X8 Thust Angle?

Hi all,


I have reworked the motor mount on my X8 by adding vibration damping and an extra wooden plate on the inside of the styrofoam firewall for robustness.

After doing all this, I noticed that the thrust line of the motor is pointing down (the forward end of the motor is slightly lower than the prop end). The angle is less than 5-degrees.

Is this intentional in the X8 design, or is this due to my modifications? Does your X8 have an angle similar? Should I try to zero this out? Am I correct in thinking that this would give me a pitch-up moment when the motor is powered on?



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  • hang the aircraft from a string on the prop shaft and see whether the prop axis and the string line up.

    • Great idea! I'll be doing that. Thanks.

    • My 2 cents.

      This my way of check the thrust line. After mounting the plane on a level board, I hang a plumb bob  from the ceiling pointing at the center of the nose. Then spin the plane. Much easy with the wings off.3702646783?profile=original


  • Flying test is the answer! The method of adding wooden plate is good.Do you use x8 to  do the work of aerial mapping?I mean you are concerning the vibration.

    • Yes. Flying is the answer. But,I would like to get the wing ready the best I can before. No mapping planning, yet. My goal with the X8 is a testbed for autopilot modification, and some FPV.

  • the thrust line should follow the centre line of the aircraft. It won't lie straight when the aircraft is placed on the floor. In short yes the thrust line should be zeroed out, although a few degrees won't hurt

    Remember the aircraft rotates about its COG, equivalent to putting the aircraft on a Catherine wheel pivoting at the COG. Downward thrust at the rear therefore pitches the a/c nose down

    • Thanks for the reply!

      A Catherine wheel? I had to look that up. I always liked those...

      Got it. I think my thrust angle is a bit off - not in line with the waterline of the fuselage. Now to shim my motor.

      If the aircraft rotates about the CoG, and if a down thrust is equivalent to a force pressing down on the fuselage, and if this force is applied aft of the CoG, then wouldn't this yield a pitch up moment?

    • I think our co-ordinate systems are back to front....heres a pic to explain

      Moment about x axis, Mx = d. T ie you will rotate nose down if the thrust is directed downwards

    • Yes. Exactly. We are saying the same thing - different coordinates. [It is always the coordinates!]


      Thanks much!

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