Myth: 1 G barrel rolls are impossible.

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

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:
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:
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

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. :-)

I can't believe I took the time to do this.

If you started at abaout 18000 miles an hour (you had better be pretty
high!) when you flew this path you'd end up level with the horizon.

I think this is out of the range of most general avaition airplanes.
The neat thing is, though, if you wanted to have a real aerobatic
flight experience on a simulator, this is the one to try. Just create
a craft with the ability to go that high, that fast, with thrusters
than could do this thing. Why, you could pour coffee into a cup and
claim to have the same effects in the simulation as a real pilot would
have in the craft.

wrote in message
ups.com...
I can't believe I took the time to do this.

If you started at abaout 18000 miles an hour (you had better be pretty
high!) when you flew this path you'd end up level with the horizon.


It's called orbital velocity

http://electronics.howstuffworks.com/satellite3.htm


I think this is out of the range of most general avaition airplanes.
The neat thing is, though, if you wanted to have a real aerobatic
flight experience on a simulator, this is the one to try. Just create
a craft with the ability to go that high, that fast, with thrusters
than could do this thing. Why, you could pour coffee into a cup and
claim to have the same effects in the simulation as a real pilot would
have in the craft.

On Jun 11, 1:09 pm, 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_...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.)

The answer to your question as you ask it is no. You can not perform
a "Barrel roll" and maintain 1 G. We all have 1 G pressing on us as
we are sitting at our desks, or flying straight and level in an
airplane. To perform a barrel roll, you pick a point 20 degrees off
heading (usually to the left in aircraft with US engines). You then
must execute the beginings of a loop by applying back pressure on the
stick. You can not do this without adding additional G forces. You
should be at 90 degrees bank when you are just over the point you
selected 20 degrees off the origional heading. As you continue the
roll, you will be at a point 40 degrees off the origional heading when
you have completed 180 degrees of roll and your wings should be level
with the horizion in the inverted position. As you continue the roll
the nose of the aircraft will be 20 degrees below the horizion and at
a 90 degree bank when you are back at the point 20 degrees off the
origional heading. You now continue the last quarter of the roll
while "pulling" to wings level - again you can not do this without
adding G.

I have done thousands of barrel rolls - and have done them with open
bottles of water on the dash - same principle as swinging a bucket of
water over your head and not spilling any. As long as you keep
positive "G" (not gee) force on the plane - the water will not spill -
let it go negative and you will have a mess.

If the question you are asking is can this maneuver be done by adding
1 additional G unit (now you would be at 2 G's) the answer is you
could rotate around and probably not spill the water, but you would
not execute what is considered a "Barrel Roll" - it would be more of a
sloppy aileron roll where you end up lowing altitude from your
origional position.

A "slow roll" is one where the aircraft follows a straight line and if
you are doing these on a horizontal line you will not keep "positive"
G's on you and the aircraft.

SS2MO wrote

As you continue the roll, you will be at a point 40 degrees off the
origional heading when you have completed 180 degrees of roll and
your wings should be level with the horizion in the inverted position.

How about 90 degrees off the original heading when inverted?

Bob Moore