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Date: Tue, 24 May 2011 13:23:22 -0400
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Subject: Re: [LML] Re: L-IV Choice of Engine
From: John Hafen <j.hafen@comcast.net>
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Correct me if I'm wrong, please, but I seem to remember that the WWII =
Merlins were designed to last 200 hours.  And that was overkill based on =
the circumstances. =20

John Hafen
IVP 413AJ
TSIO 550, 300 hours

On May 23, 2011, at 7:49 AM, Ted Noel wrote:

Brent,

I am always amazed and amused at your erudition and elocution. Your =
comments are well-considered.

As one who took a different route (the Eagle V8) I have discovered the =
myriad trials of incorporating that engine into my airframe. It's =
horribly expensive and time-consuming. At the same time, it promises =
some advantages.

As for the design compromises (Cheetah vs. Draft Horse), those are =
generally issues of cam profiles, bore vs. stroke, and similar internal =
issues. Those are well known and understood. Note the differences =
between load haulers (see your note below), stationary engines, and =
cars. Designing a piston engine for various tasks isn't all that =
difficult for a competent engineer. After all, our 1930's boat anchors =
are... drum roll please... piston engines.

Probably the greatest challenge after internal design is cooling. Liquid =
cooling is heavy, and has hoses that can fail. Air cooling is lighter, =
and has exhaust valves that famously fail. Computer ignition is highly =
reliable, while magneto ignition is heavy and failure-prone.

Perhaps the best illustration of newer technology is the rapid demise of =
vacuum-driven instruments in favor of all-electric panels. So the issue =
is not the technology, it's the implementation. Liquid cooling =
eliminates certain internal compromises so that engines can live longer =
and produce more power per cubic inch, offsetting the apparent weight =
penalty of liquid cooling. They can have higher fuel efficiency. And =
they're more reliable, the key reason I went liquid. Of course, that =
last sentence hangs on the effectiveness of the cooling system...

Lest anyone think that the ideas I've listed above are pie-in-the-sky, =
remember the P-51, P40, P38, and Spitfire. They all flew with liquid =
cooled Allison or Merlin engines.

It's not the idea. It's the execution.

Ted Noel

On 5/23/2011 8:03 AM, Brent Regan wrote:
> Market forces require that, to be successful and survive, consumer =
products must be designed to satisfy a selection of requirements imposed =
by the consumer. Over time and competition, natural selection refines =
the design so that it is either better optimized and competes or it =
falls into the dustbin of history.
>=20
> Engines, while simple in concept, are spectacularly diverse in =
implementation. When you think "engine" think "mammal" and then imagine =
all the different species of mammals. Most all are successfully =
reproducing. Each is optimized for a particular set of conditions that =
allows them to dominate in a specific niche. The same is true for =
engines. Every mass produced engine is optimized for a specific set of =
requirements and no two requirement sets are the same.  Taking an engine =
from one application and inserting it in another results, de facto, in a =
sub optimal situation. You could couple the 350 Hp diesel engine from my =
truck to a weed whacker and it would indeed whack weeds but the =
portability requirement would not be met.
>=20
> Aircraft engines are designed with the primary requirements of  light =
weight, low speed, high continuos percentage power, high reliability and =
a narrow power band. Think "Draft Horse".
>=20
> Automotive engines are designed for low cost, high speed, low =
emissions, high peak power and  wide torque range. Think "Cheetah".
>=20
> What would happen if you hitched four Cheetas to your plow?
>=20
> Modern automobile engines have benefited in billions of dollars in =
development with the ONLY goal of making them more attractive to =
automobile buyers. The corollary is that all that effort  has been =
expended to make automobile engines that deliberately do not directly =
satisfy the requirements of aircraft.
>=20
> The landscape is littered, both figuratively and literally, with well =
meaning, would be aircraft engine designers who share a common inability =
to learn from history.  Perhaps driven by the false assumption that =
desirable automobile engine characteristics can be selectively =
transplanted into an aircraft with the simple transposition of hardware. =
The problem, of course is that all the "not desirable" for aircraft =
characteristics are part of the bargain. Eating the brains of your enemy =
won't give you their wisdom but it may give you Mad Cow disease.
>=20
> People who know enough to design an aircraft engine are wise enough =
not to.
>=20
> Brent Regan
>=20
> --=20
> For archives and unsub =
http://mail.lancaironline.net:81/lists/lml/List.html
>=20
>=20
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>=20
>=20

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