曝光台 注意防骗
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is on the ground. That is why this design
appears to ‘‘levitate’’ off the ground without much
apparent pitch change.
(12) Some canard designs are very sensitive
to rain or other types of contamination on the leading
edge and/or top of the airfoil. Contamination in the
form of water droplets, frost, crushed insects, or even
poorly applied paint will disturb the laminar flow
over the canard and lift is lost. When decreasing lift
over drag (L/D) performance, the chances for an
accident increase.
2. FLIGHT TEST CONSIDERATIONS.
Technically, a canard type aircraft cannot stall, or
at least it will not stall in the normal fashion. A
pilot testing the aircraft for stability characteristics
should approach such testing with caution in mind.
a. Under certain conditions, usually consisting
of aft c.g. problems, the main wing may stall
before the canard surface. In this case, extreme pitchup
can occur until the canard surface or strakes stall.
The aircraft would then pitch down to a near-level
attitude, however the airspeed would be approaching
zero and the angle of attack could approach or exceed
45 degrees. This condition (high-alpha), could be so
stabilized, with the aircraft in a deep stall, that recovery
might not be possible.
b. Testing for pitch stability in a new design
or a just-completed aircraft built from a kit or from
plans is a requirement the pilot needs to consider
prior to carrying passengers. Pitch stability tests are
conducted to ensure that the aircraft does not exhibit
any dangerous flight characteristics but must be
approached and conducted in a logical and sensible
manner.
(i) Positive pitch stability is exhibited
when the aircraft trimmed for hands off level
flight, returns to that state when a control force is
applied and released.
(ii) Neutral pitch stability is achieved
when the aircraft remains in the pitch attitude
attained when a control force is applied.
(iii) Negative pitch stability is demonstrated
when the aircraft departs from the pitch
attitude attained when a control force is applied and
continues to increase in amplitude.
c. The aircraft should be weighed and the c.g.
carefully calculated. At the same time, determine the
weight needed and the moment calculated to load
the aircraft at the most forward and aft c.g. limits
recommended by the designer. Beginning at the most
forward c.g., trim the aircraft to a hands off condition
and slowly reduce the power, maintaining altitude
by increasing pitch attitude. When the stick reaches
the full aft position, momentarily release the back
pressure followed by full aft stick. The aircraft, in
demonstrating positive stability, should return to its
original pitch attitude and remain there. The aircraft
should display positive stability characteristics.
d. Other tests may be conducted by adjusting
the c.g. further aft and observing the tendency of
the aircraft. At some point near the aft c.g. limit,
you may experience neutral stability, or the point
where the aircraft no longer recovers by itself from
the upset. Moving further aft in the c.g. range from
this point will cause the aircraft to diverge from the
trim path in the direction of the upset (neutral stability).
e. Some designers and builders have installed
adjustable, moveable ballast containers in the aircraft
to allow the c.g. to be adjusted forward or aft during
flight. If testing is to be accomplished outside the
65
5/24/95 AC 90-89A
recommended range, it is advisable to consider the
installation of a ballistic recovery system or spin
chute system. In addition, the pilot should make a
decision about leaving the aircraft if the test becomes
untenable.
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AC 90-89A 5/24/95
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5/24/95 AC 90-89A
CHAPTER 8. ULTRALIGHT AIRFRAME INSPECTION
‘‘You can learn 10 things by learning one.’’ Japanese proverb
SECTION 1. DIFFERENCES
1. OBJECTIVES. To serve as additional
resource for ultralight test pilots and to help the new
owner develop a flight test plan for the ultralight.
2. DEFINITION. The term ‘‘Ultralight’’ means
a fixed wing vehicle that is powered by a conventional
2 or 4 cycle, gasoline powered engine and
is operated under Part 103. It has one seat and does
not exceed 254 pounds, excluding floats and safety
devices. In addition, the ultralight can be unpowered,
in which case the weight is restricted to 155 pounds.
The powered ultralight’s fuel capacity cannot exceed
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