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How can I deal with this Horiz. Stab

pczar3

Well Known Member
Patron
Well I am finally at the point of mounting my horizontal stab on my VERY slow build 6A. After wrestling with the stab for a while I decided to check the rear spar mounting bars. One, the blurry image, is the good side. The square is flat against it and the other leg falls right on the center line (picture 1). The other side is offset towards the back of the plane 0.125 on the outside and one sixteenth on the inside. Has anyone else run into this and what was the fix? Thanks in advance.

ZdaKJjtStw4sYjYFJNXoBnimfBGOPeWEJTvw_87UEFqfK7JAdmycdgCYrKgYN46cZwi4HX5PiAjbCcBMzcB-tux-YeHyTRc6CJ8c_QzNKWq5euOfu0xJTqOESOq6TZj9yR1o1NEg5_VKw4h8TZ5MdOyEbfj0pmz8VwqNLPgkokBoESN1ZnlOgk0td8ZFU6rc2aRu9M39kuU8LF8TKLrnQpUL1AdaytjftFr62nXHK3GyIhrrBu-HnSwMwTP35mmqeuEwGFc7WDjyz8gl39F2wIVfb-cSuLHTt58M1-sleIucBuNo4KoDDG_O3bxFMos1l4RjyIvAdoD_3a3svoEeS_bKygxi5QlqJQjRZYHxi6VPjTfzADKkB_Zc4xO4GOXiFxzf_fwhJ4z3pc-Tu_sXpAWObqNsN-nURcmx0-eIyFehqIpd_cy01lQbAcm3jGluUO5gARh8QGJe2qEd2X4nP0p2s9amCpWI59WdHVqCJJO7gWXp4sPtLVcHGhlTp6t_m83tBQ7_r272Wad9zYNOyqnnLuB8QiS31-NzWqTtx8fzrHEivT9W4mRE60ItNG5rzDdXLvTeMJgxU49LchAbWgAMyy_JNq30atjnANaNc0Ats7xIfIN-ZGS07k6yfr-qoSiW6wuc-44wG6n8Cw00dQQMnMnfInvm5IKolu6ILjpI=w676-h902-no

Here's the good one:
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This is the problem!
vFxmHSC_MFttmA64GsMUwNFD8nBp1psemwIE5uqZp7GsX2OBXdu38qmh-Cq2l_L_jKIhlawe0DWtx4Pz4es3eaUBEm5KAVs1Gai9H5gL77DGt_SA-S0Gp7uy6Q2LK-GuWUxchgnOtQCpYG6lCwjO0lVeBPcmBS7dcOWqotvNMqQJ_PfxlKvCE-W4zAFhm6TLvo7BHopEwEXjyvWJZyE98rJ1Zw_4bGYfiDTEblxaIUnjRKTqFox5xDHsNWbnBplB5brSZxAWwGcYBi0UF1BhclbnxIvssB3X7Y-Kw5W82kFvJFYlppJ99c_VU-NfJtL60XbT81jeo18GBtHIqvHQPsWGSxnNlg0_i6nysc96zjss59RSEwd3-0MTA_Z4l3sk391-9JNkTTmFSPsky6gzTZUnyhAL64eiodbvkvMx1BADnkJJm3sYUeifsaTSjC7oXmG16WG8mcBGacom2cO6dMSNCVDPrbMVcWFcQQiF_Uq4UTZjM6V4OF3OrRPt7m4fZ3letaLn6fdZYv46XeosDqwzRDoey8Ai5GYhCa8N8K7DOBd4dw195QNDMsWVS3DWZbR6cfpM9AOKZddANIIrLMB0vCXeBPTmrE66um182Q1SSuKvxAJpnGFClZh0K9c3XIqwLxqPnBhRsxz-Y4AVsFAzuN_oDoTIOkC4rEf_nurH=w676-h902-no


I hope the pictures show up now. I see them when I look at the page.
Any help appreciated!
Paul
 
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Back to the drawing board trying to insert pictures

Well I guess I was done in by google photos. I'll try again!
Paul
 
I would ask Vans. If they allowed a shim that would be an easy fix. But I suspect that they would not due to the bending stresses in that joint. It should be in pure tension under load.
 
Photos work now, but not sure what the design tolerances are, so you need Scott McDaniels to address this one. Or some of the sages here.
 
Clamp your HS into position onto the tabs, with the .125 spacer installed under the HS Spar per plans. Find the fuselage center line and then measure from the fuselage center line, as far forward as you can, like the firewall or seat back brace, back to each HS tip. Compare those measurements. I believe this process is documented in the manual. This will tell you if that bulkhead is indeed square or not. You might get lucky as variances in the HS might offset those of the bulkhead. You might find you have less of an issue than you think.
Also, examine the bulkhead and see why that bar is twisted.
 
Mine were like that too, but that stab only needed very slight re-alignment. Remember even half an inch of movement at the tip is a tiny movement at the root. A call to Van's definatley a good idea if you have any concerns though!

Alex
 
You might need some custom angled shims. Do you know a local home shop machinist? Easy for them to make. If not PM me. Above all, don't panic. My vertical fwd spar missed its pickup on the hstab by 1/2"! I was able to work around that. These older kits are not as easy to build. Creative shimming required.
 
I think a shim would be called for and be acceptable, and I also bet that this was probably not that uncommon on the not pre-punched -6 fuselages.

A call to Vans should be made to confirm, but as a previous poster mentioned install the horizontal first with clamps and align per the plans so that you have an exact measurement of the thickness of any shims needed.
 
However you shim it, make sure the head of the bolt and the nut are on parallel planes. So if the stab is one one plane and the mounting tab is at a 3 deg angle to it with a 3 deg shim, make sure you have a shim under the head of the nut so that you are not putting a bending load on the bolt when you tighten it.
 
Thanks for all the replies

It is interesting that I measured from the front of the firewall to the bulkhead with this twist and it is within a 32nd of an inch compared to the other side. It must be the bulkhead itself that has the slight twist. I'll probably go with the shims and as they say "build on". Thanks again for all the help and suggestions.
Paul
 
Agree with getting your stab clamped in place and aligned to see where you are at. May end up not being an issue. Properly placed shim(s) would be a solution if need be.

Hang in there and stick with it. Us 6A builders/flyers need to stick together!
 
It is interesting that I measured from the front of the firewall to the bulkhead with this twist and it is within a 32nd of an inch compared to the other side. It must be the bulkhead itself that has the slight twist. I'll probably go with the shims and as they say "build on". Thanks again for all the help and suggestions.
Paul

The bulkhead may be square flange to flange but it is common in these vintage kits for the web to have a slight buldge or roundness. In other words, the web may not be flat. My guess is that is what is causing the twist.
You might be able to manipulate this into shape by relieving the slot in the deck. I would find what is causing this problem before I just jumped to the conclusion that a shim is your salvation.
 
I bought a second hand RV-4 kit and one of the rear bulkheads was riveted in the wrong location. I wound up with a 5/16" gap on the vertical stabilizer front spar attach point. Vans said that a 5/16" spacer in that area was perfectly acceptable.
 
I bought a second hand RV-4 kit and one of the rear bulkheads was riveted in the wrong location. I wound up with a 5/16" gap on the vertical stabilizer front spar attach point. Vans said that a 5/16" spacer in that area was perfectly acceptable.
That is common procedure for VS. However, I have never seen it on a HS. Again, I would want to know why it is the way it is before I contemplated a fix. As it has been mentioned, shimming an out of alignment "twist" is very different than shimming to a parallel or square surface.
 
Van's has the final say in resolving this but I would bet that if you measured from tip to nose on most RV-6s, you would find that the measurements are not the same.
 
Van's has the final say in resolving this but I would bet that if you measured from tip to nose on most RV-6s, you would find that the measurements are not the same.

I wouldn't bet against you!
My main bulkhead is 1/4" off as it came from the factory as a QB. Hence, I have one wing neutral and one with 1/2" sweep. Doesn't affect anything.

Paul, if you can resolve the twist in the bar to allow the HS Spar to be flush to it, all should be good.
At the top of that bulkhead there is a 3/4 x 3/4 x 1/8 angle. The bars rivet to the bulkhead and to that angle. Both bars should be flush to the face of that angle. Perhaps the F-116 Bulkhead assembly isn't flush to that angle on that one side. As mentioned, this could be caused by the web not being flat, but as I look at the plans, that bulkhead web doesn't have much meat at the top where it attaches to the angle. It gets cut out to allow the push rod to pass through.

I would make sure that bar is indeed riveted to the angle and is flush to it. Should be able to see with a mirror.

Call Vans when you figure out what is going on. I am just not a fan of shimming out problems until you know what the cause is. You might discover more things that need attention and the empennage group is one area you just don't mess with.
 
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I bought a second hand RV-4 kit and one of the rear bulkheads was riveted in the wrong location. I wound up with a 5/16" gap on the vertical stabilizer front spar attach point. Vans said that a 5/16" spacer in that area was perfectly acceptable.

Only 5/16" ? Lucky:D Mine was half an inch!
 
Here is what is going on... finally

Well I spent the better part of the weekend measuring and doing more head scratching. When all was said and done, I can see the control stop angle is set at a very slight angle towards the front of the plane. By slight, I mean about a sixteenth of an inch on the starboard side. While standing and looking I noticed the stab mounting bar looked a bit strange. I put a straight edge on that and realized I must have hit it at some point because is was not true. I trued everything up, put the HS on the plane and did the measurements to the middle of the fuselage up front. All it will take is about .020 on the pilot side and everything will be lined up. HS tips are on the button and everything else looks good. I think I'll bolt things up and get ready for the VS mount.
Thanks again to this great group for all the help and encouragement.
Paul
 
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