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.

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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 would like to make a note for the record. When you order a vari-prop, each system has custom made blades, not off the shelf anything. They design the blades based on your aircraft performance envelope. So the twist is right for YOUR application, not just close as the nearest off the shelf part from Warp or Sensinich. Yes it does cost some money, yet still about half the price of a new certified CS, and 14 lbs less.
Sure, I sound like a commercial, but when one cites prop twist not being right as a common failure in prop installations, you will get what you pay for. Cheap and "close" or spot on and pricey. I don't think one could come up with a similar system from scratch with all custom fabricated parts for much less money invested in tooling, materials, testing and time. If you can, send me a quote, I'm listening.
C. Smith

I can see where you are coming from (in Ca speak) :)
You have a STOL airplane so low speed thrust is very important.

My C182 prop is 50 pounds. Minus 14 is still 36 pounds not counting
the gov.

The exact twist is a function of cruise speed.
Have you chosen a cruise speed? It is not sensitive function however
120 MPH is a long way from 200 MPH.

Are the blades hollow carbon fiber? The unit I saw had wood blades.
That will reduce efficiency due to the thicker tips required.

Hollow carbon blades drastically cut the weight of the hub.
The radial load on the hub is the mass of the blade times circumferential
velocity of the blade CG SQUARED divided by the radius of
the blade CG. Sensenich blades are hollow carbon fiber.
Extremely light. A narrower Warp Drive solid carbon blade is 2 pounds.
You would need at least 3 and maybe 4.

Paul Lamar


Actually, (common confusion) my chosen aircraft is not very STOL, although with a CS prop and 250HP (and maybe some VGs) it just may turn out that way. Design spec for the CH-640 put cruise at 150-160 mph (I hate it when they use mph, aircraft should all use knots). VNE of 175mph. T.O. roll of 1000ft with 180hp fixed pitch prop.

I don't know if carbon fiber is an option, as I'm a long way from needing the prop, I didn't badger Larry too much. But I wouldn't be surprised if it is possible for some more coin. The website says a 2 blade prop weighs somewhere around 16lbs prop only. Their big market right now seems to be the UAV market.
I figure at least 2 years before I'm airborne again. Finished flaps last month, almost done with ailerons. Hope to start the wings in July.

I do like the sound of your manual pump control. If you can increase the diameter of the input cylinder, the hydraulic advantage becomes greater. Just find a place for it. Could end up with a single stroke design.
C. Smith

I think you mean smaller. The initial idea was .5 inch diameter and Larry
felt that was too large for the pressure and volume required in one stroke.

Paul Lamar