Cobra CM-4008/36 400Kv Motor Propeller Data
Magnets Motor Wind Motor Kv No-Load Current Motor Resistance I Max P Max (6S)
22-Pole 36-Turn Wye 400 RPM/Volt Io = 0.52 Amps @ 21v Rm = 0.151 Ohms 18 Amps 400 W
 
Stator Outside Diameter Body Length Total Shaft Length Shaft Diameter Motor Weight
24-Slot 45.5 mm,  1.791 in. 23.9 mm,  0.941 in. 33.5 mm,  1.319 in. 4.00 mm,  0.157 in. 106 gm,   3.74 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 0.39 A 0.44 A .49 A .52 A 398 RPM/Volt @ 21V 0.151 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 12x4.5-MR 5 18.5 7.79 144.1 6,371 33.2 1117 39.40 7.75
APC 13x5.5-MR 5 18.5 10.36 191.7 6,070 31.6 1414 49.88 7.38
APC 14x5.5-MR 5 18.5 12.61 233.3 5,807 30.2 1656 58.41 7.10
APC 16x5.5-MR 5 18.5 17.87 330.6 5,169 26.9 2089 73.69 6.32
GemFan 12x4-MR-W 5 18.5 7.40 136.9 6,422 24.3 1063 37.50 7.76
GemFan 13x4.5-MR-W 5 18.5 9.12 168.7 6,205 26.4 1261 44.48 7.47
GemFan 14x4.5-MR-W 5 18.5 10.81 200.0 6,018 25.6 1493 52.66 7.47
GemFan 15x4.5-MR-W 5 18.5 11.72 216.8 5,905 25.2 1601 56.47 7.38
GemFan 16x4.5-MR-W 5 18.5 15.26 282.3 5,485 23.4 1878 66.24 6.65
RC-Timer 11x5.5-CF 5 18.5 6.18 114.3 6,574 34.2 830 29.28 7.26
RC-Timer 12x5.5-CF 5 18.5 9.56 176.9 6,160 32.1 1179 41.59 6.67
RC-Timer 13x5.5-CF 5 18.5 12.38 229.0 5,836 30.4 1432 50.51 6.25
RC-Timer 14x5.5-CF 5 18.5 16.50 305.3 5,352 27.9 1652 58.27 5.41
RC-Timer 15x5.5-CF 5 18.5 21.19 392.0 4,722 24.6 1782 62.86 4.55
 
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 11x4.5-MR 6 22.2 8.15 180.9 7,695 32.8 1213 42.79 6.70
APC 12x4.5-MR 6 22.2 10.62 235.8 7,376 31.4 1545 54.50 6.55
APC 13x5.5-MR 6 22.2 13.97 310.1 6,972 36.3 1894 66.81 6.11
APC 14x5.5-MR 6 22.2 16.87 374.5 6,601 34.4 2168 76.47 5.79
APC 16x5.5-MR 6 22.2 23.91 530.8 5,876 30.6 2735 96.47 5.15
GemFan 11x4-MR-W 6 22.2 7.25 161.0 7,808 29.6 1118 39.44 6.95
GemFan 12x4-MR-W 6 22.2 9.69 215.1 7,490 28.4 1451 51.18 6.75
GemFan 13x4.5-MR-W 6 22.2 12.17 270.2 7,182 30.6 1737 61.27 6.43
GemFan 14x4.5-MR-W 6 22.2 14.32 317.9 6,913 29.5 1993 70.30 6.27
GemFan 15x4.5-MR-W 6 22.2 15.62 346.8 6,748 28.8 2115 74.60 6.10
GemFan 16x4.5-MR-W 6 22.2 20.04 444.9 6,122 26.1 2401 84.69 5.40
RC-Timer 11x5.5-CF 6 22.2 8.47 188.0 7,652 39.9 1166 41.13 6.20
RC-Timer 12x5.5-CF 6 22.2 13.03 289.3 7,080 36.9 1605 56.61 5.55
RC-Timer 13x5.5-CF 6 22.2 16.98 377.0 6,576 34.3 1892 66.74 5.02
RC-Timer 14x5.5-CF 6 22.2 21.71 482.0 5,836 30.4 1996 70.41 4.14
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.