ORIGINAL: SAFZERO
Really? I was not aware of that? But why?
SAF
The BEC in the typical ESC is limited to how much current it will handle. Four or more servos--especially fairly large ones like the H9 Cessna would need-- would draw more current than it can sink, and burn it up. Higher voltage packs also mean the BEC has to convert from a higher voltage down to 4.8v for the radio, resulting in a lot of heat generated, with the same result.
A plane this size doesn't need the minimal weight savings from using a BEC vs. a separate receiver battery pack. You lose the convenience of not worrying about an extra battery to charge, but you gain peace of mind.
A popular alternative to a separate rx pack in larger planes is something like a [link=http://www.koolflightsystems.com/ultimatebec.htm]UBEC[/link] . You would have to calculate what the max expected combined servo current would be for the Cessna, and make sure the UBEC can sustain that much.
Also--don't depend on the 'arming switch' on an ESC to keep the motor from starting up unexpectedly. The switch only kills power to the receiver, not the motor. You are depending on the hope that nothing goes poof (like an internal ESC short, switch wiring short, or switch failure) by trusting the switch. It's not a safe gamble, IMHO. The best failsafe for preventing the motor from self-starting is to always keep the motor battery unplugged until just before you intend to fly.
Rick