Rivets in place of screws

[Scott]

Hi All
Any thoughts on using solid
rivets in place of PK screws on
The wing leading edges?

Did the factory always use screws?

Thanks
S

[Robert Lees]

Re: Rivets in place of screws

Yes they did.

How would you get a bucking bar on the inside of the nose ribs

[Scott]

Re: Rivets in place of screws

No problem because the skins only extends about half the distance to the front spar on the bottom.

[N95334]

Re: Rivets in place of screws

Why would want to change it? Been working for years and years

[Scott]

Re: Rivets in place of screws

True enough, but steel screws into aluminium was to aid production. Not really aircraft standard. Solid rivets are lighter, smaller, stronger and eliminate dissimilar metal issues.

[Hank Jarrett]

Re: Rivets in place of screws

I actually like the idea and think the quality could be better, but the legal issues are a problem. Can you "improve" a design without violating the original TC? I kind of don't think you can, at least not without an STC. If you could get your FSDO to approve it without paper work beyond a log entry I would do it on mine, but I doubt the guys at the FAA will be willing to do it.
See what some of the IAs here think, but I am betting they will say you will need an STC. It would sure be easier to drill out the rivets than some of the rusted up screws I had to take out!

Hank

[astjp2]

Re: Rivets in place of screws

Substitution of hardware is a minor alteration. But screws allow the leading edge to be removed for inspection for corrosion and repairs, screws were the standard which was set by both Piper and Taylorcraft. Manufacturers have the right to set standards that do not comply with normal FAA guidance. That is why Cessna has allowed nylocks in their flight controls, because their engineers found it to be satisfactory and meet the regulations. PK screws are acceptable and is negligible for weight. Tim

[Hank Jarrett]

Re: Rivets in place of screws

I understand Tim, but he wants to substitute rivets for the screws. If I was doing it I would ask my IA since he is the one who will be inspecting my work. As an IA would you sign off on the substitution and what would you ask him to log? From a pure safety standpoint I would have no problem, BUT I am an engineer, not an IA. From a structural standpoint I think the rivets would be better, but don't know if my IA would sign off on it.

Hank

[astjp2]

Re: Rivets in place of screws

Being legal, yes, for practical reasons, I would say no, stick with original, it works and allows for removal for repair. I have done a 337 for someone to use Marson rivets to hold the fabric on stamped ribs. With the limited available of wire, it is a practical minor modification. Tim

[Garry Crookham]

Re: Rivets in place of screws

All commenting on this might want to be aware that Scott is in Canada and is an experienced AME--Canada's equivalent of our A&P/IA. His blog on CF-CLR shows a high standard of workmanship that we all should try to achieve.

[N95334]

Re: Rivets in place of screws

What about stainless steel screws?

[N96337]

Re: Rivets in place of screws

What about stainless steel screws?

When you put stainless and aluminum together, as soon as there's moisture, you've built a good battery....corrosion wise. I've cussed I don't know how many "mechanics" that thought they were really doing a good thing by putting stainless screws in. The best is good old slotted, cad plated steel PK screws. Simple, effective and as said before, the standard for many years.
John

[Scott]

Re: Rivets in place of screws

I kinda think we end up in a similar galvanic condition with the cad plated screws because the plating is removed as the screw cuts into the aluminium. The remaining cadmium provides some sacrificial benefits I guess but for how long. The result is corrosion spreading out from each screw, which is what I have on my old skins.

Having said that, this is one of those issues that seldom becomes a real problem because of time ie after 20 or more years it won't look very nice but will most likely still be functional.

Anyway, thanks for all the input. I'll continue to mull this over until it's time to install the skins.

Btw... test fitted the wings today. All went reasonably well and very happy with the symmetry check (phew).
S

[Mark Bowden]

Re: Rivets in place of screws

Scott, to improve corrosion resistance with either the screws or rivets you can install them with wet epoxy primer. It works better with rivets than screws for the reason you mention. However the CAD plate can protect even with what looks like a pretty good scratch to the substrate for a long time.

If you put the screws in wet, it will make it more difficult to remove if and when the time comes. Conversely they will be less likely to back out in service.

This is a common practice, especially where you have to put fasteners in carbon/epoxy parts, mix it up in a Dixie cup and dip them as you install or brush on and install. It is time consuming and messy but is another layer of protection if desired, like if you operate near the sea coast.

Mark

[N95334]

Re: Rivets in place of screws

Instead of epoxy what about dipping the screw in Zinc Chromate prior to installing.