Carbon Fiber and Avionics

[jnmeade]

Is there reference information available that gives information on the electrical and RF frequency characteristics of carbon fiber as used in aircraft such as the Flight Design? My question has to do with VHF and HF comm frequencies, transponders, grounds and so forth.
If Dynon has some published information on how to address carbon fiber in the avionics realm, that would be great.
I'm really looking for more than anecdotal information.

 

[Dynon]

Sorry - we don't have any technical information on this front.

 

[GalinHdz]

Is there reference information available that gives information on the electrical and RF frequency characteristics of carbon fiber as used in aircraft such as the Flight Design?  My question has to do with VHF and HF comm frequencies, transponders, grounds and so forth.
If Dynon has some published information on how to address carbon fiber in the avionics realm, that would be great.
I'm really looking for more than anecdotal information.

RF frequencies can't, for the most part, penetrate carbon fiber construction very well just like it can't penetrate aluminum. RF antennas must be on the outside of a carbon fiber fuselage not on the inside like you can with a fiberglass airplane. A rule of thumb for RF issues, treat carbon fiber just like you would aluminum and you will be fine.

 

[dynonsupport]

I would not say for sure that it is acceptable to use the carbon fiber airframe as a ground plane for an antenna. RF doesn't go through it well, but a hole drilled in it also isn't a good electrical connector. So it isn't as simple as just treating it like Aluminum.

Really this is a question for the people that made the plane and did specific testing on the specific materials they used. In this case, Flight Design. I'd imagine there is more to "carbon fiber" Than just "carbon fiber." I bet the resin and weave used matter, and so does the strand size.

Worst case, treat it like the worst of both worlds, aluminum and fiberglass. You need external antennas with specifically created ground planes.

Call up Boeing and ask for the 787 guys. I'm sure they will pick up the phone

 

[GalinHdz]

I would not say for sure that it is acceptable to use the carbon fiber airframe as a ground plane for an antenna. RF doesn't go through it well, but a hole drilled in it also isn't a good electrical connector. So it isn't as simple as just treating it like Aluminum.

Really this is a question for the people that made the plane and did specific testing on the specific materials they used. In this case, Flight Design. I'd imagine there is more to "carbon fiber" Than just "carbon fiber." I bet the resin and weave used matter, and so does the strand size.

Worst case, treat it like the worst of both worlds, aluminum and fiberglass. You need external antennas with specifically created ground planes.

Call up Boeing and ask for the 787 guys. I'm sure they will pick up the phone

OK so maybe I oversimplified by saying "treat it like aluminum". I meant that for RF penetration characteristics not for electrical current characteristics . It blocks RF propagation, similar to an aluminum airframe, hence antennas have to be on the outside of the airframe. Carbon fiber does not conduct electrical current so in that sense you can't treat it like aluminum and will need an appropriate electrical ground plane for any antenna. Mea Culpa!

 

[Orf]

I find that my mobile phone will not work in my carbon fibre aircraft. Is this caused by the carbon fibre? and is there a solution?

 

[RVDan]

I deal with Carbon Fiber structures on a regular basis. When it comes to electrical characteristics CF is the worst of all worlds. It is conductive enough to block RF but not enough to be good for lightning or as a ground path or ground plane. On modern airframes CF is usually overlaid with a copper mesh (in the laminate) for lightning protection, but it won't work well as a DC ground path and is difficult to get to work as a ground plane.

So with regards to using it for electrical - treat is as it was fiberglass. When it comes to RF transmissivity, treat it as metal.

But- you can have a short to it and it will conduct enough to make the circuit fail.

Dan

 

[Jim_Lee]

The carbon fiber Phoenix Motorglider has never used a ground plane and the radio, transponder, and ADSB antennas all work great. We have never had a problem. Sorry for the anecdotal information.

 

[GalinHdz]

The carbon fiber Phoenix Motorglider has never used a ground plane and the radio, transponder, and ADSB antennas all work great.  We have never had a problem.  Sorry for the anecdotal information.

The antennas they use might not require a separate ground plane. These ( http://www.advancedaircraft.com/ ) are the antenna I used in my composite KIS4 Cruiser. They work great!