[lostpilot28]

I sent the following e-mail & accompanying picture to Van's Support guys several months ago:

Hello,
I've begun the section where I mount the Horizontal Stab to the fuselage and I have an "edge distance" question. My QB seemed to have pretty short sections of angle underneath the part of the fuselage where the HS-710/714 gets bolted. Basically, I followed the directions, measure a few times, then drilled the 4 holes. They look great from the top, but as the attached pictures show, the outer bolts are a little close to the edge of the angle.

Is this OK? Should I replace the angle and start over?

I ended up calling them about it the next day since I didn't get a quick reply and they said that they brought it up to their Engineer and showed him the picture. He said that since there isn't much side loading happening back there that this was not a problem...don't worry about it. But, if I really wanted to do something to "feel better" I could either replace the angle (not recommended because of messing up the rivet holes when drilling the first ones out), or I could add a piece of aluminum to the top of the deck plate and rivet it to the longeron in place of the thick aluminum spacer between the deck plate and HS.

Both sides of this angle are short...I'd say about 1 bolt diameter from the center of the hole. This is a Quickbuild and it's apparent they didn't know that the angle needed to go all the way to the inboard edge of the longeron. So, the shortness of the angle is the root cause of the edge distance problem. Again, Van's said that this was OK, and that most loads would be downward anyway and wouldn't pose a problem.

A friend of mine has the same problem on one side with the same piece of angle. I believe the other side is OK. Is there anyone else out there that's seeing this problem on their kits? Particulary the QB?

A suggestion that seemed viable was to use a thin piece of steel (.040") and make a 3 inch long plate that sits under the nut of these 2 bolts. It would provide side-bearing strength to prevent the AN3 bolt from pulling out of the angle with the edge distance problem. It seems to me that for the bolt to pull out of the edge of the angle (even though it's very thin), the other side of the angle would have to push in, which doesn't seem likely.

Any of you structural engineers out there have some constructive feedback? Would the steel plate help? Should I just leave it alone?

Thanks!

 

[AlexPeterson]

Sonny, fix it in one way or another, or it will just keep bugging you.

I think your idea of a bar on the nut side (the side we see in the photo) is good. I'd use aluminum, .125" like the angle, and maybe drill out the one rivet which is just to the right of the open bolt hole in the picture. Then put a third bolt there, or near that drilled out rivet. That way you would have two solid bolts holding the bar to the existing angle. Then move on!

 

[TSwezey]

You could also just put an aluminum doubler on there. Just cut a small section of the 1/8" aluminum out of a piece of angle and do what you were going to do with the steel. You could drill out a few of the rivets to hold this doubler in place.

edit:Alex you obviously type faster than me! Same solution!

 

[SvingenB]

The best advice is to follow Van's advice. There is something fundamentally wrong with "fixing" a problem in an aluminum construction with steel. Steel is a very different metal.

 

[lostpilot28]

The best advice is to follow Van's advice. There is something fundamentally wrong with "fixing" a problem in an aluminum construction with steel. Steel is a very different metal.

Well, I would tend to agree with that except the only use that this small piece of steel would be doing is preventing the outer bolt from moving outward to the point of breaking through the edge of the aluminum angle. I suppose I could do the same thing with a thick piece of alumimum and use longer bolts...I don't think overlaying another piece of angle will work because the holes would be too close to the radius and the nut wouldn't sit flush.

 

[az_gila]

Mixed already....

The best advice is to follow Van's advice. There is something fundamentally wrong with "fixing" a problem in an aluminum construction with steel. Steel is a very different metal.

Yeah... the bolt is steel and the angle is aluminum... it's a mixed bag already! No fundemental defect...

gil A

 

[whd721]

I had the same issue on the RV9 I am working on. The first owner managed to drill the outside HS bolt hole too close to both edges. The longeron and the angle under (F710B on the RV9) the longeron. After removing the Aft Deck I replaced the F710B, but could not erase the hole in the longeron edge.
The solution I worked out with Vans was to extend the 1/8" shim under the HS attach angle fore and aft two rivets. The shim was roughly a rectangle shape under the HS attach angle, now it is a 5 1/4" long shim on the outside (covering four rivets and both bolts ), the original shim length on the inside with connecting lines for a rough trapezoidal shape.
The 1/8" angle longeron with an extra hole is compensated for by an additional 1/8" shim spanning the hole.

 

[GAHco]

Load pattern.

If the load pattern is to put the bolt in tension put a washer and nut on it and your good.

If it is in shear do what you need to grab more edge distance.

But what I suspect is that it is in mostly a combination load and that is where neither one of us knows the percentage of possible tension vs shear.

Under normal flight loads this would not scare me, but.........

These planes are not built to handle just normal flight loads

Applying an appropriate 2024 aluminum strap of the same thickness, about 4 to 6 inches long and riveted to the same piece using existing rivet holes and then drilling the bolt hole very carefully from the top so the new strap has all the right edge distances is a repair I would believe in.

I have seen many posts on this issue, it seems to be a common problem.
Once my fuselag is done I will take this part slow and careful.

But beware, I aint no engineer, heck I don't even know how to drive a train.

 

[SvingenB]

Well, I would tend to agree with that except the only use that this small piece of steel would be doing is preventing the outer bolt from moving outward to the point of breaking through the edge of the aluminum angle. I suppose I could do the same thing with a thick piece of alumimum and use longer bolts...I don't think overlaying another piece of angle will work because the holes would be too close to the radius and the nut wouldn't sit flush.

The problem is that steel is a much stronger material. It doesn't stretch and flex nearly as much as aluminum. Adding a ad hoc steel member in there makes a discontinuity in the construction regardless of thickness, size etc. Unless you know exactly what you are doing, discontinuities will create stresses rather than releive stresses. On top of this the chemical properties of steel is also very different. In your case it probably will not cause any harm, but...

The engineer at Van's is the one most likely to give you the best answer, since he knows the construction in and out. He has given you 3 options; do nothing, replace the angle, or add another plate as reinforcement (on the other side?). Wouldn't it be best to follow one of these advices?

 

[SvingenB]

Yeah... the bolt is steel and the angle is aluminum... it's a mixed bag already! No fundemental defect...

gil A

A bolt has a very specific purpose and is a part of the design. An ad hoc "feel good" steel plate is not. That is the difference.

 

[Rick6a]

Oh really?

There is absolutely nothing fundamentally wrong with using steel in a repair in aluminum. In fact, it IS used all the time in aircraft sheet metal repairs. I dubbed one engineer I knew as "Mr. Steel" because every time I saw him coming I knew what his repair disposition was going to be no matter how trivial the damage was. Van's most likely did not recommend steel for this repair for a very simple reason. The material is more difficult to work with than aluminum and requires machining that surpasses the average builders' tool capability and/or skill level. To suggest metal dissimilarity makes its use undesirable when repairing aluminum structure has absolutely no basis in fact and is a totally false assertion. Of course, its use does require increased corrosion control practices and may be another reason why Van's did not suggest its use....besides its inherent strength not really being necessary in this application.

 

[TSwezey]

Sonny:

I quoted the advice given to you by Van's because it makes perfect sense. In the process of building my RV-8, I encountered many situations very similar to yours, and the engineers at Van's were the #1 resource for help in rectifying simple mistakes like your own. They still are. If you are new to building these airplanes, the sooner you learn to rely on the original designers rather than on forums for technical expertise, the sooner you will have that peace of mind you are looking for. Don't you think the engineers at Van's know what 4130 steel is? Had it been the better option, they would have suggested it. Now get to work!

(Soap box is now placed gently under the workbench where it belongs)

Because Van's is 100% correct all the time! Can I say nosewheel problems?
If it were my plane I would fix it!

 

[TSwezey]

By the way you probably could have fixed it in less time it took to call Van's! 20-30minutes at most to add a 1/8 aluminum shim!
Do you think you would find an edge distance that close on a certified aircraft? NO.

 

[Christopher Murphy]

add strap

drill out that verticle rivet, add the strap. Don't use steel.

Chris Murphy
A&P
former lead sheet metal mech for UAL.


P.s. It is probably ok the way it is but it's not right. Its an easy fix, make it right.

 

[GAHco]

Edge distance

By the way you probably could have fixed it in less time it took to call Van's! 20-30minutes at most to add a 1/8 aluminum shim!
Do you think you would find an edge distance that close on a certified aircraft? NO.

The industry standard edge distance was 1.5 x dia when I was inspecting and fixing planes for a living.

I have seen this on certified aircraft, it doesn't look good on them either.

This will be an eye opener for some,

THE DISTANCE IS MEASURED FROM THE CENTER OF THE HOLE!
That leave the distance from the edge of the hole to be 1 x dia.

Seems very little but thats what the minimum was.

I have not check ac43-13 on this in a while, if anyone has the time let us know if it has or has not changed.

 

[lostpilot28]

drill out that verticle rivet, add the strap. Don't use steel.

Chris Murphy
A&P
former lead sheet metal mech for UAL.


P.s. It is probably ok the way it is but it's not right. Its an easy fix, make it right.

With the discussion steering toward the use of steel and why I shouldn't use it, I started thinking that I could do the same thing with a flat piece of aluminum. I'd need longer bolts, of course...which I have plenty of since my QB came with AN3-12A bolts for the center section which were too short.

This information is good stuff...keep it coming...I've got a 2nd e-mail into Van's and I'll wait to get their response in e-mail form so I can relay that here. I agree that they ARE the authority in this regard, but I still like to get other's opinions and perspectives.

 

[C-GRVT]

edge distance "authority"

Can anyone point to the authority that specifies the necessary edge distance for a bolt?
I have proceeded on the assumption that it is the same formula as for a rivet, but have tried in vain to find where edge distance requirements are stated for a bolt. AC 43-13 is silent on the question (unless I missed it), and I have not found it specified in a number of other sources in which I checked.
Bill
RV-6A
finishing kit

 

[Mel]

The industry standard edge distance was 1.5 x dia when I was inspecting and fixing planes for a living.
THE DISTANCE IS MEASURED FROM THE CENTER OF THE HOLE!
That leave the distance from the edge of the hole to be 1/2 x dia.
Seems very little but thats what the minimum was.

Measured from the center of the hole leaves 1/2 dia. to be subtracted, leaving 1X dia. to the edge the way I figure it.
Did I missread something?

 

[sprucemoose]

Can anyone point to the authority that specifies the necessary edge distance for a bolt?

http://www.vansaircraft.com/public/Specs.htm
This is not a direct answer to your question, but you'll find a lot of goo information on edge distance. The most important thing is that the 1.5X rule of thumb is just that, a rule of thumb. The actual Mil-Spec distance is slightly less than 1.5X. This is very useful data when deciding whether to replace a part based on edge distance.

 

[SvingenB]

There is absolutely nothing fundamentally wrong with using steel in a repair in aluminum. In fact, it IS used all the time in aircraft sheet metal repairs. I dubbed one engineer I knew as "Mr. Steel" because every time I saw him coming I knew what his repair disposition was going to be no matter how trivial the damage was. Van's most likely did not recommend steel for this repair for a very simple reason. The material is more difficult to work with than aluminum and requires machining that surpasses the average builders' tool capability and/or skill level. To suggest metal dissimilarity makes its use undesirable when repairing aluminum structure has absolutely no basis in fact and is a totally false assertion. Of course, its use does require increased corrosion control practices and may be another reason why Van's did not suggest its use....besides its inherent strength not really being necessary in this application.

Well, I don't want to comment about the ways of "Mr Steel". In the Air Force (loong time ago, but not everything is forgotten) I learned to use the same alloy when repairing aircrafts. Looking in my Aircraft Sheet Metal book that came with the tools from Avery, it say exactly the same thing.

Somehow I tend to believe more in Air Force training courses and published books, than some reference to a "Mr Steel" on the internet.

By using a steel plate to fix the problem as sketched further up here, I can think of three possible outcomes considering we do not know what the actual load situations are, nor do we know the strains in the original design compared to the steel plate:

1. The holes in the steel plate are a few micrometers closer together than the original holes. In case of a shear load to the left this may cause most of the load to be transferred to the inner most bolt, one bolt takes the load of two.
2. The holes in the steel plate is some micrometers further apart. In this case most of the shear load will be transferred to the outher most bolt, which is worse than the situation you want to prevent.
3. The shear load is negligible, in this case the steel plate simply work as a heavy, oversized and corrosive washer.

But this isn't really important. What's important is to follow the suggestions given by the engineers at Van's because they know the design inside out - all of it, not just fractions here and there often based on incomplete information.

 

[Rick6a]

.........There is something fundamentally wrong with "fixing" a problem in an aluminum construction with steel......

Nowhere did I suggest the use of steel as a repair material for this particular condition. I am not a qualified engineer nor do I pretend to be. I do however challenge the blanket statement quoted above that I know to be completely inaccurate. I know the statement to be false because as a longtime sheet metal assembler and riveter...."SMAR"....on uncounted occasions I have been directed by highly qualified engineering personnel to make repairs on aluminum structure using steel repair stock.

I do agree that as far as the specific problem outlined and the subject of this thread goes....consulting with Van's is generally the best source for qualified informed advice.

 

[TSwezey]

Measured from the center of the hole leaves 1/2 dia. to be subtracted, leaving 1X dia. to the edge the way I figure it.
Did I missread something?

Thank you Mel.

 

[GAHco]

Good catch!

Measured from the center of the hole leaves 1/2 dia. to be subtracted, leaving 1X dia. to the edge the way I figure it.
Did I missread something?

Thanks Mel.

You didn't miss a thing, fixed original post.

Must been slightly slysdexic this morning

 

[SvingenB]

Nowhere did I suggest the use of steel as a repair material for this particular condition. I am not a qualified engineer nor do I pretend to be. I do however challenge the blanket statement quoted above that I know to be completely inaccurate. I know the statement to be false because as a longtime sheet metal assembler and riveter...."SMAR"....on uncounted occasions I have been directed by highly qualified engineering personnel to make repairs on aluminum structure using steel repair stock.

I do agree that as far as the specific problem outlined and the subject of this thread goes....consulting with Van's is generally the best source for qualified informed advice.

OK The thing I found a bit strange was the intention to ignore Van's advice and instead go for a solution involving a steel plate and with a possibility to redistribute the load (shear load if any) in unknown ways, without knowing what kind of load the bolts are meant to take.

 

[Mel]

Must been slightly slysdexic this morning

I'm glad taht never heppans to me!

 

[az_gila]

Analysis...

Can anyone point to the authority that specifies the necessary edge distance for a bolt?
I have proceeded on the assumption that it is the same formula as for a rivet, but have tried in vain to find where edge distance requirements are stated for a bolt. AC 43-13 is silent on the question (unless I missed it), and I have not found it specified in a number of other sources in which I checked.
Bill
RV-6A
finishing kit

I asked this to our friendly (RV-4 builder) Mechanical Engineer at work a long time ago....

His answer was that every joint needs to be individually calculated for stress... the thickness and strength of any fittings and plates vary a lot more than riveted aluminum sheet. The bolt is usually much stronger than the material it is clamping (certainly with aluminum)... if the failure mode is tear out, the a steel fitting can have a much smaller edge distance due to the inherent extra strength of the material (or it can be thinner... hence my earlier post...)

He concluded that each joint needs it's own analysis, and edge distance might be less than 2x.

gil A

 

[az_gila]

Materials and tolerances....

......
By using a steel plate to fix the problem as sketched further up here, I can think of three possible outcomes considering we do not know what the actual load situations are, nor do we know the strains in the original design compared to the steel plate:

1. The holes in the steel plate are a few micrometers closer together than the original holes. In case of a shear load to the left this may cause most of the load to be transferred to the inner most bolt, one bolt takes the load of two.
2. The holes in the steel plate is some micrometers further apart. In this case most of the shear load will be transferred to the outher most bolt, which is worse than the situation you want to prevent.
......

Not wishing to be too argumentative, but each scenario you mention for 1 and 2 above would be identical if an aluminum strip/plate was used.

I think building/manufacturing tolerances and load paths are being discussed in the above statement, not the relative strength of materials.

Steel does have it's place for fittings.... check out the RV-6 wing spar joiner plates...
A good mix of aluminum and steel....

gil A

 

[SvingenB]

Not wishing to be too argumentative, but each scenario you mention for 1 and 2 above would be identical if an aluminum strip/plate was used.

You are probably right. But the fix is trying to unload the shear load at the outer edge near the first bolt to the second bolt. The compressive tension in the bolt due to shearing is originally distributed over 1/4 to 1/2 inch or so. All that force in now going to be distributet over 0.04 inch on the second bolt and comes as an addition to the tension and shear that bolt is originally meant to take. This compressive tension is potentially larger than the shear tension itself, considering the fix work as intended. An aluminum plate will at least distribute the load over a much larger area on the bolt, and cause less stress in the bolt.

Again, considering the bolts directly take all the shear load, I find it hard visualizing a load situation where the fix will work as intended unless the holes in the fix-plate is closer together than the original holes, forcing the two bolts closer together so the first bolt never really contacts the left edge of the hole. But is this any different than simply elongating the edge-hole even further towards the edge? I think not.

To be honest, I believe in Van's engineers. I also believe that using that steel plate is a very poor solution to a theoretical situation that don't exist. Consequently, the steel plate will have no effect, bad or good, unless Van's engineers are wrong in which the solution will potentially have some unwanted effects that should be analyzed further.

 

[GAHco]

Choose carefully

Choose carefully, and execute carefully the fix you feel will be the safest.

No doubt there will be differences of opinion, but it is your that counts when its done.

Be safe and have fun.

 

[SvingenB]

Did a quick search and found this article about an experiment done to find distribution of shear loads on bolts with different clearences. It isn't 100% applicable since they only use fingertight bolts, but the results clearly show the principles of the load distribution.

shear loads