Roger
Something bugs me - my Pathfinder flying on .018" x 66' lines, using a 12x6 APC Pusher prop at 9000 RPM, timer set about 5:45, and used 2650 mah or so out of a 4S pack.

You are using a little over 3300 mah over 6:33 out of a 5S pack - that is a huge total power difference, I swagged 38% after adjusting for the flight times.

Mine is flying roughly 5.3 sec laps, you are flying 5.0 sec (line size?)

Hey Dennis,

I am flying on 64' long 0.18 dia lines.  If I slow the rpm down to 9000 with the lower lap times, the plane sags on the overheads.  I have to keep the rpm around 9300 to 9500 to have good line tension though out the flight.  I'm sure that my Pathfinder has a lot of drag and is also quite heavy. 

Roger

Alan,

I agree, I am on a steep learning curve.  As I mentioned previously, I was very surprised that the smaller lighter motor used more power than the larger motor.  That is why I posted the information.  I tried to set everything the same for both motors but it is probably impossible to get everything exactly the same.  With the smaller motor running much warmer, it seems that at least some of the power differance was probably just lost as heat.  The smaller motor also pulled a few more amps that the larger motor.

Roger

Just for fun, I tried to model your Turnigy 3548(800) and compare it to an AXI2826-12.

I used the free DriveCalc program. It actually has both motors in its database, which means someone made some measurements on the motors and inputted them into the database.

What I did was set them up with an APC11-5.5 TE prop--because the 11.5.5 prop nominally draws the same current statically as the APC12-6 TE prop. Then I tried to get your observed inflight RPM (~9500 rpm) by adjusting the "voltage". I'll post two png graphic files of the two motors in this config. What is nice is DriveCalc tells you some useful info on the motors---more than you get from the manufacturer usually. I note the Turnigy is slightly smaller than the AXI 2826---maybe the 2820 would have made a better comparison.

I do note that Drivecalc claims the effective kV for the Turnigy is 702 rpm/V (the "n_s" parameter. Compare to the 800 rpm/V manufacturer number.

The green dots on the curve show the 9500 rpm points. The blue line is rpm vs current, the greenline is the motor efficiency, and the red line in the OUTPUT power (to the prop). If you look at the set of numbers on the lower right hand side of the window (just above the reliability sliders), the values for the green dots are given, including the power input (what we normally measure). I note the AXI claims it needs 394 watts to the Turnigy 440 watts to turn the prop at this rpm. I also note the "dynamic" resistance for the AXI is  64.6mOhm and the Turnigy is 166mOhm, a considerable difference. How much of that is due to the smaller size of the Turnigy and its lower kV (more winds) and how much to the winding packing efficiency--I don't know.

But anyway, from this you can see that the Turnigy needs more power than this AXI, and that extra power is basically turned into heat.

They didn't have Roger's original motor, so that's why I chose the AXI, which I bet is larger than the Turnigy, but smaller than the original motor.

Enjoy!!

Note after---Added my Scorpion SII3020-780 plot. This is the motor I use on the Vector. It is pulling 394 watts to turn the prop (coincidently the same as the AXI.)

Roger,
Like I said, the DriveCalc program is free and can be downloaded from http://www.drivecalc.de/

They probably have the other Turnigy motors in the data base. Like I mention, someone typically runs a series of props and noload runs at WOT on the motor, and then out the amps, volts, and rpm into the "add motor" window. The program uses these values to calculate how the motor is performing and then draws the curves. As long as you bracket the region you actually run the motor (rpms, amps,..) then it is probably pretty accurate--as accurate as the measurements anyway.

They have versions for Windows, Mac, and Linux.

Down at the bottom of the page is "Prop Calc", another neat program for propeller calculations. The only issue with Prop Calc is that they don't have a lot of data for commonly used propellers (I mean the APC TE series).

And in the final analysis, if the rpm are held constant, the plane should perform the same.

Assuming that the weight is the same.

Yesterday, I tried my Turnigy SK 35-48 900kv motor coupled with a 4000 mah 4S 20C battery for the first time.  I must have missed something with the setup because I had difficullty setting the rpm on this motor.  I also had inconsistant lap times with this setup that I have not experienced with other motor combinations using the 5S battery.  The flight was really quite good but the motor used more mah than any other larger motors so far and the lap times started at about 4.7 sec (way to fast) and dropped to about 5.3 ( a bit to slow) at the end of the flight.  I am not going to consider the data on this flight as valid because I don't believe that the govenor was working properly on the ESC.  I need to go back to the drawing board and check my setup and try another test flight.  I think I am going to change my settings to fixed rpm on the ESC and try that.  One good thing about this combination is that the weight dropped from 72 oz to 64.7 oz.

Roger