February 5, 2015 Dmitriy Yavid, Broad Shoulder Consulting LLC Broad Shoulder Consulting LLC Electronics, Mechanics, Optics, Software

Broad Shoulder Consulting LLC Electronics, Mechanics, Optics, Software  Presented here are basic estimates, based on elementary physics, public information and common sense. Should not be construed as actionable engineering analysis or design guide  Contain no confidential information  Assume delivery of 500 W of power to an UAV similar to Bird Eye 650, via either photovoltaic conversion or thermal engine  Presented at the request of Dr. Arie Lavie and Dr. Avner Sharon, with a goal of facilitating future R&D projects on the title subject

Broad Shoulder Consulting LLC Electronics, Mechanics, Optics, Software  Conversion efficiency ~40%  1250 W of optical power is needed to provide 500 W mechanical power  Max. power density on PV panels ~6 kW/m^2  0.2 m^2 of PV area minimum is needed  Difficult to get uniform light distribution across the panel: practically, should be ~0.5 m^2 to accept Gaussian beam  Panel weight ~1 kg, assuming 1 mm thickness with support structures and wiring  Light falling off the panel will be lost: real efficiency down to perhaps 30…35%  Electric motor has its own weight and losses too

Broad Shoulder Consulting LLC Electronics, Mechanics, Optics, Software  Optimization of material for a single wavelength  Electrodes configuration: denser electrodes reduce electric losses and increase optical losses  Optimization of size and shape: larger panel – more light collected, but more weight too  Angle of incidence: oblique angles reduce the PV efficiency, but increase the horizontal range of UAV. Some surface optics may be helpful  PV Panel cooling: efficiency drops if temperature not optimal  Adaptive electronic control of working point on V-I curve

Broad Shoulder Consulting LLC Electronics, Mechanics, Optics, Software  Max Thrust: 5.5 lbs  Engine Weight: 0.8 lbs  Diameter: 2.34“  Length: 7“  RPM Range: 85,000 to 245,000  Max Temp: 690C  Fuel Rate at Full Power: 3 fl oz per minute Modeled on P20-SX: one of the smallest commercially- available turbojets

Broad Shoulder Consulting LLC Electronics, Mechanics, Optics, Software  Based on simple power model – see next slide  P20-SX can theoretically deliver ~16 kW, at 29% efficiency  Scaled for 500 W, would be: ◦ ~2 cm diameter, ~6 cm long, weigh ~12 g  Realistically, though: ◦ Thermal efficiency usually drops with size: hard to contain heat ◦ A gearhead would be needed to drive a propeller from the turbine (jet is not efficient at low speed) ◦ Still needs optical collector, albeit much smaller than PV panels ◦ Perhaps, ~100 g engine with ~20 % efficiency can be hoped for

Broad Shoulder Consulting LLC Electronics, Mechanics, Optics, Software

Broad Shoulder Consulting LLC Electronics, Mechanics, Optics, Software  Type of the engine: turbine is not the only option  Heat exchanger material: higher temperature improves the efficiency and reduces the size  Heat distribution: non-uniformity leads to efficiency loss and/or burnouts  Thermal Isolation: improves efficiency and protects other parts of UAV from extreme heat  Bearings and other mechanical parts: typically, don’t scale down well, may be oversized

Broad Shoulder Consulting LLC Electronics, Mechanics, Optics, Software  Photovoltaic conversion is a tried and trusted way to generate electric power  No fundamental issues: just good engineering is needed  Thermal engine is a novel concept, which needs more development and may not work at all  Thermal engine promises considerably smaller size and weight  Photovoltaic conversion will probably have somewhat higher efficiency