How to set a big-@$$ rivet

[wingnut]

Del,
Are you making new struts?

No, I'm not making anything. I'm proving (or not) a process. If I'm satisfied with my process, then I'll be installing serviceable fittings into a serviceable lift strut tube. If I'm not satisfied, then I'll buy a serviceable assembly.

[c170b53]

I appreciate the info shared in this post and it's a great reminder to myself of how little I know. . Thanks everyone !

[wingnut]

I appreciate the info shared in this post and it's a great reminder to myself of how little I know. . Thanks everyone !

Jim,
I am curious how you would approach this. I respect your experience very much. I do not see that much has been learned here in this thread, yet. In your work, do you have access to data that will save me time?

[c170b53]

I'll do some research but really Del I'd say I'm a dabbler at best in sheet metal / structural work. I like what you are doing in that you are following the same process a manufacturer would by trying out a process and then carrying out destructive testing to vet the results. I just hope that you will be able to recoup the costs, something that likely has deterred others from going down this road.

[c170b53]

Just to follow up; talked with our structures guys and it seems that Del's approach is sound. First thing that was mentioned was DD's but sourcing the rivets would be difficult plus without a heat treat bath and post storage, I doubt this makes sense for piece work. Most think a 9x and very heavy bar would work to drive an AD rivet of this size, success would depend on the hole quality and the suggestion for a 1 D length at each end so the rivet wouldn't dump. I'm sure I'm not telling anything new to Del here.
I've looked at IPC's for several Cessna's and see the ms20426ad10-30 is called for all holes on early struts, post the hi- shear rivet. Sure enough somehow I have such a strut. My XP has both 426's and 470's at the strut ends, the flush rivets installed where the strut fairings at their ends are in close proximity to the holes and where the fairings widen underneath, hidden are the 470's.

[wingnut]

That's good news Jim. Thanks

[cessna170bdriver]

I'll keep all this in mind the next time I do steep turns in'98C.

[n2582d]

I've looked at IPC's for several Cessna's and see the ms20426ad10-30 is called for all holes on early struts, post the hi- shear rivet.

I'm puzzled as to why Cessna wound countersink the strut attach holes at 82 degrees and then use 100 degree AN426 rivets. I would think the way to get the most shear strength (other than using AN470 rivets) would be to have shallow 100 degree countersinks and most of the head and tail shaved.

For those with struts using Hi-Shear NAS 178-10-26 rivets I thought this information from the International Birddog Association might be worth archiving:

Replacing HiShear wing strut rivets

A couple of weeks ago I received a phone call concerning the replacement of the HiShear rivets in the wing struts. Those giant rounded rivets holding the strut fitting into the end of the strut tube. The HiShear rivet is no longer being made, but a suitable replacement came from Cessna’s structural engineering department.

I’ll quote from the fax I received from Mr. Charles Pate:

"I do not have access to the exact data that pertains to the fasteners and hole tolerance used during manufacture of the wing struts, used on the many versions of the Bird Dog. The L-19A,OE-1, OE-2 parts catalogs that we have do not specify the strut to fitting fasteners by part number, but the artwork looks like HiShear rivets.

"The parts manual for the US Army Cessna O-1 and TO-1 Observation and Training aircraft does have the fasteners called out by part number. Figure 156 of this manual indicates that the fasteners attaching the strut fittings to the wing strut tube are NAS 178-10-26 pins with NAS 179-10 collars. They are steel Hi Shear rivets with aluminum collars and may be replaced with any steel fastener of similar strength and shank diameter tolerance.

"Example: The shank of the common AN5 bolt is identical to the shank of the NAS 178-10 in material and diameter tolerance. Higher strength and closer tolerance diameter fasteners such as NAS 1430 Huck Stump Pins, NAS 1450 Huck Pull Pins, NAS 464-5 bolts and HL18-10 HiLoc Pins could also be used. I suggest that to assure that the load transfer is equally shared by all fasteners in the group, hole quality needs to be high and the diameter should be such that the fasteners are a 'press fit'.

"If the holes are worn excessively, a press fit may still be possible and adequate edge margin maintained by reaming oversize and using one of the above fasteners that can be obtained in 1/64 inch oversize diameters. Ream holes to provide a 0.0005 to 0.0015-inch interference fit and maintain a hole edge distance (e/d) of at least 1.5 on the fittings and strut end tubes. Install fasteners with wet chromate, or similar primer.

"I hope this information can be of assistance in returning some L-19’s to flying status." - C. Pate.

[wingnut]

Gary,
I believe the manufactured head style is irrelevant. I believe both ends of the rivet are by design intended to be formed shop heads, in part due to the length/depth of rivet/hole, to get adequate expansion throughout. With this mind, I don't understand the IPC call out for 426 rivets. They could be 470 rivets and not matter for this purpose. The alloy of the rivet, the quality of the hole, the depth of countersink, and method of installation are the important things.
This 82 degree countersink is no deeper than a full depth 100 degree (in this specific application), and an 82* will have greater shear strength than a 100* (a 50* will have more shear than an 82* and so on until we get to zero with a button head). I would prefer to use interference fit Hi-Tigue fasteners (they cold work the newly smooth reamed hole as you press them in). Next would be Hi-Loc, then bolts/nuts, then button head rivets. But the Boss wants flush rivets
I'm not an engineer, but I will be comfortable replicating Cessna's flush rivet attachment method, or I won't do it.

[n2582d]

... I do not see that much has been learned here in this thread, yet. ...

As a novice sheet metal A&P I have learned a lot. Of course it helps to know so little! For example, I've never heard of a hi-tigue fastener before. Del, I appreciate the time you've taken to explain your thinking on this strut repair; it's been enlightening. It is so rare to see AMTs with your caliber of craftsmanship and attention to detail these days. We can only hope you have an apprentice or two in tow.

Next week I'll be attending Kent White's metalworking workshop. I've been looking forward to attending one of these for years--quite jazzed!

[Bruce Fenstermacher]

Gary, I'm jealous. Kent White! I've bout a few videos, and materials from him and with my crappy torch that is WAY to big, was able to make some very nice aluminum welds. Yes Folks oxy/acetylene aluminum welding. Unfortunately, due to my lack of practice and or prior experience in the science, I would NOT attempt to weld an aluminum joint for anything other than on test/practice material. I would turn two perfectly good aluminum parts into a puddle of aluminum. it would however be a fine puddle of aluminum.

Of course, your going for his metal working class and not welding. I'm still jealous.

[n2582d]

Gary, I'm jealous. Kent White! ...

Yeah, he's another rare example of a craftsman with metal. Poke around his website to see examples of his work, it's absolutely amazing.

Of course, your going for his metal working class and not welding. I'm still jealous.

No Bruce, this workshop is sort of a sampler course; it includes welding aluminum. Here's the schedule. I'll be eating huge slices of humble pie as I have never welded aluminum and my last real welding project was a 1941 BF12-65 Taylorcraft restoration 30 years ago. I don't know if the workshop is full or not but I'd love to see other 170 owners there. Kent encourages us to bring projects we are working on. I'll be bringing my panel cover. As a nice bonus this meets the requirements for the IA renewal.

[GAHorn]

...I would prefer to use interference fit Hi-Tigue fasteners (they cold work the newly smooth reamed hole as you press them in). Next would be Hi-Loc, then bolts/nuts, then button head rivets. But the Boss wants flush rivets
I'm not an engineer, but I will be comfortable replicating Cessna's flush rivet attachment method, or I won't do it.

My '53B has AN5 bolts, per the referenced data. When it was first noticed by Cleo Bickford he condemned the things, then contacted me later to apologize and inform me that he'd discovered that Cessna may have installed AN bolts on up to five aircraft on the assembly-line during a parts-shortage in late 1952. (SN25713 rolled off the line in Nov. '52)
I don't know his resource for that info, but (Cessna Chief Prod. Test Pilot) Mort Brown also was not surprised over it when I asked him. He also mentioned the importance of properly-reamed holes if the bolts are to equally share the workload.

We are going to miss original-source guys more and more and time marches on.

Miles, those struts are hardly stressed in steep turns and shouldn't be any concern. Most over-load failures result in the wing twisting into a negative incidence as the trailing edge rotates upward and the leading edge rotates downward, while the struts hold the front spar just like they are supposed to.

[hilltop170]

I haven't run the stress calculations but I feel fairly confident that correctly sized hardwood dowel rods would carry the loads imposed on those fasteners. Not that I'm going to try it anytime soon.

[cessna170bdriver]

...Miles, those struts are hardly stressed in steep turns and shouldn't be any concern. Most over-load failures result in the wing twisting into a negative incidence as the trailing edge rotates upward and the leading edge rotates downward, while the struts hold the front spar just like they are supposed to.

I said it would just be something I'd think about, not be particularly concerned about. I have the utmost confidence that when my airplane leaves Del's s shop it will be in better condition than it's been since I've owned her.

I don't know how true it was but I remember Dad telling the story of a guy who supposedly looped a J-3 with a pencil in the rear strut fitting at the fuselage.