Grumman F6F Hellcat Belly Tank

Another interesting question - what are the different F6F 150-gallon belly tanks?

I don't have a complete answer but I do have some information. First, the F6F belly tank had to be nonstandard because of the location of the oil cooler air outlet.

It was located pretty close to the desired center of gravity, which is where you want the disposable load to be if at all possible so the cg doesn't change much when you use fuel, drop bombs, etc.

When the Navy decided the F6F needed more fuel, Grumman developed an attachment approach evaluated on an early F6F (note the wheel covers) that provided clearance with the oil cooler air outlet.

It was refined to this (note that it has the later rectangular pylon):

The two retaining straps kept the tank from falling off and allowed it to be jettisoned (note the two holes on either side of the oil cooler air outlet above that allow them to be attached to standard bomb shackles). The pylon on the aft end of the tank contained the plumbing that transferred the fuel in the tank to the airplane's fuel system and along with the two sway braces, provided the separation between the tank and the bottom of the fuselage.

The leading and trailing edges of the early production pylon was curved instead of straight as on the subsequent one.

Note the rectangular profile of the later pylon fairing on 69Z versus the early streamlined one on 68Z. The latter is white to match the bottom color of the early F6F camouflage. The tanks were obviously interchangeable.

The early tank appears to have invariably had a vertical flange, separating the left and right halves of the tank.

The later tank had a vertical flange initially as shown in the illustration above and then was subsequently produced with a horizontal flange.

The tank was also changed from aluminum to steel at some point, possibly in conjunction with the change in the pylon fairing shape, because of the relative availability of steel versus aluminum.

In April 1945, a Service Change was issued to enable the F6F to carry the new "universal" 150-gallon tank. The retaining straps were basically the same, the forward sway braces were interconnected, a fuselage mounted strut was added to hold the aft part of the tank away from the fuselage, and a flexible hose was added to transfer the fuel from the tank to the original fitting on the bottom of the fuselage.