Douglas D-558-1 Skystreak

The D-558-I "Skystreaks" were among the early transonic research airplanes like the X-1, X-4, X-5, and XF-92A. Three of the single-seat, straight-wing aircraft flew in a joint program involving the National Advisory Committee for Aeronautics (NACA), the Navy-Marine Corps, and the Douglas Aircraft Co. from 1947 to 1953. In the process, the Skystreaks set two world speed records.

The (Roman numeral) I in the aircraft's designation referred to the fact that the Skystreak was the phase-one version of what had originally been conceived as a three-phase program, with the phase-two aircraft having swept wings. The third phase, which never came to fruition, would have involved constructing a mock-up of a combat-type aircraft embodying the results from the testing of the phase one and two aircraft.

The three aircraft, equipped with Allison J-35-A-11 turbojet engines, gathered a great deal of data on handling qualities, tail loads, buffeting, pressure distribution, plus static and dynamic longitudinal as well as lateral stability and control and the effects of vortex generators on undesirable handling characteristics. Together with other transonic research airplanes, the D-558-I research results validated the data from wind tunnels then being developed by the NACA, which required basic data for comparison to ensure there were no unforeseen errors in their development.

The three Skystreaks flew a total of 229 times from 1947 to 1953, including 101 contract flights in the number one aircraft (Bureau No. 37970-NACA 140), 46 by the Skystreak number two (Bureau Number 37971-NACA 141), and 82 by the number three aircraft (Bureau Number 37972-NACA 142). NACA 140's flights were all completed as part of the contractor program, although Caldwell flew it on four passes on August 20, 1947, averaging 640.663 miles per hour over a measured course, setting a new world airspeed record. Five days later, however, Marine Major Marion Carl surpassed the record, flying NACA 141 an average 650.796 miles per hour in four passes over the course. The NACA never flew the number one airplane, using it instead for spares support of the number three aircraft.

NACA 141 made 27 flights by Douglas, Navy, and Marine pilots before being instrumented for NACA flights, all flown by Howard C. Lilly. Although both NACA 140 and 141 had been painted scarlet for improved visibility, in flying the aircraft both Douglas and NACA personnel discovered that the scarlet color was difficult to discern against the dark blue desert sky. During the winter of 1947-1948, NACA repainted NACA 141 with a white color.

In the spring of 1948, Lilly flew five research flights gathering data on directional stability. On April 29, he reached a speed of Mach 0.88 at 36,000 feet (roughly 580 miles per hour). Unfortunately, on his next flight, the compressor section of his J-35 engine disintegrated, severing the elevator and rudder cables and resulting in his loss of control over the airplane at a comparatively low speed and altitude. He died in the subsequent crash. Following the recommendations of the accident board, Douglas technicians added duplicate control cables, armor plating around the emergency fuel pump and fuel lines, and wire-wound fuel hoses to NACA 142, repainting it white in the process.

In 1949, NACA pilots Robert A. Champine and John H. Griffith began flying NACA 142, gathering data about handling qualities, aileron effectiveness and pressure distribution. On November 29, 1950, following the conclusion in June of the extended pressure-distribution studies, NACA pilot A. Scott Crossfield began a series of buffeting, tail loads, and longitudinal stability investigations that lasted until October 1951. NACA pilots Walter P. Jones and Joseph A. Walker also participated in this series of flights.

The data that resulted enabled the armed services and industry to advance the state of the art in the century series of fighters and other aircraft built in the 1950s, using data from the research airplanes in the areas of controllability, stability, changes in stability and in tailplane orientation. Like the X-1, D-558-I, and D-558-II, all the century series fighters employed movable horizontal stabilizers because the research airplanes had shown that they provided excellent controllability near the speed of sound, whereas the elevator was ineffective in providing pitch control in that speed range.

NACA 140 is located at the Naval Aviation Museum in Pensacola, Fla. NACA 142 is at the Marine Corps Air Ground Museum, Quantico, VA.