Paul I respectfully disagree. One of the biggest troubles for some
systems, like a 20B
RV-10 will be the lack of a CS prop. That is saying that a fixed pitch
won't work at all
but carrying enough pitch for cruse/top speed will lengthen takeoff
distance by a
significant amount.
Bill Jepson
Not if you start with a p-port 3 rotor. How many RV10 out there have 375
HP?
Paul Lamar
I also disagree about the need for a PRSU that will handle a CS prop, but
when I looked at the Variprop website, its only rated for 300hp. If a NA
20B P-Port will make 375hp (not sure about that), I'm not sure it would hold
up. Certainly the 20B P-Port will make more that 300 hp in any case. I
think the greatest need is for a PRSU that will take a CS prop. At this
point, everyone just has to settle for what we can get and hope for a new
product!!
Don
Don,
I'm in total agreement with Paul that a P-port 20B will make major HP. In a talk with
Daryl Drummond he said you would have to intentionally hold it back to make only 300!
I agree that it would be best if the CS could be a light one. Senstitch (sorry I never
could
spell their name right) Is doing a new all composite CS. Egg Subaru has been selling them.
They have several blade configurations. Just a possibility.
Bill Jepson
Hi Paul,
This may be a good time for a survey. IE Everyone who would pay XXX dollars
MORE to have Constant Speed Prop Capability---line up here. Everyone who is
positive they will Always Be Content with Fixed Pitch ----line up here.
Even if a builder never uses the capability of the hollow shaft, he/she may
want it simply to enhance the aircraft value at resale time. The big
question is "How Much???" There is about a $5000 difference between a CS
prop and a Fixed pitch, and a Governor can be bought for around $2000
rebuilt. These are investments you can chose to make OR CHOSE NOT TO MAKE
if you have a hollow shaft. If you have a solid shaft this option is not
available. I've been very intimate with Tracey's gearbox and have not yet
found a way to adapt it to a CS prop that I would feel comfortable flying
with, so I believe a "clean sheet" design would be approiate.
I have also
watched your Rhino renderings for PSRU's. I have no feel for how much
more/less your new designs would cost COMPLETE, but for the most part I
cannot see where a hollow shaft vs solid shaft should cost more than around
$500 dollars differential. Most of that differential is simply in the cost
for large bearings which seem to get exponentially more expensive with size
increase. The two big costly problems a CS PSRU must overcome are bearing
size/life and seals which must now retain high pressure instead of just
drain pressure. A fair survey would have to account for the additional
cost, but I think the results maysurprise you.
Dave M
It is not just the price and extra weight of the PSRU. Constant speed props are not
cheap. They are in the category of $10,000. Mark S is apparently rich :)
--------------------------------------------------------------------------------
I am not going to promise anything but I had a few ideas that might work.
One of the big problems with hydraulic props is you need a source of high pressure oil.
On the order of 100 psi or more. There is not a rotating seal made in the world that
will rotate on a 2 inch shaft at 3000 RPM and still accommodate a pressure of 100 psi.
The way the aircraft engines do it is use a very wide plain bearing journal on the nose
of the crankshaft and pump enough high pressure oil flow into that bearing so leakage
out the side is not a problem. Now assuming we use a plain bearing the job of the
governor is to jack up the engine oil pressure and regulate it at over 100 psi.
Governors are not cheap running over $1000.
The next problem is what do you use for a plain bearing shell? You can buy a Lycoming
front main bearing shell for big bucks and copy the front part of a Lycoming engine.
That is the low tech, high weight, big buck way of doing it. The shaft must be very
carefully made out of vacuum remelt, shot peened and polished high quality steel hogged
out of a sold chunk. The cheaper way is go up on the shaft diameter a few tenths of an
inch and drastically reduce the stress in the shaft so cheaper materials and
manufacturing processes can be used. That is exactly what Ross did and what I am going
to do.
Now here is idea one. Make an electric motor powered oil pump and PWM control the oil
pressure with a cheap single chip computer with feed back from the engine tach. A lot
cheaper than a $1000 dollar certified prop governor driven off the e-shaft with a cog belt.
Paul Lamar
Hi Paul,
The beauty and reason for the long time acceptance of the hydraulic prop
governor is the total lack of reliance on the aircraft electrical system.
Same can be said of magneto sparked ignitions. These systems were the ONLY
reliable methods of solving the problems at hand at the time. Once
certified by the FAA, it became an onerous task to make changes. However,
as we are now seeing in certificated engines, the FADEC systems are
becomming common. Even the FAA is recognizing the reliability of modern
electronics. A single chip computer can read the output of an engine
control CPU and command instant adjustments......but why adjust an electric
motor to adjust a hydraulic pump?? Consider having the electric motor
directly operate a ball screw that would run in and out carrying the prop
blade control mechanism with it. Perhaps a ball screw (or aka linear
actuator ) can be found in a package size that would fit within a reasonably
sized hollow shaft. This would eliminate oil, oil seals, oil reservoirs,
oil leaks, etc, in favor of a sealed angular contact ball bearing at each
end of the shaft. Depending on the specs (read $$$'s ), the bearings would
be replaced at XXX hours. KIS theory. Dave M.
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