Underside Attack
The Underside Attack provides an effect just opposite that illustrated in the overhead pass. Here, an attacker generates a radial G higher than total G upon his aircraft (you will recall that in the top half of the loop, radial G is greater than total G) and may be expressed by the following formula:
Gt = Gr - Cosθ
If we assume the same attack conditions as illustrated in the overhead pass – 30° angle-off, 4 total G – we get the following results:
Gr = 4 + 0.866 or
Gr = 4.866
In terms of G, this attack seems to provide an apparent advantage, however this does not always hold true. For example: If an attacker performed an underside attack in an F-100, he would experience a rapid speed decay, because of gravity as well as induced drag. As a result, since speed determines G available, the attacker would have much less total G. In addition, because of airspeed decay, the attacker would diminish the fighter-target ratio. As a consequence, the attacker’s max-G point would be forced farther out – in angle-off, and range – causing a further reduction in both total and radial G. As a result, the F-100 would not gain appreciably by this attack, since total G available is reduced sufficiently to cancel out the advantage of a higher radial G. However, if this same attack were executed in an aircraft with a very high power-to-weight ratio and a low drag profile – such as the F-104 – the attack could be invaluable, since high speed decay and G bleed-off would not occur.