Myth: 1 G barrel rolls are impossible.

Poor misunderestanding boy. Consider the cirumstance when the moon's
shadow is cast on the earth. Every movement then, until it's 90
degrees displaced, has an acceleration component away from the sun.
For that matter, 180 degrees later, when it lies along the earth path,
moving toward the moon, it has an acceleration vector with a component
away from the sun.

Basic mechanics.

Heavens, I teach psych, and know this stuff.

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.

Mxsmanic wrote in
:

El Maximo writes:

Where is that defined?

What type of standard orbit would pass through a planet's surface?


One you would fly.



Bertie

writes:

Poor misunderestanding boy. Consider the cirumstance when the moon's
shadow is cast on the earth. Every movement then, until it's 90
degrees displaced, has an acceleration component away from the sun.
For that matter, 180 degrees later, when it lies along the earth path,
moving toward the moon, it has an acceleration vector with a component
away from the sun.

As I've said, plot the actual paths around the Sun. You'll see that the
moon's path is always concave to the Sun, that is, it is never accelerating
away from the star.

Heavens, I teach psych, and know this stuff.

I didn't think that celestial mechanics was part of the psychology curriculum.

Mxsmanic wrote in
news
writes:

Poor misunderestanding boy. Consider the cirumstance when the moon's
shadow is cast on the earth. Every movement then, until it's 90
degrees displaced, has an acceleration component away from the sun.
For that matter, 180 degrees later, when it lies along the earth
path, moving toward the moon, it has an acceleration vector with a
component away from the sun.

As I've said, plot the actual paths around the Sun. You'll see that
the moon's path is always concave to the Sun, that is, it is never
accelerating away from the star.

Heavens, I teach psych, and know this stuff.

I didn't think that celestial mechanics was part of the psychology
curriculum.


Fjukktard



Bertie

Acceleration is defined as the rate of change of velocity. These
quantities are called vectors, not scalers, because there's a
direction associated with them, but we don't need to worry about that
right now.

There are times when the moon is accelerating away from the sun. That
does not mean its velocity is away from the sun, only that it is
decreasing. If it is decreasing then it is accelerating in the other
direction.

Mechanics are not part of the psych courses, you're quite right about
that. Never the less, the statement I made above is correct.

Also, for what it's worth, I'm not a pilot, at least not in the
certified sense. I probably get 50 hours of dual in a complex single a
year though, flying with my husband, and yes I know how to, in a real
airplane, fly a ILS approach under the hood to minimums and land.




On Jun 18, 2:49 am, Mxsmanic wrote:
writes:
Poor misunderestanding boy. Consider the cirumstance when the moon's
shadow is cast on the earth. Every movement then, until it's 90
degrees displaced, has an acceleration component away from the sun.
For that matter, 180 degrees later, when it lies along the earth path,
moving toward the moon, it has an acceleration vector with a component
away from the sun.

As I've said, plot the actual paths around the Sun. You'll see that the
moon's path is always concave to the Sun, that is, it is never accelerating
away from the star.

Heavens, I teach psych, and know this stuff.

I didn't think that celestial mechanics was part of the psychology curriculum.

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

In article ,
says...
Dave Doe wrote:

To put it another way, if you closed your eyes, you wouldn't know you've
done a roll (given you go for the 'non-standard' 1G roll), other than
the initial sensation of beginning the turn, and then the sensation of
the turn stopping.


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.

I agree with your standard barrel roll exactly - but make the point:
* if you don't do it standard...
* ie don't pitch up
* don't pitch to recover level
* etc

ie do *not* do the standard barrel roll - and do not adjust pitch, other
than to counter any G (+ or -) that will occur in such a roll due to
airspeed changing, ie maintain 1G throughout the roll.

--
Duncan

On 2007-06-18 07:01:05 -0400, Bob Moore said:

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

This is exactly what is causing all the "confusion" on this thread
concerning barrel rolls.
Many manuals (yes, including the Navy) teach ballel rolls as a
precision maneuver beginning from a specified entry and proceeding with
exact heading changes desired at exact points in the roll. The 90
degree heading change at inverted is usually found in this "classic"
description for the execution of a barrel roll.
This is fine if learning to do a barrel roll in this manner is your
goal, but no one in this thread should be misled into thinking that
acheiving these heading changes is REQUIRED to execute a barrel roll.
You can execute a barrel roll as tightly or as loosely as the
airplane's flight envelope will allow.
Putting out here that a 90 degree heading change, or ANY specific
heading change at ANY point in the roll is a requirement for executing
a barrel roll in an airplane is misleading and totally incorrect.
Dudley Henriques

On 2007-06-18 08:52:34 -0400, Dave Doe said:

In article ,
says...
Dave Doe wrote:

To put it another way, if you closed your eyes, you wouldn't know you've
done a roll (given you go for the 'non-standard' 1G roll), other than
the initial sensation of beginning the turn, and then the sensation of
the turn stopping.


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.

I agree with your standard barrel roll exactly - but make the point:
* if you don't do it standard...
* ie don't pitch up
* don't pitch to recover level
* etc

ie do *not* do the standard barrel roll - and do not adjust pitch, other
than to counter any G (+ or -) that will occur in such a roll due to
airspeed changing, ie maintain 1G throughout the roll.

Again I'm totally lost as to what you are trying to say with this, but
in the interest of clarification, it's the pitch input that is creating
the helical arc for a barrel roll. No positive pitch; no helical arc.
No helical arc, no barrel roll.

The heading change realized at any point in the roll by this helical
arc will be a direct result of the combination of pitch input and the
roll rate applied.
You can perform a barrel roll at any time and at any beginning nose
attitude by rolling the aircraft and applying a diagonal pitch input at
the same time. The one common denominator in all this is thatany barrel
roll requires offset positive pitch input.
In military training, you initially learn barrel rolls as a precision
maneuver requiring specific heading changes at various points in the
roll. If you go into fighter lead in training, you re-address the
barrel roll scenario once more in the BFM/ACM stage of your training as
a maneuver classified as ANY roll performed in 3 dimensions through 3
dimensional space.
This completely opens the Pandora's box on the issue of barrel roll,
which is then dealt with as moving the aircraft through all 3
dimensions as tightly or as loosely as the envelope will allow.
Dudley Henriques