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.

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

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.

Do you see the word "acceleration" anywhere in my "myth" statement? I have
no idea what it is you think you are trying to say, but it has nothing to
do with the myth I am attempting to debunk.

You appear to be confusing acceleration and force (you appear at times to
treat them as the same thing), among other faults in your thinking. If
taken literally, all your statements regarding the physics of the situation
are incorrect.

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.

With any luck your monitor will fall on you.

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.

Maybe it'll fall at 10 Gs and do me a favor.

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.

Sigh. Yes, the force that is felt is greater then one g-force at the
beginning and end of the maneuver. But that is not the case "during the
roll" itself. Again, as in the other post of yours I responded to, you
appear to be confusing force and acceleration.

"Mxsmanic" wrote in message
...
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.

God I love it when you so certainly prove your ignorance!!!!

You made my day!!!!

"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.

The few that I've done, and it is only a few, the g forces were noticeably
less at the top of the roll. I was still pressing into the seat, but not as
much. Just as in a loop, the g forces are lower at the top of the loop.

mike

"Jim Logajan" wrote in message
.. .
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.

Sigh. Yes, the force that is felt is greater then one g-force at the
beginning and end of the maneuver. But that is not the case "during the
roll" itself. Again, as in the other post of yours I responded to, you
appear to be confusing force and acceleration.

In which the pilot always experiences "positive" G forces, but not constant
1 g. That seems to be the argument here. It varies throughout the maneuver.

mike

"Robert M. Gary" wrote in message
ups.com...

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