How Tilt-Rotors Could Boost the Utility of Wing-in-Ground Craft

Several national defense departments operate military airplanes that combine fast efficient flight with the ability to touch down on and lift off from very confined surroundings. There is scope to adapt such technology to civilian commercial service wing-in-ground (W.I.G.) vehicles to enhance the way in which such vehicles provide service when wave and ice conditions prevent touch down / lift-off on the water.

Introduction

Future growth in domestic and international air travel is expected to overcrowd many of the world’s coastal airports. Vehicles such as hovercraft and wing-in-ground effect technology can operate with minimal terminal facilities compared to airline transportation.

During the 1950’s, a British company developed a hybrid cross between helicopter and airplane in a concept called “Roto-dyne.” It featured both a helicopter style of rotor as well as airplane propellers installed on short wings to provide fast forward propulsion. While “Roto-dyne” could lift off and touch down like a helicopter, it incurred much lower operating costs than helicopters.

A cash-strapped British government shelved the project. However, the British and American air forces developed military aircraft capable of touching down and lifting off like a helicopter, while being capable of high speed forward flight with the fuel consumption of a conventional military airplane. The variety of aircraft technology includes tilt-rotor and tilt-wing aircraft along with aircraft capable of redirecting forward thrust from jet engines into vertical downward thrust that lifts the plane upward. Such aircraft easily touch down on and lift off from decks of ships as well as confined land-based locations.

Civilian Commercial Service

At the present day, battery powered quad-rotor drones are being introduced into short-distance parcel delivery service. Tilt-rotor drones with wings offer the combined options of vertical take-off and landing while reducing forward flight energy consumption. At some geographic locations, there would be scope to combine the quad tilt-rotors of a drone with ground effect wings to allow autonomous drones to travel close to the surface of inland waterways to double and even triple effective overall operating range, allowing for autonomous parcel transfer between coastal distribution hubs.

The option of combining tilt-rotor technology with ground-effect wings provides the basis to develop a vehicle capable of touching down on and lifting off from designated coastal land locations.  Ground effect vehicles are classified as boats despite having wings. Powerful headwinds cause ground effect wings to produce an air dynamic between water surface and wing underside that includes powerful updrafts, which bounce off the water surface and into the wing’s underside. This keeps the speeding W.I.G. vehicle aloft. By comparison, fast air flow across conventional airplane wings produce a low-pressure zone or partial vacuum across each wing upper surface, with conventional air pressure under each wing keeping the plane aloft at high altitude.

For equal weight and equal travel speed, ground effect vehicles traveling slightly above water surface require 25-35 percent of the thrust of airplanes flying at 10,000-feet. Peak energy efficiency occurs at a flight elevation of five percent of W.I.G. vehicle wingspan. Some W.I.G. vessels can travel at an elevation of 40-45 percent of wingspan, with equivalent energy consumption of an airplane. W.I.G. vehicles typically touch down on and lift off from water and seaplane runways.

Assisted Lift-Off

While ongoing development of tilt-rotor technology continually improves lift-off performance of military aircraft, that same technology can be adapted to improve lift-off performance of W.I.G. vehicles that accelerate along a paved coastal runway. The height and location of tilt-rotors ahead of the main wing would re-direct a fast airstream to flow under each wing to increase low-speed lift. Some W.I.G. designs could feature multiple parallel tilt-rotors installed ahead of each wing with possible installation of additional parallel tilt-rotors behind each wing. Future light-weight, long-life battery technology with high energy storage density offers such a possibility.

A large-scale tandem wing W.I.G. vehicle could feature parallel sets of tilt-rotors installed ahead of each of both the forward and rear trailing wings, with the possible option of installing an additional set of parallel tilt-rotors behind each of the rear wings. At cruising speed, multiple rotors would increase propulsive efficiency by increasing the mass of slower moving air required to maintain travel speed. Upon arrival, multiple rotors would tilt to produce massive downdraft and equivalent reverse thrust effect to slow the vehicle and enhance touch-down performance on short land-based runways.

Electric Power Technology

Multiple advances are occurring in electric power technology and becoming applicable to aircraft and maritime transport application, including wing-in-ground effect vehicles. Smaller, high-pressure closed-cycle gas turbine engines weigh far less than present day engines, including when driving electric generation machinery. Ongoing development in lithium-sulfur battery technology promises lightweight batteries capable of holding up to three times the energy of lithium-ion technology.

Small-scale autonomous parcel delivery drones powered by multiple electrically driven propeller-rotors could be the starting point to develop future tilt-rotor propelled wing-in-ground effect variants. Development of small-scale technology also provides the basis by which to develop full-scale electrically powered tilt-rotor propelled wing-in-ground effect commercial vessels capable of carrying revenue passengers and/or freight.

Market Niches

Market niches for ground effect vehicles include crew transportation to and from offshore oil and gas platforms, offshore rescue services, military coastal patrol along with commercial passenger and freight transportation services. One parcel freight company identified a niche for a parcel carrier technology that travels faster than ships and incurs much lower cost than air freight. Countries such as Indonesia, Malaysia, Greece and Philippines include multiple islands that are within ferry vessel and short-haul commuter aircraft range. Passenger carrying ground effect vessels would offer competitive travel durations while incurring much lower energy costs than commuter aircraft. Ground effect vessels would be especially competitive against commuter aircraft along routes of under 200 miles, operating between coastal cities along the same shore or between a mainland city and an offshore island.

Conclusions

While developing a hybrid W.I.G. vehicle propelled by tilt-rotors will require research, tilt-rotor technology is becoming a proven technology. The development of lightweight, long-life, high-capacity battery technologies along with gas turbine-electric technology enhances future development prospects for tilt-rotor W.I.G. vessels capable of touching down on land-based locations.

Electrically-driven tilt-rotor technology enhances prospects for short take-off performance along suitable runways. The most likely course of development of tilt-rotor W.I.G. vehicles would be small-scale, battery-powered delivery drones that could travel above the water surface along inland waterways, such as between New York City and Albany or Philadelphia and Baltimore.