When do controls return to neutral?

Ron Wanttaja writes:

Generally, no. The weight of the elevators usually put them in the full-down
position.

Does this effect disappear before you are moving fast enough for the
elevators to affect the aircraft's attitude?

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In article ,
Mxsmanic wrote:

Do you have a marked "zero point" for the trim, or do you just trim
until it feels right for the circumstances, and then trim again the
next time as required, without worrying about whether the trim is
truly "zero" or not?

There are marks/indicators, however they are mechanical pointers which
are subject to deviation. In actuallity, yes, you move the trim control
until the pressure is neutralized (in the case of elevator for the the
speed and power setting, and for rudder until the yaw ball is centered).

"Mxsmanic" wrote in message
...
Do you have a marked "zero point" for the trim, or do you just trim
until it feels right for the circumstances, and then trim again the
next time as required, without worrying about whether the trim is
truly "zero" or not?

Most aircraft have an index mark for "Take-Off" trim position. I'm pretty
damn sure that MSFS shows this index mark as well.

If I understand correctly, in a real aircraft, it all just
depends on circumstances, and you don't have to know or care about any
"exact" neutral (?).

Essentially, yes. real aircraft controls have the points that they go
when you apply zero force to them. In general, you trim such that
these points of zero force correspond to the aircraft flying straight
and and level at the altitude, speed and power setting of your
choosing.

Understand that most trim settings (especially pitch-wise) only
correspond to one particular speed (and to a lesser excent altitude)
configuration. That is, lets say I trim for 110 knots at 4000 feet,
75% power, and fly hands off for a bit. now - if I pull back on the
yoke, i'll trade some of my airspeed for climb ("zoom climb")... the
further I get off my "target" speed, the greater the yoke is going to
push against my hands... now - the "weird" thing (not really when you
think about the physics, but certainly not intuitive to sim-drivers) is
that if I then decide to release the yoke, the aircraft will
_completely automatically_ return to its trimmed airspeed, and pretty
close to its original altitude.

It actually won't go straight to the trimmed altitude and airspeed,
it'll do a number of oscilations faster and slower than the trimmed
speed until it ends up back to where it was trimmed for. That is why
flying with the trim is generally a bad idea - fly with the yoke, trim
off the preassure = flying precisely.

(also, just so there is no confusion, this has NOTHING to do with an
autopilot, my aircraft doesn't have one - its simply the way the shape
of the airplane is designed to interact with the airflow).

Do you have a marked "zero point" for the trim,

There is a "takeoff point" for the trim system, generally set to
provide good yoke feel for Vy climbout. Once you are climbing however,
trim is completely relative. There's generally no "Move the trim lever
this much to change trim X mph"... That is a fundamentally backwards
way of thinking. Once you are airborne, simply use the yoke to SET the
aircraft off of its currently trimmed configuration, and then use the
trim controls to adjust the trim configuration to the current
configuration- that is really most of flying.

or do you just trim
until it feels right for the circumstances, and then trim again the
next time as required, without worrying about whether the trim is
truly "zero" or not?

Bingo - that's it exactly.

So in a real aircraft, a different trim position also represents a
different yoke position? That seems logical.

I wonder how fly-by-wire aircraft handle this.

There was some discussion on A.net about this - Boeing goes to great
lengths in their FBW systems to keep the 'feel' of traditional
hydrolics, trim and everything. Airbus, on the other hand, just has
the aircraft automatically and always trim for 1-G flight.

I.E, the airbus actually flies more like your flight simulator than my
Piper

I read that a drawback to Cirrus aircraft is that they use springs for
feedback, so it's hard to tell where the control surfaces actually
are.

I haven't read that either way - but I think you over-estimate the
necessity of knowing where your control's "really" are.

Everything in flying is relative, from the moment you take off, you're
changing from one configuration to another - not simply "setting"
configurations- your control inputs are thus always relative.

Mxsmanic wrote:
Ron Wanttaja writes:

Generally, no. The weight of the elevators usually put them in the full-down
position.

Does this effect disappear before you are moving fast enough for the
elevators to affect the aircraft's attitude?

On the ground the ailerons tend to flop around whereever you turn them.
They also flop in the wind a lot (which is why you tie them down). Once
you start rolling and air goes over them they (in modern, non-aerobatic
planes) tend to return to center, like a car's wheel.
On some planes the elevator rests full forward on the ground and takes
a bit of strength to hold them in any other position, however once
moving they go to their trim position. Older Bonanza's are an example
of this, they have "heavy" controls on the ground but are nice and
smooth in flight. The Mooney elevator is a very different creature so
it works differently. Rudders always wants to go what ever position the
nose wheel is in on the ground because of spings that connect the wheel
with the ailerons.
BTW: On high performance planes moving the rudders also moves the
ailerons because they are interconnected to create smoother turns.
Slipping requires working against the springs and requires a little bit
more strength than on a C-172.

-Robert

Gig 601XL Builder writes:

Most aircraft have an index mark for "Take-Off" trim position. I'm pretty
damn sure that MSFS shows this index mark as well.

It does on some aircraft, but for things like that one cannot be sure
if the sim is duplicating the real aircraft or just providing an
indicator for convenience (because there are no other ways to get the
information in simulation). On the Baron I usually fly it appears to
be the real thing, and there's a range shown for take-off, although I
still take off with the trim set to zero.

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EridanMan writes:

That is, lets say I trim for 110 knots at 4000 feet,
75% power, and fly hands off for a bit. now - if I pull back on the
yoke, i'll trade some of my airspeed for climb ("zoom climb")... the
further I get off my "target" speed, the greater the yoke is going to
push against my hands... now - the "weird" thing (not really when you
think about the physics, but certainly not intuitive to sim-drivers) is
that if I then decide to release the yoke, the aircraft will
_completely automatically_ return to its trimmed airspeed, and pretty
close to its original altitude.

The sim behaves the same way, but without any control forces as
feedback. However, it is indeed counter-intuitive at first. It
dawned on me quickly enough why this is so, but initially one tends to
think that an aircraft will go straight into the ground once it is
pointed down, or infinitely high once it is pointed up. (Thinking a
bit about the laws of physics rapidly shows that this cannot be the
case, but the influence of popular notions is strong.)

That is why
flying with the trim is generally a bad idea - fly with the yoke, trim
off the preassure = flying precisely.

It's the latter part that's hard to simulate.

What I sometimes do is set the autopilot for my altitude, let it set
the trim (which it does with much greater precision than I have
available to me), and then shut it back off, with the aircraft trimmed
for my current altitude. If I'm on A/P for a long time and I wish to
fly with it off, I adjust power until the A/P has trim set to zero,
then I shut off the autopilot. This gives me a stable aircraft with
neutral trim, which insures that I have full control authority in both
directions. (If I were to shut off the A/P while it has heavy trim in
place, I might not have the authority I need later, unless I carefully
retrim myself, which is awkward for reasons I have already stated.)

There is a "takeoff point" for the trim system, generally set to
provide good yoke feel for Vy climbout.

I see that on several aircraft in the sim. I don't use take-off trim
because I don't want to be misled into thinking that I have more climb
ability than I actually have. By leaving trim neutral I can tell how
much I have to persuade the aircraft to climb, and so I have less
chance of an unpleasant surprise if I need more elevator authority.

Once you are airborne, simply use the yoke to SET the
aircraft off of its currently trimmed configuration, and then use the
trim controls to adjust the trim configuration to the current
configuration- that is really most of flying.

I try to do this. It's awkward with no feedback, but it's still
possible from watching the instruments. And the better I know a given
aircraft, the better I can estimate how much to change things to get
it trimmed quickly.

Still, I don't think I trim nearly as much as many real-world pilots.
Unless I plan to be in the same attitude for quite some time, I leave
the trim alone. I especially worry about it being a distraction
during critical phases of flight--spinning the trim wheel while I
should be looking at instruments or talking to ATC seems risky. And
from what I understand, the only advantage of trim is that it
eliminates excess control pressures ... but I can tolerate those for
the brief period of take-off and landing.

There was some discussion on A.net about this - Boeing goes to great
lengths in their FBW systems to keep the 'feel' of traditional
hydrolics, trim and everything. Airbus, on the other hand, just has
the aircraft automatically and always trim for 1-G flight.

Another reason to prefer Boeing. Boeing designs for pilots; Airbus
designs for computer gamers.

I.E, the airbus actually flies more like your flight simulator than my
Piper

See above (I wrote the above before reading this).

I haven't read that either way - but I think you over-estimate the
necessity of knowing where your control's "really" are.

Maybe. I guess it's from association with other types of vehicles.
One doesn't set a car to veer consistently to the right, for example,
but cars don't move in three dimensions.

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Robert M. Gary writes:

On the ground the ailerons tend to flop around whereever you turn them.
They also flop in the wind a lot (which is why you tie them down). Once
you start rolling and air goes over them they (in modern, non-aerobatic
planes) tend to return to center, like a car's wheel.

And does this happen before you actually have enough control authority
to use the ailerons, or roughly at the same time that you have that
authority? I'm wondering if the airspeed sufficient to "neutralize"
the surfaces is lower than the airspeed necessary to make them useful
for controlling the aircraft.

BTW: On high performance planes moving the rudders also moves the
ailerons because they are interconnected to create smoother turns.
Slipping requires working against the springs and requires a little bit
more strength than on a C-172.

FWIW, I successfully slipped the Baron yesterday, I think. Being at
about 6500 feet for a runway only a mile or so away at 30 feet, I was
able to lose thousands of feet fairly quickly by slipping. The
aircraft in the sim seemed to behave just as I've heard it described
for slips in real life.

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Mxsmanic wrote:
Robert M. Gary writes:

On the ground the ailerons tend to flop around whereever you turn them.
They also flop in the wind a lot (which is why you tie them down). Once
you start rolling and air goes over them they (in modern, non-aerobatic
planes) tend to return to center, like a car's wheel.

And does this happen before you actually have enough control authority
to use the ailerons, or roughly at the same time that you have that
authority? I'm wondering if the airspeed sufficient to "neutralize"
the surfaces is lower than the airspeed necessary to make them useful
for controlling the aircraft.

I don't know, I never tried to let go of the ailerons during take off.
I'm sure it happens pretty quick though.
-Robert

On Wed, 08 Nov 2006 19:08:40 +0100, Mxsmanic wrote:

Ron Wanttaja writes:

Generally, no. The weight of the elevators usually put them in the full-down
position.

Does this effect disappear before you are moving fast enough for the
elevators to affect the aircraft's attitude?

Beats the heck out of me....the only way to know would be to *not hold* the
stick during the takeoff roll.

It's a moot point, since I usually keep the elevators full down for the initial
part of the takeoff roll. Gravity is already putting the stick where I want it.
In any case, the mechanical advantage is good enough that holding the stick all
the way back isn't any strain.

IIRC, there was a French observation plane in the early days of WWI that didn't
have cables to pull the ailerons both ways. The ailerons drooped all the way on
the ground, and gradually came to a faired position as the plane accelerated for
flight. Moving the stick just pulled an aileron back down; the one on the
opposite side didn't go up. Sort of an inverse spoiler for roll control.

Ron Wanttaja