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Empenage Mounting issue

jlbpropilot

Active Member
So I have started on an 8 project that is quite a ways along. When I went to attach the horizontal stab to the fuse today I noticed an issue with the holes that have been previously drilled. As you can see by the pictures, when the 4 holes drilled in the front spar have bolts in them that leaves about a 3/16" gap between the rear spar and the tabs that it attaches to. Am I missing something? Doesn't seem like a likely place to mis drill. Thanks



Guess I don't know how to post the pictures.
 
Angle

There should be a piece of angle under the rear spar about 3" long between the two longerons. If it were missing, it would leave about 3/16" gap.
 
This one doesn't have any angle on the rear spar but there is angle of the front spar. The rear attaches to two vertical 1/4" straps the come up from below
 
I can?t see your pictures but, if I remember correctly you use a 3/16? spacer on the rear spar to level the HS before you drill the holes. It doesn?t lay flat on the fuselage.
 
Can someone help me post a picture. I have searched all over for instructions. This would help my cause.

I don't have any reason to believe the incidence of the horizontal isn't correct. The puzzling thing is the forward/aft location.
 
There's a lot of options, so here's the one I think is easiest:

go to imgur.com, click on top left "new post". Drag and drop your picture to it. The result will be a link, like imgur.com/p/aioasjdfiojaso - just post that link in here.

You can get fancier by embedding the pictures, or posting clickable links, but to get going that is the quickest.
 
Thank you Ctennis. as you can see in the pictures, when the bolts are installed to hold down the front spar, this leaves a gap for the rear spar. Leaves me scratching my head. Its always challenging picking up where someone else left off.
 
Joel, it is hard to tell in the picture if the plane of the aft spar is behind the slot for the ears. There was one here in the past and the ears were not vertical. They should be.

First take a rule and slide down the spar to see where it intersects on the deck, then you might check to see if the ears are perpendicular to the deck. HS might have to be off.


One like this was posted here recently ( last month or so?) but I can not find it.
 
I will walk down the hangar and check that. I do believe it is aft of the slots, The ears did appear to be vertical and not bent. I will double check however
 
The drawing shows the spacers under the front spar, I understand that. My issue is when the bolts are installed vertically which attach the front spar to the fuse, there is about a 3/16" gap between my rear spar and and stab attach bars. My rear spar sits aft which leads me to believe that when the 4 holes drilled in the front spar it must not have been correctly installed. The only solution i can come up with is a spacer between the rear spar and the attach bar to take up the 3/16" space
 
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Drawing 27 and 27A

It is drawing 27 and 27A in my set of drawings, but they are for the older (not match-drilled) fuselage, so the numbering may have changed.

In any case, the rear spar of the horizontal stabilizer is supposed to go behind the vertical bars, but clamp right to them. It appears your previous builder for some reason set up the stabilizer too far far aft.

Have the holes been drilled through the rear spar and vertical bars yet?
-If yes, then it appears the previous builder for some reason decided to shift the stabilizer aft. Strange. Is the incidence angle correct? There are some spacers that need to be inserted temporarily to hold the stabilizer at the right incidence angle while drilling.
-If no, then I wonder why the previous builder drilled the forward holes at this stage.

Lets see if we can brain-storm some fixes for you.

One option for you would be to make a set of shim plates to fit between the vertical bars and the rear spar. This, plus using appropriate length bolts, should be fine. But a few other issues are going to appear down the road because of this. One is the possibility that the elevator horn will interfere with something that limits the 'up' elevator travel. Note that the angle F-812B is made to provide the up elevator stop, and you notch it as needed so that the elevator horn hits it at the correct elevator angle. Shifting the stabilizer aft is going to require a deeper notch into the F-812B. Hopefully the elevator horn won't hit anything else. The next issue is that the joint of the forward fin spar to the forward stabilizer spar is going to be different. The F-681 joiner is going to be shifted aft too, so that it will want to mount to the aft face of the forward fin spar, rather than the forward face as shown on the plans. You will also need to make a different spacer like F-885 to fill any gap, but it is hard to predict where that is all going to fit until you mount the stabilizer and the rear fin spar. The last issue, a minor one, will be that the fiberglass empennage fairing is not going to fit very well. That's OK, they usually do not fit great anyway -- I did some custom fiberglass work to make my fairing fit around and under the stabilizer leading edge, and this fit issue would be resolved then.

Another option might be to replace the components in the fuselage that have been drilled, so that the stabilizer could be mounted in its proper location, shifted 3/16" forward from where it is now. The F-810C angle would not be too difficult to replace. Unfortunately, the outboard holes also go through the upper longeron, F-887. This is a problem. You don't really want to splice a new piece of longeron in place of the old, although that could be done. With a new F-810C angle providing good bolt bearing area, it might be OK to just make a second hole in the longeron. Not generally accepted practice, for sure, and definitely would want to get buy-in from Vans. You would have to be very careful drilling the new hole, because if the drill gets into the old hole at all, it is going to steer the drill wrong. Could put an aluminum plug in the old hole first, that would help. You would end up with two holes through the longeron that are right next to each other, like a figure-8. Again, this is not generally allowed so you would want to discuss it with Vans. The saving detail here is that the hole would go through a new F-810C angle in the proper place and that would hold everything together.
 
Excellent information Steve. You are understanding exactly what I was trying to convey. Yes, all 8 holes are drilled (4 in front spar angle, 4 in rear spar) that attach the stab bars. For whatever reason the horizontal must not have been tight against the mounting bars when the front 4 holes were drilled. No idea if the incidence is correct as of yet. The rear spar holes definitely require the spar to float above the fuse when mounted which is good.

The good news is that when mounted using the 4 bolts in front the vertical stab lines up just fine and i don't see a problem. If Im understanding correctly the front face of the Vertical mounts to the aft face of the horiz stab. In my case this is true.

The stops have already been notched. I simply put a digital level on the elevators when in the neutral position and zeroed out my level. If that is an appropriate way to measure I end up with 26 degrees up and 24 degrees down travel to the stops. This is with the horizontal mounted slightly aft of where it ultimately should have been but with spacers could be safely mounted

Sound correct?
 
My drawing shows the fin spar joiner (F-681) mounting the aft face of the stabilizer spar, and then the fin spar goes on the front face of the joiner, with a spacer. Yours will probably want to have the fin spar behind the joiner, so the front face of the fin spar fits against the joiner, and then the front face of the joiner fits against the aft face of the stabilizer spar. You can put whatever shims you need in there to get everything to mate well.

So it sounds like making some shims to fill the gap between the vertical mounting bars and the forward face of the stabilizer rear spar will solve all your problems as long as the elevator horn doesn't hit anything.
 
What does the hole location in F-810C-1 look like?
and longeron edge distance ?
e8s45f.png



for ref, 2005 drawing 78
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I have a QB -8 kit. I had to shim the left vertical bar to fill the gap between it and the rear horiz stab spar, to get the correct alignment. Sterling at Vans had no issues with that. The shim was only 0.032? though.

Out of interest, is your kit a QB?
 
I would want to use an inspection mirror to check the edge distances for the forward holes. I just went through installing my 7A HS a couple of days ago and it's pretty difficult to get these holes positioned exactly right. In fact, I had to make a new F-710B to make sure it would be correct. Given that your HS appears to be positioned incorrectly make sure you check the forward bolts.

I think you need to talk to Vans about any spacers you are thinking of installing between the bars and the aft spar. I admit that seems like the best path forward since you already have holes in the longerons that are too far aft though.
 
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