Myth: 1 G barrel rolls are impossible.

wrote:
Hang on, let's keep things simple:

1. If I enter a coordinated turn, I experience an increase in Gs.
2. If I enter a descent, I experience a decrease in Gs.

If I do these two things at the same time, it is possible to enter a
descending turn without any change in Gs. Just as long as I
continously feed in enough down elevator to offset the increasing Gs
from the turn, the force on the airframe and me, the pilot, will stay
at 1 G.

Of course, all combinations are indeed possible. But this interesting
special case of the situation exists, doesn't it, in which there is no
change in the force felt by the pilot?


On Jun 14, 3:36 pm, Mxsmanic wrote:
writes:
'Some combination', 'several possibilities.' I'm confused by this -
can you be more precise? What are the possibilities?
You can move and accelerate in any combination of three dimensions, with any
combination of acceleration rates, almost. You have to calculate the
direction and magnitude of the net acceleration vector to determine exactly
how much force is acting upon the pilot, and in which direction.

Some of it is (or should be) intuitive. For example, if you turn the aircraft
to the right, you'll be accelerated to the right.


There is a special case where you can unload the airplane in roll to
increase the roll rate. It's done in fighters all the time in ACM. You
can experience it in your everyday light aerobatic airplane by doing an
aileron roll from a nose high roll set position, then as the airplane
goes past the first knife edge position, go forward on the pole to
unload the wings but not enough to go negative. Keeping the aileron in
hard while you do this increases the roll rate and as a side effect
flattens the roll in pitch at the same time making it prettier :-)

Dudley Henriques

wrote:
Hang on, let's keep things simple:

1. If I enter a coordinated turn, I experience an increase in Gs.
2. If I enter a descent, I experience a decrease in Gs.

If I do these two things at the same time, it is possible to enter a
descending turn without any change in Gs. Just as long as I
continously feed in enough down elevator to offset the increasing Gs
from the turn, the force on the airframe and me, the pilot, will stay
at 1 G.

Isn't there some sinister name for this
when it happens to a non-IFR pilot in a cloud?

Jim, you don't have to do the physics for a 1 g roll. click on

stanford.edu/~sigman/one_g_roll.html for a really neat analysis.

Page down toward the end of sigman's article to see the actual flight
paths that it takes. It's a neat read.

Oh, for the nonbelievers in Newton and vector analysis and such (Mx
whatever comes to mind) don't bother.

OPPS, It's www.stanford.edu/~siegman/one_g_roll.html


On Jun 14, 7:19 pm, wrote:
Jim, you don't have to do the physics for a 1 g roll. click on

stanford.edu/~sigman/one_g_roll.html for a really neat analysis.

Page down toward the end of sigman's article to see the actual flight
paths that it takes. It's a neat read.

Oh, for the nonbelievers in Newton and vector analysis and such (Mx
whatever comes to mind) don't bother.

On Jun 15, 10:29 am, Jim Stewart wrote:
wrote:
Hang on, let's keep things simple:

1. If I enter a coordinated turn, I experience an increase in Gs.
2. If I enter a descent, I experience a decrease in Gs.

If I do these two things at the same time, it is possible to enter a
descending turn without any change in Gs. Just as long as I
continously feed in enough down elevator to offset the increasing Gs
from the turn, the force on the airframe and me, the pilot, will stay
at 1 G.

Isn't there some sinister name for this
when it happens to a non-IFR pilot in a cloud?

Graveyard spiral dive

wrote:
Jim, you don't have to do the physics for a 1 g roll. click on

stanford.edu/~sigman/one_g_roll.html for a really neat analysis.

Page down toward the end of sigman's article to see the actual flight
paths that it takes. It's a neat read.

Oh, for the nonbelievers in Newton and vector analysis and such (Mx
whatever comes to mind) don't bother.

OPPS, It's www.stanford.edu/~siegman/one_g_roll.html

Fascinating - thanks for finding that! Amusing to note that a physicist of
that caliber was motivated to explore the situation due to an older thread
on the same subject on the same Usenet newsgroup! I considered setting up
the same situation using Mathcad 2000 (it can generate animations, so I
think I could have set up appropriate parametric equations and created a 3D
movie). But I just don't have the time at the moment to do that.

At least I feel better that my physical intuition didn't fail me.

The nit pickers may (reasonably) argue that the trajectories don't yield
the "barrel roll" spiral they might insist on, but such is life. I should
have titled this thread "Myth: 1 G rolls are impossible," and dispensed
with the word "barrel."

Wasn't the demonstration of the ignorance of physics by some of the
posters fun?

I don't think a GA airplane has the control authority to do one of
these 'rolls' but maybe.

But you could start the thing with a coordinated turn and forward
yoke, and maybe get to 45 degrees bank and a lot of downward pitch
maintaining 1 G before getting back to straight and level,

His first model with 10 seconds total time means 320 fps downward
velocity, about 200 kts down at its end. He pointed out the total
altitude loss from start to finish was 1600 feet or so, but then
comes pull out from lots of vertical speed. Moral: start high and
pull out smoothly or turn the airplane into a kit.






On Jun 14, 8:47 pm, Jim Logajan wrote:
wrote:
Jim, you don't have to do the physics for a 1 g roll. click on

stanford.edu/~sigman/one_g_roll.html for a really neat analysis.

Page down toward the end of sigman's article to see the actual flight
paths that it takes. It's a neat read.

Oh, for the nonbelievers in Newton and vector analysis and such (Mx
whatever comes to mind) don't bother.
OPPS, It'swww.stanford.edu/~siegman/one_g_roll.html

Fascinating - thanks for finding that! Amusing to note that a physicist of
that caliber was motivated to explore the situation due to an older thread
on the same subject on the same Usenet newsgroup! I considered setting up
the same situation using Mathcad 2000 (it can generate animations, so I
think I could have set up appropriate parametric equations and created a 3D
movie). But I just don't have the time at the moment to do that.

At least I feel better that my physical intuition didn't fail me.

The nit pickers may (reasonably) argue that the trajectories don't yield
the "barrel roll" spiral they might insist on, but such is life. I should
have titled this thread "Myth: 1 G rolls are impossible," and dispensed
with the word "barrel."

Dudley Henriques wrote:

There is a special case where you can unload the airplane in roll to
increase the roll rate. It's done in fighters all the time in ACM. You
can experience it in your everyday light aerobatic airplane by doing an
aileron roll from a nose high roll set position, then as the airplane
goes past the first knife edge position, go forward on the pole to
unload the wings but not enough to go negative. Keeping the aileron in
hard while you do this increases the roll rate and as a side effect
flattens the roll in pitch at the same time making it prettier :-)

Why does this work?

Matt

wrote:
Jim, you don't have to do the physics for a 1 g roll. click on

stanford.edu/~sigman/one_g_roll.html for a really neat analysis.

Page down toward the end of sigman's article to see the actual flight
paths that it takes. It's a neat read.

Oh, for the nonbelievers in Newton and vector analysis and such (Mx
whatever comes to mind) don't bother.


A very nice analysis and it confirms that you can't execute a barrel
roll from straight and level flight while maintaining 1G. You either
lose a lot of altitude and end up in a steep dive or you have to pull up
(and thus exceed 1 G) if you want to end up at the starting altitude.
Case closed. :-)

Matt

tbaker27705 opined

Jim, you don't have to do the physics for a 1 g roll. click on

stanford.edu/~sigman/one_g_roll.html for a really neat analysis.

Page down toward the end of sigman's article to see the actual flight
paths that it takes. It's a neat read.

Oh, for the nonbelievers in Newton and vector analysis and such (Mx
whatever comes to mind) don't bother.

It's http://www.stanford.edu/~siegman/one_g_roll.html


-ash
Cthulhu in 2007!
Why wait for nature?