Hello.

APU.
http://en.wikipedia.org/wiki/Auxiliary_power_unit
The only thing it is used for is running equipment on the ground while the engine is off and to assist in starting.
You can not easily crank the main rotor of a helicopter as you can spin the prop of a fixed wing by hand.
However you can wrap a rope around the front spindle of that small engine and pull.
And this means of starting was quite common in the era that the Bell 47 came out in.
http://www.tractorbynet.com/forums/g...ony-motor.html
Batteries were not as compact as today nor as reliable and the electrical load of tube type radios just on receive was something to deal with.
And remember we a talking VHF here, at least a dozen tubes plus vibrator.
If the aircraft was equipped with another radio simply double the current.
Remember that a helicopter was used as a scout and so radio contact with both the ground and other aircraft was vital.
Just like tractors no longer you pony motors but simply better batteries and starters as a rule, most aircraft no longer have the small engines but good batteries and solid state radios.
But if you want to hand start a helicopter this is just about the only way.