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gear (if applicable) and flaps in the up position. The
pilot’s minimum entry altitude for these tests should
be no less than 10,000 feet AGL with the cockpit
secured.
NOTE: The following procedure is one way,
but not the only way, of conducting a spin
test and executing a recovery. Non-conventional
aircraft may require significantly different
spin recovery control applications.
The pilot should evaluate these procedures
and determine if they are compatible with
the aircraft before attempting any spin testing.
b. The basic technique used to get a clean spin
entry is to continue to reduce airspeed at about a
1 mph/knot a second rate in level flight, carburetor
heat on, and the power at idle.
(1) As the aircraft stalls, APPLY FULL
RUDDER in the desired spin direction, followed
immediately by full aft movement of the control stick
keeping the ailerons neutral.
(2) The transition from a horizontal to a
vertical flight path takes approximately three or four
turns and is referred to as the incipient stage of the
spin.
(3) During the incipient spin, the dynamic
and inertia forces have not achieved equilibrium.
Many aircraft can recover from the incipient spin
phase, but may not be able to recover from a steady
spin.
(4) The normal spin recovery technique is
to apply full rudder opposite to the direction of yaw
(check the turn needle). Move the control stick
smoothly and fairly rapidly forward towards the
instrument panel until the rotation stops.
(5) Quickly center the rudder and ease out
of the dive. Do not attempt to pull up too rapidly
because the structural limits of the aircraft can easily
be exceeded, or the aircraft can stall again. Recover
from the first deliberate spin after a half a turn.
c. If the aircraft is not built for aerobatics,
no further spin testing is required, It is recommended
the instrument panel be placarded ‘‘SPINS PROHIBITED.’’
d. If further spin testing is required, it is
strongly recommended the services of a professional
flight test pilot be used.
56
AC 90-89A 5/24/95
SECTION 6. ACCELERATED STALLS
‘‘Does it pass the Common Sense test?’’ U.S. Air Force, Thunderbird
1. OBJECTIVE. To further explore the stall
characteristics of the aircraft.
a. An accelerated stall is not a stall reached
after a rapid deceleration. It is an in-flight stall at
more than one g, similar to what is experienced in
a steep turn or a pull up.
NOTE: Do not attempt this or any other
extreme maneuver unless the designer or kit
manufacturer has performed similar tests on
a prototype aircraft identical to the amateur-
builder’s aircraft.
b. The two standard methods for accelerated
stalls are the constant g (constant bank) and constant
speed (increasing bank). Most preferred of the two
is the constant bank method in which the airspeed
is decreased and the angle of bank is held constant,
until the aircraft stalls. It is the most preferred
because the potential violence of any accelerated stall
is largely governed by the increasing g load and airspeed.
c. As with every test, plan the sequence of
events. Start with small bank angles -- 30 degrees
will produce 1.15 g. Decelerate slowly, ball in the
center, do not over control. Work up incrementally
to a two g, 60 degree bank.
d. The aircraft does not have to develop a deep
stall each time. The pilot needs only to record the
airspeed and bank angle in which the aircraft hits
the pre-stall buffet. Recover by adding power and
reducing the angle of bank.
57
5/24/95 AC 90-89A
CHAPTER 6. PUTTING IT ALL TOGETHER: 36 HOURS TO —————?
‘‘Beware of false knowledge; it is more dangerous than ignorance.’’ George Bernard Shaw
SECTION 1. MAXIMUM GROSS WEIGHT TESTS
1. OBJECTIVE. To develop aircraft performance
data across the weight and CG ranges.
a. Up until this point, all tests have been performed
well below the test aircraft’s maximum gross
weight, with the possible exception of single seat
aircraft designs. A complete series of flight tests at
maximum gross weight from stalls, rates of climb,
angles of climb, stability, retraction tests, slow flight,
through accelerated stalls should be investigated.
b. These tests should demonstrate that the aircraft
has been successfully flown throughout the CG
range, and will operate in and at the full range of
aircraft weights from minimum to full gross weight.
The findings should be documented in the aircraft’s
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