Originally Posted by Richie Simpson
Watts is a measure of Power, more power the faster the fan turns, making more thrust & speed.
Efficiency in motor means it will run longer not faster
" in ducting means it will make more thrust on less power (watts)
Light weight means it will accelerate quicker, not go faster
Bottom line is more watts (power) is faster
I canít help but pick up on a few of these points...
Quote "Efficiency in motor means it will run longer not faster"
IMHO this is not true ... An efficient motor will convert electrical energy to mechanical work more efficiently... That means for a given electrical power input in Watts, it produces more torque or spins faster (or both) than an 'inefficient' motor. If the electrical power input in Watts is the same then length of run will be the same regardless of motor efficiency. You can only increase run length by reducing the Watts or by increasing the capacity of the battery.
Quote: "Light weight means it will accelerate quicker, not go faster"
This would be 'almost' true for a car or any vehicle supported on wheels, however it is not the case for an aircraft in flight... Induced drag is proportional to lift and lift (in level flight) is equal to weight. Therefore more weight = more drag and more drag = lower flying speed.
Quote: Bottom line is more watts (power) is faster
This is way over simplified... there are lots of factors to be considered, motor input power is one variable that effects top speed but it's probably not the most important... Drag for instance is proportional to the airspeed squared therefore reducing drag is a far more effective way of increasing top speed than increasing power.
Assuming that your model will be fast just because it uses up lots of Watts is like assuming your car will be fast simply because it consumes a lot of gas
The 'real' bottom line is electrical Watts do not push an aircraft forward, thust is what we are really after. As mentioned previously I suspect Watts is used simply for convenience on the assumption that it is reasonably proportional to thrust... This assumption may or may not be the case depending on other design variables.