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Gary C. Buster LPT wrote:

OUCH!!!   Paul, wouldn't the prop be cleared a

little better for wheel

landings (2point on the mains) with maybe a 7 foot

or so???

Gary C. Buster LPT
gbuster@ballistic.com
Tyler, Texas

Sure it would but if the gear box is 5:1 I think we
would be
in trouble with a seven foot prop. Best to design
the airplane with
the worst case in mind and keep your options open.

The Lancair IV does not have the large diameter
option
for a couple of reasons. First is the limited height
of the
tri gear. Second is the direct drive engine.

I would also rather not use a three or
four blade prop because I think a two blade is more
efficient
for top speed. Rare Bear had to go to four real wide
blades
to absorb the HP and still takes off and lands in a
three point attitude.

The tip velocity of the prop is the vector sum of
the
forward speed and the tip tangential speed. I think
it
might be better to slow the tip tangential speed
while still
absorbing the engine HP with a two blade prop. This
means
changing the PSRU ratio or decreasing the diameter
of
the prop and making the blades wider. I think
changing
the ratio may be preferable. BTW The old Schneider
Cup
racers had pretty efficient 9.17 foot diameter props

in their day.

It is a very interesting problem. The Osprey V22 is
an
extreme example. A lot is going to depend on the
ratio
of the PT6 clone gear box.

If I were building a Reno racer I think I would have
a long talk with Don Bates and run a few
configurations
through his prop optimiser program.

Paul Lamar

Vance Jaqua wrote:

IMHO I think a Reno unlimited racer must be at least
50 percent of the weight, and 70 percent of the span
of the mean competitor - even if you are faster, at
some
time you will be in the wake of Dreadnaught or
similar, and you will end up making like a desert
submarine. I also think that contra rotating props is
the way to go
not so much for efficiency which is nice - but then
the busy pilot can "cob" it any time without fear of
"P"
factor. This probably means at least 1500 bhp - Vance

I was worried about turbulence myself. No competive single
engine rotary powered airplane is going to meet that 
weight criteria.

I guess that is why they call it Dreadnaught.
It can probaly fly in the wake of a fully loaded
747.

The P factor with an 8 foot prop must be something to 
behold. Good point Vance. I see no cheap way around that
problem. A counter rotating gear box will not be
cheap. Perhaps we can find one in Russia :-)

I remain the ever optimistic Paul :-)
 
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