Save time, weight, and the possibility of having radio interference by getting a Smart-fly or electrodynamics optical ignition kill unit. Using a servo-activated switch does you no good if you lose Rx power in the air. You would obviously be in a world of trouble already if that happened, but it would be worse if the engine is still running full boar at the time of impact. with these optical units, the ignition will shut off if power to the rx is lost. They also have a light you can plug into them that will come on whenever the ignition is on, so you know for sure, on the ground that your ignition is on or off - not so with a servo-activated switck. By the way, these units weigh a whopping 0.6 ounces...