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VERTICAL TAKEOFF AND LANDING TECHNOLOGY: DR. JOHN ZUK 
Congressional Testimony, 05-09-2001

I am very pleased to have the opportunity to testify before you today on the subject of vertical and short takeoff and landing transport aircraft and their potential to revolutionize short haul air transportation. This class of vehicle, which would operate independent of conventional jets, could significantly increase airport capacity, reduce airport delays, and increase national mobility and accessibility. I will use NASA's experience and knowledge gained from vertical flight and powered lift research, using tiltrotor technology as a prime example, to inform you of the challenges and opportunities. I will present some quantified benefits from recently conducted studies. An alternative to building costly new runways at airports is desired.

One such way is Runway Independent Aircraft Operations (RIA Ops). If key challenges are met, RIA Ops could be expeditiously implemented at a low cost and become a practical way of meeting a class of the future air travel demand. RIA are defined to be types of aircraft that can operate on runways less than 3000 feet. These aircraft are characterized by excellent low- speed performance and control capabilities and capable of full- spectrum operations under Instrument Meteorological Conditions (IMC). They would use approach and departure corridors that are separate from conventional jets. RIA Ops could expand hub airport capacity and reduce delays without enlarging the airport physical boundaries or increasing the noise impact from these additional operations.

Runway Independent Aircraft could operate independent of jet transports at hub/spoke airports, by using stub runways, tarmac, and vertiports under IMC. Today, short takeoff and landing (STOL) aircraft, such as the deHavilland Dash 7, operate on stub runways at some airports, such as Washington Reagan. These aircraft may operate independent of the fixed wing jet transports in Visual Meteorological Conditions (VMC). However, these types of aircraft cannot operate independently in all conditions due to the lack of aircraft capability, approved flight procedures, and airspace/airport operations infrastructure. Under IMC, this class of vehicle, as well as helicopters, must be sequenced into conventional fixed wing traffic flows.

Typically, short-haul aircraft at large, hub airports comprise 40% of the total aircraft operations and are responsible for only 20% of the passengers. For each short-haul operation moved from the long runways to the RIA Ops landing and takeoff areas, one long-haul, large, jet transport could be added to the long runways. To enable RIA Ops, a new terminal procedure, called "Simultaneous Non-Interfering" (SNI), must be developed. The SNI procedures will also allow productive use of currently unused airspace over the airport. Two recently completed studies showed potentially large benefits of RIA Ops.

The NASA Intercenter Systems Analysis Team (ISAT) sponsored a FY 2000 study, conducted by Logistics Management Institute (LMI), to determine the impact of RIA replacing short-haul aircraft. Using LMINET, a 64-airport queuing model of the National Airspace System, the relative throughput improvement for CY 1997 would have been approximately 10% increase in operations without extreme short takeoff and landing (ESTOL) operations and up to 26% with ESTOL operations.

The LMI study also estimated the flight delay based on the FAA unconstrained demand forecasts for 2007 and 2022. All planned additional runways that have completed their environmental impact studies were included in the LMINET analysis. RIA were constrained to operate only at airports that could accommodate an independent RIA landing area at least 5000 feet from existing operational runways. RIA replaced both turboprop and regional jet revenue flights on flight segments of less than 500 miles. Results showed that RIA Ops could reduce the 2022 predicted delay by over 80%.

A 1999 Newark Airport Task Force study was undertaken to find ways of reducing delays and increasing Newark Airport capacity. The Task Force examined almost every conceivable possibility, from new technologies, equipment, and procedures, to a new runway. A future state was examined where there would be 100,000 more annual operations than today. Except for a new runway, a runway independent aircraft provided the greatest benefit. In terms of annual delay reduction costs, the tilt rotor benefit was estimated to be $900M, compared to a new runway benefit of $1.2B. In addition to operating among hub/spoke airports, these vehicles could operate to general aviation (GA) airports. This would enable a rapid expansion of airline service to areas that are not currently served. Hence, the air transportation system could readily transform to a more distributed system.

A rapid, more efficient service would be realized by landing closer to the terminal, thereby minimizing aircraft taxi time, noise and emissions. Thus RIA could increase national mobility and accessibility, with minimum environmental impact. In order to operate IMC, successful RIA must satisfy a variety of vehicle requirements. Based on knowledge gained from NASA tilt rotor technology program, I will now review some of the most important of these requirements. Recognizing the potential of the tilt rotor for airport congestion relief, beginning in FY 1994, NASA embarked on an eight-year Short Haul Civil Tilt rotor (SHCT) project, which ends this year.

The project goal is to overcome the principal inhibitors to enabling civil tilt rotor operations in the National Air Transportation System. Goal achievement would enable low-noise, safe operations for a forty-passenger commuter aircraft. V-22 technology was chosen as the baseline. I am pleased to say that the SHCT noise reduction goal of 12-dB from the baseline has been significantly exceeded. The combination of a Higher Harmonic Control source noise reduction and two segmented noise abatement flight procedures, has a potential total noise reduction of 20 dB, which is equivalent to a factor of four reduction in perceived loudness.

A future SHCT must fly in adverse weather, while maintaining airline levels of safety and minimizing noise impact. This means that Level I handling qualities (low workload) for normal flight operations under adverse weather and low-noise flight condition must be achieved. Also, acceptable (Level II) handling qualities with safe recovery must also be achieved under emergency conditions. This is critical for all RIA Ops. Much was learned from the SHCT project activity, which primarily used piloted simulations. The biggest challenge was to overcome the high- workload landing phase, where, in the tiltrotor`s case, a steep 9- deg. noise abatement approach is flown, under adverse weather conditions, into a tight landing area, and a loss of an engine occurs at the critical decision height. To make flying easier under these conditions, technologies such as controls, displays and procedures were developed.

The combination of these technologies with new landing procedures, found in piloted simulations, resulted in achieving the specific goal of Level I Handling Qualities for normal operations under adverse weather conditions, and acceptable (Level II) Handling Qualities with safe recovery under emergency conditions. Much of what was learned in the tilt rotor case can be applied to other RIA. Now I will address specific RIA landing and take-off performance characteristics. Runway Independent Aircraft range from vertical takeoff and landing (VTOL) to STOL. These include VTOL (e.g. helicopters - vertical take off), ESTOL (e.g. tilt rotors - runway length less than 500 ft), super STOL (civil variants of the Air Force's Advanced Tactical Transport - runway length less than 1000 ft), and STOL (runway length less than 1500 ft) aircraft. Although the passenger capacity of RIA aircraft would range from less than 20 to over a hundred, the operational niche is expected to take advantage of airports with runway lengths ranging from zero to 3000 feet.

For example, the NASA/Boeing Quiet Short Haul Research (QSRA) Aircraft, flown in the 1980`s, required only a 1500-foot runway. The QSRA had excellent low- speed handling qualities and was relatively quiet. Jet engine exhaust was directed over the wing, effectively shielding the ground from jet noise during takeoff. RIA Ops are possible today due to advances in communications, navigation, and surveillance, especially differential GPS and display technologies. Low installation and infrastructure cost combined with wide-area availability enables an expansion of precision instrument navigation and guidance. As I have previously mentioned, in order to enable RIA Ops, Simultaneous Non-Interfering procedures must be developed.

To achieve this capability, I will mention some technical issues that must be resolved.

1) What types of aircraft are best suited for RIA Ops?
2) What are the relationships between the performance of runway independent aircraft, including low-speed control capability, and the amount of controlled airspace required for independent Category IIIA operations in high air-traffic density?
3) How will environmental impact be mitigated?
4) What is the impact of RIA Ops on the future Air Traffic Management System?

By addressing these issues, the large benefits of Runway Independent Aircraft Operations could be achieved. In conclusion, Runway Independent Aircraft Operations are a potentially revolutionary way of operating at hub airports, offering an alternative to building new runways while providing needed community access from underutilized community airports. If key challenges are met, RIA Ops could be expeditiously implemented at a low cost and may represent a practical way to substantially address the future air travel demand and rapidly expand airline service to areas that are not currently served. In the more distant future, Runway Independent Aircraft could completely by-pass conventional large airports and operate between very small landing areas. These landing areas could be located much closer to travel demand centers and enable easy access to other modes of transportation.

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