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777drvr

Well Known Member
Hi Guys,

I'm working through a snag list on my recently purchase RV-4 and could use some advise on a structural repair .

At F410 the .025 skin has worked past the AN426 AD3 rivets in a few places . It appears as if the .025 skin was CS instead of dimpled and it eventually worked through . The skins and former flanges appear to be OK otherwise .

I'm pretty sure any countersunk solution is out the window so I was thinking of replacing the 7 bottom rivets with AN470 AD4's or Cherrymax rivets. The size of the pulled out AN426 AD3 heads is larger than the shank of the AD4's but I think it would overlap enough and would certainly be better than what I have now ! Or should I go AN5 ?

Any advise would be appreciated !

Marc

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This is a pretty heavily loaded portion on the -4.
I would go on up to -5 rivets.
 
Marc,

When I built my -9 I used AD4's to hold the aft most bottom skin in place because of the pounding I figured that area would take, being a tail dragger and all. I called Van's and they didn't have a problem with that minor change.

Your challenge will be dimpling through all that structure. A pop-rivet dimpler might work but I don't really know.
 
I don't think dimpling or CS'ing is an option right now . I'm willing to take a hit on the cosmetics and go with the universal head AN470's or Cherrymax rivets . If I go with solid rivets I'll have to bribe one of my skinnier friends with beer to shimmy down the tail !

Marc
 
777drvr said:
I don't think dimpling...is an option right now . Marc
Click to expand...
Marc,

A dimpling solution is NOT necessarily out the window. Where is it written in stone that you have to use round head rivets?
Think of the flush screws that attach RV fuel tanks.

If it were my airplane, I'd likely ream the holes up to .160, then redimple the holes to accept 8-32 screws and install
structural NAS 1202 or similar:

http://www.aircraftspruce.com/catalog/hapages/nas1202.php

The dimpling process itself is not very hard to accomplish, but because of the location, would require that skinny helper's
assistance for a few minutes:

http://www.vansairforce.com/community/showthread.php?t=18391

As an alternative to shooting AD5 rivets, there would be little chance of dinging or denting the skin either.
If in doubt, feel free to contact Van's and run the idea by them.
 
PRELOAD

It looks like those rivets were preloaded pretty heavily. I would consider adding a shim in the opened up area to reduce future preloading. Since its a hidden from view area, put in AN470 4 rivets or 5's if the holes are too big, like Mel suggested.
Steve Barnes The Builders Coach
 
Another idea

My concern is that you won't have edge distance with number 5 rivets. I would look at using dimpled AN960D4 washer to replace the material chaffed out from under the head of the original fastener. Use an NAS 1097AD-4 rivet in a #3 dimpled washer. Good luck.
Andrew
 
Hi Guys,

You'll have to bear with me because I'm not a builder but have been learning quickly about how these airplanes are built by reading books, the plan set , talking to local experts and spending way too much time on these forums soaking it all in !

I thought dimpling was out of the question because all the pieces are in place right now . I didn't think that you could dimple 3 layers in one shot . The .025" outer skin overlapping the .040" aft skin and the .032" bulkhead flange . In total .097" . A little thick I thought .

I just found some oversize shank CherryMax rivets that have a shank diameter of .140" . That's a bit closer to the head diameter of the AN426-3 that was originally in the skin . May be the easiest solution ....

Steve,

I'll see how preloaded the skin is when I drill out all the rivets I'm going to replace.

Marc
 
Andrew,

Another interesting idea but probably the biggest hit on the looks .

I'm thinking that any repair is better than it is now . The airplane has 600 hrs on it right now but I don't know how long it took for this to happen.

Marc
 
Here are several options I would consider,

1. upsize the holes to -4 rivets and intsall button heads (470's) Maybe even -5 s if the countersinks don't clean up with the 1st oversize.

2. Because of the deformation on the inside, you can install Hi-lock blind fasteners. They will come in -5 diameter but not in -4 (as I remember). They will "draw" the inner blkd flange flush with the skin. They are also close tolerance fastenters and won't "work" as will a screw.

3. You could install a "lap splice repair". Basically ad a filler to the fwd side to make the exterior skins flush then an outer doubler using the existing row of fasteners as one row then a row aft and 2 rows fwd. AC 43.13 will give you an example of this repair. Petty simple, strong and looks factory. You will be able to use countersunk fasteners. Use the existing rivet spacing and your extra rows should be approx. 75% of the rivet pitch.
 
A bunch of great suggestions ! I see a number of votes for AN470-AD4's and 5's . Is there any reason not to use the equivalent sized CherryMax rivets ? I have no rivet gun experience ( although I have one) and thought the Cherrys would be easier..... I wouldn't have to bother my skinny friend !


Marc
 
The problem with the Cherrymax is that they have poor tension strength. Your rivets failed in tension so it is clear there is significant tension loads on those fasteners. You need a fastener with better tension strength. A screw would be an easy solution. Just looks bad. You also need to be able to pull that blkd flange flush with the skin. A screw will do that. Make sure you get all the chips out. From the photo it looks like there is quite a bit in there. I like the Hi-lok option as the button head is very small and they are easy to install. It will be tough to draw that skin tight with a regular rivet. You can use a screw temporarily as you rivet an open hole.
 
Actually, the rivets are intact . The .025" skins look to be countersunk even though I understand that .032" is considered the minimum for countersinking an AN426-3 rivet. The rivet pulled through the thin skin in those locations . I was hoping some sort of rivet with a bit of a flange would do the job .
 
NAS1241AD

rivet is the same flush size as the oversize cherry that you are looking at. You can find them at Genuine Aircraft Hardware. Use NAS1242AD for universal head. True, anything to tighten it up will be an improvement. Also something fairly easy to keep an eye on. Good luck.
Andrew
 
apkp777 said:
...I do like the Hi-lok option as the button head is very small and they are easy to install..
Click to expand...
I still prefer a flush screw solution but if I were going to accept protruding fasteners on my RV's airframe, I really do like your hi-lok solution. In the production
environment I installed thousands of the fastener type over the years so I think it may be misleading to characterize the protruding head of a Hi-Lok fastener
as "very small." For comparative purposes, the photo shows how using an .070 splice plate I fabricated (substantially thicker material than called out in
the plans) I attached the vertical stab to my -6A. I did it that way just because I could. Note the considerable difference in head diameter when a close
tolerance 5/32 hi-lok is compared next to an AD4 rivet. Cosmetically, this may or may not be important to an owner about to embark on a repair but he should
be correctly informed.

As for ease of hi-lok installation, that really depends on a lot of things. There is "easy" and there is precise. In close tolerance applications, high quality hole
preparation is absolutely mandatory if the hi-lok is going to serve in the capacity for which it is intended. That means (among other things) final hole size for a
5/32 nominal hole should be achieved with a proper reamer (not a twist drill) and to a precise dimension to meet minimum (.302) and maximum (.384) protrusion
standards. I am describing tools not likely to be possessed by a non-builder.

My previous comments assumed a skill set already developed and tool assortment commonly possessed by the typical RV builder.

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Those Hi-Lok rivets look like the ideal solution to me.
Again, hole preparation is very important.
Also, you will probably want to shim where necessary to relieve stresses.
 
Another thought

You could:

- Cut a strip of aluminum that would match the flange of the bulkhead in width and extend to the sides as far as necessary to extend beyond the ends of the failed joint.

- Drill out the failed rivets and enlarge the holes as necessary for #8 screws (8/32).

- Debur the holes and edges.

- Have skinny friend hold the aluminum strip in place on the bulkhead flange and mark the holes with a "Sharpie" pen (blue preferred).

On your workbench:

- Drill 1/8" diameter holes in the aluminum strip where it is marked.

- Cleco a platenuts to the 1/8" holes with a bronze colored cleco (1/8").

- Drill a 1/32" hole in the aluminum strip through the one of the platenut mounting holes.

- Add a silver cleco in the hole to secure the platenut against rotation.

- Drill a 1/32" hole through the other mounting hole in the platenut (you are using the platenut as a drill guide).

- Repeat the platenut drilling process at every location marked on the aluminum strip (which will become a nut plate).

- Carefully enlarge all of the 1/8" holes to 1/4".

- Debur all of the holes.

- Countersink the 1/32" holes for 1/32" dia. flathead rivets strength of these holes is not important.

- Rivet #8 floating platenuts to the nut plate with 3/32" flathead rivets.

Back at the airplane:

- Dimple the holes aluminum skins and bulkhead flange for #8 flathead screw using a die with a hole in the center, a socket head screw, a dimpled #8 platenut and an allen head wrench. Each screw may only be good for one dimple. (I got my die from the guy in Littleton, Colorado that sold me my pitot mount)

- Have skinny friend hold nut plate in place so you can cleco every thing together for assembly with bronze clecos.

- Remove a cleco and install a #8 flathead screw until the assembly is complete.

There are a lot of variations on this approach but the main thing is to think through the repair thoroughly before committing and once started don't worry about stopping to think if what you are doing doesn't look right. Good luck.

Bob Axsom
 
Rick,

I too have installed thousands of Hi-Loks, When comparing a -4 rivet to a -5 Hi-Lok, the -5 is bigger, However, he needs to install a protruding head fastener that has the ability to draw everything tight. I don't know of another fasterner that has the head size of a Hi-Lok. Maybe "very small" was an overstatement. I should have said "relatively small" at least compared to other fastener options. It doesn't sound like the gentleman has a ton of sheetmetal exp. Having purchased this plane from someone else. Personally I would try to use a rivet shot from the instide and accept a bucked tail on the exterior. However, that gets trick as you probably know.

Hi-Loks are easy to install. He can get by with a 5/32 drill bit and not get into decimal sizes. Also, he could use a low profile nut and thin washer. Looks like a -2 or -3 length will do. I would buy -3's and use washers to correct any length discrepencies. up to 3 aluminum washers would be perfectly acceptable if necessary.

In the end, a hi-lok looks good which is important.

A screw would be a option. Certainly simple. He can find a low profile titanium screw that would look pretty well.
 
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Thanks !

Thanks to all who have weighed in on this one . The responses run the gamut from simple to a little more involved .

I'm going to start with the simple . I'll use the oversized -4 CherryMax rivets and see how that works out . This area is very easy to inspect regularly and this repair doesn't preclude a more involved response in the future if necessary. It will certainly be better than what I have now .

On to the next question ...

Marc
 
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I actually used the 5/32" CherryMax rivets and the repair worked out well . The skin pulled down nicely and only required Cleco pull to make it come together .

I did learn a little something about protecting the surface when strong arming the pop rivet gun . Push ,push , bammm ! . Nice big scratch in the paint . I won't let that happen again . So figuring that this was a predictable occurance , I protected that area with cardboard . Push , push , bam ! It jumped the other way . Another scratch !!! I finally got smart and cut a 1' hole in the cardboard to surround the work area. Worked great ! . Well , I needed to find matching paint anyway ....


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Marc
 
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