Catapult launch, acceleration limit

Hey guys, my first post here.
Working on a X8 flying wing, intended for S&R operations. We launch it using a catapult. There are no problems when we have to launch it unequipped using moderate tension on the catapult’s springs, in AUTO mode it flies perfectly off the catapult at the preset angle, instant Gforce at around 6-7Gs.
But once we load the wing it needs some more punch for a good takeoff, so we increase the springs’ tension to an output of 8-9Gs on the wing, here the show begins. First the wing levels itself after leaving the catapult and only after that continues to execution of TAKEOFF command at the given climb rate.
Could you suggest any ideas on how to instruct the pixhawk to continue the climb after this instant takeoff impulse instead of first levelling the plane?
PS. here is a video of a successful launch of the unloaded wing.

Hi @Anto6ka, do you have a dataflash log of a takeoff with higher payload? A lower payload comparison log may also be useful.
Cheers, Tridge

Hi @tridge , here’s a *.tlog file, you can check a successful takeoff-landing cycle at 75,6%, the nose dive can be clearly seen there. The plane was moderately loaded, I guess the issue persists on unloaded wing too, it just worsens with increased tension. Will also extract dataflash logs now.

Hey @tridge , here is the *.log file.
Thank you,

Problem solved. Thanks.

1 Like

How you solved? I have to help a friend to do the same task whit a 2.20 heavy flying wing. Than’ks.

I have worked on several parameters, but I guess the main cure came from lowering TECS_VERT_ACC from default 7 to 5 in my case. Was playing with this param for a while to analyze the feedback. At 5 it doesn’t fight the initial impulse with pitch control.

I have sorted the issue a while ago and just wanted to share my experience because the solution came from an obvious yet unexpected “at some point” direction.
Firstly I would like to thank the forum and especially @jmack for helping reaching the core of the problem by eliminating all possible weak points one by one.
There is no tangency with acceleration, TECS_VERT_ACC, NAV, STALL PREVENTION and a couple of others I have been messing with on my way to the launching dive cure, however it was a good experience to visualize the effects of those params that most of us don’t touch during normal Arduplane operations.
My main problem was the attack angle of the wing inside the launching system, the launch carriage was aligned with the rails, however because of X8’s wing geometry the attack angle of the wing was resulting in a negative value, about -5°. So during the launch the airflow was forcing the wing into a dive, and it was the code that was correcting for that side-effect and not vice-versa as thought before.
After adjusting the carriage to +5° and later +6° in relation to the rail we started getting perfect launches, now increasing spring tension became our friend and not a foe as before. Before, an increased tension would result in a more agressive dive becaused of an increased airflow pushing on top of the wing.
After sorting this issue I managed to load the wing to its planned 5+kgs AUW and get stable take-offs.
Thanks to everybody for their help, both active and passive.


Here is how the plane behaves on Auto takeoff and landing.


HI Anton,

congratz. I have similar problem with my wing, what parameters you deal with ?


Hi @juvinski ,
it depends on what issue you have run into, exactly. In my case, the main issue was the wing’s angle inside the carriage, which had to be increased by a value of +6° attack angle from the initial state, to get rid of nose diving.
Post a video or a description of your wing’s behavior n takeoff, also, adding a log might be a good idea.

Hi @Anto6ka,

sorry for the delay - I was finishing a new plane and was rainning too.
I testes a takeoff today, and I had a nose dive when I try to takeoff - I’m using a bungee launcher and when I free the the airplane instead to gain altitude simply dive

This is the log file for this takeoff:

Best regards

Well, hello guys. I am working on a same plane with kinda the same goal - plane to do waypoint mission autonomously. Also i am trying it to do the landing and takeoff autonomously as well. I have zero experience with ardupilot before this project. So can you give me the parameters you have dialed in? Or any tips and tricks? And where is the cog in this delta wing?