The Tu-144LL Handling Qualities Assessment

In Phase I, typical flights involved a climb and acceleration to supersonic speeds and cruise altitudes, 15 minutes of stable supersonic cruise, a descent and deceleration to subsonic cruise conditions for subsonic test points, and finally, approach and landing work.[1507] All 19 Phase I flights were accomplished by Tupolev crews. Flights 20 through 23 incorporated the NASA pilot evaluations at the beginning of Phase II. The descrip­tion of the Handling Qualities Assessment Experiment 2.4/2.4A will cen­ter on these flights, because they are of more special interest to NASA.[1508]

Working with Tupolev chief test pilot Sergei Borisov and project engi­neer Vladimir Sysoev, USPET developed a set of efficient handling qual­ities maneuvers to be used on these flights. These maneuver sets were derived from the consensus reached among USPET members regard­ing the highest-priority tasks from Mach 2 to approach and landing. To assist the pilots, specifically defined maneuvers were repeated for dif­ferent flight conditions and aircraft configurations. These maneuver sets included

• Integrated test block (ITB): The ITB was a standard block of maneuvers consisting of pitch attitude captures, bank captures, heading captures, steady heading sideslips, and a level acceleration/deceleration.

• Parameter identification (PID) maneuvers: The PID maneuvers generated either a sinusoidal frequency sweep or a timed pulse train in the axis of interest and contributed to the dataset needed for the LOES analysis.

• Simulated engine failure: This consisted of retarding an outboard throttle to minimum setting, stabilizing on a trimmed condition, and performing a heading capture.

• Slow flight: Accomplished in both level and turning flight, this maneuver was flown at minimum airspeed.

•

Structural excitation maneuvers: These maneuvers con­sisted of sharp raps on each control inceptor to excite and observe any aeroservoelastic response of the aircraft.

• Approaches and landings: Different configurations were specified to include canard retracted, lateral off­set, manual throttle, nose retracted (zero forward vis­ibility), simulated engine out, visual, and Instrument Landing System (ILS) approaches.52

Flight 20 was flown by an all-Russian crew but was observed from a control room at the Gromov Russian Federation State Scientific Center at the Zhukovsky Air Development Center.

This flight provided USPET with an excellent opportunity to observe Tu-144 planning and operations and prepared the team for the NASA piloted flights. With a better sense of Tupolev operations, USPET was able to develop English checklists and procedures to complement the Russian ones. Fullerton and Rivers learned all of the Russian-labeled
switches and controls and procedural calls. USPET made bound check­lists from the cardboard backs of engineering tablets, because office mate­rial was in short supply at that time in Russia. Flight 20 also allowed USPET engineers Jackson, Cox, and Princen and pilots Fullerton and Rivers to develop a working relationship with Tupolev project engineer Sysoev in developing the test cards for the U. S. flights. The stage was set for the first flight of a Tu-144 by a United States pilot.

Flight 21 was scheduled for September 15, 1998. Fullerton and Rivers agreed that Fullerton would pilot this flight and Rivers would observe from the cockpit, taking notes, timing maneuvers, and assisting with the crew coordination. As it turned out, Fullerton’s communications failed during the flight, and Rivers had to relay Tupolev pilot Sergei Borisov’s comments to Fullerton. Borisov sat in the left seat and Fullerton in the right; Victor Pedos occupied the navigator’s seat and Anatoli Kriulin the flight engineer’s station. Rivers stood behind Borisov and next to Pedos. Jackson and Cox had seats in the Gromov control room. Flight 21 was to be a subsonic flight with handling qualities maneuvers completed by Fullerton during the climb, Mach 0.9 cruise, descent, low-altitude slow – flight maneuvering, and approach and landing tasks. Because of the shortage of tires, each flight was allowed only one landing. The multiple approaches flown were to low approach (less than 200-feet altitude) only.

The flight is best described by the flight test summary contained in a NASA report titled "A Qualitative Piloted Evaluation of the Tu-144”:

Shortly after take-off a series of ITBs were conducted for the take-off and the clean configurations at 2 km altitude. Acceleration to 700 km/hr was initiated followed by a climb to the subsonic cruise condition of Mach 0.9, altitude 9 km. Another ITB was performed followed by evaluations of a simu­lated engine failure and slow speed flight. After descent to 2 km, evaluations of slow speed flight in the take-off and landing con­figurations were conducted as well as an ITB and a simulated engine failure in the landing configuration. Following a descent to pattern altitude three approaches to 60 m altitude were con­ducted with the following configurations: a canard retracted configuration using the ILS localizer, a nominal configuration with a 100 m offset correction at 140 m altitude, and a nom­inal configuration using visual cues. The flight ended with a visual approach to touchdown in the nominal configuration.

However, due to unusually high winds the plane landed right at its crosswind limit, necessitating the Russian pilot in com­mand to take control during the landing. Total flight time was approximately 2 hours 40 minutes. The maximum speed and altitude was 0.9 Mach and 9 km.53

The flight completed all test objectives. Thorough debriefs ensued, the obligatory postflight party sponsored by Tupolev was held, and USPET began intensive training and planning for the first supersonic flight, to be flown just 3 days later.

September 18 opened cool, clear, and much less gusty than the pre­ceding days. Flight 22 would be a Mach 2 mission to an altitude of 60,000 feet, with at least 20 minutes flight at twice the speed of sound. Rob Rivers was the NASA pilot for this flight. Pukhov’s only requirement for Rivers was that he no longer need his crutches by flight day. Two nights before, Bruce Jackson had helped Rivers practice using a cane for over an hour until Rivers was comfortable. At the next day’s preflight party, Rivers demonstrated to Pukhov his abilities without crutches, and his approval for the flight was assured. At 11:08 a. m. local time, the Tu-144 became airborne.

The flight is described below in Rivers’s original flight test report:

Flight Profile. The flight profile included takeoff and accelera­tion to 700 kilometers per hour (km/hr) to intercept the climb schedule to 16.5 kilometers (km) and Mach 2.0. The flight direction was southeast toward the city of Samara on the Volga River at a distance of 700 km from Zhukovsky. Approximately 20 minutes were spent at Mach 2.0 cruise which included an approximately 190 degree course reversal and a cruise climb up to a maximum altitude of 17.3 km. A descent and decel­eration to 9 km and Mach 0.9 was followed by a brief cruise period at that altitude and airspeed prior to descent to the traffic pattern at Zhukovsky Airfield for multiple approaches followed by a full stop landing on Runway 30.

Flight Summary. After all preflight checklists had been com­pleted, the evaluation pilot taxied Tu-144LL Serial Number

77144 onto Runway 12, and the brake burn-in process was accomplished. At 11:08 brakes were released for takeoff, power was set at 98° PLA (partial afterburner), the start brake was released, and after a 30 sec takeoff roll, the aircraft lifted off at approximately 355 km/hr. The landing gear was raised with a positive rate of climb, the canard was retracted out of 120 m altitude, and the nose was raised out of 1000 m altitude. The speed was initially allowed to increase to 600 km/hr and then to 700 km/hr as the Vertical Regime Indicator (VRI) profile was intercepted. Power remained at 72° PLA (maximum dry power) for the climb until Mach 0.95 and CG of 47.5% at which point the throttles were advanced to maximum power, 115° PLA. The climb task was a high work­load task due to the sensitivity of the head up pitch refer­ence indicator, the sensitivity of the pitch axis, and the continual change in CG requiring almost continuous lon­gitudinal trim inputs. Also, since the instantaneous center of rotation is located at the pilot station, there are no cock­pit motion cues available to the pilot for pitch rate or atti­tude changes. Significant pitch rates can be observed on the pitch attitude reference indicator that are not sensed by the pilot. During the climb passing 4 km, the first of a repeating series of bank angle captures (±15°) and control raps in all three axes (to excite any aircraft structural modes) was com­pleted. These maneuvers were repeated at 6 km and when accelerating through Mach 0.7, 0.9, 1.1, 1.4, and 1.8. The bank angle captures demonstrated rather high roll forces and relatively large displacements required for small roll angles. A well damped (almost deadbeat) roll mode at all airspeeds up to Mach 2.0 was noted. The control raps showed in gen­eral a higher magnitude lower frequency response in all three axes at subsonic speeds and lower magnitude, higher frequency responses at supersonic speeds. The pitch response was in general of lower amplitude and frequency with fewer over­shoots (2-3) than the lateral and directional responses (4-5 overshoots) at all speeds. Also of interest was that the axis exhibiting the flexible response was the axis that was perturbed, i. e., pitch raps resulted in essentially only pitch responses. The motions definitely seemed to be aeroservoelastic in nature,

and with the strong damping in the lateral and directional axes, normal control inputs resulted in well damped responses. Level off at 16.5 km and Mach 1.95 occurred 19 minutes after takeoff. The aircraft was allowed to accelerate to Mach 2.0 IMN as the throttles were reduced to 98° PLA, and a series of control raps was accomplished. Following this, a portion of the Integrated Test Block set of maneuvers consisting of pitch captures, steady heading sideslips, and a level decel­eration was completed. The pitch captures resulted in slight overshoots and indicated a moderate delay between pitch atti­tude changes and flight path angle changes. The steady head­ing sideslips showed a slight positive dihedral effect, but no more than approximately 5° angle of bank was required to maintain a constant heading. No unpleasant characteristics were noted. At this point the first set of three longitudinal and lateral/directional parameter identification (PID) maneuvers were completed with no unusual results. By this time a course reversal was necessary, and the bank angle and heading cap­ture portions of the ITB were completed during the over 180° turn which took approximately 7 min to complete at Mach

1. 95. During the inbound supersonic leg, two more sets of PID maneuvers with higher amplitude (double the first set) con­trol inputs were completed as were several more sets of con­trol raps. Maximum altitude achieved during the supersonic maneuvering was 17.3 km.

The descent and deceleration from Mach 2.0 and 17 km began with a power reduction from the nominal 98° PLA to 59° and a deceleration to 800 km/hr. During the descent bank angle captures (±30°) and control raps were accomplished at or about Mach 1.8, 1.4, 1.1, and 0.9 with similar results as reported above. The aircraft demonstrated increased pitch sensitivity in the transonic region decelerating through Mach

1.0. The pitch task during descent in following the VRI guid­ance was fairly high in workload, and the head-up pitch ref­erence indicator was very sensitive and indicated fairly large pitch responses from very small pitch inputs. Since the CG is being transferred aft during supersonic descent, frequent pitch trimming is required. A level off at 9 km at Mach 0.9 was accomplished without difficulty, and an ITB (as described

above) was completed. Further descents as directed by air traffic control placed the aircraft in the landing pattern with 32 metric tons of fuel, 6 tons above the planned amount.

Five total approaches including the final full stop land­ing were completed. These included a straight-in localizer only approach with the canard retracted; an offset approach with the nose raised until on final; a manual throttle off­set approach; a manual throttle straight-in approach; and a straight-in visual approach to a full stop landing. The first approach with the canard retracted was flown at 360 km/hr due to the loss of about 12 tons of lift from the retracted canards. Pitch control was not as precise in this configuration. There was also a learning curve effect as the evaluation pilot gained experience in making very small, precise pitch inputs which is necessary to properly fly the aircraft on approach and to properly use the pitch reference indicator. After terminating the approach at 60 m, a canard retracted, gear down low pass up the runway at 30-40 m was completed in accordance with a ground effects experiment requirement. The nose-up approach demonstrated the capability to land this aircraft with the nose retracted providing an angling approach with some sideslip is used. The offset approaches were not representative of the normal offset approaches flown in the HSR program since they are to low approach only and do not tax the pilot with the high gain spot landing task out of the corrective turn. No untow­ard pitch/roll coupling or tendency to overcontrol the pitch or roll axes was noted. The manual approaches were very interesting in that the Tu-144LL, though a back-sided air­plane on approach, was not difficult to control even with the high level of throttle friction present. The engine time con­stant appears reasonable. It was noted that a large pitching moment results from moderate or greater throttle inputs which can lead to overcontrolling the pitch axis if the speed is not tightly controlled and large throttle inputs are required. The full stop landing was not difficult with light braking required due to the decelerating effects of the drag parachutes. The flight terminated with the evaluation pilot taxiing the aircraft clear of the runway to the parking area. 16 tons of fuel remained.

All test points were accomplished, and several additional optional test points were completed since the flight remained ahead of the planned fuel burn. One additional approach was completed. The planned flight profile was matched very closely, and all flight objectives were achieved.54

Onboard recording was used to gather all of the data, because the flight profiles took the Tu-144LL far out of telemetry range. Subsequent to each flight, Tupolev would produce a data time history plot, including over a dozen measured parameters plotted on the vertical axis versus time on the horizontal axis. On one plot, the entire flight could quickly be viewed. From the plotted time histories, much additional data could be ascertained. By comparing fuel quantity expended versus time, for example, fuel flows could be determined. This contrasts with the meth­ods in NASA in which, with paper supplies not of concern, the practice

The Tupolev and NASA flightcrews after the completion of the last U. S. piloted evaluation flight, with Tu-144LL “Moscow" in the background. NASA.

is often to plot individual time histories. USPET members felt that this straightforward Tupolev method showed great merit.

Flight 23 was completed September 24, after several days of weather delays. Gordon Fullerton was the NASA evaluation pilot for this flight, which was very similar to flight 22. The only differences occurred at Mach 2, at which Fullerton simulated an engine failure at the beginning of descent from just over 10-mile altitude and in the landing pattern in which a clean pass was flown for a photographic opportunity, and two simulated engine failure approaches and an additional ILS approach were accomplished. All test objectives were achieved.

The USPET team was feted to a final postflight party and, jokingly, according to Professor Pukhov, was not allowed to leave until a prelim­inary report was completed. The U. S. team completed the report and departed September 26, with a mutual exchange of best wishes with the Tupolev Tu-144 project staff. Four more Phase II flights were completed with the Tupolev crew to gather more handling qualities data and data for the other six experiments. After Sergei Borisov shut down the engines following the last flight in winter 1999, the Tu-144 never flew again.

NASA TM-2000-209850 thoroughly describes the operational qual­ities of the Tu-144LL. A brief description will be presented here. The Tu-144 taxied much like a Boeing 747 with mild cockpit accelerations and nominal cockpit overshoots while turning. Throttle friction was extremely high because of the rerouted throttle cables for the retrofit­ted NK-321 engines. The engines had operational limits and restrictions, some peculiar to a specific engine, but they performed well through­out the flight envelope, were robust and forgiving at Mach 2 cruise, and responded well in the landing pattern. Takeoff acceleration was very rapid, and the takeoff speeds were quite high, as expected with unstick occurring at 220 mph after 30 seconds of ground roll. A very high ambi­ent noise level and moderate buffet were experienced, with the nose drooped to the 11-degree takeoff position and the canard extended. With the nose retracted, the forward view was blocked, and the view through the somewhat distorted and crazed side windows was poor. Because the rate dampers were required to be engaged at all times, the unaugmented characteristics of the aircraft were not investigated. Pitch forces were moderately heavy, and small pitch inputs resulted in significant longi­tudinal motion, creating a tendency to overcontrol the pitch axis. The lateral forces were high, and large displacements were necessary for small roll rates, resulting in poor pitch-roll harmony. Roll inputs would
often couple into undesired pitch inputs. With poor pitch cues because of the visibility issues mentioned earlier, the pilot relied on the Sensitive Pitch Angle Indicator for pitch control. The pitch axis was the high workload axis, and this was exacerbated by the rapid center-of-gravity changes because of fuel transfer balancing in the transonic range. Roll response was very well-damped, with no proverse or adverse yaw, even with large lateral inputs. Precise bank angle captures were easy to accomplish. The aircraft demonstrated positive speed stability. Rudder inputs produced a positive dihedral effect and were well-damped/ deadbeat, but rudder pedal forces were very high. Full pedal deflection required 250-300 pounds of force. All of these characteristics were invariant with speed and configuration, except for the slightly degraded handling qualities near Mach 1. With the exception of the heavy con­trol forces (typical of Russian airplanes), the Tu-144 possessed adequate to desirable handling qualities. This result disputed the data taken in Phase I and led engineers to uncover the artificial 0.25-second time delay in the Damien DAS that produced such questionable handling qualities data.