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separated airflow over the wings and or tail. The
ailerons will continue to operate in the attached air
flow until the aircraft’s stall speed is reached and
the wing stalls.
d. Begin by using the same procedures
employed on the first flight. Secure cockpit items
and put on carburetor heat. Decelerate slowly at 1⁄2
MPH/knot a second. Make small control inputs, keep
the ball centered, and note the aircraft’s reaction.
46
AC 90-89A 5/24/95
e. Let the aircraft stall and recover immediately,
with stick forward and increasing power.
Note the stall speed.
f. Practice the same stall sequence several
times at 1⁄2 mph/knot speed deceleration rate to determine
the power-off, one g stall speed. Practice the
same stall series with flaps, starting with the lowest
setting first and working slowly to the full flap
configuration. Record the findings.
g. After exploring the stall and recovery
behavior in a slow deceleration with the ball in the
middle, try a series of stalls with flaps up and then
flaps down with a faster rate of deceleration. Do not
exceed the deceleration rate expected in normal operations.
2. STALLS.
a. Power on Stalls. As before, use the same
procedures moving from the known to the unknown.
Increase power incrementally and run a stall test at
each new power setting until full power is reached.
It is not advisable to jump straight from idle to full
power with the resultant large changes in pitch attitude,
torque reaction, and slip stream effect on the
wing and tail.
b. Conducting Power on Stalls. It is recommended
that the aircraft be stabilized in level
flight at low cruise power. The power-on stall is
reached by slowly increasing the power to the desired
power setting. The pilot then steadily increases the
pitch attitude until the aircraft experiences the stall
buffet. Remember to keep the ball in the center until
the onset of the stall buffet.
(1) The power on stall may be more likely
to cause a wing drop than one at idle. This is due
to torque reaction and because the propeller slipstream
tends to keep the flow of higher velocity air
over the inboard (root) section of the wing despite
the higher angle of attack. This allows the root portion
of the wing to continue flying after the wing
tip stalls, dropping a wing.
(2) Tip stalls usually do not give advance
warning and will almost invariably result in some
severe wing drop. These stalls are more likely to
result in a spin, even if the controls are not mishandled.
If the spin does not develop, considerably
more height will be lost in the recovery than if the
stall had been straight-ahead nose down.
(3) If the pilot yields to instinct and tries
to correct the wing drop with aileron, it could result
in a spin. Since a sharp wing drop could be regarded
as the onset of spin auto-rotation, the recommended
corrective action is to reduce power, exercise prompt
application of full opposite rudder combined with
lowering the nose to the horizon or below. Take care
to avoid this situation until the aircraft’s spin behavior
has been tested.
(4) Perform the same sequence of events
for power on stalls as power-off stalls, unless limited
by the designer’s instructions. Record all findings
for the aircraft’s flight manual.
NOTE: Aircraft with retractable gear will
have to go through a separate series of slow
flight and stall checks with gear extended,
with and without flaps. Record the different
stall speeds for each configuration in the aircraft’s
flight manual.
47
5/24/95 AC 90-89A
FIGURE 6. Climb Airspeed and Altitude Graph
c. Best Rate of Climb Speed Tests. To determine
the best rate of climb for the aircraft, the following
procedures are suggested:
(1) Perform the tests in smooth air, free
from thermal activity. Select an altitude (e.g., 1,000
feet AGL) as a BASE attitude. Use a heading 90
degrees to the wind and for the best results, reverse
the heading 180 degrees after each climb test.
(2) Begin a full throttle climb well below
the predetermined BASE altitude and stabilize at a
preselected airspeed approximately 15 mph/knots
above the predicted best rate of climb speed. As the
aircraft passes through the BASE altitude, begin a
one minute time check. At the end of 1 minute,
record the altitude gained. Descend down below the
BASE altitude. Decrease the airspeed by 5 mph/
knots and run the test again. After each succeeding
test, the pilot should decrease the airspeed by 5 mph/
　
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