The Lockheed “Flatbed” was a proposed cargo aircraft design from the 1980s that mounted large loads “in the open” on the back of the aircraft, similar to a flatbed truck. Conventional cargo designs generally “mass out” before they “bulk out”, meaning that they often fly mostly empty inside. In this case the aircraft is carrying around a large fuselage for no reason, adding mass and drag and thereby lowering performance. Nevertheless, they need to have oversized cargo bays for the cases where they have to carry bulky loads, rare as these may be.
According to the Lockheed design, the flatbed or open-air section would be used to haul cargo containers, outside vehicles or machinery. In fact, most of the cargo would be housed in removable modules, much like the huge containers stacked on the cargo ships that ply the world’s oceans.Importantly, the Flatbed design also allowed for passengers on board, who would be sat in a removable module. The passenger module could be the same size as the cargo hold area or fairing.
These modules could be uploaded and unloaded as a single unit, whereby they’d slide forward off the bed or deck of the open cargo area onto or from a special-purpose truck.The aircraft would be designed to sit low to the ground, allowing loading trucks to drive up to the aircraft and push loads onto the cargo deck. Parallel I-beams would be used as the primary load-carrying structure for the cargo hold, atop which metal sheeting would ensure a smooth walking surface.
As with most cargo aircraft, the Flatbed would have rollers in the cargo hold that would allow loads on pallets to be rolled on and off with ease.The Lockheed Flatbed was designed to deal with instances of when a plane “masses out” before it “bulks out”.This essentially refers to when a plane reaches its maximum take-off weight or MTOW before the cargo bay’s volume is at capacity. It is a huge headache for the cargo industry and military alike, which is why Lockheed went full steam ahead with this design.