Would a grounded carbon fiber overlay on the firewall, inside the nacelle-cowling, etc., act as an effective RFI shield?

Carbon fiber is extremely conductive electrically. Take it from there....

Easy to tell who uses the latest stuff
I find it is impossible to creat interferrence as long as the ignition is in proper repair
I use 2.4 radios .
Come to think of it I have never had an ignition interferrence issue -I also use shielded cable types , exclusively

I think I was about 12 when I learned about carbon conductivity. I foolishly stuck a pencil into the arc of a Jacobs Ladder. Sucker must have tossed me 10 feet....

I'm with you all the way on the ignitions systems Dick. You almost have to cheat your way into generating rf issues. Unless it started out as a cheap and crappy ignition system most all the probelms people have are from failing to read and follow directions or from using old and worn out parts.

I feel like I have asked a really stupid question. My reasoning is this . The plug and cable are surounded by a grounded metal plug cap and wire mesh. What does this do? Is this setup part of the shielding? I have heard mention of a resistor type plug about which, I confess, know ziltch. Amoung other things you say? Anyway, a CF fus must carry the antenae on the outside because the CF interferes with the incoming RF. Does it not stand to reason if the CF won't let it in, it won't let it out? Another layer of protection is a good thing, No?

Better not to try and reinvent the wheel. Simply follow the manufacturers instructions. The wire sheathing and cap design is the rf shielding. The cap likely already has a resistor inside, negating the need for a resistor plug. Go to the CH ignitions web site and read up on their installation instructions and explanations.

You won't find many full carbon fuselages. When you do they will likely be on UAV's. Even the larger Comp Arfs have only a little cf as part of the structure. Use an external antenna on an all carbon fuse if you want clean signal transfer.

I think you will find all spark plugs used in RC are resistor plugs. If the part number stamped on the plug has an R in it, it is a resistor plug. Yes, it is almost a necessity for interference free ignition, even when using the plug cap and shielded wire. I have not used the plug cap on any of my planes (at least 10 different ones over the past 12 years) and using regular PPM 72 MHz systems and have never had any ignition interference. These were, with one exception, all magneto ignitions.

The smaller plugs now common in some brands are NOT resister types
a small resister is imbedded in the caps of DA, for example.

CARBON and its conductivity?
I guess a carbon lattice is not the best way to conduct electricity, 4 free electrons that will make a beautiful and strong lattice with other carbon atoms, hence the strength of the carbon to carbon links.
To be a good conductor we need free electrons.

The principle behind RFI shielding (Radio frequency Interference) is to cancel one of the two components of the electromagnetic wave, either the electrical component or the magnetic one.
Maxwell depicted this in the Electromagnetic theory. Faraday applied this principle to shield from the electric field.
There will be not electric components inside a Faraday cage; which by the way is the principle behind the RF shielding.

So the best shielding materials are typically those with free electrons that is metals; cooper, silver, gold, aluminium, etc. Those are the ones we want to cancel the electric component of any RFI.
New alloys are also used; however still need to have free electrons to allow good conductivity that is low resistance (ohms).

Best insulators= no free electrons, you name it: Calcium, Potassium, etc
In the middle; carbon, silicon (aka semiconductors), that is medium to high resistance, poor conductivity. As a mater of fact Carbon is the base material to manufacture resistors. In Radio Shack you still find those.

Probably an excess of carbon may will cancel or create a cage (I am reluctant to call a carbon fiebr fuselage a Faraday cage) and that may explain their "shielding" properties.
However the carbon atoms are not the best conductors, no way.

I have used a copper-based paint that has a resistivity close to that of a metal. It brushed on like thickened latex house paint.

My application was to create a dielectric roll for corona treatment. The roll itself was wound using filament wetted with a high-dielectric epoxy. The inside of the roll was coated with this copper paint. I remembered measuring less than 2-3 ohms across a 100" long roll.

This paint was also advertised for forming continuous, six sided EMI/RFI shield inside a plastic box. Unfortunately, you would have to buy 5 gallons or so at a time, and it was not cheap.

A screen made of some conductive or low resistance material such as cooper, makes more sense to me to shield against RFI/EMI, however it posses one question;
How would this screen will affect the receive lobe of the antenna?
If using 2.4 GHz radio the wavelength becomes very small, therefore the likelihood of screening the RF energy coming form the transmitter may be very low.
I don´t want to find out if this is not true.

I still think that best way to shield against the RFI/EMI coming form the spark plug is by using the shielded resistor plugs.
This stops the offending source of this interference right there where it belongs, just where they are created.

If the ignition box or other components develops hot spots due to poor shielding, frayed RF cable shielding, lose connections, metal to metal friction caused by high engine vibrations, etc, then this is other history.

For any secondary source of RFI/EMI, use whatever trick you may think off, plastic servo arms, plastic clevis, phenol pushrods, etc.
Some may argue that they use metallic clevis and metallic push rods without any problem whatsoever, that’s fine as long as that works for them.

Distance is another way to get rid of the EMI/RFI, some may argue that they locate ignition vs. receiver or other electronic components close each other without any problem, that’s ok too. They may have a very good shielding built up in their respective ignition boxes or spark plug connectors, cables, etc. or ... lucky guys.

Hey guys...line that cowl with Kryptonite!!!! Capt,n

If Superman supplies Kryptonite and he can confirm that is conductive , then maybe.
However don't ever think a CF cloth will provide RFI/EMI shielding IMO.

Super fast discharge/spark generates harmonics and ringing in a non-resistor plug. The resistance softens the discharge (slower di/dt) and thus no radio interference to speak of. Metal to metal rubbing is the culprit, not the ignition itself.

Some time ago I spent half a day looking for radio interference sources. I used an oscillator to trigger the CDI in lieu of a hall sensor on our engine. I had the spark plug laying on the bench sparking away. With the 'antenna' near enough to almost touch the spark itself or anywhere near the CDI board, I saw zero, nil, nata, nothing that would register on my digital phosphor scope. The 'receiver' was a germanium diode/LC tank. However, when I rubbed/scratched a screwdriver tip on something metal nearby I would pick up beaucoup noise even feet away from the antenna.

I mentioned the copper paint just because someone asked. In other words, I do not believe shielding any box will buy anyone anything in our gassers. Getting rid of metal rubbing contacts and minimize engine shakes will eliminate our woes.

I work with MRI machines, and I know what you are talking about.
Metal to metal is the main source of spurious signals to these machines.
The only other ingredient in this receipt is the presence of high magnetic field.
I am talking about very low signal levels, perhaps 4 dbm or more.
The metal to metal friction causes "white pixel" on the MRI images. These are high energy signals with a very high amplitude and very narrow (very short duration).
Just about any mechanic component in the machine may cause these signals.
They may also be produced from electric malfunction such as high voltage electric arcs (lose connections, failing electronic components such as diodes, or passive components arching, etc).

I guess to accurately charecterize the spark plug ring and their armonics we may want to use a spectrum analyzer.
The scope by itself may not tell you the whole history.

Coronabob,

I've used the copper type paint on gps equipmnt and understood what you were talking about all too well.

Albatross,

My original point was that c/f would not make an effective rf shield, which you finally stated yourself above. If you go back a little ways in time you can look up how the c/f structure of the Beech Starship required a separate metal cage to meet lightning strike requirements.

As far as the Jacobs Ladder was concerned, since wood is definately NOT conductive, what other path did the electricity from the ladder follow to toss my body a painful distance other than the graphite/carbon pencil lead? Let's not forget that carbon fiber is derived from graphite, right?

Just don't put your receiver nor the antenae close to, nor on top of the spark plug! Don't have a direct metal to metal connection with the carb push rod, use plastc connectors. You will do fine! If all else fails, as others have said, read and follow the engine manf. instructions and have some really happy flying!

No. You need to completely enclose the engine for an effective shield. Enclosing the prop gets messy

Yes the pencil lead the high electrostatic discharge, graphite is the preferred path for the electricity to flow as oppose to wood.
In order to equalize the highly unbalanced electric charges just about any path may be good with enough voltage differential.

The Jacobs ladder may use as much as 12 K Volts or more to work, so the unbalanced charges are just ready to follow any path.

[link=http://www.instructables.com/id/How-to-build-a-Five-Foot-Tall-Jacob_s-ladder/]Jacobs Ladder experiment[/link]

Yes, CF & Graphite are varieties of the same element. Will allow electric charges to follow? Yes but limited, inefficiently, this low conductivity will show up in form of heat.
We use carbon to manufacture regular resistors, they can transport electrons (current, Amps, I) however at high cost (Watts, heat, etc) due to its inherent high resistance (ohms).

Does this mean we have to install ceramic bearings and teflon coat the piston? Capt,n

Rather than a couple of electrical engineers trying to baffle everyone with B/S wouldn't it be a lot simpler to just follow the ignition manufacturer's instructions?

There are two type of EMI/RFI

1) Radiated.
2) Induced.

The shielded spark plug connectors (with resistor) will take care of the radiated EMI/RFI.

The secondary source, induced. Will be up to us to eliminated, employing any known mean (CF or plastic pushrods, plastic servo arms, plastic clevis, opto couplers, enough distance, etc) this induction is created by any conductor or set of conductors, wires, screws, engine mounts, batteries, creating "circuits" or loops, etc. Once these loops are created, all it takes is to open these loops to generate those feared RFI/EMI noise in our airplanes .
If the proper conditions are met, then this induced noise will become another source of type 2.

Our intricate set of wires inside the fuselage, connectors, batteries, etc, will be a good path for any induced EMI/RFI.
Will this noise be amplified, maybe? Will be attenuated maybe. It all depends on the how good we are to enhance them or reduce them. If one of these loops finds its way through a clevis and a metallic servo arm (for example). Then we are calling for a metal to metal friction: the loops will intermittenlty be opened, therefore they may very well trigger RFI/EMI events.

Now, a large mass of metal such a cylinder, crankcase and ball bearings moving like crazy, will easily adsorb any additional electric charge. If we can put it in one word the large mass represented by the engine acts like the actual “ground”. Will be the zero potential if you want.
So don’t worry about this friction.
You don’t have to think about ceramic bearings and so.
It is metal to metal friction, however is large enough with a lot of free electrons that will draw any current generated by 1 or 2 above.

now that we all know that carbon fiber will shield rf signals. what do you guys think about the a123 batteries. with no reg. or is li-ion with regulator better?

CF is not a good material to built RF shielding.
Is not a good conductor, does not have magnetic permeability.

The is 1st line o defense: a shielded spark plug (with resistor), then the rest just mater of use common sense.
It has been spelled in this forum and other similar forums.
Protect your investment in this hobby; I guess this is what everyone is concerned.
I guess this is what matters, obtain the right information, use it the right way, apply it and enjoy.

You don't have to be electrical engineer to understand those facts, search in the web for more information, here is one:

[link=http://en.wikipedia.org/wiki/RF_shielding]RF shielding[/link]

Happy Hollidays to all

Albatross

Please refer to this forum to a thread started by Valhala re Gas Saito page 14 about half way thru where a fellow experienced servo jitters even though using 2.4 ghz. He had just got the engine back from Hoizon ,I believe, with a new ignition system installed. We have all witnessed a fellow preflighting his plane at the airfield, come up with a jittery servo(s), and spend the rest of the afternoon unsucessfully trying to find the source.(Gremlins???) It is now obvious to me that CF does not make a "Faraday Cage". But it does have inherent RF absorbtion qualities. Skin effect ? Why not use it and leave the rest of your investment to operate in it's shadow?