Jay Honeck wrote:
I do believe this thread proves the old Usenet adage that "anyone will
argue anything". For you to be questioning the rather obvious fact
that high-power/low-power engine operations are harder on an aircraft
than steady-state engine operations illustrates a remarkable, um,
quality.
Jay, this simply isn't an "obvious fact" and I'm not convinced it is a
fact at all. You have provided one mechanic who thinks your way and
several of us have provided mechanics who disagree. This is hardly the
scenario that would surround an "obvious" fact.

I am apparently speaking a foreign language here, because I'm having a
hard time comprehending how normally intelligent people can argue this
point. Let's see if I can 'splain myself.

1. High power operation of an engine puts increased strain on
EVERYTHING. Seals, rods, gears, accessories. You name it, high power
operation is harder on your engine than low power operation.

Stress (and the strain it induces) isn't a problem in a well-designed
engine or any other structure. As long as the strain remains well below
the elastic limit, virtually no harm is done. I say virtually, as
depending on the material fatigue issues may arise if the stress is high
enough and the cycles large enough. As long as the oil film isn't
compromised, the higher stress does NOT cause any additional wear. Why
can't you understand this?

And the seals and accessories are not much aware of how much power the
engine is producing. They are much more concerned with RPM and the RPM
isn't a direct measure of power output.


2. Going from low to high power abruptly (and that, remember, is the
crux of this issue; I don't think anyone is arguing that gradual/
gentle application is terrible for your engine -- although it WILL
wear it out faster) puts sudden, abrupt pressue on those
aforementioned seals, rods, gears, pistons, cylinders, accessories.
This is what is known as "BAD", in my world.

Again, unless you are exceeding the limits of the materials, the metal
doesn't much care how fast you apply the load. Jay, you need to
understand that not all things yield to intuition. Many material
properties and engineering principles are not intuitive.


3. Your engine has a certain number of revolutions in it before it
reaches TBO. Might be a million, might be a billion -- I don't know.
Whatever that number, if you run at higher RPMs, you will reach that
finite limit sooner. Stuff run at high RPM wears out quicker.

Do you have even one shred of data to back up this claim? I believe
that NOT running an engine is THE fastest way to kill it. Starting it
often is the next fastest way. And running it is the way to make it
last longest. I doubt that the average number of revolutions per hour
is much higher for T&G practice in the pattern as it is for cruise.
Many folks fun at lower than cruise RPM in the pattern and the higher
RPM during climb-out is offset to a large degree by the lower RPM during
descent.

RPM alone does not wear out an engine.


And, most importantly to this thread, engines rammed from 900 RPM to
full power, and back, over and over, are going to wear out sooner.
Same with props, automobiles, lawn mowers, motorcycles, blenders,
chain saws, snow blowers, and virtually any other mechanical device
you can name.

I don't believe that to be true and you have shown absolutely no data to
substantiate that. I worked as a logger for 5 years and we used Stihl
brand saws almost exclusively. They ran at 6 - 8,000 at full tilt and
were started and stopped dozens of times each day and went from idle to
full throttle to idle hundreds to thousands of times each day (several
times limbing just one tree). The engines were simply bullet-proof. We
literally never wore out a single Stihl engine. Something else always
happened to the saw before the engine wore out. We ran these probably
1,500 to 2,000 hours per year as we worked 6 day weeks and often 10 hour
days.

Jay, I appreciate that you are saying what you believe to be correct
based on your intuition, but I don't believe your intuition is correct
in this case. The skidders, saws, and trucks that we ran the hardest
always lasted the longest. We had one skidder that the operator ran
more sedately as he thought it would make it last longer (he felt as you
do about engines). It didn't make 3,000 hours (not much for a Detroit
Diesel). When we tore down the engine, the transfer ports were half
closed with carbon. When the engine shop saw it the reason they said
the engine had to be rebuilt prematurely was that it wasn't operated at
FULL THROTTLE as Detroit Diesel intended it to be operated. This caused
it to run too cool and build up carbon.


Matt