From the early days of aviation, the design of airports was a paramount issue. From the narrow grass runways of the 1920s to the wide concrete lanes of today, airport design has come a long way. However, a new concept of the airport may hold promise for the future-the circular airport. During this blog, we’ll present both the advantages and disadvantages of circular runways and their future impact on aviation.
The concept of circular runways has been around for a number of years. In 1919 a circular runway was proposed for downtown Manhattan with the idea of getting direct air access to NYC. This would be accomplished by connecting the runway to a series of skyscrapers. While a practical idea at the time, having an airport on top of major buildings conflicted with the architecture of the area and was only useful for light aircraft. In 1957 the circular airport concept was first designed for jet aircraft. Such an approach was considered because jetliners of the era required more runway than their piston-engined counterparts. The British designer, Sir H. Temptest thought a circular or endless runway, while expensive to build, would save the cost of lengthening existing airports on a long-term basis. By 1964, the US military expressed interest in the idea and conducted a series of tests at the General Motors Proving Grounds near Mesa, Arizona. These tests have conducted a circular based track with a circumference of five miles and a radius of eight-tenths of a mile. The track was forty-five feet wide and was banked from nearly zero degrees on the inside to twenty-two degrees on the outside, which corresponds to the equilibrium take off and landing speeds varying from zero knots to about one-hundred-forty knots. Though pilots found it difficult to land with the correct roll angle on the speed circle corresponding to the landing speed. However, pilots reported that the runway tended to correct their errors regarding landing speed, the point of touchdown and degree of bank. Aids such as a marking on the runway helped them for positioning. After several trials, pilots adjusted to the track and reported exceptional lateral stability with the aircraft finding it’s natural line on the runway corresponding to its speed.
While the Mesa tests were successful, it was nearly fifty years before further research was conducted on circular runways. This was largely due to construction costs of circular runways, which require about twice the length of linear runways, as well as the precise banking of the runway. However, interest in the concept was revived in 2011 as a result of the “Fentress Global Challenge: Airport Of The Future” study initiated by two university students, one from Standford and the other from Malaysia’s University Of Science, concurrently as the Dutch consortium NLR began to research the feasibility of circular runways. Both studies indicated a number of advantages associated with circular runways. The first advantage is both a safety and fuel consideration. Since the runway is a circle, an aircraft may both take off and land in a direction which avoids the effects of crosswinds, enabling a safe landing or takeoff. The aircraft also saves fuel in the process, as well having fewer emissions to the environment. Circular runways allow air controllers to control takeoffs and landings at any point along the circle, thus reducing noise pollution. Circular runways can handle the same number of departures or arrivals as straight runways. While the runway length is about twice that of a straight runway, the airport as a whole takes about one-third the space of a linear airport. Construction costs have also decreased in recent years, with the cost of a circular airport at about 1.5 times the cost of a straight airport. Also, by having less total space than a linear airport, circular airports are more adaptable to smaller communities. However, circular runways have a few disadvantages. Perhaps the most difficult aspect of operating from a circular runway will be landing on a banked runway since the weight of the wings is not shared equally and could damage the plane’s tires due to unequal stress. Landing from a corner will also be difficult and pilots will need training specific to circular runways.
Circular runways are feasible with current technology and construction techniques. Today’s aircraft characteristics allow takeoffs and landings with both speeds and low altitude bank angles compatible with operation on a circular track. The circular runway accommodates intermodal transport, in addition to improved operations planning and navigation equipment. Perhaps the greatest obstacle to circular runways is that of public acceptance.