Best place for CG along roll axis

Crash Lander writes:

Mxsmanic, ask these questions over there. I guarantee you'll get the answers
you're looking for over there.

I'm getting good answers here.

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BTIZ writes:

and most any real airplane will drop the nose without aft stick pressure
when rolled into a turn.

I don't recall mentioning turns.

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"Mxsmanic" wrote in message
...
After constantly struggling with a heavy nose in several aircraft it
occurred to me that having a fat pilot in front and nothing else was
moving the CG forward. I put some weight in back and moved the CG
further back over the wings, and handling improved greatly. Is there
a way (other than consulting a manual each time) to determine exactly
where over the wing is the best place for the CG? MSFS is kind enough
to show me a diagram with the current CG marked, but I don't know how
far back I should try to place it.


The best place for the CG along the ROLL axis is somewhere near the middle.
Moving weight from front to back won't make a difference in this case.

In real life, you do have to consult the manual and do the math if you are
flying with a load you haven't already calculated to get the CG in range
from front to back.

Also, in real life there is a difference between having the CG too far
forward and not using the trim properly.

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Geoff
The Sea Hawk at Wow Way d0t Com
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Using the roll axis to define CG location is not the classical way it
is done, however when weight is added up front or in back, it does move
the CG along the roll axis, since the axis about which the aircraft
rolls runs generally from nose to tail. The classic way is to state the
CG is at a location along the MAC (mean aerodynamic chord), usually
stated as percent of MAC.

Bud


Capt. Geoffrey Thorpe wrote:
"Mxsmanic" wrote in message
...
After constantly struggling with a heavy nose in several aircraft it
occurred to me that having a fat pilot in front and nothing else was
moving the CG forward. I put some weight in back and moved the CG
further back over the wings, and handling improved greatly. Is there
a way (other than consulting a manual each time) to determine exactly
where over the wing is the best place for the CG? MSFS is kind enough
to show me a diagram with the current CG marked, but I don't know how
far back I should try to place it.


The best place for the CG along the ROLL axis is somewhere near the middle.
Moving weight from front to back won't make a difference in this case.

In real life, you do have to consult the manual and do the math if you are
flying with a load you haven't already calculated to get the CG in range
from front to back.

Also, in real life there is a difference between having the CG too far
forward and not using the trim properly.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

"Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com writes:

Also, in real life there is a difference between having the CG too far
forward and not using the trim properly.

I had the weight far enough off that trimming didn't leave me much
elevator travel for maneuvering. That's what made me realize that
something was wrong.

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Trimming doesn't change the ability of the horizontal stabilizer to
correct for CG location, etc. It merely adds in an initial deflection
of the elevator so as to make the effort needed by the pilot to move it
is small. Imagine having to hold a constant twenty pounds of elevator
on a cross country .

Bud

Mxsmanic wrote:
"Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com writes:

Also, in real life there is a difference between having the CG too far
forward and not using the trim properly.

I had the weight far enough off that trimming didn't leave me much
elevator travel for maneuvering. That's what made me realize that
something was wrong.

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writes:

Trimming doesn't change the ability of the horizontal stabilizer to
correct for CG location, etc. It merely adds in an initial deflection
of the elevator so as to make the effort needed by the pilot to move it
is small. Imagine having to hold a constant twenty pounds of elevator
on a cross country .

But doesn't trim in most aircraft involve moving the elevator with a
trim tab? That is, if the elevator is moved up by the trim, then
there's that much less travel remaining in the elevator in that
direction. So if you have quite a bit of trim, your safety margin for
additional elevator movement is reduced. Right?

In an aircraft in which the entire stabilizer moves for trim, I
suppose you could set any amount of trim and still have full travel in
both directions (doesn't the 737 work this way?).

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Recently, Mxsmanic posted:

writes:

Trimming doesn't change the ability of the horizontal stabilizer to
correct for CG location, etc. It merely adds in an initial deflection
of the elevator so as to make the effort needed by the pilot to move
it is small. Imagine having to hold a constant twenty pounds of
elevator on a cross country .

But doesn't trim in most aircraft involve moving the elevator with a
trim tab?

On many aircraft, the trim tab moves independently of the elevator, and on
others the elevator is adjusted.

That is, if the elevator is moved up by the trim, then
there's that much less travel remaining in the elevator in that
direction. So if you have quite a bit of trim, your safety margin for
additional elevator movement is reduced. Right?

Trimming the elevator reduces the amount of effort required by the pilot
to hold altitude. If one is carrying a lot of "up" trim, for example, then
the aircraft is likely to be near critical AOA. The last thing you'd need
is have a lot more "up" elevator movement available.

In an aircraft in which the entire stabilizer moves for trim, I
suppose you could set any amount of trim and still have full travel in
both directions (doesn't the 737 work this way?).

The overall range of a stabilizer's movement is usually the same
regardelss of trim settings. IOW, you don't usually get more "up" than
full "up".

Neil

Mxsmanic wrote:

But doesn't trim in most aircraft involve moving the elevator with a
trim tab? That is, if the elevator is moved up by the trim, then
there's that much less travel remaining in the elevator in that
direction. So if you have quite a bit of trim, your safety margin for
additional elevator movement is reduced. Right?

Yes, that's what I tried to say.



In an aircraft in which the entire stabilizer moves for trim, I
suppose you could set any amount of trim and still have full travel in
both directions (doesn't the 737 work this way?).

This contradicts what you said in the first paragraph. No, the 737 nor
any other plane could possibly have this ability. This is like saying
that the 737 can be loaded out of the allowable CG range, or the
elevator (or stabilator) can be moved past the stall angle of attack
(which is what limits it's travel in the first place). The elevator has
only so many degrees it can rotate up and down before it stalls. Trim
doesn't change this.

Bud

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Perhaps I misinterpreted what you said. Let's start with the example
that a certain plane has a usable elevator range of +/- 25 deg. from
level. If after loading the plane and taking off, it turns out that 5
deg of nose up trim(5 deg of elevator movement) is required for the
plane to be trimmed out in flight, that means that only 20 deg of up
elevator remains available to the pilot.

Regards,
Bud


Mxsmanic wrote:
writes:

Trimming doesn't change the ability of the horizontal stabilizer to
correct for CG location, etc. It merely adds in an initial deflection
of the elevator so as to make the effort needed by the pilot to move it
is small. Imagine having to hold a constant twenty pounds of elevator
on a cross country .

But doesn't trim in most aircraft involve moving the elevator with a
trim tab? That is, if the elevator is moved up by the trim, then
there's that much less travel remaining in the elevator in that
direction. So if you have quite a bit of trim, your safety margin for
additional elevator movement is reduced. Right?

In an aircraft in which the entire stabilizer moves for trim, I
suppose you could set any amount of trim and still have full travel in
both directions (doesn't the 737 work this way?).

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