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Here’s a follow-up on my previous note. Thanks
for the comments.
Dan writes,
“I haven't seen all that many crashes in my life,
but the ones that stick in
my mind are those that happened during the
takeoff phase. Sure, that's
probably because I was at the airport when they
happened so I got a
ring-side seat. Just the same, they happened - so
I'll push the throttle in
gently on initial power-up, and leave the thing
alone till I can make a safe
landing”.
Dan, I’ve seen a few also, but we need answers to
some questions to draw the correct conclusion.
1 How many of those accidents happened because
the pilot did not select max power for takeoff?
2 How many of those accidents happened because
the pilot did select max power for takeoff?
3 How do those answers relate to our high
performance airplanes?
The window for making a safe landing does not
open at 1000’, it opens when you push the
throttle in. I you happen to be taking off on a
long runway surrounded by houses or otherwise
unlandable terrain that window may actually be
closing as you approach 1000’.
Rob writes,
“Do you do your run-ups at full RPM also? Seems
to me that's in keeping with
your philosophy”.
I have heard of pilots who do full power runups
before an especially critical takeoff, and I have
watched many pilots park on the centerline and
run up to max power for several seconds prior to
brake release, but I have yet to land on a runway
that requires a max performance takeoff.
Hopefully I never will since landing requires 50
to 100% more runway than takeoff. I’m comfortable
with an occasional launch at max power.
Rob continues,
“And if you think you're operating the engine in
a manner to
cause it to fail, I have to ask why you're doing
it? Wouldn't you rather
take off at a lower setting and push it up to
100% at 1000 feet altitude? Didn't think so”.
Right you are Rob, my 360-A1A can’t make 100% at
1000’above most airports unless the pressure is
very high and/or the temperature is very low.
Like it or not, for those of us with normally
aspirated engines, the first power reduction
begins when the tires leave the runway and ends
when we level off, I simply accelerate the
process sometimes.
More importantly, engine failure can lead to
fire, always a scary thing, especially in a
plastic airplane. I would rather experience that
at 50’ agl, 2000’ down an 8,000 foot runway at an
airport with fire trucks and a trained crash
crew, than at 1000’ agl over a densely packed
city. That’s why I wrote,
“I make full power takeoffs at airports with
runways that are very long and numerous. The idea
is to stress the engine as hard as possible to
detect any developing weakness under circumstance
where a landing straight ahead or a circle to
land on a crossing runway is possible. Throttle
back before exceeding gliding range to the
airport”.
Rob continues,
“Parts with a fatigue life are designed by
derating the allowable material
stress to account for the cyclic loading on the
part. For an engine that's
easy. 2500 RPM times 2000 hours tells you how
many loading cycles will be on
every part. I don't think that running the
engine at an economy setting will
prolong the life of pistons, connecting rods, and
the like due to a reduced
number of stress cycles”.
If the number of stress cycles is the dominant
factor in determining fatigue life, why do Top
Fuel Dragsters have a TBO in the neighborhood of
three minutes? And why do so many fail to make
TBO? Peak stress is an important factor in the
determination of fatigue life and the
relationship is very nonlinear, that is, a modest
reduction in peak stress can pay off with a much
greater life extension. That is why I generally
reduce manifold pressure about the same
percentage as RPM.
I’ve put over 1,300 mostly wonderful hours on my
engine since new and hope that will be a small
fraction of the ultimate total. Suppose I rebuild
the engine at 2000 hours and keep some key parts
like the crankshaft. Is there any test to
accurately measure the number of safe revolutions
remaining in that crankshaft, or should the FAA
rule that all engines be melted down at 2000
hours? I believe going easy on the engine now
improves the odds for a safe second run.
Brent writes,
“Funny you should mention it though, I never
believed those stories. There was never any data
to back them up and I am a
freak when it comes to data.
Think outside the box. What box? There is a box?
Statistically, every person in this country has
one testicle, on average,
except Don Goetz, who now has an extra set in
brass”.
Thanks for the kind words Brent. Can anyone
recommend a good proct… oops, I mean a good
urologist for Don.
A factor I failed to mention is noise. It is to
our advantage to be good neighbors and we are
fortunate to fly planes with enough performance
to have that option.
We each make our choices and take our chances,
good luck to all.
=====
BILL HANNAHAN
WFHANNAHAN@YAHOO.COM
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