A variable pitch Thermofan as developed by Quinton Hazell. The operating rings are made of unreinforced acetal copolymer due to its high degree of thermal expansion. The blades are made from a similar material but have a glas reinforcement. The variable pitch cooling fan was invented by Aubrey Wagstaffe and his original demonstration model of 1976 is held by the Science Museum, London. For his 1976 model an electric drill rotated the fan, heated by an element from a toaster. As the temperature rose, the pitch of the blades increased, and the increased airflow was indicated by a wind vane.
© Science Museum / Science & Society Picture Library