Fighter Combat - Tactics and Maneuvering

APPENDIX 407
aircraft surfaces. In the high-subsonic speed range, critical Mach number is
usually increased substantially by unloading, which delays the sharp rise
in wave drag until the fighter reaches higher speeds. Unloading also tends
to reduce the severity of this wave drag once the aircraft accelerates past
MCR. These high-speed effects are quite evident in the example of Figure
A-16. The impact of unloading on the acceleration performance of a fighter
is, however, highly dependent on the fighter's aerodynamic design.
One further method of increasing fighter acceleration is by the use of
gravity; a steep dive will often multiply acceleration many times. Such a
dive may follow unloading, which causes the aircraft to fly a ballistic
trajectory resulting in gradually steepening dive angles. If altitude is available,
however, a sharp pull-down to a steep dive attitude, followed by
unloading, produces the most rapid long-term acceleration. Discounting
the effects of thrust, the acceleration of an aircraft in a dive is a function of
its "density/' that is, its ratio of weight (actually its mass) to drag. When
two fighters are similar in all respects except that one is heavier, the
heavier aircraft will accelerate faster in a dive and, assuming structural
considerations allow, will have a faster terminal velocity. Likewise, with
two fighters of the same weight, the cleaner one (i.e., the one with less
drag) will dive better. (This is why a brick falls faster than a feather in air.)
Sustained Turn Performance
In order for a fighter to make a level (constant-altitude) turn, load factor
must be increased above 1 G. As load factor is increased at a given airspeed,
Figure A-16. Effects of Unloading on Acceleration