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#11
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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 |
#12
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Myth: 1 G barrel rolls are impossible.
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. |
#13
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Myth: 1 G barrel rolls are impossible.
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. |
#14
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Myth: 1 G barrel rolls are impossible.
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. |
#15
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Myth: 1 G barrel rolls are impossible.
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. |
#16
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Myth: 1 G barrel rolls are impossible.
"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!!!! |
#17
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Myth: 1 G barrel rolls are impossible.
"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. |
#18
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1 G barrel rolls are impossible.
"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. |
#19
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Myth: 1 G barrel rolls are impossible.
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. |
#20
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Myth: 1 G barrel rolls are impossible.
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 |
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