Douglas X-3 Stiletto
A jet research aircraft built by Douglas Aircraft Company to explore sustained Mach 2 flight, low-aspect-ratio wings and the large-scale use of titanium. Two were approved but only one was completed: substitute Westinghouse J34 engines left it severely underpowered, and it passed Mach 1 only in dives, reaching Mach 1.208. Its lasting contribution was an inadvertent 1954 demonstration of roll coupling that fed a NACA research programme, and a wing form later used in the F-104. The aircraft survives at the National Museum of the United States Air Force.
Why It Mattered
The X-3 was designed to do something no research aircraft had yet done: take off from the ground under its own power, settle into a sustained cruise at Mach 2, and land under its own power at the end of the flight. Along the way it was to settle whether very short, low-aspect-ratio wings were practical, and whether titanium could be used on a large scale in an aircraft structure. It never came close to the speed it was designed for, because its intended engines failed to meet their requirements and far weaker Westinghouse J34s took their place. Its lasting value came instead from its shape: with engines, fuel and structure concentrated in a long, narrow fuselage, it mirrored the fighters then being developed, and in 1954 it gave researchers a dramatic demonstration of roll coupling.
Design Notes
The airframe was a needle: a long, slender fuselage with a tapered nose, carrying small wings that NASA describes as short and stubby, of very low aspect ratio. Titanium was used on a large scale in the structure, and NASA counts the type among the first aircraft to use the metal. Two Westinghouse J34 turbojets sat buried in the fuselage, substituted when the planned engines failed on thrust, size and weight; NASA's assessment is that they left the aircraft severely underpowered and difficult to control. It took off from the ground under its own power, as designed, but needed a speed of 260 knots to do it.
Operational History
Construction of a pair of X-3s was approved on 30 June 1949. The second aircraft was never finished: partially completed, it was canceled amid engine and airframe problems, its components used for spare parts. The one completed aircraft was delivered to Edwards Air Force Base on 11 September 1952. On 15 October, during a high-speed taxi test, test pilot Bill Bridgeman lifted it off the ground and flew about a mile before settling back onto the lakebed. The official first flight came on 20 October and lasted about 20 minutes. Bridgeman made 26 flights in all, counting the hop, by December 1953. Even in dives it barely went supersonic: its first supersonic flight needed a 15-degree dive for Mach 1.1, and its fastest, on 28 July 1953, reached Mach 1.208 in a 30-degree dive. The aircraft then passed to the U.S. Air Force for an abbreviated programme on low-aspect-ratio wings; Lt. Col. Frank Everest and Maj. Chuck Yeager each made three flights, counted as NACA flights. Walker's checkout flight on 23 August 1954 opened the NACA series: eight research flights that September and October covered longitudinal stability, structural loads and pressure distribution, then lateral and directional stability. On 27 October 1954 Walker rolled it abruptly at Mach 0.92; it pitched up 20 degrees, yawed 16 degrees and gyrated five seconds before he regained control. On the next test point he dived to Mach 1.154 at 32,356 feet and rolled again; loads ran from −6.7 to +7 G, leaving the fuselage at its limit, close to breaking up. The NACA opened a research programme into it — several F-100s had suffered similar incidents — and the X-3 stayed grounded for nearly a year. Walker made ten more flights between 20 September 1955 and the last, on 23 May 1956.
Afterlife
After the final flight the aircraft was retired to the Air Force Museum; Wikipedia dates its transfer to the National Museum of the United States Air Force at Wright-Patterson Air Force Base, Ohio, to 1956. There it is displayed in the museum's Research & Development Gallery. NASA's assessment is that the type never delivered the Mach 2 cruise data it was built to gather, but that its short service was of value. Its wing form was taken up in the F-104, it was one of the first aircraft to use titanium, and its very high takeoff and landing speeds forced improvements in tire technology.