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Chapter-4 Slow Flight-V20_Sport Pilot Handbook 8/30/2021 5:49 PM Page 17

Chapter 4: Slow Flight Delight 4-17

Power Applied vs. Climb/Descent Rates
Looking at the accompanying figure, you’ll see a different (non traditional) way of expressing the airplane’s power curve in terms of
vertical speed curves. The three vertical speed curves shown in different colors below compare airspeed to climb/descent rate for
three different power settings. Each vertical speed curve represents the airplane’s climb or descent rate (feet per minute on the vertical
section of the graph) for a given airspeed (on the horizontal axis) based on three different power settings. Each curve also identifies
the region where vertical performance is reversed (region of reversed command) or positive (region of positive command).
At maximum power (magenta vertical speed curve), the airplane’s maximum speed in level flight (position A) is approximately 98
knots and its minimum speed in level flight is approximately 45 knots (position C). Starting at position A, if you raise your nose, your
rate of climb would increase, eventually reaching a maximum at 69
knots (position B), also known as your best rate of climb speed Performance in the Region of Reversed Command
or Vy. Continuing to raise the nose moves you into the region
of reversed command, the orange shaded area. This results in
a decrease in climb rate until you’re at 45 knots with zero rate
of climb (position C).
When you reduce engine power, you shift the vertical
speed curve downward and to the left slightly. For in-
stance, if you reduce your engine power to 2,100
RPM, the minimum speed required to maintain alti-
tude is 62 knots (position D). This is the top of the
blue colored vertical speed curve line. To the right of
62 knots is the region of positive command, the
green shaded area. Lowering the nose and acceler-
ating to 85 knots (position E) results in a 400 fpm
rate of descent and pulling aft on the controls and
slowing from 85 knots to 62 knots results in a de-
crease in descent rate leading to level flight. This is
a normal (positive) response of the controls and it’s
what you’d expect when operating in the region of
positive command.
However, pulling aft on the controls and slowing
from 62 knots (position D) to 48 knots (position F) re-
sults in a descent rate of 150 fpm. This occurs be-
cause you’re now operating in the region of reversed
command. This is the reverse of how you expect the
flight controls to work. That’s is why we call this area
the region of reversed command.
If you reduce power to idle (purple vertical speed curve), then your minimum de-
scent rate occurs at a speed of 59 knots (position G). This is also known as your
minimum sink speed and results in a descent rate of 650 fpm. If it were necessary to
make contact with the surface at the slowest possible vertical speed, you’d certainly
want to use a speed of 59 knots and land into the wind for the slowest groundspeed.
The takeaway point here is that during slow flight in the region of reversed command, it’s tempt-
ing for you to control your altitude with pitch adjustments (elevator movements) rather than power
adjustments. For instance, if you attempted to correct for a descent at minimum controllable airspeed
(MCA) by applying elevator back pressure, you’ll simply descend faster. If you attempted to correct for
a slight climb at MCA by moving the elevator control forward, you’ll climb faster. Therefore, in the region of reversed command, it’s al-
ways best to correct for airspeed changes with pitch (elevator) adjustments and altitude deviations with power (throttle) adjustments.
After adding power, you simply accept whatever climb rate results. And when I say “accept,” I
don’t mean you have to say out loud, “I accept the climb rate and claim it for Spain!” unless, of
course, you want to. And please don’t expect a substantial climb rate when attempting to climb at
th
MCA. If you do, you’re likely to be as disappointed as you were at your 10 birthday party where
you hoped for a BB gun and got a record by BB King, instead.
Smaller, underpowered airplanes just don’t perform well at slow speeds, and this is something
that you should know and understand. The lesson here is that you aren’t going to do much climbing,
if you climb at all, at speeds near MCA. In most instances, the only way to make an airplane climb
at these very slow speeds is to lower the nose and speed up a little. Why? Since you’re operating on
the back side of the power curve, speeding up decreases induced drag as you move toward the best
L/D speed. If you attempt to go around while close to the ground and behind the power curve,