the 57 to 65 pound weight of a metal constant speed prop.
BTW don't you believe me about the length of the line contact
being proportional to the torque capacity of a gear set? :-)
The Enginair is about 1.5 inches long while the Ford six pinion
is 4.8 inches long. That is a huge difference with the overwhelming
advantage to the Ford planetary set. Am I not clear about this??
marc wiese wrote:
I'll have to let EPI's Jack Kane reply to this.
It seems every engineer (me included) seems to have a different way to
solve a problem.
EPI did test the units using turbo prop metal blades using the ARP-880 cs
prop flange like is used on the V8's, and which is used on the PT6 and
TPE-331............ EPI proposes a unit of about 40 lbs, and the offset is
up in the air. Paul, you can contact Jack at Epijk@aol.com and perhaps
influence the design for the good of all of us. I expect open minds on a
subject like this, not turf battles. If there is a fatal flaw problem
with EPIs approach, lets hear it.
Maybe there is no "right" way, just lots of ways.
Marc--
I am not saying it is intrinsically bad. This is not a turf battle.
Their way is excellent for a V8. In fact it is
the only way for an upright V8. Toyota found that out the hard way as
they started with a real nice small and compact planetary but it put
the prop shaft in the wrong place. They spent millions. What offset is good
for a V8 is bad for a rotary engine. What offset is bad for a rotary engine
is good for a V8. If you consider all the rotaries
flying with Ross psru's with ford planetaria's the total experience we
have with the Ford planetary on the rotary is probably 10,000
hours or more. The failures so far have not been due to the
basic gear set. They have been due to the omissions of the
gear thrust bearing and perhaps inadequate oiling provisions.
When EPI gets 1000 hours on one of their 40 pound units and fly
it all over the country like Tracy Crook, Chuck Dunlap and Dave
Atkins have, I will change my mind. I will also say right here
and now if it uses custom gears you will not be able to buy it
for anywhere near $2500. Try $6,000 to $10,000. We are fortunate
indeed to have the low cost Ford and light weight planetary gear
set so adaptable to our needs.
Aviation history has shown that successful engine designs
are based on what has gone before. The rotary is a rare
exception to this rule. I suspect however that the design of
PSRU's is within the scope of this rule.
It is premature for me to have any discussions on this matter
with Jack Kane unless of course he was planning on using
the Ford or some other low cost planetary gear set :-)
I'll say it again. The length of the line contact is proportional
to the torque capacity of a gear set. Almost any planetary line contact
is much longer than any spur gear line contact anywhere near its
weight. Is this clear enough?
Paul Lamar
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