Edge Distance Problems for R-1003 and R1004

[plhamilton]

I have commenced working on the Rudder and I am wondering about the edge distance for the parts R-1003 and R-1004. I had completed all the skin drilling and was about to start final deburing before dimpling.

Photo 1

The first photo is the spar end of R-1003A. The hole has been final drilled to #30. I have shaved off most of the joiner to the R-1003-B piece, but not all of it, there is a very small quantity of it remaining which you can see. You can also see the roughness of the edge in this photo. When I measure the edge distance from the edge of the hole to the original edge (not one cut down by me, it is only about 0.132" which is way less than the 0.1875" required for a 1/8th rivet hole. So from where I sit, the manufacture of this part must be wrong, either that or my understanding of edge distance is incorrect. Can anyone confirm this for me.

Photo 2

The second image is the R-1004A part which has been drilled to match the Rudder Horn. The edge distance for the hole closest to the rear spar is 0.168 which is again to small. When I was originally working on the R-1004B piece, I had made a mistake and had to order a replacement. This meant that I had access to a pristine R-1004A part, so I clecoed it up to the Rudder horn and drilled it.

Photo 3

The third photo is that part, you can see the original joiners have not been removed. I drilled this part to test whether I had made a mistake, and lo and behold, the edge distance is only 0.1675". Again this is below my expectation of 2D (2X.125=.25) from the centre of the hole or .1875" from the edge of the hole.

I can only think that I am making a mistake here, but it certainly isnt the measurements as I have checked them over a number of times. It would also be pretty difficult to drill the R-1004-A part incorrectly as the Rudder Horn makes a substantial drill jig...

[Phil]

Paul,

Are you measuring from the center of the hole, or from the edge?

http://www.orbitform.com/modules.php...edia&sp_id=111

[flion]

Yes, his numbers are correct for edge-to-edge distance. Paul, if you take the R-1003 and R-1004 to be 'composite' pieces, then the edge distance is Ok in assembly. I was more worried about the edge distance along the entire A/B joints for those ribs, which has the rivets holding the two parts in shear. I think they skimped a bit on the material for those parts. But I don't think it's a manufacturing defect (as opposed to an engineering problem) because I ordered parts for a second rudder - not happy with my trim-tab modification, not a problem with Van's design - and those ribs are exactly the same as the ones I got a couple of years ago.

I tend to trust Van's engineering maybe more than I should. I did raise my eyebrows over those edges, but on the whole the RV-10 rudder is way beefier than the RV-6A rudder, which has end ribs but the rest are simply angle stiffeners not joined at spar or trailing edge (unless you used a bit of RTV). So my guess is that the engineering of the rudder ribs makes up for the end ribs but I have not checked this with Van's. I will say that the first rudder I completed seems more than strong enough and, with the fairings in place, I'd be really surprised to see cracking on those parts. I also have not heard prior builders who are flying report any problems. But you've raised my awareness; I'm adding a new line item for the inspection document I'm preparing.

[plhamilton]

Hi Phil,

I tend to work using the rule of 0.1875 from the edge of the hole to the edge of the sheet for a 1/8th rivet hole. It makes for easier measurement. It is the number that Vans use as I understand it. Unfortunately, it just misses by quite a margin here...

cheers

Paul

[plhamilton]

Hi Patrick,

Thanks for the input. I thought I was going crazy after I measured these up. This discussion has reinforced my thinking on using nutplates for all the fibreglass fairings so I can get them off and have a good look around every couple of hundred hours. I am hoping that you are going to publish your inspection document, I think it would be a good document to share. I have a couple of items for my version of it already.

cheers

Paul

[J Twilbeck]

Paul,
Working in the aviation industry as an aircraft structure engineer the standard practice I have learned for low stress areas accepts a 1.5D edge distance. Published bearing allowables for the material in 1.5D E.D. can be found in the FAA Publication MMPDS.
So for this application a #4 rivet is 0.125 shank diameter. The hole is around 0.128.
0.128 x 1.5 = 0.192 from middle of hole to edge OR
0.128 x 1.5 -(0.128/2) = 0.128 from edge of hole to edge of part

I believe you measurements were 0.132 which would be acceptable in my eyes.

(This in no way is a justification for the engineering or lack thereof from Van's)

[J Twilbeck]

Paul,
Some more info to help you feel better about edge distances. I'm sure this is info people know, but just in case, here are the numbers for your particular scenario.
There are three ways a rivet will tend to fail:
1. Rivet shears under load.
2. Material fails in bearing.
3. Material fails in shear tear out.

Assumptions:
Material is 2024-T3 Aluminum Sheet 0.040" thick.
-Material values as published in FAA MMPDS for 1.5 ED
Rivet is MS20470AD4 Rivet
-Rivet values published in E-Systems Structures Manual

1. Rivet shear strength 388 lbs
2. Material Bearing allowable is Fbru=104ksi
Therefore the max material bearing strength is 0.128in x .040in x 104ksi = 532lbs
3. Material Shear allowable is Fsu=39ksi
Therefore the max material shear strength is (0.132inx2) x 0.040in x 39ksi = 411.8lbs Equation as published in Bruhn's Analysis and Design of Flight Vehicle Structures.

Conclusion, the 0.132" "Edge to Edge" distance you are measuring (with the assumptions made above) show that the rivet will fail before the material will. Even if your edge distance was 2D.

(Again this in no way justifies the engineering or lack thereof from Van's)

...build on : )

[plhamilton]

Thanks Justin,

That is very helpful response and it makes me feel a great deal better about the "rules" and the binary interpretation I was using. There is so much to learn and I am grateful for the assistance that everyone has provided.

I received over night a response from Vans over night as well.

===========
I don't think you've done anything wrong, but the parts are correct. As punched, some holes are below a 2D edge distance. But that is just a rule of thumb - not an inviolable standard. So if you had to choose where to drill holes, that is what you'd do. In these cases, the engineer who designed it decided that it didn't matter and a lesser distance was acceptable.
===========

This has been an invaluable learning experience for me. At this stage, I plan to look at each edge distance before cleaning up edge. If the distance is 2D then I will work to ensure that I do not compromise that number (as I did on the R-1004A). If it is less, then I will assume that it has been engineered to that specification. In all instances, I will assess the risk of the number in the context of the position in the airframe and if I have a concern, I will add it to my inspection list for periodic examination.

Cheers and Thanks to all

Paul

[MElstien]

I just separated the rib halves last night and deburred them. Today I measured the edge distances and found the same measurements as the original poster. Glad to know VANS finds this acceptable.

I will write to them anyway so I have a record in my files.

+1 for nut plates for the fairings. Of course I say that now, before I have to do them.