Final answer:
The maximum Category D circling airspeed in the NAS is typically 165 KIAS, which enables pilots to maneuver safely and maintain obstacle clearance. operation within the flight envelope during circling maneuvers in visual flight conditions while ensuring obstacle clearance requirements are met.
Step-by-step explanation:
The question pertains to aviation regulations, specifically the maximum circling airspeed for Category D aircraft in the National Airspace System (NAS). This is not explicitly provided within the given reference material; the reference discusses the drag coefficient and its effects on vehicles like cars and planes but does not detail aviation circling airspeeds.
For Category D aircraft, which are typically large, heavy, and fast, the maximum circling airspeed under U.S. Federal Aviation Regulations is typically 165 knots indicated airspeed (KIAS). This airspeed allows pilots to maintain a safe margin of operation within the flight envelope during circling maneuvers in visual flight conditions while ensuring obstacle clearance requirements are met.