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Date: Mon, 23 May 2011 10:49:44 -0400
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From: Ted Noel <tednoel@cfl.rr.com>
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Subject: Re: [LML] Re: L-IV Choice of Engine
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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.
>
> 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.
>
> 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".
>
> Automotive engines are designed for low cost, high speed, low 
> emissions, high peak power and  wide torque range. Think "Cheetah".
>
> What would happen if you hitched four Cheetas to your plow?
>
> 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.
>
> 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.
>
> People who know enough to design an aircraft engine are wise enough 
> not to.
>
> Brent Regan
>
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