How the transition altitude affects the flight time

The 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.

When planning a flight in WingtraPilot, the first step is to define 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 between 20 and 120 m, depending on the environment. When changing these parameters, you should be extra careful and take into account the height of natural or artificial objects in the flight area. The transition altitude should not be lower than the height of the surrounding objects in the direction that the transition will take place. For example, if you set the home position between buildings, you should determine the height of the tallest building and adjust the transition altitude such that it is higher than the tallest building by at least 20m.

In hover mode, the drone climbs up using only the power of the motors, while in cruise mode, the drone flies using the thrust force and the power of the motors. The thrust 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 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 the 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 100mTA Table1

Example 2 

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

RTH

    The above graphs demonstrate that a larger transition altitude increases the battery consumption and reduces the flight time, as more power will be consumed during landing.

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