I'm not trying to make friends, I'm trying to get down to the truth.
Nobody seems to agree on anything in this domain, and I have to wonder
why. It seems to be a part of aviation that is filled with mythology,
rumor, and urban legend, but few hard facts appear to circulate, and
for some reason the actual recommendations of the engine and aircraft
manufacturers are often discounted in favor of rumors, which doesn't
seem very rational (although it is a fairly typical human behavior).

There are a couple of reasons for this (besides ego). First, there are
many kinds of airplanes, and they are all different. Yes, they are all
basically the same (well, most of them anyway), but the differences can
bite if you're not aware of them. Stall charactaristics, engine design
and performance, wing shape, T- or conventional tail, canard... it goes
on. If you learn in one airplane, and from there "know" how airplanes
work, you may find that in a different airplane you know stuff that
ain't so.

There are rules of thumb developed to help bridge this - not running
oversquare is one of them. It's a convenient coincidence that the RPM
and MP numbers, in common units, line up the way they do, and line up
close to the edge of the envelope. Keeping undersquare is safe for most
(spam can) engines, running oversquare requires a peek at the POH to see
how much oversquare in this engine under these circumstances is ok. So
the rule of thumb gets taught, and it gets learned as a hard and fast rule.

Some limits and procedures are designed by lawyers. Consider the
Cirrus' spin recovery technique: pull the chute. I've never spun the
beast, but I bet it would recover conventionally if it didn't get too
far into the spin.

There is also some room for technique. There is no "best" power
setting, for example. What you use depends on what you want, and what
you're willing to give up. And whose airplane it is.

Also airplanes are expensive, and pilots are discouraged in a number of
ways from doing destructive testing on them. A lot of our knowledge
comes from the manuals (where the companies have done their own testing
and given us the digested results they choose), and the necessarily
limited experience of their own and their instructor, and authors of
books they've read.

In some cases the instrumentation just isn't good enough to achieve the
measurements you want. Some airplanes have no engine meters at all, you
pull back the mixture until the engine runs roughly, then you push it
back until it's smooth, then push it back "a little more". How much
more? However much your instructor taught you. (I've seen POHs that
are no better).

So why are the POHs not as good as they could be? I'm sure it's about
sales and liability. Anything that goes in a POH is fair game as "this
is why he crashed", right or wrong. If it's not there, there's nothing
to point to. And it costs money to do the research, so why not just
sell more airplanes by marketing instead?

So, us pilots are left to figure it out as best we can. Look at the
actual instruction booklet that came with the Piper J-3 cub, and see how
little it says.

Jose
--
He who laughs, lasts.
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