them or cover them with Monokote. I think I like that idea even better than the dowel method.

My favorite strut attachment point is a piece of phenolic board protruding from the wing with a little hole drilled in it for the clevis to attach to. Make it long enough on the inside of the wing to reach all the way to the top spar. Glue it to the back of the spars like a shear web. The protruding part can be about a quarter to 3/8" in diameter with the hole drilled right in the middle. Then put a little bit of balsa around it for the Monokote to stick to. You could easily use a quarter inch stick glued to the back of the spar with a little notch for the phenolic board.

Don't make your fitting from plywood because it will splinter sooner or later. I can't recommend a source for phenolic board right off the top of my head. Phenolic is what circuit boards are made of, but what you want is the raw board without traces, holes or the green solder mask that gets applied in the electronics factory. I have several pieces that have been with me for over 15 years. I think I got them from the tool crib at the aircraft overhaul facility where I used to work. We used to sharpen one side, wrap the other end with tape, and use them to scrape paint and gunk from the airplanes.

K&S used to make airfoil shaped aluminum tubing. It was specially for struts. Use wood in the ends where you put your mounting bolts through. Great stuff. Check your local hobby shop for it. My LHS has it.

Go here for the airfoil shaped tubing! I'm sure they have other sizes also.

DUH! Missed the stuff in Tower when I looked for end fittings. That alum streamline tube is just the thing! Next order will include it. THANKS !

WARNING!!!!

When using these for load bearing structures, be sure to FILL them with some sort of hardwood sticks. Then make sure your attachment mechanism goes through the wood.

The aluminum tubes DO fatigue crack. You can ask how I know but I did not like the answer. It got real exciting and not fun once.

Hobby Lobby used to sell airfoiled hardwood sticks in sets of 2 that worked very well. I have started going to the local hardwood dealer and buying spruce sticks (1x1/2) and used a belt sander to airfoil them when the LHS tried to charge me $8 PER STICK on a build that needed 4 sticks. Now I do it that way for fun and cheap. The LHS finally figured out their mistake, 2 years too late.

Jim AMA 1428

DUH! Missed the stuff in Tower when I looked for end fittings. That alum streamline tube is just the thing! Next order will include it. THANKS !

I'm wondering how an aluminum tube is better than a wire through balsa wood. Aluminum tubing would be very fragile when it comes to ordinary handling and hangar rash. Also, you have to attach something to the end of the aluminum, then attach the clevis or other fitting to the end of the something that you attached to the aluminum. Also, aluminum cracks easily under flight conditions. I wouldn't bother with it.

I'm not trying to plead my case or anything. I'm just thinking of practical applications of different materials.

Yes, you have to put some wood in the ends. BUT IT LOOKS SO DAMNED COOL!

.

How about the "brute force" method?

one of these on each end of a long 6-32 threaded rod which runs through the center of a hollow fiberglass shaft. like these

Tighten up the ends to put the rod under some tension, and the arrow shaft under some compression,

8-32 screw attached to hard points on the bottom of the fuselage and the bottom of the wing

Brutally strong but UGLY !!

But that's what I did