With a 2.85 gear box and 7000 RPM max you are looking at about 215 HP.
    Assuming you install a dry sump system the big questions is how the
    drain back oil out of the rotors oil will behave. It might drain
    back better than a plugs up engine :) On the other hand the main bearing
    oil drain backs point straight down and they may be more of a problem.

    Paul Lamar



Ben Baltrusaitis wrote:

Paul,
Don't you think I would be able to turn almost 8,000 rpm with
the MT CS 3-blade prop and Tracy's 2.85? The prop is rated at 2800
max rpm. What hp is reachable at that rpm? Do I have to go to a 3.15 ratio?
Given that the main bearing drain back would be a problem, what do
you think would be the inverted flight time limit--assuming
no modification to the main bearing?
Thanks!
Ben

Yes of course. I did not know they ran that prop that high. I assumed
2700 which would be 7700. My guess at 8000 would be about 220 to 225 HP.
The new rating on the RX8 engine is 237 HP at 8500.

What is the prop diameter? You need a large
diameter for an aerobatics airplane to get good low speed thrust.

Like a helicopter :)

For a good aerobatics engine you might consider a supercharger
and a larger prop with the 2.85 psru. That will give you good
HP at the lower RPMs limited by the larger prop diameter. Don't
forget you will still need an intercooler.

Your guess is as good as mine on the main bearing oil drain
back. I don't know what will happen. You might want to build
a test stand with the engine mounted up side down.

Paul Lamar

Paul on the contrary. Most Aerbatic props are not big. they use 3 blade for low end thrust. My
neighbors Extra 300 is swinging a 70" 3- blade MT hydraulic on the IO-540. Of course a lower
top speed will also be achieved with the cruise pitch. They only problem I see is a greater
torsional load on the forward bearings of Tracy's redrive. Maybe accelerated wear?
Paul I have been working with Don over at Hayes Rotary about a set up he did for a customer on a
dry sump install on a car. He had done the modification work to the front housing but the
customer supplied the pump. Can you give me an idea on a suitable electric pump for this? Hayes
said he could do it for half of what Powersport was doing it for. That was approx $1,500. That
would be the solution to this inverted delemma!
Doug Mueller
RX-6 13BT
N900DM
Henderson,NV

There is no doubt that three blades help as well.
I think they are smaller so they can run the direct drive Lycoming engine faster
and get more HP.

Have you measured the diameter on a geared Russian radial engine prop on the Sukoi. Great
vertical penetration and IMHO why they dominated unlimited for so many years.
I tried to talk Gene Hackman into using a geared Lycoming a few years ago.
I did not know if the Lycoming gear box would take it as the regular
Lycoming aerobatics engine crank and prop shaft are beefed up.

This geared low speed prop advantage was over come when Extra went to
light weight carbon fiber construction.

There is no beating a helicopter for vertical penetration.
If Vance were here he would agree with me. The larger the diameter
the better the low speed thrust.
Paul Lamar

I will happily agree on that point with you Paul. Dem Helo's know how to
reach for the sky.
Royce

Hey Guys, I was not trying to say that the Heli blades didnt work better. 
I was just trying to use it
in a practical application guys. He was talking about an airplane 
not a heli. Those wonderful long
efficient blades would be great as a runway grater...LOL. The most 
clearance he would have with that
prop is 6 inchs of ground clearance maybe.

Doug Mueller
RX-6 13BT
N900DM
Henderson,NV

That's why that Sukoi had such long landing gear :)

Paul Lamar
 
The AirCraft Rotary Engine NewsLetter.  Powered by Linux.
ACRE NL web site. http://home.earthlink.net/~rotaryeng/            
Copyright 1998-2003 All world wide rights reserved.