On 2007-06-11 18:41:50 -0400, "mike regish" said:

The few that I've done, and it is only a few, the g forces were noticeably
less at the top of the roll. I was still pressing into the seat, but not as
much. Just as in a loop, the g forces are lower at the top of the loop.

mike

"Jim Logajan" wrote in message
.. .
Mxsmanic wrote:
Jim Logajan writes:

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. ;-)

It has to vary during the roll, because the constant 1 G acceleration
due to gravity does not change. The net acceleration of the aircraft
must always be at least one G in consequence, and if the aircraft
begins a climb or ends a descent, it _must_ be greater than +1.0 G.

Sigh. Yes, the force that is felt is greater then one g-force at the
beginning and end of the maneuver. But that is not the case "during the
roll" itself. Again, as in the other post of yours I responded to, you
appear to be confusing force and acceleration.

Easing off the g through the apex is called "the float". You do this
because as soon as the lift vector goes below the horizon you pick up 1
extra +g available. In other words, you can easily tighten up the
maneuver losing the constant arc of the roll if you don't ease off the
g. Same for going over the top in a loop or any maneuver where a
constant arc is desired over the top.
Since the theoretical objective anyway :-) is to keep the roll arc
constant in a barrel roll, you ease off the g through the apex to avoid
picking up that extra 1 positive g available and by doing so tightening
up the roll arc.
So the bottom line is that the positive g does indeed vary through a
barrel roll and it is always at some positive g value with the 1
exception being flying through the float with the wings unloaded. I
should note that in the true sense of explaining a barrel roll, going
to 0 g through the float would be out of the context of a true classic
barrel roll which must remain constant throughout the roll.
Dudley Henriques