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gear is extended and the flaps are lowered in some airplanes.
The nose tends to pitch down with gear extension, and when
flaps are lowered, lift increases momentarily (at partial flap
settings) followed by a marked increase in drag as the flaps
near maximum extension.
Control technique varies according to the lift and drag
characteristics of each airplane. Accordingly, knowledge of
the power settings and trim changes associated with different
combinations of airspeed, gear, and flap configurations will
reduce instrument cross-check and interpretation problems.
[Figure 5-60]
For example, assume that in straight-and-level flight
instruments indicate 120 knots with power at 23" Hg
manifold pressure/2,300 revolutions per minute (rpm), gear
and flaps up. After reduction in airspeed, with gear and flaps
fully extended, straight-and-level flight at the same altitude
requires 25" Hg manifold pressure/2,500 rpm. Maximum
gear extension speed is 115 knots; maximum flap extension
speed is 105 knots. Airspeed reduction to 95 knots, gear and
flaps down, can be made in the following manner:
1. Maintain rpm at 2,500, since a high power setting will
be used in full drag configuration.
5-43
Figure 5-61. Insufficient cross-check. The problem is power and not nose-high. In this case, the pilot decreased pitch inappropriately.
Trim Technique
Trim control is one of the most important flight habits to
cultivate. Trimming refers to relieving any control pressures
that need to be applied by the pilot to the control surfaces to
maintain a desired flight attitude. The desired result is for the
pilot to be able to take his or her hands off the control surfaces
and have the aircraft remain in the current attitude. Once the
aircraft is trimmed for hands-off flight, the pilot is able to
devote more time to monitoring the flight instruments and
other aircraft systems.
In order to trim the aircraft, apply pressure to the control surface
that needs trimming and roll the trim wheel in the direction
pressure is being held. Relax the pressure that is being applied to
the control surface and monitor the primary instrument for that
attitude. If the desired performance is achieved, fly hands off. If
additional trimming is required, redo the trimming steps.
An aircraft is trimmed for a specific airspeed, not pitch attitude
or altitude. Any time an aircraft changes airspeed there is a
need to re-trim. For example, an aircraft is flying at 100 knots
straight-and-level. An increase of 50 rpm will cause the airspeed
to increase. As the airspeed increases, additional lift will be
generated and the aircraft will climb. Once the additional thrust
has stabilized at some higher altitude, the airspeed will again
stabilize at 100 knots.
This demonstrates how trim is associated with airspeed and
not altitude. If the initial altitude is to be maintained, forward
pressure would need to be applied to the control wheel while
the trim wheel needs to be rolled forward to eliminate any
control pressures. Rolling forward on the trim wheel is equal
to increasing for a trimmed airspeed. Any time the airspeed
is changed, re-trimming will be required. Trimming can be
accomplished during any transitional period; however, prior
to final trimming, the airspeed must be held constant. If the
airspeed is allowed to change, the trim will not be adjusted
properly and the altitude will vary until the airspeed for which
the aircraft is trimmed is achieved.
Common Errors in Straight-and-Level Flight
Pitch
Pitch errors usually result from the following errors:
1. Improper adjustment of the yellow chevron (aircraft
symbol) on the attitude indicator.
Corrective Action: Once the aircraft has leveled off and
the airspeed has stabilized, make small corrections to
the pitch attitude to achieve the desired performance.
Cross-check the supporting instruments for validation.
2. Insufficient cross-check and interpretation of pitch
instruments. [Figure 5-61]
5-44
Example: The airspeed indication is low. The pilot,
believing a nose-high pitch attitude exists, applies
forward pressure without noting that a low power setting
is the cause of the airspeed discrepancy.
Corrective Action: Increase the rate of cross-check of all
the supporting flight instruments. Airspeed and altitude
should be stabilized before making a control input.
3. Acceptance of deviations.
Example: A pilot has an altitude range of ±100 feet
according to the practical test standards for straight-and
level-flight. When the pilot notices that the altitude has
deviated by 60 feet, no correction is made because the
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Instrument Flying Handbook仪表飞行手册上(104)
