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***image1***Certainly one of the most beautiful fighters ever made for the U.S. Air Force was the Lockheed F-90, built in response to an Air Force requirement issued at the end of World War II for a long-range jet escort fighter intended to be a jet replacement for the P-51 Mustang.
Lockheed’s “Skunk Works,” led by designer Kelly Johnson, developed the XF-90 – a large, swept wing, twin-engine jet that carried the very heavy armament of six 20-millimeter cannons and was expected to have a combat range of over 900 miles and a 600 miles per hour top speed.
The XF-90 incorporated a number of unusual structural features, including a vertical
stabilizer that moved backward and forward as the horizontal stabilizer moved.
Another feature of its structure was the use of heavy gauge 75ST
aluminum rather than the then-standard 24ST aluminum alloy. This made the aircraft very strong and able to pull 12.5G (eat your heart out, Viper drivers).
However, the sturdy structure made the F-90 very heavy and there were problems finding engines powerful enough to give the 30,000 pound fighter the power it required and a low thrust. Weight ratio is a killer for a fighter.
After several false starts, the XF-90 was fitted with two J34 engines with afterburners, making it the first jet aircraft to have this type of engine thrust augmentation. But even with the afterburners, it was grossly underpowered. Test flights at Edwards Air Force Base, Calif., showed that on hot days, it required a takeoff run of several miles!
Jet assist takeoff bottles were eventually fitted for takeoff but even though the XF-90 was capable of a top speed of over 670 miles per hour at altitude and could go supersonic in a dive, its performance remained inadequate.
The low power of the late 1940s’ jet engines caused both the Air Force and Navy to
scuttle a number of designs that were promising aerodynamically, but heavy. The Air Force moved to lighter fighters like the F-86, which weighed about one third as much as the F-90.
However, as jet engines became more powerful, there would still be problems getting high performance out of jet aircraft because of an inadequate understanding of aircraft drag at transonic and supersonic speeds, particularly between Mach 0.8 and 1.2. This was eventually solved by the Whitcomb “area rule” design, also known as the “coke bottle” fuselage.
While the F-90 never achieved production status, it lived on in popular culture as the second aircraft flown by the “Blackhawks” of comic book fame.
