I have some 3/16" and 1/4" carbon fiber and fiberglass hollow rods
that I would like to permanently bend a small amount to match the
2" or 3" diahedral in a wing. Is it possible to heat these enough
to bend them without breaking them or losing all of their strength?
Has anyone tried this sucessfully.

Vette

vette,

The CF rods bend, but the CF tubes cannot bend as far as I can see.

Maybe I didn't try hard enough, though.

Viper

Heating them enough put a permanent bend in will destroy the bond between the resin and c/f or glass. You will have no strength left.

The only way I know to build in dihedral is to cut them and join at an angle, either with metal joiner or just by wrapping the joint with CF and resin.

Steve

Bending carbon fiber tubes are not possible without destroying the strength because of the very rigidity that gives the carbon fiber it's strength characteristics. It doesn't stretch, and if you compress it, it loses it's strength. Compare it with a shoestring. If you keep it stretched between your hands, it won't go any further. If you move your hands one inch against each other, it wont be strong until you stretch it out again. If you manage to bend a carbon fiber tube, you will compress the inside of the bend, and it will lose strength. However. You might join two pieces of tube this way: Sand the joining ends to half of the angle of your dihedral. Glue them together with thin CA. (This is just to hold them for the next step.) Wet out a piece of carbon fiber cloth with thin slow curing laminating epoxy. The piece should be as wide as the circumference of the tube, and some length (depending on the diameter, ca 6-7 times the diameter should do the trick.) to each side3 of the joint. Start with the inside of the angle, and stick the cloth to it. Now do the same for the other side. Use some duct tape, start outside of the cloth, and wind it tight around the tube and cloth. Some surplus epoxy will come out. Wipe it off with a balsa stick as you go. Try to keep the cloth straight as you wind. When cured, remove as much as possible of the tape, sand off the rest. Be careful not to sand down through the fibers. Repeat the process a couple of times, and you have a joint as strong as the tube itself.

Just in case there was any confusion - you can't do this!
They have to be formed with the bend in them to work.
..a

Yup. However its easy enouh to use tube, cut teh ends to for teh angle - or use a short piece of wire inside - then epoxy togther and warp the joint with tow or cloth and epoxy it up.

File off excess for a decent looking join.

Theoly other way i have made curves out of CF is to laminate thing strips together with CA and/or Epoxy.

Expensive!

the woven sheath slipped over the part to be bent wetted out with resin and held in a jig till cured.

I think there was a how -to in an old sailplane magazine, they made a mold with the bend routed into each half with a ball end mill. A one-off way of doing it would be to bend an aluminum tube with the ID the same as the desired OD into a v shape. Wind enough carbon tow into a circle, you need enough to fill the aluminum tube completely after wetted out, tie a string around one end of the flatted loop and pull into the tube, trying to not get any voids. After hardening, etch the aluminum off with pool acid. Clear as mud?

Sorry for the Bump but, I didn't feel making a new thread for the same subject was worth taking up server space.

My question is.....

How tight a radius can I bend 1mm carbon rod to, in short I want to make a figure of 8 shape where the ends have a radi of 60mm, I would be lashing the center of te 8 to hold shape.

Originally Posted by djdavies83

Sorry for the Bump but, I didn't feel making a new thread for the same subject was worth taking up server space.

My question is.....

How tight a radius can I bend 1mm carbon rod to, in short I want to make a figure of 8 shape where the ends have a radi of 60mm, I would be lashing the center of te 8 to hold shape.

I just tried a length@60-broke.Managed to get an 85,broke at 70.
You owe me a length of 1mm carbon
Stuart.

Oooh, sorry Stuart, also it looks like the smallest radius I could use for this idea is 63 according to my Draftsight mockup,
I think if I went larger than 63 the prop guard of one blade would interfere with opposite blade, is there .5mm or would that be too fragile if it exists?

http://www.easycomposites.co.uk/Cate...Fibre-Rod.aspx
They go down to .28mm
Stuart

This is the sort of thing you simply do on your own by trial and error such as Stupot did for you. You tighten the radius until it snaps then figure on keeping anything else about 8 to 10mm bigger so it's not too close to the limit.

Sincw you already know that a 1mm round rod will snap before it bends this tight look at using a flat ribbon like carbon strip. Best would be to use two very thin flat ribbon like rods and glue them together around a form. The result will be far less close to the final snapping point so it won't tend to blow apart if deformed such that the tighter bend radius due to the deformation exceeds the minimum bend radius.

I see that this Easy Composites has a 0.5x3mm strip. Two layers of that laminated around a suitable size form with epoxy between the two layers would likely produce a highly durable and not overly stressed protective hoop around your props.

Like the man said,these pages can only take you so far.At some point you'll have to do some trials.Order one of each of .28 .5 and the strip,and see what you can do with them.
Let us know how your idea progresses.
Stuart

Ps the rods etc will arrive coiled.Take care opening the package

BMathews, Stupot, thanks for your advice (and sacrifice Stupot) once I have a little play money I'll sure order them three type of carbon for this project, I'll report back once I have something physical made up.