# Flight Time Calculation for Mikrokopters using Matlab

September 25th, 2010 by Speedy

Hi Guys!

This week Holger wrote a request in the Mikrokopter forum for a tool to calculate the flight time of a Mikrokopter based on basic parameters:

• Thrust curve of a Motor (grams over current)
• Number of Motors
• Mikrokopter Weight without Lipo
• Lipo Weight
• Lipo Capacity
• Losses
• LipoFactor (g per mAh – typical 50-100 g/Ah) – Here is also a nice List from Nabazul from the MK-Forum

With this data it is possible to calculate the flight time.

Also I created very interesting plots of flight time over Lipo capacity and flight time over payload. (It would also be possible to creat a 3D plot with both parameters)

I decided to make the calculation with a little Matlab script (M-File) that you can download here.

Here are some plots with the following settings (these settings are not very realistic, sorry – they are only choosen to test the skript):

• Motors = 4
• MKWeightWithoutLipo = 500g
• LipoWeight = 800g
• LipoCapacity = 2500
• Losses = 0.1;

Thrust Characteristic (source: http://www.mikrokopter.de/ucwiki/FlugZeit)

• Roxxy2827-35
• 10” EPP
• 4s Lipo

Polynomial (3rd grade) fit of the measurement points.

Flight Time over payload calculated out of the thrust characteristic curve.

And the most interesting plot is the plot of the flight time over capacity of the lipo battery. Here also the weight of the MK changes with the capacity of the lipo. This is done by the LipoFactor which is calculated by LipoWeight / LipoCapacity * 1000 (about 320 g/Ah in this example)

As you can see there is an optimum at about 3500 mAh for this setup. After that it does not make sense to take a lipo with a higher capacity (assumption: the LipoFactor is constant over capacity).