CF to CF RF Noise

[grizzlyone]

Would a slowly rotating CF rod within a close fitting CF tube have the potential to generate RF noise?
This question is asked hypothetically. I am not investigating a problem, just curious...
Cheers
Griz

[AndyOne]

Griz,

One fellow in our club was having all sorts of glitching problems with a small delta pusher with a s400 motor. I had a look and it wasn't initially obvious what was wrong. Some of the other club members were flying identical models with no problems. I happened to touch the prop nut and it felt very hot, when I checked, I found that the prop had been slipping on the aliminium driver, it was a carbon prop. With the prop nut loosened, I spun the prop on the shaft and all the controls went wild. It was carbon to metal noise and it was the worst I've ever seen so I see no reason why carbon to carbon wouldn't create noise also.

Mechanically, carbon running in carbon is probably not the best bearing combination, Carbon in PTFE would be a much better solution.

Andy.

[grizzlyone]

Thanks Andy,
I suspected that might be the case...I'll have to rethink my intended design. I'm playing with 3D foamies. I've been utilizing 3mm CF tube in the elevator as a stiffener/torque transfer. I would like to get closer to a full flying stab utilizing, perhaps, a 3" hinge line and thought I could run 3mm tube as the bearing/hinge attached to the stab and 0.06" rod through the tube and continue it as my elevator stiffener... I've got some 0.06 fiberglass rod that should suit...I'll have to play and see how much friction is involved in the tube.
Cheers
'Sperimentin' Grizzly

[vintage1]

Ive used torque rods from CF in CF tube. I did't notice a significant problem.

I'd test it out, but make sure you have an alternative handy if it gives problems.

[JMP_blackfoot]

The problem is intermittent contact between carbon and/or metal parts.
One alternative option we found successful is to electrically connect the moving parts together.
Use thin flexible wire, scrape the carbon piece, wrap the flex wire around and apply conductive paint and let dry. We had the same problem with our Twisteuse horten wing, where the carbon tube lead edge rotates in a carbon tube bearing. We also applied some silicon grease to reduce friction between the carbon parts.