Visual aid... take a model airplane, hold it between your
finger tips on the nose and tail. Rotate it so it turns on
the fuselage. That's a plain roll or aileron roll. When
you get inverted you use forward stick to keep the nose up,
you get negative Gs inverted.
Hold the model by the cabin area and rotate it to a nose up
attitude of 30 degrees and then rotate it so the plane
rotates about the tilted vertical axis... that's a snap roll
or horizontal spin.

Hold the model by the tail with your right hand and hold
your left arm straight out. move the model around your left
arm so it is wings level when you start with both arms
straight ahead, the airplane wings are knife-edge when above
your arm, inverted when your right hand is to the left of
the left arm, etc. That is a barrel roll.



--
James H. Macklin
ATP,CFI,A&P

"Dudley Henriques" wrote in message
nk.net...
|
| "Bob Moore" wrote in message
| . 121...
| Dudley Henriques wrote
| I seem to remember the Navy defining barrel rolls in
the J Stage of
| training in the F9F-8 Cougar as a shallow dive at about
95% to 350kts;
| level off and trim; then roll the airplane around a
point 45 degrees
| off the nose to either side; initial acelleration to
about 3g's; the
| nose should reach a point about 45 degrees above the
horizon at the 90
| degree point; the roll rate was adjusted to achieve a
90 degree
| heading change at the 180 degree point inverted; ; you
looked for
| about 180 to 200 kts at the top inverted where you were
looking at
| about 1+g if you did it right; as the nose came through
the back side,
| you adjusted the roll rate to nail level flight again
at your initial
| entry speed of 350kts. You would play the g from the
initial 3 during
| the entry down to the 1 at the top, then play back in
the 3 during the
| recovery back to level flight.
|
| And that seems to be the way that the IAC defines a
barrel roll at the
| posted reference. They and the Navy make no reference
for doing them
| any other way. Neither does William Kernsher who has an
oustanding
| reputation for instructing and writing books on
aerobatic instruction.
|
| But all this dosen't change the fact that a barrel roll
can be done
| much tighter than this and doing it that way dosen't
change the fact
| that you are doing a barrel roll :-))
|
| Just point me to the references that make this point.
:-)
|
| Bob Moore
|
| I see.
|
| Well, I have been using Bill Kershner myself for as many
years as he's been
| publishing and am in complete agreement with both his and
the service ways
| of defining barrel rolls. I think what you and I have
going here is a matter
| of definition within the definition so to speak, which
admittidedly can be a
| bit confusing. :-))
| All this means is that we're saying the same things only
defining it
| somewhat differently. I'm simply defining it a bit deeper
by shrinking the
| area in which the roll can be performed. Everything else
is the same.
| Let me put it this way. Both Kershner and the Navy have
chosen a specific
| set of parameters to define the execution of a barrel
roll. These parameters
| are fine, and are in use on a daily basis by most
competent instructors
| teaching aerobatics.
|
| What I'm saying is that the same identical 3 dimensional
roll described by
| both Kershner and the Navy can be performed to much
tighter parameters.
| The main point of defining a barrel roll isn't the size of
the roll, or the
| points chosen by any particular reference source to define
how the roll
| should be done, but the fact that the roll takes the
airplane through 3
| dimensional space using a 3 dimensional maneuver. This is
a unique maneuver
| that we define as a barrel roll. It's a barrel roll if
it's tight, and its a
| barrel roll if its flown to the specifications used by
either Kershner or
| the Navy.
| All Kershner and the Navy have done is to choose one
specific set of
| parameters that define a barrel roll for training
purposes. What they have
| done is choose parameters to produce a maximum training
result, and they are
| correct to have done it this way. As I have said, I also
have taught barrel
| rolls this way.
| I'm also saying however, that any roll flown through three
dimensional space
| using a three dimensional maneuver can be defined as a
barrel roll. In BFM
| and ACM, there are other terms used for these rolls. They
can be called
| "displacement or lag rolls" for example, where an attacker
will go out of
| plane and perform a 3 dimensional roll opposite the
defender's flight path
| to regain angle off and maintain nose to tail separation
to avoid an
| overshoot in the plane of the defender. The main point is
that if this roll
| goes through 3 dimensions, its a barrel roll.
| If you want a Navy source to confirm all this , simply
copy what I've said
| here and drop it in an email to either TPS (the test pilot
school at Pax),
| or out to Top Gun at Miramar. I believe they will verify
for you if need be.
| Dudley Henriques
|
|