Here's all the info you need to calculate how long your planes can fly for!
Do you want to fly safely in the knowledge that you won't run out of fuel? Well, you can take the time to estimate your flight times. Before you do this, however, you'll need to know about the three components of the calculation: Battery Capacity, Battery Discharge, and Average Amp Draw. 
Battery Capacity
For the calculation to work, you have to translate your battery’s capacity (usually in milliampere-hours) into amp-hours. To convert milliampere-hours to amp-hours (mAh to Ah), take your battery capacity and divide it by 1000.
Example: 2200mAh/1000 = 2.2Ah.
Battery Discharge
As we all know, you can't fly with a LiPo battery until it is completely flat. This is because there is a limit on how many amp-hours you can discharge before the battery isn't able to be recharged. What this means is that the effective capacity of a LiPo is only 80% of your total amp-hours. To work out 80% of your battery discharge, simply multiply your battery capacity in Ah by 0.8.
Example: 2.2Ah x 0.8 = 1.76A effective capacity.
Average Amp Draw
The final component of the calculation requires you to know the average amp draw of your aircraft on a flight. You can find out how much your motor draws (or multiple motors draw) by using a measuring tool during a bench test. If you don't have one of these, you can get an indication of how many amps you'll draw from the spec sheet of your motor.
The Formula
Flight time = (Battery Capacity x Battery Discharge / Average Amp Draw) x60
Quick process:
- Take your battery capacity in amp-hours and multiply by battery discharge in amps.
- Divide by your average amp draw in amps.
- Multiply by 60 to give you your total in minutes.
It's as simple as that.
Quick Reference Examples
Flite Test Power Pack C
With a 1800mAh battery: (1800mAh/1000) x 0.8 / 20A x 60 = 4.32 minutes
With a 2200mAh battery: (2200mAh/1000) x 0.8 / 20A x 60 = 5.28 minutes
With a 3000mAh battery: (3000mAh/1000) x 0.8 / 20A x 60 = 8.4 minutes
Testing It Out
To make sure that your estimations are accurate, you'll want to make a few test flights. Following a landing, after the estimated flight time has expired, you can check to see if your battery has 20% left in the tank. If it's slightly off, you can alter your estimation for that battery and aircraft. All that's left to do is fly to the max!
If you found this article helpful, hit that recommend button!
Other Articles You Might Like
EDF Vs. Jet Engine: What's the Difference?
Flying RC in Cold Winter Weather! TOP TIPS!
Article by James Whomsley
Editor of FliteTest.com
Contact: james@flitetest.com
YouTube Channel: www.youtube.com/projectairaviation
2) Fly plane until it crashes
3) Stop Timer
Log In to reply
Example: 2.2Ah x 0.8 = 1.76Ah effective capacity.
The h was left out of 1.76Ah.
Log In to reply
The third example calc is wrong, the final time is 7.2
Log In to reply
For example: (1800mAh/1000) x 0.8 / 18A x 60 = 4.80 minutes. 4m80sec it's a value that does not exist since seconds overlap at 60. Thus the result is 480 seconds which converted to mm:ss is 8 minutes. You can use this tool to convert seconds to mm:ss format: https://www.tools4noobs.com/online_tools/seconds_to_hh_mm_ss/
Log In to reply
Log In to reply
2200*cell count/1k?
Example:
2200 mah 20C
2200*cell count/1k
2200*20/1k=44A
2200mah at 44A would run for 3 minutes
Log In to reply
Additional questions.... How does the formula change for example in these conditions..
1) using a voltage step down BEC from 7.4 to 5v. I would guess another multiplier for some efficiency loss ?
2) what if you are using a 1s with voltage booster to 5v ? what would be the multiplier then?
3) does any of your advice above change if using a NiMh setup instead of a LiPo, or it doesn't matter type of battery, only total Mah? ( assuming what ever battery you have, has the capability to provide the required aps drain )
Log In to reply