Using Brodak's ARF Super Clown and their turn-key electric setup, should I be able to get two patterns out of one fully charged battery? The Clown's power system could handle a bigger model, and some day it will. At the moment I don't think I can get two flights per battery charge, but it would be close. I did what looked like a pattern, only uglier, in 4:25 to the end of the clover. Motor run was 6 minutes, and the battery had just about 50% capacity remaining after landing. So, I'm a little fast, and a little long, seems like if I dialed the RPMs down a tad, and cut the time to 5:30ish, that might put me near 40% power use. Two flights and I would be real close to 20% reserve.
I didn't get a lap time, but if I dial back RPMs then obviously it will take longer to do a pattern. So I'll try 5:30 and see how much more time I can trim.
The question I have is about battery drain. This setup has a 3S 3300mAh 20C battery. If I can get a full pattern done and on the ground using less than 40% of the battery capacity, will the second flight also use 40%? I would expect that as the pack drains and the voltage drops, the ESC will keep RPM steady by drawing more amps. My gut tells me the second flight will use more capacity than the first, and two "40%" flights will drop the battery below the 20% threshold. If this is not the case and battery drain is indeed linear, then two "40%" flights would be okay.

I really doubt you will get 2 full patterns out of that setup. The full pattern when properly done takes right around 5 minutes to get to the end of the 4 leaf clover. I usually set my flights to about 5:30. We were barely getting the pattern out of a flight streak with a similar set up on it. Batteries in that size and class are not expensive. You may be better off with a few more batteries.

Understood, and I have a few more batteries. But the original question stands, is battery drain linear? Or will the second flight consume more than the first one?

Hi Jim,
 I suspect your 2nd flight would pull more than "another 40%" out of your battery. I'm sure those a lot more clever than me will be able to confirm or shoot me down in flames but by my reckoning you need X watts to fly the model through the various manoeuvres and those watts are amps multiplied by Volts. Given a fully charged pack is ~4.2v per cell (So 12.6v for a 3 cell pack). After your 1st flight you have say 60% left that equates to a cell voltage of around 3.9v or ~11.7v for the pack. Now you do another flight and you still need the same amount of watts for the manoeuvres but you are starting off with a lower voltage so your amps draw for the 2nd flight will be higher. Remembering you have a fixed amount of mah available in the pack (In your case 3300) I would expect you to pull more of your available 3300mah out of the pack on the 2nd flight.   

A typical discharge curve for a Lipo cell is shown below..



Much better as Dennis says to reduce the pack size and therefore the overall flying weight (Unless you need the weight to make it balance).

TTFN
John.

Hello Jim,
Don't believe the gas gauge thingy. They are innacurate quite often.
Do trust the number in milli-Amp-hours that your charger says it put in, and remember that you don't waqnt to use more than 75% of capacity.
If you really are only using 35% capacity, then your batteries will last much longer than if you push them, and charge times will be short.

Regards,
 Dean

I second what Dean said!! Do NOT rely on what the charger says is the % remaining in the battery after a run!! Are you sure that your charger does not tell you how many mah it put into the battery during the recharge?? If it does not a new charger is a good idea.

Hi Jim,
No wonder you were hoping to squeak two flights from one charge!
something's amiss. There are two possibilities:
the charger itself, or a damaged battery that takes forever to balance.
You should be able to measure (carefully) each individual cell for matching, maybe 10 minutes after a flight but before putting back on the charger.
If the cells match within 0.05V and it still takes forever, then the charger is your culprit.

take care,
  Dean P.

You have all shared your wisdom with me, and I truly appreciate it. It's not that I didn't believe what you all said, in fact, deep down inside, I suspected you were right. But now I can say with certainty that I am unable to get two full flights out of one charged battery.
I guess I'm the kind of guy that needs proof.
All is well, and no harm done, the low power landing was smooth as silk. Even the deeply discharged battery seems no worse for the wear.

Thanks, John. That charger has dropped off my radar now. I think I'm going to buy the icharger 106b. Seems like several people have that one, and while it's not the best out there, it has some good features and is very reasonably priced. A big step up from the one I currently have...

http://www.icharger.co.nz/Products/106B-.aspx

Jim,

It is William DeMauro that has server suplies and his email address is demauj@verizon.net