Caculating Edge Distance

[TJay 1041]

So I would like to either ream out my lift strut bolt from 5/16 to 3/8 or if I don't have enough edge distance I may just go to a NAS bolt. So in reading a bunch I found that the standard is 1.5D to 2D+.030 of the bolt measured from the center. Now I'm not quite sure what that all means so I am looking for some help. Or if someone has the wings off a kitfox 1050 just go measure your edge distance on the lower lift strut.

[EDMO 1078]

TJay,  You are only increasing the hole diameter by 1/16" (.062"), so you are making it only 1/32" (.031") on a side larger - IMO, not enough to worry about - I can measure my KF3 and give you dimensions from edge of 3/8" diameter hole to outside of strut fitting later today.  EDMO

.450" rough-measurement with a dial caliper from edge of .375" hole toward rear of plane to edge of fitting, and same for edge of hole toward wingtip.  ED

Edited 20 Jun 2016 by EDMO

[1avidflyer 1983]

I measured my Kitfox 4  1200 GW and took a pic or two of what I saw.  Then I looked at my Avid MK IV with a 1150 - 1200 GW, and it uses a 5/16" bolt.  If it was me, I don't think I would monkey with it.  Avid tested their STOL wing to over 5 Gs with no problems. That was a 911 lb GW, but if you do the math, that would still be over 4 Gs on a 1150 GW.  Also, their wing wasn't damaged in the test.  How far could it have gone before it broke??? Jim Chuk

[EDMO 1078]

We went thru this some time ago - Someone calculated the area and shear strengths of the 5/16 bolt to be less than the two 1/4" bolts combined that attach the strut to the wing - The 3/8 bolt is slightly more than the two 1/4" bolts combined.  I don't think that it is necessary, but mine have the 3/8 bolts, and if it makes you feel better, then do it.  

You can read my measurements on my post above Jim's.   EDMO

Edited 20 Jun 2016 by EDMO

[1avidflyer 1983]

5/16" bolt cross section is .077 sq in.  a 3/8" is .110 sq in.   Two 1/4" bolts together have .098 sq in.   I have heard that there is more force on the front spar than the rear.  Not sure how much if any difference there really is.  Jim Chuk

[dholly 718]

TJay- this is my KF 4-1050 prior to the normal reaming done during fuselage prep.

 

[Geoffrey Thorpe 31]

An AN-6 bolt in double shear should be good for about 16000 pounds. An AN-5 is about 11000. (per attached)

My calculations for my 1300 pound Merlin GT (single strut) comes up to 5100 pound of tensile load in the strut at 3.8 G - but those are my numbers, ymmv, use at your own risk, no warranty expressed or implied, do not attempt at home, etc.

Just off the top of my head, I would guess that the loads on the two struts on something like an Avid would be on the order of 75% front, 25% rear (+- 100% or so).

AN3THRUAN20-REV12.006281.pdf

[TJay 1041]

Well it looks like everyone else has about 3/8 to 7/16 of an inch Material on the outside, that's kind a of a bummer for me because I only have 5/16 of an inch of material  left, now I have to decide how big my balls are or do more welding, and I hate welding right next to finished fabric. thanks for the reply's guys.

[EDMO 1078]

TJay,  The other thing to consider is if your fork on the struts will pivot around the fuselage fitting - If you have too much material from hole to rear the fork could bind up.  You probably have about 3/4" of material on the front of the fuselage fitting where the angle is - There will be no wear to speak of from swinging the wings.  I wouldn't be afraid of the 5/16" to the rear with a 3/8" bolt, or even using a 5/16" bolt.   Even my Kitfox 1 with the 5/16" bolt did not break the fuselage fittings when the plane landed in a tree and one wing was totally demolished and the other badly bent.  EDMO

Edited 21 Jun 2016 by EDMO