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In a message dated 12/4/2003 1:25:20 PM Eastern Standard Time, ALVentures@cox.net writes:
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 aircraft's...
> 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
> 230HP at 6,000RPM. 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 230HP output at
> 6,000RPM, and that's assuming that you are getting 100%
> Efficiency from your PSRU.
This part is accurate. The horse power is not doubled. Torque is doubled.
No PSRU operates at 100%
> efficiency. Say for instance that you have a 20%
> Loss.
A 20% loss in the PSRU would mean that 20% of the BTUs in the fuel consumed by the engine, will appear in the PSRU. In most cases there is no cooling at all for the PSRU, as in the Belted Air Power, system, or the PSRU is cooled by engine oil, as in the gear type PSRU. This number is ridiculous 3 to 4% is closer to the fact.
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.
> Up to 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.
The winner of this years Sun&Fun race was Tracy Crook in an RV-3 powered by a rather stock Mazda 13B engine with a planetary gear PSRU, at 209 MPH. Outrunning all of the "real" airplane engines.
The proof is in the pudding is it not.
>
> 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>!!!
I built quite a few Corvair engines, and I am wondering "why" also. Without a PSRU, the Corvair will have trouble breaking 100 HP.
>
> 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 dimensions 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.
An 18 cylinder version of this engine can be seen in the Air Force Museum. The design has been around since before W.W. ll. Piper dragged this engine through certification and the manufacturer decided that it was suddenly worth more money than Piper did, or anyone else for that matter. I will believe they are selling completed units when I see one fly over at an airshow. More likely they are still collecting investors to support further development. Why not just sell the certified version retail? Or a lesser version for the homebuilt market? Plus it has all of that "complicated" water cooling.
>
> Just trying to throw some input into the debate.
> Bill
Lynn E. Hanover
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