Boeing received a patent this week on a system for generating electricity from the kinetic energy of landing aircraft. The patent (8,123,163) describes a system in which the landing gear drives an electrical generator, and the generated electricity is transferred by induction to wires in the runway.
A generator is included in each wheel of the aircraft. When the wheels spin during landing, generated electricity is run through coils of wire (52) in an "induction shoe" (12). This generates a magnetic field that is picked up by a conductive grid in the runway. In addition to generating electric currents in the runway-based grid, the physical resistance of the system helps reduce the load on the traditional braking system.
Boeing proposes two uses for the electricity generated by landing aircraft. First, the runway can be fitted with resistive heating elements that protect the runway from damaging freeze-thaw cycles.
In the northern latitudes the primary contributing factor to runway and taxiway surface deterioration is from the freezing and thawing of the moisture absorbed into the paving materials. Heating of taxiway surfaces has been proven effective at Chicago O'Hare airport where there is a test strip of conductive asphalt in place.
Second, and even more ambitiously, the electricity can be stored and re-used by operating the system in reverse during takeoff: the runway is energized with current, and an aircraft's induction shoe picks up that current and drives the electric generators on each wheel as electric motors.
The stored power recovered from the dynamic braking of one aircraft landing is supplied out to another aircraft which is taking off.
In this takeoff-assist system, the electrified runway drives the aircraft forward "in the same manner as is now employed by some high speed train and trolley systems." The takeoff-assist system is analogous to (and for commercial flight, far preferable to) the Air Force's 1950s trials with "small rocket motors which ... were jettisoned after takeoff."
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