Sonex-B standard tail elevator up deflection.

[Chuck26287]

I have a question for builders who have installed the standard Sonex tail kit (horizontal stabilizer/elevator with vertical stabilizer/rudder). I am installing the HS/elevator right now. The plans call for a measurement of 3.25”, +/- 0.0625”, from the aft side of the vertical fin lower spar channel to the aft side of the HS main spar. As you first set the HS/elevator in place, you cannot push it even close to where it needs to be due to the HS skins being in the way. This is where you have to do the dreaded and time-consuming skin trimming to custom fit the HS. I realize the goal here is to get it seated far enough forward on the tail cone box (forward toward the back edge of the turtle deck) that you achieve 25 degrees of up elevator deflection.
I am currently at a measurement of 3.289”, leaving me 0.0235” of forward movement tolerance remaining, so I am in spec on my forward position. I am also just shy of being in contact with the turtle deck skin edges with the HS forward spar. I have the skins trimmed to the spec of having between 0.4mm and 1.6mm gap to the fuselage sides. This appears to be just as it should be. However, I cannot achieve 25 degrees of up elevator deflection. In troubleshooting this, I noticed when the elevator horn (EH) hits the upper rear angle as the elevator up stop, it does not hit with the flat portion of the EH tip, and it does not hit the flat vertical portion of the angle piece, as is depicted in the plans. The portion of the angle which is acting as the stop is in the curve of the “U” in the horizontal section of the angle. It actually appears the EH is not long enough and does not protrude down into the tail cone box far enough to make contact with the flat portion of the angle piece. The photo shows what I’m talking about.
I have verified both the forward spar and the main spar are in full contact on the upper longerons, so there is nothing preventing the EH from extending all the way down into the box to hit the stop.
Since the fuselage was a quick built by the factory, I am really concerned that I did something seriously wrong in my tail kit build, but I can’t for the life of me see what that would be. The tail went together beautifully, and I thought it was right on plans.
The only way I see to achieve 25 degrees of up elevator deflection is to custom trim/reshape the end of the elevator horn so that it achieves the full deflection specified. I have no problem with custom fitting this for the deflection, I am just concerned that I need to in the first place. My real concern is from the fact that this method of adjusting/fitting to achieve proper deflection is exactly what the plans say to do for the rudder with the rudder horn, yet they don’t mention trimming the EH anywhere in the plans. Is there a reason the plans don’t mention this as a viable method to achieve specified deflection for the elevator?
I have not drilled HS mounting holes yet, and don’t want to until I better understand why I am in this state, and how to fix it acceptably. Any help will be very much appreciated.

[Mike53]

Just a quick thought. Have you kept up with all revisions ? I missed a revision when building my Onex and had the same issue .i couldn't get proper up elevator. For me it was a revision that called for the removal of that spacer block you have behind the angle piece . Once I removed it I was still shy of the up elevator noted in plans but was enough for satisfying the min. up elevator plus a couple degrees.
The B model is still fairly new so i would imagine there are lots of revisions.

[Chuck26287]

Just a quick thought. Have you kept up with all revisions ? I missed a revision when building my Onex and had the same issue .i couldn't get proper up elevator. For me it was a revision that called for the removal of that spacer block you have behind the angle piece . Once I removed it I was still shy of the up elevator noted in plans but was enough for satisfying the min. up elevator plus a couple degrees.
The B model is still fairly new so i would imagine there are lots of revisions.

I did go through and check for all the updates that weren't already in my plans, and my plans were recently enough printed that there were only a few revisions I had to annotate. Nothing pertained to this.

Good thought, though.

[gammaxy]

Oh man, it's been a long time since I thought about this, but I think I had the exact same problem. If I remember correctly, minor adjustments to how the control horn is riveted to the elevators can significantly affect the geometry. If you look at my log, you should see several places where I ended up grinding material so everything fit. I'm pretty sure this is the norm even if you build exactly to the plans.

https://chrismadsen.org/2013/12/tail-in ... rol-stops/

[thomasjones42]

Steve,
A Onex plans revision dated 3/26/2020 changed the up elevator requirement on that plane from 25 degrees to 18 degrees minimum. I along with a lot of other people struggled and failed to get to 25 degrees before this was changed. I'm curious why it was changed for the Onex but not the Sonex. You might inquire of Kerry.
Tom Jones

[Chuck26287]

Steve,
A Onex plans revision dated 3/26/2020 changed the up elevator requirement on that plane from 25 degrees to 18 degrees minimum. I along with a lot of other people struggled and failed to get to 25 degrees before this was changed. I'm curious why it was changed for the Onex but not the Sonex. You might inquire of Kerry.
Tom Jones

I had heard the Onex was now different. Not sure why the Sonex was not changed as well. I did send the write-up to Kerry at Sonex Tech Support and am waiting to hear back from him on it.

Chuck