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Would you rebuild this horizontal?

Gearhead51

Active Member
Patron
This aircraft has been flown since 1990 and currently has 853 hours on the tach time. I have the airplane apart for its first conditional inspection under my ownership. My very thorough IA noticed that there are shims and rivets missing under this horizontal stabilizer spar, and it doesn't bolt to the longeron as shown in the attached photos and plans. There are no cracks and he says it's "not working" which is good, but it's not to plans. I'm not sure what plans were used to build this aircraft or if there have been changes to the plans. The earliest copy I have is 1988, and I don't know if there were plans from an earlier time that might have been used. Vans says the older plans should be the same.

This airplane has been through numerous conditionals and inspectors and this has never been written up in the logbook. My IA suggests that I build a RV7 horizontal. I guess technically it won't be "to plans" either.



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It sounds like you have already talked to someone in our tech-support department, and I would think that would be enough of an answer versus polling the masses, but since you’re asking I will add my opinion that I think everything should be rebuilt so that it matches the original drawings.
I have a lot of experience with RV sixes and Ken assure you that the plans have always showed the outboard bolts being common to the fuselage longeron. Unfortunately, to fix this correctly it’s going to involve more than just building a different horizontal stabilizer. The lateral angle that is under the rear deck on the fuselage is also going to have to be replaced so that all new holes for the forward stabilizer spar attachment can be drilled in the proper locations.
Having said all that, they are experimental aircraft after all and if it has held up fine until this point and you are comfortable with it and not going to be constantly having it nagging in the back of your mind then you are free to leave it as is as long as somebody is willing to sign off the “condition” inspection (they are not conditional inspections).
 
I have spoken with Vans tech support. They suggested I also come here and ask if anybody has suggestions. If I have the tools going, the lateral will be replaced as well along with other corrections.
 
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HS attach

It looks a lot like the RV7 HS Attach.
The angle should go all the way across and nest under the longerons. The spacer is riveted on top through the aft deck then the outboard HS bolts go through the assembly. Shims sit on top of the aft deck between the HS and aft deck. It's a tricky spot to drill.
Based on the photos, I would think the HS incidence is off but maybe I read it wrong.
Here is the same area on the RV7 plan.
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If I am seeing the pix from inside correctly, the bolt is not going thru the longeron or it is very close to the edge. If that is the case, I am not sure how building a new HS will help with that.
Again, if my viewing is correct and the longeron has been drilled on its edge, I recommend to reinforce that but also check with the mothership to get their advise. The major force on HS is downward unless negative G is pulled so the four bolts as they are ought to do the job.
 
Please fix

In the photos it looks like the attaching angle on the horizontal stabiliser is too short to overlap the longerons in the fuselage, in order for the outer bolt to go through both the longeron and the stabiliser angle.

Also, the plan image indicates that the lower angle extending further out than it actually does, and the inner HS ribs should be outboard of the longerons. Check the position of these ribs versus the plan dimensions. It appears that they are located too far inboard, which originally prevented the outer two bolts from being correctly positioned through the longerons and the angles that are below and above.

Note this connection also indirectly carries some of the loads from the vertical stabiliser. If there was a structural failure in flight then it would be catastrophic. I personally would not ride in this plane until it is fixed.:eek:
 
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I recall seeing a Vans engineered repair for these mis drilled bolts. It involved a gusset plate riveted to the longeron. But I can’t seem to find the .pdf
 
I recall seeing a Vans engineered repair for these mis drilled bolts. It involved a gusset plate riveted to the longeron. But I can’t seem to find the .pdf

I think that is only for correcting issues where the edge distance on the bolt hole through the longeron is compromised, not when the hole isn’t even present.
 
Its definitely not right...

While it is definitely not right, I can assure you that you are not the only one with this issue. I know of other airframes with over 1,000 hours that are still out there flying.

Clearly the structural integrity is not what it should be however there has to be a "fix" that will result in a less invasive repair besides the complete replacement of the main fuselage longeron. You need to think about ways you could help transfer the loads from the HS Spar to the Longeron and it looks to me like there could be more than one solution.

I fully undersrtand why VAC are not able to assist but what about a robust discussion with an experienced aviation strutural engineer in your region?


I wish you well.
 
I agree. Also looks like the bolt hits the longeron at least partially on the picture. If that is correct there might not be enough edge distance in the longeron left so that gives you the next issue…. .

There must be some type of gusset you can bolt into the longerons on both sides and over the angle bracket so the bolts from the horizontal stab go through it which will provide equal or more strength then the original design.

Oliver


While it is definitely not right, I can assure you that you are not the only one with this issue. I know of other airframes with over 1,000 hours that are still out there flying.

Clearly the structural integrity is not what it should be however there has to be a "fix" that will result in a less invasive repair besides the complete replacement of the main fuselage longeron. You need to think about ways you could help transfer the loads from the HS Spar to the Longeron and it looks to me like there could be more than one solution.

I fully undersrtand why VAC are not able to assist but what about a robust discussion with an experienced aviation strutural engineer in your region?


I wish you well.
 
Thanks gentlemen for your input. The bolt is so close to the longeron that the washer and head is over it, but the longeron isn't drilled. The bolts were originally in upside down and I flipped and retorqued them. I know that the lower lateral angle and the missing doubler are not correct. I also apologize for my use of "conditional." Having grown up in a Cessna 150, annual is the word and I guess the "L" sound at the end of the word is burned in my brain. This is my first foray into experimental. I will say this Vans thing is awesome.

I guess I should have asked the question another way. How would you fix this issue? There aren't any RV6 horizontal "kits."

Would you somehow repair THIS horizontal (if so, how)?

Buy all of the individual parts and build a NEW 6 horizontal?

Buy a qb 7 horizontal and attach it to the 6 fuse? Vans says it's heavier, but can't tell me how much

Engineer a bracing solution to properly transfer loads?

Consider its 32 year history and keep flying it?
 
In the photos it looks like the attaching angle on the horizontal stabiliser is too short to overlap the longerons in the fuselage, in order for the outer bolt to go through both the longeron and the stabiliser angle.

Also, the plan image indicates that the lower angle extending further out than it actually does, and the inner HS ribs should be outboard of the longerons. Check the position of these ribs versus the plan dimensions. It appears that they are located too far inboard, which originally prevented the outer two bolts from being correctly positioned through the longerons and the angles that are below and above.

Interesting observation above. Is it at all possible that this horizontal was installed too far forward?
 
Interesting observation above. Is it at all possible that this horizontal was installed too far forward?

I was going to suggest the same thing. The proximity of the inboard stabilizer ribs to the longeron and upper deck suggests that the stabilizer is installed too far forward. The bolt holes appear to be close to the correct location in the stabilizer spar angles, yet they miss the longeron. See how the inboard edge of the stabilizer skin, and inboard rib overlay the fuselage deck, roughly to the line of rivets that attach the deck to the longeron.

This is puzzling when you think of the domino-effect of this - What is going on at the rear attachment? How would the fin fit?

I think it is time to remove the stabilizer so you can see what is going on underneath there. Take measurements to compare the locations of the fuselage bulkheads to what is shown on the plans. It may be that the stabilizer is ok and does not need to be rebuilt, but rather re-located to its correct position on the fuselage. (I say this looking at the locations of the bolt holes in the stabilizer spar angles, which look about right)

Also, on the interior picture, it looks like there IS a drilled hole in the longeron, just fwd of the current attachment - what is that about? It is partially occluded by the transverse angle. I think you should dig deeper into this to get a complete understanding of how this is built different than the plans.

In addition to the stabilizer attach bolts, you mentioned that there are missing rivets where the fuselage aft deck panel rests on the transverse angle. Those rivets are important for achieving proper torsional stiffness of the aft portion of the fuselage, so be sure to install those when you attack this.
 
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I was going to suggest the same thing. The proximity of the inboard stabilizer ribs to the longeron and upper deck suggests that the stabilizer is installed too far forward. The bolt holes appear to be close to the correct location in the stabilizer spar angles, yet they miss the longeron. See how the inboard edge of the stabilizer skin, and inboard rib overlay the fuselage deck, roughly to the line of rivets that attach the deck to the longeron.

It may be that the stabilizer is ok and does not need to be rebuilt, but rather re-located to its correct position on the fuselage. (I say this looking at the locations of the bolt holes in the stabilizer spar angles, which look about right)

Also, on the interior picture, it looks like there IS a drilled hole in the longeron, just fwd of the current attachment - what is that about? It is partially occluded by the transverse angle. I think you should dig deeper into this to get a complete understanding of how this is built different than the plans.

In addition to the stabilizer attach bolts, you mentioned that there are missing rivets where the fuselage aft deck panel rests on the transverse angle. Those rivets are important for achieving proper torsional stiffness of the aft portion of the fuselage, so be sure to install those when you attack this.

Good observation. Zooming in on the plans, I see that the aft deck should be attached as well. We saw that hole in the longeron. Since I can't find the original builder all we can do is speculate. I'd GUESS there may have been a rivet there, but I don't see any witness marks.

I hadn't considered the horizontal being too far forward. I'll look at that.

The guy doing my condition inspection stuck his mirror in there and said "that isn't right" within seconds. His credentials are quite impressive IMHO, but he's not just an A&P and DAR. After going over everything else he says it's in good shape, and I'll have a good aircraft after this issue and the Lycoming oil pump AD is taken care of. He wants me to crack the case because of calendar time. That looks like a winter project... or I need to find another O-360 to build. I'm still amazed that neither was ever flagged in all those years. I'm glad this guy is looking over my RV. We are fortunate to have a guy like this in the airpark and EAA chapter.

We had some discussion at our EAA meeting last night, and I'll have plenty of help correcting the issue. We are going to start having "hangar parties." Grill some burgers and build some planes. Good times. I really appreciate this forum and the guys at Vans answering my admittedly ignorant questions. I'm really in the "I don't know what I don't know" phase of this.
 
For repair; be aware many of these parts that need drilled out are over 1/8” thick and care must be taken when drilling out the rivets so you don’t elongate the holes. The lower Angle on the horizontal stabilizer that protrudes past the 2 end ribs will need to be replace with a new angle because the holes attaching it to the longerons were drilled in the wrong place (this will require drilling out the 2 end ribs). Also take note on the older models the kits were not nearly as refined as the newer models. The plans don’t show it but on my rv6a I built I had to file the horizontal end rib flanges a bit in order to have the lower attach angle of the horizontal stab protrude far enough over the longeron for edge distance. My recommendation is to perform the following SB on the horizontal stab since you’ll have it apart https://www.vansaircraft.com/wp-content/uploads/2019/01/sb14-01-31.pdf.

Next the angle beneath the deck that is riveted to the bulkhead in the fuselage and extends over the longeron with the 1/8” spacer between itself and the fuselage deck will need to be replaced as well. Make sure this replacement Angle extends all the way to the vertical wall of the longeron on either side (this will give the attachment bolt of the horizontal stabilizer the most edge distance).

Next I see in your picture a hole in the longeron for a bolt that was drilled in the wrong place and no bolt is installed. This has weekend the longeron and needs addressed. Vans in the past has approved a repair in which a doubler is installed on the fuselage deck that extends several inches in front and behind the miss drilled hole in the longeron. The 1/8” doubler will replace the spacer block that goes on top of the deck and beneath the horizontal stab on that side of the fuselage only. I’ve attached a picture of a repair done on a RV6A showing this doubler.

Bill
 

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Note in the picture above the rivet right in front of the outside hole that goes through the longeron should not have been drilled into the doubler. This hole would correspond with the hole that was drilled through your longeron as well. Leave this hole alone in the longeron and skip it on the doubler
 
Rivets.....

In addition to the stabilizer attach bolts, you mentioned that there are missing rivets where the fuselage aft deck panel rests on the transverse angle. Those rivets are important for achieving proper torsional stiffness of the aft portion of the fuselage, so be sure to install those when you attack this.

Not to throw another observation in but the rivets I can see: most of the shop heads show they were over-driven, some shop heads being flat against the aluminum. The one between the two nuts was not driven enough. Sometimes it is better to leave those than drill them out and reset them, however. This is a tough area to get to but if you have it apart and are drilling things out already you might want to consider a better rivet set.

Part of me would like to look around the airplane and see what the rivets elsewhere generally look like.....:(
 
you might want to consider a better rivet set.

Part of me would like to look around the airplane and see what the rivets elsewhere generally look like.....:(


I'm the 4th owner of this RV. I don't currently have any rivet tools, but there are quite a few sets available for me to use. I'm currently researching what to buy as far as metal working tools. The airplane has been thoroughly inspected. The other squawks were minor and fixed (besides the Lycoming oil pump AD). This is the only one that I wasn't sure of.
 
When I was building my RV-7 back in 2009, I mis-drilled the HS attachment holes and felt I did not have enough edge distance going through the fuselage longeron. Talking with Van's they advised this "repair" which I accomplished. We have seen several other RVs over the years that either had poor edge distance in this area or bolts that did did not even go through the longeron.

Original hole location viewed from below

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Parts fabricated: .125 and .063 6061T6


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Left side - components on top

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Finished repair on left side top

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Right side components on bottom:

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The concept is pretty self explanatory by looking at the photos.
 

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Repair

Nice work. I always wondered why Vans didn't redesign that area. It took me days of measuring and contemplating to drill those two holes.
 
For repair; be aware many of these parts that need drilled out are over 1/8” thick and care must be taken when drilling out the rivets so you don’t elongate the holes. The lower Angle on the horizontal stabilizer that protrudes past the 2 end ribs will need to be replace with a new angle because the holes attaching it to the longerons were drilled in the wrong place (this will require drilling out the 2 end ribs). Also take note on the older models the kits were not nearly as refined as the newer models. The plans don’t show it but on my rv6a I built I had to file the horizontal end rib flanges a bit in order to have the lower attach angle of the horizontal stab protrude far enough over the longeron for edge distance. My recommendation is to perform the following SB on the horizontal stab since you’ll have it apart https://www.vansaircraft.com/wp-content/uploads/2019/01/sb14-01-31.pdf.

Next the angle beneath the deck that is riveted to the bulkhead in the fuselage and extends over the longeron with the 1/8” spacer between itself and the fuselage deck will need to be replaced as well. Make sure this replacement Angle extends all the way to the vertical wall of the longeron on either side (this will give the attachment bolt of the horizontal stabilizer the most edge distance).

Next I see in your picture a hole in the longeron for a bolt that was drilled in the wrong place and no bolt is installed. This has weekend the longeron and needs addressed. Vans in the past has approved a repair in which a doubler is installed on the fuselage deck that extends several inches in front and behind the miss drilled hole in the longeron. The 1/8” doubler will replace the spacer block that goes on top of the deck and beneath the horizontal stab on that side of the fuselage only. I’ve attached a picture of a repair done on a RV6A showing this doubler.

Bill

Thanks William!!!
 
When I was building my RV-7 back in 2009, I mis-drilled the HS attachment holes and felt I did not have enough edge distance going through the fuselage longeron. Talking with Van's they advised this "repair" which I accomplished. We have seen several other RVs over the years that either had poor edge distance in this area or bolts that did did not even go through the longeron.

Original hole location viewed from below

View attachment 30998

Parts fabricated: .125 and .063 6061T6


View attachment 30999


Left side - components on top

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View attachment 31003

Finished repair on left side top

View attachment 31004

Right side components on bottom:

View attachment 31005

The concept is pretty self explanatory by looking at the photos.

Fantastic Dougweil! Thanks for the input. For whatever reason, I must not have been wording my questions correctly with Vans, or they've decided to pull back from giving advice that goes contrary to the plans... which I understand.
 
Fantastic Dougweil! Thanks for the input. For whatever reason, I must not have been wording my questions correctly with Vans, or they've decided to pull back from giving advice that goes contrary to the plans... which I understand.

There is a difference between something just clearly not built to plans, and
errors made while building to the plans.

The above fix is for the latter.

If you had a situation where the holes were just miss drilled slightly but where close to where they should be ( I wouldn't classify them as close in this case), then you probably would have been offered the engineered solution to use doubler plates to reinforce the area.

In your case you need to discover why the overall width of the fuselage is in conflict with the width of the horizontal stab. (as has already been mentioned by others).
The issues with the fuselage structure are easily rectified (add doublers on each side and replace the aft deck plate and lateral angle).
Making the existing horizontal stab fit will probably be a bit more challenging but still might be possible, and could be done in conjunction with installing the fwd spar reinforcement as described in the related S.B. All depends on some of the dimensional details of your specific airplane that can vary from one to another because of each being custom built from non pre-punched parts.
 
There is a difference between something just clearly not built to plans, and
errors made while building to the plans.

The above fix is for the latter.

If you had a situation where the holes were just miss drilled slightly but where close to where they should be ( I wouldn't classify them as close in this case), then you probably would have been offered the engineered solution to use doubler plates to reinforce the area.

In your case you need to discover why the overall width of the fuselage is in conflict with the width of the horizontal stab. (as has already been mentioned by others).
The issues with the fuselage structure are easily rectified (add doublers on each side and replace the aft deck plate and lateral angle).
Making the existing horizontal stab fit will probably be a bit more challenging but still might be possible, and could be done in conjunction with installing the fwd spar reinforcement as described in the related S.B. All depends on some of the dimensional details of your specific airplane that can vary from one to another because of each being custom built from non pre-punched parts.


Scott, I appreciate your input. I'm not sure why it would matter WHY it was built this way. The bolts are so close to the longeron that it looks like they went through the edge in the pictures. I wasn't the builder and was only looking for some insight on how to CORRECT the error somebody else made.

These possible issues were mentioned by VAF members, and I'll look into them. I'd originally thought about posting here, but I really wanted to speak with the Vans mothership before I came here. I'm glad the Vans representative told me to come here and ask.
 
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Scott, I appreciate your input. I'm not sure why it would matter WHY it was built this way. The bolts are so close to the longeron that it looks like they went through the edge in the pictures. I wasn't the builder and was only looking for some insight on how to CORRECT the error somebody else made.

These possible issues were mentioned by VAF members, and I'll look into them. I'd originally thought about posting here, but I really wanted to speak with the Vans mothership before I came here. I'm glad the Vans representative told me to come here and ask.

What I was trying to convey as a difference but apparently failed to, is that if the outboard bolts had gone through the longeron but had poor edge distance as is most common when there are issues here, whoever you were communicating with in tech-support would have likely been offering the engineered fix of adding a Doubler. Since the holes weren’t even anywhere close to where they should have been, I think that’s why that wasn’t offered. I hope that explains it better.
 
Don, I sent you a PM -- a private message.

In case you are new enough that you are unfamiliar, you can access your messages from the link in the upper right corner of your forum screen.
 
Short Cut?

I think the h-stab spars may have been cut short.

1. As noted the inboard ribs appear to overlap the fuselage too much.

2. From the top the bolts appear to be in the right spot relative to the rib.

3. From the bottom the bolts are too far inwards, missing the longeron and giving the appearance of too far forward h-stab. This would be difficult to accomplish without both mis-locating the bulkhead the lower angle attaches to and maintaining clearance for the rudder.

4. The angle attached to the h-stab appears to be maybe a 1/4" longer than the 9 3/4" lower spacer called out on the drawing. It should be two full longeron widths longer.

5. The 9 3/4" lower spacer appears snug against the longeron, yet the drawing shows clearance. It could be that the revised 9 3/4" (R1) dimension made for a snug fit, or if it measures out to 9 7/8" it could have been a solution to the bolts getting right close to the longeron.

I'd check the dimensions of the h-stab. This problem might precipitate unusual cuss-words when attaching fairing. Any clues in that section of the builder's log?

This is fascinating.
 
One nice thing about the 6 is that the plans are fully dimensioned. You could build one from raw stock.
So, you should be able to confirm the HS dimensions, and all other things in that area. Remember, unless a QB, the fuselage jig set a lot of critical dimensions.
Need to find the root of the problem before making a plan of action.
 
This is like looking for a unicorn in the horse coral, but I wonder if it might be an RV-4 stabilizer? That would explain it being too narrow.
 
Root cause & fix

Here's a few pics of the relevant drawing including revisions to 1992. It appears that the OP's HS-614 (the angle that attaches the HS to the deck and longerons) does not have the little "ears" that extend out over the longerons. A simple check is to verify the length of the lower angle, which should be 11.0"

On my RV-6A project it was not necessary to relieve the HS ribs and skins as illustrated in the dwg because there was no interference with the HS-614 "ears".

If it turns out that the only issue is that the HS-614 is too short then I suggest investigating a doubler 1/8" x 1" x 11" to be riveted onto the existing HS-614 angle. The 4 existing bolts will be retained and lengthened by 1/8". Two additional bolts can then connect the longeron and HS-614, with spacer in between approx 1/8" as required. The shims that set the HS incidence will need to be re-made wider to include the new bolts.

Good luck, I hope there is a relatively simple fix that will give safety and peace of mind.
 

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