Vaughn Mann wrote:

Tracy, help me on the figures here, If I'm running a 2.85:1 ratio, and

my engine is turning 7000 rpm, my prop rpm would be 2,456 right?  This of
course is almost supersonic tip speed depending on dia. of the prop. also.
But if I know that I would prefer to use my ultimate torque rpm on my
particular engine, let's say it's 5000 as an example rpm, that may be not
only more efficient but run cooler and of course longer lived (less wear)
quieter and more practical for me I would need to slow my engine down but
keep the prop speed of 2298, about the same (154 rpm dif.) as before right?
So in this situation the higher gear ratio of 2.176:1 would give me more
versatility in the more efficient cruise realm.  But if I was a racing
everywhere I went then I would want the ratio and prop combination that
would give me the max hp rpm and the max prop rpm that would allow it for
full throttle flying everywhere I go.  Does this make sen! se?

I'm flying a RV-6 with the 180 hp O-360 now but am looking to the

conversion of the Rotary in the future if Avemco will cover me.  Funny how
they will cover some if  they already have the rotary in it and others who
want to convert, they seem to use that against us to jack the rate beyond
practicality or cancel altogether.  Ironic how one has to weigh expensive
ancient Lyc technology cost as opposed to high insurance cost because one
wants to move into a much more reasonable and dependable and economic design
isn't it?

Thanks for your thoughts,  Vaughn

Hmmm,   I'm not really sure I followed that but the basic thing I was
getting at in my first  message on this subject was that regardless of what
the theoretical best prop and gear ratio is,  There seem to be no actual
props you can buy that are optomised for high speed (200 mph range) and
relatively low prop rpm.   Even if Paul's point of giving up some takeoff
performance in order to get better cruise is stipulated, there is still no
prop for sale that gives you the improved cruise.

I'm even less qualified to comment on insurance than I am on props!

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

I'll ask Don Bates if he has a list of prop suppliers that use his program.
Don?

Paul Lamar
 
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