Procedure for calculating weight and balance

TxSrv writes:

A trim tab does not necessarily "interfere" with the flow of
air over a control surface.

It can't work unless it does so.

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Recently, Mxsmanic posted:

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.

You are presenting yet another absurd scenario that has no relation to the
reality of flying. Nobody flying a real plane will "forget" about trim set
near the limits of it's travel, because the control forces are a constant
reminder.

Neil

"Anno v. Heimburg" wrote in message
...
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.

Which, depending on how the airplane is designed, may or may not result in
the desired force from the elevator to keep the aircraft in level flight
with the Cg somewhere within range.

I would suspect that on a lot of aircraft with flying tails (e.g. T-18 which
is one example that I have flown) , some deflection between the elevator and
the trim would be necessary to trim properly during all normal cruise when
the Cg is within the limits. And I would further suspect that whoever
designed the aircraft was aware of that fact, and would have set the limits
of the elevator travel with that in mind.


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


I'll agree with that.

On the other hand, Captian Kirk frequently took the Enterprise into the
Neutral Zone when he suspected that the Romulans were threating the
Federation.

--
Geoff
The Sea Hawk at Wow Way d0t Com
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When immigration is outlawed, only outlaws will immigrate.

Neil Gould writes:

You are presenting yet another absurd scenario that has no relation to the
reality of flying. Nobody flying a real plane will "forget" about trim set
near the limits of it's travel, because the control forces are a constant
reminder.

When the aircraft is correctly trimmed, there are no control forces to
serve as a reminder. And some aircraft don't have control forces.

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Tony, great explanation!

To add a little to this fun little conversation, what strikes me is
what it reveals about the result of someone teaching himself to "fly"
via a PC "simulation". I work in the aviation simulation industry, and
MSFS could conceivably be describes as a "training device", OK for
procedures and avionics training, but not for primary flight training.
As a result of his self training, MXS has been completely misled by the
way his "game" flies, and is drawing some wrong (if somewhat
interesting) conclusions!

The whole concept of the trim limiting the control authority is a
classic example of this. In a real aircraft, as previously stated, the
trim is used to relieve control pressures. It does not limit control
authority (except for the very limited effect of a trim tab fully
deflected, which is allowed for in the design of the control surface),
since the control authority is required to be sufficient to cope with
any conceivable need. I think the worse case is usually full gross (or
max landing) weight landing at full forward CG - that will drive the
size and power of the elevator. Any bigger, and pitch becomes too
sensitive at higher speed and adds useless drag.

Also, MXS does not seem to appreciate that the control position (of the
elevator) is a function of the speed (or AOA) of the aircraft, not the
trim position. I can slow down and crank in full nose down trim and
fly just fine with the stick almost fully aft - and get a good workout
in the process! And as the pilot, I know I'm slow since the stick will
be in my lap. As I then crank the trim in, the control surface will
not change position (especially on aircraft with no trim tabs), but the
stick forces will go away (without the stick moving). But I will not
add or remove any control authority - the stick is still way aft! As
a pilot, you are taught this from the beginning - the relationship
between stick position, speed, angle of attack, CG, etc. Their
interrelation is what makes flying so interesting - and where low level
PC "simulations" fail the most.

Oh, by the way, many aircraft do not have any trim tabs at all - most
gliders use springs in the control circuit, J-3 Cubs move the
horizontal stabilizer, the F-4 I used to fly changed the neutral
position of the whole flying tail, etc...

Oddly enough, the F-15 is an exception that actually acts the way MXS
thinks - the flight control system is always resetting itself to 1g
(always in trim), so when you slow down, the stick doesn't move. On
takeoff, if you add a forward trim input, you will extend your takeoff
distance since you will get less angular deflection when you pull full
aft stick to rotate. So maybe MXS should get an F-15 addon to MSFS!

MXS, if you really want to learn about changing CG to affect flying
performance, try a gliding sim like Condor (it is supposedly much
better than MSFS anyway). In high performance gliding, we carefully
adjust our CG for minimum trim drag (usually set to 30 - 40 % forward
of the aft CG limit), carry water ballast to go faster, don't have any
trim tabs (springs instead) and in flapped gliders, control speed with
the flaps. That concept should keep you busy for a while!

Finally - MXS, if you want to have enough control authority "just in
case", then set your speed to just under Va (maneuvering speed). That
way, by design, you can pull back on the stick all you want and not
break the plane - faster and you can over-G and bend things; slower and
you will just enter an accelerated stall a bit earlier. And you can
set your trim wherever you want....

Cheers!

Kirk
Ls6-b "66"

Mxsmanic wrote:

And some aircraft don't have control forces.


Just curious. Which aircraft type-certificated by FAA would
they be? I'm thinking here of what FAR 23.155, et al. says
about this.

F--

Mxsmanic wrote:

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.


For Mxsmanic only:

Please define "servo tab" and "anti-servo tab" and how they relate to
the horizontal stabilizer.

TxSrv writes:

Just curious. Which aircraft type-certificated by FAA would
they be? I'm thinking here of what FAR 23.155, et al. says
about this.

23.155 only applies to certain types of aircraft. Additionally,
23.155 doesn't explain exactly what the control forces must represent,
only their minimum magnitude.

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writes:

The whole concept of the trim limiting the control authority is a
classic example of this. In a real aircraft, as previously stated, the
trim is used to relieve control pressures.

In a real aircraft, trim is used to deflect a larger control surface,
so that control pressures are not required to deflect it. The control
surface moves, which means it moves closer to one stop and further
from the other. This reduces remaining control authority in the
direction of the former, and extends it in the direction of the
latter.

MXS, if you really want to learn about changing CG to affect flying
performance, try a gliding sim like Condor (it is supposedly much
better than MSFS anyway).

Unfortunately, I'm only interested in powered flight.

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Mxsmanic wrote:

23.155 only applies to certain types of aircraft. Additionally,
23.155 doesn't explain exactly what the control forces must represent,
only their minimum magnitude.

And if we add a similar provision in Part 25, we now have
100% of all U.S. civil aircraft with fixed wings. Does
"minimum magnitude" allow for zero control force like you
said? Only in MSFS with a joystick with no springs, or
controlled with mouse or keyboard.

F--