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F-18 Retrofit Controller

Abstract

The interest in increased flight safety, aircraft survivability, and performance improvements has led to significant advances in the design of adaptive fault tolerant (reconfigurable) control systems. There have also been a handful of flight tests of reconfigurable control methods, including the Self-Designing Controller (SDC) developed by Barron Associates. The purpose of the current work is to lessen the gap between the research and application of these methods by developing and flight testing low-cost add-on modules for current Navy fleet aircraft.

Problem

Important factors contributing to the loss of aircraft and life include flight control failures, mechanical, electrical and hydraulic malfunctions, midair collisions and adverse environmental conditions such as icing. Military aircraft must also contend with additional sources of failure, including more extreme operating conditions and the possibility of battle damage.

In many cases, the aircraft is physically capable of recovering from failures through the judicious (but unconventional) use of the remaining aerodynamic control surfaces and propulsion system. However, the handling qualities can change considerably and performance characteristics can degrade such that a majority of pilots would not be able to control the aircraft. A digital flight control system that can reconfigure an aircraft to compensate for these failures offers significant benefits for military and commercial vehicles.

Despite the advances in technology and several key demonstrations, there is a substantial gap between the research and application of fault tolerant control methods. Reasons include:

1. Industry is unable to apply the research to current generation aircraft.
2. Industry desires to use "proven" design methods for next generation aircraft.
3. Industry is reluctant to abandon familiar certification practices.
4. Federal certification authorities often lack the resources sign off on novel technology for production systems.

Solution/Approach

Barron Associates is developing a reconfiguration capability that is an upgrade to, rather than a replacement of, the production control system. This approach can overcome many of the technical, financial, and certification roadblocks to industry use.

Reconfiguration is accomplished by computing increments to the pilot's commands that remove unwanted motions during maneuvering with control surface failures, battle damage, and mechanical, electrical, or hydraulic problems. This add-on (retrofit) control system is unobtrusive - i.e., it only generates nonzero reconfiguration commands when the aircraft is responding unexpectedly. Another key advantage of the approach is that the command limiting, structural filters, and safety logic of the production control system remain in effect. This lessens certification requirements compared to other reconfigurable control methods.

The scope of the effort includes non-real-time simulation studies using a high-fidelity F/A-18 simulation, piloted simulation tests in Boeing's aircraft dome simulator, and hardware bench tests in the Navy fleet support flight control computer (FSFCC).