Cobra CM-3515/20 650Kv Motor Propeller Data
Magnets Motor Wind Motor Kv No-Load Current Motor Resistance I Max P Max (5S)
14-Pole 20-Turn Delta 650 RPM/Volt Io = 0.78 Amps @ 15v Rm = 0.058 Ohms 34 Amps 630 W
 
Stator Outside Diameter Body Length Total Shaft Length Shaft Diameter Motor Weight
12-Slot 43.0 mm,  1.693 in. 47.0 mm,  1.850 in. 50.6 mm,  1.992 in. 5.00 mm,  0.197 in. 199 gm,   7.02 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 0.70 A 0.78 A 0.85 A 0.92 A 637 RPM/Volt @ 15V 0.058 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 11x4.5-MR 4 14.8 14.01 207.3 8,085 34.5 1354 47.76 6.53
APC 12x4.5-MR 4 14.8 17.99 266.3 7,739 33.0 1679 59.22 6.31
APC 14x5.5-MR 4 14.8 28.09 415.7 6,918 36.0 2399 84.62 5.77
APC 16x5.5-MR 4 14.8 38.18 565.1 6,125 31.9 2940 103.70 5.20
GemFan 11x4.7-MR 4 14.8 17.55 259.7 7,778 34.6 1583 55.84 6.09
GemFan 12x4.5-MR 4 14.8 21.14 312.9 7,492 31.9 1691 59.65 5.40
GemFan 12x4-MR-W 4 14.8 16.42 243.0 7,873 29.8 1564 55.17 6.44
GemFan 13x4.5-MR-W 4 14.8 20.33 300.9 7,551 32.2 1862 65.68 6.19
GemFan 14x4.5-MR-W 4 14.8 23.56 348.7 7,260 30.9 2141 75.52 6.14
GemFan 15x4.5-MR-W 4 14.8 25.86 382.7 7,081 30.2 2294 80.92 5.99
GemFan 16x4.5-MR-W 4 14.8 33.46 495.2 6,506 27.7 2718 95.87 5.49
RC-Timer 11x5.5-CF 4 14.8 14.27 211.2 8,053 41.9 1256 44.30 5.95
RC-Timer 12x5.5-CF 4 14.8 21.91 324.3 7,436 38.7 1721 60.71 5.31
RC-Timer 13x5.5-CF 4 14.8 28.05 415.1 6,916 36.0 2057 72.56 4.95
RC-Timer 14x5.5-CF 4 14.8 35.96 532.2 6,322 32.9 2316 81.69 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 10x4.5-MR 5 18.5 16.36 302.7 10,002 42.6 1629 57.46 5.38
APC 11x4.5-MR 5 18.5 20.28 375.2 9,630 41.0 1984 69.98 5.29
APC 12x4.5-MR 5 18.5 25.74 476.2 9,145 47.6 2423 85.47 5.09
APC 14x5.5-MR 5 18.5 39.04 722.2 7,989 41.6 3266 115.20 4.52
GemFan 10x4-MR-W 5 18.5 16.09 297.7 10,019 38.0 1574 55.52 5.29
GemFan 11x4-MR-W 5 18.5 17.49 323.6 9,893 37.5 1800 63.49 5.56
GemFan 12x4-MR-W 5 18.5 22.89 423.5 9,394 35.6 2251 79.40 5.32
GemFan 13x4.5-MR-W 5 18.5 28.26 522.8 8,915 38.0 2640 93.12 5.05
GemFan 14x4.5-MR-W 5 18.5 32.68 604.6 8,544 36.4 2975 104.94 4.92
GemFan 15x4.5-MR-W 5 18.5 35.90 664.2 8,277 35.3 3164 111.61 4.76
RC-Timer 10x5.5-CF 5 18.5 13.91 257.3 10,239 53.3 1378 48.61 5.35
RC-Timer 11x5.5-CF 5 18.5 20.85 385.7 9,582 49.9 1861 65.64 4.82
RC-Timer 12x5.5-CF 5 18.5 31.65 585.5 8,652 45.1 2446 86.28 4.18
RC-Timer 13x5.5-CF 5 18.5 39.95 739.1 7,937 41.3 2785 98.24 3.77
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.