Dave Stevens, the writer/artist of the original graphic novel, gave the film's production designer Jim Bissell and his two art directors his entire reference library pertaining to the Rocketeer at that time period, including blueprints for hangars and bleachers, schematics for building the autogyro, photos and drawings of the Bulldog Cafe, the uniforms for the air circus staff, and contacts for locating the vintage aircraft that were to be used. Stevens remembers that they "literally just took the reference and built the sets".
The actual Gee Bee used in filming was only allowed to land a very limited amount of times during its time working on the movie, as landings are extremely hard on the landing gear of this particular plane.
The Gee Bee racer was nicknamed "The Widowmaker" and "The Flying Coffin" because it was incredibly difficult to fly and was prone to crashing. Because of its speed and maneuverability, some pilots still raced it despite the danger.
In the original graphic comic book by Dave Stevens, the inventor of the rocket pack was Doc Savage, a 1930s pulp novel hero. However, due to licensing considerations, Disney did not seek permission from Conde Nast, the copyright holder of Doc Savage, and opted to substitute Doc Savage with the flamboyant billionaire Howard Hughes.
A scene where Neville Sinclair sends a message to Berlin (coded first on an authentic Enigma machine found for the production) was filmed, but cut due to running time constraints.
Dave Stevens: The creator of the original comic book appears as the man in the test flight movie, who has the rocket pack strapped to his back.