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Barrel Roll And g's Quest.



 
 
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  #1  
Old July 9th 03, 06:39 PM
Robert11
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Default Barrel Roll And g's Quest.

Hello:

I'm not a pilot.

Saw a show on the first 707 on the WINGS TV channel regarding the barrel
roll
the test pilot did (unexpectedly) on the first test flight of the dash-

They said that he was able to maintain a constant 1g during the maneuver.

Here's where i'ma bit confused.

Seems to me that at the top of the roll, he would have had to be rolling at
a rate
sufficient to have centripital force equal to 2 g; such that when you
subtract the normal downward
1 g, there's a resultant 1 g left acting in the conventional direction
(tending to pull the engines away from the wings-the same
as if in a normal level flight)

If so. what happens to the 2g when the plane is at the 3 and 9 o'clock
positions?
The resultant there would be over 1g, wouldn't it ?

What am I misssing, or mis-interpreting ?

If someone could walk me thru the maneuver, and the resultant g's at the
various
positions, would be most appreciative.

Also, could exactly the same result(s) be obtained via an aileron roll ?

Thanks,
Bob


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  #2  
Old July 9th 03, 10:55 PM
Kyle Boatright
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Default


"Robert11" wrote in message
...
Hello:

I'm not a pilot.

Saw a show on the first 707 on the WINGS TV channel regarding the barrel
roll
the test pilot did (unexpectedly) on the first test flight of the dash-

They said that he was able to maintain a constant 1g during the maneuver.

Here's where i'ma bit confused.

Seems to me that at the top of the roll, he would have had to be rolling

at
a rate
sufficient to have centripital force equal to 2 g; such that when you
subtract the normal downward
1 g, there's a resultant 1 g left acting in the conventional direction
(tending to pull the engines away from the wings-the same
as if in a normal level flight)

If so. what happens to the 2g when the plane is at the 3 and 9 o'clock
positions?
The resultant there would be over 1g, wouldn't it ?

What am I misssing, or mis-interpreting ?

If someone could walk me thru the maneuver, and the resultant g's at the
various
positions, would be most appreciative.

Also, could exactly the same result(s) be obtained via an aileron roll ?

Thanks,
Bob



Several answers and a correction...

The roll wasn't on the first test flight. It occurred sometime later in the
program.

If you listen to acro folks, what the -80 did wasn't a barrel roll. A
barrel roll is more or less a skewed loop. The -80 did a modified aileron
roll, which began with the aircraft in a climb, so the nose didn't drop too
far by the time the roll was complete. The pilot simply pitched up, held
the elevator in it's normal (cruise) position, and held the yoke over to
command a roll.

The airplane flew at 1 g or so except for the pitch up and the (probable)
pull-out at the end of the roll when the nose was probably slightly below
the horizon.

As to your 1 G vs 2 G at the top of the roll question, aerodynamically, the
airplane was at more or less 1 g the whole time. However, coming over the
top, it accelerated downwards at roughly 2 g's - one from gravitational
forces and one from aerodynamic forces.

Hope this makes things clear...


KB


  #3  
Old July 9th 03, 11:58 PM
Simon
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Thare are four differing rolls, aerodynamically.

The aileron roll is primarily around the longitudinal access, there being a
little pitch before the roll.
The barrell roll is a blend of pitch and poll, in other words using two
axes.
The slow roll is a roll whereby the lift vector is moves from the wings to
the fuselage to the wings.
The above three are all flying, and not stalled.
The snap roll is a a spin from an accelerated stall.

There are not four points to consider in a barrel or aileron roll, there are
an infinite number of points. Since pitch is involved there will be some G
forces above 1 on the entry and rollout, however small that difference from
1g may be. With sufficient power and slowness of roll, it is possible to
approach 1G throughout the entire meneuver.

Hope that helps.

Simon
  #4  
Old July 10th 03, 01:24 AM
Robert Moore
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"Robert11" wrote
Saw a show on the first 707 on the WINGS TV channel regarding
the barrel roll the test pilot did (unexpectedly) on the first
test flight of the dash-


Boeing 367-80, prototype for the KC-135 and B-707. No, it wasn't
a barrell roll despite what the test pilot, Tex Johnston said in
the interview. The following is quoted from an aerobatic web site.

From: http://acro.harvard.edu

The Barrel Roll is a not competition maneuver. The barrel roll
is a combination between a loop and a roll. You complete one loop
while completing one roll at the same time.
The flight path during a barrel roll has the shape of a horizontal
cork screw. Imagine a big barrel, with the airplanes wheels rolling
along the inside of the barrel in a cork screw path.
During a barrel roll, the pilot experiences always positive G's. The
maximum is about 2.5 to 3 G, the minimum about 0.5 G.

Bob Moore
ATP B-707, B-727
CFI ASE-IA
PanAm (retired)
US Naval Aviator 1958-1967
  #5  
Old July 10th 03, 02:32 AM
vincent p. norris
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Kyle Boatright and Bob Moore are correct, and it shouldn't be
necessary for anyone else to support their responses, but there seems
to be so much confusion about this topic that I add my voice to
theirs.

vince norris


  #6  
Old July 12th 03, 01:39 AM
vincent p. norris
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Two days ago, I thought I posted a response but it hasn't shown up, so
here goes again:

I just want to add my support, for what it's worth, to Kyle
Boatwright and Bob Moore, who are quite right about the barrel roll.
For some reason beyond my ken, misunderstanding about the barrel roll
seems to have nine times nine lives. Or perhaps nine to the ninth
power lives.

As I said a couple of years ago in a discussion similar to this one, I
suspect the root of the problem is that "barrel-roll" has become one
word, like "nose-dive" so that the general public believes that there
is no other kind of roll.

vince norris
  #7  
Old July 12th 03, 01:47 AM
Larry Fransson
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In article ,
vincent p. norris wrote:

As I said a couple of years ago in a discussion similar to this one, I
suspect the root of the problem is that "barrel-roll" has become one
word, like "nose-dive" so that the general public believes that there
is no other kind of roll.


Barrel roll, nose dive, tailspin, Learjet (or Leer Jet, as I've seen it
on a local news program), and Piper Cub.

--
Larry Fransson
Aviation software for Mac OS X!
http://www.subcritical.com
 




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