First screw up - lots of oversize holes

[DaX]

Originally Posted by szicree

Setting those rivets takes significantly more pressure and will probably result in some pretty lumpy skins. I'd just bite the bullet and get a new skin. Trust me, this won't be the last thing you have to make twice

The way I see it, I'll try the AD4's, and if I screw the skin up, I'll re-purchase. What do I have to lose?

[johnp]

Originally Posted by DaX

The way I see it, I'll try the AD4's, and if I screw the skin up, I'll re-purchase. What do I have to lose?

only a little time.

i don't think you'll have much trouble -- after all, you're back-riveting, aren't you? seems to me back-riveting is the easiest kind to do well. (just don't rivet past the end of the back plate.)

[DaX]

Well, I finally had a chance to work again last night - I fired up the compressor, set everything up, and actually sunk two rivets before I stopped. I noticed that there were radial cracks in almost every hole on the stiffeners. I assume this is from drilling dimpling drilling dimpling.

I bit the bullet and ordered new skins and stiffeners. I now have a large quantity of scrap 0.020". I guess I'll just drink a beer to the first of many (but hopefully not too many) re-orders!

[DGlaeser]

Originally Posted by Mel

Matt,
"oops" rivets are not intended to be used in a continuous row. They are only for one here and one there. If you have drilled to 1/8", then you should use AD4 rivets.

In a highly stressed location, I'd agree. But for rudder stiffeners, using 'oops' rivets in this situation will not cause a problem (I'm an AE who did structural design for McDonnell Douglas - now Boeing).

[Rick6a]

Originally Posted by DGlaeser

In a highly stressed location, I'd agree. But for rudder stiffeners, using 'oops' rivets in this situation will not cause a problem (I'm an AE who did structural design for McDonnell Douglas - now Boeing).

Dennis,

I talked with an IA & DER who before retirement was chief flight test engineer at McDonnell-Douglas in St. Louis about this very issue. In short, he knows his stuff. Confirming my suspicions, according to him, ANYPLACE on the RV airframe where it is called out to use MS426AD3 rivets, it would be perfectly acceptable to substitute NAS1097AD4's with absolutely no loss in strength. In fact, sheer strength would increase dramatically and according to him, tension concerns are a non issue. Why? I touched upon it in a previous post....the head diameter is virtually the same. Interestingly, the tension policy established at McDonnell was arbitrary because failure of a solid rivet in tension is highly unpredictable. In reality, failure in tension is largely influenced by the quality of the SHOP head. He mentioned that tension failure calculations for solid rivets were actually different between the F-4 program and the F-15 program and both were established as business decisions more than anything else.

He suspects that Van's curious policy of discouraging the use of too many 1097s in a row is for one reason or another merely a business decision and is not supported by engineering facts. He said anyone who seriously doubts should refer to MIL-HDBK-5 which in the aerospace industry is considered the "bible."

Similarily, I also talked with a long time Van's employee about why Van's does not actively encourage the use of 1097s when installing nutplates....even though their own shop uses them in the application! He too was at a loss to explain the policy, begging he was to far down the food chain to know for sure. He guessed that if given the choice, some foolhardy builder out there might attempt to use 1097AD3's in place of 426AD3 rivets and that would be a bad thing. He further guessed that rather than risk that happening, Van's made a business decision.

[az_gila]

Originally Posted by Rick6a

.....
He said anyone who seriously doubts should refer to MIL-HDBK-5 which in the aerospace industry is considered the "bible."
......

Rick, I did this, and the MIL-HDBK-5 only give numbers for NAS1097 rivets when used in fairly thick skins in a countersunk hole... unlike the 426AD rivets, which are listed with shear and tension numbers for both double dimpled and countersunk applications...

gil A

[LettersFromFlyoverCountry]

Ah, you've reached a critical point in the build process, and I don't mean a particular screw-up on a particular part. You've reached the point where you get to set your standards. Whose advice are you going to take? What is your level of comfort with conflicting advice? What will be the ultimate arbiter, the experience of some people who say one thing, even if it disagrees with standards and the advice of other people with experience? What the situations at which you'll compromise your standards.

I don't mean to be flip at all, but I can overstate how important these questions are and the standards you establish here will be the standards to which your plane is built, of course.

To me, this is the hardest part of homebuilding -- deciding when good enough is good enough based on whatever evidence you gather.

Good luck.