Dennis,
My own "belief" is that it is better to match the motor to your battery---in other words I would say if you can keep the throttle at ~75% of full throttle (at the end of the flight), you will achieve the higher efficiency.

Now I have done what you are doing with my Electric Super Clown and its stock motor. It also is a 1500kV motor, which with the original ESC/timer from Brodak, was made to run with a ~9-4 prop at a relatively high rpm. Eventually I was running it with a 10-7 APC prop at much lower rpms, using a CC35ESC and a JMP-2 timer. I found that it ran pretty good, and I was using ~1700mAHr from a 3s2100mAHr battery. So in this case the CCESC was doing a reasonable good job at converting the higher voltage 3s and low amps to a lower voltage higher amp run. However you are making the ESC work harder. I am not positive how efficient the ESC is working at lower throttles.

Currently I am running a kv=1088 Scorpion 3020-12 motor with a 4s1p 2100mAHr battery in my ENobler. Originally I was using two 3s1p 2100mAHr batteries in parallel, and in that case the kV was reasonably matched at my 9000rpm run. Now with the 4s1p battery, the original 1088 kV motor is a little high in kV. For grins I have wired up a 3020 motor kit myself. This new motor has a measured kV of ~880. My plan is to get the ENobler dialed in with last year's setup, then switch motors and do nothing else. I will be curious how much power the newer motor will draw. So maybe I'll have an answer for you in a month or so.

Here is a picture of the new beast!

Hi Guys,
The figure we are using recently is around 70% ... take the nominal voltage of the battery times Kv then times 0.7. That should be the running RPM you aim for. This, together with line length and desired lap time, dictates the pitch of the prop.

Why 70% ? Forget the governor for a second   
We (Hunt and I) started out at 100% throttle and a low (4-1/2") pitch prop. Efficiency is marginally better at full throttle than anywhere else, and 50% throttle is the worst, but the penalty is small. The "wasted" energy largely goes into making the windings of the motor  a little warmer and also into making them "sing" which is what folks, who change over to using a governor, hear. The problem at full throttle was that the battery voltage caused maybe a tenth and a half slowdown during the flight.

Then we tried the governor, and upped the pitch on the same prop to maybe 5". The governor had enough headroom to maintain lap times as the battery dropped in voltage.

Then we went up in pitch and down in governor RPM, so that when the governor loop "firewalled" the throttle there would be more peak power available. We kept going up in pitch, until we had to run RPMs at 70% of Kv times Vbatt. Could we go further?

Yes! The peak power going uphill will be better, at the price of more copper losses and louder motor singing. Just why this is so requires an understanding of the difference between the average current in a switched power driver and the RMS (root mean square) current. The copper heating is related to the RMS. You don't want me to bore you with math!

later,
Dean

Dean

Thanks for the latest formula. It really has helped my bench test on E-flite 480-910kv
twin motors. I had been running too high RPM (9600) with APCe 9x6 which pulled too
many amps. With your formula I revised the RPM to 8900 and upped pitch to 6.2 .
This has given me a much smoother run and still the pitch speed is OK and amps are
better. Watts per pound(in) are 125 which should be good flying. Hoping for my first
flight next week.

  Walt
 

Hello All,

Hi Dennis,
Sounds great!

Walt,
Good luck and keep us informed.

Dean