Bob Moore wrote:
Jim Logajan wrote
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. ;-)

My name is Bob Moore :-)

Hi Bob. Glad you could make it to B.R.A. (Barrel Rollers Anonymous.) :-)

Just what is a barrel roll has been debated between "Big John",
Dudley, and myself at least twice in the past. It IS difficult to
describe without having a model airplane in one's hand and flying it
through the maneuver.

How come you don't seem to belive the following from Wikipedia?

You know what is odd? The flight path of the maneuver I wrote about
appears to violate the Harvard definition you quote (it can't be done in
a straight horizontal path - my corkscrew/helical path must follow a
parabolic arc) but oddly the Wikipedia definition leaves me a big "out."
Straight down. ;-)

Drop the nose straight down so as to make the plane & pilot weightless.
Then start doing horizontal loops so the centrifugal force yields the
equivalent of one gravity of weight. At least the longitudinal axis of
the helical path will maintain a constant direction - but the pilot will
quickly be screwed. :-)

Barrel roll
From Wikipedia, the free encyclopedia

This article is about the aerial sport. For the military operation,
see Operation Barrel Roll.
A barrel roll occurs when an object (usually an airplane or roller
coaster) makes a complete rotation on its longitudinal axis while
following a helical path, approximately maintaining its original
direction. The G load is kept positive (but not constant) on the
aircraft throughout the maneuver, commonly not more than 2-3 G.

In aviation, the maneuver includes a constant variation of attitude in
all three axes, and at the midpoint (top) of the roll, the aircraft is
flying inverted, with the nose pointing at a 90-degree angle
("sideways") to the general path of flight. The term "barrel roll" is
frequently used, incorrectly, to refer to any roll by an airplane (see
aileron roll), or to a helical roll in which the nose remains pointed
generally along the flight path. In fact, the barrel roll is a
specific and difficult maneuver; a combination of a roll and a loop.
It is not used in aerobatic competition.

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.