HOW DOES OUR ELECTRIC POWERTRAIN COMPARE TO THAT OF A TYPICAL RECIPROCATING INTERNAL COMBUSTION ENGINE?
According to a 2019 New York Times report, air travel currently accounts for 2.5% of global CO2 emissions, and those emissions are expected to triple by 2050. Decarbonizing aviation with electric aircraft powered by renewable energy therefore stands as viable mitigation to greenhouse gas emissions and the corresponding global warming. By building an electric ultralight airplane, we hope to gain a deeper understanding of the advantages and shortcomings of electric airplanes, and hopefully document it in sufficient detail for other aircraft enthusiasts to experiment with electric powertrains as well.
How does our electric powertrain compare to that of a typical reciprocating internal combustion engine? To answer this question, we first compared our motor and speed controller to the popular Hirth F-33 and Rotax 227 two-stroke reciprocating internal combustion engines. We then compared our lithium battery system to the standard 5 gallon limit of aviation fuel as defined in 14 CFR Part 103.
As shown in the table above, the MGM Compro REB30 motor and HBC speed controller match or outperform both internal combustion engines in every category besides price. Most importantly, electric motors are mechanically much simpler than an internal combustion engine, which makes them cheaper and easier to operate and maintain. While an internal combustion engine may have tens of moving parts, our electric powerplant has only one. This eliminates issues such as carburetor icing, fuel pumping, and regular overhauls which can be costly and time consuming. Additionally, while internal combustion engines waste the majority of the energy stored in gasoline in the form of heat, our motor and speed controller have a combined efficiency greater than 80%.
POWER SOURCE COMPARISON
TOTAL POWERTRAIN COMPARISON
For more information on how we went about designing our custom battery pack, check out our lithium battery comparisons spreadsheet. We compare the best battery cells (as of early 2020) based on real testing data to get estimates on weight, capacity, power density, and much more. The spreadsheet also includes a handy calculator which will automatically generate the detailed specifications of a battery pack based on your system voltage and continuous power requirement. We selected the Samsung 40T 21700 cell because of its relatively low cost per kWh, high discharge, and high power density. The Samsung 25R 18650 cell came in a close second with a proportionally higher discharge rate bua higher cost and slightly reduced power density. The higher proportional discharge rate reduces the minimum number of cells to meet a specific power requirement and creates a lighter battery at the expense of losing a little bit of capacity per kilogram and paying a bit more per kWh.