They're like bad dreams: They just keep coming back. "They," of course, are the half-truths and tall tales that come up from time to time and include "getting on the step," never running "oversquare" and using reduced-power takeoffs to baby your engine. AVweb's Linda Pendleton takes on these myths and offers a few guidelines to help you make up your own mind.
November 13, 2000
|About the Author ...
Linda D. Pendleton is Manager
of Computer Graphics and Animation for
She is also the author of a book, Flying Jets, and scriptwriter for
several of the training videotapes published by King Schools, including
"Navigation from A to Z," "METAR/TAF Made Easy," and "Handling Emergencies."
Linda is an ATP with Citation 500 and Learjet type ratings, and a CFI with
airplane, instrument and multiengine ratings. In her 10,000+ hours of flight
experience, she's flown US Mail, freight, corporate, charter, commuter, and
served as an FAA-designated examiner for the Citation 500.
is nothing that can prepare one for a life of poverty like being an on-demand
flight instructor in Chicago in the winter. Don't talk to me about your
starving artists none of them was required to pre-heat a frozen 150 in
below-zero windchill just to make a buck. (Yeah, I know, I'm starting to sound
like my folks "you young whipper-snappers don't know what it was like
in the 'old days'. I had to walk five miles to the airport and home in the
snow and it was uphill both ways!")
I cherish the memories of those days, but what I really remember and
miss are the hangar-flying sessions. We'd sit around the flying club office
there on the third floor of the Butler hangar at Midway, drinking coffee and
chatting. George Thor could be counted on to contribute if he was around.
George was in his late 80s and still carried a first class medical. He was an
active instructor, and, boy, did he have some stories. His first airplane was
a Curtis Jenny that came in a crate "batteries not included, some
assembly required." Sometimes the corporate or airline types who
instructed occasionally "to keep their hand in" would honor us with
their bored presence, but mostly it was just us working stiffs. There were a
lot of the "there I was flat on my back" type stuff, some good tips
and pointers, and then there were the half-truths based on fact.
Among them all, three myths kept cropping up in each new generation of
pilots. I sure wish I knew how they keep being propagated.
Myth #1 Getting It "On The Step"
must admit, this confused me for quite a while. The old timers would swear by
this technique for getting a little extra performance out of their
Cessna/Cherokee/Mooney and looked down on us "kids" who didn't
subscribe to the technique. For the uninitiated, the story goes that you can
get a couple of extra miles per hour (airspeed indicators were in MPH then.
I'm convinced that this was a marketing thing 115 mph just sounds faster
than 100 knots.) cruise performance if you get the airplane "on the
step." The "step" was alleged to be a mythical
"just-right" angle of attack which minimized drag and allowed an
airplane to cruise at a higher airspeed than normal on the same power.
"Just put it on the step" the ol' timers admonished. "It's
amazing. You won't believe the increase."
Well, I didn't believe it. Seemed to me that if such a phenomena existed,
the airplane manufacturers would have seized upon it and you would see
advertising along the lines of "Our step is easier to find!" and
"Take the big step up to..." and "Only a step to
faster..." and the like. Never happened. If the marketing types don't
exploit it, it probably doesn't exist, I reasoned, so I asked for a
demonstration. Joe one of the good ol' boys consented to educate the kid
and so we headed for the flight line.
We took off and flew south from Midway over the farmlands and the demo
began. Joe explained that we were going to conduct the cruise tests at 3,500
feet MSL and so when he climbed through that altitude, I asked about the
deviation. "Oh," he explained, "that's part of getting the
airplane on the step." We leveled at 3,800 MSL and Joe reduced the power
to the cruise setting and immediately began a descent to 3,500 feet. At 3,500,
he leveled off and asked me to note indicated airspeed. That done, he reduced
power and descended to 2,000 feet. After Joe established cruise configuration
at 2,000, he pushed the throttle in, raised the nose, and began another climb
to 3,500. This time, at exactly 3,500 feet MSL, Joe pulled the power back to
the cruise setting and pushed the nose over to the level attitude. When he
pointed out that the indicated airspeed was now about 10 miles per hour slower
than in the first test, I saw the fallacy of the "getting it on the
simple physics. Joe did everything the same almost in each test. Each
time, at the top of his climb, he reduced the power to the cruise setting, and
therein lies the problem. In order for an aircraft to accelerate from the
speed at which it is currently flying, there must be an excess of power or
some other force above the power required to keep it in level flight. In
the first test, Joe used the acceleration of gravity to get the airplane up to
speed after he had reduced the power. Remember the dive to altitude? In the
second test, there just was not enough excess power to accelerate the airplane
to cruise speed. Oh, to be sure, it would have slowly gained speed, but it
would have been a long, drawn-out process.
For just about any airspeed you pick, there will be two power settings that
will accomplish that speed one for a high drag/high angle of attack
configuration and one for low drag/low angle of attack. Reducing power to
cruise speed before achieving cruise performance will put you square in the
We did the test a third time. This time we climbed to 3,500 feet and pushed
the nose over to level attitude. We adjusted the pitch attitude and trimmed
the elevator as the airplane accelerated. Finally, when the airplane had
reached cruise speed, we reduced the power to the cruise setting, and, voilà,
we were at the same speed we had accomplished by "getting it on the
Myth #2 - Never Fly Your Engine "Oversquare!"
I am amazed that this particular piece of misinformation continues to exist
in the face of printed information to the contrary, but an applicant for a
commercial pilot certificate voiced this on an oral exam last week. This
erroneous folk wisdom cautions pilots that selecting a power setting with a
manifold pressure in inches higher than the RPM in hundreds is damaging to the
engine e.g., 2300 RPM dictates using no more than 23 inches manifold
have never been able to track down the origin of this one, but it seems that
it may stem from the admonitions of countless CFIs to always reduce the
manifold pressure before the RPM on power reductions, and increase the RPM
before the manifold pressure on power increases. Valid and correct advice.
Managing power in this way can help prevent the selection of a power setting
not healthy for your engine. Leaving the manifold pressure at climb setting
and pulling the prop back to 16-1700 RPM would create serious stresses and
pressure in your engines. Since CFIs try to teach techniques that will not be
harmful in any situation and which minimize maintenance on their flight
school's airplanes, they have always said "reduce manifold pressure
first, increase manifold pressure last." This advice does NOT imply,
however, "Never run your engine over-square."
What can we do then to protect our engine if the old "rule of
thumb" will not work? Start with the information manual or pilot's
operating handbook (POH) for your airplane. The engineers write these
manuals, but they have a generous amount of input from the legal department,
also. Now do you think those legal eagles are going to let the engineers give
you a power setting that is going to get them sued for accelerated wear caused
by following the manufacturer's recommendations? Never happen! The power
setting table for the Piper Cherokee Lance, PA-32R-300, shows various power
settings for obtaining 65% power. If you choose to use 2200 RPM, you have a
range of available manifold pressure settings from 24.7" at sea level
to 22.5" at 8,000 feet. All "oversquare!" When you look at the
power setting tables for turbocharged engines, you'll find that they are
usually flying in the "oversquare" condition.
"Oversquare" is Good
In fact, flying your engine oversquare can be very good for it. As long as
you are using a power setting allowed by the manufacturer in the power setting
tables, use the lowest RPM you can for the percent power you want and then
select the corresponding manifold pressure. How is this good for your engine?
The higher the RPM you use, the more often the pistons go up and down in the
cylinders. More revolutions mean the metal changes position more often, which
causes more friction and consequently more wear. Your propeller will also be
more efficient at a lower RPM. The higher the RPM setting, the closer the tips
of the prop blades are to the speed of sound and all the compressibility and
high drag effects associated with operation in that regime.
You'll also find the lower RPM settings are quieter and easier on you and
your passengers. Sometimes you'll find a legal power setting that just doesn't
make your engine happy. This is caused by the particular
airframe-engine-propeller combination and will usually result in increased
vibration. Just change to another permitted power setting and all should be
Myth #3 - Reduced-Power Takeoffs Will Save Wear And Tear
On Your Engine
always dangerous to take the procedures used in one type aircraft and adopt
them without modification to a different type, and this particular myth is a
prime example. Air carriers very often use what they call
"reduced-power" settings for takeoffs on long runways. "Reduced
power" is a misleading term, however. The term that should probably be
used is "less than the maximum power allowable under ambient
conditions." This makes sense in a turbine engine, where higher power
settings always result in higher RPM and higher operating temperatures. In
normally-aspirated piston aircraft, using less than full throttle on takeoff
is detrimental to your engine and possibly your health.
Some Major Differences
One of the major differences between jet engines and reciprocating engines
in the takeoff regime is the manner in which their cooling is accomplished.
Although both engines are air cooled, a reciprocating engine is also cooled by
fuel. With the throttle full open, extra fuel pumped into the cylinders
provides cooling at high power settings. If you do a partial power takeoff
less than full-throttle your engine will not get that additional cooling
fuel and will run hotter. Heat is not a friend of an engine (although, neither
is running your engine too cool, but that's another story) especially when
defeating the engine's built-in cooling provisions causes that heat.
Aside from defeating the engine's built-in cooling provisions, a
reduced-power takeoff in a piston aircraft puts you square in the middle of
the test pilot regime. Air carrier jets that use this approved technique have
charts that show the exact power setting, the runway required for takeoff at
the reduced setting and the climb gradients available both with all engines
functioning and with a power loss on takeoff. You won't find any charts in the
performance section of your POH listed "Takeoff Distance Required At Some
Power Setting Less Than Full Throttle" or "Rate of Climb At Some
Arbitrary Power Setting Less Than Full Throttle."
So, What's A Pilot To Do?
of the most valuable learning resources available to a new (or even
not-so-new) pilot is the thousands of hours of accumulated experience found in
almost any pilot lounge. Hangar flying sessions can be informative and
enlightening, but they can also perpetuate the kinds of misinformation we've
been discussing. How do you assure yourself you've gotten the best and most
correct information? Just follow a few common sense guidelines:
If a technique claims to offer significantly better performance than the
aircraft flight manual or POH, be very skeptical. It's in the
manufacturer's best interest to show you how to get the most out of your
airplane and techniques not found in the manufacturer's instructions at
the least won't work and at the worst can cause real damage to your
airplane and possibly ruin your whole day.
Be skeptical of techniques or procedures that do not seem to be backed
up by any written documentation. If you can't find references to the
procedure in any of the FAA's flight information materials, manufacturer's
materials or in publications by major aviation periodicals or authors,
it's probably just another aviation myth.
Be skeptical of things that "they" say. You know the
statements that start out with "They say you can...." You'll
never be able to track "them" down to verify the procedures
"they" claim are gospel. And "they" will never be
around to pay for the damage you may incur.
Take responsibility for doing the research to verify the techniques and
procedures you hear about in hangar flying sessions. You'll learn lots and
save yourself some grief.
Remember that even though it makes sense that a 10,000-hour veteran
should have more knowledge than a 97-hour beginner, it ain't necessarily
so. There will always be those few pilots out there that manage to stay
lucky for an incredibly long time before their folly catches up with them.
All in all, you can learn lots by listening to experience so long as you
always listen with a critical ear.