My X8, still no success.

My X8.

I'm at my wits end!! Any help will be VERY MUCH appreciated.

Things I have changed  and tested after each change with no results:

1) Level the APM to the center line of X8, re did all "Initial Setup" in MP
2) remove the end point on travel, was 80% now 100%, re-did all "Initial Setup" in MP
3)Changed firmware to V2.76 from V2.78b, and also re-did all "Initial Setup" in MP

4) I have also re-leveled the plane with a 5* pitch up, and still no success.

5) I did a ground check by double checking control surface movements.

 a) manual mode..Pull stick back, both elevons go up. Pushed stick forward, both elevons go down. Stick right, right elevons go up, left elevons goes down. Stick left, left elevons go up, right goes down.

 b) FBWA mode…. Put nose up both elevons goes down. Put nose down, both elevons go up. Banked to right, right elevon go down, left elevon goes up. Bank to left, left elevon goes down, right elevon goes up.

Every thing "Ground tests" great.

Still, no change, when going into FBWA or Mission, or RTL it will start descending and I have little control if any "Nudging". I have to go into "Manual"

I have almost no trim in MANUAL MODE, if any would be 3mm (1/8") up. It is touch nose heavy.


See attachment...logs files


PS, can anyoneS download there Param file or Tlogs of there X8




Thanks for any help.



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  • Since there is a vast wealth of knowledgeable people on here, I have some questions. First off, my X-8 is being used for the AUVSI international UAS competition, and It has not flown yet. It is going to be fairly heavily loaded. I'm expecting 3-3.5KG AUW. I have a few power systems, and I'm not sure which to choose and how well they will preform. I have 2x 4AH 4S Lipos in parallel, this motorthis motor, and 12x8 and 12x6 folding and non folding props. I'm thinking of using the 1100KV motor with a 12x8 prop, does anyone have any ideas on how it will perform? 

    Second, I need to set the level with the nose up slightly, correct? I know that you can change the level position manually in the parameters for fine tuning of level flight, so it's not too big of a deal.

    Thirdly, can someone post a picture of where the CG is? I prefer not to throw a grand into the ground ;)

    Finally, I have a serious problem with airspeed sensors. My current sensor is inaccurate, causes the plane level to fly around wildly, and only ever results in crashes on the last few times I've put ardupilot in one of my planes. I am pretty sure that my sensor is not one of the defective ones, but it is possible it is broken. Does anyone know why these rapid HUD changes and inaccuracies happen? Thank you so much for your help in advance!

    • Austin,

      I have no pictures on my CG but this is the measurements.

      My CG is at the holes in the wing which are exactly 17" (43.2cm) from the nose or.... 10 3/8" (26.35cm) from the trailing edge. I have yet had a tip stall or spin... It flys very well in Manual mode


    • Thank you very much! I have my first test flight with 4 big lipos in the nose just for counterbalance this morning, I'll let you know how it goes!


  • It finally flew great

    It Flew for 30 minutes before running out of battery. I did some tuning in the mean time.
    Patient is a virtue.
    Thanks again, Brian :-)))

    FYI, I did 3 different changes at the same time before flying this time.

    6) I did put the APM on the CG, spread the electronic out, and loaded the params that are attached below

    1) thru 5) are the changes I did, which are stated at the beginning the this post

    P.S. Also like to thank all who have helped me out.

    X8 param1.param

    • Great to hear!

  • Where is the CG in relation to the nose? I dont have an x8 (but want one) but with all that weight up front it looks to be very nose heavy. I cant see the motor and light weight electronics off setting the li-po's.

    Does it fly well in manual mode?

    • Ben,

      I might be running a heavier  motor with a larger prop. Most guys I see run a 4s battery were I'm running a 6s. My CG is at the holes in the wing which are exactly 17" (43.2cm) from the nose or.... 10 3/8" (26.35cm) from the trailing edge. I have yet had a tip stall or spin... It flys very well in Manual mode. FYI, My total ready to fly weight (AUW) is 2860 gram (6.3 pounds), each battery weight is 450 grams, totaling 900 grams of battery.

      Thanks, Brian

    • Hi brian,

      Most swept wings have the cg around the 1/2 cord ( at the root of the wing) or a little bit forward of that.  The holes in the picture look to be about right. Might be worth trying a more aft cg for more control though. Try small increments. 

      Dont worry too much about tip stall. Thats pretty much fixed into the design of the wing and the amount of washout at the tip. Spinning without a rudder is always a problem! Lol

      Do you find you need lots of elevator to hold a climb? The more nose heavy the more control input needed to make a change. If its sensitive in pitch then prob tail heavy. 


    • Moderator
      Don't move the CG back on the X8, if it too far back stall recovery can be very hard. On two occasions with two different X8's I had a tip stall and the resulting spin was practically unrecoverable, I tried everything my 20 years of flying experience had and I could not get either plane out of the spin. It's worse if you have an autopilot in and on as it makes the situation worse. The balance point I used was just ahead (about 1cm) of the forward two finger holes underneath.
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