I just finished reading the second article on auto engines
in the August Kitplanes. I came away with the impression that 
the author felt that piston speed was the only criteria for 
engine life. Nothing could be further from the truth.

An engine will run all day long at 5000 RPM with no load. The piston
speed is right up there but the thermal load and the cranksaft torsional
deflections among a lot of other tings would be near nothing. RPM or 
piston speed is NOT the same as HP! The amount of HP generated 
continuously is the real criteria for engine life. 

He did mention a couple of tests that GM uses but the engines are 
junk after these 300 hour test. Nobody has run an automotive engine 
for 2000 hours at 75% power. No mention was made of the cranksaft 
or other parts in the engines fatigue life. No mention of the exhaust 
valve life at 75% power long term.

He also mentioned a Lexus engine had passed certification. No telling
what parts were changed in that engine compared to the car version.

Other automotive racing engines were mentioned but no mention was made of the 
high strength aircraft quality alloys use in those engine's critical parts
replacing the cast iron and powdered metal parts of the stock production engines.

It is extremely important what kinds of materials are used in an AC engine. 
Cast iron and powdered metal are typically used in automotive engines that 
spend their life generating 30 HP. These are the materials cited in the article
as being advanced. Yes they are advanced for automotive engines as they
are cheaper than the high strength 4130 and 4340 chrome molly alloys 
typically used in aircraft engines. In that sense they are advanced.

Two tables were published. One for aircraft engines and one for automotive engines.
This implied that they were somehow equivalent. Nothing could be further from
the truth. The materials the various parts of each type of engine are entirely
different and were not specified in the tables. Further more dimensions
of the various parts were also not specified. Things like main and rod
journal diameters, torsional resonant frequencies of the crank shafts,
valve stem diameters and temperatures at max and cruise power etc,, etc, etc.. 
All of this affects the stress level and hence the life of the part.

Bottom line is; no way will a modern automotive piston engine
equal an aircraft engine. The two devices are designed to do different
jobs. Never the twain shall meet. If anything the two designs are diverging.
I am very disappointed in that series of Kitplane articles.

The author and editors of Kitplanes should know better and need 
to read these books.

Taylor's series of books is the best there is. The bible of 
engine design. 

The Internal Combustion Engine in Theory and Practice. 

Volume 1: Thermodynamics, Fluid Flow, Performance. Second Edition 
Revised. 

Volume 2: Combustion, Fuels, Materials, Design. Revised. Charles 
Fayette Taylor. The MIT Press Cambridge Massachusetts, and London 
England.  
 
Paul Lamar
 
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