Cell voltages are a very undependable measure of battery usage, partially because the mid part of the discharge curve is very flat, and partially because the cell voltage varies with temperature, current draw, and just about everything else.  You want to look at the amount of capacity that's returned to the cell during charge.  I assume your charger reports how much it puts back into the cell -- how much is it?

If you take that "capacity returned" number and multiply it by 1.25 to get a cell capacity, then those cells should end up being discharged by 80% at the end of each flight.  That's the smallest cell size that you want to use.

I just ran your reported numbers through a spreadsheet that I have, that distills the numbers from the various planes in the "list your setup" thread here.  It doesn't pencil out.  At 42 ounces and three cells, I get a prescription for 3500mAh cells (assuming a 75% charge use at each flight).  I'm also predicting that you'd need 300W average power and 400W peak, which would leave you with a pretty hot motor.  Also, for the Kv of that motor with three cells, you want to launch at something more like 8000 RPM (assuming you're using an ESC with 'helicopter mode' governing).

Either you're managing with a lot less power than the rest of the folks on the list, or you're really flogging your motor and especially your batteries.  And if I'm not mistaken about the launch RPM, you're also seeing some sagging toward the end of the flight.

Hello Dwayne,
Glad to hear it's going well.
Tim and Wynn are steering you right. The total charge delivered by the charger is the real measurement.
Just because I am a little more conservative on battery usage, I'd say to multiply the actual charge put back in after a flight as read off the charger, by 1.33 in order to assure 75% battery usage or less.
Granted, a lighter battery might get you under 40 ounces and that could allow you to use thinner lines and maybe even improve performance.
let us know how how it goes,
   Dean P.

Thanks guys lots to learn yet, I'll let you know what the numbers are next time I go out, btw when I'm done with a flight the first thing I do is check the batt and motor and both are just barley warm not even close to being hot.
Thanks again
Dwayne

Thanks everyone, here's my set up.
E-Flite 15
11X7 apc tractor
3200 3 cell
Shulz F2B esc
Kim Doherty Timer programer
Max rpm with this batt is 8550
I did some bench runs last night and backed the rpm down to 8300 I'll try this and see how the lap times are.
Thanks again
Dwayne

Thank you so much everyone I just got back from the feild your numbers were dead bang on for a 3 cell I need at least a 3700ma batt, I have a zippy 3000 4 cell I'll fly tonight to get an idea of what size batt I'll need to order.
Thanks again this forum rocks!!
Dwayne

Ooopsie! I see that I stated rpm ranges for 11 x 5,5 as 8400 to 8700. It's just the old age thing again! Sorry, the rpm range is in the 9400 to 9800 rpm range. I try to fly with 65 foot lines (center to center) and lap times of around 5.2 to 5.4 secs, but this all depends on your own preferences and model performance.

This is what makes e-stunt so great because you can dial in the rpm of choice without changing props if the prop is more or less in the right pitch range. Let us know how the 4-cell works. Thanks.

Keith R

If you were flying with that 11x7 then you should get slightly less draw.  The real reason you want to do it, however, is because it should make your motor and ESC both run a bit cooler.  That's because with the flatter prop and higher RPM, the motor will be generating pretty much the same shaft horsepower, but it'll be drawing less current to do it (and "seeing" a higher voltage, which will make up the power).  That lowered current means less loss in both the motor and ESC, and lower temperatures.

Ok so lets see if I have this now...Less pitch means less load on the motor even at higher rpm's and therefore draws less current which means I can run a smaller lighter battery...   Is that about right?
I'm also  wondering now if the E-Flite 15 might be to big for a Twister and maybe I need something smaller.

Well...

At the motor, what you get back in lower current you'll pay for in higher voltage.  In fact, at the motor the flatter prop may well be less efficient, because of skin drag.  But both the motor and ESC will waste less power as heat because of the lower current.  So even if you don't gain that much efficiency overall, you'll be heating up motor and ESC less, which is a good thing.