Part 1 of this series on the early U.S. and Soviet supersonic fighter jets discussed the developments up to and including the YF-100 Super Sabre. Part 2 of the series explains the development of the Douglas XF4D-1 Skyray.
Douglas XF4D-1 Skyray
The design of the Douglas XF4D-1 Skyray was truly an exercise in critical thinking (thinking out of the box).
Its design genesis in many ways was the direct result of groundbreaking work performed by the famed German aerodynamicists, Dr. Alexander M. Lippisch in Delta wing and tailless aircraft design.
The Skyray was afforded the distinction of being the US Navy’s first supersonic (at sea level) carrier-borne interceptor, and in many ways set a precedent in high-speed carrier aircraft design.
The Skyray, designed for the interceptor/fighter role, conformed to its mission requirements in a 1947 paper requirement.
The requirement was stipulated by the US Navy and its pending interest in the Delta wing as a means of achieving supersonic speed for future carrier aircraft.
Douglas engineers, under the guidance from perhaps the most noteworthy of aerodynamicist, Ed Heinemann, A. M. O. Smith, Kermit Vane very and Gene Root, did something revolutionary for fighter jet design:
The engineers elevated the art of aerodynamic design to newer heights, setting a standard for other companies to follow.
The cutting edge technology of the XF4D-1
The XF4D-1 was considered cutting edge at the time. It was tailless in design architecture sporting a wing of a high leading-edge sweep of 52.5° and of low aspect ratio.
XF4D-1 Wing design
It was, however, not considered a true Delta in shape but rather a modified Delta, highly effective in its design.
Its wing root (t/c) (thickness to chord ratio) was held to 7% while its tip (t/c) maintained 3.5%. This further defined its low aspect ratio wing platform.
It was slated to be powered by a Westinghouse XJ40-WE-8 afterburning turbojet.
This unit provided 7,500 lb. of static thrust and up to 10,500 lb. with full after burning.
This power plant would eventually be replaced by the Pratt & Whitney J57-P8a afterburning turbojet. This produced 10,500 lb. of static thrust and 14,500 in full afterburning.
This was due to the stark unreliability of the Westinghouse unit.
Engine inlet design
The XJ40 when used was fed by two triangular side wing root inlets without the benefit of any boundary layer removal control. This was later added to facilitate the use of the J57 turbojet.
One very important design/performance characteristic afforded by its highly swept low aspect ratio modified Delta tailless design was the low wing loading that contributed to its phenomenal climb rate of 18,800 ft./min. and its exceptional maneuverability.
U.S. Navy XF4D-1 contract finalization
The US Navy finalized the contract in December 1949, eventually yielding two prototypes designated by No. 124586 and 124587.
The Skyray began its test flight program on 23 January 1951 without the use of its proposed Westinghouse XJ40-WE-8 turbojet.
This was largely due to its unavailability caused by constant developmental problems encountered with the new Westinghouse unit.
An Allison J35-A-17 non-afterburning turbojet of 5,000 lb. maximum thrust was substituted and placed into prototype 586.
Achieving Mach 1, joining the list of early supersonic fighter jets
It would not be until 16 October 1953 that the Skyray would exceed Mach 1 in level flight at the hands of Lt. Cdr. James B. Verdin.
If the Westinghouse XJ40-WE-8 turbojet conformed to its developmental schedule, the Skyray would have been the first Mach 1 capable aircraft in the world instead of the North American YF-100 Super Sabre.
The Skyray experienced a rather abbreviated carrier deployment. It exposed and initiated its fraternal order of naval aviators to the art of flying and controlling a rather unstable aircraft.
Its Douglas-designed and built flight control system aided in suppressing this anomaly in part, prompting its pilots to fly the Skyray with great skill and care. Yet being careful not to overfly or to overstress the airframe was necessary in this regard.
The nickname for the XF4D-1
The “Ford” as it was affectionally known was quickly eclipsed by more advanced aircraft, falling victim to technology never-ending ascendancy towards perfection.
This design was not only necessary from a technical standpoint but it allowed the United States Navy to display its technical bravado, especially to other branches of the military—namely the US Air Force.
Part 2 of this series on the early U.S. and Soviet supersonic fighter jets discussed the development of the YF-100 Super Sabre. Part 3 of the series will discuss the development of the Soviet Union MIG-19.
Story: ©2020 Thomas E. Gardner. You can contact the author here.
Featured Image: Douglas F-4D-1 Skyray, Los Angeles-area in the background. National Naval Aviation Museum.