How transition altitude above ground impacts flight time

The main goal of this article is to provide an insight into the transition altitude parameter and how this influences the battery consumption and consequently the flight time.

One of the main factors defined in WingtraPilot during flight planning is the home position and its parameters: the transition altitude and the transition direction. You can find more information about the definition of these parameters here: https://knowledge.wingtra.com/create-a-new-flight-plan.


Tr_Alt1

The default transition altitude is 50m, but it can be adjusted, depending on the environment, to between 20 and 120m. During this process, the user should be extra careful and take into account the height of natural or artificial objects in the flight zone. If the transition altitude is wrongly defined, and if altitude is too low in comparison to surrounding objects, the drone will enter cruise mode too low, which could lead to crashing into tall obstacles. 

 

For example: The user has set up the home position between buildings. During flight planning, a user should determine the height of the tallest building and adjust transition altitude such that it is higher than the tallest building by at least 20m.

 

During hover mode, the drone climbs up using only the power of the motors, while during cruise mode, the drone flies using the thrust force and the power of the motors. That force moves an aircraft through the air by overcoming the drag. Therefore, the battery consumption differs between the two flight modes; in hover, the drone climbs up only if the force of the motors is bigger than the force of gravity; while in cruise mode the drone has the help of the thrust.  For this reason, the battery consumption is 6 to 7 times faster during hover. Consequently, the longer the hover regime in a flight, the earlier the low battery RTH will be triggered. 

 

To better understand how the transition altitude affects the battery consumption and therefore the flight time, we will simulate several flights with different transition altitudes:

 

  • Transition altitude set to 30m
  • Transition altitude set to 50m
  • Transition altitude set to 70m
  • Transition altitude set to 90m
  • Transition altitude set to 110m

 

On the graphs below, you will see the percentage of the remaining battery at the moment the low-battery RTH is triggered based on the transition altitude. For all calculations, we assume that the following parameters are constant: wind speed, current distance to home, minimum RTH altitude and current flight altitude. 

 

Example 1

 

  • Wind speed 1 m/s
  • Current distance to home 500m
  • Minimum RTH altitude 60m 
  • Current flight altitude 100m

TA Table1

Example 2 

 

  • Wind speed 8 m/s
  • Current distance to home 1000m
  • Minimum RTH altitude 60m 
  • Current flight altitude 120m

TA Table2

You can see from these example graphs that a larger transition altitude increases the battery consumption and reduces the flight time, as more power will be consumed during landing (hover down) and the adaptive RTH will be triggered earlier. 

 

The presented results demonstrate that increasing the transition altitude by 20 m will trigger RTH earlier by about 10.7 percent of the remaining battery time.