There was extensive coverage of manned and unmanned electric aircraft at the recent "Electric Vehicles Land Sea Air" in Stuttgart Germany with considerable questioning by a fascinated audience.
Dr Michael Schier of DLR German Aerospace Center gave a riveting talk into electric vehicles when on the ground, thus saving money, noise and pollution and making airliners independent of tow tugs thus speeding operations. He made a permanent magnet synchronous motor with a simple winding technology and planetary gearing. Two motors are used per aircraft with four 12.5 kW fuel cells. The first flight with this system is this week. In answer to questions he said that, although he uses a synchronous permanent magnet motor, it can give regenerative braking at a later stage (braking when taxiing not when landing). He noted that the fuel cell can provide lavatory water and heat for the aircraft as by products.
Professor Guilio Romeo of the Polytechnic University of Turin heads up the European ENFICA-FC project. A 73 meter wing span solar UAV surviving 125 km/hr jetstream was successfully flown. 7-8 duration is achievable. The best multilayer 41% efficient GaAsGe photovoltaics could not be afforded so silicon was used. Such UAVs are cheaper and better than satellites because they can stay on position. Iridium links were demonstrated in fishery studies. The US spends much more on this sort of thing - an $89 million project with Boeing seeks 20km altitude five year endurance. This uses a fuel cell with hydrogen produced by solar. Structural carbon fibre may replace Kevlar but this is not a silver bullet: it must be optimised.
High temperature PEM fuel cells are favoured by Prof Romeo because of their high efficiency. He has flown a two seater aircraft with a 20kW 105 kg fuel cell from Intelligent Energy. It can even take off on the fuel cell alone, though safety of this is not yet fully proven. On one flight the fuel cell failed and return was executed using the lithium-ion battery. A 6.2 kWh Kokam lithium polymer battery, delivering 20 kW, and a synchronous brushless motor were used. A next step is to add a propeller that is quieter because the propeller is the main source of noise remaining. A world record of 39 minutes endurance was achieved for this type of fuel cell plane.
On a linked theme, Andor Holtsmark presented for Lange Aviation on Antares H2/H3 - From High Performance Sailplane to Research Aircraft. These have exceptionally low maintenance, vibration and noise and superb reliability and simplicity of operation and the drive unit stows into the fuselage when out of use. Moving from NiMH to Li-ion nearly doubled the altitude achieved and range 245 km. Lange developed its own BMS and motor controller for the 42 kW externally revolving brushless synchronous motor without a gearbox. The SAFT batteries have a pedigree in military and other aircraft for non traction purposes and a remarkable 15-20 years life is anticipated, the 3000 meter ceiling currently specified can be exceeded in future.
He noted that electric airplanes are fine at high altitude unlike diesel planes for example. He then went on to talk about development of high temperature PEM fuel cell planes under EC schemes. Once again, as with land vehicles, a lithium-ion battery is needed as well. 50 hrs 6000 km with 180 kg payload is sought in a motor plane (not a powered glider) because "the market is enormous for this". It uses a methanol water reformer to produce the fuel cell hydrogen. The two wing pods contain a fuel cell and battery driving what is therefore a two propeller aircraft. Batteries are the primary performance limitation. Reducing motor fuel cell, and reformer weight will help.
Professor Ella Atkins then described the remarkable achievement of an unmanned seaplane. The air data system turned out to be the primary challenger. The first version had no energy harvesting but the second version used GaAs photovoltaics and targeted holding position at night is appropriate weather . Standard LiPo batteries and inertial navigation are used with GPS backup. Unlike other UAVs the goal is to go upwind then land but in the unusually challenging marine environment. For example, although the propellers did not break while chewing waves, the pitot tubes jammed. Anemometer backup was introduced.
Much lies ahead including sense and avoid, satellite weather link, sonar, radar and machine vision. There will be collaboration with industrial partners to work with biological, chemical and other payloads.
To register to attend the next "Electric Vehicles Land Sea Air" conference to be held San Jose, CA, USA in November, please follow this link http://www.idtechex.com/electric-vehicles-usa-11/ or contact Teresa Henry at T.Henry@IDTechEx.com .
For more read Electric Aircraft 2011-2021 .