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 b

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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.

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A few years ago a few of us teamed up to build an electrically adjustable
constant speed prop.  It was called the LAEV prop.  Butch did the final
hub
design and build, Bill Freeman did the blade design, Perry Mick built the
carbon blades and yours truly did some of the early concepts.  Butch
disappeared for secret reasons along with the prop.  If I knew and told
you
I would have to kill you.  One of the revolutionary ideas was how the
blades
were retained by ball bearings in a one piece hub design.  The balls were
fed in one at a time through a access holes closed by a threaded plug.
This
saved pounds of weight.  We looked into getting a patent but nothing came
to
fruition.  The one piece hub was welded 4130 steel and the balls were also
steel.  If you make the hub from anodized aluminum light weight Torlon
balls
are used just like the balls used in racing sail boat winches.  No steel
races required This design combines the rotating oil pressure ring of the
Variprop and the Torlon ball trick to cut the cost and weight.  A hand
pump
like a garage jack is used to change the pitch.  It also uses off the
shelf
Warp Drive or Sensenich hollow carbon fiber RV blades.  This is done by
using split clamps specifically contoured for each type of blade.  A 3
blade
version is possible.  No attempt to cut weight was done yet as this is a
concept 3D.  Knocked out in an over night session using Rhino 3D.


Paul Lamar


  Hey Paul,

  This is a really nice design.  How much testing has it survived?

  I'm not clear on the operating mechanism.  I would like to know how much
  work would be involved to modify the assembly so that the pitch could be
  adjusted and locked on the ground using a screw arrangement maybe?

Mark LaPierre


  Just a spring loaded piston with a groove that fits the pitch change
  pins.
  Not drawn so far. If you want to build one let me know and
  I will work on it some more.

  No testing so far.

  Paul Lamar


  Here is what the piston looks like. Just a couple of simple slots
  that engage the pitch change pins. Shown in high pitch with
  the spring fully compressed. When pressure is release the piston
  moves back bringing the blades into low pitch.

  As far as locking it into a position other than
  full fine pitch I can see no simple way of doing that.
  Why would you want to do that when you can get a ground
  adjustable hub for way less money?

  Paul Lamar

 I may have the bull by the tail, but, if one was to vary the pitch
 wouldn't you push IN the pitch control? normally ie convention has it
 that pushing in the pitch control the pitch goes to fine, 20 pounds of
 pull on the control/ pump would feel as if one was pulling the
 dash/panel into ones lap.
  John Burey

 So if it won't take 20 pounds it is too weak :)

 That is for the original  one stroke method.
 The latest method is many strokes of low force
 (say 2 pounds). Each stroke increases the pitch by
 a SMALL amount. Just like a hydraulic garage jack.

 The prop starts out in fine pitch for take off as does
 the C182. Also if the oil is lost the spring forces
 the prop into fine pitch. There is a separate oil
 supply for the prop control. It does not use engine oil.

 Paul Lamar

 I think I see how you are working it now, I thought it was one push of
the control to go into fine pitch!! so I assume that one would have to
pump now and then to readjust the pitch as required, because the
oil/fluid would leak thru the slip-ring type of thing on the prop shaft,
because at 2500 rpm it will be difficult to seal completly.:-(
 John Burey.

No more difficult then the front of a CS prop Lycoming or Continental
crankshaft subject to the same pressure. In fact we can use the
same "stretch over" seal. They normally don't leak but they do fail
from time to time.

Paul Lamar


Rather than a push pull knob or lever perhaps consider a small crank wheel.
The blade tensioner on my sawmill is simply a piston with a fine thread
acting as the master cylinder feeding three slave cylinders. It runs 2700
psi and will hold that for weeks at a time (when I forget to release it, bad
for the blade). You would be able to make very fine adjustments and yet cycle
the full range quickly. Clockwise for coarse, ccw for fine would seem fairly
intuitive.

John

Sounds great. With a counter on the wheel it could give
you an indication what the pitch is set to.

Paul Lamar