Methods for altitude changes

Mxsmanic wrote in
:

EridanMan writes:

FWIW, Trim was the single largest aspect of aircraft piloting that my
simulation experience simply did not prepare me for... I mean, the
concept is there, but how often you need it and why simply never came
across clearly.

I suppose so ... but how long did it take you to learn to adjust trim
by relieving pressure on the yoke? Thirty seconds? Three minutes?

I've never experienced a simulated aircraft control that didn't have
a substantial dead spot in the middle and feel extremely artificial.

Well, you have to look at it a different way. On a (PC) sim, the
"dead spot" actually corresponds to "zero control pressure," or at
least that's how it usually seems to work (I think it depends on how
the aircraft is modeled, but good add-ons work this way). In other
words, you can trim by holding the yoke or joystick away from its
neutral position and then trimming until you can leave the joystick in
the neutral position. This is very similar to relieving control
pressure. The joystick of the sim does not use absolute positioning.

Also, I'm reasonably sure that yoke forces are exponential, rather
than linear, and that this plays a large roll in the 'feel issue'...
Something to consider.

I don't know. It would be interesting to see the curves of spring
resistance plotted against the forces exerted on the yoke when out of
trim.

I wouldn't fret about that... the main mechanism the pilot's use to
handle phugoid oscillations isn't available to you (yoke pressure),
so your operating at an understandable disadvantage there.

Better for it to be harder than easier. It means that flying the real
thing would be easy compared to flying the sim.

My guess is that this actually has more to do with the FS 747 model
loosing accuracy at the limit's of the aircraft's envelope.

I'm not so sure. The 747-400 has a custom-written model that is
independent of MSFS. They supposedly spent years working on it. But
nobody flies 747s at 2000 feet and 355 knots in real life (I think),
so it doesn't matter that much. The oscillation was very small, but
you can "feel" that the aircraft is oscillating a bit in watching the
instruments.

I would imagine most simulation makers would choose to optimize
the model to provide the most realistic behavior for the portions of
the aircraft envelope that sim pilots will spend most of their time
in, but this will come at a cost of poorer simulation of the
extremes.

But is low altitude and high speed really an extreme, or just
different?

Raises an interesting question as to how AP's deal with phugoid
oscillations, I have no idea.

I presume they work predictively, by calculation how much correction
to apply ahead of the aircraft. Pilots can't do this as well.

It's like having a weight swinging on a chain: If you try to
compensate for the swinging reactively, it takes forever to get it to
stop. But if you anticipate the movement of the weight and compensate
for it as it happens, you can get the weight to stop swinging entirely
in one or two swings.

I'll say it again though - there is no more 'neutral trim' than there
is a 'neutral AOA' as far as the pilot is concerned, by simple,
fundamental definition. The mechanisms behind the trim are not our
concern, what matters to us is that the aircraft provides a mechanism
to remove yoke pressure throughout the aircraft's operating range.
Period.

I can't agree. If you pull the yoke way back and then trim to
eliminate yoke pressure, you're not at all in the same state you'd be
in if you had the yoke pretty much in a middle position and then
trimmed to that. In the former case, you're close to the end of
travel for the control surface; in the latter case, you have plenty of
margin for movement in both directions.

If you've trimmed for a lot of nose-up pitch and you suddenly decide
you need more, you may find that none is left. If you trim for a more
neutral pitch, there's plenty there when you need it. Trimming for
extreme pitch attitudes could lull you into thinking that you are
further from the extremes of pitch than you actually are.

This is why I'm hesitant to trim for extreme pitch attitudes. I want
to be reminded that the pitch is still fairly extreme. If I just trim
the yoke pressure away, I might forget.

This actually suggests to me that the 'neutral trim' position your
aircraft provides is actually a bit behind Vy (closer to Vx?)

I don't know. What I do know is that zero on the trim indicator
corresponds to neutral trim in that the trim tabs are flush with the
elevator.

That's like saying you should always fly in the middle of the
aircrafts airspeed envelope because it gives you the most options to
speed up or slow down... its somewhat irrelevant to the point of
having an aircraft that can operate in a wide envelope.

If the aircraft is well designed, you should have full control
authority at any trimmed AOA.

That isn't possible if you are using trim tabs; it's possible if the
entire stabilizer moves. If you have tabs, the tabs move the control
surface, but the range of movement of that surface does not change.
So if you trim such that the surface moves towards one of its
extremes, the remaining authority at that extreme is reduced.

I suppose that in small aircraft the position of the yoke after
trimming gives you a visual indication of the actual position of the
control surfaces. My concern, though, is that you might apply a lot
of trim and then forget that you have done so, and when you then try
to push or pull the yoke you find that you've already trimmed out most
of the movement of the control surface, leaving you with very little
margin. But perhaps if you can see the yoke move, this is less of a
problem.

Without the necessary tactile inputs, this may be somewhat futile.

Why? If it works on the sim, it willl work in real life, even though
real life may also offer a simpler method.

No it won't moron.

Bertie

Mxsmanic wrote in
:

writes:

Then why bother asking how real airplanes fly?

I know how real airplanes fly.

No, you don't.


Bertie