Mounting vertical stabilizer

JurgenRoeland · #1 07-08-2019, 05:38 AM

I'm kind of puzzled on a part in the manual in the section "fitting the vertical stabilizer".

The instructions read: "Take measurements from the tip of the vertical stabilizer to both tips of the horizontal. Adjust the vertical stabilizer
until the measurements are equal and the stabilizer is truly vertical."

What to they mean with the "tip" of the vertical stabilizer. The bottom or top forward tip ? the forward side or the back side ?
In any case, I'm kind of confused. The vertical stabilizer has a 1/4" offset to the left build into the F-781 vert stab attach plate. So how can you need "measurements to be equal left and right". That doesn't make sense to me. If they would be equal, the tip of vertical would be exactly on the centerline of the fuselage. So I'm not sure what they mean here with this line in the manual.

So far, I have run a string through the hinges that attach the rudder on the back of the vertical stab and tried to have the string completely center through the holes. That tells me the forward/back and left/right aligment is ok.
Not sure what more you can measure if there is this offset. As long as you have the centerline on the bottom tab f the F-781 in line with the centerline of the horiz stab forward spar (and as such fuselage), I assume there's not much more you can do.

pilotkms · #2 07-08-2019, 07:30 AM

From the top of the vert stab, where the rudder overhang stops (mine is 7 1/8? from the rear of the vert stab skin), measure from that point down to the farthest and most rearward point on the horiz stab. The vert stab offset impact, if any, at that point is insignificant. Do Same for both sides. This was my ?roughly? vertical point.

Then, Verify equality by measuring from a high rivet on the vert stab with a far outside rivet on the horiz stab, both sides. The rivets were CNC positioned. Remeasure and remeasure again. Repeat until u are satisfied.

Been a while but I think I confirmed with a laser level too.

wirejock · #3 07-08-2019, 08:31 AM

I called Vans with the same question. Drove me nuts that they put that in the manual.
I was told to get as close as possible. So I picked a point further aft and measured to that point. Getting the fishing string perfectly centered and plumb through all three brackets was far more time consuming and far more important. That makes sure the rudder isn't binding.
By the way, don't trim the forward bracket per Vans drawings. It's way too much. Had to make a new one.

jcarne · #4 07-08-2019, 01:12 PM

I think you may be over complicating it. You can pick almost anything on the VS and HS as long as you are consistent. I did something very similar to Keith.

jcarne · #5 07-08-2019, 01:14 PM

Quote:

Originally Posted by wirejock

I called Vans with the same question. Drove me nuts that they put that in the manual.
I was told to get as close as possible. So I picked a point further aft and measured to that point. Getting the fishing string perfectly centered and plumb through all three brackets was far more time consuming and far more important. That makes sure the rudder isn't binding.
By the way, don't trim the forward bracket per Vans drawings. It's way too much. Had to make a new one.

Interesting Larry, the 5/8" trim was perfect on mine.

Robin8er · #6 07-08-2019, 02:11 PM

I measured mine from 2 or 3 different points. I just used a tape measure and used rivets as my reference points. Once I got is as close as I possibly could, I drilled it. It worked for me.

JurgenRoeland · #7 07-12-2019, 12:12 PM

Thanks for all the advice guys. Will give it a try tomorrow.

Snoho3 · #8 09-28-2019, 08:02 AM

Hi folks - I'd like to jump in here with a semi-related question. The thread heading fits, for those doing a search and who might have the same question later...

I'm in the process of mounting my vert. stabilizer. I've verified it is vertical per the plans (and above advice), and have the elevator stop bracket drilled and mounted to the longerons/aft deck. But I am confused that the plans say to superglue a single washer onto one side of the aft elevator stop bracket surface (so that it acts as a spacer) to accommodate the stab offset? The vert stab already sits flush with the bracket now and if I add just a single washer in one location between the rear spar of the vert stab and the stop bracket, it would seem to add some twist to the assembly, as well as a gap on one side of the nesting parts.

The build threads that I follow don't mention this and the pics aren't clear. Can anyone explain the purpose of this washer? Is it really necessary and why? Again, the plans aren't clear to me. Thanks in advance.

jcarne · #9 09-28-2019, 11:53 AM

Quote:

Originally Posted by Snoho3

Hi folks - I'd like to jump in here with a semi-related question. The thread heading fits, for those doing a search and who might have the same question later...

I'm in the process of mounting my vert. stabilizer. I've verified it is vertical per the plans (and above advice), and have the elevator stop bracket drilled and mounted to the longerons/aft deck. But I am confused that the plans say to superglue a single washer onto one side of the aft elevator stop bracket surface (so that it acts as a spacer) to accommodate the stab offset? The vert stab already sits flush with the bracket now and if I add just a single washer in one location between the rear spar of the vert stab and the stop bracket, it would seem to add some twist to the assembly, as well as a gap on one side of the nesting parts.

The build threads that I follow don't mention this and the pics aren't clear. Can anyone explain the purpose of this washer? Is it really necessary and why? Again, the plans aren't clear to me. Thanks in advance.

The nose of the vertical stabilizer is offset to the left 1/4" from the center line of the fuselage. This angle should leave a small gap between the fuselage and the VS rear spar assembly which gets "filled" with the washer.

Snoho3 · #10 09-28-2019, 05:19 PM

Thanks for your reply - just seems odd to have a single spacer washer in that location. When tightening down the four bolts at the bottom of the rear Vert Stab spar (spar to fuse mating) there is no spacer on the left side. I'd think this introduces a pre-load condition. In any case, I've added the washer and continue to build on.