An all-mechanical flight control system is potentially adaptable for high-temperature operation, high structural stiffness, lighter weight, and increased reliability. As part of a continued development program of new control system concepts, a mechanical cascade toroidal servo was tested on the North American Aviation, Inc/Los Angeles Division F-100 flight control simulator. This was the second toroidal servo tested. The improvement over its predecessor was primarily the reduction of pilot operating forces. This mechanical servo incorporated a miniature servo into the input control linkage of the original servo configuration. In this way, the pilot controlled the miniature command or pilot servo and subsequently controlled the power servo with reduced input force. This mechanical servo, like its predecessor, was based upon a proportional control concept which converted unidirectional rotational mechanical energy to provide bidirectional control surface motion through power hinges at the surface as a function of pilot input commands. This paper will discuss in detail the results of this latest test program. It will bring to light those static and dynamic characteristics of the servo and of the complete control system. It will compare the performance of this latest servo configuration with those of the original and, when possible, compare the performance with a conventional hydraulic system. The mechanical failures that occurred during the test program will be reviewed. Recommendation for further development of mechanical servos will be made.