Myth: 1 G barrel rolls are impossible.

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.)