X-31: Prelude to tailless flight? : Page 3 of 3

test points. A new control law version that incorporates added logic to emulate a tailless aircraft throughout the entire X-31 flight envelope will follow. The new version will add thrust control of the engine to the thrust-vector control, further enhancing aircraft response in the quasi-tailless mode.

After all quasi-tailless flight data have been evaluated, the X-31 will proceed with the next step in the follow-on program: physically reducing the size of the present vertical tail and rudder. Ability to control the aircraft should thrust vectoring fail will determine the new size of the tail and rudder. These tests will verify the quasi-tailless results with flight data from a truly destabilized airframe.

Finally, after installation of a deployable/retractable stabilization and control device, such as a flip-up, all-moving vertical fin, plans call for removing the vertical tail completely.

Where does this all lead? Post-stall performance has already attracted the attention of air forces around the world. Now, the possibility of replacing aircraft surfaces with vectored thrust capability promises substantial reduction in aircraft weight, aerodynamic drag, fuel consumption, and radar signature. While the latter is important to military personnel, less weight, drag, and fuel consumption are of significant interest to the commercial airline industry.

Militarily or commercially, if the results prove as good as they look, the X-31 program could eventually result in increased employment for aerospace engineers worldwide.

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