Oversize wing spar rivet holes

[Thermos]

Hello all,

While countersinking my wing spar reinforcement plates (the "waffle" plates) for platenut rivets, I found that the prepunched #40 holes for these rivets were actually almost #30. I did a little more checking, and the #30 rivet holes for the rib rivets are almost 5/32". That makes for a lot of oversize rivet holes in this part.

I still consider myself a 'newbie' builder, and perhaps these holes are really ok. But everything I learned building the tail kit tells me that these holes are a problem - oversize holes lead to weak riveted joints.

Has anyone else noted this on their wing spars?

Thanks,

Dave

 

[Jamie]

I'm not sure what the rivets on the 'wing spar reinforcement plates' are you mention...(maybe my memory is already getting hazy w/ regard to the wings ), but the rib rivets should definately be AN470AD4 rivets. My pilot holes were fine. I would just give Van's a hollar.

Just curious. Are you SURE the pilot holes are 5/32? If so, you should be able to put a #8 scew through the holes. If you can put an AD4 rivet in those holes without enlarging them there is definately something fishy.

 

[Thermos]

Thanks, Jamie.

Here's an example of the rivet holes in question. This is a #30 rivet in one of the wing spar reinforcement plate holes, not quite 5/32" but close.

The odd part is that the the holes appear to be "coned", for lack of a better word - the diameter is smaller on the opposite side of the plate. And if this really is wrong, then my rear spar reinforcement plates are messed up too. The holes on one side are too big for a #30, and too small (or perhaps just right) on the other.

Spoke with Ken Scott at Van's late last week, he'd never heard of anything like it. Emailed some pics also, no response yet.

Anyone else receive a wing kit in mid-August? If so, I'd be interested to know if your spars look the same.

Dave

 

[TShort]

I'm not 100% clear on what you mean by "wing spar reinforcement plate holes" - could you post another pic to clarify?

Thomas
-8 wings

 

[Thermos]

The wing spar reinforcement plates are those plates with rectangular cutouts that Van's rivets to the aft side of the main spar web.

Dave

 

[LettersFromFlyoverCountry]

I'm confused too. As I recall, the ribs don't rivet to the doubler plates. But it's been over a year.

 

[CFI1513840]

Same Problem

Dave,

After reading this thread, I checked my spars, which were shipped in July. I have the exact same problem on my right spar, although the left one looks ok, I'll be interested in knowing what Van's has to say. I think I'll drop them a line. Thanks for the heads-up.

Ken Howell
Glenwood Maryland
RV-7 Wings

 

[CFI1513840]

Oversize hole measurement

Dave,

I did a little further checking on my right spar. The holes are cone-shaped like you mentioned. I found that a #26 drill will just fit into the large end of the hole. Thats .147 compared to .128 for a #30, so the hole is about 19 thousandths oversized on the large end. I would expect that if you made the shop end of the rivet on the largest side, it would fill in ok, as it only needs a few thousandths and only on the large end. The other option would be to go with 5/32 rivets. It will be interesting to see what Vans says. I wonder if this was a tooling problem? Possibly a dull bit in the punch press?

Ken

 

[Mark Burns]

Dave,

After reading this thread, I checked my spars, which were shipped in July. I have the exact same problem on my right spar, although the left one looks ok, I'll be interested in knowing what Van's has to say. I think I'll drop them a line. Thanks for the heads-up.

Ken Howell
Glenwood Maryland
RV-7 Wings

Ken and Dave,
I've checked my right spar and I have the same thing, although not as bad.
I've got the main ribs already riveted on but the nose rib rivet holes are cone shaped as mentioned earlier. I think this is just the nature of punching holes.
A dull punch would make worse I'm sure.

My nose rib holes are .138 on the large end, and .126 on the small end.

Military Specifications MIL-R-47196A say that the max hole diameter for a 1/8" rivet is .135 (The range is .125-.135)
If you average the small end and the large end I'm still ok I suppose.
The taper doesn't seem to be linear either. It's more of a bell shape than a cone.

http://home.flash.net/~gila/rivet_spec/rivet_a.htm

My right spar is S/N 71768R
We should start looking at these S/N's to see if there is a pattern of the punch getting dull.

My left spar has all of the holes in question filled with rivets already, and I didn't notice anything unusual.

All these rivets do is hold the ribs onto the spar anyway
I'm not going to loose any sleep over this one.

Mark

 

[Thermos]

Ken and Mark (and anyone else!),

I exchanged emails with Scott Risan at Van's on this topic, and also talked with him today on the phone.

According to Scott, the "coned" holes are a byproduct of the die used to punch these holes in the spar reinforcement plate (and other parts too), as the die for a #30 hole is 0.018" to 0.028" oversize to accomodate the punch. So, the hole enlarges as the punch presses through the material.

He also discussed this with Ken Krueger and the engineering staff. They indicated that holes 0.015" to 0.020" oversize would be ok, since a driven rivet would still expand to fill the hole.

By the way, I was really impressed with the response I got from Scott and the Van's folks. I tend to get wrapped up in obsessive little details like this, but Scott pulled other parts, measured them, talked to the folks who run the punches, and consulted Engineering just to answer my questions. There aren't too many other companies where you get customer service like that from the general manager.

Anyway, that's what I found out and for now, I'm pressing on with my spars as they are. Ken, if you do contact Van's could you share what you learn?

Dave

 

[CFI1513840]

Response from Vans

Dave, Mark,

I got a quick response from Bruce Reynolds at Vans, in which he said:

"The slightly oversize hole in the doubler is not a concern. The rivet
will expand to fill the hole. Nothing needs to be done."

The serial number of my right spar is 71792R.

Pressing on...

Ken

 

[Thermos]

Thanks Ken!

Dave

 

[CFI1513840]

Revisiting oversize holes

On closer inspection, I noticed the shop heads of a few rivets on my rear spare doubler plate were slightly less than the 0.5 D thickness required. I'm pretty sure I used the lengths called out in the plans. I debated about trying to drill them out but decided it would probably do more harm than good, especially now that the flap brace and top skin are riveted on.

The cause could be the fact that some of the holes in the doubler plates were slightly oversize as discussed in this thread. Out of curiosity, I calculated the material volume required to fill a cone shaped hole and compared it to the recommended rivet length. It turns out if a rivet hole is 1/32 oversize on one end as seen in some parts, the amount of material left after expansion may not be enough to form the .5 D shop head thickness. In that case, it might be a good idea to go to the next longer rivet to provide a little extra for the shop head.

 

[jcoloccia]

How did you measure the rivets? The avery gauges are a little conservative.

 

[CFI1513840]

Avery Gauge

I did use the Avery gauge, but they also look a little thin using the eyeball. I'm pretty sure they're less than .5 D, but not by much. I should have paid more attention when I was setting them. I think at this point, drilling them out will probably result in less strength than I already have. I don't think it's a significant problem but I'm going to have my Technical Counselor take a look.

 

[az_gila]

Use these numbers

I did use the Avery gauge, but they also look a little thin using the eyeball. I'm pretty sure they're less than .5 D, but not by much. I should have paid more attention when I was setting them. I think at this point, drilling them out will probably result in less strength than I already have. I don't think it's a significant problem but I'm going to have my Technical Counselor take a look.

Just us the spec. numbers from here...

http://home.earthlink.net/~gilalex/

Don't use this old link from an earlier post...
http://home.flash.net/~gila/rivet_spec/rivet_a.htm
I haven't paid for this web site for 6 years.. don't know how long it'll last....

Get a good pair of dial calipers and measure it... you are probably OK...

gil in Tucson

 

[CFI1513840]

Better Measurement

I used a feeler gauge and straight-edge and came up with a miniumum .048" for the shop head on three or four rivets on the rear spar doubler. That's 1/64" shy of .5 D (.062), or to put it another way it's .38 D. I might run this one by Vans to see what they say.

 

[jcoloccia]

If you look at Gil's link, you'll see that the minimum height for a 1/8 rivet .050. You're .048 is DARN close. That'll give you an idea of just how conservative those gauges are. .060 is dead center of the minmum and maximum mil-spec heights.

Remember...you're not making jewelery. You're making a plane designed to be built by people with primitive tools in their garage. Call Vans, though...you'll sleep better at night and won't worry so much about stuff like this anymore.

And your instincts are dead on....driling those rivets out will likely just make things worse and leave you with a mess on your hands.

 

[CFI1513840]

Reply from Vans

The following is the full text of the reply I received from Vans. I feel better now. One thing for sure, building this thing, I never stop learning. I guess that's the education part. I'll be glad when I get to the recreation. Van's reply follows:



"Leave 'em alone.

DRILLING OUT RIVETS
One of the common calls we get is ?I had to drill out a bad rivet and
now the hole is oversize. What do I do??.
Sometimes this is done multiple times in the same hole and now the
hole is so large that the builder has to use a
bolt and nut instead of a rivet. See below.
EXCERPT from Alcoa Aluminum Rivet Book, dated 1984.
?The standards to which driven rivets should conform are frequently
uncertain. In addition to dimensions and perfection of shape, inspection is concerned with whether the drive head is coaxial with
the shank (not ?clinched?) and whether there is excessive cracking of the heads. It has been determined that even badly
cracked heads are satisfactory from the standpoint of static strength, fatigue strength and resistance to corrosion. (Poorly set and
cracked) rivet heads were tested in tension to determine how well formed a head has to be in order to develop full strength. The tensile
strengths of all the rivets were within five per cent of the strongest. The test indicated that minor deviations from the
theoretically desired shape of head are not cause for concern or replacement. The second rivet that is driven in any one hole likely to
be more defective than the first because the hole is enlarged and rivet will be more likely to buckle and form an imperfect
head.Tests have shown that very small rivet heads are sufficient to
develop the strength of the rivet shank, even when the rivets are subject to a straight tensile pull?.where a large head is not needed
for appearance, smaller sizes of drive head should be used to decrease the required driving pressures.?

 

[CFI1513840]

Thanks

John, Gil,

Thanks for the advice & link. I printed the spec and will keep it in the shop. Here's what all the fuss was about.