Adaptive performance optimization (APO) is an approach for improving aircraft performance without the need for extensive modifications of hardware. In this approach, one exploits existing redundant control-effector capabilities by providing for automatic reconfiguration of control-surface deflections to achieve a minimum-drag trim condition.

The application of adaptive performance optimization (APO) to transport aircraft, utilizing redundant control effectors, can be a significant factor for improving the profitability of airlines.

For example, the use of APO to effect a 1-percent reduction in drag for the U.S. fleet of wide-body transport airplanes could result in savings of approximately $140 million per year [assuming that fuel costs $0.70/gallon ($0.19/L)].

Figure 1. A Transport Airplane Was Modified for use in experiments on APO.

Preliminary design work has been performed for implementation of variable camber in transport airplanes, with APO serving as part of the basis of a new approach to actuation and control of wing trailing-edge control surfaces. The possibility of deriving a benefit from the application of APO to either a new full variable-camber design or to a retrofit to an existing transport airplane depends on the existence of a potential for optimization; in particular, it depends on the existence of a redundant control-effector capability (that is, more than one means of trimming out the forces and moments to obtain a steady-state flight condition). Most transport aircraft have significant capability in this area, though in some cases, minor modifications could be necessary. APO addresses a systematic means of utilizing of this capability. Controls and/or variables that can potentially play a role in optimization of performance of current and future transport aircraft include elevator, horizontal stabilizer, outboard aileron, inboard aileron, flaps, slats, rudder, center of gravity, and differential thrust. The key technological challenge to in-flight optimization of performance of transport aircraft is identification of incremental drag to an accuracy better than 1 percent.

Figure 2. The APO Algorithm analyzes flight data and adjusts symmetric aileron deflection to minimize drag.

An L-1011 airplane has been modified for use in a NASA program of flight research in APO for transport airplanes. The modifications (see Figure 1) consist of (1) addition of a research engineering test station; (2) addition of an actuator (one on each wing) to drive the outboard ailerons symmetrically; (3) addition of an instrumented trailing cone to obtain true static pressure; (4) connecting into the basic airplane instrumentation system to obtain engine, control surface, and other measurements; (5) addition of an embedded navigation system with Global-Positioning System (GPS) and inertial-navigation subsystems; (6) addition of a state-of-the-art airdata computer; and (7) addition of a data-recording system.

In the cruise mode, the APO algorithm commands a smooth, long-period excitation of a redundant control surface — specifically, a symmetric excitation of outboard ailerons. The forced excitation is smooth enough and of sufficient duration that the mach- and altitude-hold autopilot modes "mask" the quasi-steady pitching-moment drag changes that occur during maneuvers that involve changes in the throttle setting, stabilator angle, and/or angle of attack. The resultant data are analyzed to determine the minimum-drag configuration, and the redundant controller is configured appropriately (see Figure 2).

This work was done by Glenn B. Gilyard of Dryden Flight Research Center. For further information, access the Technical Support Package (TSP) free on-line at under the Machinery/Automation category, or circle no. 198 on the TSP Order Card in this issue to receive a copy by mail ($5 charge).

This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to the Technical Information Specialist, Dryden Flight Research Center; (805)258-3720. Refer to DRC-95-22.