i was trying to fiddle with my scorpion motors and got some information online on the flight time one can get. I thought this was an interesting read.. (if not already available in rcindia)

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

When it comes to selecting a motor and battery for an electric helicopter, in the end, many times it comes down to a matter of choice. You can run a 450 class heli with 325mm blades on 3-cell, 4-cell, 5-cell or 6-cell Li-Po batteries. For simplicity, most people go with a 3-cell pack. For this, the Scorpion HK-2221-6 motor (4400 Kv) is very popular, and works very well with a 10 or 11 tooth pinion gear.

For people that want longer flight times, or higher efficiency, they go to a 4-cell pack and use the HK-2221-10 motor, which has a Kv of 3000. Some of the newer 450 machines, such as the Outrage G5 use a 6-cell battery, and the HK-2221-2010 motor, which has a Kv of 2010.

Higher voltage setups are generally more efficient, because they operate at lower currents, and this lowers the I-squared R losses in the motor.

A 3-cell 2500mah battery, a 4-cell 1800mah battery, and a 6-cell 1300mah battery all have basically the same energy content, which is calculated by taking the battery voltage and multiplying in by the battery capacity, in Amp-Hours, to get Watt-Hours of energy capacity.

If you use 4.2 volts per cell for the voltage, then the 3-cell 2500mah battery has 12.6V x 2.5AH or 31.5 Watt-Hours of energy storage. The 4-cell 1800 pack would have 16.8V x 1.8AH or 30.3 Watt-Hours, and the 6-cell 1300mah pack would have 25.2V x 1.3AH or 32.8 Watt-Hours of energy. Since all three of these batteries have basically the same energy, they would all fly a helicopter for about the same amount of time.

Looking at the motor performance, all three examples given above will fly the helicopter about the same, but the higher voltage set-up will be a bit more efficient.

Higher cell counts require lower current levels to produce the same power. Lower currents cause less energy lost as heat in the ESC and wiring.

The Watt-Hour rating of a battery is like the capacity measurement of a fuel tank, and is a direct indication of how long you can fly. More Watt-Hours will give you longer run times, given a constant load. Depending on the size and weight of a helicopter, it will take around 75 to 100 watts of power per pound to hold a helicopter in a hover,and as much as 300 to 400 watts per pound during 3D flying.

If you have a helicopter that requires 300 watts of energy, and you have a battery that has a capacity of 30 Watt-Hours, then you can fly for 30/300 or 1/10 of an hour, which is equal to 1/10 of 60 minutes or 6 minutes. If you were to increase the battery size to 45 Watt-Hours, then you would be able to fly for 9 minutes. A 50% increase in battery capacity yields a 50% increase in flight time.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++