Have you seen the optically isolated kill switch that comes with the mega smoke system from RC Showcase? You get the smoke pump plus a built in optical kill switch for something like $88.00. Other smoke pumps like this cost $100.00 just for the smoke pump. Their unit gives you a kill switch and smoke pump for way less.

http://rcshowcase.com/html/accessories/smokepumps.html

Whit an FM or PCM receiver a choke servo will be vulnerable to RFI and may shut off your engine when you least expect it. The same is true of an Optical Kill Switch which may experience a false signal due to RFI in the receiver. At least it will not pick up any noise through the switch cable (which acts like a virtual antenna).

Well, if you place the servo at least 6-8 inch from the motor, use nylon push-rod and assure no metal contact in the setup, a choke servo will no cause RFI. Have been using this setup on three gassers with PCM rx. No problem at all.

The good news is that people have been flying both FM and PCM with gas planes, chokes, ignition cutoffs, etc for a lot of years. A lot of years before 2.4 DSS was available. Works just fine. Engines don't just quit for no reason with PCM and choke servos or ignition cut-offs. I've got 5 gas planes and never had an engine quit due to RFI kicking out either.

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I know of at lest one instance when a noisy ignition was activating an RCAT Igniton Cut Off and killing the engine. When the owner switched from PCM to Futaba FASST the system was able to "mask" the problem, althogh the engine problably is still transmiting tons of RFI

Sure sounds like it was quiting for a reason. 2.4 just masked a significant problem. Depending on the actual root cause, the plane could still run into some issue in the future if the problem worsens, don't you agree?

Absolutely............

I am not an expert but I do have an opinion. I just built my first gasser., a Jerry's Big Boy with a Brillelli 26ss . I bought and installed a optical kill switch. It weighs next to nothing... definately lighter than a servo, mounting blocks, linkage, ball connectors, etc. That being said, the weight of all that mechanical stuff would have little to no effect on my plane. I did have the carb linkage come loose on my walbro because I used a clevis instead of a ball link. Too fast to land, not enough acceleration to climb out safely in a strong crosswind, while I was trying dragging my wheels through high grass to slow down. I nosed in...luckily I did no damage to my plane but that is when I bought the opti-kill switch. If I make it 25-30 years in this hobby, I MIGHT be good enough where I build everything correctly, no failures, etc. but I feel more comfortable with a secondary way to plan where and when to stop an airplane I no longer fully control.
Mike

Mike,

That's a terrific first gas plane, and one of my favorites. Wisdom comes from experience and you've now got some. Continue to enjoy your JBB!

The risk of RFI should be eliminated by a range check. With correct setup, RFI is not a concern.

With a choke servo, the ignition circuit is physically isolated from the receiver component.

Just for the record, spark plugs and if you like ignition units will transmit RF you just have to make sure your Rx, cables and ignition are far enough apart to not pick it up.

2.4Ghz is not as prone to RF, not imune but not as prone to RF interfearance due to operating on a different frequency, it does not mask it, a PCM Rx on FM will mask a problem, that's why I test my instalations with a PPM Rx first and then install my flight system.

Just my two cents woth.

Mike

You can loosen up a spark plug or cable in flight and the RFI noise generated will overwhelm any FM system, and that's something you can't find out from a range check. Trust me, it happened to me.

Theoretically speaking PCM should be impervious to engine generated RFI noise thus masking the problem, but when the noise is too recurrent you should be able to note a loss of control resolution or poor control response. Now, it's my understanding that spread spectrum technology systems which operate in the 2.4gH frequency area will not detect RF noise which is situated around 60 Hertz, thus fully masking the noise source.

What happened to the engine in your case? Did it quit?

Right after the spark plug fell off from the engine and the engine quit, there was no more noise and I had a non eventual dead stick landing.