The Space Shuttle program took on the challenge of providing a manual landing capability for an operational vehicle returning from orbit. Some complex challenges were encountered in developing the longitudinal flying qualities required to land the Orbiter manually in an operational environment. Approach and landing test flights indicated a tendency of pilot-induced oscillation near landing. Changes in the operational procedures reduced the difficulty of the landing task, and an adaptive stick filter was incorporated to reduce the severity of any pilotinduced oscillatory motions. Fixed-base, moving-base, and in-flight simulations were used for the evaluations. In general, flight simulation proved to be the best means of assessing the low-speed longitudinal flying qualities problems. Overall, the Orbiter control system and operational procedures produced a good capability to perform routinely precise landings with a large, unpowered vehicle that has a low lift-to-drag ratio. Nomenclature ALT= approach and landing test DFBW = digital fly-by-wire FSAA = flight simulator for advanced aircraft L/D = lift-to-drag (ratio) PIO(s) = pilot-induced oscillation(s) STS = space transportation system TAEM = terminal area energy management TIPS = total in-flight simulator VMS = vertical motion simulator

An in-flight investigation of the effect of pure time delays on low LID space-shuttle-type landing tasks was undertaken. The results indicate that the sensitivity of the pilot ratings to changes in pure time delay in pitch is strongly affected by the task and only slightly affected by changes in control system augmentation mode. Low LID spot landings from a lateral offset were twice as sensitive to pure time delay as normal low LID landings. For comparison purposes, formation flying was also investigated and was found to be less sensitive to time delay than the landing tasks. AGL ASL c CAS C* DFBW g I Jy KIAS I' M ** PIO PR s SAS 7 A Nomenclature = above ground level = above sea level = mean aerodynamic chord = command augmentation system = N z -(V co /57.3g)q -L/qs -dC L /da = dC L /3d e -M/qsĉ dC m /(dqc/2V) = dC^/(dac/2V) = dC m /dd e= digital fly-by-wire = acceleration due to gravity = 32.2 ft/s 2 = prefix for improved system = pitch inertia, ft-lb-s 2 = indicated airspeed, knots = pitch rate feedback gain = lift force, Ib = pitching moment, ft-lb = normal acceleration, g = pilot-induced oscillation = pilot rating = pitch rate, deg/s or rad/s = dynamic pressure, lb/ft 2 = Laplace transform variable = stability augmentation system = time delay, s = true airspeed, ft/s = crossover velocity = 324 ft/s = angle of attack, rad = angle of attack rate, rad/s = flight-path angle, deg = increment

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