Science Forums 2

[CraigD]

This talk of compressed air motors on bicycles reminds me of an odd one a bike collector friend of mine showed me.

The precise origin of the bike was uncertain – it had a head badge listing a no-longer-existant Baltimore, MD, USA store, but likely wasn’t built there. Its wheels, rims, crankset and 3-speed hub was from an 1950s Raleigh. It’s frame, which was steel, appeared handmade. Best guess dated it at from the late ‘50s to early ‘60s.

The bike had an air compressor/motor driven by a wheel that could be engaged and disengaged from the side of the front tire. It looked much like an oversize electric generator, an accessory commonly used to power lights on bikes through the ‘70s. Two air hoses attached it to a thumb-operated valve on the handlebar that allowed the rider to select a compressor (brake), closed, and motor position, another hose connected to the frame’s top tube, via a hand-removable coupling.

Compressed air was stored in the frame’s top and down tubes, which were larger diameter than usual, but not extremely, looking about like a modern-day Cannondale. A small metal line behind the head tube made an air connection between the top and down tubes.

You could flip the compressor to engage the front wheel with the thumb switch in compressor mode to use it as a brake, compressing air in the frame. Switching to motor mode gave you 10-20 seconds of a low-speed “hill climbing assist”. You could also detach the hose to the compressor/motor from the frame, and replace it with a hose with an air chuck on one end to use to inflate the tires.

It was fairly quiet in compressor mode, ear-splittingly loud in motor mode. Opened the thumb valve with the motor disengaged from the wheel made it to spin like mad. The valves and hose couplings got too hot to handle, but never to cold to handle. Overpressuring the frame-tank appeared to be prevented by the compressor leaking when it reached a maximum pressure.

The compressor/motor was lubricated with ordinary light machine oil, through uncapped holes.

I’ve not been able to find any mention of this bike on the internet, other than occasional forum posts claiming either to have seen it or similar bikes, or claiming that their existence is a myth.

My other favorite compressed air-powered vehicles are my dear, departed Air Hog toy airplane, and various of the vehicles in existence today (see the wikipedia article “compressed air car”). The tiny Air Hog engine was expecially nice, because it was made of clear plastic, so you could see how its piston, crank, and valves worked.