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Another HS00001 / SB 14-01-31 edge distance issue

warrenkm

Member
Hello, long (long long) time lurker and new builder here (brand new emp kit too). Like many people I am having trouble with getting all the bits of the front spar lined up in such a way as to make sufficient edge distances on HS-00001. I won't divulge the quantity of "extra" 702s I have in my junk bin. Anyway, unless I drive HS-00001 all the way up to hit the flange and of course into the radius of HS702 I'm not going to make 2x diameter. When I look at SB 14-01-31 it mentions an edge distance requirement of only 1.25x (which I do make). Anyone notice this? Can someone explain the discrepancy between the usual edge distance criterion and what Van's is showing here?

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Since this is a stressed part, most are reluctant to make an off plan suggestion. Personally, I am not sure of the question. You might just get your specific question in order and call Vans about this. You can radius the edge to fit better in the inside radius. Just don't leave a sharp edge on it.

Here is a video of a retrofitted SB kit. Pretty good. It might give you some hints.
https://www.youtube.com/watch?v=HgE0T8EMaZk
 
Since this is a stressed part, most are reluctant to make an off plan suggestion. Personally, I am not sure of the question. You might just get your specific question in order and call Vans about this. You can radius the edge to fit better in the inside radius. Just don't leave a sharp edge on it.

Here is a video of a retrofitted SB kit. Pretty good. It might give you some hints.
https://www.youtube.com/watch?v=HgE0T8EMaZk

Thanks for the response. To get straight to it - I am curious why the SB from Vans mentions an edge distance of 1.25X whereas it's traditionally 2X the rivet diameter. It's entirely possible I'm missing something very simple or misreading the text.

In my case I make the 1.25X (5/23" edge-to-edge distance in the above SB excerpt) but don't come close to 2x. If it ends up being an issue I'll roll my own HS00001 as I think no matter what I do with the factory part I'll end up with an edge distance problem somewhere.

I emailed Vans this morning so for posterity's sake I'll post the answer when I receive it.
 
This is one of the worst designed parts in the empennage. I was nervous with the edge distance as well. I ended up going through 2 front spars and 2 doublers before I gave up and ordered some blank stock from ACS to fabricate my own doubler with slightly larger "ears" that I radiused to fit tightly in the flange radius. Perfect 1/4"+ edge distance now as measured from the center of the hold to edge of part.
 
The response was:

"What you have looks to fall into the minimum allowable edge distance as determined by our engineers. From what I see in your pictures you can continue on whit what you have.

There are a number of builders that have done this over as you noticed but it?s possible they were building this before our engineering team reevaluated the required edge distance. "

I don't know exactly what analysis they did but they found the reduced edge distance is okay. I ended up remaking the part and while I didn't get as much edge distance as I would've liked it's quite a bit more.
 
I finally broke down and bought some .060 stock and made a slightly larger doubler per Vans suggestion and got the edge distance required. The YouTube video is great but good luck having it turn out that easy to get the repair done. I do however appreciate the guys that took the time to make the vid.
 
As I see it the minimum edge distance they specify in the SB seems to be fine. These planes were flying fine without the doubler, it was introduced to stop cracking. Also the SB mentions 5/32" center of rivet to edge; that only leaves 3/32" from edge of rivet (not a lot). It also mentions that if your edge distance is not in spec to go ahead and add one in between the rivets to address this. That's my 2 cents, hope it helps someone along the way make a decision.
 
Just had same problem

I just wasted some time with this as well. Just to clarify to future builders if you are building a new kit to plans you still need to look at the sb anyway because there is a lot more info in the sb than in the plans. The edge distance exception of 5/32 from Vans solves my problem. Also pay close attention to the fit between hs-00001 and the bend radius in hs-702. I put a radius on the edge and found that it was still digging in.

On another note I have an engineering backround and wondered why the rivet specs never consider material thickness in the edge distance equation. It doesnt make sense to me that .125 aluminum needs the same edge distance as .016. This is probably why vans allows a reduced edge distance on the .060 doubler.
 
SB 14-01-31 issues

Did the SB and didn't like the result due to edge issues and not getting the doubler rivets equidistant about the rib attach rivet line and having the shop head interfere with the bend in the rib lip. (my bad)
Bought new forward spars, doublers and new ribs, disassembled the stabilizer and rebuilt with the new parts.
I took it slow and very carefully during the rebuild and spent a lot of time cross checking the design and manufacturing assembly process that Vans had documented. There is a lot that is not in the instructions or on the drawing so it made me feel better about the mistakes I made doing the SB. I am not surprised that a number of builders are having a problem with this SB. If I were doing it again I would drill out a number of skin rivets to provide better access to the forward spar and make it easier to perform the modification.
I decided to reattach the ribs using Cherrymax rivets due to not feeling very proficient with an offset rivet set in a tight location despite setting a dozen or so rivets in a tightly spaced test piece with the offset tool in the rivet gun. Certainly a skill that I need to worked on.
 
Generic vs. specific

As I see it the minimum edge distance they specify in the SB seems to be fine. These planes were flying fine without the doubler, it was introduced to stop cracking. Also the SB mentions 5/32" center of rivet to edge; that only leaves 3/32" from edge of rivet (not a lot). It also mentions that if your edge distance is not in spec to go ahead and add one in between the rivets to address this. That's my 2 cents, hope it helps someone along the way make a decision.

Note that the 2D edge distance is only a generic guideline.

If the manufacturer/designer uses a different number, such as 1.25D, for a specific location, then that is the number to use.
 
Offset Rivet set

...I decided to reattach the ribs using Cherrymax rivets due to not feeling very proficient with an offset rivet set in a tight location despite setting a dozen or so rivets in a tightly spaced test piece with the offset tool in the rivet gun. Certainly a skill that I need to worked on.
I bought a bunch of cherry max rivets in both -4 and -5 in anticipation of doing this work, with the same fear. I ended up using all -4 normal rivets that Van's supplied with the SB kit.
What I found was that:
  1. with the HS flat on the table,
  2. the part I wanted to rivet on the bottom,
  3. good access to the area,
  4. putting the rivet gun in the larger area (manufactured head aft - yes I know!),
  5. thick cloth between the rivet gun and the skin,
  6. laying the rivet gun on the cloth directly (not trying to hold it in my hand),
  7. let the offset rivet set find it's natural location,
  8. take a lot of time to ensure the rivet gun is perpendicular to the work,
  9. take a deep breath,
  10. about a 1 sec blast (YMMV, depends on a lot of factors)
it went really well. I think I ended up with one small smiley, the rest were pretty good.

Strangely, the -4 rivets attaching the ribs were probably the most difficult, but I had almost full access. I have seen some rivet sets that look like giant crab claws out there somewhere - that would have been helpful for the last rivets. :)
 
Generic versus specific - philosophy

I suppose it depends how well the design stress numbers match up with actual in-service stresses encountered in the design lifetime of the airframe. The confidence in the number of fatigue damage cycles that can be expected to be tolerated before cracks start to propagate is dependent on the quality of the system modeling performed and the fidelity with actual stress data from flight testing. Since Vans doesn't share any of the modelling analysis data or flight test data and I assume they are using a finite element modelling tool with an appropriate mesh and a representative number of flight /stress cycles then the edge distance numbers can be whatever the design / analysis will support and we have to assume in those critical cases they have done the actual analysis and its not the case of " it will be alright you will find".
The difficulty with which the manufacturing process variability can meet those numbers is the big question and reducing edge distances below 2:1 together with manufacturing variability will result in large variability in number of flight cycles before cracks start to propagate. Ability to drill round holes of exact diameter in exactly the correct place is critical to the process. Obviously we are not going to achieve that in the amateur build world so I much prefer to stick with the textbook design guidelines for that added margin. I feel less inclined to worry if it is all going to come apart when I get bounced around in turbulent conditions.
 
I suppose it depends how well the design stress numbers match up with actual in-service stresses encountered in the design lifetime of the airframe. The confidence in the number of fatigue damage cycles that can be expected to be tolerated before cracks start to propagate is dependent on the quality of the system modeling performed and the fidelity with actual stress data from flight testing. Since Vans doesn't share any of the modelling analysis data or flight test data and I assume they are using a finite element modelling tool with an appropriate mesh and a representative number of flight /stress cycles then the edge distance numbers can be whatever the design / analysis will support and we have to assume in those critical cases they have done the actual analysis and its not the case of " it will be alright you will find".
The difficulty with which the manufacturing process variability can meet those numbers is the big question and reducing edge distances below 2:1 together with manufacturing variability will result in large variability in number of flight cycles before cracks start to propagate. Ability to drill round holes of exact diameter in exactly the correct place is critical to the process. Obviously we are not going to achieve that in the amateur build world so I much prefer to stick with the textbook design guidelines for that added margin. I feel less inclined to worry if it is all going to come apart when I get bounced around in turbulent conditions.

That is the great thing about the experimental category.... you can decide what is right for you.

For those that know they don't have the background knowledge to make structural evaluations on their own......
The SB was issued for an age related fatigue issue that no one had ever detected in the field until their attention was directed to it via the SB.

When the SB was issued, the fix was already engineered and analyzed via FEA and then evaluated further to approve corrective measures when some installers had rivet edge distance issues.
 
Well, I got into the same pickle. The most embarrassing thing is that I knew there are a lot of edge distance issues in these parts, I've read all these topics. I was just not looking where I should be! I put the layout, I measured it, stepped away and got back. Then I drilled, and it was way too close.

HS-710 looks good. I think, this is what deceived me (confirmation bias!): I saw holes lining up up, and instinctively aimed at that. I was kind of too afraid to move the hole so I don't get too close to the edge of HS-710.

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HS-702 looks good, too.

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However, HS-00001 displays some signs of trouble. The distance is way too small! However, SB does allow for 5/32, which is 0.156, and I have ~0.176. Kind of concerning, but oh well.

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HS-00005 is what I was really concerned about. Same distance as with HS-00001, but this part is very thin.

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So I contacted Van's support and initially their response was either to re-flange the rib (the way it is done in SB) with wider flange or to replace the parts.

I then asked what distance would be acceptable for the rib given that I am too anxious to move the hole around (as I might get it too close to the edge of HS-710!). They told me that the edge distance is the same as for the HS-00001, 5/32.

So I got confused because I have more than that (well, at the time I haven't drilled the hole yet, it was a projected location)? On which they said that if I can keep it more than 5/32, I should be good.

After I drilled the hole, I got edge-to-edge distance of .103. Which is somewhere about 0.167 edge distance (the hole is the final size of #30). Terrible, but should work?..

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This is exactly where I'm at in my build. I don't know that there is a way to maintain edge distance on HS00005, HS00001 and the reinforcement angle HS710 at the same time. I predrilled the holes in HS00005, assembled everything with the skins. I was preparing to match drill these parts together and realized that I was about to ruin the spar and reinforcement angle. I don't really know how to proceed here. I'm going to reorder HS00005 and try again I guess.
 
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