How To...Keep In Trim While Flightsimming
By Derek G. Swanson (23 March 2004)
Baron 2D panel, trim controls on right
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This article is about making best use of the trim control, which can
make sim flying a whole lot easier. If you're new to flightsimming,
these tips may save you a lot of pain and frustration. If you often
fly with autopilot, learning how to trim well can mean you do more
hand flying.
What does the trim do?
In most real planes the elevator includes a small section which can
be pivoted up or down into the airflow helping the elevator stay in
the position set by the control column. This removes the control
column back pressure and enables the pilot to fly "hands off". By
trimming the plane correctly, the pilot can keep it stable at the
required pitch attitude during all phases of flight. Many planes
also have trim tabs on the aileron and rudder, but we will
concentrate on the elevator, as this has most value in simming.
How does this benefit flight simulator?
Well, in a real plane, the control column axes have quite a long
movement or "throw", making very small pitch adjustments possible as
well as leaving "room" for more control when the trim is set. In
simming, the throw of joysticks and yokes is not to scale and also
(particularly for joysticks), spring resistance can be quite strong.
Using the trim control, very small pitch adjustments can be made
which allow you to bring the stick back to neutral while keeping the
plane at the required pitch attitude. Result - smoother flying and
less tired wrists! We'll refer to joysticks here but the
principles are exactly the same for a yoke.
FS Trim controls
Most of the default MS planes have trim controls in the 2D cockpit
panels which can be controlled either by the mouse or the default
keyboard strokes (numeric keypad No. 1 for nose down and No. 7 for nose
up). Using the mouse can be very tricky while flying and remember
that you must have the "num lock" OFF to use the keys. It may also
be a good idea to set a slow keystroke repeat (in Windows control
panel) to give finer control for small increments. If you have a
stick with several buttons, you can assign two of them for nose up and
down trim within the "assignments" section of the "control" settings
in the "options" menu. Make sure you activate the repeat function to
enable large scale changes. Some sticks have a trim wheel - assign
this if you have one. If you use a force feedback stick, you'll feel
the back-pressure release as you trim, exactly like real world
trimming.
Most default panels with trim controls have easily readable
increments. Although none are numbered (not really needed in the
real world) some have an identified take-off setting (marked "T/O").
One initially confusing aspect is that some trim gauge indicators
move in the opposite direction to that you'd expect. So, using the
No. 7 key for "nose up" makes the indicator go DOWN the screen. This
is best interpreted as the indicator mimicking the down movement of
the tail or pull back of stick - but you get used to it.
Some add-on aircraft designers use the MS default trim indicator in
their panels, but often there is no trim gauge. If you find an
aircraft with a trim gauge you like, you can insert it into any
panel. My tutorial on editing FS2002 aircraft
(FSPLANED.ZIP)
details how to do this. The best trim gauge I've seen
"HuntT7_Trim.gau" came from an add-on aircraft. This gauge is
clearly marked with numbered increments and the sections are marked
"nose up" and "nose down". (You'll find this gauge in my upgrade for
the default FS2002 minipanel gauges -
FULSCREN.ZIP).
When should I use the trim?
Basically, all the time! Let's take a flight to see when and how.
Amended mini-panel, trim on left
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During take-off, most flightsim planes need some "nose-up" trim to
get airborne. Have you had the frustration of taxiing along at over
100 knots wrestling with the stick and trying to lift off before we
hit that house ahead? Answer - set the trim with some nose-up
attitude before starting the take-off roll. Each plane may be
different in the amount of trim needed - just experiment until it
unsticks easily at the specified airspeed. Setting the trim
correctly will often result in the plane lifting off gently by
itself. (TIP: Once you've worked out how much trim to use, make a
note of it in the kneeboard notes for future reference.)
During the climb, once the gear is up and flaps are raised,
you can use the trim to hold the required climb attitude, or at least
to give you more stick travel to play with. Key point - the amount
of trim needed will always vary with the airspeed and vice versa, so
be gentle and watch the ASI. You shouldn't use the trim to increase
or decrease the climb, but first set the attitude or ascent rate with
the stick; let the airspeed settle then start inching the trim whilst
simultaneously returning the stick position nearer neutral.
In the cruise the trim can really come into its own. If the plane
has a stable flight model, you should be able to trim it to fly
"hands off" straight and level almost as good as the autopilot. If the
plane includes rudder and aileron trim you can also set those if
needed. Some sim planes cruise with the trim at neutral whereas
others need a few degrees nose-up or nose-down. Generally, the
higher the airspeed, the more nose-down trim will be needed and
vice-versa. Remember the effect of airspeed on trim and be patient!
Set the power, watch the ASI and be prepared to re-trim
occasionally.
To descend in a well trimmed plane you only need to reduce the power
and she should begin to sink with a small nose down nudge of the
stick. If you want to achieve a particular FPM descent rate, just
gently adjust the power until you get it and your airspeed should
stay the same as in the cruise. Remember, if you change the airspeed
in the descent, you should re-trim.
During approach you may need to gradually feed in nose-up trim as the
speed decreases. When on final, it's often best to reset the trim
to the same value you used on take off. Although this may mean you
have to use some forward stick initially, as you reduce speed and
flare for the touch down, you should find that pitch sensitivity is
much less and you have plenty of stick movement for the flare.
Boeing 777 a "glass" trim version
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Tips on achieving good trimming
- You need a good frame rate (minimum 15 frames per second). Slow
frame rates mean a slow response to control inputs and trim is no
different.
- When you are at a stable cruise you can cheat and set the trim by
activating the autopilot altitude hold (ctrl+Z) for say 30 seconds,
then quit the autopilot (Z) to fly manually at the set trim.
N.B. Point 3 below applies only to FS2002 aircraft. Although the
amendments described may apply to other Flight Simulator products,
the author accepts no responsibility for any damage or loss of
function as a result of following it outside of FS2002.
- If you find that trimming a particular plane requires too much or too little trim movement, amend the aircraft.cfg file to correct this, as below:
- Use Windows Explorer or My Computer to browse to the folder of
the individual aircraft you wish to work on. On a typical FS2002
install this will be c:\program files\Microsoft
Games\fs2002\aircraft\ZZZZ (where ZZZZ is the name of the aircraft
folder).
- Open the folder and you will see the aircraft.cfg file.
- Make a copy of the aircraft.cfg file (right mouse click and select
"copy" option) and paste it (right mouse click and select "paste"
option) in the same open folder. This should appear as "copy of
aircraft.cfg".
An add-on panel with trim gauge added
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- Right mouse click the original aircraft.cfg file and select the
"open with" option. A small window will pop up asking you to select
a program to use. Browse down the list until you see "Notepad" and
highlight this with the mouse. Then tick the "Always use this
program to open these files" box , then click "OK" when the file will
open.
- Scroll down the file and look for the section titled "[flight
tuning] (if it's not there, open up the aircraft.cfg from any of the
default MS planes, and copy and paste the section to your aircraft's
.cfg file). Find the line that says "elevator_trim_effectiveness =
1". Amend the number up or down (probably best to double or halve at
first), save the file then load up the aircraft to fly it and test
the impact of the change. Make further adjustment in small
increments of 0.2 until it responds as you want it. Remember to
always save the file after each amendment.
So that's it. Trimming while simming copies real world pilots and
makes life much easier. You'll probably be able to hand-fly with
much more precision and perhaps not need the autopilot - and that's
got to be more fun!
Derek G Swanson
derek.swanson10 @ ntlworld.com
