When a plane is flying and pulling G’s, the nose and tail are being pushed down by gravity but the center of the plane is being held up by the lift of the wings. As a result, the belly skin in the mid-fuselage area is loaded in compression and can buckle. This is a particular issue for planes with fuselage mounted main landing gear (eg F-15, F-16, F-18, and Gripen) since the belly skin has cutouts for the wheel wells. To ensure that the skin doesn’t buckle, structural longerons are added to support the skin. Indeed, as seen in the first photo, FEJ installed a ~3/4” wide honeycomb strip on the belly centerline between the wheel wells. However, they then cut away most of the strip near the front to install door cylinders and notched the strip at its midpoint (though nothing is attached at this point). This has seriously compromised the structure.

The notch in the belly longeron seems to line up with the middle former seen in the second photo. However, the former doesn’t extend deep enough to reach the longeron. Perhaps the former was reduced sometime during development. Regardless, the notch in the longeron remains though it serves no purpose yet it compromises the strength of structure.

Regards,

Jim