A RC kill switch is basically a cut off switch of a gas engine ignition operated via the radio transmiter (TX). The idea is that the engine’s ignition kill switch it’s safer to be on the TX than on the model itself. Of course the engine can be killed by the throttle trim but it’s not 100% guarantied if the servo or the connection rod fails. The switch itself may be mechanical (analog) or electronic (optical).
A mechanical kill switch consists of a servo (it can be a once-crashed servo that isn’t quite control surface trustworthy) and a micro switch.
The mechanical setup with a servo and a micro switch is still popular among pilots which are still using magneto equipped engines such as Zenoah G 62 SL.
It has some disadvantages such as:
1. Possible servo failure.
2. Minor interference (glitches) to receiver due to moving parts of the micro switch.
3. Inability to kill the engine in case something goes wrong with the receiver’s (RX) power supply.
Optical on/off switch
The optical on/off switch is handy in case something happens and you need to kill the engine remotely. For example, the throttle servo fails or the throttle gets stuck somehow with the engine running. Worse scenario is having the engine stuck at a fast idle, too fast to land and too slow to fly. It is really impossible to reach up there as the plane flies by to try to flip the switch! Several brand names kill switches are available in the market today such as:
The optical on/off switch has the advantage to automatically kill the ignition when the RX is off, so you can, even if your RX has a wrong failsafe and is non-responsive (that would be your own programming error by the way, but never mind) to kill the engine by just switching off your RX. Mechanically operated kill switch, will not kill your engine in case something goes wrong with the RX power supply, but the optical switch WILL.
It is equipped with an indication led for armed ignition, preventing you from a full afternoon of fruitlessly hitting the propeller! Plug in the unit to an AUX channel on the TX. Then hook up the power in line to the battery and the power out line to the CDI module.
Then when the Radio is up and running, toggling a switch on the TX turns the CDI unit on or off. Since it is optically isolated any RFI on the wires going to the RX are kept to a minimum.