The F-4(FV)S was a 1966 McDonnell proposal for a variable-geometry version of the Phantom. It was viewed as possible replacement for the failed General Dynamics/Grumman F-111B fleet defense fighter, and as a less expensive alternative to the Grumman F-14 Tomcat.
There were two versions envisaged--the F-4J(FV)S based on the F-4J and intended for the US Navy, and the F-4M(FV)S based on the F-4M and intended for the Royal Air Force.
The F-4J(FV)S offered a 57 percent parts commonality with the stock F-4J. Since the existing inner wing of the F-4J was too thin to accept pivots, an entirely new high-mounted wing was adopted. The inner wing glove contained the pivots and was fixed. The outer wing panels could be varied in sweep between 19 degrees and 70 degrees. The trailing edges of the variable outer wing panel contained full-span spoilers and flaps. The horizontal stabilizer was redesigned and replaced with one that had no anhedral. The new high-mounted wing required that the undercarriage be redesigned and located in the lower fuselage. Internal fuel capacity was increased from the F-4Js 2000 US gallons to 2601 US gallons. The F-4J(FV)S was to have been fitted with an AN/AWG-10 system modified to provide multi-shot capability. The primary armament was to have been four AIM-7F Sparrow air-to-air missiles.
It was anticipated that the F-4J(FV)S would have a 11 mph slower approach speed than that of the standard F-4J, and that it would have a significantly improved performance, with a higher ceiling, better acceleration times, and a shorter turning radius.
At the same time, the McDonnell company offered the F-4M(FV)S to the Royal Air Force. It bore much the same relationship to the RAF's F-4M as did the F-4J(FV)S to the US Navy's F-4J. It was to be powered by a pair of 20,154 lb.s.t. Rolls-Royce RB-168-27R turbofans. It was anticipated that production aircraft would be available by the end of 1971.
A further improved version, the F-4(FV)S was also proposed to both the US Navy and the RAF. It was to be powered by the General Electric G31/10S092B, with a first flight envisaged in March of 1971. McDonnell proposed 200 F-4M(FV)S aircraft, followed by 400 F-4(FV)S aircraft.
Neither the US Navy nor the Royal Air Force showed sufficient interest in the variable-geometry Phantom to order a prototype. In particular, the US Navy found that the capabilities of the variable-geometry Phantom were no match for those of the Grumman G-303 fighter, which was to eventually emerge as the F-14 Tomcat