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.
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 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.
The original inventor of the rocket pack was thirties pulp novel hero Doc Savage, the Man of Bronze, in the original graphic comic book by Dave Stevens. However, because of 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.
Billy Campbell, who once studied commercial art, made sure to read the Dave Stevens graphic novel, on which this film was based. He got the part after getting a haircut to make himself look identical to the character in the graphic novel.
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.