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Myth: 1 G barrel rolls are impossible.



 
 
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  #1  
Old June 11th 07, 07:09 PM posted to rec.aviation.piloting,rec.aviation.student
Jim Logajan
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Posts: 1,958
Default Myth: 1 G barrel rolls are impossible.

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.)
  #2  
Old June 11th 07, 07:22 PM posted to rec.aviation.piloting,rec.aviation.student
Robert M. Gary
external usenet poster
 
Posts: 2,767
Default Myth: 1 G barrel rolls are impossible.

On Jun 11, 11:09 am, 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.)


Did I miss some context? Was there a debate about this? There are
videos on youtube of people doing barrel rolls with a cup of coffee in
their lap.

-robert

  #3  
Old June 11th 07, 07:37 PM posted to rec.aviation.piloting,rec.aviation.student
Jim Logajan
external usenet poster
 
Posts: 1,958
Default Myth: 1 G barrel rolls are impossible.

"Robert M. Gary" wrote:
Did I miss some context? Was there a debate about this? There are
videos on youtube of people doing barrel rolls with a cup of coffee in
their lap.


Most everyone agrees that keeping the coffee in the cup is possible. What
some people don't seem to believe is possible is that the force felt by the
pilot (or tea/coffee) can be 1 gee during the entire roll. They believe it
has to vary during the roll. I'm hesitant to name names. ;-)

So yeah, I think there is some need to clear the air.
  #4  
Old June 11th 07, 08:05 PM posted to rec.aviation.piloting,rec.aviation.student
john smith
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Posts: 1,446
Default Myth: 1 G barrel rolls are impossible.

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


Um... I cannot visualize this. Could you produce an animated computer
graphic that depicts the flight path and g-loading throughout the maneuver?

[Just kidding!!!]

Thanks.
  #5  
Old June 11th 07, 08:22 PM posted to rec.aviation.piloting,rec.aviation.student
Don Tuite
external usenet poster
 
Posts: 319
Default Myth: 1 G barrel rolls are impossible.

On Mon, 11 Jun 2007 15:05:24 -0400, john smith wrote:

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


Um... I cannot visualize this. Could you produce an animated computer
graphic that depicts the flight path and g-loading throughout the maneuver?

[Just kidding!!!]

I'd settle for a description of the control inputs.

(also kidding)

Don

  #6  
Old June 11th 07, 08:51 PM posted to rec.aviation.piloting,rec.aviation.student
Mxsmanic
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Posts: 9,169
Default Myth: 1 G barrel rolls are impossible.

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.
  #7  
Old June 11th 07, 08:54 PM posted to rec.aviation.piloting,rec.aviation.student
Mxsmanic
external usenet poster
 
Posts: 9,169
Default Myth: 1 G barrel rolls are impossible.

Jim Logajan writes:

Most everyone agrees that keeping the coffee in the cup is possible. What
some people don't seem to believe is possible is that the force felt by the
pilot (or tea/coffee) can be 1 gee during the entire roll. They believe it
has to vary during the roll. I'm hesitant to name names. ;-)


It has to vary during the roll, because the constant 1 G acceleration due to
gravity does not change. The net acceleration of the aircraft must always be
at least one G in consequence, and if the aircraft begins a climb or ends a
descent, it _must_ be greater than +1.0 G.
  #8  
Old June 11th 07, 10:00 PM posted to rec.aviation.piloting,rec.aviation.student
[email protected]
external usenet poster
 
Posts: 684
Default Myth: 1 G barrel rolls are impossible.

On Jun 11, 1:54 pm, Mxsmanic wrote:
Jim Logajan writes:
Most everyone agrees that keeping the coffee in the cup is possible. What
some people don't seem to believe is possible is that the force felt by the
pilot (or tea/coffee) can be 1 gee during the entire roll. They believe it
has to vary during the roll. I'm hesitant to name names. ;-)


It has to vary during the roll, because the constant 1 G acceleration due to
gravity does not change. The net acceleration of the aircraft must always be
at least one G in consequence, and if the aircraft begins a climb or ends a
descent, it _must_ be greater than +1.0 G.


Bertie! He's doing it again!!!!

  #9  
Old June 11th 07, 10:08 PM posted to rec.aviation.piloting,rec.aviation.student
george
external usenet poster
 
Posts: 803
Default Myth: 1 G barrel rolls are impossible.

On Jun 12, 9:00 am, wrote:
On Jun 11, 1:54 pm, Mxsmanic wrote:

Jim Logajan writes:
Most everyone agrees that keeping the coffee in the cup is possible. What
some people don't seem to believe is possible is that the force felt by the
pilot (or tea/coffee) can be 1 gee during the entire roll. They believe it
has to vary during the roll. I'm hesitant to name names. ;-)


It has to vary during the roll, because the constant 1 G acceleration due to
gravity does not change. The net acceleration of the aircraft must always be
at least one G in consequence, and if the aircraft begins a climb or ends a
descent, it _must_ be greater than +1.0 G.


Bertie! He's doing it again!!!!


Well you have to admit where he does his 'aerobatics' he is under 1g
constantly
ROTFL
Where we do aerobatics its somewhat different as we do them in
aeroplanes...

  #10  
Old June 11th 07, 10:11 PM posted to rec.aviation.piloting,rec.aviation.student
alexy
external usenet poster
 
Posts: 53
Default Myth: 1 G barrel rolls are impossible.

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.
 




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