Endurance of drone

ArduCopter Copter 4.0
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21

I have a quad with the same motors and props, and I use a Tattu 6S 8Ahr pack. Despite having some unusual constraints with the frame design, without any useful payload it’s around 2.5 kg, and will hover or cruise efficiently for close to 40 minutes, using about 80% of the battery’s rated capacity.

Power to cruise at 10 m/s is about the same as hover due to translational lift.

I’ve flown at weights up to about 3.6 kg, and safe endurance drops to around 15 to 18 minutes. I think 900 g per motor is above what T-motor recommends for the MN4006, but for enduance builds I’ve found that I do well to push them a little harder.

All the advice regarding weight is spot on - for hover and slow cruise flight. However, if your goal is to achieve some cruise speed capability, steeper pitch props and a heavier disk loading are critical, as is a streamlined body. Super light copters with flat props can never fly fast efficiently. I’m not sure an hour is achievable for a quad like that though.

22

A guy named renatoa came up with some math for calculating flight times. I use it for all of my drones.

Here is his post on RCGroups:

" For any platform of any size and weight, the flight time is the result of:

time = whkg / (1000*R / eff_gw) * 60, where

whkg = battery energy density, in Watt hour / kg, ranging from about 150 for the high C packs to 270 for LiIons. 10C Multistars are 185.
R = ratio between AUW and battery weight
eff_gw = motor/prop efficiency, grams per Watt, taken from mfr data.
Be aware to get from table the efficiency for the intended thrust, and for 50% throttle !
Efficiency greatly depends on load, so don’t use efficiency stated for 1kg, to compute flight time of 2-3 lg platform !
Also, don’t use values for more than 60% throttle, the platform will be unstable, no more room for motors to do their control job…

As I wrote, this formula works for ANY size platform and energy source, lets do the math for some particular cases:

Case I Ph2
battery wh/kg = 5.2(Ah)11.1V/0.37(kg) = 156wh/kg
R ratio between AUW and battery = 1250/370 = 3.4
propulsion efficiency = 11g/W
time = 156 / (10003.4 / 11) * 60 = 30 min

Case 2 the 129 min record
battery wh/kg = 266Wh/kg - typical LiIon energy density
R ratio between AUW and battery = 3.4/2 = 1.7
propulsion efficiency = 14.1g/W
time = 266 / (1000*1.7 / 14.1) * 60 = 132 min

And finally, my 30 min case
battery wh/kg = 165, I use a Zippy Compact, having a bit more energy than the average LiPo
R ratio between AUW and battery = 0.75/0.195 = 3.8
propulsion efficiency = 11g/W - using Phantom 2 clone
time = 165 / (1000*3.8 / 11) * 60 = 28 min

As you can see from the above, reasonable precision of all estimations, proving this formula is valid for any configuration, so now you have a tool that should tell you what is wrong in your setup, and where to work to improve flight time.

The biggest unknown for most users is the propulsion efficiency, for this reason I think is mandatory to not buy stuff without manufacturer precise specification of this parameter."

I have attached a spread sheet that will do the math for you.
Calc.zip (9.2 KB)

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