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Feature Article: Trim Use
Correct use of the trim requires that control pressures be
applied to hold the desired flight attitude. Then the trim is
adjusted to relieve present control pressures. Some initial change
in trim should always be made since it reduces drag. If the aircraft
is in an accelerating or decelerating mode anticipatory trim changes
may be desired. Proper trim is a necessary part of flying from
both operational and safety standpoints. The skill of the pilot
is proportional to ability to trim.
Being able to trim the aircraft for any attitude requires that
the pilot adjust the amount of download on the horizontal tail
surfaces. It is this downwload that overcomes the nose weight
of an aircraft. Download is 'lift' of the tail surfaces directed
opposite to the lift of the wing. Refer to the Flight Training
Handbook, AC 61-21 Page 277.
The important thing in using trim is always to be able to keep
track of where it is. This is the reason I urge you to use a finger
tip rather than a pinch. The fuel/pilots location in the c-150/152
are so near the CG that the trim movement will be rather constant.
Any variation will be corrected if everything is predicated on
beginning at a constant. The constant that I use has always been:
Level cruise at 2400 rpm and hands off.
This constant works just a well if using C-172 or C-182. The
presence of a rear-seat passenger will be corrected for using
this constant. Pipers trim differently. Flaps change pitch attitude
significantly but require very little trim adjustment. As you
know the indicator markings are often illegible or not calibrated.
A slipping trim cable is a frequent problem.
Last Modified July 19, ©2018 TAGE.COM