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XF-88 Voodoo
By December 1945 the AAF had decided that it wanted an all jet combat force of fighters and bombers to replace successful generations of propeller-driven types.
As explained by David Baker in his book US Air Power 1945–1990 Volume 1: US Fighters and Fighter-Bombers 1945-1949, the requirement for the XF-88 arose from experience with the P-51D Mustang as a long-range escort fighter for bombers over Germany and on 1 April 1946 McDonnell began work on its Model 36 for a pure-jet successor to that aircraft. Designated XP/XF-88 Voodoo, it bears a name not to be confused with the later and more successful aircraft of a similar name, the F-101 Voodoo which was developed out of the XF-88 when in 1950 the Air Force wanted a replacement for the F-84, outclassed by the Russian MiG fighters in the Korean War.
For power, initially McDonnell focused on the Westinghouse J34-WE-13 turbojet engines with a thrust of 3,000lb (13.3kN) and put two in the wing roots to minimise asymmetric thrust should one fail but they were relocated to outer locations in the lower fuselage with intakes in the wing roots and exhausts on the underside of the rear fuselage which allowed additional fuel for the long-range mission.
This would be the same configuration as that eventually adopted for the F3H Demon and F-4 Phantom II of the late 1940s and early 1950s, respectively. For the XF-88, however, initially McDonnell wanted a V-tail in an attempt to reduce the effects of compressibility at high-subsonic speeds. There were to be dive brakes in the aft fuselage and a forward cockpit above the nose which would incorporate six 20mm cannon.
Disappointing speed
McDonnell received approval to proceed on 7 May 1946 with a contract the following month for two prototypes (46-525 and 46-526). A mock-up inspection during mid-1946 brought some changes including a 40 degree sweep on the root intakes, which now had a boundary-layer ramp to assist with pressure recovery, and replacement of the V-tail with a conventional layout and high-mounted horizontal surfaces to avoid efflux impact. The design had originally displayed straight wings but the advantages of a swept configuration prevailed and it was to have an ejection seat. The final design was accepted on 14 February 1947, when McDonnell received a formal contract.
The XF-88 made its first flight on 20 October 1948 at the hands of test pilot Robert M Edholm and over tests proved it to be a capable and adequate aircraft but, as with so many of these early jet-powered fighters, the speed was disappointing. For the XF-88 however, it proved inadequate when compared to the F-84 and the F-86. In an attempt to increase performance, the J34-WE-22 with a thrust of 3,600lb (16kN) and short afterburners was installed in the second prototype which made its first flight on 26 April 1949. These engines gave it a slightly higher speed but the additional fuel for power boost negated its value as a long-range escort fighter.
The first turboprop aircraft in the world to exceed Mach 1
When flight trials were completed the Air Force gave McDonnell indications that it wanted to place it in production and the company planned to install Westinghouse J46 engines with a thrust of 3,980lb (17.7kN) to provide a further improvement in speed. But tight financial constraints and a policy change brought cancellation of the XF-88 in August 1950.
Yet the aircraft did have a truly unique place in aviation history. Modified as a high-speed propeller research aircraft and fitted with an Allison XT-35-A-5 turboprop engine in the nose, for which the nose leg had to be relocated to one side, the first prototype was redesignated XF-88B and began flight trials on 14 April 1953 from Langley Field, Virginia. It was able to achieve just over Mach 1 in a dive, thus becoming the first turboprop-powered aircraft in the world to exceed the speed of sound.
US Air Power 1945–1990 Volume 1: US Fighters and Fighter-Bombers 1945-1949 is published by Helion & Company and is available to order here.
Photo credit: U.S. Air Force
