[Tom] likes to build little helicopters and decided to build one that runs on compressed air. (Video, embedded below.) Turns out it was a little harder than he thought. Originally, he was trying for a compressed air quadcopter. He’d already worked with an air turbine, but putting on a vehicle that can lift itself into the air turns out to have a lot of hidden gotchas.
[Tom] went through a lot of design considerations to arrive at the helicopter design. He considered counter-rotating props, but there were a host of problems involved. He finally settled on a single prob with a tail rotor that resides on the far end of a long boom to allow the resulting lever arm to reduce the work required of the tail rotor.