Aero-Tips!
A good pilot is always learning -- how many times have you heard
this old standard throughout your flying career? There is no truer
statement in all of flying (well, with the possible exception of
"there are no old, bold pilots.") It's part of what makes aviation
so exciting for all of us... just when you think you've seen it
all, along comes a scenario you've never imagined.
Aero-News has called upon the expertise of Thomas P. Turner,
master CFI and all-around-good-guy, to bring our readers -- and us
-- daily tips to improve our skills as aviators, and as
representatives of the flying community. Some of them, you may have
heard before... but for each of us, there will also be something we
might never have considered before, or something that didn't
"stick" the way it should have the first time we memorized it for
the practical test.
It is our unabashed goal that "Aero-Tips" will help our readers
become better, safer pilots -- as well as introducing our
ground-bound readers to the concepts and principles that keep those
strange aluminum-and-composite contraptions in the air... and allow
them to soar magnificently through it.
Look for our daily Aero-Tips segments, coming each day to you
through the Aero-News Network. Suggestions for future Aero-Tips are
always welcome, as are additions or discussion of each day's tips.
Remember... when it comes to being better pilots, we're all in this
together.
Aero-Tips 05.15.06
We're still talking about it -- avoiding fuel exhaustion through
better fuel planning. Today let's look at percentage of power.
From Advisory Circular 61-23C, the Pilot's
Handbook of Aeronautical Knowledge:
Fuel Consumption
The rate of fuel consumption depends on many factors...
particularly the percentage of horsepower used for flight at
cruising speed.
Percentage of power
Percentage of power is the measure of power development as
compared to that engine's maximum rated horsepower. For instance, a
150 horsepower engine being run at about 112% is operating at about
75% power. Any number of combinations of manifold pressure,
propeller speed and mixture setting may result in a given
percentage of power.
If you're flying an airplane with a fixed-pitch propeller the
concept of percentage of power is not terribly usable—not
because it doesn't apply, but because you have little control over
the variables. You typically won't even see reference to percentage
of power in these airplanes' performance charts.
If you're flying a high-performance piston airplane its handbook
usually gives only a few combinations of manifold pressure and rpm
for specific percentages of power. All are based on the
sometimes-elusive "book" leaning technique. Many Pilots Operating
Handbooks (POHs) have gotten away from the whole idea of percentage
of power, offering instead simple "Recommended Power Settings"
performance charts for a limited range of unidentified power
settings.
Unless you precisely calculate percentage of power using charts or products that take
mixture and a wide range of MP/RPM settings into account, you can't
truly determine percentage of power. Remember that the horsepower curve is directly
related to fuel flow—percentage of power defines fuel
requirements.
Aero-tip of the day: Percentage of power
is one of the prime determinants of fuel burn. But unless you
follow "book" technique to the letter, your actual percentage of
power—and the resulting fuel flow -- will differ from what's
in the POH.
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