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)
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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.

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Nice Article man, should help many people. In fact I never knew people used 6S for a 450 size helis and I always thought high KV motors running at high RPMs were more efficient than low KV motors at low RPMs.

i have a few friends in uae flying the 6s... and iam upgrading to a 4s now on my furion 450... will keep posted on the outcome..

Haven't seen any one flying 6s on 450s locally. 4s is what people who need punch have been doing.

You fly a furion 450? 

hi guys,
you have left the weight difference out of this calculation........... a 6s is mighty heavy compared to a 3s.
never come across anybody flying 6s in UK on a 450, only few on a 500 size.....
this will knock the calculation out quite a bit, power seems equal enough, but with the extra weight the times would be well down on a 6s..
give some actual flight times with these results???
regards
don

6s *for the same mAH/capacity* is certainly heavier, but the claim above is that you do not need the same mAH as 3s.  It would be interesting to compare (the power, duration etc) for a 3s 2200mAH versus a 6s 1300mAH (or something like that).