The Ford 15-P design would likely have needed a lot of design rework to master the control system but it just never happened after the crash. It was likely under powered as well,
Jack Northrup had some problems on the initial flight of the N-1M in 1941. He had looked at the Horton brothers flying wing glider designs a lot for the design phase of this model. His first wing design from the late 20s, the X-216H, still had tail booms & rudder controls but it was stable. The N-1M was tail-less and became a stable platform after adjustments of the control surfaces but it was under powered. The final design had two Franklin engines and finally had enough power to make it a decent airplane.
The Horton brothers actually mastered the design system for there model 229 but the war came to a close before it could go into production. They couldn't get engines for production since they were all going to other projects. It was the first successful jet powered wing design. Jack Northrup's designs were for large recip and jet engine bombers(YB-35 & YB-49 respectively).
All of these designs were limited in flight parameters. They weren't good designs for loops or barrel rolls. They had a tendency to flip over if the pilot got too carried away with aerobatics.