With the development of supersonic aircraft, the X-plane era ushered in a new and challenging phase of flight. Researchers found that much of the knowledge accumulated from the previous, subsonic flight era did not apply to the emerging supersonic aircraft. These turbojet-powered planes also outpaced the usefulness of the wind tunnel, previously an indispensible tool of aeronautic research.This book explores the development of the X-series research aircraft, the planes that helped bridge the gap between subsonic flight and hypersonic flight.

The P-85 Goblin was the only airplane that ever flew which was designed from scratch to be operated entirely from another airplane. The development of the B-36 by the Consolidated Vultee Aircraft Corporation of Fort Worth, Texas resulted in a requirement for fighter protection for the bomber at distances from any friendly base that far exceeded the range of currently available escort fighter airplanes. Due to the inability of contemporary fighters to escort B-36 bombers all the way to their targets, the Army Air Corps initiated Project MX-472, Unconventional Fighter Design Studies, on December 3, 1942. The primary objective of the project was the development of a suitable method of protecting the B-36 on long-range bombing missions. The McDonnell Aircraft Corporation designed the P-85 Goblin to fit entirely within the confines of the bomb bay of the B-36. The little fighter was just fifteen feet long with a wing sapn of twenty-one feet.

An analysis is made of the effects of Mach number and dynamic pressure on the lift-curve slope of a large flexible swept-wing jet-propelled airplane by using flight measurements of normal acceleration and angle of attack with auxiliary instrumentation as needed. The methods and procedures used to correct the flight measurements (obtained in abrupt push-pull maneuvers) and to convert the flight test data to equivalent rigid conditions for comparison with rigid-model wind-tunnel tests are described in detail. The airplane angle of zero lift and the airplane-less-tail angle of zero lift for the Mach number range of the flight tests (0.42 to 0.81) are also presented. Excellent agreement was obtained in the comparison between flight and wind-tunnel rigid lift-curve slopes and angles of zero lift.