Professional Pilot, October 2018

PROFESSIONAL PILOT October 2018 111 printing technology is developing to produce superb material microstructure with far fewer dislocations and grain boundary problems greatly improving material performance Thus far a factor of order 5 has been achieved in some metal alloy systems Another approach for ultra performance materials is to merge nanotubes into a contiguous structural material Estimates of performance improvements are in the 3X to 8X range Continuing efforts with composites claim 10X the performance of aluminum Electric aircraft applications Unmanned Aerial Systems Development of IT capabilities navigation computing automatics to autonomy ubiquitous sensors and now electric propulsion and additive manufacturing has spawned a quickly growing market in electric Unmanned Aerial Systems UAS for a multitude of functions This in turn has prompted very rapidly developing efforts for On Demand Mobility ODM including Urban Air Mobility UAM ODM is initially piloted but will eventually be an autonomous UAS carrying passengers The ultimate market worth approx 1 trillion per year will be electric autonomous Personal Air Vehicles PAVs which operate in the street in front of an individuals holding Current ODM and UAM efforts are also investigating Vertical Takeoff and landing VTOL machines with electric propulsion distributed propulsion and flow control as enablers The literature is rife with large numbers of non helo VTOL devices and approaches with several lift fans Benefits include lower noise drag vibration cost maintenance and better safety As the costs of renewables for electricity continue to drop and batteries continue to improve it is increasingly feasible to unload the lift fans for improved acoustics For super Short Takeoff and Landing STOL operation there is the channel wing with circulation control and for lower cruise speed STOL theres various types of autogyros For PAV electric propulsion eliminates engine exhaust noise enables distributed propulsion and flow control and requires lighter engines To all this add all of the many benefits of electrics stated earlier Electric long haul transports A truss braced wing design is an example of what may be possible for an electric long haul aircraft design Use of an external wing truss provides major structural benefits and allows reduced wing weight thickness and sweep This results in a tremendously enhanced and easily maintained natural to easily forced low drag laminar flow along with increased span With a reduced wing chord laminar flow is enhanced and vortex hazards are reduced Plenningers designs for such aircraft yielded L D values in the 40s over twice current levels However the concept wasnt adopted as the extensive wingspan did not fit the FAA 80 meter box requirement for airport gate compatibility A truss braced span could be doubled and still conform to the 80 meter requirement by using an existing hinge Doubling the span would halve the wings Reynolds number and reduce drag due to lift up to 75 With engines moved to the base of the fuselage the propulsion exhaust flow could be thrust vectored obviating the weight and drag of the empennage The propulsion system ingests Advantages of electric propulsion No motor gear boxes Regenerative energy recovery during descent and landing Battery heat used for cabin heating deicing or regeneration Higher altitude operation feasible Reduced cooling drag Quieter Reduced vibration Fewer inspections No engine flameouts or restarts No fuel explosions during crashes Power train efficiency 90 twice or greater than IC GTE propulsion Much lower energy costs No power loss w altitude at high temps Continuously variable transmission High reliability High efficiency in most of power envelope Up to 6 times motor power to weight compared to combustion engines Reduced maintenance Far fewer parts Less expensive Higher torque No vehicle emissions angularity These include tip turbines for energy extraction winglets vortex diffuser vanes tip sails wing grids spheroid c tips and many other tip devices Eliminating the physical wing tips can be done by use of ring wings or joined wings and tails The trussbraced wing reduces Drag Due to Lift DDL 75 by simply doubling the span This is enabled structurally with an external truss creating a wholly new set of optimization parameters and approaches Landing gear weight reduction Generally landing gear accounts for 33 of the total weight of long haul transport fuselages and 63 the weight of supersonic transport SST fuselages making them a target to reduce weight Typically landing gear features large heavy brakes for aborted takeoffs This could be substituted with parachutes for sizable weight reductions And the gear itself is typically sized for high impact landings Such loadings might be minimized in frequency and impact strength via autonomous operations slaving the lift system to the ground proximity and descent rate Revolutionary materials and structures There are several not quite ready low Technology Readiness Level TRL approaches to significantly reduce aircraft weight via materials and structures For example nanoscale ECO 150 concept developed by Empirical Systems Aerospace This example of a turbo electric architecture uses electric generators on the wing mounted turbofan engines to power electrically driven fans