I had an idea to simplify the Vari- prop.
Replace the pump with a long control cylinder with
an attached  knob that looks like the pitch control
knob in a 182.

Here is the old message.
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The blade travel force depends on the axis of rotation position relative to
the blade cord so I don't have a blade drawing to go on.  For example if the
blade rotation axis is on the 1/4 cord point of the blade the force to
rotate the blade will be a minimum.  The force and travel is also a function
of the distance of the pin from the axis.

Again I don't have a dwg to determine that.
The force available from the control cylinder mounted behind the instrument
panel depends on the diameter of the piston used.  My guess is 100 psi is
needed to change the pitch on most hydraulic props.  If the average person
can push 20 pounds the area of the control piston would have to be .2 square
inches.  .2 square inches / 3.1416 = the radius squared or .0638 inches.
The square root of which is 0.252.  Therefor the control piston would only
need to be about .5 inches in diameter.  The travel or distance needed has
been discussed above.  The mechanical advantage is five to one so a five
inch change in the master cylinder or control knob will move the spool one
inch which should be more than enough to change the pitch throughout the
entire range.
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snips....


This was shot down by the designer Larry Morgan as not having enough force
to over come the spring.

Here is an improvement on the idea.
Since one could sense the blade angle quite easily one could use a small
hydraulic hand pump to pump up  the pitch angle to what one wanted. Then when fine pitch is needed press a button to release pressure. This would work like a common hydraulic jack and cut the weight by doing away with the motor
and the control.

Paul Lamar