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.  

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.
>
> 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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