RVJet wants to dive all the time??

Hey guys, I have a RVJET fitted with a pixhawk.

Pixhawk is mounted ~4 inches to the rear from CG, I did this to accommodate as much battery space as possible.


I did the level/sensor calibration with the bottom surface of the wing perfectly level.

In manual mode, it flew great (little bit of up elevator was required to keep a level flight). However, when I tried FBWA and LOITER, the plane dove into a 30 degree dive, and had to switch back to manual mode to save it.

I tried using AHRS_Y trim to the maximum 17 degrees, and it didn't help much. 

Does this mean...

1. I have to level the aircraft with the nose up in 30 degrees?

2. Adjust the physical servo arm, so that it will fly with a little bit of up elevator in level position? since it flies level that way in manual mode?

3. Move the pixhawk to the middle? my thought was if it was a few inches off the center, it would compensate fine.

4. combination of all three?

I already had a pretty bad crash from plane going into failsafe mode from a faulty antenna and it has been a very frustrating endeavor for me. please let me know what I should do.

Here's the log from the last crash I had. 



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  • Are you sure the plane isn't diving in order to gain airspeed? I had a similar problem in that my AUTO TUNE minimum airspeed setting was too high, therefore the plane would dive for the ground when I flipped into AT in order to gain the minimum airspeed required for the tuning process to begin. The only way to save the plane was to quickly switch back to manual mode.  After talking to a SME at 3DR it was suggested that I lower the minimum Auto Tune airspeed requirement and the problem was resolved.

  • Moderator

    Once trimmed (most "wings" need some up elevon or reflex) in manual mode, you need to do the radio calibration again to recenter the throws that the autopilot uses. And take out the AHRS_Y, set it to 0, this will change by itself after the first flight, I've been told on good authority that one should not change that despite what the wiki says or used to say.

    If you switch between FBW-A and Manual mode with the aircraft flat and level after trimming and calibration there should be no or very little movement of the elevons. Don't fly if there's a lot of movement.

    The position of your Pixhawk longitudinally should make very little, if any difference.

    • I seriously would like to buy you many beers. Thank you!!!! what you have said made so much more sense than the wiki...

      So let me try to figure out what I need to do this week.

      1. re-fly the rvjet with the payload to figure out how much trim is needed for level flight in manual.

      2. land, and re-center the servo, and adjust the servo horn adjustment to the "reflex" position.

      3. re-fly in manual to make sure its flying level with sticks centered.

      4. land, re-calibrate radio in mission planner to recenter the throws for autopilot.

      5. reset AHRS_Y to 0

      6. ensure while on ground, with wings level and armed, ensure FBWA and Manual switching results in little to no movements in elevons.

      7. enjoy proper working pixhawk.

      does that sound right?

    • Moderator

      Exactly, but just put AHRS_Y back to zero first before anything else.

      Adjusting the horn is good practice but if using a computer radio which remembers the trims then just doing the radio recalibration again after the plane is trimmed to fly level should be OK.

      Glad I could help, please let us know how it goes?

    • I will. just to make sure, I shouldn't need to do the ridiculous 30 degree nose up level calibration again right? I should be able to just level with a reflex dialed in....

    • Moderator

      Yup, presume you've done the 6 sided accel calibration once when you originally set up the Pixhawk then all should be good.

      I used to have an RVjet and if I recall correctly I needed about 2 or 3mm up reflex on the elevons.                  

    • Moderator

      What Graham said put a bit of reflex in physically.

This reply was deleted.