Since one inch (25 mm)  can make about a 20 HP difference in peak
power moving the bell mouth a couple of inches makes a large
difference. Maybe enough to make a constant speed prop unnecessary.

This idea moves the whole plenum chamber as the wires and fuel
line can be flexible.

The 1/8th inch square brass rack and pinion stuff is off the shelf from Stock 
Drive Products Hyde Park NY. The upper and lower pinions are geared together with a
small cog belt. Upper and lower racks and pinions are necessary as otherwise 
the telescopic tubes would jam. 

Attaching the brass rack to the aluminum bell mouth tube could be a problem.
I suggest soldering it to a piece of brass sheet and then screwing the
brass sheet to the .065 wall bell mouth with short 4-40 machine screws.

This is probably much cheaper than a constant speed prop.

Paul Lamar
 
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