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Apr 20, 2018, 06:02 PM
G.F. beurling
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Anybody ever witnessed an aluminum wing joiner tube fail?


I'm getting ready to build an old 11.5 pound 95" Sr.Telemaster. The kit was designed with a one-piece wing and has a steep 8 dehedral angle which will only allow me to fit a 3/4" O.D. sized aluminum into it. I'll have the outer joiner sleeve sandwiched with epoxy firmly between the upper and lower 1/2" x 3/8" wing spars, and I'm not worried about the tube breaking out of the ribs. But I am more concerned about it breaking or bending in the center. The tube I have on hand is an aluminum flag pole with a .030 wall. Can this tube handle stress of an occasional roll or loop of a big 95" winged Tele? I could buy another 3/4" aluminum tube with a .050 wall for $18 but don't know if that is overkill & unnecessary. Being I'm not an engineer, I don't know how to calculate the stresses that this tube will take right there in the center wing joint where it should be most vulnerable. (if it's vulnerable at all) If you try to bend this flagpole on your knee, it's pretty darn strong.....and is why a large flag in a strong wind doesn't bend or break it all week long. But then again, a flag is not an 11 lb Telemaster doing loops.


Has anybody ever witnessed an aluminum joiner tube on a big plane crack or bend from stress?
Last edited by G.F. Beurling; Apr 20, 2018 at 11:39 PM. Reason: mention 11.5 weight, kit, & one -piece wing
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Apr 20, 2018, 07:21 PM
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I bent/kinked one on a Great Planes Giant Sporster (84" I think). That tube was an inch or maybe more!

We all have our 'druthers, but I would reduce the dihedral a bit, especially if it meant allowing me to run a little larger OD tube.
Apr 20, 2018, 07:36 PM
If it flies, I can crash it.
rocketsled666's Avatar
Quote:
Originally Posted by G.F. Beurling View Post
The tube I have on hand is an aluminum flag pole with a .030 wall. Can this tube handle stress of an occasional roll or loop of a big 95" winged Tele?
I would say "no". A 95" wing will generate a lot of bending force.

I don't think 0.05 is much better. A 95" wing is big. I'm not sure a hollow rod is appropriate at any wall thickness.

What do you expect the all-up weight of the airplane to be? I'd hang the rod between two chair backs and load weight at the center of the rod until either the rod broke or I got to 4 or 5x the AUW (this is basically how they determine the G rating of a real airplane).

You should not design this with an assumption that your loops and rolls will always be lazy. You may have this intent when you fly, but you will invariably encounter a situation in flight where you yank the sticks harder than you expect. A sudden gust of wind, or pulling out of a loop too low to the ground, or just not paying enough attention. You need the joiner tube to be able to handle worst-case assumption (with some margin to spare) not a "nominal" case.
Apr 20, 2018, 08:43 PM
Registered User

WingJoiner


Switch to 6061-T6 .058" wall aircraft tubing from Aircraft Spruce. It telescopes inside each other from 1/2" to 2 1/4" diameter. It can be bent with an electricians tubing bender, so you might have to go see your local industrial electrician.

Kip
Apr 20, 2018, 09:27 PM
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marmalade1's Avatar
I'm going to go out on a limb: that design has been around decades. If it failed upon loops and rolls it would've been forgotten long, long ago. The kits are still made.

While the diameter sounds modest remember so are the forces generated by the modest ailerons/ elevators. Also, the forces are balanced so the opposite side wing is moved in the opposite direction (e.g. left roll means left wing pushed down while right is pulled up).

High-G pull outs are where it would be an issue.

After watching many, many YouTube videos of rc planes I've never seen a trainer type (or any type) have a wing failure from rolls/loops.

Would you put your name/brand to a plane that breaks after the 1st acro move anyone makes?

Their reputation is of a 'great plane', not 'a great plane as long as you don't try a roll of loop'.

Enjoy it.

PD
Apr 20, 2018, 09:32 PM
AMA 46133
SeismicCWave's Avatar
>>I'm going to go out on a limb: that design has been around decades. If it failed upon loops and rolls it would've been forgotten long, long ago. The kits are still made.

While the diameter sounds modest remember so are the forces generated by the modest ailerons/ elevators. Also, the forces are balanced so the opposite side wing is moved in the opposite direction (e.g. left roll means left wing pushed down while right is pulled up).

High-G pull outs are where it would be an issue.

After watching many, many YouTube videos of rc planes I've never seen a trainer type (or any type) have a wing failure from rolls/loops.

Would you put your name/brand to a plane that breaks after the 1st acro move anyone makes?

Their reputation is of a 'great plane', not 'a great plane as long as you don't try a roll of loop'.<<

The question here is if the OP is building the plane to spec or is he building is from scratch and therefore deviating from the original construction. Using an aluminum flag pole as a wing joiner tube does not sound like something that the original design called for. If the design has been around for decades the original designed may have specified a plywood dihedral brace.
Apr 20, 2018, 11:33 PM
G.F. beurling
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Originally Posted by SeismicCWave View Post
The question here is if the OP is building the plane to spec or is he building is from scratch and therefore deviating from the original construction. Using an aluminum flag pole as a wing joiner tube does not sound like something that the original design called for. If the design has been around for decades the original designed may have specified a plywood dihedral brace.
The plane is being built from an old kit that was designed as a one-piece 95" wing with a 1/4" thick x 1" ply dihydral brace at the center spars, and 1/8"thick x 3/8" braces at front leading edge and back leading edge. It will weigh about 11.5lbs. It has 3 braces total with the two 1/8" braces more useful to align LE & TE edges.
Last edited by G.F. Beurling; Apr 21, 2018 at 02:12 AM.
Apr 21, 2018, 01:04 AM
AMA 46133
SeismicCWave's Avatar
Quote:
Originally Posted by G.F. Beurling View Post
The plane is being built from an old kit that was designed as a one-piece 95" wing with a 1/4" thick x 1" ply dehydral brace. It will weigh about 11.5lbs.
I could be wrong but I don't think a 1/4" ply X 1" tall is that much stronger than a 3/4" aluminum tube. An easy way to test is to do a test on a ply brace and see how much weight it takes to break it. Then apply the same weight to the aluminum tube and see if it bends.

11.5 pound plane is not very heavy regardless of wing span. You are talking about a very light wing loading. So should not be an problem. This is not a 3D aerobatic plane or a 2 meter pattern plane.
Apr 21, 2018, 02:08 AM
G.F. beurling
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S Wave,

I edited my last post to say in addition to the 1/4" x 1" ply dihedral brace at the center upper & lower wing spars, it also has a thin 1/8" thick x 3/8" brace at front and back leading/training edges. ( ie; 3 braces total)
Yes, I agree with you that looking at it, it doesn't seem like a lot much more support when compared to a 3/4" OD alum flag pole tube with a .030" wall. However, I think now I might go the $18 and buy a 3/4" alum tube with a .050 wall. That's quite a bit thicker then my .030" walled alum flag pole. An aluminum tube with a .065" wall is also available, but that is starting to get too heavy. I think an over stressed .050" walled wing tube will crack through the ribs and break out of the wing before it ever bends in the center of the wing.
Apr 21, 2018, 07:41 AM
The runway used to be longer
Mad_Mike's Avatar
2 guys at our club built 8 foot Telemasters and they used 1/4" aluminum plate for the joiner spar.
1 of the guys put a 20cc DLE on his and he throws it around pretty good.
Apr 21, 2018, 10:36 AM
Registered User
My rascal 110 uses a 1/4" aluminum plate spar joiner. The plane is abut 17 years old. It will be more than enough.
Edwin
Apr 21, 2018, 11:45 AM
A man with a plan
Balsaworkbench's Avatar
My 8 foot Telemaster has a single 1/4" dowel in the front to hold the wing on, and two 1/4" nylon bolts in the rear. How does that compare to the strength of an aluminum tube through the middle?

I was worried about the dowel, but so far so good.
Apr 21, 2018, 02:11 PM
G.F. beurling
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Quote:
Originally Posted by Balsaworkbench View Post
My 8 foot Telemaster has a single 1/4" dowel in the front to hold the wing on, and two 1/4" nylon bolts in the rear. How does that compare to the strength of an aluminum tube through the middle?

I was worried about the dowel, but so far so good.
Balsa B,

You're confusing two different issues. You are thinking I will have a 90"-95" one-piece wing. ( as the old kit was intended.) But I'm talking about converting it into a 2-piece wing. I intend to transport the 2 wing halves, and am seeking the best way to join the two halves together. That needs to be settled before the other issue of attaching the wing to the fuselage with dowels and bolts.

And yes, you're means of fastening the wing to the fuse with dowels & bolts is what I intend to do.
Apr 21, 2018, 03:21 PM
A man with a plan
Balsaworkbench's Avatar
Not confused at all. Think about the stress on a quarter inch dowel in the middle of a wing. I suppose there's more shear stress on my dowel, and more bending stress on the joiner tube, but I thought it was an interesting comparison.

I'm still wondering why a Telemaster would weigh 11.5 pounds, though. According to the RCM construction article, spec weight is 104 oz.
Apr 21, 2018, 03:56 PM
AMA 46133
SeismicCWave's Avatar
>>I'm still wondering why a Telemaster would weigh 11.5 pounds, though. According to the RCM construction article, spec weight is 104 oz.<<

Are you sure that weight is for a 95" wing span Telemaster. 104 ounces is only 6.5 pounds. That's a bit too light for a 95" wing span for any "powered" fixed wing. (See note below)

Here is some specs from a Senior Telemaster with 91" wing span. 1,300 square inches of wing and suppose to weigh 10 1/2 pounds.

http://www.hobbyexpress.com/senior_t...39259_prd1.htm

Well I stand corrected. Yes a Senior Telemaster can weigh 6 1/2 pounds according the the blurb on OuterZone. That's incredible. 8 1/2 ounces wing loading!!!!

https://outerzone.co.uk/plan_details.asp?ID=5044
Last edited by SeismicCWave; Apr 21, 2018 at 04:09 PM. Reason: Correcting information


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