AOPA Pilot Magazine - March 2022 - 100

RUDDER & WRENCH
Vertical speed vs. airspeed (power varying)
VY(26)
VY(18)
Airspeed (KCAS)
MP=26 in
MP=18 in
Throttle idle
As throttle setting increases from idle to 26 inches of manifold pressure, the drag curve (climb rate versus airspeed) shifts upward.
For any given airspeed, increasing the throttle always increases vertical speed. With idle throttle, VY
sink airspeed, VMS
.
trim mechanism to reduce the workload in
holding the yoke in a fixed position.
Constant power
For a fixed throttle setting, the pilot
applies pressure to the yoke to set an elevator
deflection that causes the wing to
fly at a specific angle of attack. That angle
of attack then determines the airspeed at
which the aircraft flies as shown on page
99. The higher the angle of attack, the
lower the airspeed. (Beyond the stall angle
of attack, the relationship is more complicated
and those angles of attack are not
represented in the figure.) The best rate of
climb airspeed for this throttle setting, VY
,
is that which corresponds to the greatest
vertical speed and any other airspeed will
result in a lower vertical speed. The front
side of the power curve corresponds to airspeeds
greater than VY
of the power curve to those less than VY
and the back side
.
Constant airspeed
The throttle controls the rate at which chemical
energy is depleted and the pilot can
choose how it's converted to other forms of
energy. Assuming the airspeed is held constant,
increasing the throttle will always
100
AOPA PILOT / March 2022
increase the vertical speed. The figure above
shows the power curve for three different
fixed throttle settings: 26 in manifold pressure,
18 in manifold pressure, and idle.
is more naturally called the minimum
Figure 2. As throttle setting increases from idle to 26 inches of manifold pressure, the drag
curve (climb rate versus airspeed) curve shifts upward. For any given airspeed, increasing
the throttle always increases vertical speed. With idle throttle, VY is more naturally called
the minimum sink airspeed, VMS.
Front side of power curve
Consider an aircraft that is in cruise flight
at 4 degrees angle of attack as in the first
graph. In this case, both power and airspeed
are constant so the rate at which
fuel is burned exactly compensates for
the rate at which energy lost to drag. Now
suppose that a vertical gust thrusts the
aircraft up to a higher altitude. The pilot
can then reduce the throttle slightly and
the aircraft will descend as shown above.
As the aircraft approaches the assigned
altitude, the original power setting can
be resumed. By timing the power application
well, airspeed can remain constant
through the maneuver. Negative altitude
excursions can be handled analogously by
briefly adding power.
Alternatively, such altitude excursions
can be handled solely by using the yoke. If
a vertical gust causes an increase in altitude,
the graph on page 99 shows that
pushing forward on the yoke will cause
the aircraft to lose altitude. When the
desired altitude nears, the pilot can introduce
back-pressure on the yoke to return
to the original angle of attack. During the
correction, the airspeed will increase and
then settle down to the original airspeed
corresponding to the 4-degree angle of
attack. This is the way an autopilot handles
such altitude excursions.
Back side of the power curve
Now consider an aircraft in level slow flight,
as in the first graph, where the wing flies
at 12 degrees angle of attack. If a vertical
gust moves the aircraft to a higher altitude,
decreased power will allow the aircraft to
descend back to the desired altitude, just as
it does on the front side of the power curve.
Increased power can similarly correct for
negative deviations in altitude.
Now suppose that a gust increases
the aircraft's altitude and the pilot corrects
only using the yoke. Unlike on the
front side of the power curve, he needs
to pull back on the yoke control (or push
uncomfortably forward) for the aircraft
to descend back to the desired altitude. If
the angle of attack is already near the critical
angle of attack, it would be easy for the
wing to stall. In this case, losing altitude isn't
VY(idle)=VMS
CATHERINE CAVAGNARO
Vertical speed (fpm)

AOPA Pilot Magazine - March 2022

Table of Contents for the Digital Edition of AOPA Pilot Magazine - March 2022