Fixed wing quad WITHOUT control surfaces - Help please!

Ar_Di · January 12, 2018, 8:23am

Hi guys, I am new here and I have a problem which I see as being very simple yet I can’t get anyone to help,

I am developing a concept of electric VTOL aircraft with fixed wings, it is very similar to Airbus Vahana, with 2 staggered wings and 4 props per wing. I have two Pixhawk 2 in two experimental planes I am developing and I would like to adapt the SW to something more specific to my concept. Unfortunately, none of the VTOL options in Ardupilot/PX4 fit my concept.

I am using the copter firmware (Ardupilot build, mainly because of the Landing gear function) to fly the aircraft. My aircraft is controlled like a quad in vertical flight (I have 8 props for redundancy and have duplicated outputs to 4 groups of 2 props). I rotate my wings using a servo linked to the landing gear function (that way during landing the aircraft transition back to vertical automatically as the landing gear deploys). My aircraft transition from vertical to horizontal flight pretty well but once transitioned I want to control the aircraft with only thrust, I have NO control surfaces at all.

It works OK so far but there are 2 problems:

Problem #1, yaw and roll are inverted in horizontal flight compared with vertical flight, which makes it a little difficult to control by the pilot and I suspect difficult to stabilize by the autopilot too (as the autopilot does not “know” that yaw and roll are inverted).

Problem #2, I don’t believe the autopilot can control the aircraft in horizontal flight and RTL or follow a mission because the autopilot does not “know” that my props are now applying forward thrust (rather than upward thrust).

I noticed that there are a number of VTOL options in both Ardupilot and PX4 builds but none of them attempt to control the aircraft using only CCW and CW props in both vertical and horizontal flight.

Would anyone be able to help me create a new configuration that matches my airplane so that it can be flown safely with my PX4 in both vertical and horizontal configurations using only my props? (What is mean by safely is both in manual flight and in automatic flight, being as part of an automated mission or following the trigger of a failsafe).

I hope someone will be able to help,

Many thanks,
Arnaud

mohammad · June 3, 2019, 7:59am

please send drawing of this concept .

dlwalter · June 6, 2019, 9:32pm

yaw and roll are inverted in horizontal flight compared with vertical flight

I believe this was fixed in 1.9.0

github.com/PX4/PX4-Autopilot

VTOL: fix roll inversion

PX4:master ← PX4:pr-vtol_roll_inversion

opened 07:53PM - 05 Feb 19 UTC

jlecoeur

+143 -31

fixes #4797 **Describe problem solved by the proposed pull request** The VTOL …attitude controller generates reversed fixed-wing roll commands. As a consequence, all VTOL mixers currently have a minus sign on roll actuators to compensate. **Describe your preferred solution** - Fix sign of the fixed wing commands generated by the VTOL attitude controller - Fix builtin mixers - Add a parameter to force users of custom VTOL mixers to check roll control surfaces before flight - Fix builtin airframes scripts to bypass the new parameter **Flight testing** This requires extensive flight testing on all possible VTOL platforms. Test card 1: - Flash firmware on VTOL - **Before flight**: Check direction of roll control surfaces - Fly standard mission, the behaviour should be unchanged Test card 2: - set parameter V19_VT_ROLLDIR to 1 - try to arm - the system should not generate actuator commands, error messages should be displayed on QGC. - set parameter V19_VT_ROLLDIR to 0 - arm properly

AeroTH · August 8, 2019, 11:14pm

Ar_Di,
Did you come to closure on Problem #1?
Did you mean that both roll and yaw were inverted (both individually negative), or did you mean that the roll and yaw axes were swapped?
My issue is that, if calibrated to have a standard (mode 2) control layout in multicopter mode (with pitch and roll on the right stick, and thrust and yaw on the left stick), then the roll and yaw axes are swapped after transition. That is, in fixed wing flight, a right roll is executed with a left yaw stick input, and a right yaw is executed with a right roll stick input. If you came to closure on problem 1, it could help solve this.
I would like to know what the intended behavior is. Currently, the control axes are fixed to the body the same way regardless of mode. Should the control axes be switching to the correct roll and yaw sense after transition is accomplished?