Flight Training - August 2021 - 15

HOW IT WORKS
BY THOMAS A. HORNE
TWEAKING PITCH
TAKING THE LOAD OFF
SOME STUDENTS CAN BE CONFUSED ABOUT THE PITCH TRIM
wheel: that small, round, thin disc used to relieve control pressures.
Sure, the function of the control yoke/stick and rudders
are easy to comprehend. But the pitch trim wheel is a big part
of the control system mix. It comes into play every time an
airplane changes configuration-such as extending or retracting
flaps, turning, climbing, descending, or holding a selected
airspeed. And every time power is increased or decreased.
Whenever those changes occur, the airflow-and air
load-over the horizontal stabilizer and elevator also changes.
Increase power, and the nose will rise. Decrease power, and the
nose drops. If you're trying to hold altitude, you could find yourself
pushing or pulling on the control yoke with extra effort. You
need a little help to eliminate these extra forces and reduce your
workload. That's where the pitch trim wheel comes in.
The trim wheel moves the trim tab at the aft edge of the
elevator, which in turn adjusts the position of the entire elevator.
Move the trim wheel just the right amount, and the trim tab
moves the elevator to compensate for the effects of any change
in lift produced by the tail surfaces. In flight, you'll find the trim
wheel very handy in positioning the tab so that you can fly handsoff-whether
you're climbing, descending, or straight and level.
How does the pitch trim system work? The trim wheel in the
cockpit is attached to a sprocket, and a chain rides in the sprocket's
teeth. The chain is swaged (crimped tightly) to a long, woven
stainless steel cable that runs through pulleys and guides under
the panel and the cabin floor. This cable run goes all the way back
to the tailcone, where it makes a couple right-angle turns through
two more pulleys. Finally, it's swaged to another chain. This chain
also rides in a sprocket. When the sprocket turns, it moves the
trim tab actuator, which moves the trim tab up or down. You can
see the actuator's connection to the trim tab-and should inspect
it for integrity during every preflight inspection.
Having done its job moving the trim tab actuator, where does
the chain go from there? It's attached to another cable, which
runs through pulleys and guides back to the trim wheel in the
cockpit. The system is a closed loop with chains at either end.
Electrically powered trim control systems are more complicated
and use switches and servos to move the cable and
sprockets. Instead of manually moving a trim wheel, you'll press
a sliding switch on the control yoke to trim the nose up or down.
A big problem can occur with electrically controlled trim
systems: The trim motors may " run away, " sending the airplane
into uncommanded pitch movements. To stop that, pull the trim
motor's circuit breaker. Now you're back to manually trimming
with the trim wheel, just like you learned when you started flying.
tom.horne@aopa.org
Trim tab
Trim wheel
Sprocket
AOPA.ORG/FT
15
STEVE KARP
http://www.AOPA.ORG/FT

Flight Training - August 2021

Table of Contents for the Digital Edition of Flight Training - August 2021

Contents
Flight Training - August 2021 - Intro
Flight Training - August 2021 - Cover1
Flight Training - August 2021 - Cover2
Flight Training - August 2021 - Contents
Flight Training - August 2021 - 2
Flight Training - August 2021 - 3
Flight Training - August 2021 - 4
Flight Training - August 2021 - 5
Flight Training - August 2021 - 6
Flight Training - August 2021 - 7
Flight Training - August 2021 - 8
Flight Training - August 2021 - 9
Flight Training - August 2021 - 10
Flight Training - August 2021 - 11
Flight Training - August 2021 - 12
Flight Training - August 2021 - 13
Flight Training - August 2021 - 14
Flight Training - August 2021 - 15
Flight Training - August 2021 - 16
Flight Training - August 2021 - 17
Flight Training - August 2021 - 18
Flight Training - August 2021 - 19
Flight Training - August 2021 - 20
Flight Training - August 2021 - 21
Flight Training - August 2021 - 22
Flight Training - August 2021 - 23
Flight Training - August 2021 - 24
Flight Training - August 2021 - 25
Flight Training - August 2021 - 26
Flight Training - August 2021 - 27
Flight Training - August 2021 - 28
Flight Training - August 2021 - 29
Flight Training - August 2021 - 30
Flight Training - August 2021 - 31
Flight Training - August 2021 - 32
Flight Training - August 2021 - 33
Flight Training - August 2021 - 34
Flight Training - August 2021 - 35
Flight Training - August 2021 - 36
Flight Training - August 2021 - 37
Flight Training - August 2021 - 38
Flight Training - August 2021 - 39
Flight Training - August 2021 - 40
Flight Training - August 2021 - 41
Flight Training - August 2021 - 42
Flight Training - August 2021 - 43
Flight Training - August 2021 - 44
Flight Training - August 2021 - 45
Flight Training - August 2021 - 46
Flight Training - August 2021 - 47
Flight Training - August 2021 - 48
Flight Training - August 2021 - 49
Flight Training - August 2021 - 50
Flight Training - August 2021 - 51
Flight Training - August 2021 - 52
Flight Training - August 2021 - 53
Flight Training - August 2021 - 54
Flight Training - August 2021 - 55
Flight Training - August 2021 - 56
Flight Training - August 2021 - Cover3
Flight Training - August 2021 - Cover4
https://www.nxtbook.com/nxtbooks/aopa/ft_202109
https://www.nxtbook.com/nxtbooks/aopa/ft_202108
https://www.nxtbook.com/nxtbooks/aopa/ft_202107
https://www.nxtbook.com/nxtbooks/aopa/ft_202106
https://www.nxtbook.com/nxtbooks/aopa/ft_202104
https://www.nxtbook.com/nxtbooks/aopa/ft_202105
https://www.nxtbook.com/nxtbooks/aopa/ft_202103
https://www.nxtbook.com/nxtbooks/aopa/ft_202101
https://www.nxtbook.com/nxtbooks/aopa/ft_202011
https://www.nxtbook.com/nxtbooks/aopa/ft_202009
https://www.nxtbook.com/nxtbooks/aopa/ft_202008
https://www.nxtbook.com/nxtbooks/aopa/ft_202007
https://www.nxtbook.com/nxtbooks/aopa/ft_202006
https://www.nxtbook.com/nxtbooks/aopa/ft_202005
https://www.nxtbook.com/nxtbooks/aopa/ft_202004
https://www.nxtbook.com/nxtbooks/aopa/ft_202003
https://www.nxtbook.com/nxtbooks/aopa/ft_202001
https://www.nxtbook.com/nxtbooks/aopa/ft_201912
https://www.nxtbook.com/nxtbooks/aopa/ft_201911
https://www.nxtbook.com/nxtbooks/aopa/ft_201910
https://www.nxtbook.com/nxtbooks/aopa/ft_201909
https://www.nxtbook.com/nxtbooks/aopa/ft_201908
https://www.nxtbook.com/nxtbooks/aopa/ft_201907
https://www.nxtbook.com/nxtbooks/aopa/ft_201906
https://www.nxtbook.com/nxtbooks/aopa/ft_201905
https://www.nxtbook.com/nxtbooks/aopa/ft_201904
https://www.nxtbook.com/nxtbooks/aopa/ft_201903
https://www.nxtbook.com/nxtbooks/aopa/ft_201902
https://www.nxtbook.com/nxtbooks/aopa/ft_201901
https://www.nxtbook.com/nxtbooks/aopa/ft_201812
https://www.nxtbook.com/nxtbooks/aopa/ft_201811
https://www.nxtbook.com/nxtbooks/aopa/ft_201810
https://www.nxtbook.com/nxtbooks/aopa/ft_201809
https://www.nxtbook.com/nxtbooks/aopa/ft_201808
https://www.nxtbook.com/nxtbooks/aopa/ft_201807
https://www.nxtbook.com/nxtbooks/aopa/ft_201806
https://www.nxtbook.com/nxtbooks/aopa/ft_201805
https://www.nxtbook.com/nxtbooks/aopa/ft_201804
https://www.nxtbook.com/nxtbooks/aopa/ft_201803
https://www.nxtbook.com/nxtbooks/aopa/ft_201802
https://www.nxtbook.com/nxtbooks/aopa/ft_201801
https://www.nxtbook.com/nxtbooks/aopa/ft_201712
https://www.nxtbook.com/nxtbooks/aopa/ft_201711
https://www.nxtbook.com/nxtbooks/aopa/ft_201710
https://www.nxtbook.com/nxtbooks/aopa/ft_201709
https://www.nxtbook.com/nxtbooks/aopa/ft_201708
https://www.nxtbook.com/nxtbooks/aopa/ft_201707
https://www.nxtbook.com/nxtbooks/aopa/ft_201706
https://www.nxtbook.com/nxtbooks/aopa/ft_201705
https://www.nxtbook.com/nxtbooks/aopa/ft_201704
https://www.nxtbook.com/nxtbooks/aopa/ft_201703
https://www.nxtbook.com/nxtbooks/aopa/ft_201702
https://www.nxtbook.com/nxtbooks/aopa/ft_201701
https://www.nxtbook.com/nxtbooks/aopa/ft_201612
https://www.nxtbook.com/nxtbooks/aopa/ft_201611
https://www.nxtbook.com/nxtbooks/aopa/ft_201610
https://www.nxtbook.com/nxtbooks/aopa/ft_201609
https://www.nxtbook.com/nxtbooks/aopa/ft_201608
https://www.nxtbook.com/nxtbooks/aopa/ft_201607
https://www.nxtbook.com/nxtbooks/aopa/ft_201606
https://www.nxtbook.com/nxtbooks/aopa/ft_201605
https://www.nxtbook.com/nxtbooks/aopa/ft_201604
https://www.nxtbook.com/nxtbooks/aopa/ft_201603
https://www.nxtbook.com/nxtbooks/aopa/ft_201602
https://www.nxtbook.com/nxtbooks/aopa/ft_201601
https://www.nxtbook.com/nxtbooks/aopa/ft_201512
https://www.nxtbook.com/nxtbooks/aopa/ft_201511
https://www.nxtbook.com/nxtbooks/aopa/ft_201510
https://www.nxtbook.com/nxtbooks/aopa/ft_201509
https://www.nxtbook.com/nxtbooks/aopa/ft_201508
https://www.nxtbook.com/nxtbooks/aopa/ft_201507
https://www.nxtbook.com/nxtbooks/aopa/ft_201506
https://www.nxtbook.com/nxtbooks/aopa/ft_201505
https://www.nxtbook.com/nxtbooks/aopa/ft_201504
https://www.nxtbook.com/nxtbooks/aopa/ft_201503
https://www.nxtbook.com/nxtbooks/aopa/ft_201502
https://www.nxtbook.com/nxtbooks/aopa/ft_201501
https://www.nxtbook.com/nxtbooks/aopa/ft_201412
https://www.nxtbook.com/nxtbooks/aopa/ft_201411
https://www.nxtbook.com/nxtbooks/aopa/ft_201410
https://www.nxtbook.com/nxtbooks/aopa/ft_201409
https://www.nxtbook.com/nxtbooks/aopa/ft_201408
https://www.nxtbook.com/nxtbooks/aopa/ft_201407
https://www.nxtbook.com/nxtbooks/aopa/ft_201406
https://www.nxtbook.com/nxtbooks/aopa/ft_201405
https://www.nxtbook.com/nxtbooks/aopa/ft_201404
https://www.nxtbook.com/nxtbooks/aopa/ft_201403
https://www.nxtbook.com/nxtbooks/aopa/ft_201402
https://www.nxtbook.com/nxtbooks/aopa/ft_201401
https://www.nxtbook.com/nxtbooks/aopa/ft_201312
https://www.nxtbook.com/nxtbooks/aopa/ft_201311
https://www.nxtbook.com/nxtbooks/aopa/ft_201310
https://www.nxtbook.com/nxtbooks/aopa/ft_201309
https://www.nxtbook.com/nxtbooks/aopa/ft_201308
https://www.nxtbook.com/nxtbooks/aopa/ft_201307
https://www.nxtbook.com/nxtbooks/aopa/ft_201306
https://www.nxtbook.com/nxtbooks/aopa/ft_201305
https://www.nxtbook.com/nxtbooks/aopa/ft_201304
https://www.nxtbook.com/nxtbooks/aopa/ft_201303
https://www.nxtbook.com/nxtbooks/aopa/ft_201302
https://www.nxtbook.com/nxtbooks/aopa/ft_201301
https://www.nxtbook.com/nxtbooks/aopa/ft_201212
https://www.nxtbook.com/nxtbooks/aopa/ft_201211
https://www.nxtbook.com/nxtbooks/aopa/ft_201210
https://www.nxtbook.com/nxtbooks/aopa/ft_201209
https://www.nxtbook.com/nxtbooks/aopa/ft_201208
https://www.nxtbook.com/nxtbooks/aopa/ft_201207
https://www.nxtbook.com/nxtbooks/aopa/ft_201206
https://www.nxtbook.com/nxtbooks/aopa/ft_201205
https://www.nxtbook.com/nxtbooks/aopa/ft_201204
https://www.nxtbook.com/nxtbooks/aopa/ft_201203
https://www.nxtbook.com/nxtbooks/aopa/ft_201202
https://www.nxtbook.com/nxtbooks/aopa/ft_201201
https://www.nxtbook.com/nxtbooks/aopa/ft_201112
https://www.nxtbook.com/nxtbooks/aopa/ft_201111
https://www.nxtbook.com/nxtbooks/aopa/ft_201110
https://www.nxtbook.com/nxtbooks/aopa/ft_201109
https://www.nxtbook.com/nxtbooks/aopa/ft_201108
https://www.nxtbook.com/nxtbooks/aopa/ft_201107
https://www.nxtbook.com/nxtbooks/aopa/ft_201106
https://www.nxtbook.com/nxtbooks/aopa/ft_201105
https://www.nxtbook.com/nxtbooks/aopa/ft_201104
https://www.nxtbook.com/nxtbooks/aopa/ft_201103
https://www.nxtbookmedia.com