NASA Technical Memorandum 100035 Civil Applications of High-speed Rotorcraft and Powered-Lift Aircraft Configurations James A. Albers John Zuk, Ames Research Center, Moffett Field, California October 1987 National Aeronautics and Space Administration Ames Research Center Moffett Field, California 94035 ABSTRACT advanced helicopters to high-disk-loading direct Advanced subsonic vertical and short takeoff lift aircraft are discussed, including high-speed and landing (V/STOL) aircraft configurations rotorcraft, subsonic V/STOL aircraft, and sub- offer new transportation options for civil appli- sonic STOL aircraft. Future transportation cations. This paper describes a range of opportunities, along with VTOL and STOL transpor- vehicles from low-disk to high-disk loading air- tation systems, are described. The various con- craft, including high-speed rotorcraft, V/STOL figurations are compared and their advantages are aircraft, and short takeoff and landing (STOL) highlighted. This report indicates that these aircraft. The status and advantages of the vari- aircraft can satisfy many transportation require- ous configurations are described. Some of these ments and that they could be of a great benefit configurations show promise for relieving conges- to civil transportation. tion in high population density regions and pro- viding transportation opportunities for low popu- V/STOL TRANSPORTATION OPPORTUNITIES lation density regions. V/STOL aircraft can provide congestion relief for existing airports of densely populated WORLDWIDE, THERE IS A STRONG DESIRE to improve areas and have great potential as economic tools each nation's economy and quality of life. for developing regions. First, future transpor- Future world population growth, along with devel- tation opportunities for high-population density oping countries' desires to become highly indus- regions will be briefly discussed. trialized, requires efficient transportation HIGH POPULATION DENSITY REGIONS - As ground system. As always, it will be highly desirable congestion increases, short-haul intercity air to transport people and high-value cargo as transportation should increase in importance, rapidly and as economically as possible. Many primarily because of the importance of time to regions of the world lack suitable ground trans- the traveler and the growing efficiency, flexi- portation systems and have formidable geographic bility, reliability, and wider distribution of barriers. In urban developed areas, both ground air transportation services. However, the addi- congestion and air congestion around existing tion of new, large, and conveniently located airports will become severe. In most areas it is airports will be increasingly constrained by difficult, if not impossible, to expand airports, environmental, ground access, and economic fac- particularly because of the congestion and tors. Making better use of existing transporta- noise. Fortunately, there is a solution to these tion hubs and secondary and small community air- transportation problems--V/STOL aircraft. Tech- ports will become increasingly more important to nology advances in materials, propulsion, aerody- avoid serious air transportation congestion and namics, controls, guidance, and the integration ultimately business and economic stagnation. In of these technologies are yielding many promising the future, even with the use of advanced air designs that show the potential for revolutioniz- traffic control technology and wide-body aircraft ing short-haul transportation. technology, runway capacity limits will be Promising designs, including the state of reached in many of the major hub airports. development of the configurations, are described; A good example of current and future air The full range of vehicles from low-disk-loading congestion can be found in the United States. 1 Aviation in the U.S. is highly concentrated, and highways enabling a highly efficient intermodal airline hubs have become popular since deregula- transfer. Existing urban and remote heliports tion of the airline industry in 1978. Under this can also be used for most V/STOL aircraft. Cou- practice, passengers from a number of cities are pling these facility possibilities with existing funneled into a central location, where they general aviation airports, means an extensive change planes for their final destination. This vertiport ground-facility system could be availa- hub concept allows the airlines to fill the ble. Figure 2 is an artist's rendition of an planes but strains the air-traffic control and airport expansion possibility where an airport is runway system. In 1978, the airlines carried saturated with CTOL traffic and is constrained 275 million passengers; in 1987 the total is from expanding externally. V/STOL aircraft can expected to be more than 450 million. Airlines provide high-frequency, short- and medium-haul logged an average of 2000 hours of delays per day service, operating on vertipads or short runways in 1986. Operations at 17 large metropolitan and that generally can be placed on existing air- regional airports exceeded their practical annual ports. The CTOL runways can then be used for the capacity thus leading to an unacceptabe number of longer-haul, wide-body aircraft. Thus, the air- delays. Air travel is predicted to continue port capability can be greatly increased. growth at over 5% a year. As a result, opera- V/STOL aircraft offer a distinct advantage tions at some 65 major U.S. airports are pre- over the CTOL aircraft in impacted terminal-area dicted to exceed capacity before the year 2000. real estate because of the inherent characteris- Besides being a great inconvenience to the tics of V/STOL aircraft to descend and climb at traveller, the monetary costs of these delays is steep gradients. For example, a V/STOL aircraft high. In 1984, the Council of Airport Operators can make an approach to the touchdown zone on a estimates the delays cost air carriers and pas- runway or landing pad at a spiraling descent sengers over $3.2 billion. In 1987, delays have gradient of up to 9". whereas the normal descent increased to the point of being equivalent to gradient for approach to a landing by a CTOL suspending all conmiercial air service for aircraft is 3". On ascent, V/STOL aircraft can one month. follow an equally steep ascent gradient. Even with the current airport congestion and Furthermore, the characteristics of the large anticipated growth, the prospects are cur- V/STOL aircraft make feasible a curving approach rently not very good for building large new air- (or departure) in both VFR and IFR conditions ports because of environmental concerns, availa- (assuming suitable microwave landing navigation bility of suitable real estate, and costs. The facilities) which can provide considerable bene- Dallas-Fort Worth airport, constructed in 1974, fits to and flexibility in the ATC System. For was the last mafor airport built in the U.S. example, after entering the terminal area, an This airport covers about 18,000 acres, but some arriving V/STOL aircraft can proceed on a dis- aviation analysts believe major new airports crete three-dimensional routing to its initial would need 25,000 to 30,000 acres to ensure approach fix. Thereafter, the V/STOL aircraft enough of a noise buffer to avoid restrictions on can make a curving approach going downwind, par- flights. allel to the V/STOL runway, at the same time To reduce the results of airport saturation, descending at a steep gradient to touchdown point conmiunities will have to effectively use existing for a landing. Also, by applying advances in hub and secondary airports, and should consider active control, navigation and guidance systems the high payoff transportation opportunity along with cockpit automation, a V/STOL aircraft offered by V/STOL aircraft. V/STOL aircraft can be preprogrammed to fly a minimal environmen- terminal flight-path control capability will tal impact flightpath. allow the use of helicopter terminal-area flight LOU POPULATION DENSITY REGION - Future rules so that they will pose no additional burden V/STOL aircraft economic development opportuni- to crowded airports. ties include passenger service, agriculture prod- Significant airport relief can be obtained ucts, emergency services, mineral development through the use of these vehicles when they do transport, law enforcement, fishing, and high- not use existing airports, but instead carry value cargoes (l).* An example of a region which passengers almost point-to-point using verti- has many V/STOL opportunities is the Pacific ports. Figure 1 illustrates potential V/STOL Basin (2). V/STOL aircraft should be suited as a aircraft landing facilities. These include sea- passenger and high-value-cargo transport for ports along rivers or lakes that my use existing areas that lack ground transportation systems piers or barges, facilities located adjacent to or above other existing transportation modes, such as railroads, light rail or subways; and 'Numbers in parentheses designate references at end of paper. 2 which are expensive to build or maintain. Unde- independent STOL ports consisting of one or more veloped natural resources are a characteristic of ST9L runways situated at a site removed from a some remote regions. Another characteristic is CTOL airport. the relatively short and unimproved existing STOL aircraft offer a distinct advantage airport runways. Ventures that seem particularly over the CTOL aircraft by using shorter runways suited for such aircraft include mining indus- because