An aircraft control actuator that incorporates self-contained control electronics has been installed in the F-18 Systems Research Aircraft and evaluated in flight tests. This "smart" actuator is a prototype of fly-by-wire servoactuators for future advanced aircraft.

Fly-by-wire servoactuators now used in military and commercial aircraft are not "smart" in that they do not use self-contained control electronics. Generally, electronic control and monitoring of servoactuators on aircraft are accomplished within separate flight-control computers. As a result, a large amount of wire is needed to operate all the actuators on an aircraft. Especially in a large commercial aircraft, the weight of the wire is significant. Other disadvantages of such a fly-by-wire system include high cost of maintenance, vulnerability to interference by electromagnetic signals (including electromagnetic pulses), and the need for a unique flight-control interface for each actuator.

Figure 1. The Smart Actuator includes self-contained control electronics that perform functions that, in older systems, were performed within flight-control computers remote from actuators.

The smart actuator (see Figure 1) was designed to fit in the left aileron bay of the F-18 airplane. The smart actuator contains two independent electronic channels that perform actuator-control, fault-monitoring, and redundancy-management functions. Communication with the actuator has been simplified by use of standard serial data buses. Instead of wires, optical fibers are used as the communication media.

Installation of the smart actuator on the F-18 airplane necessitated two interface units. These units not only provide the electrical-to-optical interface between the smart actuator and the F-18 flight-control computers, but also provide data to the instrumentation system of the airplane. The use of the interface units also makes it unnecessary to modify the flight-control computers.

Figure 2. Nearly Identical Performances were exhibited by the smart actuator and the standard F-18 aileron actuator in a flight test. [Aileron reversal ±60° bank angle, 24 kft (7.2 km), 0.4 M, 88 q.]

The performance of the smart actuator throughout the flight-test program has been exceptional (see Figure 2). Likewise, the fiber-optic data buses used with the smart actuator performed well throughout flight testing. Moreover, the smart actuator performance was virutally identical to the F-18 production actuator. Although environmental tests revealed that the fiber-optic data buses were thermally sensitive, a maintenance-and-calibration procedure was developed to account for the sensitivities. Fiber optics were found to be satisfactorily reliable, and maintenance was easily performed. No anomalies occurred during the flight tests.

The development and flight testing of the smart actuator have proved that local control and monitoring of servoactuators is possible. Although sensitivities of the fiber-optic data buses were discovered, these sensitivities can be factored into future system designs. The use of fiber optics and serial data buses simplified integration of systems and provided valuable information regarding reliability and maintainability of fiber optics on aircraft. In addition, the use of fiber optics may translate to decreased weights, decreased costs, and decreased electromagnetic susceptibility for future aircraft.

This work was done by Kari Alvarado, Denis Bessette, Dorothea Cohen, Bill Fredriksen, Gordon Fullerton, Don Hermann, Linda Kelly, Doug Lindquist, Dick Klein, Bill McGrory, Harry Miller, Cynthia Norman, Lyle Ramey, Mauricio Rivas, Karla Shy, Joel Sitz, Daryl Townsend, and Eddie Zavala of Dryden Flight Research Center; Karen Richards of HSI; Gavin Jenney and Bruce Raymond of Dynamic Controls, Inc.; Dave Dawson and Major Dennis Trosen of the U. S. Air Force Wright Laboratories; Sean Donley of the U. S. Navy; and Bob Heagey and Bob Deller of HR Textron. For further information, access the Technical Support Package (TSP) free on-line at under the Machinery/Automation category, or circle no. 157 on the TSP Order Card in this issue to receive a copy by mail ($5 charge).


NASA Tech Briefs Magazine

This article first appeared in the June, 1998 issue of NASA Tech Briefs Magazine.

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