Originally Posted by
grognard
Hands up all those who fly IC powered models who think this is reasonable. For my money, putting a spring of any kind in opposition to a servo is generally bad practice. In this specific case, the spring will have to be strong enough to overcome the resistance of the servo with power off in order to close the throttle. No I don't have numbers but those of us who set up our own control systems know that it takes a few ounces to get the servo moving. So the servo will be fighting the spring all through each and every flight, drawing more current, running the battery down faster, and shortening the life of the servo.......
Grog is correct here , a spring heavy enough to force the throttle servo to the carb's idle position would quickly fry the servo , so the spring idea is not a solution .
Of course , gas powered models (with a spark ignition VS glow) can easily be equipped with an optical ignition cutoff that will kill the spark instantly should the TX and RX loose radio contact . I know of no such handy system for glow engine powered models , but I'm sure if it's that important some enterprising engineer should be able to come up with something . Perhaps a small "emergency battery" with a servo driver circuit that would electronically close the throttle in the event of radio system failure ?