“Urban air vehicles” have been hailed as the next revolution in aviation. Prototypes of various sizes have been flown to demonstrate basic flight (hover and climb), but in most cases there is no demonstration of full flight capability, for example conversion from vertical to level flight (conversion corridor). There are proposals for vehicles in a wide range of scales: from drones specifically designed to deliver goods, to full size vehicles for manned transportation. Most of the concepts proposed include full electric propulsion, multiple (often convertible) rotors (ducted or un-ducted, counter-rotating), and widespread use of composite materials. Start-up companies are seeking funding with high-profile demonstrations in front of the media, but many unresolved technical problems are not been solved. Large aerospace companies have joined the fray. These initiatives are fuelling expectations that achieving the next milestone is within easy reach. This paper aims to fill some gaps in understanding and curb optimism. It takes a holistic view in order to establish a scientific basis for design, manufacturing, operations.

We present a digital sampling algorithm that uses two high resolution integratingvoltmeters that are synchronized by a phase-lock loop clock to accurately measure theactive and apparent power parameters for sinusoidal power measurements. The developedsystem provides high precision measurements of the root mean square, phase and the complexvoltage ratio of the ac signal with sophisticated algorithm which process the data infrequency domain. The system was designed to be used at the Korea Research Institute ofStandards and Science as reference power standard for electrical power calibrations. Thedetail uncertainty calculations have shown that the accuracy of the measurements werebetter than 4 μW/VA (for k = 1) and the level ofuncertainty was valid for the power factor range 0 ~ 1 for both lead and lag conditions.The system is fully automated and allows power measurements and calibration of highprecision wattmeters and power calibrators at the main power frequencies of 50 and 60Hz.