Speed control of large wind tunnels

The paper describes an electronic speed control which has been installed for the composite drive of the 8 ft high-speed wind tunnel at the Royal Aircraft Establishment, Bedford. A description of the requirements of a wind-tunnel speed control is given, and several methods of control are discussed. The selected control system, which is discussed in detail, although of the conventional closed-loop technique, has special problems when gas-turbine prime movers power part of the composite drive. A full description of these special features is given, together with a mathematical analysis of the closed-loop system.