edge distance

szicree · #1 08-27-2006, 06:56 PM

Anybody want to tell me what the standard is for minimum edge distance for rivets and bolts? It seems like rivets would need more, since the rivet exerts an outward pressure when squished, but how 'bout bolts? Also, shouldn't the thickness of the material be considered also? Thanks.

RV505 · #2 08-27-2006, 07:12 PM

Get a FAR 43-13 it is all spelled out within.. I would tell you but sometimes you remeber better if you read it Yourself.

alpinelakespilot2000 · #3 08-27-2006, 07:58 PM

Quote:

Originally Posted by szicree

Anybody want to tell me what the standard is for minimum edge distance for rivets and bolts? It seems like rivets would need more, since the rivet exerts an outward pressure when squished, but how 'bout bolts? Also, shouldn't the thickness of the material be considered also? Thanks.

Both are double the diameter of the shank from center of hole to edge. That's from my Cleaveland Tools catalog insert and I'm almost sure that's what 43.13 says as well. I've wondered the same thing as you though. Common sense does suggest that in the real world it would vary depending on thickness and material. For example, does a steel weldment require the same edge distance as a thin piece of aluminum? Obviously the rivet is going to shear before the steel would give, even with very minimal edge distance. Someone at Van's pointed this out to me and told me not to worry about it when one of my AN426-4 holes in a steel weldment was 7/32 rather than 8/32. The same would likely be true of thick aluminum. I think these rules of thumb (read rules) exist because if they didn't exist, one would have to do an engineering analysis on every hole.

Interested in what others have to say though...

szicree · #4 08-27-2006, 08:51 PM

Quote:

Originally Posted by RV505

Get a FAR 43-13 it is all spelled out within.. I would tell you but sometimes you remeber better if you read it Yourself.

Thanks Mom.

szicree · #5 08-27-2006, 09:48 PM

Well, I've searched the 43-13 and find nothing about edge distance for bolts. In fact, the stuff regarding rivets seems to apply only to lap joints between thin sheets. As for the 2x rule, we violate this whenever we put a 3/16 bolt through 3/4 angle, unless we manage to get the bolt exactly on the center line. My interest in all this has to do with me trying to get my wingroot fairing to clear the forward tank attach bracket. I'm sure others know what I'm talking about. Opinions/advice/sympathy are all appreciated.

az_gila · #6 08-27-2006, 09:54 PM

Quote:

Originally Posted by alpinelakespilot2000

Someone at Van's pointed this out to me and told me not to worry about it when one of my AN426-4 holes in a steel weldment was 7/32 rather than 8/32. The same would likely be true of thick aluminum.

Interested in what others have to say though...

Steve... this is not true.... If the materials are the same (alum rivet and alum sheet) then the shear strength with respect to the edge distance is the same. That is, the rivet and the material would fail at approximately the same force.

At the minimum edge distance, the shear failure should be equal chances for (1) the rivet failing in shear, or (2) the sheet material pulling out between the rivet and the edge.

This is not true for the alum. rivet and steel weldment combination, and you will sometimes see bolt holes in steel at less than 2D edge distance.

And yes... for critical applications, every hole would be calculated separately... not as bad as it sounds, since typically each hole in a row would have the same numbers....

Some nice technical descriptions, including pictures, in these Purdue course notes.

http://www2.tech.purdue.edu/at/cours...pplement_D.pdf

gil in Tucson ... liking actual numbers...

az_gila · #7 08-27-2006, 09:57 PM

Quote:

Originally Posted by szicree

Well, I've searched the 43-13 and find nothing about edge distance for bolts. In fact, the stuff regarding rivets seems to apply only to lap joints between thin sheets. As for the 2x rule, we violate this whenever we put a 3/16 bolt through 3/4 angle, unless we manage to get the bolt exactly on the center line. My interest in all this has to do with me trying to get my wingroot fairing to clear the forward tank attach bracket. I'm sure others know what I'm talking about. Opinions/advice/sympathy are all appreciated.

Steve... you wrote this while I was composing the previous posting....

Hole for steel bolts in aluminum would be calculated separately for strength, since the failure mode would most likely be the aluminum tearing out.... That's why there is no generic edge distance rule...

See the pictures in the link in my previous post.

gil in Tucson

alpinelakespilot2000 · #8 08-27-2006, 11:16 PM

Good points Gil. What I meant to communicate was that it would take a lot more force to rip out a thick piece of aluminum than a thin sheet. Hence, given a set amount of expected sheer, a thicker piece could handle less edge distance and be as strong as a thin piece with good edge distance. Just didn't write it well. Is this more accurate?

(Obviously, none of us are suggesting that we violate edge distance just for the fun of it. That said, there are a number of places, at least in the 9 plans and manufactured parts, where Van's violates this principle. Whenever I ask Van's about it they say that it is more than strong enough given its intended purpose and that an occasional lack of edge distance won't cause the plane to fall apart).

az_gila · #9 08-27-2006, 11:21 PM

Quote:

Originally Posted by alpinelakespilot2000

Whenever I ask Van's about it they say that it is more than strong enough given its intended purpose and that an occasional lack of edge distance won't cause the plane to fall apart).

Steve,

Yes... that's the key... It has been calculated, and the designer says it's OK to perform the necessary job.

As long as the plane is then flown within it's design limits....

gil in Tucson

Pirkka · #10 08-28-2006, 01:14 PM

IMHO people are taking too seriously these strenght calculations and as we notice of Van's comments; it ain't rocket science in RVs.

For example HS: very likely the rear spar can handle all forces up to design limits and that is where the calculations are based on -- easy math with single spar. Then the front spar should only keep it's position and ribs are only to keep skins at their form (They likely add just extra strenght over the desing limits). HS design is far from optimized but that makes it easy to design, manufacture and build. It is heavy, but in planes like this it ain't problem and worth of higher optimization. This yields to the fact that if you screw single rivet it really ain't big thing.

In bigger commercial planes this kind of optimization however is necessary. How much would be HP/weight ratio in bigger Boeing compared to the RVs...? Since you don't have unlimited power source you have to optimize weights (and of course engines too).