C/LCombat E
lectrifying Combat is getting clos- er. Mark Rudner recently posted some experiments they’d been do- ing with an electric F2D. Simple
approach: slice open the bladder compart- ment and stuff in a 4-cell battery with a high discharge rating, at least 30C (30 times the rated capacity in amps). A 4S1P battery (4 cells connected in series) for a nominal 14.8 volts is good. The cost can range from $30 to $70 or more for a similar 190-gram battery. Motors are similar. An F2D size plane
needs a motor that can produce at least 400–500 watts at the prop. Inexpensive ones are available on the internet for as little as $20 shipped that can handle 50 amps at 14.8 volts, or 740 watts in. Depending on the ef- ficiency of the motor, prop, and electronic speed controller (ESC), you’d get about 400 watts at 21,000 rpm. Mark used an NTM Prop Drive Series
2836 2200 Kv motor and a Thunderpower 1300 mAh 4-cell pack and ended up with a
7–4 Taipan prop. The plane looked like it flew just fine. Speed was about 90 mph timed at five laps, or as the F2D troops like to say, 24.7/10. The only fly in the ointment is it could
only fly like that for about 1.5 minutes. The 1300 mAh battery weighs about 140 grams. A larger 1700 or 1800 battery would get around 2 minutes, but weighs 191 grams (6.7 ounces). The fuel for a normal F2D match, about 5 fluid ounces, weighs about 150 grams and runs well over 5 minutes. So, just like electric or hybrid cars, the problem is in the batteries. Affordable ones, around $25, weigh about 8–9 ounces. Light- weight, high capacity batteries would run ~$75 a pack. There is lots of fine tuning that should be able to up the performance about 50%, I’d bet, without going crazy cost wise. Mark used an old Taipan 7–4 (a good prop in the ’80s, but not even available anymore). If the newer electric props can hold up to the maneuvering loads they are probably 15–20% more efficient with thinner blades and better aerodynamics. The speed controller is a big deal. Mark used a 45-amp Castle Creations controller. They have a very good reputation and the 45 -amp model weighs only an ounce. Going up to 60 amps adds an ounce. Get-
ting the motor to run at peak efficiency can add another 20%. Adding some battery ca- pacity would extend the flight time. The NTN motor noted only weighs 87 grams. The speed controller brings the power pack- age up to the same weight as a fuel engine. So adding a couple ounces of battery could bring the flight times over 3 minutes. Add in some efficiency savings by figuring out how to tune the governor so the plane maintains a constant speed over the flight time might even add a bit more. So I think it is safe to say that electric Combat could start tomorrow for anyone wanting to experiment a bit more, and spend the time tinkering instead of flying. Believe me, by the time CIAM gets done
48 AUGUST 2012
by phil cartier You can reach Phil Cartierat 34 Sweet Arrow Dr, Hummelstown, Pennsylvania 17036, or via e-mail at
philcartier@earthlink.net
PHOTOGRAPHY: PHIL CARTIER
Gil Reedy Meet 2012 winners (above) (standing L to R): Dan Reedy, 1st; Larry Wilks, 1st Sportsman; Dan Banjock, Phil Cartier, Don Holbrook, Jeremy Rhoads; (kneeling L to R) Scott Schmidt, 2nd Sportsman; Alexander Schmidt; Roy Glenn; Neil Simpson, 1st Half A. Louis Lopez had to leave early. Ever wonder how to make a Cox Black Widow (large tank) work on a Combat plane so the needle valve doesn’t stick up and get broken? Reassemble the engine (below) with the cylinder on the right, the needle valve on the left, and the tank vents upright. The fuel line loops around ahead of the vent tubes and ends up directly behind the cylinder, between the tank mount screws. Angle cut the end so it can’t get blocked off by the backplate.
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