Jim,
I ran my Pathfinder twin with 700kv 2814 motors with a 5 cell battery for a while.  I was using 5" pitched props and it worked perfectly well.  I would guess that the 3515 740kv motor with a 5 cell battery would work just as well, though you might not have enough rpm headroom if you went will a very low pitched prop.

Rick

Has anybody used a Cobra 3515-18, 740 KV on 5 cells?  I'm putting together a Brodak P-40 ARF profile converting to electric and have the 3518-740 in my box already.  I usually run a 820 to 840 KV setup on 5 cells.

Hi Jim,

When my Circulas 46 IIe (56.25” wingspan at 65.75 oz.) was first completed I used a Cobra 3515/18 740 Kv motor and Thunder Power 5S 2800 mAh battery with a 2-blade APC 11x5.5e prop. My battery capacity was between 20%-23%. This worked well.

The APC prop is a heavy prop at .84 oz. and suffered from the blades flexing is most maneuvers, especially square turns. I was told that this can be hard on the motor bearings. I found that the 2-blade Xoar 11x6e wood prop was lighter at .45 oz. and did not flex. My battery capacity rose to 22%-26% with this prop. With 80 flights using the Cobra motor and Xoar prop, this combination worked extremely well.

However when I started to experiment with 3-blade props, my battery capacity dropped down to 7%-10%, which was too low and so I ended up changing to Thunder Power 6S 2800 mAh batteries.
I have since changed to a Bad Ass 3515/18 710 Kv motor and a Igor 12x5N 3-blade carbon fiber prop with Thunder Power 6S 2800 mAh batteries and have almost 300 flights with this combination and haven’t look back.

Hope that helps.

Dennis

Thanks Dennis:  I know a lot of guys use a 6S setup.  I have been using 5S for several years and it has worked pretty well.  Looking to keep the weight down and besides I have 12 5S TP 2800's in my battery box.  I'm going to try the 3515-18 and see how it works.  It's a profile so switching components out is not a big deal.

Hi Jim,

The 5S batteries with the Cobra motor will work very well. It was very surprising to me how much difference there was between the APC and the Xoar props. I'd probably still be using the 5S setup if I hadn't experimented with 3-blade props. It was only then that I needed 6S batteries.

Dennis