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Book Review: Converting Auto Engines for Experimental Aircraft , Finch

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Old October 18th 04, 10:14 PM
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Default Book Review: Converting Auto Engines for Experimental Aircraft , Finch

A little good information but mainly cheerleading

At one time, it was thought that auto engines were for cars, boat
engines were for boats, and airplane engines were for airplanes.
Eventually, Gardner diesel and Miller/Offenhauser racing marine
engines wound up in vehicles, Liberty, Napier Lion, Ranger and Allison
aircraft engines wound up in boats, and car engines-because of the
radically cheaper cost and superior technology of mass
production-wound up first in boats (which have completely killed the
spark ignition inboard dedicated marine engine business) and later on
in some aircraft applications.

Just as car engines in sporting craft were at first ridiculed, then
made to work-with a lot of dedicated and expensive development-well
enough to completely dominate the market, they are slowly making
inroads in the experimental aircraft field.

As with the I/O stern drives, the car engine doesn't just bolt up to
the prop. Aircraft engines are design mutants that have evolved to
handle the thrust, precession, torsional resonance, and torque
requirements of driving a heavy propeller pulling an aircraft not only
in level flight but through all phases of flight including aerobatics.
The propeller provides the inertia provided by a flywheel on other
engines, reflects severe loads to its driving member, and must be
secured to the driving member as if the aircraft's continued flight
depends on it, because it does.

"Converting" a car engine-perhaps because they are used in so many
other applications they should be called not car engines but general
purpose engines-means providing for all these requirements very much
as a inboard/outdrive or "stern drive" does on a pleasure boat. In
most cases, the GP engine turns far too fast to drive a large
efficient propeller so geared or belted speed reduction has to be
provided. The engine must retain its flywheel, albeit of aluminum
marine or "flex plate" type in some cases, and torsion damper just as
in a car or stern drive. The propeller cannot be the prime source of
inertia-a fact Kiekhaefer figured out when stock cars really were.
Propeller loads as well as the mass of the engine and its drive must
be securely reflected to the airframe. All modern spark ignition
engines are liquid cooled, so the radiator must be provided for as
well in most cases an oil cooler.

It's not impossible, but it's equally not trivial. This book consists
of a lot of irrelevant pictures and some back-of-the-envelope
drawings, and makes what is really a nontrivial task seem as though
anyone could. And anyone could, if they were a mechanical engineer, a
certified welder, skilled machinist, and experienced A&P and
automobile mechanic with a lot of time and money and not much else to

There's good reason to want to use a general purpose engine as opposed
to the grossly overpriced, inefficient, and essentially ridiculous air
cooled prewar tractor engines coming from Williamsport. However,
buying a fully designed firewall forward package or at least using a
commercially built drive and engine mounts with an engine of basic
type several other people have successfully flown a few hundred hours
with is far safer and more sensible thaan picking a random junkyard
engine and bolting it up. Several choices of reduction drive and
mounts are offered in the experimental aircraft supply chain, and if
you have the mechanical aptitude to install and maintain an engine in
a street rod or ski boat and use it successfully, there's no reason to
buy a museum piece from the clowns at 652 Oliver Street. However, this
book really isn't quite up to the task.

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