Sorry I'm late on getting in on this.
Let's talk about overshoots for a second.
There are two kinds...a 3/9 overshoot and a flight path overshoot.
A 3/9 (wingline) overshoot is caused by excessive closure. The attacker is simply going too fast and flys past the defender's 3/9 line.
The flight path overshoot is a turn radius issue. The attacker cannot match the defender's turn radius and consequently flys through it.
The defender can force a 3/9 overshoot by slowing down. He can do this one of two ways...one, simply chopping power and putting out drag...or, two, he can lose the speed by maneuvering hard to deplete his energy regardless of his power setting.
In the case of the latter (the maneuver technique), this type of maneuver is generally known as a "last ditch defense", usually against a gun attack. It's a last ditch attempt because the end result is that you are out of energy...the defense better have worked, because otherwise, you're in deep kimshi!
This maneuver comes in two types...the High G Roll Over The Top and the High G Roll Underneath. The two differ only in the direction of roll. The "top" maneuver is flown by rolling opposite the direction of turn (right turn, left roll)...and the "underneath" type is flown by rolling in the direction of turn.
Strictly speaking, these are NOT barrel rolls! They are a way of putting the brakes on aerodynamically.
In the example in question, it is debatable whether the Barrel Roll will provide the deceleration needed to force the 3/9 overshoot. In a defensive context, the Barrel Roll is intended to defeat a gun attack by making it difficult for the attacker to track the defender. The maneuver is an attempt to create an aiming problem, not a closure or flight path problem.
In any case, remember that the assumption is that the defender is pulling max G in the defensive turn prior to the initiation of the roll. He has no more G to provide an increase in turn performance...all he can do is rotate his lift vector (which is what the two last ditch maneuvers do). Any rolling maneuver such as a Barrel Roll in this situation will increase the defender's turn radius. The extent to which the roll depletes energy will be a function of the intensity of the roll...more G, more airspeed loss. At some point (as G is increased), this roll becomes the last ditch technique.
One point to consider in AH. This maneuver can be very disorienting for pilots that use snap views. If flown properly, the maneuver is not lazy. It is an aggressive, high G roll...this leads to problems with keeping the bandit in sight. In RL, when we used this maneuver, we gave up the tally momentarily to put max attention on the maneuver. Once the roll was complete, we then looked to where we thought the bandit would be. If we were successful, the bandit would be high, forward of our 3/9 line, and to the outside of the turn.
If not successful, all we had to do was check six!!
To sum it up...do not use this maneuver to force a turn radius (flight path) overshoot...it probably won't accomplish this. Use this technique to force a 3/9 line overshoot. If this is your goal, then don't popsiclefoot the maneuver. Regardless of which way you roll, keep the G at max as you roll. Your rate of roll will determine how much energy you lose...roll slower to lose more speed.
