Morgans wrote:
"Charles Vincent" wrote

In the end, it still doesn;t matter as GM is not to my knowledge selling
reciprocating aircraft engines certified or otherwise and I have not seen
any evidence many of the uncertified engines for sale are testing their
engines at this level.

I guess the point that we were making, is that although GM is not selling
uncertified engines for airplanes, a number of them do find their ways into
experimental airplanes, thus the reaction about the reliability of auto
engines.

Automotive engines today are exceptionally reliable. No where did I
impugn automotive engines. It is also obvious that all readers are not
clear on the use of the adjective "many". Many does not mean all or
even imply a majority, it at most implies more than "several".

Interestingly, it is most always not the core auto engine that experiences
failure when an auto engine conversion has problems, but the prop speed
reducer, or fuel system, or non original fuel system, or whatever else has
been added or re-engineered by the experimenter.

What the heck does that have to do with it? "Why, its the best most
reliable 200hp airplane engine you can buy, unless you insist on hanging
a prop on it -- have you considered building an ornithoper?" If it is
not reliable when configured for use in an airplane, it is not a
reliable airplane engine. The FAA endurance test requires "a propeller
ordinarily used on a similar engine" be installed, it is also required
for the vibration survey, which is another specified test. The FAA
tests and certification has specific requirements of the fuel,
lubrication and ignition system with aviation necessities in mind. I
believe the reduction unit would be part of the equipment tested, as the
type sheets list the geared and ungeared varieties as separate engines.


I hope this sheds light on why your comments got such a swift and
enthusiastic rebuttal by some here. It sounded as if you were condemning
those that used auto engines for airplanes, as a unsatisfactory, not as
tough engine as what is made as a certified engine.

It may have been enthusiatic, but it was not a rebuttal. I opined that
many (not all) un-certified engines being marketed (not built in
backyards from automotive sources) would be unable to complete the
endurance test. People responded with evidence that automotive
manufacturers did endurance testing of automotive engines configured
with accessories required for automotive use (i.e. transmissions etc)
which has nothing to do with my statement.

I am not a certified engine bigot and I believe experimental aviation
should be experimental ( I also believe homebuilts should be homebuilt
as well) I was more specifically aiming at the vendors targeting the
experimental market with uncertified engines that make outlandish claims
regarding reliability, fuel burn and most especially power. The first
two tests --

(1) A 30-hour run consisting of alternate periods of five minutes at
takeoff power and speed, and five minutes at maximum best economy
cruising power or maximum recommended cruising power.

(2) A 20-hour run consisting of alternate periods of 1½ hours at maximum
continuous power and speed, and ½ hour at 75 percent maximum continuous
power and 91 percent maximum continuous speed.

--- would highlight the fact that just camming and carbing an engine to
produce 100hp on the dyno isn't going to be enough to get it through
thirty hours of five minute 100hp bursts with a five minute cooling
period at what, 75HP?. The second test is just going to further
highlight any deficiencies in cooling. There is often a vast difference
between dyno results and useful power.

After all of the major metallurgical crankshaft problems that some of the
certified engines have had as of late, it is hard to accept that just
because it is certified, it is completely reliable.

No one said it was, but do you honestly think an honest comparison of
certified engine installations with uncertified engine installations on
a reliability basis is going to make certified engines look bad? You
would have to compare incidents per hour of operation for all certified
engines vs incidents per hour of operation for all uncertified engines.
The data I doubt exists and the data that is there is probably
not proportionate i.e. certified installations are more likely to be
reported than uncertified. As I understand it the Lycoming debacle
affected 3000-5000 engines and resulted from a combination of a change
in alloy used for the crank and the jobber forging the cranks not
holding to the forging temps required. Small details that resulted in
the crank not being up to the job of carrying prop loads at power. So
do you think uncertified engines are more immune to this than certified?
As immune? So how does some relatively low volume uncertified engine
company with parts sourced from everywhere from chinese made bubble pack
hot rod stuff, to custom machined assemblies going to track things at
that level? Particularly when most of the parts where never intended
for aviation and the part vendor is continually trying to optimize his
costs for his intended market? And your backyard assembler/builder?
Even though I am not really talking about automotive manufacturers, I
will point out that the number of auto recalls and TSB's issued on a
monthly basis is not insignificant even with their endurance testing.
Anyway, this is not intended as a diatribe against un certified engines.
I think they are great. I was really just addressing the original
poster's question on the standard day used for certified engines. I
assumed he was going to be using that information to compare his
favorite certified engine to some recently dyno'd uncertified variant
being marketed. My point was just that as I said before in this post,
there is often a vast difference between dyno results and useful power
and an endurance test ala FAA is more useful than a dyno run.

Charles