A Review of Frisbee Characteristics

Three topics are briefly reviewed here (a) surface characteristics, (b) flight records in competition, and (c) subtended angles and related distances. The author consulted with a person⁶ who had previously worked for a well-known manufacturer of Frisbees. He explained the necessity of having a smoothly curved leading edge at the circumference of the disc and tiny microgrooves in the top surface in order to create a lifting force during its spinning flight. He suggested that the addition of a dome-like structure to the top would probably reduce or destroy this aerodynamic lift. The author (later) proved that this was indeed true. The author also contacted various toy stores to inspect various Frisbee models. A total of seven different models were inspected. All possessed a glossy (specular) outer surface. Most had reflectances of about 80% or less. Of the six models produced before 1981, only two had paper labels, the other four 6 had colorful embossed drawings centered across the top surface.

Men's and women's world records for throwing Frisbees were obtained from the International Frisbee disc Association (IFA). This organization has hosted tournaments which have become qualifying events for the World Frisbee Championship. It was discovered that the men's outdoor distance record is 166 m (540 feet) and the women's record is 122 m (397 feet). These records were set in 1983 and 1980, respectively and are meant only to indicate the general range of human capability for this skilled activity. The men's world record for maximum time aloft is 15.5 seconds (1981); the women's record is 11.4 seconds (1980).

The linear width of the disc's image on the negative was 0.98 mm. The width of the 36 mm frame was equivalent to a horizontal angle of 48°. The useful ratio can be formed:

where: X = the angle subtended by the disc. This angle is 1.307°. Therefore, Tan 1.307/2 = 0.0 114 = (W/D)2 where: W = the assumed object width and D = the separation distance between the camera and object. Letting W = 9 inches, D = 32.88 feet which exceeds the hyperfocal distance. If the disc object was 10 or 50 feet in width it would have been 438 feet or 2,192 feet from the camera, respectively. And if the disc had been hovering directly over the mountain (i.e., 7,580 feet away) it would have been 173 feet in width.

Assuming that the camera shutter speed was 1/125th second and the disc image was produced by a typical Frisbee travelling at 10 feet per second, a 9 inch diameter disc moving normal to the line of sight would move 0.96 inches in his duration. Approximately 9.3% of the Frisbee's diameter would show up as a blur on the leading and trailing edge of the Frisbee's photographic image. There is virtually no blur visible on the photograph in question which strongly argues that the disc was not travelling normal to the line of sight. If it was motionless it would be far more difficult to perceive, particularly if the