The troublesome issue in electric conversion has always been weight. Although LiPo technology significantly diminishes this concern, it remains a significant design consideration. Most large electric motors have a weight comparable to their glow counterparts. The Model Motors AXI 2820 series, comparable to .20 size engines, weighs about 6 ounces. The AXI 4130 series, roughly comparable to something in the .60 to .90 (two-cycle) class, weighs about 14 ounces. The batteries are somewhat heavier than fuel, however. I’ll use a typical Kokam 2000 MaH cell for the following illustrations. Assembled into a pack, this cell weighs about 2 ounces. I generally like to power my aircraft to give me a comfortable 10-minute flight (of typical flying with 3 minutes reserve). This requires about three cells for each .10 cubic inches of equivalent glow displacement. Thus, a .20-sized aircraft would need six cells, a .40 size would need twelve cells, and a .60 size would need 18 cells. This is, of course, a starting point; my 3D-capable Hangar 9 Twist only has eight cells, but then I only fly it seven or eight minutes. But, as a rule of thumb, this suggests that the batteries for a .60-sized airplane will weigh about 36 ounces, or about 24 ounces more than the fuel for the comparable glow engine.