Rotation

Bob Moore writes:

Except in an airplane where the trim system moves the horizontal
stabilizer instead of a trim tab. In that case, there is no feel
feedback to the yoke. One must release the pressure and see if the
airplane attitude remains where desired.

Is that common?

I note that there are slots in front of the stabilizers on a 737,
implying that they pivot (for trim?). Is that in fact what they are
doing? It's hard to see on the sim.

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

Bob,
Can you explain that a little further? I don't see any difference in feel
feedback between a Cessna 182 (trim tab) and 185 (stab trim). Why should
there be a difference?

Karl
"Curator" N185KG


"Bob Moore" wrote in message
. 121...
Jay Beckman wrote
Trimming is a "feel" thing. You trim to relieve control pressures and
you can't see pressure, you can only feel it.

Except in an airplane where the trim system moves the horizontal
stabilizer instead of a trim tab. In that case, there is no feel
feedback to the yoke. One must release the pressure and see if the
airplane attitude remains where desired.

Bob Moore

karl gruber wrote
Bob,
Can you explain that a little further? I don't see any difference in
feel feedback between a Cessna 182 (trim tab) and 185 (stab trim). Why
should there be a difference?

Karl, I have no experience with in the smaller a/c, but as a Boeing
instructor (B-707, B-727), it took a good amount of time to teach a
new jet pilot how to trim because of this effect.

If from level flight, you want to raise the nose for a climb, you
pull back and obviously feel the back pressure from the elevator
being displaced relative to the stabilizer, at this point, trimming
just changes the stabilizer position without putting the elevator
in a new position relative to the stabilizer and releiving the
pressure.

Large trim changes (as in a go-around) consisted of a large number of
trim/release cycles in order to find the exact amount required.

Bob Moore

Mxsmanic wrote

Bob Moore writes:
Except in an airplane where the trim system moves the horizontal
stabilizer instead of a trim tab. In that case, there is no feel
feedback to the yoke. One must release the pressure and see if the
airplane attitude remains where desired.

Is that common?

In jetliners...Yes

I note that there are slots in front of the stabilizers on a 737,
implying that they pivot (for trim?). Is that in fact what they are
doing? It's hard to see on the sim.

Yes

And, so far, no one has mentioned that in a jetliner, the main landing
gear wheels are located far behind the aerodynamic center of rotation
when the a/c is rotated for takeoff. If the a/c is trimmed for a low-
force rotation, it will be out of trim for the initial climb.

The initial trim setting for a jetliner must be computed for each
takeoff based on the amount of load and its distribution. As I recall,
the takeoff trim setting was for the V2+10 initial climb speed.

Bob Moore
ATP B-707 B-727
PanAm (retired)

"Skywise" wrote in message
...
"Robert M. Gary" wrote in news:1157992218.361147.166330
@d34g2000cwd.googlegroups.com:

Snipola
Mike,
I think trim is just academic is MSFS because there is no control
feedback. The OP is probably setting the elevator with too much back
pressure but doesn't know it because he doesn't have the feedback.
Honestly, if you asked me what position the yoke is in on take off, I
probably couldn't tell you. In real life we expect the yoke to go to
its trim position, something that doesn't make sense in a simulator
that does not have feedback controls.
-Roebrt

I have a force feedback stick and if I don't trim right for
the phase of flight I'm in I have to provide excessive input
to maintain flight attitude. As I adjust the trim the feedback
moves the stick. Trim buttons are on my stick. I can press
them while lightly holding the stick and feel the stick move.
I know I am in trim when the stick is centered and I have a
feather touch on the stick.

When properly trimmed I can let go of the stick and maintain
flight attitude for 10's of seconds. I can even conrol climb
and descent with power adjustment without ever touching the
elevator. Or sometimes I maintain altitude with single clicks
of trim.

Before I got the force feedback stick, trim didn't make sense
since you couldn't feel it in the controls.

The hundred bucks I spent on mine were well worth the enhanced
simulation experience. Flight is much smoother and landings
are greased much more often.

Brian

I don't understand what non-force feedback joysticks you guys are using but
my MS stick is not force feedback and if I don't trim I have to move the
stick to a non-centered position which requires constant force to keep it
there. Are you guys using joysticks with no centering springs?

Except in an airplane where the trim system moves the horizontal
stabilizer instead of a trim tab. In that case, there is no feel
feedback to the yoke. One must release the pressure and see if the
airplane attitude remains where desired.

This makes no sense to me. If the airplane attitude remains "where
desired" (I presume that is the same as where you put it, using
pressure) when you release the pressure, then the pressure isn't doing
anything. How do you fly such an aircraft?

Jose
--
There are more ways to skin a cat than there are cats.
for Email, make the obvious change in the address.

"Jose" wrote in message news:1MzNg.443
This makes no sense to me. If the airplane attitude remains "where
desired" (I presume that is the same as where you put it, using pressure)
when you release the pressure, then the pressure isn't doing anything.
How do you fly such an aircraft?

The way I look at it is that you have to use a different combination of
sensory data than if you were flying a small aircraft with direct cable
controls and elevator trim.
In the 727, my recollection is that there is not a complete lack of feedback
feeling; there is a little, but it is different from flying traditional trim
tabs.

On the 727 (and, I presume, on the 707) you have a movable stabilizer, an
elevator, and elevator trim tabs. The elevator trim tabs are locked out of
the trim system as long as the electric stab trim motors are functional.
When locked out, they function as balance tabs. There is an elevator feel
computer in the 727 whose main purpose is not to provide yoke force
feedback, but it does give some little feeling to the yoke as a side effect.

The bottom line, at least in my perception, is that with some experience in
the aircraft you can become very adept at simultaneously positioning your
attitude, and adjusting the trim so you don't have to keep positioning your
attitude. Of course, as the craft accelerates or decelerates you have to
repeat the process as configuration and speed change. As a practical
matter, you are [almost] flying with the stab trim.

Bob Moore writes:

Yes

So aircraft that pivot the entire stabilizer also keep the entire
travel of the elevator available for flight, right? Seems like a
pretty bit advantage. If you use trim tabs, you sacrifice at least
part of the elevator travel when you trim to a non-neutral setting;
but if the whole stabilizer moves for trim, the entire travel of the
elevator is still there for you to use.

I wonder why smaller planes don't do this.

Also ... why does a plane like the Baron 58 have a stick pusher? I
presume you can't use it for instruction flights that teach about
stalls, since it refuses to adopt an attitude that will cause a stall.

And, so far, no one has mentioned that in a jetliner, the main landing
gear wheels are located far behind the aerodynamic center of rotation
when the a/c is rotated for takeoff. If the a/c is trimmed for a low-
force rotation, it will be out of trim for the initial climb.

The initial trim setting for a jetliner must be computed for each
takeoff based on the amount of load and its distribution. As I recall,
the takeoff trim setting was for the V2+10 initial climb speed.

How do all these calculations get done? It seems like there are a lot
of things that have to be calculated for every flight. Do pilots sit
with calculators and do it, or do they have some less time-consuming
way to cook up the necessary numbers?

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

Mxsmanic wrote
So aircraft that pivot the entire stabilizer also keep the entire
travel of the elevator available for flight, right?

Ah-Ha....you broke the code. :-)

I wonder why smaller planes don't do this.

Generally speaking, they don't have as broad a cg range as a jetliner.


How do all these calculations get done? It seems like there are a lot
of things that have to be calculated for every flight. Do pilots sit
with calculators and do it, or do they have some less time-consuming
way to cook up the necessary numbers?

Most airlines have a 'Load Control Center' with computers to do the
work, but I have worked for small charter companies where the flight-
crew (generally the copilot) works-up a Weight and Balance Form just
prior to departing the gate since a copy must remain on file in operations.

Bob Moore

"Mxsmanic" wrote in message
...
Jay Beckman writes:

That's because unless there is a specific marking (as there is for
takeoff
on the C172 both in RL and in FS9), there is no such thing as a specific
way
to set the trim for each situation.

Trimming is a "feel" thing. You trim to relieve control pressures and
you
can't see pressure, you can only feel it.

But if you have an unusual load aboard, it would seem that you
wouldn't be able to feel it until you're already in the air. Unless
you mean that you'd be able to extrapolate from previous experience
with other loads.

Define "Unusual Load." ???

If you are way over MGW or loaded well aft of the CG limit, you're already
in a very dangerous place and no amount of trim will help.

I'd just like to be able to rotate more smoothly.

Don't pull so hard...

Seriously, for most GA aircraft, when you reach Vr, you pull just enough to
set an attitude and let the plane do the work. It sounds like the dynamics
of flying "heavy iron" are a little different due to the placement of the
mains versus the CG/CL but it can't be all THAT different.

I had to modify the contact points on the 737 just because I was plowing
the tail into the runway on take-off (and the standard model doesn't take
any note of this, which meant I was cheating for a long time and didn't
realize it). The B58 pitches upward even more quickly.

Your simply being too aggressive and over rotating.

I think if I can get good at putting the stick forward in just the right
way as the nose rises I will be able to rotate smoothly, eventually, but I
will try the trim stuff.

Like I said, don't try to horse the plane off the ground...set a proper
attitude at rotation and let the plane fly itself off the ground. Once you
are airborne and accelerating, then you can worry about pitch and power to
acheive a specific airspeed (Vx, Vy, etc...)

Jay Beckman
PP-ASEL
Chandler, AZ