anyone have an easy to follow equation to calculate how much capacity a specific system will need?

I have done some calcs on what I know - but they show me needing 5800mAh for 5.5minute flight on a 890KV motor with a 4s pack.....would that be right?

Seems excessive to me

Wynn,
What does your airplane weigh (specify with or without battery please) and what length lines do you plan to use?
Typically a stunter on full-length lines consumes around 0.6 Watt-hours per ounce of all-up weight.

example:
60 ounces * 0.6 = 36 W-H. then divide by 14.4V (for 4S) and that equals 2.5 Amp hours.
you should add ~ 1/3 to this amount so that you only use 75% of the capacity and the minimum battery size is maybe 3.3 Amp-Hours.
Total energy used is roughly proportional to line length so if you are on 60's then you could get away with a 2.8 A-H pack if you could find such an animal.

hope that helps,
Dean P.

I use this,

http://www.fokkit.plus.com/control_line/ECL_Battery_Sizing_Sheet.xls

It's a simple spreadsheet I knocked up. Takes no account for line length so is only a ball park figure but seems to stack up quite well in the real world.
I generally use anything from 110-120 Watt Hours for battery sizing. and 175-200 for ESC, Battery C rating and motor selection.

Kindergarten mathematics I agree but it does the job for me...

TTFN
John.

Hi Wynn,

In your power system you will need about 11 to 13 watts of power per oz. for CLPA.

Deans #s are very accurate, I use them. They reflect some very successful ECL CLPA setups.

If you haven't already done so, you may want to look at some of the setups on the top of this section. They will give you a very good idea of what size battery you need. Almost every size CLPA plane is covered there. :-)