Hi Christoph,
I also do not understand why the batteries drain was and is so large.
The only plausible explanation is that my motors and prop. combination working on 6S is inefficient, generating a lot of heat.
I have burned one Cobra 3515/18 already and the other one is on a verge of burning.
Yesterday, I have made three pattern flights using Black Tiger 4230C motor (Kv=750, maximum current unknown) and the batteries drain was 85%! - not good. After landing the motor was hot and the batteries very warm but I could hold them in my palm for 30 seconds. I was using 11x6 3blade narrow Pol-Prop turning on the ground at 9,200 RPM., measured by the properly calibrated tachometer. The lap time on 19.40 m. long eye-to-eye lines: 5.0-5.1 sec. but there was no sufficient power overhead. The active timer was working but this effect was sort of weak. Max Throttle:190, Target Throttle:150, Min.Throttle:070, sensitivity:65. Spin 66 RPM range:7,000-10,000.
You wrote " So probably the target rpm on the larger 11.5x6 prop was set too low. How much rpm does it turn in level flight to achieve a proper lap-time?"
In my first three flights in Poland, the Target Throttle was set to 170 on 11.5x6 3 blade Pol-Prop, Cobra 3515/18 and 6S Thunder Power 2800 mAh., 25C batteries.
The Max. Throttle was 187 and Min. Throttle 070. The lap times were....5.6 - 5.7 sec. and the batteries drain after flying mostly level was 91% (!!).
We figured out that 11.5x6 3 blade Pol-Prop was simply too much for Cobra 3515/18 and changed it to 11x6 3 blade narrow Pol-Prop. The lap times dropped instantly by ...0.5 second and I could fly the entire pattern but the batteries drain was still large, 78-83%.
I know Marek and other F2B fliers in Poland but nobody could figure out what to do with my setup. Consequently, I flew in the Hradec Kralove and Zarnovica competitions using the setup I had.
Now, I am back in Toronto, Canada and I will experiment until I understand what was and is going on.
Perhaps the 6S ThunderPower I got have low quality? Perhaps they are not 2800 mAh.? Perhaps...who knows?
Good luck in Landres!
Regards,
Matt