How much do you trim?

What I see in the literature seems to vary between warnings against
spending too much trim or flying with trim tabs, and not ever trimming
the aircraft at all. So how much and when should I trim?

I understand trim to be a convenience, so that a pilot doesn't have to
constantly maintain force against the controls for long periods. Thus
it should never be dangerous not to trim, except insofar as it can be
tiring to hold an untrimmed aircraft in a given attitude for long
periods.

The thing I wonder about is the possible distraction of trimming the
aircraft. It looks like trim controls are often in spots like the
pedestal or throttle quadrant, where presumably one must direct one's
attention in order to adjust trim. It's hard to imagine doing this
during critical phases of flight such as take-off or landing, and yet
I read recommendations for trim in both cases. Where do you draw the
line between trimming unnecessarily and not trimming enough? How
often do you actually reach for the trim controls?

Also, it seems that most trim is pitch trim. I don't see much mention
of aileron or rudder trim. Do you use it? Do you ever trim out
P-factor or torque effects? I turned both back on in my sim and
adjusted them to where the vendor says they should be to match the
real aircraft, and I find them irritating, but not overwhelming (the
vendor has apparently set the most realistic factors at 50% instead of
100%, so that masochists can increase their effects beyond real life
if desired).

Another problem I have: How do you remember where you set the trim?
I know you can look, and I know that you can guess if the aircraft is
behaving strangely, but how do you keep track of where you last set
the trim? Each time I set it I tend to forget about it until some
important moment when I'm already busy with other things.

Also, I presume that most autopilots use trim for pitch control. If
you shut off the autopilot, does the trim remain whereever the A/P set
it? If so, do you change it? Is it hard to remember that the A/P has
probably changed it?

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On Mon, 09 Oct 2006 10:05:20 +0200, Mxsmanic wrote:

What I see in the literature seems to vary between warnings against
spending too much trim or flying with trim tabs, and not ever trimming
the aircraft at all. So how much and when should I trim?

I haven't trimmed in about two years. Plane doesn't have cockpit-adjustable
trim. I just bend the metal tabs on occasion.

Ron Wanttaja

Trim every time you change pitch. Trim when needed even in level
flight. Basically, you trim whenever you need it, and that is fairly
often. IDEAL airplane would have trim in all three axis, but most small
GA don't.

I consider trim to be the most important control on the plane. I learned to
fly in a $250 used hang glider-the original Rogallo "you-stall-you-die"
design. I didn't realize how out of balance it was until I took it on the
first soaring flight. After a half hour my arms were cramped and it was
really difficult to control. My second hang glider flew hands off and the
entire flying experience in it just didn't compare to that first glider. I
spent 5 1/2 hours over Mt. Greylock one time.

I got into an ultralight next, and that was also out of trim with no means
to adjust it in flight. If I let go of the stick, it would start going down
and to the right. Again, my arm would cramp after about 45 minutes and I
always felt I was balanced on the point of a pin and one moments inattention
would have me falling off.

My Tripaver has the trim handle overhead. It is a crank style rather than a
wheel, but at this point I don't even have to look for it. My hand goes
right to it and the inputs are automatic. Trim wheels are the same. Just
trim out the control pressure and you're along for the ride. I once flew
from Block Island to Barnes in Westfield-about 85 miles-without ever
touching the yoke (after takeoff) until I flared for landing. At one point I
noticed I had lost 100'. My front seat passenger was leaning forward looking
out the window. I had him sit back and we came right back to altitude, where
I kept the altimeter pinned on my desired altitude for the entire flight.

Trimming is much less distracting and effortless that constantly monitoring
and correcting your airspeed and altitude. One of the biggest problems
people have when landing is not trimming the plane for approach speed and
attitude. When you have to grip the yoke and maintain pressure on it all the
way in, it makes it harder to use the fine touch it takes to make a nice,
gentle touchdown.

The only time you need to visually check the trim setting is for takeoff.
While flying, it is set by feel. One thing that might make this more
apparent to you is a feedback controller. I used to use the Force Feedback
controller and it made simming a lot more realistic.

mike

"Mxsmanic" wrote in message
news
What I see in the literature seems to vary between warnings against
spending too much trim or flying with trim tabs, and not ever trimming
the aircraft at all. So how much and when should I trim?

Mxsmanic wrote:
What I see in the literature seems to vary between warnings against
spending too much trim or flying with trim tabs, and not ever trimming
the aircraft at all. So how much and when should I trim?

Trim to releave control pressure for any given attitude that you plan
to maintain for more than a few seconds.

Another problem I have: How do you remember where you set the trim?
I know you can look, and I know that you can guess if the aircraft is
behaving strangely, but how do you keep track of where you last set
the trim? Each time I set it I tend to forget about it until some
important moment when I'm already busy with other things.

Elevator trim: You don't have to keep track of it. You should just feel
when it's needed. Set it to neutral when procedures call for it -
before takeoff, that's about the only time you need to worry about its
exact position, except for big airliners, which I believe have to have
trim reset to 0 before landing as well. If you can't relax your hand on
the yoke because your input is needed to correct pitch at any given
time -- time to trim. Ailerons and rudder trims are a bit different.
Those are mostly used to keep coordinated flight once straight and
level.


------------------------------------------
Ed.
PP-ASEL, PA-28-161, FRG

The discussion of trim in a flight sim on a PC is academic. In an
aircraft, trim is not so much a "convenience" as you seem to think.
Flying a plane out of trip is a big distraction.

Most planes have elevator trim, some planes have aileron trim and some
have rudder trim. Having all 3 means you can trim the plane to fly
pretty much wherever you want it to.

You ought to save up your pocket money and take a discovery flight then
you can see and feel the things you're asking about.

Mxsmanic wrote:
What I see in the literature seems to vary between warnings against
spending too much trim or flying with trim tabs, and not ever trimming
the aircraft at all. So how much and when should I trim?

I understand trim to be a convenience, so that a pilot doesn't have to
constantly maintain force against the controls for long periods. Thus
it should never be dangerous not to trim, except insofar as it can be
tiring to hold an untrimmed aircraft in a given attitude for long
periods.

The thing I wonder about is the possible distraction of trimming the
aircraft. It looks like trim controls are often in spots like the
pedestal or throttle quadrant, where presumably one must direct one's
attention in order to adjust trim. It's hard to imagine doing this
during critical phases of flight such as take-off or landing, and yet
I read recommendations for trim in both cases. Where do you draw the
line between trimming unnecessarily and not trimming enough? How
often do you actually reach for the trim controls?

Also, it seems that most trim is pitch trim. I don't see much mention
of aileron or rudder trim. Do you use it? Do you ever trim out
P-factor or torque effects? I turned both back on in my sim and
adjusted them to where the vendor says they should be to match the
real aircraft, and I find them irritating, but not overwhelming (the
vendor has apparently set the most realistic factors at 50% instead of
100%, so that masochists can increase their effects beyond real life
if desired).

Another problem I have: How do you remember where you set the trim?
I know you can look, and I know that you can guess if the aircraft is
behaving strangely, but how do you keep track of where you last set
the trim? Each time I set it I tend to forget about it until some
important moment when I'm already busy with other things.

Also, I presume that most autopilots use trim for pitch control. If
you shut off the autopilot, does the trim remain whereever the A/P set
it? If so, do you change it? Is it hard to remember that the A/P has
probably changed it?

Doug writes:

Trim every time you change pitch. Trim when needed even in level
flight. Basically, you trim whenever you need it, and that is fairly
often.

So how do you know when you need it?

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mike regish writes:

The only time you need to visually check the trim setting is for takeoff.

I usually take off with trim neutral. I've heard varying opinions
about how to set it for that phase of flight.

While flying, it is set by feel.

But if you set by feel, how do you keep track of how much control
surface movement you have remaining? If the trim has a control
service held very near the limit of its travel, you might run out of
space when you need it.


One thing that might make this more
apparent to you is a feedback controller. I used to use the Force Feedback
controller and it made simming a lot more realistic.

I've heard opinions for and against. Some say it improves the feel,
others say the feel is there but very different from the real thing,
so much so that it's better to do without. Personally, on the one
hand feedback is hard to find and expensive, and on the other the
feedback would vary by aircraft, anyway, so there'd be no one ideal
feedback setting (and I fly with a joystick, while most aircraft are
using a yoke).

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B A R R Y writes:

Oh that's right... Your simulator doesn't have control pressure.

It has springs, which serve much the same purpose. It's tiring to
hold the controls against a spring, too.

What does an A320 have?

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Robert Chambers writes:

The discussion of trim in a flight sim on a PC is academic.

Hardly. Trim does the same thing on a simulator that it does in real
life.

In an aircraft, trim is not so much a "convenience" as you seem
to think.

A lot of aircraft and pilots seem to do without it, so obviously it is
not necessary.

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