Vought F4U Corsair Bomb Racks

 A brief history...

 The Vought XF4U-1, like the Bell XFL-1 and Grumman XF5F-1, had small bomb racks located within the wing structure. These were actually antiaircraft bombs, aimed by a downward-vision window between the pilot's legs. This capability was determined to be unworthy of incorporation in the production design. For a bit more more, see https://thanlont.blogspot.com/2008/06/antiaircraft-bombs.html

Since adding bombing capability to the Corsair was desirable, Brewster (contracted to be a second source for F4U production early in WW II) designed an adapter to be mounted under the center fuselage for the standard Mk 51 bomb rack. To provide clearance for opening of the intercooler flap that was located there, like the center-line fuel tank it was attached to existing structure ahead of and behind the flap (a small cutout in the aft edge of the flap was required). This is the original design; a redesign that followed was similar but simpler.

 Note that the F3A was a Brewster-built Corsair and the FG-1, Goodyear's.

According to Dana Bell, who can be relied on for the accuracy of his statements, the Brewster adapter came first and crude imitations created in the field, followed. 

Note that the Mk 51 bomb rack used the two logs on the bomb and the field adapter, the single one.

Production bomb-carrying capability was added to the F4U-1D with a pylon under each inner wing.

In this case the fairing that was provided to cover the bomb shackle is not present on either side. Vought also provided a removable fairing to close out the bottom of enclosure when bombs or fuel tanks were not carried.

The inner wing bomb racks were carried over to the F4U-4.

The F4U-5 was produced with a center-line pylon capability similar in design to Brewster's with a more streamlined fairing. There is still a gap between the pylon and the fuselage so the intercooler flap can be opened.

 It doesn't seem to have been frequently carried and even when photographed, not well lit.

The front end of the pylon is secured to a fitting that is bolted to the engine mount and the aft end is secured to a fitting on the main spar located just aft of the main wing spar.