If you're one of the millions of air travelers who must drive by half a dozen perfectly good small airfields to get to a passenger airport, there may be hope yet. Boeing has been awarded a patent for a tilt rotor Vertical TakeOff and Landing (VTOL) aircraft capable of carrying up to 100 passengers. By combining vertical lift and hover capacity of a helicopter with the speed and range of a conventional airplane, it could one day turn small airports into passenger hubs.

Boeing has had considerable experience with military VTOL aircraft, like the V-22 Osprey and its derivatives, but current tilt-rotor aircraft aren't suitable for civilian use and the few attempts, including the AugustWestland BA609, can only handle six to nine passengers. Part of the problem is the military tilt rotors include many features that make them impractical for civilian use.

A quick glance at the V-22 shows where these problems lie. The Osprey and similar aircraft have a high-wing configuration that requires the aircraft to have a heavier construction with extra reinforcements to not only support the engines, but to protect the fuselage from being crushed in the event of a crash.

Conventional tilt-rotors, such as the V-22 Osprey are not practical for civilian passenger use(Credit: US Navy)

This configuration also makes maintenance and fueling more difficult, and it has safety issues because the plane cannot float in the event of a water landing. In addition, the undercarriage must be installed in the fuselage because the wings are too high for the wheels, and the wings can't be used to store fuel because of the danger of leakage into the fuselage and cabin. And then there's the problem of airports being built for low-winged craft, so taxiing, loading, and unloading aren't easy.

Another problem is the engine mounting. Most tilt rotors have two engines – one in each wingtip nacelle right behind the rotors. These may be combined to share the lifting load through a drive shaft, but for safety reasons, each engine must be 50 percent larger than needed in case the other engine fails. If the engines aren't interconnected, they need to be even larger. This means the need for even stronger wing supports with heavier reinforcements to hold the larger engines.

According to the patent, Boeing is looking at something more along the lines of a 100 passenger regional aircraft. In the description, the Boeing passenger tilt rotor has low wings set toward the bottom of the fuselage as in a conventional airplane, doesn't need special crash reinforcement, and can float in a water landing. In addition, it can carry fuel in wing tanks, can operate from conventional airfields, and can be equipped with mid-cabin exits without elaborate slides.

One way in which Boeing aims to achieve this is by moving the engines away from the rotor nacelles at the tips of the wings to the middle of the wing. This way, each rotor can be powered by two or more engines through a common gearbox in various configurations. This means the individual engines can be less powerful and more compact, yet in combination can provide the necessary power for flight even is one should fail.

In addition, the engines are fixed, which simplifies many of the systems and the weight of the wings, as well as improving ground clearance and payload capacity. Also, the wings can be configured so that their power trains are completely independent of one another.

Since this is just a patent, there's no indication that this aircraft or any variant is slated for production, but if it were, it could act as a regional passenger aircraft capable of operating from small airfields, city airports that normally couldn't handle such a large passenger craft, and even remote heliports.

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