Procedure for calculating weight and balance

Mxsmanic,

This is why I prefer to stay near neutral trim.


So you go ahead and do that in your little game. Jeeze, you elaborately
construct a problem that simply doesn't exist in real life. Get over
it.

--
Thomas Borchert (EDDH)

Thomas Borchert wrote:

Ok, you got me curious. No default position in all Cessnas I have flown.
Not in the Bo. Nor in the Tobago. Not in the Cirrus nor the DA-40 or the
-20. Nor any other plane I can remember INCLUDING the big airliners in
MSFS.

The position where the control surfaces align with the stabilizer, that is,
no deflection upwards or downwards. At least that's what I interpreted the
expression to mean. I freely admit I'm clueless, though.

NB that I'm not saying that this position is necessarily marked anywhere,
nor that it is relevant to actually flying the plane.

TxSrv writes:

Then you definitive statement about "how far you are from
each stop" was flat wrong.

No, there are simply some aircraft designs to which it does not apply.
There are a lot of ways to design control surfaces.

--
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Thomas Borchert writes:

Ok, you got me curious. No default position in all Cessnas I have flown.

Both neutral and default positions were mentioned. While there is no
default position, there is most definitely a neutral position, wherein
the trim tab is aligned with the control surface, so that it creates
no deflecting force.

--
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Anno v. Heimburg writes:

NB that I'm not saying that this position is necessarily marked anywhere,
nor that it is relevant to actually flying the plane.

It is slightly relevant. If you have a substantial amount of trim set
for a control surface, the distance remaining to the limits of its
travel are substantially modified, and you may forget about the trim
and mistakenly believe that you have more remaining control authority
than actually exists.

Also, if you have trim set but you think it's neutral, you may be be
actively compensating for changes induced by the trim. In some
aircraft, you can see the position of the controls and deduce that
some trim must be in effect, but in other aircraft you cannot.

Both of these potential problems can be avoided by keeping a strong
awareness of the trim state of the aircraft. As long as you keep in
mind that you've applied x trim while flying, you should be fine.

--
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BT writes:

how far from each stop when?

Trim tabs deflect control surfaces towards one of the limits of their
travel. The greater the trim applied, the greater the deviation, and
the less the amount of travel remaining.

--
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Anno v. Heimburg wrote:

Okay, now that I've made the mistake of reading this discussion, you've got
me curious: How does your plane's trim work? It's obviously not a trim tab.
And how can there be no neutral/default position of the elevator or the
trim device?

It's the common anti-servo tab across entire trailing edge
of the elevator. The trim tab position indicator is marked
only as to a "takeoff" setting, which is roughly in the
center. There is a sweet spot for aerodynamicists where all
three horiz flying surfaces are in trail, not marked on the
indicator, and it is forward of "takeoff," well toward nose
down. A logical way to set tail incidence is so everything
is in trail at 75% cruise velocity in std atmosphere at the
alt where you can have the best cruise book number
(marketing, really). As long as you still comply with Part
23 re trim effects.

In MSFS, the indicator has a center mark, an apparent
"default". In a typical real airplane, this ain't cruise.
Where MX is getting all screwed up besides not understanding
the the lift/drag effects of trim (it's almost a whole
chapter in Dr. S. Hoerner's classic text, Fluid Dynamic
Lift), is assuming MSFS knows when all surfaces are in
trail. Such a tiny flight model tweak would be bizarre for a
game sim which doesn't even fully understand air density.

All trim essentially does in MSFS is tweak the same variable
as elevator to allow for centering springs in joysticks.
I've removed the springs from some of my joysticks, because
then one fiddles less if at all with trim, and it can make
hand flying even the jets easier. Much less unrealistic
phugoid chasing.

F--

Mxsmanic wrote:

The neutral position of a trim tab is the position in which it does
not intefere with the flow of air over the control surface....

A trim tab does not necessarily "interfere" with the flow of
air over a control surface. You need to read Hoerner's books.

F--

Mxsmanic wrote:
BT writes:

how far from each stop when?

Trim tabs deflect control surfaces towards one of the limits of their
travel. The greater the trim applied, the greater the deviation, and
the less the amount of travel remaining.

False. Except possibly in MSFS.

F--

The following comments are really intended for new pilots -- Mx is
beyond help.

Real pilots in real airplanes set trim so they do not need to maintain
pressure on the yoke during norrmal cruise operations. That may not be
a consideration for sim games.

The aft cg position is most ofter determined so that the airplane still
pitches nosedown when the wings stall. If the weight is too far forward
elevator authority is a serious limit -- the pilot may not be able to
get the nose up during low speed operations, like take-offs.

The physics of flight (Mx had already demonstrated he does not accept
Newton's approximations of motion in other threads the careful reader
will smile at my use of the word 'approximations' since he or she will
understand their limitations) would suggest airplanes are more
efficient with cg close to center of lift since when loaded that way
the airplane is not made artificially heavy because the elevator is not
exerting negative (downward) lift. One could argue that 'neutral'
aircraft loading would be such that the elevator would not have to add
either upward or downward force.

If you're close to either limit, airspeed is your friend.




On Jan 7, 7:45 am, Mxsmanic wrote:
BT writes:
how far from each stop when?Trim tabs deflect control surfaces towards one of the limits of their
travel. The greater the trim applied, the greater the deviation, and
the less the amount of travel remaining.

--
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