URBAN AV OPS
Variety of V/STOL design concepts could herald age of urban aviation
As world population continues to rise, long runways and space to accommodate them are increasingly unavailable.
NASA concept for a 100,000-lb civil transport capable of carrying 80–100 passengers at 300 kts or more.
Earlier planning theories suggested that airport congestion might be relieved to some extent by more direct interurban air transportation over distances up to 500 nm between airports or—preferably—between urban areas themselves.
A detailed study of civil tiltrotor potential, updated by Boeing in 1991, concluded that a pressurized, 39-passenger derivative of the V22 Osprey had "significant market potential." Notably, New York Airways at its peak carried only 267,000 passengers, variously operating 25-seat Boeing Vertol 107 and 28-seat Sikorsky S61L helicopters.
If urban aviation is to profitably relieve airport congestion, it will need the 80 to 100-seat models and higher speeds envisaged by NASA and others. Such aircraft are unlikely to appear before 2030—consequently, the prospects for interurban airline service using large civil rotorcraft will languish until then.
While relief of airport congestion may be a remote goal, a 2007 NASA study notes that "the current hub-and-spoke system does not serve rural, regional and intra-urban travel well for travel distances less than 500 miles, and consumers still choose to use automobiles 20 times more often for trip distances of 100–500 miles.
Automobiles capture 76% of all trips greater than 100 miles, and airlines only 19% with an average auto speed of only 35 mph—an indicator that there is opportunity for greater mobility in the future."
The introduction of 9 to 19-passenger V/STOL aircraft operating on-demand corporate services under Part 91/91K to bypass airports would reinvigorate interurban business aviation over medium stage lengths. To support these missions, modest investment is required to establish suitable vertiports and STOLports with surface links to both target urban areas and associated airports. The motivation for the community is to enhance the utility of the urban area, thereby increasing its appeal, commercial vitality and tax base.
V/STOL designs with potential for urban aviation
Coaxial rotor with pusher prop
Vectored thrust, ducted propeller (VTDP)
There remains the need serve points within the urban area. Other than for public and emergency service operations, noise will continue to be the major source of objection to intra-urban aviation. It is unlikely that aviation will serve multiple points within the urban area until new technologies, like electric propulsion, become available.
The electric helicopter shows great promise. In 2010, Sikorsky unveiled the Project Firefly electric helicopter demonstrator based on an S300C (formerly Schweizer 300C) airframe. Initial endurance was only 15 min at 79 KTAS, but this will improve as lithium air battery technology matures.
New designs will run 2 electric motors—one in the main rotor and another in the tail rotor to reduce weight and eliminate the need for a drivetrain.
Pending the introduction of such technology, intra-urban air transport must—with few exceptions—continue to rely on intermodal links with existing surface transportation services.
The accompanying table summarizes major V/STOL designs currently available to urban aviation. Range is comparatively limited because the main characteristic distinguishing V/STOL aircraft is the high required thrust-to-weight ratio.
The dominant strategy adopted uses a power system common to both VTOL and propulsion and further development is largely reliant on the evolution of motive power—in the main, turbine engines.
The aircraft at the forefront of urban aviation are the AW609, the Eurocopter X3, the Sikorsky X2 and the GBA Heliplane, each representing very different design approaches.