Snips...

This would be no problem at all if Tracy went to the 2.85:1 PSRU.
Prop rotates in right direction.

Paul Lamar

This would be a good point for me to get input on interest on the

2.85 : 1

drive.

It is now apparent that the RX-8 and the Renesis engine are actually

going

to arrive so I've moved ahead on plans for the 2.85 drive.   I

consider

this

the main reason for using the higher ratio.  I'll be ready to cut

metal on

the prototype after getting the next batch of 2.18 drives done.

Opinions vary on this but here is mine:  Unless you are swinging a

long

prop

(at least 75" or more) or plan to run your engine at 7000 rpm or

higher, I

still think the 2.18 : 1 drive is the best compromise.  This is

especially

true if your airplane is in the 200 mph or more range.  The only

exception

to this may be gyros or other low speed aircraft where very wide

chord or

multi-blade (4 or more) props can be used.

You don't have to commit to buy now but I'd like to get a reading on

how

much interest there is in this ratio.

Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com

What ever turns you on Tracy :-)

IMHO the current engine can also benefit from the 2.85:1 ratio with
the current diameter props. There is nothing fundamentally different
about the structure of a  Renesis engine that somehow makes it
better for 7000 RPM. 9000 RPM no question about it...it's better!

I'm already on the list for Tracy's 2.85 (double check that Tracy).  My

13B

is rigged for those RPM, I figure a 6000 rpm cruise and 8500 full on

with a

three or four blade fixed pitch prop (LAEV when it's ready).  This

should

make for an easy 175 kias cruise in the RV-4 and 210-ish flat out.

Personally I like the idea of an easy cruise turning the prop at 1900
running 160 kts.

Mike McGee, RV-4 N996RV, O320-E2G, Hillsboro, OR
13B in gestation mode

If you use a fixed pitch prop on a slow turning out put shaft you
will go from somewhat stalled prop on your take off roll to
hopelessly stalled. Slow props on fast planes almost beg
for the controllable "high priced spread".

I also will state again - that I have not seen dyno data that supports
increased horsepower at 7000 rpm for a modestly modified
13b engine. Vance J

Yes but it will become unstalled at some point in the takeoff run.
Just because it is stalled does not mean it has no thrust.
Besides, you don't have to use full throttle at the beginning of the
takeoff run. Feed the throttle in slowly.

In the unlikely event the HP is increasing in some strange function
do you really suppose it cannot generate more HP at 7000 RPM if
it is generating 180 HP at 6000 (worst case scenario) and 
270 HP at 9200 RPM? :-)

I admire you for your world class pessimism on the rotary.
A never ending challenge for me. When you finally get on board
with the rotary we will see some great proselytizing efforts
on your part I am sure :-)

Paul Lamar
 
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