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High Speed Research

Aircraft manufacturers of several nations are developing technology for the next plateau of international aviation competition: the long-range, environmentally-acceptable second generation supersonic passenger transport, which could be flying by 2010.

Predicting large-scale increases in demand for long-haul overwater passenger transportation early in the next century, market experts see a need for some 500 next generation supersonic transports worth an estimated $200 billion and 140,000 jobs.

This McDonnell Douglas conceptual design for a Mach 2.4 (1600 miles per hour) supersonic transport is sized to carry about 300 passengers over a distance of 5,000 nautical miles. A NASA/industry High Speed Civil Transport research effort is a first step toward determining whether such a plane can be economically viable and environmentally acceptable.

Capturing a major share of that market is vitally important to a U.S. aerospace industry that is transitioning from a traditionally defense-dominated product line to a commercially driven manufacturing activity. To help boost the industry's competitiveness, NASA is conducting a High Speed Research (HSR) program that addresses the highest priority, highest risk technologies for a High Speed Civil Transport (HSCT). The HSR program is intended to demonstrate the technical feasibility of the vehicle; the decision to proceed with full-scale development will be up to industry.

The program is being conducted as a national team effort with shared government/industry funding and responsibilities. The team includes NASA's Langley, Lewis and Ames Research Centers and Dryden Flight Research Center; engine manufacturers GE Aircraft Engines and Pratt & Whitney division of United Technologies; airframe manufacturers The Boeing Company, McDonnell Douglas Corporation and Rockwell North American Aircraft Division; other manufacturers; materials suppliers; and academic institutions.

Shown at a March 1996 rollout ceremony, the Russian TU-144LL supersonic flying laboratory is participating in NASA's High Speed Civil Transport research program.

The team has established a baseline design concept that serves as a common configuration for investigations. A full-scale craft of this design would have a maximum cruise speed of Mach 2.4, or about 1,600 miles per hour, only marginally faster than the currently operational Anglo-French Concorde supersonic transport. However, the HSCT would have about double the range and triple the passenger capacity of the Concorde, and it would operate at an affordable ticket price, estimated at 20 percent above comparable subsonic flight fares.

Phase I of the HSR program, which began in 1990 and continued through 1995, focused on environmental challenges: engine emission effects on the atmosphere, airport noise and the sonic boom. Much research remains to be accomplished in these and other areas, but Phase I established some clear lines of approach to major problems and spawned confidence among team members that environmental concerns can be satisfied.

Phase II, initiated in 1994, focuses on the technology advances needed for economic viability, principally weight reductions in every aspect of the baseline configuration, because weight affects not only the aircraft's performance but its acquisition cost, operating costs and environmental compatibility. In materials and structures, the HSR team is developing, analyzing and verifying the technology for trimming the baseline airframe by 30-40 percent; in aerodynamics, a major goal is to minimize air drag to enable a substantial increase in range; propulsion research looks for environment-related and general efficiency improvements in critical engine components, such as inlet systems. Phase II includes computational and wind tunnel analyses of the baseline HSCT and alternative designs. Other research involves ground and flight simulations aimed at development of advanced control systems, flight deck instrumentation and displays.

The Russian TU-144LL supersonic flight laboratory employs a mechanical system to "droop" the nose section. This technique is necessitated by the fact that the airplane lands nose high and pilots could not see the runway with the nose in standard flight position. The NASA/industry High Speed Research team is working on an alternative approach (see photo opposite).

In 1996, the HSR program moved beyond laboratory investigations into the actual supersonic flight realm through a NASA agreement with the Russian Tupolev Design Bureau, developers of the first supersonic transport, the TU-144, which first flew in passenger service in 1977. Under the agreement, a modified TU-144LL supersonic flying laboratory is providing up-to-date information of "real world" conditions in which the next generation supersonic transport will fly. The TU-144LL rolled out of its hangar on March 17 to begin a six-month, 32 flight test program.

The TU-144LL can fly at Mach 2.3, or about 1,500 miles per hour, close to the speed of the HSCT baseline concept (Mach 2.4) and is thus an ideal vehicle for NASA studies of high temperature materials and structures, acoustics, supersonic aerodynamics and supersonic propulsion.

The TU-144LL is one of 17 TU-144s built. The major modification for the HSR work is a change of engines. The original engines were replaced by newer and larger NK-321 augmented turbofans initially employed to power Tupolev's TU-160 Blackjack bomber. Among a number of other upgrades and modifications, the jetliner's passenger seats were removed to make room for the six NASA/U.S. industry experiments' instrumentation and data collection systems. Two additional experiments are to be conducted on the ground using a TU-144 engine.

The flight deck portion of the HSR program also progressed to flight status in 1996 with a series of tests to investigate a "synthetic vision" concept that could obviate the need for forward-facing cockpit windows. The reason for this departure from conventional design philosophy is the fact that a supersonic transport of the baseline configuration would land nose-high-as do the Concorde and the TU-144-with the flight deck 45 feet above the runway and more than 50 feet forward of the landing gear. In that position, the pilots have no view of the runway ahead of them.

Future jetliners may employ a design technique that eliminates forward-facing cockpit windows and substitutes a 3D computer-generated color display to give the pilots "synthetic vision" on takeoffs and landings. Already flight tested, this system could save thousands of pounds of weight that could be more productively used.

In the first generation supersonic transports-the Concorde and the TU-144-the forward vision problem was solved by use of a mechanism that lowers-or "droops"-the forward part of the nose section for takeoffs and landings and thereby affords a clear view forward. The mechanism, however, imposes a heavy weight penalty that is not considered acceptable for the second generation vehicle.

A potential solution devised by the HSR team is the external visibility system (EVS), a group of sensors and imaging systems that would feed large-format cockpit displays of high resolution imagery and computer graphics. The EVS could eliminate forward-looking cockpit windows and obviate the need for the heavy, expensive mechanical nose-drooping system.

In the second generation supersonic transport, the EVS could save thousands of pounds of droop mechanism weight, weight that could be used to allow increased passenger capacity or greater range. The synthetic vision system might also find utility in subsonic air transportation, allowing pilots to fly and land safely in low visibility conditions; that would enable increasing the number of flights in poor weather, reducing terminal delays and cutting costs for airlines and passengers.

The HSR synthetic vision system was tested in a series of flights in 1995-96 at NASA's Wallops (Virginia) Flight Facility and at Langley Air Force Base in Hampton, Virginia. Sensors tested included a digital video camera, three infrared cameras and two microwave radar systems. The tests were flown on Langley Research Center's Transport Systems Research Vehicle (TSRV), a Boeing 737 equipped with a windowless research cockpit in the passenger section in addition to the normal windowed cockpit, and in a Westinghouse BAC 1-11 avionics test aircraft.

The flight test program consisted of two phases. During the sensor data collection phase, the TSRV and the BAC 1-11 flew typical approach, cruise and holding patterns, testing the capability of the sensors to detect airborne traffic and ground objects. During the pilot-in-the-loop phase, the TSRV flew approaches and landings controlled from the research cockpit and tested the pilots' ability to control and land the aircraft relying only on sensor/computer-generated images and symbology.

All planned in-flight test points were achieved, and extensive data was collected from the radar, infrared and video sensors. More than 80 windowless piloted approaches and landings were successfully conducted by pilots from Langley and Ames Research Centers, Boeing and McDonnell Douglas. Initial pilot comments and performance reports were encouraging with respect to the feasibility of using sensor/symbology displays for flight path control.

In addition to the principal members of the HSR team, the flight deck research included Honeywell, Inc., Phoenix, Arizona; Rockwell Collins, Cedar Rapids, Iowa; FLIR Systems, Portland, Oregon; and Westinghouse Electric Corporation.