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knots until reaching an airspeed that is 10 mph/knots
higher than the stall speed of the aircraft. Record
the airspeed and altitude gained for each climb on
a graph similar to figure 6.
(3) The airspeed that shows the greatest
gain in altitude is the aircraft’s best rate of climb
speed (Vy).
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AC 90-89A 5/24/95
FIGURE 7. Best Rate of Climb Speed Graph
d. Best Angle of Climb Speed Tests.
(1) Best angle of climb speed can be found
by using the same chart developed for the best rate
of climb tests. Draw a line (tangent) from the zero
rate of climb feet per minute (see figure 4) outward
to a point, on the rate of climb airspeed curve. Where
both lines touch, draw a line straight down to the
airspeed leg of the chart.
(2) The airspeed that the line intersects is
the best angle of climb airspeed.
e. Slow Flight Test.
(1) For added safety, the slow flight tests
should be performed at 6,000 AGL or higher to allow
room for spin recovery. THE PRIMARY PURPOSE
OF THESE TESTS IS FOR THE PILOT TO
BECOME FAMILIAR WITH THE AIRCRAFT’S
HANDLING QUALITIES AT THE MINIMUM
GEAR UP/DOWN AIRSPEEDS AND POWER
SETTINGS.
(2) The tests should be done with and without
flaps. Start the tests at an airspeed of 1.3 times
(X) the stall speed of the aircraft. Once the aircraft
is stabilized and maintaining its altitude, reduce the
airspeed by 5 mph/knots. Maintain the altitude. Keep
reducing the airspeed until approaching a stall.
(3) Maintain 5 mph/knots above the previously
determined stall speed. This figure is the initial
slow flight airspeed. Practice with each flap setting,
noting its affect on the aircraft’s performance.
If the aircraft has retractable gear, test in all gear
and flap combinations. These tests will have to be
run later in the flight test program but with the AIRCRAFT
AT GROSS WEIGHT to determine the
actual slow flight airspeed and stall speeds.
(4) Remember, to help reduce the possibility
of unplanned stalls in slow flight configurations,
avoid bank angles of more than 5 degrees. When
all the test data has been evaluated, and if the aircraft
is equipped with a stall warning horn or indicator,
set the stall warning at 5 mph/knots above the aircraft’s
highest stall speed.
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5/24/95 AC 90-89A
SECTION 3. HOURS 21 THROUGH 35: STABILITY AND CONTROL CHECKS
‘‘A superior pilot uses his superior judgement to avoid those situations which require the use of superior
skill.’’ Old Aviation Proverb
1. OBJECTIVE. To determine the aircraft’s
stability limits and range of control.
2. GENERAL. Before attempting to satisfy the
requirements of Federal Aviation Regulations
§ 91.319 Aircraft Having Experimental Certificates:
Operating Limitations and declaring that the aircraft
is controllable throughout the normal range of
speeds, two things must be done.
a. Perform another complete inspection of the
aircraft, including oil changes and fuel system filter
checks.
b. Carry out a close examination of the stability
and control characteristics of the aircraft. Stability
and control checks will be centered around the three
axes of the aircraft: longitudinal or roll axis (ailerons),
the lateral or pitching axis (elevators), and the
vertical or yaw axis (rudder).
c. All tests need a starting point. The starting
point for stability and control checks is called the
state of equilibrium. An aircraft is said to be in a
state of equilibrium when it experiences no acceleration
and remains in a steady trimmed condition until
the force or moment balance is disturbed by an
atmospheric irregularity or by pilot input.
FIGURE 8. Static Stability
3. DEFINITIONS.
a. Static Stability: (positive) is when an aircraft
tends to return to the state of initial equilibrium
position following a disturbance.
b. Static Stability: (neutral) is when an aircraft
remains in equilibrium in a ‘‘new’’ position, following
a disturbance from an initial equilibrium position.
c. Static Stability: (negative) is when an aircraft
tends to move further in the same direction as
the disturbance that moved it from the initial equilibrium
position (figure 8).
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AC 90-89A 5/24/95
FIGURE 9. Time
d. Dynamic Stability: is the time history of the
movement of the aircraft in response to its static
stability tendencies following an initial disturbance
from equilibrium (figure 9).
e. Test for Static Longitudinal Stability.
(1) This test should be done first. All tests
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