Originally Posted by needlenoses
Ok; been away for a bit; I picked up an E-flite Power 15 which mounted perfectly into the PZ Spitfire. Changed out the 30 amp esc to a 40 amp esc.
Now I am up against it. PROPELLORS.
The stock PZ prop 9.5X7.5 only uses 16.4 amps/152.8 watts.
I tried a spare 11X7 and this prop only uses17.6 amps/162.7 watts
The power 15 is good for up to 42 amps max burst and 425 watts.
With these two props the esc pulses and is not happy.
I was using a 2600ma 3 cell 25c.
And i have a 2250 4 cell i might try out.
I can only have the prop so long due to ground clearance.
Looking for any ideas on props to try, even a three bladed prop.
Check out www.motocalc.com
for a computer program that might help. It's free for 30 days, then $39. You should be able to get enough out of the program in 30 days before spending $$$$. The E-flite Power 15 outrunner is listed in motocalc, with 950KV, 2A no load, 0.03 ohms winding resistance, and 5.4 ounces.
If your ESC pulses, it might be that your battery is not capable of putting out the required current. That is causing the battery voltage to drop below safe limits, resulting in the ESC kicking in its LVC (Low Voltage Cutoff) limits. In fact, your number of 162 watts and 17 amps indicates your three cell LiPo is only putting out a bit over 9 volts. From what little experience I've got with LiPos, that voltage should be closer to 10 Volts DC. (99% of my experience is with those A123 cells, much to heavy for your models. It would take a 4 Series A123 battery to replace your 3 cell LiPo, those 4 cells will weight about 10 ounces.)
I ran the numbers on your setup with a 11X7 prop, 3 cell Flightpower 2100 LiPo. Motocalc suggests it should run at 34 Amps, 10 Volts, 340 Watts, and should turn that 11X7 prop at about 8000 RPM. If you go to a 4 cell LiPo, that prop will have to be something like 9 X 6 or similar. Motocalc suggests your motor will turn that 9x6 prop at about 11,000 RPM or so.
As for prop sizes, IMHO, stay away from those real light flimsy "Back yard flier" props. Those flimsy props won't hold their shape when running higher power levels. When running power levels like this, your motor should be outfitted with a prop like the APC-E series of Electric props.
That extra volt makes a substantial difference in power output. If you can locate one, I'd try a new 3 cell LiPo. Be VERY careful with that 4 cell LiPo. Going from three to 4 cells will about double the power input to your motor, using the same prop. That could burn up stuff. If you don't have one, now is the time to pick up one of those wattmeters, available from a number of different suppliers.
Also, there are several other computer programs that are available, some of them are free.