Procedure for calculating weight and balance

All it does is relieve the pressure. If there were no trim at all the elevator would be in the exact same position, it would just suck to have to hold it there.

Well, not exactly, not on all aircraft. Consider a trim system which
uses a trim tab. The tab projects (say) up, causing the elevator to
trail down as its neutral position, pushing the tail up and thus the
nose down. Once equilbrium has been reached (no pressure), clamp the
elevator in that position, and trim in such a manner that the tab no
longer projects up. Now, the elevator is (slightly) more effective at
pushing the tail up, because the trim tab is no longer in the airflow in
the opposite direction. The nose will be pushed (slightly) further
down, and the clamp will be resisting pressure. If you release the
clamp, going to a new "no pressure" condition, the elevator =will= move.

Looked at another way, if you come from an untrimmed position (with this
same aircraft), and position the yoke wherever it needs to be in order
to maintain the condition you want (say, straight and level, FSOA), and
then clamp the yoke in that position, you will be at the chosen
condition. But if you trim, the movement of the trim tab =will= have a
(slight) aerodynamic effect. When you actually achieve "no pressure",
you will be (slightly) out of trim for the effect you want.

1: I understand the effect is slight, perhaps even not noticable, but
I'll bet it can be measured.

2: I understand that when a real pilot actually trims for "no
pressure", there is a feedback loop where "no change in flight
condition" also feeds into it, so the above discussion is academic.

3: I understand that this will not be true, or will not be true for the
same reasons, for other trim systems.

However, the quoted statement above is not true, and if Mx made that
statement, he would have been jumped on, just because it's Mx making
that statement.

Jose
--
He who laughs, lasts.
for Email, make the obvious change in the address.

Newps writes:

All it does is relieve the pressure. If there were no trim at all the
elevator would be in the exact same position, it would just suck to have
to hold it there.

That's just it: If there were no trim at all, the elevator wouldn't
be there. It would be in its neutral position. Of course you can
_push_ it there, but with trim set, it goes there and stays there
without being pushed (by you).

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Mxsmanic,

It would be in its neutral position.


Jeeze, you really don't want to understand, do you? There is no
"neutral position".

The position that keeps the plane flying at a certain speed is
depending on load, cg and a lot of other factors. It varies with all
those - and with the speed you want to fly. The position desired by the
pilot can be held by the pilot - OR he can use trim to have the
elevator stay in the desired position, to relieve himself of the
control force otherwise required. If you fly a cruise speed of 150
knots in a Baron, you'd still have different elevator positions
depending on CG location. In fact, the position would change during the
flight with fuel burn. Which would be "neutral"? "Neutral" doesn't make
any sense.

Where the elevator actually is in a desired attitude, is completely
irrelevant with regard to control of the airplane - once you've adhered
to the limits of all contributing factors with regard to certification.

--
Thomas Borchert (EDDH)

Thomas Borchert writes:

If you fly a cruise speed of 150
knots in a Baron, you'd still have different elevator positions
depending on CG location. In fact, the position would change during the
flight with fuel burn. Which would be "neutral"?

The one that aligns the trim tabs with the control surfaces.

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In article ,
says...
Thomas Borchert writes:

If you fly a cruise speed of 150
knots in a Baron, you'd still have different elevator positions
depending on CG location. In fact, the position would change during the
flight with fuel burn. Which would be "neutral"?

The one that aligns the trim tabs with the control surfaces.

What if it's a spring type system, rather than a trim tab - what is the
neutral position for that?

--
Duncan

Duncan writes:

What if it's a spring type system, rather than a trim tab - what is the
neutral position for that?

The same.

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Mxsmanic wrote:
Newps writes:
All it does is relieve the pressure. If there were no trim at all the
elevator would be in the exact same position, it would just suck to have
to hold it there.

That's just it: If there were no trim at all, the elevator wouldn't
be there. It would be in its neutral position. Of course you can
_push_ it there, but with trim set, it goes there and stays there
without being pushed (by you).

In this case, you really need to listen to what Thomas and others are
saying. There is no neutral position. There is just a natural
position for a certain flight regime.

Therefore, if you are hand-flying, and you move the trim, the airplane
will react. The pilot will notice this (it's impossible not to).

I'm trying to think of a relevant example using a car or roller coaster
or other easy to understand situation, but I don't have enough coffee
in me yet :-) Perhaps someone else can some up with something.

Kev

Kev writes:

In this case, you really need to listen to what Thomas and others are
saying. There is no neutral position. There is just a natural
position for a certain flight regime.

The neutral position for trim tabs is the position in which the trim
tabs are aligned with the control surface. The neutral position for
control surfaces is the position in which they are aligned with the
surfaces to which they are attached (wings or stabilizers).

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Mxsmanic wrote:
Kev writes:

In this case, you really need to listen to what Thomas and others are
saying. There is no neutral position. There is just a natural
position for a certain flight regime.

The neutral position for trim tabs is the position in which the trim
tabs are aligned with the control surface. The neutral position for
control surfaces is the position in which they are aligned with the
surfaces to which they are attached (wings or stabilizers).

Ok Anthony, you have perfectly loaded your aircraft so the that it trims out
to what you like to call nuetra or default. What are you going to do once
you have burned off fuel and the CG changes?

Gig 601XL Builder writes:

What are you going to do once
you have burned off fuel and the CG changes?

Adjust the trim. Ideally, I'd be in an aircraft where the fuel load
is already at that ideal neutral point, and so very little adjustment
would be required.

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