FanWing: A Flying Lawn Mower

What do you get if you cross a reel lawn mower with an airplane? The answer is FanWing - a low-speed airplane concept. Unlike a traditional fixed-wing airplane, the FanWing can generate lift independent of its forward airspeed. The source of its lift is a cross flow fan resembling the cylindrical blade on a reel lawn mower.

FanWing is a concept under development by Patrick Peebles using minimal resources and tools. His team (mainly Peebles) has built scale models of his concept and tested the concept in a homemade wind-tunnel. Peebles has no formal aeronautical training. Sound familiar? Peebles continues a long tradition of aeronautical hobbyists that extends back to the beginning of flight and the Wright Brothers.

How It Works

A traditional fixed-wing airplane uses forward motion to ensure that air flows over its wings. The airfoil shape of a wing is such that air traveling over its upper surface accelerates, thus reducing its pressure according to Bernoulli's principle. The air traveling under the lower airfoil surface typically remains close to its original speed and pressure, so there is a pressure difference between the upper and lower airfoil surfaces that results in an upward force, known as lift. The FanWing uses the same principle to produce lift, but instead of an airfoil it uses a cross flow fan to accelerate the upper surface air and thus produce a lift force that keeps the airplane aloft.

The effect exploited by the FanWing is similar to the Magnus Effect. The Magnus Effect accounts for the lift generated by a rotating cylinder or ball - observed in many ball sports and often referred to as a curve ball. The FanWing can be viewed as a more efficient method to accelerate the air around a cylindrical path and thus generates significantly more lift than a rotating cylinder.

Advantages

Sharing some of the characteristics of a helicopter allows the FanWing to perform short-take-offs-and-landings (STOL). Also it can travel slower than an equivalent fixed-wing airplane, which is ideal for surveillance duties. The FanWing is likely to be quieter than a helicopter, where blade tip speeds can approach supersonic speeds and cause excessive noise.

During landing, traditional airplanes fall under the influence of ground effects, which increase lift just at the moment when they want to reduce lift and touchdown. The FanWing doesn't suffer from ground effects, because the lift-giving fan can be throttled down independent of forward airspeed and distance to the ground.

Disadvantages

The FanWing's slow speed is a disadvantage for transport missions - it's unable to match the efficiency of a traditional fixed-wing airplane. Also the large cross-sectional area of the FanWing is likely to cause higher drag than a fixed-wing equivalent, leading to a further reduction in range and speed.

If there is an engine failure on the FanWing and the lift-producing fan stops rotating, then it will simply fall out of the sky. A traditional fixed-wing airplane and a helicopter can both glide (helicopters can glide using autorotation) in the event of an engine failure.

Prospects

The FanWing concept is a novel idea that may find a niche application that fits its unique performance characteristics, possibly as a low-speed surveillance Unmanned Aerial Vehicle (UAV). Either way the concept is testament to the unbounded ingenuity of hobbyists.

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