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Info- Shy edge distance on main longeron at F-714 Aft Deck

Desert Rat

Well Known Member
Let me start by saying that this story has a happy ending, but I searched the interweb for a couple of hours and while I found tons of info on blowing e.d. on the F-711D angle on the back side, when it comes to the longerons in that area I got nada So, I'm posting here with the idea that his might be helpful to somebody in the future if they run into the same thing.

Right after the flip, the plans have you level the fuselage both directions, check/adjust for twist, and then drill the aft deck to the longerons and aft bulkhead structures.

The aft deck only fits one way, and the two rivet holes just fwd of the F-711C vertical bars are about 1/2 rivet diameter further inboard that the rest of that row, therefore if the aft deck isn't dead nuts centered in that area, it's likely that you'll blow the e.d.

After doing the arithmetic, it looks like in my case, if the aft deck was centered with machine shop precision, there would be about .005" extra margins on each side, so I know I can't possibly be the only person that's faced this.

Cut to the chase, here's my correspondence with Vans. I'm not saying that anything goes in this area, but as you can see, there are room for at least minor deviations on this particular rivet hole.

Obviously this is for informational purposes only, and absolutely not be taken as blanket approval to start being all willy nilly with edge distance, especially thru critical structure! Call Vans for your own situation.

Hi Terry

At this point on the longeron short edge distance is not a problem as just aft of this rivet hole you have a large notch for the vertical bars. What you have is acceptable for this location.

Sterling

From: Terry Shortt <[email protected]>
Sent: Friday, March 19, 2021 6:38 AM
To: Support <[email protected]>
Subject: Longeron edge distance question @ F-714 aft deck- looking for a sanity check

Good morning Guys,

Drilled the aft deck yesterday and while I have good e.d. on the F-711D Angle, the #30 hole just fwd of the starboard F-711 vertical bar is a little shy on the longeron. The pre-punched holes in the F-714 aft deck are a little more inbd there than the rest of the row, and I didn't really think about it at the time. After match drilling, the e.d. came up to be .148”. If my arithmetic is correct, this is about .009 below min ED per Mil-Spec. call it .010 for good measure.

The one on the port side came out at about .165” so I really don’t know what I could have done differently other than pull the pilot holes outbd a little bit. Even if I had readjusted the F-714 to split the difference and had machine shop precision, there is only a few thousandths to play with there. My longerons are just that distance apart.

Please let me know your thoughts.

Terry



EDIT- Based on some comments below, I can see how I could have been more clear with my numbers. Since it' difficult to accurately measure to the empty space that defines teh center of a hole thats already there, all the measurements that I reference above and show in the photos are from the edge of the hole. Edge distance was calculated by measuring from the edge of the hole with a micrometer, then adding 1/2D to calculate the distance to the center of the hole, which is where edge distance is defined. The end result was a calculated edge distance of .2105" which is about .008 less that the mil-spec minimum of .219" for a 1/8" rivet.
 

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Thats correct in an abstract way, but if the hole is already there, then the center is a point in empty space, so to get a precise measurement with a micrometer, you measure from the edge of the hole and then add 1/2 D to get the number you would compare to the min edge distance requirement.

In this case, .148 (distance to edge of hole) + .0625 ( 1/2 hole diameter) = .2105. which is about .008 less than the published Mil-Spec minimum of .219 to the center of the hole for a #4 rivet.
 
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I haven't reached this point yet, though I seem to recall reading about the importance of getting that angle and the one on F-710 to nestle as closely into the longeron as possible. I got the impression that its common to cut these just a bit short and run into this problem.
 
True, but that’s a different issue. I got that same heads up and was diligent about making sure that wasn’t a problem. You can see that area in the second picture above and edge distance is fine as long as you take care to make the angle long enough when you fabricate it and radius the ends so it nests properly. This is on the top side
 
True, but that’s a different issue. I got that same heads up and was diligent about making sure that wasn’t a problem. You can see that area in the second picture above and edge distance is fine as long as you take care to make the angle long enough when you fabricate it and radius the ends so it nests properly. This is on the top side

Whoops, sorry! I see the difference now.
 
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