Cobra CM-4520/14 400Kv Motor Propeller Data
Magnets Motor Wind Motor Kv No-Load Current Motor Resistance I Max P Max (6S)
14-Pole 14-Turn Delta 310 RPM/Volt Io = 1.45 Amps @ 21v Rm = 0.032 Ohms 60 Amps 1330 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. 48.3 mm,  1.902 in. 6.00 mm,  0.236 in. 342 gm,   12.06 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 1.14 A 1.24 A 1.34 A 1.45 A 413 RPM/Volt @ 21V 0.032 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 14x5.5-MR 5 18.5 19.48 360.4 6,854 35.7 2365 83.42 6.56
APC 16x5.5-MR 5 18.5 29.63 548.2 6,480 33.8 3445 121.52 6.28
APC 18x5.5-MR 5 18.5 38.87 719.1 6,144 32.0 4395 155.03 6.11
GemFan 16x4.5-MRW 5 18.5 24.01 444.2 6,693 28.5 2878 101.52 6.48
RC-Timer 14x5.5-CF 5 18.5 27.30 505.1 6,563 34.2 2609 92.03 5.17
RC-Timer 15x5.5-CF 5 18.5 39.04 722.2 6,138 32.0 3299 116.37 4.57
RC-Timer 16x5.5-CF 5 18.5 44.42 821.8 5,943 31.0 3787 133.58 4.61
RC-Timer 17x5.5-CF 5 18.5 49.82 921.7 5,770 30.1 4188 147.73 4.54
RC-Timer 18x5.5-CF 5 18.5 60.80 1124.8 5,411 28.2 4891 172.52 4.35
 
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 14x5.5-MR 6 22.2 26.75 593.9 7,979 41.6 3322 117.18 5.59
APC 16x5.5-MR 6 22.2 39.63 879.8 7,472 38.9 4692 165.50 5.33
APC 18x5.5-MR 6 22.2 50.80 1127.8 7,038 36.7 5826 205.50 5.17
GemFan 15x4.5-MRW 6 22.2 24.37 541.0 8,095 34.5 3152 111.18 5.83
GemFan 16x4.5-MRW 6 22.2 32.05 711.5 7,777 33.1 3950 139.33 5.55
RC-Timer 13x5.5-CF 6 22.2 27.72 615.4 7,945 41.4 2887 101.83 4.69
RC-Timer 14x5.5-CF 6 22.2 37.90 841.4 7,541 39.3 3591 126.67 4.27
RC-Timer 15x5.5-CF 6 22.2 53.19 1180.8 6,966 36.3 4341 153.12 3.68
RC-Timer 16x5.5-CF 6 22.2 59.60 1323.1 6,734 35.1 4923 173.65 3.72
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.