I think you might be thinking off a different film. I remember a similar story - gunner stuck in gun turret and the wheels of the plane won't descend, which means the turret will be destroyed when the plane belly-lands. One of his crew-mates draws a pic of the plane with large cartoon wheels and his drawing comes to life and the plane lands safely. It was one section of one of those films with about four different stories in it - I can't remember what the film was called but I think it might have had something to do with Steven Speilberg. Now, I'm not suggesting for a moment that you thought that Memphis Belle ended with the plane sprouting large cartoon wheels, but both the films came out in the early 90s so it's possible you could be mixing up that one element!