Approximate solution of minimum induced drag of wings with given structural weight

light reaching the photomultiplier. If one beam is unaffected but the other is deflected in the vertical plane, a smaller net change in the photomultiplier current would result. In full-scale operation over a runway, the laser beams should propagate above and parallel to the runway. Existing runway approach light towers on both ends of the runway could be used to house the necessary system of mirrors. This would not, therefore, add any new protruding structures adjacent to the runway. The beam separation and height above ground are variables which must be determined for best system response to a vortex. For safety, the laser wavelength should be selected such that the light beams would not transmit through the aircraft windshields. The laboratory tests described above indicate that, in principle, a full-scale system of this type should be able to detect wingtip vortices over a runway.