Why did the F4 Phantom have angled rear tail wings?

By: Graham Cox

The F4 was designed in the 1950s, an era when much of the science of supersonic flight was in its infancy, with new discoveries made regularly.

The F4 was a development of the F3 Demon, and the prototype is a simple, clean design with none of the iconic features the Phantom became known for.

Notably, it had a flat, high-ish tailplane to clear the short twin exhaust nozzles. The wings also lacked the upswept tips, and the air intakes were very simple affairs.

Looked right, so it should fly right, right? So they built it and flew it. Oh dear.

Many aerodynamic problems were discovered. One of these was that the high tailplane was totally blanked by the wing at high angles of attack (for example during landing), leading to terrible pitch control and stability. The tailplane needed to either be much higher (a T-tail) or much lower. But a T-tail was a major redesign and not practical for a carrier-borne aircraft that needed a low fin to fit in a deck hangar, and lowering the tailplane couldn’t be done because the exhaust nozzles needed clearance. Simple solution – just cant the tailplane downwards (anhedral) so that it was effectively a much lower tailplane but having the original mounting points.

The dihedral wingtips were a similar fix: the aircraft wasn’t sufficiently stable in roll, but adding a few degrees of dihedral to the whole wing required a complete redesign. Since the tips folded up anyway for carrier use, it was simple to add more dihedral to the tips, averaging out to the equivalent of the needed overall couple of degrees.

The air intakes went through some evolution as well. From the simple F3 intakes above to these:

Adding inboard splitters and ramps to avoid supersonic compressor stall, and then to the final shape.

Practical cheap fixes to a not very correct initial design, in other words. But that’s usually the reality for almost any successful complex machine, be it plane, car, truck or anything else.

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