From what I am reading here (I'm just starting into electric stunt) it sounds like 3 cell lipos are not being used. It seems like they were in the past. What size planes or limits does using this cize battery pack produce?

Thanks,

bob

Bob,
A 3 cell LiPo has ~11V of potential. If you look at the kv values (found on the motor specs) most people are using, then by multiply the kv by the voltage, you can find the no-load (=no prop!!) maximum rpm for that battery. Recognizing that maximum power delivered by a motor shaft is just 1/2 of that max rpm value, and that normal straight and level flying is somewhere between that 60-70% of the maximum value (above the power peak), then you can calculate the rpm you typically will be using.

So for example, the kv for the Brodak Super Clown motor is 1500 rpm/V. So with a 3 cell LiPo, the max unloaded rpm is just 11V* 1500 rpm/volt- 16500 rpm. Since we will prop it to be ~75% of this value, this gives an rpm of 12375 rpm. So in this case a 4 pitch prop is reasonable. The diameter choice sets exactly how much power you will draw, and you need to chose it to be in the 12000rpm range. That's roughly a 9-4 for this setup.

The popular choice for most people is the AXI 2826/10. This has a kv of 920. The same 3 cell Lipo would have a max rpm of 10000rpm, and at 75% max, that would translate to an rpm of 7500rpm--a little low for most people. If you went to 4 cells in series, you would be up to a little of 14V, giving the 75% rpm value 9660rpm--more in our comfort range and also allowing the ability to play with the ESC.

Of course the weight of a battery tends to tell you how much fuel you have, so for the same plane, you can play with kv and prop pitch and cell count, but in the end, the battery weight of whatever you choose (3 cells in series for low current draw, or 3 cells in paralle (for a higher current draw) will tend to be similar--in the same battery technology of course.

Number 1), that's what was suggested!
But number two, that's typically what I use with LA25's which are spinning at similar speeds. I think that's the main point. My rule of thumb for a glow is that if the static rpm is under 10k rpm, I think about a 5 or 6 inch pitch. Over 10krpm, I think of 4 inch pitch. Over 12k I think in the 3 inch pitch range. Also you are somewhat limited by the pitch selection of electric props (I haven't seen much or any under 4 inch pitch. I go for props designed for electric systems because I think they waste less of the motor's power because they are a lot thinner.

What I didn't really say much about was how to figure the total power needed (what diameter). For that you need to listen ans look at suggestions. The larger motors can handle more power because they have more cooling surfaces, and I think that they can use larger diameter wire for the windings (=less resistance) than a smaller motor. I look at the Hobby Lobby Site--they have a lot of suggested glow power equivalents for the different size motors.