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