Cobra CM-4520/18 310Kv Motor Propeller Data
Magnets Motor Wind Motor Kv No-Load Current Motor Resistance I Max P Max (6S)
14-Pole 18-Turn Delta 310 RPM/Volt Io = 0.99 Amps @ 21v Rm = 0.044 Ohms 45 Amps 1000 W
 
Stator Outside Diameter Body Length Total Shaft Length Shaft Diameter Motor Weight
12-Slot 54.9 mm,  2.161 in. 42.8 mm,  1.685 in. 48.0 mm,  1.890 in. 6.00 mm,  0.236 in. 340 gm,   11.99 oz
 
Test Data From Input 12.0 V 15.0 V 18.0V 21.0V Measured Kv value Measured Rm Value
Sample Motor Io Value 0.79 A 0.86 A 0.92A 0.99 A 325 RPM/Volt @ 21V 0.044 Ohms
 
Prop Prop Li-Po Input Motor Input Prop Pitch Speed Thrust  Thrust Thrust Eff.
Manf. Size Cells Voltage Amps Watts RPM in MPH Grams Ounces Grams/W
APC 16x5.5-MR 5 18.5 15.57 288.0 5,350 27.9 2267 79.97 7.87
APC 18x5.5-MR 5 18.5 21.04 389.2 5,146 26.8 2996 105.68 7.70
RC-Timer 15x5.5-CF 5 18.5 20.50 379.3 5,171 26.9 2286 80.64 6.03
RC-Timer 16x5.5-CF 5 18.5 23.90 442.2 5,042 26.3 2620 92.42 5.93
RC-Timer 17x5.5-CF 5 18.5 27.21 503.4 4,931 25.7 2963 104.52 5.89
RC-Timer 18x5.5-CF 5 18.5 33.64 622.3 4,710 24.5 3532 124.59 5.68
 
Prop Prop Li-Po Input Motor Input Prop Pitch Speed Thrust  Thrust Thrust Eff.
Manf. Size Cells Voltage Amps Watts RPM in MPH Grams Ounces Grams/W
APC 16x5.5-MR 6 22.2 21.18 470.2 6,244 32.5 3137 110.65 6.67
APC 18x5.5-MR 6 22.2 28.35 629.4 5,972 31.1 4107 144.87 6.53
RC-Timer 14x5.5-CF 6 22.2 19.54 433.8 6,310 32.9 2403 84.76 5.54
RC-Timer 15x5.5-CF 6 22.2 28.41 630.7 5,968 31.1 3099 109.31 4.91
RC-Timer 16x5.5-CF 6 22.2 33.08 734.4 5,798 30.2 3604 127.13 4.91
RC-Timer 17x5.5-CF 6 22.2 37.46 831.6 5,643 29.4 3962 139.75 4.76
RC-Timer 18x5.5-CF 6 22.2 45.42 1008.3 5,352 27.9 4654 164.16 4.62
Propeller Chart Color Code Explanation
   The prop is to small to get good performance from the motor. (Less than 50% power)
   The prop is sized right to get good power from the motor. (50 to 80% power)
   The prop can be used, but full throttle should be kept to short bursts. (80 to 100% power)
   The prop is too big for the motor and should not be used. (Over 100% power)
PLEASE NOTE:
The Data contained in this Prop Chart is based on actual measurements, taken in a controlled test environment, at an altitude of
512 feet above sea level.  The test voltages used are based on the standard output of a Li-Po battery under load, which is 3.70 volts
per cell.  If you are using a battery that is larger in capacity than normal, or has a very high C-rating, then your actual voltages will
be higher than those shown in the chart, and this will result in a higher current and power value for every prop used.  You should
always test your actual power system with a watt meter before flying your model to make sure that you are not exceeding the 
recommended current and power ratings of the motor being used.  The prop recommendations in this chart assume that the motor
receives adequate cooling throughout its operation.  If your motor is being used inside a cowl or fuselage, you must ensure that
the motor receives sufficient airflow, and does not get too hot during operation.  It is always best to use a prop size that pulls no
more than 80% of the motors maximum recommended current value to ensure safe operation under all conditions.