I'm curious what designs you guys would consider flops: Honestly...
A flop why?
1. Bad air frame?
2. Bad engine/s?
3. Bad armament/electronics?
Post war the number of actual flops was pretty small and most could be tied to reasons 2 & 3.
There are exceptions
Inspiration for Star Wars pod racers?
Converting a piston engine plane to jets wasn't always a good idea
Believe it or not, these were carrier planes.
The Chance Vought F7U might be considered a flop
First went to sea in non-testing deployments in late 1955, out off 320 built all were retired by the end of 1959.
A lot of prototypes/experimentals were flops, but that is what they are are for. To push the boundaries of knowledge or technical limits of the time.
Production programs of scores or hundreds of aircraft that have to be yanked from service and scrapped or shuffled off to 3rd/4th tier duties (instructional airframe) were rare post war.
A lot ot the weapons systems of the late 40s and the 50s left something (a lot of something) to be desired but that was not the responsibility of either the airframe maker or the engine maker.