George:
Many thanks for your comments which I
found to be very helpful.
I want to continue this dialog and have
added more material below to continue the Q and A. My replies are in green. But
first I want to make a big picture observation.
Certified engines
have well defined operating envelopes based on extensive testing, technical
knowledge, and millions of hours of field experience. Buyers deserve that
depth of knowledge because they did not sign up to be test pilots.
Experimental engines and
aircraft have an overt statement of increased risk – the sign that says “Experimental.”
So in experimental, we are all test pilots to an extent. Your implication
is that because we do not fully test, document, and frequently do not
understand changes we make, we should not make those changes. But we are
not GAMI or Continental or Lycoming. We do not have the resources to do
that kind of testing, and therefore have to be less knowledgeable.
But we love to fly and experiment. That
is the nature of our hobby. It is not the nature of Cessna, Piper, et al.
Your objection is in effect that we
should not experiment because we do not know the new limits of operation and
therefore take on additional risk when we operate without this knowledge.
But we (should) know we are taking extra
risks.
The problem is that many in the
experimental community do not acknowledge the risk, and more important do not
know when they are creating extra risk.
As an engineer I agree with your
assessment about distinguishing between knowns and unknowns. As an
experimental enthusiast, I welcome the option to experiment, but I try to do so
with care and understanding. We all need to continually improve
this understanding. That is why this forum is important and useful.
Ultimately it all depends on your world
view and willingness to take responsibility for your actions. But that is
another topic.
I’ll get off this soap box with two
suggestions for all of us: “Get thee understanding.” “Understand
Increased Risk.”
Now, to improve understanding, let’s
continue the dialog
INDUCTION AIR TEMPERATURE.
That one is OFTEN badly overlooked and it is a major driver WRT
detonation.
Thanks for highlighting. It is an
excellent warning for the turbo guys, and for those of us who operate from cold
to very hot climates. Make adjustments in your engine operating
habits when induction air temperatures climb.
Hot plugs are almost
exclusively a pre-ignition issue, not a detonation issue. But
then pre-ignition is a much uglier thing than detonation.
Thanks for the correction. Does one
then run as cold a plug as possible while avoiding plug fouling?
The problem is that I have NEVER seen an
experimental aircraft that had properly defined that "smaller
envelope" with appropriate markings and limitations on the instrument
panel.
I agree. So I think the best
benefit is for experimental guys with modified engines to recognize that while
they do not know how much smaller their envelope may be, it will be
smaller and they should act accordingly. I don’t know how fast
my car can take a particular corner (I am not a racer), but stock or modified,
wet or dry road, I know to drive conservatively if I do not want to bend the
car.
But WHERE are the boundaries of that envelope???
Unfortunately most of us will never know,
but we should recognize that the boundaries are NOT same as for the certified
engine. So I would assert that if you modify your engine, DO NOT to try
to go to the certified limits of (for example) CHT. I wish I knew
what was appropriate for my engine, but I don’t. But I do know I
should be conservative on MAP, Temperature, and Mixture. I am. And
I know I am experimenting and taking some risk in so doing. It was
my choice. I hope it was informed.
-
and thus they continue to
operate with the "hope" (not a method) that they
will be "OK".
This brought a smile. Once while
wandering around OSH, Brent Regan and I
formulated a theory. The Greeks believed that all matter in the universe
was made up of Earth, Air, Fire and Water. At OSH, we
concluded that the local world was made up of Hope, Denial (of the laws of
physics), Money, and Bullshit. So I guess I agree with you.
It is reasonable only in the context of
two further constraints: - - the owners really do want to be
"experimental test pilots"
Here we come full circle. By
definition in experimental they ARE test pilots. The question is whether
or not they recognize it.
and they are comfortable with hoping that
they have fully explored the relevant envelope. Without the instrumentation and tests,
how can they except to rely on guys like you, honest vendors, and their own
understanding?
Two questions:
1) What benefit to you think you get from the 10:1 CR
? Better fuel
economy. I estimated maybe 6% better compared to 8.5:1 CR, but the dyno data
from a reliable source (and relayed to me by Doug Brunner as I recall) suggests
that 310 HP is raised to maybe 325, corrected, or an improvement of maybe 5% in
the real world. That is $4 an hour at cruise where I operate. Full
disclosure – as an old engineer, I now place more merit on efficiency
than raw speed.
2) Have you marked your CHT with a redline at some number
below 460 d F? Absolutely
YES. I am not sure what the right number is, but as you may know, I am a
fanatic about cooling and cooling drag. I have an engine monitor with a
Bitching Betty on yellow and red bands, and she starts bitching at 350F (bottom
of yellow, where I am reminded to take corrective action) and she gets serious
at 400F which I recently reset as bottom of the red. I try to run at 320F
and below, particularly during take off and high power climb. I
know those high compression pistons need extra attention. I watch very
closely, particularly in light of GAMI suggestions and this very discussion.
Let the education process continue!
Regards,
Fred, AKA Captain Tuna, Chicken of the
Skies