Hi Guys:
I have this old timer, an 8ft. Span, Cloud
Cruiser. It has 2 wing joiners, .3125”
diameter x 16.0 inches long Steel. They weigh
about 5.8 once’s each! I’m thinking of substituting
.3125” diameter carbon fiber for them both
The wing is 96” span with a 13” chord.
The wing joins at the center. Do you think
.3125” diameter pulltruded c/f rod, will do the job?
Plane would not be full aerobatic but the
Occasional loop or spin would be desirable.
Or...would you suggest I substitute 2, 1/16 sheet
carbon fiber joiners and permanently attatch the wing halves
Together. The full depth of the main spar is about 1.25”
And the rear spar is about .800” depth. I would have to
Surgically remove both wing tubes, prepare a flat surface between the spars, with the c/f sheet joiner epoxied
Against the spar webs! But then I’ll have an 8 ft
Wing to tote around. If I go this route, I’ll have
To take the wing down the stairs! No elevators and
No subway rides! No bus rides! What fun is that? Just kidding,
Remembering stories my dad told me about building
And flying model airplanes in the 1930’s. All replies welcome!
Sincerely,
Jon B. Shereshaw

I like the round rod idea.

Do the joiner rods need to be bent for dihedral? If yes, you will need to fabricate them yourself - not too difficult, but some materials will be needed. Let me know if you need process details for this.
Pultruded rods can't be bent or joined reliably enough for this kind of stress. Strength-wise they are more than adequate to replace steel.

Steel joiners flex, carbon ones don't. Would this be an issue?

a single 6mm carbon rod is enough for an F3RES 2M sailplane, your ~8mm rods are a LOT beefier

Three Quarters of a pound of wing joiners?? Holly Crap!! Carbon rods will be fine. With that much weight difference you may have to re balance the plane.

Scott

16 inch long joiners?
Would have though you could halve the length of each. I used 12" on a 4m glider wing.
Be aware that steel joiners will bend but carbon will snap, often without warning. I would go up a size in joiner when swapping for carbon (personal opinion).
Perhaps swap the rear most joiner for carbon, sort of compromise that may also save some nose weight.

I changed from steel to carbon rod of the same diameter on my 2.2m Pilatus B4 sloper. Pretty sure they are 5/16” like yours, but it's not here to measure. I've had no problems. Like Jon I'm doing any dramatic aerobatics, just occasional big loops and fast dives. I think you'll be OK with carbon.