Does anyone know the correlation between hovering time, flight time, and battery life on a copter? How much of the battery will be used just to hover and how much is used to to fly over a distance?

Thank you!

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This calculator should help with some of the questions here:

http://controls.ae.gatech.edu/dbershad/EMSTAirTimeCalculator.html

It allows you to calculate performance in hover and forward flight.

I have done a fair bit of empirical testing and I have yet to see improvements in forward flight efficiency vs hovering. I think maybe at our scale (~12" props) and speeds (<20ms) the difference is negligible. Recent testing with a iris x8 showed no perceivable reduction in power for forward flight at any speed, and a significant increase in power for flight over 10 m/s. About double for 20 m/s.

When doing calculations, I figure that I can fly about 5.6 grams per Watt of power.  This is my average with just straight flight at 35 MPH in GPS-driven flight mode (straight and level), using 10" props, 1100KV motors, 4 cells.

I have a TURNIGY 10000mAH/10C 4 cell battery that weighs 890g (HK SKU 912700006-0).  These larger batteries generally have more power per gram of weight, so I think this is a good starting point.

If I lift NOTHING but the battery (no frame, no motors, no props, no ESCs, etc) and I get a lift of 5.6g/W it will take 159 Watts just to lift the battery!   The battery has 10A/H  X  16V = 160 Watt/hours of capacity. But I want my battery to last, so I can use only 85% of that. So the usable battery capacity is 136 Watt/hours.

136 available Watt/hours divided by a usage of 159W means that I will be able to fly my battery 0.855 hours = 51.3 minutes.

Remember I'm only lifting the battery!

If my craft weighs the same as the battery (difficult to achieve), then my flight time will be 51.3/2 = 25.6 minutes.  And if my craft weighs twice as much as the battery (do-able) then my flight time will be 51.3/3 = 17.1 minutes. Sound familiar?

The only ways to "beat" this problem is -

1. Find suitable batteries that have higher energy density. Hopefully, some will be developed soon.

2. Use larger props, which are more efficient and will lift more grams per Watt.  20" props can get you 10g / Watt. But don't forget that the larger frame and props will add weight.  You won't be able to fly as fast, either.

Charles Linquist said:

2. Use larger props, which are more efficient and will lift more grams per Watt.  20" props can get you 10g / Watt. But don't forget that the larger frame and props will add weight.  You won't be able to fly as fast, either.


And the somewhat counter-intuitive part is that your ship will be less stable. Raising the CG closer to the lifting plane or even higher will help, but only so much.

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