For the helicopter pilot who has everything.
 

Impress your friends and neighbors. Be the only person on the block to have a flying coaxial lawn sprinkler.

Simply connect one end of your garden hose to the fitting on the sprinkler's high-pressure area, Then connect the other end to the water tap. The more you turn on the tap the higher the sprinkler will fly.

http://www.unicopter.com/1311.jpg

Description of Operation:
Water from the hose enters the high-pressure area. It then exits this area via the Roots-type-blower lobe gears. These gears drive the pinion gears which drive the two ring gears, which drive the two counterrotating rotors. The water exits through ports along the trailing edge of the blades and sprinkles the lawn.

Also Make Money:
On a sunny day, set up lawn chairs and charge people for watching the rainbow.
On a windy day, charge your neighbor for watering his lawn.

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:8
Alternate Application from the Department of Demented Designs:

OTHER: Miscellaneous - Thoughtless Ideas - Engine for Coaxial Rotor

Fit a bucket with a hole in its base to the top of the beast and you've got a self-hovering shower. Of course, the user will have to be prepared to run or suffer a haircut when the water runs out.

My first car had an engine like that....it spat oil out instead of water, but sure was pretty to watch.

Finally died when the Exhaustalator jammed and created to much head pressure for the Wringle Value, and that was that.

Push bikes are far healthy in any case.

Red Wine

You could have easily fixed that car with some new muffler bearings, and replace the Wringle Value with an OEM Kneuter Valve:D

spinoff: lovely gift for your favorite pilot
 

. . . self-washing helicopter. While he's away, drill into the two rotor hubs (they're up at the very top on each side).

Screw in a y-adapter for garden hose, with rotating joint. Suspend hose from handy tree to keep it out of the way of rotor.

Drill 10 small holes in bottom of each blade so the water can squirt onto the helicopter.

Turn on water. Start engine. Self-washing helicopter.

He'll be speechless!