### Flight time vs. battery life

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!

#### Replies

• 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.
• 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.

• 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.

• Hi all,

Is anyone aware of the ratio of the power consumed by a drone while ascending, descending and flighting forward?

• you can calculate, pretty acurately by using, https://www.google.com/search?q=static+thrust+calculator&ie=utf....

you know your prop data, weight, incoming voltage, and your motor resistance. Take your quad weight, divide by 4, this is the theroritcal thrust per prop, play with the calculator to find the right rpm to match the thrust to the required prop hover thrust. This will also give you your watts required. Now take your watts and find the motor inefficiency, IR^2 losses, watts/batt voltage= amps, plug in your amps and multy by the motor resistance^2, now add these watts to your useful power watts. Now that you have (total hover watts)/(battery watts/hour). Batteries are rated in useful amp*hrs. So a 5000 mAh battery will discharge that many amps effectively over an hour. So you should have some fraction like .25 hours, convert to minutes by multiplying by 60. For a safety factor of 5% loss is pretty liberal as it accounts for increased output in winds 5 to 10 mph.

It's all pretty simple math, just a lot of steps to get useful number. I've made excel file, to take out the dumb steps, but once you understand that, you can figure out different multirotor configurations without much problem, and if you are using APC props you can use their data tables to figure out a lot more.

I used my data to calculate 28 minute flight time on my quad, which actual flight came down to 25 minutes, because I set my quad to rtl at 10% battery level

static thrust calculator - Google Search
• Also you can use the additional payload weight and batteries to calculate new durations, Like doubling up batteries 5000 mAh gave me an estimated 43 estimated flight, which is 53% increase, which is definitely reasonable, but I why loose the extra 10 minutes for convince?

• Wow! I have learned a lot from this discussion. I thank everyone for their contributions.

I am new to the field and bought too much of a machine and I am not getting the flight time I wanted (at least 20 min).  I bought a 3DR X8 and is only giving me around 7 min. with a 6000mAh battery.   I am thinking I should remove some motors and see how it does with only 4.

• This is a good exchange, lulz. I want to see the crash reel. Order lots of spare props and arms. They'll come in handy!

• Sorry, I had to :)

No offense Kate :)))

Actually, I think that girls being interested in UAVs is great (seriously).

And my questions are probably poorly formulated :)

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