Myth: 1 G barrel rolls are impossible.

I don't know how anyone can make it more clear than that. If you don't
believe this, you have never done barrel rolls and should do so, with
appropriate plane and instructor, before saying any more.

Dudley Henriques wrote:


Not sure exactly where you are with this, but as what you are saying
pertains to barrel rolls begun from level flight or from a position with
the nose below the horizon, don't forget that the entire gist of the
misunderstanding that has been running rampant on this thread about
barrel rolls and doing them at 1 positive g can be centered and
completely focused on the fact that it's the ENTRY and the EXIT of the
roll, and how these two factors interplay into the roll itself that is
causing all the confusion.
The one factor that can't be taken out of the barrel roll scenario is
that no matter how you cut it, if PITCH is a factor in a barrel roll,
there will be an indication on a g meter above 1 g as that pitch change
is being made. In a normal barrel roll you have pitch change as the nose
transverses the roll in it's helical path.
If a barrel roll requires the nose of the aircraft to be above the
horizon during the entry and then again brought back to the horizon
during the recovery (as it does) you will absolutely be showing more
than 1 positive g on the g meter during the roll, and if it's a
retaining double needle g meter, after the roll when you bring the
airplane home........period! This is a fact of life. As soon as the
aircraft's nose shows a positive nose rate in PITCH as it's raised
during the roll entry and then again during the recovery as it's raised
again to level flight, that g meter will leave 1 and show more than 1
positive g.

Now here is the part that is causing all the confusion. ONCE the nose
has been raised above the horizon (and that over 1 g has been registered
on the g meter) as you feed in aileron you can PLAY WITH THE BACK
PRESSURE being applied and EASE OFF the positive g to a LOWER LEVEL if
desired over the top of the roll, but that level can't be unloaded below
1 g or the arc of the roll will be destroyed. It's the COMBINATION of
roll and pitch that is producing the roll arc and those TWO pressures
MUST be maintained to produce the roll.
So the bottom line is simply that to do a barrel roll where the nose
must be both above and below the horizon line starting from level flight
you need over 1 g during the entry and exit, but you can reduce the g to
1 through the top of the roll if desired.

Dudley Henriques

You're right about a barrel roll, of course, I like that you can
rotate the wings through 360 degrees and maintain 1 G.

You could also, I think, start the 'roll' with an upward velocity
component of 320 feet a second and end it level, but hardly at the
same altitude (you'd be 1600 feet higher).

An even more interesting question would be, is there an airplane that
can fly this flight path? I think it would take massive control
surfaces to be able to pull a G with the yoke.


On Jun 14, 9:55 pm, Matt Whiting 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.

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

wrote in message
oups.com...
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.


Hmmmm....some of the trajectories for varying "initial roll angles" look
kinda like my drawing
somewhere above in this thread. Especially the ones to the left side of the
graph with higher
initial angles. Only I was trying to imagine a scenario where you end up
straight and level rather
than finishing in a high-speed dive as Siegman's model shows. I was thinking
more along the lines
of pulling up the nose throughout the maneuver to induce the 1g, resulting
in a corkscrew dive which
you would gradually flatten until the end of the roll. By pulling up the
nose to create the g-force you
would not have to accelerate downward to "outrun" the acceleration of
gravity. Of course Siegman's
model more closely approximates a barrel roll where I think I ended up with
a gradually opening
spiraling dive. Mine was just a thought experiment....no math involved. :-)

I think by chosing an initial climb rate of 320 fps (!!) you can do
this 1 G roll and end up level but 1600 feet higher, or at a lower
rate , maybe 160 fps, and end up at the same altitiude as you started,
but going down 160 fps. (superposiiton works!)

I sure can not think of a 1 g track that would get you straight and
level from a dive, unless the dive took you through the center of the
earth.


Hey, there's the answer. You have to go really fast so that your fall
rate is compensated by the earth being a sphere. That would be pretty
fast!

This part of the thread belongs over in the physics newsgroup.


On Jun 14, 10:34 pm, "muff528" wrote:
wrote in message

oups.com...

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.

Hmmmm....some of the trajectories for varying "initial roll angles" look
kinda like my drawing
somewhere above in this thread. Especially the ones to the left side of the
graph with higher
initial angles. Only I was trying to imagine a scenario where you end up
straight and level rather
than finishing in a high-speed dive as Siegman's model shows. I was thinking
more along the lines
of pulling up the nose throughout the maneuver to induce the 1g, resulting
in a corkscrew dive which
you would gradually flatten until the end of the roll. By pulling up the
nose to create the g-force you
would not have to accelerate downward to "outrun" the acceleration of
gravity. Of course Siegman's
model more closely approximates a barrel roll where I think I ended up with
a gradually opening
spiraling dive. Mine was just a thought experiment....no math involved. :-)

wrote:
You're right about a barrel roll, of course, I like that you can
rotate the wings through 360 degrees and maintain 1 G.

You could also, I think, start the 'roll' with an upward velocity
component of 320 feet a second and end it level, but hardly at the
same altitude (you'd be 1600 feet higher).

An even more interesting question would be, is there an airplane that
can fly this flight path? I think it would take massive control
surfaces to be able to pull a G with the yoke.

I'm not an aerobatic pilot, but pulling 1G with the elevator isn't hard
on any airplane I've flown.

Matt

Matt Whiting wrote:
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

Several factors effect roll rate, roll acceleration and roll inertia.
Basically why this works is that unloading the airplane while rolling
(aileron roll basically, not a slow roll) minimizes much of the
effectiveness issues experienced by the ailerons especially at low
airspeeds and high load factors when the wings are generating a fair
amount of lift. Anytime you want to maximize the roll rate, unloading
will achieve this. The exact point where the rate is maximized by
unloading will vary from aircraft to aircraft but basically the rule
still applies.
Dudley Henriques

Matt Whiting wrote:
wrote:
You're right about a barrel roll, of course, I like that you can
rotate the wings through 360 degrees and maintain 1 G.

You could also, I think, start the 'roll' with an upward velocity
component of 320 feet a second and end it level, but hardly at the
same altitude (you'd be 1600 feet higher).

An even more interesting question would be, is there an airplane that
can fly this flight path? I think it would take massive control
surfaces to be able to pull a G with the yoke.

I'm not an aerobatic pilot, but pulling 1G with the elevator isn't hard
on any airplane I've flown.

Matt

Actually Matt, all you need to do with most g meters is to "tweak" the
stick with an instant of positive pitch pressure and release it. You
will register over 1 g just doing that :-))
Dudley Henriques

writes:

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.

Yes. Note, however, that you must _accelerate_ downward, and not merely drift
downward at a constant rate.

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.

The additional G from the acceleration towards the center of the turn will be
constant, but the offsetting G from the descent will be constant only if you
continuously accelerate downward.

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?

Yes. It sounds a lot like a spin.

george writes:

Graveyard spiral dive

Which probably isn't a coincidence, since pilots likely get into these
precisely because they maintain "normal" G forces.

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.

Yes. Note, however, that you must _accelerate_ downward, and not merely drift
downward at a constant rate.

Right. A major part of your argument in this thread has been that it
is impossible to change the direction in which the plane is travelling
without accelerating the plane. Your own analysis, based on my
questions, clearly shows that it is possible to change the direction
the plane is going in without deviating from the 1G being exerted.
Note that the I am not denying that the aircraft is accelerating in
this situation. But it is doing so without a change in force being
felt. So where your argument breaks down is in the assumption that if
changing the direction requires acceleration, then acceleration will
require a change in G force.

I am not saying that this is, in of itself, proof of the possibility
of the 1G barrel roll. It does, however, clearly indicate a flaw in
your argument. I find it odd that you find it so hard to believe that
people can believe that changes in direction are possible without
accelerations being felt, given that by your own admission, these
people are actually correct.


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?

Yes. It sounds a lot like a spin.

What? It sounds very little like a spin - try entering a spin with no
change in G force!