NASA's Contributions to Aeronautics, Volume 2 by National Aeronautics & Space Administration. - HTML preview

CASE

15

NASA’s Flight Test of the Russian Tu-144 SST

Robert A. Rivers

The aeronautics community has always had a strong international flavor.

This case study traces how NASA researches in the late 1990s used a Russian supersonic airliner, the Tupolev Tu-144LL—built as a visible symbol of technological prowess at the height of the Cold War—to derive supersonic cruise and aerodynamic data. Despite numerous technical, organizational, and political challenges, the joint research team obtained valuable information and engendered much goodwill.

Case-15 Cover Image: Tupolev-144 SST on takeoff from Zhukovsky Air Development Center in Russia with a NASA pilot at the controls. NASA.

On a cool, clear, and gusty September morning in 1998, two NASA research pilots flew a one-of-a-kind, highly modified Russian Tupolev Tu-144LL Mach 2 Supersonic Transport (SST) side by side with a Tupolev test pilot, navigator, and flight engineer from a formerly secret Soviet-era test facility, the Zhukovsky Air Development Center 45 miles southeast of Moscow, on the first of 3 flights to be flown by Americans.[1] These flights in Phase II of the joint United States-Russian Tu-144 flight experiments sponsored by NASA’s High-Speed Research (HSR) program were the culmination of 5 years of preparation and cooperation by engineers, technicians, and pilots in the largest joint aeronautics program ever accomplished by the two countries. The two American pilots became the first and only non-Russian pilots to fly the former symbol of Soviet aeronautics prowess, the Soviet counterpart of the Anglo-French Concorde SST.

They completed a comprehensive handling qualities evaluation of the Tu-144 while 6 other experiments gathered data from hundreds of onboard sensors that had been painstakingly mounted to the airframe in the preceding 3 years by NASA, Tupolev, and Boeing engineers and technicians. Only four more flights in the program awaited the Tu-144LL, the last of its kind, before it was retired. With the removal from service of the Concorde several years later, the world lost its only supersonic passenger aircraft and witnessed the end of an amazing era.

This is the story of a remarkable flight experiment involving the United States and Russia, NASA and Tupolev, and the men and women who worked together to accomplish a series of unique flight tests from late 1996 to early 1999 while overcoming numerous technical, programmatic, and political obstacles. What they accomplished in the late 1990s cannot be accomplished today. There are no more Supersonic Transports to be used as test platforms, no more national programs to explore commercial supersonic flight. NASA and Tupolev established a benchmark for international cooperation and trust while producing data of incalculable value with a class of vehicles that no longer exists in a regime that cannot be reached by today’s transport airplanes.[2]

HSR and the Genesis of the Tu-144 Flight Experiments

NASA’s High-Speed Research program was initiated in 1990 to investigate a number of technical challenges involved with developing a Mach 2+ High-Speed Civil Transport (HSCT). This followed several years of NASA-sponsored studies in response to a White House Office of Science and Technology Policy call for research into promoting long-range, high-speed aircraft. The speed spectrum for these initial studies spanned the supersonic to transatmospheric regions, and the areas of interest included economic, environmental, and technical considerations. The studies suggested a viable speed for a proposed aircraft in the Mach 2 to Mach 3.2 range, and this led to the conceptual model for the HSR program. The initial goal was to determine if major environmental obstacles—including ozone depletion, community noise, and sonic boom generation—could be overcome. NASA selected the Langley Research Center in Hampton, VA, to lead the effort, but all NASA aeronautics Centers became deeply involved in this enormous program. During this Phase I period, NASA and its industry partners determined that the state of the art in high-speed design would allow mitigation of the ozone and noise issues, but sonic boom alleviation remained a daunting challenge.[3]

Encouraged by these assessments, NASA began Phase II of the HSR program in 1995 in partnership with Boeing Commercial Airplane Group, McDonnell-Douglas Aerospace, Rockwell North American Aircraft Division, General Electric Aircraft Engines, and Pratt & Whitney. By this time, a baseline concept had emerged for a Mach 2.4 aircraft, known as the Reference H model and capable of carrying 300 passengers nonstop across the Pacific Ocean. A comprehensive list of technical issues was slated for investigation, including sonic boom effects, ozone depletion, aeroacoustics and community noise, airframe/propulsion integration, high lift, and flight deck design. Of high interest to NASA Langley Research Center engineers was the concept of Supersonic Laminar Flow Control (SLFC). Maintaining laminar flow of the supersonic airstream across the wing surface for as long as possible would lead to much higher cruise efficiencies. NASA Langley investigated SLFC using wind tunnel, computational fluid dynamics, and flight-test experiments, including the use of NASA’s two F-16XL research aircraft flown at NASA Langley and NASA Dryden Flight Research Centers. Unfortunately, the relatively small size of the unique, swept wing F-16XL led to contamination of the laminar flow by shock waves emanating from the nose and canopy of the aircraft. Clearly, a larger airplane was needed.[4]

That larger airplane seemed more and more likely to be the Tupolev Tu-144 as proposals devolved from a number of disparate sources, and a variety of serendipitous circumstances aligned in the early 1990s to make that a reality. Aware of the HSR program, the Tupolev Aircraft Design Bureau as early as 1990 proposed a Tu-144 as a flying laboratory for supersonic research. In 1992, NASA Langley’s Dennis Bushnell discussed with Tupolev this possibility of returning to flight one of the few remaining Tu-144 SSTs as a supersonic research aircraft. Pursuing Bushnell’s initial inquiries, Joseph R. Chambers, Chief of Langley’s Flight Applications Division, and Kenneth Szalai, NASA’s Dryden Flight Research Center Director, developed a formal proposal for NASA Headquarters suggesting the use of a Tu-144 for SLFC research. Szalai discussed this idea with his friend Lou Williams, of the HSR Program Office at NASA Headquarters, who became very interested in the Tu-144 concept. NASA Headquarters had, in the meantime, already been considering using a Tu-144 for HSR research and had contracted Rockwell North American Aircraft Division to conduct a feasibility study. NASA and Tupolev officials, including Ken Szalai, Lou Williams, and Tupolev chief engineer Alexander Pukhov, first directly discussed the details of a joint program at the Paris Air Show in 1993, after Szalai and Williams had requested to meet with Tupolev officials the previous day.[5] The synergistic force ultimately uniting all of this varied interest was the 1993 U.S.–Russian Joint Commission on Economic and Technological Cooperation. Looking at peaceful means of technological cooperation in the wake of the Cold War, the two former adversaries now pursued programs of mutual interest. Spurred by the Commission, NASA, industry, and Tupolev managers and researchers evaluated the potential benefits of a joint flight experiment with a refurbished Tu-144 and developed a prioritized list of potential experiments. With positive responses from NASA and Tupolev, a cooperative Tu-144 flight research project was initiated and an agreement signed in 1994 in Vancouver, Canada, between Russian Prime Minister Viktor Chernomyrdin and Vice President Al Gore. Ironically, Langley’s interest in SLFC was not included in the list of experiments to be addressed in this largest joint aeronautics research project between the two former adversaries.[6] Ultimately, seven flight experiments were funded and accomplished by NASA, Tupolev, and Boeing personnel (Boeing acquired McDonnell-Douglas and Rockwell’s aerospace division in December 1996). Overcoming large distances, language and political barriers, cultural differences, and even different approaches to technical and engineering problems, these dedicated researchers, test pilots, and technicians accomplished 27 successful test flights in 2 years.

The Tu-144 Flight Experiments Project

While negotiations were underway in 1993, leading to the agreement between the United States and Russia to return a Tu-144D to flight status as a supersonic flying laboratory, the HSR Program Office selected NASA Dryden to establish a Project Office for all Tu-144 activities. This initially involved developing a rapport with a British company, IBP, Ltd., which served as the business representative for Tupolev, now known as the Tupolev Aircraft Company (or Tupolev ANTK) after the economic evolution in Russia in the 1990s. Ken Szalai and IBP’s Judith DePaul worked to establish an effective business relationship, and this paid dividends in the ensuing complex relationships involving NASA, Rockwell, McDonnell-Douglas, Boeing, Tupolev, and IBP. A degree of cooperation flourished at a level not always observed in NASA–Russian partnerships. Having a business intermediary such as IBP navigate the paths of international business helped ensure the success of the Tu-144 experiment, according to Dryden Tu-144 Project Manager Russ Barber.[7]

Originally, the Tu-144 flight experiment was envisioned as a 6-month, 30-flight program.[8] As events unfolded, the experiment evolved into a two-phase operation. This was due, in part, to the inevitable delays in an enterprise of this magnitude and complexity, to learning from the results of the initial experiments, and to data acquisition issues.[9] By 1995, after two meetings in Russia,the HSR Program Office, Boeing, Rockwell, McDonnell-Douglas, and Tupolev established the requirements for returning a Tu-144D to flight and fabricating an instrumentation system capable of supporting the postulated lineup of experiments.[10] From a list of some 50 proposed experiments, the NASA, industry, and Tupolev officials selected 6 flight experiments for inclusion (a 7th was later added).[11]

A somewhat complex international organization developed that, despite the superficial appearance of duplication, ended up working very smoothly. NASA Dryden represented the HSR Program Office as the overseer for all Tu-144 activity. Boeing was contracted to install the instrumentation system, a complex task with over 700 individual pressure transducers, accelerometers, thermocouples, boundary layer rakes, pressure belts, microphones, and other sensors. NASA Dryden installed a complex French-built Damien digital data acquisition system (DAS) for five of the original six experiments.[12] The remaining experiment, a NASA Langley Structure/Cabin Noise experiment, used its own Langley-built DAS.[13] In a sense, traditional roles had to be adjusted, because Boeing, as the contractor, directed NASA, as the Government Agency and supplier, when to provide the necessary sensors and DAS.[14] Boeing and Tupolev would install the sensors, and NASA would then calibrate and test them. The Damien DAS ultimately became problematic and led to some erroneous data recording in Phase I.[15]

Tupolev assumed the role of returning the selected Tu-144D, SSSR-771114, to flight. This was no trivial matter. Even though 771114 had last flown in 1990, the engines were no longer supported and had to be replaced (as discussed in a subsequent section), which necessitated major modifications to the engine nacelles, elevons, and flight deck.[16] As Tupolev was completing this work in 1995 and 1996, IBP acted as its business interface with NASA and Boeing.

In general, the HSR program funded the American effort. The cost to NASA for the Tu-144 flight experiment was $18.3 million for 27 flights. Boeing contributed $3.3 million, and it is estimated that Tupolev spent $25 million.[17] Tupolev gained a fully instrumented and refurbished Tu-144, but unfortunately, after NASA canceled the HSR program in 1999, Tupolev could find no other customers for its airplane.

During the initial program definition and later during the aircraft modification, a number of HSR, Dryden, and Langley personnel made numerous trips to Zhukovsky. HSR managers coordinated program schedules and experiment details, Dryden personnel observed the return to flight efforts as well as the instrumentation modifications and provided flight operations inputs, and Langley instrumentation technicians and researchers assisted with their experiment installation. Among the Dryden visitors to Zhukovsky was NASA research pilot Gordon Fullerton. Fullerton was the NASA pilot interface during these development years and worked with his Tupolev counterparts on flight deck and operational issues. In an interview with the author, he recalled the many contrasts in the program regarding the Russian and American methods of engineering and flight operations. Items worthy of minute detail to the Russians seemed trivial at times to the Americans, while American practices at times resulted in confused looks from the Tupolev personnel. By necessity, because of a lack of computer assets, the Tupolev pilots, engineers, and technicians worked on a “back of the envelope” methodology. Involvement of multiple parties in decisions was thus restricted simply because of a lack of easy means to include them all. Carryovers from the Soviet days were still prevalent in the flightcrew distribution of duties, lack of flight deck instrumentation available to the pilots, and ground procedures that would be viewed as wholly inefficient by Western airlines. Nevertheless, Tupolev produced an elegant airplane that could fly a large payload at Mach 2.[18]

As the American and Russian participants gained familiarity, a spirit of trust and cooperation developed that ultimately contributed to the project’s success. The means of achieving this trust were uniquely Russian. As the various American delegations arrived in Moscow or Zhukovsky, they were routinely feted to gala dinners with copious supplies of freely offered vodka. This was in the Russian custom of becoming acquainted over drinks, during which inhibitions that might mask hidden feelings were relaxed. The custom was repeated over and over again throughout the program. Few occasions passed without a celebratory party of some degree: preflight parties, postflight parties, welcoming parties, and farewell parties were all on the agenda. Though at times challenging for some of the American guests who did not drink, these social gatherings were very effective at cementing friendships among two peoples who only a few years before uneasily coexisted, with all of their respective major cities targeted by the other’s missiles. To a person, the Americans who participated in this program realized that on a personal level, the Russians were generous hosts, loyal friends, and trusted colleagues. If nothing else, this was a significant accomplishment for this program.

Nineteen flights were completed by early 1998, achieving most of the original program goals. However, some data acquisition problems had rendered questionable some of the data from the six experiments.[19] The HSR Program Office decided that it would be valuable to have United States research pilots evaluate the Tu-144 in order to develop corporate knowledge within NASA regarding SST handling qualities and to ascertain if the adverse handling qualities predicted by the data collected actually existed. Furthermore, there were additional data goals developed since the inception of the program, and a seventh experiment was organized. The resumption of the test flights was scheduled for September 1998. The HSR Program Office and Boeing selected Gordon Fullerton from Dryden and NASA research pilot Robert A. Rivers from Langley as the evaluation pilots. Fullerton had been the Dryden project pilot for the Tu-144 modification and refurbishment, and he was familiar with the Tupolev flightcrews and the airplane. Rivers had been the HSR project pilot for several years, had participated in every HSR flight simulation experiment, served on two HSR integrated test development teams, and had performed an extensive handling qualities evaluation of the Concorde SST the previous year. To accompany them to Zhukovsky were two NASA flight control engineers, Timothy H. Cox from Dryden and E. Bruce Jackson from Langley, and Boeing Tu-144 project handling qualities engineer Norman H. Princen. Jackson had completed extensive work on flight control development for the HSCT Reference H model. During summer 1998, the team members worked together to develop a draft test plan, flew both the Ames and Langley 6-degree-of-freedom motion simulators with the Reference H model, and began studying the Tu-144 systems with the rudimentary information available in the United States at that time. On September 4, they departed for Zhukovsky.

Onsite in Zhukovsky

The United States Pilot Evaluation Team (USPET)[20] arrived in Moscow on Sunday, September 6, 1998, and was met by Professor Alexander Pukhov and a delegation of Tupolev officials. (Ill fortune had struck the team when NASA Langley research pilot Robert Rivers severely broke his right leg and ankle 2 weeks before departure. Because visas for work in Russia required 60 days' lead time and because no other pilot could be prepared in time, Rivers remained on the team, though it required a great deal of perseverance to obtain NASA approval. Tupolev presented relatively few obstacles, by contrast, to Rivers’s participation.) Pukhov was the Tupolev Manager for the Tu-144 experiment and a former engineer on the original design team for the airplane. At Pukhov’s insistence, USPET was billeted in Zhukovsky at the former KGB sanitarium. Sanitaria in the Soviet Union were rest and vacation spas for the various professional groups, and the KGB sanitarium was similar to a large hotel. The sanitarium was minutes from the Zhukovsky Air Development Center and saved hours of daily commute time that otherwise might have been wasted had the team been housed in Moscow.

The next day began a very intense training period lasting 2 weeks but was punctuated September 15 by the first flight by American pilots, a subsonic sojourn. The training was complicated by the language differences but was facilitated by highly competent Russian State Department translators. Nevertheless, humorous if not frustrating problems arose when nontechnical translators attempted to translate engineering and piloting jargon with no clear analogs in either language. The training consisted of one-on-one sitdown sessions with various Tu-144 systems experts using manuals and charts written in Russian. There were no English language flight or systems manuals for the Tu-144, and USPET’s attempt over the summer to procure a translated Tu-144 flight manual was unsuccessful. Training included aircraft systems, life support, and flight operations. Because flights would achieve altitudes of 60,000 feet and because numerous hull penetrations had occurred to accommodate the instrumentation system, all members of the flightcrew wore partial pressure suits. Because of the experimental nature of the flights, a manual bailout capability had been incorporated in the Tu-144. This involved dropping through a hatch just forward of the mammoth engine inlets. The hope was that the crewmember would pass between the two banks of engines without being drawn into the inboard inlets. Thankfully, this theory was never put to the test.

Much time was spent with the Tupolev flightcrew for the experiment, and great trust and friendship ensued. Tupolev chief test pilot Sergei Borisov was the pilot-in-command for all of the flights. Victor Pedos was the navigator, in actuality a third pilot, and Anatoli Kriulin was the flight engineer. Tupolev’s chief flight control engineer, Vladimir Sysoev, spent hours each day with USPET working on the test plan for each proposed flight. Sysoev and Borisov represented Tupolev in the negotiations to perform the maneuvers requested by the various researchers.[21] An effective give-and-take evolved as the mutual trust grew. From Tupolev’s perspective, the Tu-144 was a unique asset, into which the fledgling free-market company had invested millions of dollars. It provided badly needed funds at a time when the Russian economy was struggling, and the payments from NASA via Boeing and IBP were released only at the completion of each flight. The Tupolev crewmembers could not afford to risk the airplane. At the same time, they were anxious to be as cooperative as possible. Careful and inventive planning resulted in nearly all of the desired test points being flown.

The Aircraft: Tu-144LL SSSR-771114

The Tu-144 was the world’s first Supersonic Transport, when it took off from Zhukovsky Airfield on December 31, 1968. The design of the aircraft had commenced in early 1963, after the Soviet Union selected the Tupolev Design Bureau for the task. The famed Andrei Tupolev named his son Aleksei Tupolev to be chief designer, and over 1,000 staff members from other design bureaus were temporarily assigned to Tupolev for this project of national prestige.[22] For the researchers to evaluate the wing design, a Mig-21 fighter was configured with a scaled model of the wing for in-flight testing. The prototype was completed in the summer of 1968, and in December of that year, Eduard Yelian piloted serial No. SSSR-68001on the Tu-144’s first flight. The Tu-144 first exceeded the speed of sound on June 5, 1969 and achieved speeds in excess of Mach 2.0 on May 26, 1970, in every case just beating Concorde.[23]

The prototype was displayed at the Paris Air Show for the first time in June 1971. Tragically, the second production aircraft crashed spectacularly at the 1973 Paris Air Show. This, in combination with range capabilities only about half of what was expected (2,200 miles versus 4,000 miles), led to Aeroflot (the Soviet national airline company) having a diminishing interest in the aircraft. Still, a number of significant modifications to the aircraft occurred in the 1970s. The engine nacelles were move farther outboard, necessitating the relocation of the main landing gear to the center of the nacelles, and the original Kuznetsov NK-144 engines were replaced by Kolesov RD-36-51A variants capable of 44,092 pounds of thrust with afterburner. With these engines, the type was redesignated the Tu-144D, and serial No. SSSR-74105, the fifth production aircraft, first flew with the new engines in November 1974. Cargo and mail service commenced in December 1975, but Aeroflot crews never commanded a single Tu-144. Only Tupolev test pilots ever flew as pilots-in-command. On November 1, 1977, the Tu-144 received its certificate of airworthiness, and passenger service commenced within the Soviet Union. Ten percent larger than the Concorde, the Tu-144 was configured with 122 economy and 11 first-class passenger seats. Only two production aircraft served on these passenger routes. The service was terminated May 31, 1978, after the first production Tu-144D crashed on a test flight from Zhukovsky while making an emergency landing because of an in-flight fire. After this crash, four more Tu-144s were produced but were used only as research aircraft. Two continued flying until 1990, including SSSR-771114. The fleet of 16 flyable aircraft accumulated 2,556 flights and 4,110 flying hours by 1990.[24]

After the 1994 U.S.–Russian agreement enabling the HSR Tu-144 flight experiments, SSSR-77114 was selected to be refurbished for flight. The final production aircraft, 77114, was built in 1981 and flew only as a research aircraft, before being placed in storage in 1990. Amazingly, it had only accumulated 83 flight hours at that time. Because the RD-36-51A engines were no longer being produced or supported, Tupolev switched to the Kuznetsov NK-321 engines from the Tu-160 Blackjack strategic bomber as powerplants. [25] Redesignated the Tu-144LL, or Flying Laboratory, 77114 first flew under the command of Tupolev test pilot Sergei Borisov on November 29, 1996.[26]

The Tu-144, although it seems outwardly similar to the Concorde, was actually about 10-percent larger, with a different wing and engine configuration, and with low-speed retractable canard control surfaces that the Concorde lacked. It also solved the many challenges to sustained high-altitude, supersonic flight by different means. Where documentation in the West is complete with Concorde systems and operations manuals and descriptions, NASA and Boeing engineers and pilots could find no English counterparts for the Tu-144. This was due in part to the secrecy of the Tu-144 development in the 1960s and 1970s. Therefore, it is worth briefly describing the systems and operation of the Tu-144 in this essay.

This system description will also give insight into the former Soviet design philosophies. It should be noted that many of the systems on the Tu-144LL were designed in the 1960s, and though completely effective, were somewhat dated by the mid to late 1990s.[27]

The Tu-144LL is a delta platform, low wing, four engine Supersonic Transport aircraft. Features of interest included a very high coefficient of lift retractable canard and three position-hinged nose structure. The retractable canard is just aft of the cockpit on top of the fuselage and includes both leading- and trailing-edge flaps that deflect when the canard is deployed in low-speed flight. The only aerodynamic control surfaces are 8 trailing-edge elevons, each powered by two actuators and upper and lower rudder segments. The nominal cockpit crew consisted of two pilots, a navigator situated between the two pilots, and a flight engineer seated at a console several feet aft of the navigator on the right side of the aircraft.

The Tu-144LL was 215 feet 6 inches long with a wingspan of 94 feet 6 inches and a maximum height at the vertical stabilizer of 42 feet 2 inches. Maximum takeoff weight was 447,500 pounds, with a maximum fuel capacity of 209,44