On 2007-06-11 21:42:18 -0400, Bertie the Bunyip said:

"Robert M. Gary" wrote in
oups.com:

On Jun 11, 12:51 pm, 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.

A barrel roll is not about the longitudinal axis of the plane, that is
an aileron roll.


Nope, a roll about the longitudinal axis of the airplane is a slow roll.
actaully that's not entirely correct either since a perfect slow roll
follows a perfectly staight line, which means the axis of the aircraft
must change in realation to the line of flight throughout.
A slow roll is, hower, a one G roll. The 1 G should always point
earthward, though.


An aileron roll is actualy not dissimilar to a Barrel roll in flight
path.


Bertie

Actually Bertie, think about it for just a moment. In a slow roll, you
do indeed roll the airplane on it's longitudinal axis but the roll line
isn't exactly straight.
The reason for this is that you have to pull the nose up to it's
inverted level flight attitude before commencing the roll. If you're
flying something fast like a T38 for example or with a symmetrical wing
like a round wing Pitts it isn't as pronounced as slow rolling
something with a cambered wing but it's there just the same.
The actual shape of a slow roll done correctly will look like a capital
letter D or a reverse capital letter D depending on the roll direction,
but take a slow roll to the right and it's easy to see. The bottom of
the vertical line on the left side of the D represents your initial
nose position beginning the roll. You have to fly up the line to the
top of the D which represents the inverted level flight nose attitude
of the aircraft. The roll initiates there and looks from the ground as
a straight line on the longitudinal axis. You roll the aircraft and
hold it while rolling it through the first knife edge and inverted at
the top of the vertical line on the D. This puts the airplane through
inverted exactly at it's inverted level flight nose attitude. Then, as
you pass through inverted and begin the back side of the roll, you have
to fly the airplane down the right side arc of the D to put the nose
back at it's erect level flight attitude again completing the roll.
The effect as seen from the ground is indeed a roll done in a straight
line, but for the pilot doing the roll, there is that slight vertical
pitch input to the roll set position and the easing off back down that
vertical line through the second knife edge back to level flight.
I should add that the higher the performance of the rolling aircraft,
the shorter that vertical line on the D will be.
For example, that line is much more pronounced in something like a
Citabria than it is in the Decathlon, but there is a pull to the roll
set even in the T38 if you want it to look good from the ground.
When I flew an aerobatic eval flight with the Snowbirds Tutor in 71,
one of the first things I noticed about the jet was the need to get the
nose a lot higher in the roll set for a slow roll than in the Talon.
You don't even want to know how high you have to get the nose to get a
slow roll out of a Cessna Aerobat :-))))

Dudley Henriques