# Lateral/directional stability and control using differential thrust

Hello everybody!

I have a personal project that consists on designing an autopilot for stability and control of an experimental fixed-wing aircraft with no vertical tail.

The target is to use differential thrust in its engines to control the yaw attitude and moment the same way the rudder is used.

At this stage of the project I am using Gazeebo to try to simulate a fixed-wing aircraft with two engines but I haven’t found any airframe that uses more than 1 engine. That’s why I am a bit unsure on the steps to follow.

So far I’m thinking on the following:

• Create a new mixer that has outputs for 2 engines and link them with yawing
• Create a new airframe that uses that mixer
• Simulate a coordinated turn or a flight with lateral winds to see if the differential thrust works

What do you think? Maybe you could provide me with your feedback and ideas.

Thank you all,
Juan

Neat project! Is coordinated turns still working in PX4? @dagar might know.

I have a personal project that has been sitting on the back burner for a while with the idea towards differential thrust for yaw/roll control. I figured most of it could be handled in the mixer. Haven’t actually tried yet.

Hi all,

Just to give you an update on this project I started in March and now I am presenting to complete my MEng. Just in case anybody wants to follow from here because the deeper I investigate, the more there is to do!

I achieved to use differential thrust modifying the mixer. I managed to use the concepts explained in the tool located at “Firmware/src/mixer/geometries/tools” that is used for multirrotor mixers to calculate the mixing matrix for a fixed-wing aircraft. I used a simple mixer for each motor with the inputs from the B_px matrix

The only topic I couldn’t answer is the min and max values to use for the inputs from the roll and yaw accelerations required from the controller. I made some numbers with A320, A380 and An-225 data and found that the more engines the aircraft has, the less percentage of the total thrust must be saved to get the same moment that the VTP would generate at worst conditions.

Another problem I faced is that none of the models available for Gazebo have more than 1 motor, so I could not test it, which was my next step until I noticed I was running out of time.

Hope this info can help anybody out.

See you next time!