I have been flying electric R/C for more than ten years, so I know the basics of electrics. I have also flown C/L stunt with glow engines about the same time. Now I'd like to start electric C/L with 15. and .20 size stunters. OS 15FP turns  an 8x4 prop at about 12-13,000 rpm and OS 20FP the same with a 9x4. What kind of electric setups would be equivalent in power? I'm from Finland, Europe and would really appreciate if somebody could give advice about e.g. suitable AXI or Hacker motor sizes and also usable battery packs. Very little has been written about smaller electric C/L stunters in this forum so far.

T. Uolevi Heinonen

There is no reason that the smaller planes cannot be done. I have flown a "stock" 1/2a Baby Clown Arf with a small outrunner motor and a 2s740mAHr ThunderpowerLite 740mAHr battery that basically was only slightly heavier than the Cox Blackwidow setup.

In the above case I was forced to run a maximum 6" diameter prop for the particular contest (you need someway to define what "1/2 A" is in the absence of a "real" way to measure displacement in an electric system). 

Anyway that doesn't matter to you!

So to give you a baseline, I fly a SuperClown Electric Arf that weighs in at 28 oz ready for takeoff. That included the stock Brodak motor (basically the weight of an AXI2814 motor) and a 3s2100mAHr battery, a 10-7 APC electric prop . I give more details in the above list. The reason I mention this is that I also have a "full" size FLiteStreak Arf with a Fox15 turning a 7-4 prop at some reasonably high rpm that flies quite nicely on 52 foot lines. I don't recall the weight of that setup, but it also is pretty light (why I went with the Fox15BB engine).

So I would argue is to get away from spinning a small prop at high rpm.

Here would be a good setup I think for a "true" 15 sized airframe, like a Sig Akromaster, which I have flown with an FP10. For motor I would choose either the Scorpion 3008, or AXI equivalent (2808?), or even consider dropping down to the smaller diameter 22xx series (probably the longest one of that series). As to battery, I would consider a 2s2100mAHr pack (~3.5oz)  or any other pack with a total capacity of 4200mAHr divided into as many cells as you like (e.g. a 3s1400 should work too). Obviously adjust the motor kV to give you an unloaded rpm in the 12-14 krpm range. I might go for a 9 inch prop to provide the thrust at a lower rpm than you would have with a higher revving IC engine. I believe a larger slower turning prop is more efficient, and helps keep the battery weight down.

Just my preference!

The Sig Akromaster Profile is a 34" wingspan plane---I am not positive what the area is (it wasn't given). It is claimed to be ok for 15-19 sized engines, but I think those are "old style" baffled engines, not the newer Schneurle types. Like I said, I flew mine with an FP10 and had plenty of power.

what do you think of this motor

Turnigy C3530-1400

Input Voltage : 7.4V~11.1V (2~3S Li-po)
KV : 1400 rpm/V within 10%
Nb. of turns : 22 Delta
Max. efficiency current : 10~15A
Current capacity : 22A/60s
Internal Resistance : 76 mohm
No Load current @ 7V: 1.19A
Dimensions : 35mm X 30mm / 1.38in X 1.18in
Shaft diameter : 4mm / 0.16in
Weight : 77g / 2.72oz
Number of poles/magnets : 14
Recommended model weight : 600~1300g / 21~45oz
Power equivalent : .12,2stroke

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=2141&Product_Name=TR_35-30B_1400kv_Brushless_Outrunner_(Eq_AXi_2808

I am building a sig akromaster just picked up the kit today as its raining.  I am also unsure of how I want to mount the motor and battery. The wing area is 250 sq in.