Douglas D-558-I Skystreak by Special Hobby

1/72 scale
Kit No. 72159
Cost: $26.00
Decals: One version
Comments: Short run kit; injection molded plastic with engraved panel lines; photo etch details for cockpit (instrument panel with accompanying film insert, seat straps), wheel wells and landing gear; choice of bubble top or knife-edge canopies; resin wheels and cockpit tub

History

The D-558-I “Skystreak” was among the early transonic research aircraft, including the Bell X-1, Northrop X-4, Bell X-5, and Convair XF-92A. Three of these single-seat, straight-wing aircraft flew in a joint program involving the National Advisory Committee for Aeronautics (NACA), the U.S. Navy and Marine Corps, and the Douglas Aircraft Company from 1947 to 1953. In the process, the Skystreaks set two world speed records.

The division of responsibility among the partners was that Douglas flew the first Skystreak to investigate its performance, handled major maintenance and performed any modifications. The NACA’s Muroc Flight Test Unit, redesignated the High-Speed Flight Research Station in 1949 and today named the NASA Dryden Flight Research Center, purchased fuel and oil from the U.S. Army Air Forces (U.S. Air Force after September 1947), provided and installed instrumentation, performed the flight research on the number two and three aircraft, and took care of routine flight maintenance and inspections. The Navy paid the expenses of Douglas Aircraft, including engine overhaul and replacement, and its pilots did some of the flying.

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.

Douglas pilot Eugene F. May flew the number one Skystreak for the first time on April 14, 1947, at Muroc Army Airfield (later renamed Edwards Air Force Base) in California. The goals of the program were to investigate the operation of a straight-wing configuration in the lower third of the transonic speed range (which extended from roughly 0.7 to 1.3 times the speed of sound) and to obtain data about flight in that speed range that were not available from existing wind tunnels.

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. Both kinds of data were then available for use by designers of new military aircraft, such as those in the century series of fighters (F-100, F-102, and so forth).

Design
The need for transonic research airplanes grew out of two conditions that existed in the early 1940s. One was the absence of accurate wind tunnel data for the speed range from roughly Mach 0.8 to 1.2. The other was the fact that fighter aircraft like the P-38 “Lightning” were approaching these speeds in dives and breaking apart from the effects of compressibility-increased density and disturbed airflow as the speed approached that of sound, creating shock waves. People in the aeronautics community-especially the NACA, the Army Air Forces (AAF), and the Navy-agreed on the need for a research airplane with enough structural strength to withstand compressibility effects in the transonic region. The AAF preferred a rocket-powered aircraft and funded the X-1, while the NACA and Navy preferred a more conservative design and pursued the D-558, with the NACA also supporting the X-1 research.

The Navy contracted with Douglas to design the airplane, and in the course of the design process, the D-558 came to be divided into two separate phases, with phase one being a straight-wing turbojet aircraft and phase two consisting of a swept-wing design with turbojet and rocket propulsion. The Douglas design team, headed by Edward H. Heinemann, used NACA information and airfoil shapes. It tested its models in NACA and California Institute of Technology wind tunnels. And it relied on NACA recommendations, such as putting the horizontal stabilizer of the D-558-I high on the vertical tail to avoid the wake from the wing.

As with the X-1, the D-558-I also featured, at NACA suggestion, a horizontal stabilizer that was thinner than the wing so as to avoid simultaneous shock wave effects for the wing and horizontal tail. Also at NACA suggestion and like the X-1, the stabilizer was movable in flight to provide pitch (nose up or down) control when shock waves made the elevators ineffective. At the time, this “flying tail” design was also being incorporated into such aircraft as the North American F-86 Sabre, and significantly improved handling at the transonic speeds at which maintaining control of aircraft became difficult.

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.

Although it was slower and more conventional than the rocket-powered X-1 and D-558-II, the Skystreak performed valuable services as a first-generation transonic research airplane. Even the loss of NACA 141 and Howard Lilly served a purpose because it resulted in a greater appreciation for the dangers of research flying. As a result, the safety modifications to the Skystreak were also made to other research airplanes, especially the Northrop X-4 and the Bell X-5.

Together with the X-1 and the D-558-II, the Skystreak was one of the few sources of data on transonic flight conditions in the period 1947 to 1950 until the NACA developed better wind tunnels. These aircraft then contributed data to validate that derived from the tunnels by providing a reality check in the form of corresponding information from a real flight environment. Embodying the state of the art in aeronautics when built, these aircraft also tested whether the various components in their design operated together when flown.

Specifications

Length: 35 feet
Height: 12 feet
Wingspan: 25 feet
Powerplant: One Allison J-35-A-11 engine (developed by General Electric as the TG-180), rated at 5,000 lb of static thrust. Fuel capacity: 230 gallons aviation fuel (kerosene)

The Kit

Special Hobby’s D-558-1 Skystreak is injection molded in grey and comes in their trademark side-opening black box. It consists of 34 plastic parts (two of them clear canopies). The kit’s grey parts come on a single sprue. There are an additional 13 resin parts including wheels, a cockpit tub featuring raised details on both sidewalls, a photo-etch fret, and a film insert for the main instrument panel. The decals are by Aviprint and appear to be of excellent quality, with a semi-gloss sheen to them.

The kit has some refined touches that will serve to dress up a rather visually unremarkable airframe, including a choice of the original bubble top canopy or the later and more aerodynamically efficient “knife edge” canopy; a photo etch instrument panel, photo-etch parts to provide some internal wheel well detail, as well as oleos for the landing gear. The resin parts are crisply molded and will greatly improve the look of the landing gear, and make the cockpit assembly more interesting for modelers. Mostly importantly for the finished look of the kit, the part for the splitter within the intake appears to be accurately curved and to scale, neither too thick nor too thin.

Conclusion

This is very nicely done kit with impressive detail for 1/72 scale. To my eye, it is more appealing that its 1/48 scale brother also produced by Special Hobby. If you have an interest in X-planes and other aircraft that mark the important aviation milestones on the path to conquering the sound barrier, then this kit will peak your interest. Highly recommended.

Reference

  • http://www.nasa.gov/centers/armstrong/news/FactSheets/index.html
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