Expanded Electric Motor Propulsion Duration for UAS

Lockheed Martin announced the successful operation of a remote laser power transfer technology using their Stalker UAS in a wind tunnel test that proved the capability of 48 hour operational duration (Quick, 2012). The remote power transfer system, Power Link developed by LaserMotive, has the potential for significant refueling and endurance expansion of the silent Stalker UAS (Cook, 2012; Quick, 2012). The test, stopped once the goals of the analysis were met, indicated positive endurance results with more energy stored in the battery system at the conclusion than at the start (Cook, 2012; Frink, 2012).

This announcement is a clear indicator that the usability of electric propulsion systems has matured to the point of serious performance gains over their internal combustion (IC) counterparts for small unmanned aerial systems (SUAS). In 2005, I developed a research study that examined the cost and performance associated with these two types of propulsion systems (i.e., IC and electric motors), which indicated the smaller the airframe the more efficient and cost effective it becomes for unmanned operation (Terwilliger, 2005). My study relied upon a direct comparison of standard brushed electric motors and nickel metal hydride (NiMh) batteries, which have been supplanted by use of brushless motors and  lithium-polymer (LiPoly) batteries (expanded capacity, lower weight; Terwilliger, 2005). The following comparison depicts the differences between equivalent (i.e., voltage and capacity) NiMh and LiPoly batteries:

NiMh to LiPoly Size and Weight Comparison:
The following information was taken from the product description of the Venom Racing 6-cell 3300 mAh NiMH Battery (Hobby-Lobby, 2012b):
Length (L): 5.375"
Width (W): 1.75"
Height (H): 1"
Total size/area (L x W x H): 9.4063
Weight 12.1oz

The following information was taken from the product description of the 3300mAh 2S 7.4V 25C LiPo Battery (Hobby-Lobby, 2012a):
Length: 5.35"
Width: 1.69"
Height: .51"
Total size/area (L x W x H):7.55 (80% of the size of NiMh equivalent)
Weight 5.93oz (49% of the weight of NiMh equivalent)

This comparison indicates the current generation of LiPoly batteries have a reduced footprint and weight for the equivalent voltage (7.2v) and capacity (3300 mAh). With the enhanced capabilities of such components, a new examination into cost and performance to determine where the line between the two technologies now meet would merit consideration.

13 July Update: BAE Systems has announced the development of a solar power system that can be used to form the structure of an airframe (Leung, 2012). Such as system, composed of hard composite material,  is believed to eliminate the need for batteries altogether for some uses (Leung, 2012). Coupling this technology with Power Link, backup high capacity-low weight batteries, and increased efficiency motors has significant potential for extending the endurance of unmanned aircraft.

8 November Update: A joint research effort between Rice University and Lockheed Martin have found a potential method for increasing the capacity of Lithium-ion batteries by almost three (Falconer, 2012).  This increase would be made possible by crushing a silicon anode film so that is has a total surface area 50 times more than crushed silicon alone (Falconer, 2012).  Such an increase is believed to be a significant power storage breakthrough with implications for mobile electronics and electronic vehicles (Falconer, 2012).

REFERENCES
Cook, J. (2012, July). Laser power test extends flight time of spy plane to 48 hours. Geekwire. Retrieved from http://www.geekwire.com/2012/laserbased-power-system-extends-flight-time-spy-plane-48-hours/

Falconer, J. (2012, November). How to boost lithium battery performance - just add crushed silicon.
Retrieved from http://www.gizmag.com/crushed-silicon-lithium-ion-battery/24885/

Frink, T. (2012, July). Lockheed Martin and LaserMotive user laser to power UAV for 48 hours. Retrieved from http://www.militaryaerospace.com/articles/2012/07/lockheed-martin-and-lasermotive-use-laser-to-power-uav-for-48-hours.html

Leung, I. (2012, July). Integrated solar power storage eliminates batteries. Electronic news. Retrieved from http://www.electronicsnews.com.au/news/integrated-solar-power-storage-eliminates-batterie

Gizmag. (2012). laser-power-stalker.jpg [image file]. Retrieved from http://images.gizmag.com/hero/laser-power-stalker-uas.jpg

Hobby-Lobby. (2012a). 3300mAh 2S 7.4V 25C LiPo battery [product description]. Retrieved from http://www.hobby-lobby.com/3300mah_2s_7.4v_g6_pro_lite_25c_lipo_1036076_prd1_1039183_prd1.htm

Hobby-Lobby. (2012b). Venom Racing 6-cell 3300 mAh NiMH battery [product description]. Retrieved from http://www.hobby-lobby.com/venom_racing_6_cell_7.2_3300_mah_nimh_battery_187617_prd1.htm?pSearchQueryId=3741991

Quick, D. (2012, July). Stalker UAS flight time improved by 2,400 percent using laser beams. Gizmag.com. Retrieved from http://www.gizmag.com/laser-powered-stalker-uas/23283/

Terwilliger, B. (2005). Cost and performance analysis of internal combustion (IC) engines versus electric motors for use as unmanned aerial vehicle (UAV) propulsion system. Daytona Beach, FL: Embry-Riddle Aeronautical University, Extended Campus. Retrieved from https://sites.google.com/site/etprepository/repository/BT-GRP-Final-02-09-05.pdf