Ok, let's collect all the clues:
It flew in the fifties, only one was ever constructed, it was based on an existing aircraft of which many flew, it was experimental (and unsuccessful), was American, propeller aircraft and had something that could be detached from the aircraft on the ground (not bombs or small parts, something really big). The principle (the big detachable thing) is kind of in use in some huge helicopters today which look really weird when they don't have the big box singe it's just a cockpit and the engine left.
