My comments on the message below are two.  One is that someone believing
that hp is doubled by gearing down 2:1 may not have the prerequisites
for the class on doing an engine conversion.   The other is that the
power lost in the redrive is at least 10 times lower than suggested;
maybe 2 - 3%.  Otherwise the planetary type could never be cooled by the
trickle of oil running through it.

Al

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of Eric Ruttan
Sent: Thursday, December 04, 2003 8:23 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Fw: [canard-engines] Auto engines in aircrafts...

forwarded for comments.

From: "William Epperson" <bill_eppy@yahoo.com>
To: <canard-engines@yahoogroups.com>
Sent: Thursday, December 04, 2003 6:37 AM
Subject: [canard-engines] Auto engines in aircrafts...


> Some common misunderstandings in dealing with an auto
> conversion is that many people fail to take into
> consideration certain factors, mainly one.  Say for
> instance that you have an auto engine that develops
> 200HP at 6000RPM.  You are using a PSRU that has a 2:1
> step down.  You'd think that would double your power,
> nope.  You'll still only be getting 200HP output at
> 3000RPM, and that's assuming that you are getting 100%
> efficiency from your PSRU.  No PSRU operates at 100%
> efficiency.  Say for instance that you have a 20%
> loss.  You now have a motor that in all essence is
> equal to a 160HP direct drive motor with a 3000RPM
> output.  20% may seem excessive.  But go look at some
> of the PSRU manufacturers, this is not out of line.
> Upto 25% is fairly common.  Geared PSRU's typically
> have a lower efficiency loss.  Say you want to replace
> a I0-360 motor with a auto conversion.  You'd need to
> make 210HP at 5500RPM with a 2:1 converter and 15%
> PSRU loss to achieve the replacement output of the
> I0-360 at 160HP.  If you are running an auto engine at
> 5500RPM, your fuel economy is fairly high for this
> size motor.
>
> It's been mentioned and some people have wondered why
> Subaru motors have been pulled in favor of a Corvair
> motor.  The Corvair motor does not have the
> complicated systems associated with it that a liquid
> cooled motor has to deal with.  It's aircooled like
> most other aircraft engines.  It's power is generated
> at a fairly low range, again like aircraft motors.  If
> you had a Subaru running at 6000RPM with a 30% loss at
> the PSRU it could output 160HP and still be equal to
> the Big Bore version of the Corvair.  And the Corvair
> would be much lighter and use up much less fuel.
>
> I'm currently building one of these Corvair motors.
> Why?  Because I can <insert stupid smiley thing
> here>!!!
>
> Sometimes you have to look at your final operating
> costs when considering the financial implications of
> an auto conversion.
>
> There's an engine that I've been watching for several
> years now.  The company has finally started building
> and selling these engines.  It's known as a Dyna-cam
> motor.  It's about 265lbs. dry weight.  It outputs
> 200HP at a very low 2000RPM with a torque output of
> 525 ft lbs. at 2000RPM.  It's smaller than most
> aircraft 4 cylinders.  It's deminsions are 13" x 40"
> length.  Very streamlined.  This motor has even been
> certified, although they are concentrating on the
> experimental market at this time.  The engine is not
> cheap by any means.  But I think that it will be
> proven to be a very remarkable motor.  I'm personally
> going to wait for the diesel version of this motor.
>
> Just trying to throw some input into the debate.
> Bill


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