The 1980 Flash Gordon movie was a completely berserk masterpiece of weird visuals and over-the-top insanity. But it could have featured even more striking designs in one area: master designer Chris Foss (Alien, A.I., Jodorowsky's Dune) created designs for the Hawkmen's rocket sled that Flash rides, which weren't used.
These amazing rocket sled designs come via Film Sketchr, which also posted a video of Chris Foss talking about his work on the film, in which he says:
Dino De Laurentiis called me when Flash Gordon was almost ready to go into production and asked me to come and see them in the studios because he wanted new versions of some of the designs that had already been done, which he obviously didn't like. And, specifically, he wanted me to redesign the 'Space Scooter.'
I saw Dino De Laurentiis, he gave me a verbal brief. I was then taken down to the department that was physically building the stuff and we discussed what this thing was supposed to do in the film. And I then went away and, over a long holiday, produced the designs for it.