Procedure for calculating weight and balance

Mxsmanic wrote:

BT writes:


Changing the trim setting does not change the set screws (Stop bolts) that
limit the amount of Rudder, Aileron or Elevator travel.


But it does control how far you are from each stop.

It does no such thing.

Recently, Peter Dohm posted:

Oh, by the way, many aircraft do not have any trim tabs at all - most
gliders use springs in the control circuit, J-3 Cubs move the
horizontal stabilizer, the F-4 I used to fly changed the neutral
position of the whole flying tail, etc...

Thanks, presumably on behalf of many, for an excellent overview.

BTW, in the case of the fully trimming stab on the J-3 Cub, DC-9, and
some others; as well as the fully trimming tail of the F-4, Mooney
M20, and others; it does seem hypothetically possible that the
control authority could be influenced--but that would be a side
effect of obtaining a design goal, rather than a feature in itself,
and certainly outside of any area of expertise which I might have.

The question isn't whether the control surfaces would be closer to one
stop or another, it's whether you have still full control authority, a
concept that totally escapes Mxsmanic. What he fails to see is that you
don't need more "up" than it takes to get the plane into a stall or more
"down" than it takes to get the nose pointed at the Earth, and no amount
of trim will remove that control authority. If he was capable of
understanding that when trimmed fully "up", it takes much less "up" to go
past critical AOA than the elevator can still provide, or if trimmed fully
"down" the plane could still be taken into a dive that can exceed Vne, he
wouldn't persist with such nonsensical notions as this one that he's been
flagging around for months, now. Every pilot that has responded to him has
explained these facts to him, but he refuses to learn. Anything.

Neil

Neil Gould wrote:
Recently, Peter Dohm posted:
BTW, in the case of the fully trimming stab on the J-3 Cub, DC-9, and
some others; as well as the fully trimming tail of the F-4, Mooney
M20, and others; it does seem hypothetically possible that the
control authority could be influenced--but that would be a side
effect of obtaining a design goal, rather than a feature in itself,
and certainly outside of any area of expertise which I might have.

The question isn't whether the control surfaces would be closer to one
stop or another, it's whether you have still full control authority, a
concept that totally escapes Mxsmanic. [...]

Well, I suspect the concept would escape most non-pilots, because it is
a logical conclusion if you've never felt the actual pressures.

In any case, a lot of us have, I'm sure, enjoyed the in-depth responses
from a talented few, and perhaps learned a bit here and there. So
thank you!

But a big No Thanks for the totally non-informative responses from the
usual group of suspects. I guess the people who can't clearly explain
a concept will always feel the need to resort to frustrated insults and
one-liner non-answers.

Kev

Kev wrote:



Well, I suspect the concept would escape most non-pilots, because it is
a logical conclusion if you've never felt the actual pressures.

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.

Newps wrote:
Kev wrote:
Well, I suspect the concept would escape most non-pilots, because it is
a logical conclusion if you've never felt the actual pressures.

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.

Yes. And that's the kind of good, clear, short description which is
sorely needed in this thread.

Much better than all the other responders that answered: "No it
doesn't work that way." And then threw in an insult to show how
superior they are. Gee, they were really informative. Not. ;-)

Trim is, I think, the single hardest concept to get across to someone
using MSFS. You can argue until you're blue in the face to most users
(not just Mx), and they'll not be convinced of the major difference in
sim and real life.

I just don't understand why CH Products or anyone else has not come out
with a force feedback yoke and a good driver. They'd sell a ton to
pilots.

Btw, a while back, I ran across a website with instructions to add
electric trim to a CH yoke. The trim used a servo motor to physically
move the center point. I wish I could find it again. Oh wait. Google
to the rescue:

http://www.flightsim.com/cgi/kds?$=main/howto/chtrim.htm

Kev

Neil Gould wrote:
You are presenting yet another absurd scenario that has no relation to the
reality of flying. Nobody flying a real plane will "forget" about trim set
near the limits of it's travel, because the control forces are a constant
reminder.

Umm. Nobody *hand* flying should in theory forget about trim setting.
(We all know the problems that can be caused by autopilots or FBW
systems mucking with the trim behind a pilot's back ;-)

Of course, sometimes pilots *do* forget... thus the number of take-off
accidents caused by the trim being in the wrong place. Yes, at the
last second they feel the extra control force coming in, but it's too
late.

Kev

Kev wrote:

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.


Yes. And that's the kind of good, clear, short description which is
sorely needed in this thread.

Much better than all the other responders that answered: "No it
doesn't work that way." And then threw in an insult to show how
superior they are. Gee, they were really informative. Not. ;-)




MxIdiot is a complete and utter moron and deserves everything he gets.
Plus it's fun.

Kev wrote:


Umm. Nobody *hand* flying should in theory forget about trim setting.


(We all know the problems that can be caused by autopilots or FBW
systems mucking with the trim behind a pilot's back ;-)

In the types of planes we're talking about here the autopilot doesn't
actuate the trim. The STEC's will even tell you that you need to trim
and in which direction.



Of course, sometimes pilots *do* forget... thus the number of take-off
accidents caused by the trim being in the wrong place. Yes, at the
last second they feel the extra control force coming in, but it's too
late.

Maybe in jets or King Air's but not spam cans.

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:

In the types of planes we're talking about here the autopilot doesn't
actuate the trim.

I'm talking about all types of planes. Not everyone flies a tin can.

--
Transpose mxsmanic and gmail to reach me by e-mail.