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1. Power can be measured in watts. For example: 1
horsepower = 746 watts
2. You determine watts by multiplying ‘volts’ times
‘amps’. Example: 10 volts x 10 amps = 100 watts
Volts x Amps = Watts
3. You can determine the power requirements of a
model based on the ‘Input Watts Per Pound’ guidelines found below,
using the flying weight of the model (with battery):
- 50-70 watts per pound; Minimum level of power for decent
performance, good for lightly loaded slow flyer and park flyer
models
- 70-90 watts per pound; Trainer and slow flying scale
models
- 90-110 watts per pound; Sport aerobatic and fast flying
scale models
- 110-130 watts per pound; Advanced aerobatic and high-speed
models
- 130-150 watts per pound; Lightly loaded 3D models and
ducted fans
- 150-200+ watts per pound; Unlimited performance 3D models
NOTE: These guidelines were developed based upon the
typical parameters of our E-flite motors. These guidelines may vary
depending on other motors and factors such as efficiency and prop
size.
4. Determine the Input Watts per Pound required to
achieve the desired level of performance:
Model: Hangar 9 P-51 Miss America
Estimated Flying Weight w/Battery: 9.0 lbs
Desired Level of Performance: 90-110 (100 average)
watts per pound; Fast flying scale model
9.0 lbs x 100 watts = 900 Input
Watts per Pound of power (minimum) required to achieve the desired
performance
5. Determine a suitable motor based on the model’s
power requirements. The tips below can help you determine the power
capabilities of a particular motor and if it can provide the power
your model requires for the desired level of performance:
- Most manufacturers will rate their motors for a range of
cell counts, continuous current and maximum burst current.
- In most cases, the input power a motor is capable of
handling can be determined by:
Average Voltage (depending on
cell count) x Continuous Current = Continuous Input Watts
Average Voltage (depending on
cell count) x Max Burst Current = Burst Input Watts
HINT: The typical average voltage under load of a
Ni-Cd/Ni-MH cell is 1.0 volt. The typical average voltage under load
of a Li-Po cell is 3.3 volts. This means the typical average voltage
under load of a 10 cell Ni-MH pack is approximately 10 volts and a 3
cell Li-Po pack is approximately 9.9 volts. Due to variations in the
performance of a given battery, the average voltage under load may
be higher or lower. These however are good starting points for
initial calculations.
Model: Hangar 9 Miss America
Estimated Flying Weight w/Battery: 9.0 lbs
Input Watts Per Pound Required for Desired
Performance: 900 (minimum)
Motor: Power 60
Max Continuous Current: 40A*
Max Burst Current: 60A*
Max Cells (Li-Po): 5-7
6 Cells, Continuous Power
Capability: 19.8 Volts (6 x 3.3) x 40 Amps = 792 Watts
6 Cells, Max Burst Power
Capability: 19.8 Volts (6 x 3.3) x 60 Amps = 1188 Watts
Per this example, the Power 60 motor (when using a
6S Li-Po pack) can handle up to 1188 watts of input power, readily
capable of powering the P-51 Miss America with the desired level of
performance (requiring 900 watts minimum). You must however be sure
that the battery chosen for power can adequately supply the current
requirements of the system for the required performance. You must
also use proper throttle management and provide adequate cooling for
the motor, ESC and battery.
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