XF-86C / XF-93A PENETRATION FIGHTER
Last revised: September 1, 2002
Writen by: Greg Goebel
While the Sabre was engaged in heavy combat across the Pacific, the design was being updated back in the States. Design work on the "NA-157" or "XP-86C" was begun in late 1947, in response to a USAF requirement for a "deep penetration" fighter. North American's XF-86C, as it was redesignated in 1948, won the competition against the Lockheed "XF-90" and the McDonnell "XF-88" (which would eventually evolve into the F-101 Voodoo), with the Air Force ordering two prototypes.
The XF-86C had a bigger and longer fuselage than the F-86A. The increased size was to accommodate 5,909 liters (1,561 gallons) of internal fuel to meet the range requirements, while the the increased length was to allow fit of an afterburning Pratt & Whitney J48-P-6 engine with 2,800 kilograms (4,500 pounds) thrust.
The J48 was an improved, afterburning version of the Rolls-Royce Nene centrifugal-flow turbojet, manufactured in Britain as the Tay, providing 2,835 kilograms (6,250 pounds) dry thrust and 3,625 kilograms (8,000 pounds) afterburning thrust. The J48's exhaust had a two-piece clamshell variable-size outlet.
The fuselage was designed using the new "area ruling" concept developed by NACA engineers, which specified that changes in an aircraft's cross-sectional area should be minimized to ensure smooth airflow at high speeds. As a result, the fuselage was "pinched" slightly along the wing roots. The result of all the changes was a somewhat inelegant machine compared to the F-86A, with a porpoise-like body and fat appearance. In fact, the aircraft was so clearly different that the USAF redesignated the type the "XF-93A" in 1948.
The nose intake was replaced with air intakes at the sides, leaving the nose available for SCR-720 radar, and the new aircraft was armed with six 20-millimeter cannon instead of six 12.7-millimeter guns, with 225 rounds per gun. The XF-86C's greater weight required reinforced landing gear, with dual wheels on the main gear. The twin air brakes of the Sabre were replaced with a single large air brake under the fuselage.
The XF-93A had excellent performance and range, and it could be fitted with stores pylons for external tanks to give even greater range, or to carry up to 900 kilograms (2,000 pounds) of bombs, rockets, or other stores. The Air Force ordered 118 production F-93As in 1948.
The first XF-93A prototype performed its initial flight in January 1950, again with George Welch at the controls. Only two were built, the contract having been cancelled a year earlier, since the USAF's new Boeing B-47 bomber was so fast that it didn't really need fighter escort, and money was tight anyway. Mid-air refueling would soon kill the "penetration fighter" concept completely.
The two XF-93A prototypes were completed as test articles, and flown in this role by NAA, the USAF, and NACA, eventually ending up as NACA property. They were used in various experiments into the late 1950s, in one case fitted with scoop-type air intakes instead of the original flush intakes, and then scrapped.
