I happens to have a lot of faith in GM engines. They , like
everything else, are not perfect. Chevy had camshaft problems in the
distance past,and the timing chain is the first thing you dump when
you hop up the engines, gears are much more reliable.However it is
the Chryslers that like to jump teeth with their plastic gears etc.
Fords had problems in their V8's a decade ago with too few threads
holding the spark plugs.Aircraft engines are made with the finest
steel and techniques available...................in the 1940's!! If
I have such a high opinion of the word "certified" I would not be
looking at alternate engines.They published my letter in the latest
Flying mag. on that subject. Another reason for the nickel content
is for a bit better corrosion resistance, which a/c have more than
many cars. The nickel content also add some toughness, but I don't
think they have any where near as much as in amour plating.
Auto engines had incremental improvements through the years, while
aircraft engines are at a stand still, and still have lead in the
gas. The auto industry, easily 100 times the size, within a time
span of 3 years, had the lead removed starting in 1975?Basically
with hardened valve seats and to get the necessary octane with more
refining without the lead. Now they use ethanol.They had incentive
from governments, especially Calif.
A 400 HP engine only use a small fraction on the highway, that is no
indication of the engine's toughness. A Chevy small block 350 cubic inch
can easily put out twice that or even more in dragster applications
where the engine life is 1 mile.
I heard of how they pushed these engines during endurance testings, some
with pictures of the turbo glowing red hot.So a race modified 400 HP
Chevy LS engine at 350 HP cruise would easily outlast the standard 2000
hr. TBO , the TBO times could rival that of a PT-6! I think the % of
certified engines that made it to TBO is around 5% or less.
But the piston engine do have several inherit disadvantages, compare
with rotary and turbines, more part count, liquid cooling, and the re
drive, one more thing to go wrong.
The re drive I think is only troublesome for the smaller HP
applications, where there are more space, weight and budget
constraints. Even Rotex, with their engineer resources available to
them, had their shares of AD's.By the time you get to 300 HP, I
don't hear as much complaints.All turbines have re drives, for prop,
fan or accessories, yet the PT-6 have a reputation for reliability.
One thing the Viking engines(and Rotex) taught me, they use Evans
coolant. This stuff boil at 375F, a significant margin in borderline
detonation cases in boosted engines. That means I only need a
minimal amount of pressure (0-5 Psi?) to aid circulation and to
forget the pressure for raising the boiling point.That increase
reliability. The engine may run a bit hotter. Tony Lam
A race modified V8 is lucky to last a 24 hour race.
It took GM several years on a Le Mans programed dyno to get a Chevy
V8 to last 24 hours. We had to back off on the sprint car power red
line. As it was, GM used all aircraft qulity parts. The engines were
then worth over $100,000 in today's dollar. The fundamental problem
is inadequate bore spacing and the V8 configuration,
http://www.rotaryeng.net/DS-smith-art.pdf
Smithsonian Air & Space magazine article "Power Struggle" by Don
Sherman, January 1997, page 72. Excellent ten page article (with
many pictures) about auto engines in airplanes. A brief history of
all auto engines in airplanes and a more detailed history of the
twenty year, twenty million dollar development of the Chevy V8
based, all aluminum Orenda liquid cooled aircraft engine. At this
time (Jan 1997) and well after the article was written the engine
failed its FAA 150 hour full power certification test due to a
crankshaft problem after 20 years of very expensive development.
It was finally certified in 1998 by Transport Canada.
Extensive changes have been made to the basic Chevy big block engine
including a parallel cooling system with dual coolant pumps as
opposed to the serial cooling system with single pump as typically
found in automotive engines. Parallel cooling systems were
considered to be essential in the 1920's on liquid cooled aircraft
engines.
Engine length is almost everything to a car designer. Engine cooling
compromises are made by simezing the cylinder walls in automotive
engines. Crankshaft life at high continuous power is compromised by
shortening the length, leaving too little room for adequate size
journal fillet radii. In my opinion this engine will not be
successful until it is re-designed from a clean sheet of paper to be
a real aircraft engine. If that happens they might as well go to a
horizontal opposed configuration for lighter weight.
Orenda is now in the process of moving the project to Nova Scotia
and injecting another 32 million dollars of mostly Canadian
government money. They are also attempting to market the engine to
the homebuilt market. I don't expect many takers at over $100K per engine.
Recently Lancair gave up after spending a lot of money installing
the engine in a special airplane called the Lancair Tigress.
The engine and the Tigress were donated to the EAA museum as
a tax write off.
The Orenda company is now bankrupt.
http://www.rotaryeng.net/DS-smith-art.pdf
Paul Lamar
Tony,
All of the big three used nylon on the camshaft timing gears to reduce NVH,
and they all fail in time due to the nylon becoming brittle. When this happens
they ALL come out of time and depending on the circumstances may destroy the
engine.
Drag race engines can put out phenominal power for a short time and then
they are rebuilt. Road race engines have to last longer and thus are not built
to rev as high to get the HP. Endurance race engines are pretty much spent
when done a 24 Hr race.
This all boils down to design usage and duty cycles. When you move outside
the design duty cycle you have to re-engineer most everything. The internal
forces on a reciprocating piston engine are extreme when using a high duty
cycle. To make an engine last for 24 hours at race power requires a lot of
extremely expensive components. Forged crankshafts, connecting rods, pistons,
valves to name a few. When Chevy built the endurance engines, the titanium
rods is one part that got attention.
The Ford that blew the plugs out are not an ancient fact. They were on the
earlier Mod motors of 10 to 15 years ago. All have screwed up on the
engineering at some time or another. Some may be attributable to the bean
counters getting their noses in the engineering department where they should
not be allowed.
If YOU feel comfortable with an automotive piston engine conversion in an
experimental AC, you are welcome to it. You can not use a crate engine as is
from the factories as they will not usually stand up to the HIGH duty cycle.
As usual there are exceptions but in this case they will be few and far between!
In my opinion the ONLY ACCEPTABLE engine alternative to certified is a
rotary engine due to the low internal stresses experienced.
Dale Davies
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