In flight simulator X-Plane 8.15, the F-4 Phantom 2 can fold the tip of its wings (well, variable sweep). Is that useful? Why would a pilot fold the wing? To reduce lift for short landing?
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asked Dec 6, 2017 at 15:31
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6$\begingroup$ The wing folding is only meant to save space on a carrier during storage, it is not for in-flight use. Are you asking about sweeping or folding? $\endgroup$– Ron BeyerCommented Dec 6, 2017 at 15:35
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2$\begingroup$ Seems to be dedicated to parking on aircraft carriers similarly to aircraft operated on carrier operations. There seems to be one occurrence of a flight with wings folded according to this article, but it likely was just an error of operation. Some people might know more about it. $\endgroup$– Pierre ChevallierCommented Dec 6, 2017 at 15:36
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7$\begingroup$ Who says that the F-4 could not fold its wings in flight? $\endgroup$– Peter KämpfCommented Dec 6, 2017 at 16:15
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4$\begingroup$ Woah, X-Plane 8.15!? 11.20 was just released! $\endgroup$– SnakeDocCommented Dec 18, 2017 at 17:01
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2$\begingroup$ @JonathanIrons It is indeed brutal on most computer systems, mine barely runs it smoothly. Well, I'm glad you're enjoying it, x-plane and aviation in general is quite fun. $\endgroup$– SnakeDocCommented Dec 20, 2017 at 16:12
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3 Answers
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As several of the comments have mentioned, the F-4 have the option of folding the outermost section of their wings, as shown in the picture below. 
The main purpose of this was simply to save precious space on aircraft carriers, it had no use when flying. There have been some incidents where wings have either started to fold during flight or where the pilot forgot to unfold before takeoff, but it was not designed for this. Many other naval aircraft have the option of folding their wings in a similar manner, such as the F/A-18.
The F-14 Tomcat uses a completely different mechanism to adjust the wing sweep while flying, and although it had a special "parking setting" for the sweep, it was used to adjust the wing sweep according to the speed of the aircraft.
The A-7 Corsair II and the F-8 Crusader also had wing folding, but in addition they could also adjust the attitude of the wing while flying, primarily to improve visibility for the pilot when landing as seen below.
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3$\begingroup$ The F-8 had variable AoA, the A-7 did not. $\endgroup$– KoyovisCommented Dec 7, 2017 at 8:41
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In U.S. Navy and Marine Corps F-4 Phantoms, the wing fold mechanism was controlled and powered by hydraulics, since the pilot had to fold the wings after landing for taxiing around on the deck. The USAF versions of the Phantom, on the other hand, had this hydraulic capability removed, and there was a pin in the top of the wing, (if I recall), just inboard of the wing fold, which, if it was protruding, indicated that the wing fold was unlocked. It was, obviously, a critical pre-flight step to check that this pin was flush, not protruding.
There was at least one incident where the aircrew failed to notice that the pin was protruding, and took off anyway. Needless to say, the wing folded shortly after rotation and liftoff, with catastrophic results.
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2$\begingroup$ Is there online documentation of that incident? $\endgroup$ Commented Dec 18, 2017 at 18:13
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7$\begingroup$ @rclocher3 here is the incident where one wing folded. The short story is the plane lost control completely after rotation, but the pilots managed to narrowly escape by punching out when the jet was momentarily upright. There was another incident where a pilot took off with both wings folded. He landed safely. $\endgroup$– kevinCommented Dec 18, 2017 at 20:32
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1$\begingroup$ Cool, thanks for tracking those down! $\endgroup$ Commented Dec 19, 2017 at 0:42
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On our RF-4C's the pilot could not fold the wings the crew chief had to do it. It was part of the 25 hour check to fold them and inspect and lube them.
