Myth: 1 G barrel rolls are impossible.

Dudley Henriques wrote in
news:2007061122074775249-dhenriques@rcncom:

On 2007-06-11 21:42:18 -0400, Bertie the Bunyip
said:

"Robert M. Gary" wrote in
oups.com:

On Jun 11, 12:51 pm, Mxsmanic wrote:
Jim Logajan writes:
Myth:

It is impossible to perform a barrel roll such that the pilot
feels exactly 1 gee of force perpendicular to the floor of the
cockpit.

No maneuver that involves a change in altitude can maintain exactly
1 G along the net acceleration vector (including perpendicular to
the cockpit floor). This is not a myth, it's a fact.

The only roll you can perform that does not involve more than 1 G
of net acceleration is one that involves no change in altitude,
such as a roll precisely about the longitudinal axis. But no roll
that maintains the net acceleration vector perpendicular to the
cockpit floor is in this category.

A barrel roll is not about the longitudinal axis of the plane, that
is an aileron roll.


Nope, a roll about the longitudinal axis of the airplane is a slow
roll. actaully that's not entirely correct either since a perfect
slow roll follows a perfectly staight line, which means the axis of
the aircraft must change in realation to the line of flight
throughout. A slow roll is, hower, a one G roll. The 1 G should
always point earthward, though.


An aileron roll is actualy not dissimilar to a Barrel roll in flight
path.


Bertie

Actually Bertie, think about it for just a moment. In a slow roll, you
do indeed roll the airplane on it's longitudinal axis but the roll
line isn't exactly straight.


Not for competition. You're judged by the line you fly. Mind you, if you
can make it look like you're not pushing the nose all over the place,
all the better.


Bertie

Jim Logajan wrote:

Myth:

It is impossible to perform a barrel roll such that the pilot feels exactly
1 gee of force perpendicular to the floor of the cockpit. (Barrel roll is
defined here as the maneuver depicted by the definitions and diagrams on
these website:
http://en.wikipedia.org/wiki/Barrel_roll
http://www.flightsimbooks.com/jfs/page74.php
http://home.comcast.net/~john.schnei...arrel_roll.jpg )

Fact:

The aspect that I think appears to mislead people is the presence of a
gravitational field and an implied requirement that the axis of the helix
must remain straight and parallel with the (flat) ground. But the latter
requirement can be dispensed with and still yield a recognizable helical
flight path - and that is enough to make a 1 gee barrel roll possible. The
"trick" is accomplished by superimposing two equations of motion:

(1) Start with a "zero gee" parabolic trajectory. So basically the plane
travels laterally over the ground while first traveling up (and then down)
such that the pilot would feel weightless absent any other motions. The arc
is a classic parabola.

(2) Superimpose by vector addition the centrifugal force of the plane
"flying" a circle around (and along) the moving center established by the
parabolic trajectory in (1).

(3) Set the radius and angular speed of the circle in (2) to yield one gee
equivalent force and rotate plane's attitude to keep the centrifugal force
vector perpendicular to the floor. End of procedure.

A reasonable nit pick is that the axis of the helix of the barrel roll
doesn't remain "straight and level." But none of the definitions explicitly
state that requirement. And in any case, it is possible to end the 1 G
barrel roll at the same altitude at which it began.

So there. :-)

(If there is a demand (and I can find more time) I can work out and post
the complete set of equations of motion.)
I wonder if the "confusion" may be whether one considers the barrel
roll to include transition from and return to level flight.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

Jim Logajan wrote:
Myth:

It is impossible to perform a barrel roll such that the pilot feels exactly
1 gee of force perpendicular to the floor of the cockpit. (Barrel roll is
defined here as the maneuver depicted by the definitions and diagrams on
these website:
http://en.wikipedia.org/wiki/Barrel_roll
http://www.flightsimbooks.com/jfs/page74.php
http://home.comcast.net/~john.schnei...arrel_roll.jpg )

Fact:

The aspect that I think appears to mislead people is the presence of a
gravitational field and an implied requirement that the axis of the helix
must remain straight and parallel with the (flat) ground. But the latter
requirement can be dispensed with and still yield a recognizable helical
flight path - and that is enough to make a 1 gee barrel roll possible. The
"trick" is accomplished by superimposing two equations of motion:

(1) Start with a "zero gee" parabolic trajectory. So basically the plane
travels laterally over the ground while first traveling up (and then down)
such that the pilot would feel weightless absent any other motions. The arc
is a classic parabola.

You have to pull more than 1 G (what is a gee anyway?) to enter the
parabolic trajectory so you've flunked already! :-)


(2) Superimpose by vector addition the centrifugal force of the plane
"flying" a circle around (and along) the moving center established by the
parabolic trajectory in (1).

(3) Set the radius and angular speed of the circle in (2) to yield one gee
equivalent force and rotate plane's attitude to keep the centrifugal force
vector perpendicular to the floor. End of procedure.

A reasonable nit pick is that the axis of the helix of the barrel roll
doesn't remain "straight and level." But none of the definitions explicitly
state that requirement. And in any case, it is possible to end the 1 G
barrel roll at the same altitude at which it began.

So there. :-)

(If there is a demand (and I can find more time) I can work out and post
the complete set of equations of motion.)


I'd like to see it. And you have to start straight and level and end
straight and level. :-)

Matt

"Matt Whiting" wrote in message
...



I'd like to see it. And you have to start straight and level and end
straight and level. :-)


No, as a matter of fact, you don't have to start straight and level, or end
striaght and level to do a full roll.

The man is not posting a puzzle, he is stating a hard fact.

Reread his post.

"Jim Logajan" wrote in message
.. .
Myth:

It is impossible to perform a barrel roll such that the pilot feels
exactly
1 gee of force perpendicular to the floor of the cockpit. (Barrel roll is
defined here as the maneuver depicted by the definitions and diagrams on
these website:
http://en.wikipedia.org/wiki/Barrel_roll
http://www.flightsimbooks.com/jfs/page74.php
http://home.comcast.net/~john.schnei...arrel_roll.jpg )

Fact:

The aspect that I think appears to mislead people is the presence of a
gravitational field and an implied requirement that the axis of the helix
must remain straight and parallel with the (flat) ground. But the latter
requirement can be dispensed with and still yield a recognizable helical
flight path - and that is enough to make a 1 gee barrel roll possible. The
"trick" is accomplished by superimposing two equations of motion:

(1) Start with a "zero gee" parabolic trajectory. So basically the plane
travels laterally over the ground while first traveling up (and then down)
such that the pilot would feel weightless absent any other motions. The
arc
is a classic parabola.

(2) Superimpose by vector addition the centrifugal force of the plane
"flying" a circle around (and along) the moving center established by the
parabolic trajectory in (1).

(3) Set the radius and angular speed of the circle in (2) to yield one gee
equivalent force and rotate plane's attitude to keep the centrifugal force
vector perpendicular to the floor. End of procedure.

A reasonable nit pick is that the axis of the helix of the barrel roll
doesn't remain "straight and level." But none of the definitions
explicitly
state that requirement. And in any case, it is possible to end the 1 G
barrel roll at the same altitude at which it began.

So there. :-)

(If there is a demand (and I can find more time) I can work out and post
the complete set of equations of motion.)

Excellent post Jim, thanks. I saw this come up in another thread last week
or so, and didn't want to take the time to debate it. But reared it's head
again.

Excellent example. I hope people will take time to read and understand the
message before making a fool of themselves.

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.

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."

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?