How To Estimate the Flight Time of a Battery

by FliteTest | December 5, 2018 | (4) Posted in How To

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:

  1. Take your battery capacity in amp-hours and multiply by battery discharge in amps. 
  2. Divide by your average amp draw in amps.
  3. 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!


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Article by James Whomsley

Editor of FliteTest.com

Contact: james@flitetest.com

YouTube Channel: www.youtube.com/projectairaviation 

COMMENTS

thenated0g on December 6, 2018
1) start timer
2) Fly plane until it crashes
3) Stop Timer
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txkflier on December 7, 2018
It should have said:

Example: 2.2Ah x 0.8 = 1.76Ah effective capacity.

The h was left out of 1.76Ah.
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How To Estimate the Flight Time of a Battery