A governor is in its underspeed condition when the engine is operating at a speed lower than the governor calls for. The condition occurs when the blades of a propeller move to a higher than normal angle for a constant speed condition for any reason. When the speed drops below the RPM for which the governor is set, the resulting decrease in centrifugal force lowers the pilot valve, thereby opening the propeller-governor metering port. Oil is directed to the propeller in the proper direction to correct the underspeed condition. See also overspeed governor.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved