F4H (F-4) Phantom Main Landing Gear Shrink Mechanism

Airplane designers sometimes want to make the landing gear shorter when it is retracted, i.e. compress the shock strut from its extended position when it is in the air, for various reasons. Here are a couple of examples of nose gears that "shrink":

http://tailhooktopics.blogspot.com/2019/07/mcdonnell-f2h-banshee-nose-landing-gear.html

https://tailhooktopics.blogspot.com/2019/04/mcdonnell-f3h-demon-nose-landing-gear.html

The main landing gear on the F4H Phantom is another example but one that is even less obvious. Note that the tricky part of providing a shrink capability is that the lower portion of the strut must be allowed to extend and compress freely when the gear is extended.

This Jean-Marc Moulin picture shows the basic elements of the F4H main landing gear shrink mechanism.

Note that there are three components to the mechanism: the upper shrink link, the lower shrink link, and the idler that connects them, all located on the rear outboard side of the main landing gear shock strut.  The lower shrink link is attached to the lower part of the shock strut and can slide freely through the idler until the link reaches a stop on its upper end (the scissors or some other feature within the strut probably establishes the length of lower strut travel but the stop is necessary for the shrink function). That allows the shock strut to extend about 17-18 inches when the wheel is not on the ground. Also note the location of the pivot point of the upper shrink link, which is outboard of the pivot point of the main landing gear strut itself.

When the landing gear is retracted, these three components, combined with the location of the upper shrink link pivot point, cause the shock strut to compress significantly.

Because the upper shrink link pivot point is outboard of the strut's pivot point, it is in effect shortened that many inches relative to the shock strut when the landing gear is retracted. That pulls the idler up against the strut, which causes the lower shrink link to pull the lower part of the shock strut on which the wheel is mounted back up into the upper part.

This Howard Mason picture shows the components of the mechanism on the left main gear from the rear.

 Howard Mason