Stability and Control Issues with Variable Sweep
Variable wing sweepback is an attempt to combine the best performance, stability, and control characteristics of straight and swept wings. Straight wings have benign low – speed stability and control characteristics, good low-speed maximum lift, and low cruise drag, while sweptback wings have low transonic and supersonic drag and good high-Mach – number stability and control. In a variable-sweep airplane, wings are spread fully, orunswept, at low speeds and are swept back at high Mach numbers.
16.1 The First Variable-Sweep Wings – Rotation and Translation
The designers of the first variable-sweep airplanes, the Messerschmitt P1101, the Bell X-5, and the Grumman XF10F-1, found it necessary to move the wing inboard ends forward on the fuselage as the wing tips were moved aft. This was to keep the wing’s mean chord in about the same fore-and-aft position along the fuselage. This kept the distance from the airplane’s cg to the wing aerodynamic center about the same as the wing was swept back.
It can be imagined that the complication of a wing-fuselage attachment that translated as well as rotated was a powerful deterrent to aircraft designers. In fact, while this was the only available variable-sweep method, the concept turned up only in research aircraft.