ORIGINAL: Brenner
I'm a little new at this, so I hope the more knowledgeable posters here will cut me some slack, but I've been trying to figure out if electric is they way to go vs glow for pattern flying, and I've come to the following conclusions.
Li-Poly battery technology has inherent disadvantages when it comes to safety, reliability, cost, and charging time. Other than that they work fine. Flying in contests isn't much of a problem because of the time available between rounds to recharge the packs, but anyone who wants to head on out to the flying field and get some practice time in, has to charge as many packs as they expect to need, because charging at the spur of the moment at the field is a time consuming thing to do.
The answer seems to be with the new a123 packs, but they have disadvantages as well. Specifically, if you duplicate the 10s2p Li-Poly pack arrangement, you end up with at least 14 ounces more weight with an a123 pack vs with a Li-Poly pack. This is a big problem, because most 2m electric pattern planes are right at 5 kg, so there's no extra margin available to accomodate the extra weight.
Anyhow, I've done a little figuring and I've come up with the following table:
....................................Li-Poly......A123 #1.....A123 #2.....A123 #3
C-Rating...........................20............30. .............30.............30
Volts/cell..........................3.7...........3.3... ..........3.3............3.3
Cells in Series...................10............10......... .....11..............8
Packs in Parallel.................2..............2......... ......2...............2
Ah per Cell.......................2.5............2.3..... .......2.3.............2.3
Weight per Cell (kg)..........0.05...........0.07.........0.07.... .......0.07
Volts................................37........... .33.............36.3..........26.4
ma.hours.........................5000.........4600 ..........4600.........4600
Watts.............................1850.........227 7..........2505.........1822
Continuous Current......... ..50.............69..............69............69
Pack Weight (kg).............1.00..........1.40...........1.54 .........1.12
The first column shows a typical Li-Poly configuration. Column A123 #1 shows an A123 pack in a 10s2p configuration. Column A123 #2 shows an A123 pack in an 11s2p configuration which should generate voltage about equal to the Li-Poly configuration. This could be used as a direct replacement for a Li-Poly pack. Column A123 #3 shows an A123 pack in an 8s2p configuration. This pack would have lower voltage, but the weight would be almost as light as the Li-Poly pack, and the available wattage would be similar as well.
I'm thinking that this A123 #3 configuration would be absolutely perfect. The only problem is that it needs a new motor that will run at lower voltage, and draw more current. Does anyone know of a motor that work with this pack and output the kind of power needed for f3a pattern flying?
Since a 210-220 kv motor works well on the 37 volt setup of the 10S lipo, then you would need a motor that would compensate for the voltage drop by raising the kv rating. The kv of this motor would need to be approx 300 kv to generate about the same rpm on the same prop. Since most outrunner motors for pattern flying are around the 210-230 kv range due to the wide spread usage of the lipo setups, it might be a little tough to find a motor with that rating. I have had good luck with the Dualsky motors and in checking the specs for the 6360 size motor, the highest kv is 235. However, the next smaller motor, the 6350 size has a 310kv motor that might work. It is the XM6350CA 12T model. And they are only $130 or so plus shipping. The 6360 motors are the same physical size as the AXI 5330 but the 6350 series are about 6 oz lighter than the AXI 5330 series.
Woodie