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Mistake on front spar flange (08-04)

P

pilotlanham

Member
I made a silly mistake whilst working on page 08-04, it calls out the following "Clamp the spar cap in place. Match-Drill #30 the 1/8 [3.2 mm] holes of the spar web into the entire length of the spar cap" - unfortunately I mixed the web/flange instructions and incorrectly drilled the #30 on the spar FLANGE across the approx 50 holes that are shared with the spar cap.

Reading ahead the flange holes then get countersunk for the skin dimples. An oops rivet could work in theory, but as I understand it is not suitable for a row of rivets - so I think I would have to go with the next size up rivet. I have also called Vans support and the person did seem to think it'd be okay to continue so long as I don't break the edge distance rule.

From my quick maths, I think in it's current state the edge distance isn't broken, but if I countersink these holes would it then break the edge distance rule?

Here's a few photos to hopefully convey the mistake, what's your take?

img_5128.jpg
(Image showing front spar flange + spar cap incorrect holes)
img_5138.jpg
(Image showing the general area of work)
img_5137.jpg
(Image showing the measurement of distance)
 
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Measured edge distance doesn't have anything to do with whether the material is countersunk or not. It's just the distance from the center of the hole to the nearest edge of the material. That dimension requirement is called out in Table VIII and figure 2 in Mil-spec MIL-R-47196A or as a minimum thickness out of section 5 of the build manual, which says that minimum thickness for countersinking a 1/8" hole is .050

As with all things like this, the manufacturers engineering will supersede a mil-spec or advisory circular, but if not you can always fall back to those documents.
 
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Interesting I did check Section 5 again and couldn't find a reference to whether a countersunk hole had a different edge distance from the standard 2x, but the figure of 2.5x has been mentioned to me elsewhere for a countersunk hole, so I assumed that was a real thing - perhaps not!

I'll check section 5 again, and also MIL-R-47196A and see if I can find any reference to the correct edge distance measurement
 
pilotlanham said:
Interesting I did check Section 5 again and couldn't find a reference to whether a countersunk hole had a different edge distance from the standard 2x, but the figure of 2.5x has been mentioned to me elsewhere for a countersunk hole, so I assumed that was a real thing - perhaps not!

I'll check section 5 again, and also MIL-R-47196A and see if I can find any reference to the correct edge distance measurement
Click to expand...

My Bad- I don't think I explained that very clearly. Sorry, It's 5 o'clock in the morning here :). I'm going to go back and edit my prior comments.

I just looked it up. For a #30 rivet It's defined as .281" in figure 2 of that mil-spec.

Vans section 5 just says min thickness for a #30 countersink is .050". It's in section 5.5
 
If it's any consolation, I made the exact same mistake. It was the first day of my build. I, too, was not up to speed on the lingo (web/flange, etc). Fortunately I haven't made a mistake like that since then. I ended up replacing the parts.
 
pilotlanham said:
I made a silly mistake whilst working on page 08-04, it calls out the following "Clamp the spar cap in place. Match-Drill #30 the 1/8 [3.2 mm] holes of the spar web into the entire length of the spar cap" - unfortunately I mixed the web/flange instructions and incorrectly drilled the #30 on the spar FLANGE across the approx 50 holes that are shared with the spar cap.

Reading ahead the flange holes then get countersunk for the skin dimples. An oops rivet could work in theory, but as I understand it is not suitable for a row of rivets - so I think I would have to go with the next size up rivet. I have also called Vans support and the person did seem to think it'd be okay to continue so long as I don't break the edge distance rule.

From my quick maths, I think in it's current state the edge distance isn't broken, but if I countersink these holes would it then break the edge distance rule?

Here's a few photos to hopefully convey the mistake, what's your take?

img_5128.jpg
(Image showing front spar flange + spar cap incorrect holes)
img_5138.jpg
(Image showing the general area of work)
img_5137.jpg
(Image showing the measurement of distance)
Click to expand...

I think that machine countersinking will break the edge distance because the resulting hole will be bigger than 1/8 and there would not be enough material left at the edge. Alternatively, both the spar and cap flanges could potentially be dimpled instead of machined.

I also recall something about 2.5 edge distance for flush rivets. It might have been in AC43-13 1B but I need to check. Typically any time that I lay out rivets I always try to get 5/16 edge distance.

Ideally a replacement spar would be inexpensive and easy to obtain, but sadly that's not the case at the moment, especially if you are in UK. I think that every builder ends up with some trashed parts in the corner of the shop, sooner or later.
 
The important consideration is the thickness of the material the spar is made of, that you will be machine countersinking for a dimple for 1/8 inch flush rivet, which is .007 deeper than it would be for a net fit of the rivet.
This would require the spar material to be .063 thick.
I don’t remember for sure what it is but I’m pretty sure it’s less than that. If I am correct, then replacing the parts is necessary.

One tip that may be helpful.
Holes in parts are usually punched at or just under the diameter of the fastener that will eventually be installed in them. So anytime you are about to drill, whether it’s match drill or final drill, through a pre-punched hole, and you are going to be appreciably changing the whole diameter, double check, or even triple check because that only occurs in a few specific locations.
 
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Yea, I've put an order in for a replacement part just in case - but being in the UK, and Vans being in their current state I am not sure how long it'll take, or how expensive the shipping will be - hence why I wanted to see if it was salvageable.

Certainly a mistake I don't plan to make twice, was easily avoidable for sure!
 
Tom023 said:
Both the front and rear spars are .063 (HS-00902 HS-00903) according to the parts list, so per Scott's post above the larger rivets may be acceptable.
Click to expand...

Thanks Tom
I just couldn’t remember for certain so wanted to lean towards being conservative in a recommendation.
At .063, 1/8” rivets would be acceptable.
 
We made exactly this same mistake but on the horizontal stab spar. We opted to replace the spar, considering its criticality. It was a $650 mistake :(
 
I've spoken to Vans, and sent a bunch of measurements and info via email, and they have said that the clearances are all within limit and to build on with upsized rivets - so I think that's what I will do - although I did put an order in for a new front spar so will see if I get any updates on that today before I make a final decision.
 
thehagg501 said:
Does the attached spar cap also add to the total dimension in this case?

More discussion here
https://vansairforce.net/community/showthread.php?t=209025
Click to expand...

No
The deciding factor is whether the part being machine countersunk is thick enough that the hole will not be enlarged when the c. s. is cut to the proper depth.
For an 1/8” rivet the minimum is .050 for a net (flush) fit of the rivet head. Add .007 deeper to accept a dimple and the minimum is then .063.
 
I did this mistake with my spar of the the HS and when I contacted VANS to see if I can use the next size rivet, they gave me a unambiguous no. so I replaced the spar.
 
georgemohr said:
We made exactly this same mistake but on the horizontal stab spar. We opted to replace the spar, considering its criticality. It was a $650 mistake :(
Click to expand...

Same here. Edge distance was short by 1/32 but I was not willing to violate it at all. Part was $60 - shipping was $500+.
 
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