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Pitch vs. trim in flight phases



 
 
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  #161  
Old June 3rd 08, 12:57 PM posted to rec.aviation.piloting,rec.aviation.student
Michael[_1_]
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Posts: 185
Default Pitch vs. trim in flight phases

On May 30, 3:50*pm, Robert Moore wrote:
The Boeing 707, and perhaps others, trimmed in this same fashion.
Trim...Relax....Trim some more...Relax...Do it again.......


I'm not familiar with the 707 systems, but a friend of mine flew the
DC-9 and told me it had the same jackscrew trim arrangement as the
short wing pipers (scaled up of course) so I would expect it might
behave the same way. Anyone who has actually flow the DC-9 care to
comment?

Michael
  #162  
Old June 3rd 08, 01:32 PM posted to rec.aviation.piloting,rec.aviation.student
BDS[_2_]
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Posts: 149
Default Pitch vs. trim in flight phases


"Michael" wrote in message
...
On May 31, 10:56 am, Tina wrote:
The overlooked or ignored difference is if one turns the trim in the
wrong direction in a real airplane pressure on the yoke increases.


No, this is not universally true. I've flown airplanes where this is
not true, and clearly so has Robert Moore. These are certificated
airplanes ranging from light piston singles to transport category
multiengine jets.

Oh, if you keep doing it long enough, yes, you will eventually feel
something - but if you depend on this as your primary cue, you will
never get it right. You just need to know which way to adjust the
trim, and you need to keep moving the yoke to maintain pitch attitude.

Pilots are trained to trim to reduce yoke pressure -- it is obvious
and becomes instinctive. Sims of the everyday variety do not provide
that feedback.


And neither do some airplanes. If you are trained to depend on that
cue, you are SOL in those planes.

We do not live in a single cue world.

Michael

*******

Well then, once you get to the point of having no pressure on the yoke,
what's the point of trimming any further?


  #163  
Old June 3rd 08, 05:57 PM posted to rec.aviation.piloting,rec.aviation.student
Michael[_1_]
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Posts: 185
Default Pitch vs. trim in flight phases

On Jun 3, 8:32*am, "BDS" wrote:
Well then, once you get to the point of having no pressure on the yoke,
what's the point of trimming any further?


The point is not that you get to where there is no pressure on the
yoke. The point is that moving the trim without moving the yoke will
never get you there. You have to move the yoke as you move the trim
to get to where the pitch is correct without applying pressure.

Michael
  #164  
Old June 3rd 08, 09:55 PM posted to rec.aviation.piloting,rec.aviation.student
More_Flaps
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Posts: 217
Default Pitch vs. trim in flight phases

On Jun 3, 11:53*pm, Michael wrote:
On May 31, 10:56*am, Tina wrote:

The overlooked or ignored difference is if one turns the trim in the
wrong direction in a real airplane pressure on the yoke increases.


No, this is not universally true. *I've flown airplanes where this is
not true, and clearly so has Robert Moore. *These are certificated
airplanes ranging from light piston singles to transport category
multiengine jets.


Hi Michael,

Here's my understanding : If the yoke gives force feedback of the out
of trim condition (you hold attitude and then trim) then if you turn
the trim the wrong while then holding attitude yoke pressure will
increase -as Tina says. If it doesn't then you are not holding
attitude OR the stick is not connected directly to the elevator
surface (e.g. elevator is hydraulic or trim surface powered). I know
the latter is the case for big planes (where elevator forces are too
large for one armed man power) but what light piston single are you
thinking about?

Cheers
  #165  
Old June 4th 08, 06:02 PM posted to rec.aviation.piloting,rec.aviation.student
Michael[_1_]
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Posts: 185
Default Pitch vs. trim in flight phases

On Jun 3, 4:55*pm, More_Flaps wrote:
Here's my understanding : If the yoke gives force feedback of the out
of trim condition (you hold attitude and then trim) then if you turn
the trim the wrong while then holding attitude yoke pressure will
increase -as Tina says.


In theory this is right - but in practice you will have to turn it a
long time before the increase is noticeable with certain trim systems.

If it doesn't then you are not holding
attitude OR the stick is not connected directly to the elevator
surface (e.g. elevator is hydraulic or trim surface powered).


There is a third option - this is where the trim surface is not
connected to the elevator - which is indeed the case. The yoke forces
come from the elevator not being 'in trail' with the stabilizer in
such a system. Since the angle of the stabilizer changes very little
as trim is applied, the force on the yoke in a given position also
changes very little. If you move the yoke in the correct direction to
maintain the pitch attitude, the force on the yoke will change as it
should - but this is also the case in a primitive sim since the stick
has a spring return.

I know
the latter is the case for big planes (where elevator forces are too
large for one armed man power) but what light piston single are you
thinking about?


I'm thinking of the short wing Pipers - the most popular of which was
the TriPacer.

Michael
 




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