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Additional Hole in Center Section Bulk Head

RV7AJeremy

RV7AJeremy

Well Known Member
Hello all,
I would like to add two additional holes (symmetrical, one on each side) in the center section bulk heads for additional conduit runs.
I asked the mother ship and this was the response:
"Jeremy: I'm afraid we cannot to approve or disapprove builder modifications. Without testing, there's no way to get real data on their effects."

I also had one of the T-38 structures senior mechanics that works in the fabrication shop here on base take a look and he didn't think there would be any issue at all (I know, not an engineer, but he has been working on and making modifications to T-38s for over 25 years) He said maintain the same spacing that exists in the two holes that are in the middle.

Additionally, the plans approves the one hole to be increased up to 3/4"

Here are a few images:
photo9bt.jpg


photo8hq.jpg


photos.PNG




I think it will be fine, but what are the thoughts from the group?
 
Odd. I asked what I thought would be a similar question not too long ago.

"On DW16 there is a Note 2 which talks about optional SB625-8 snap bushing for additional wiring runs. Where can this "extra" hole be put since it has to go through the fore and after center section? And this is a very important structure in the plane."

Vans response was:

If you need to add holes for wires in the center section or rear spar carry through areas you need keep in mind normal edge distances for the size of hole, no larger than 5/8. Also it is best to have the hole as low as possible without drilling into the heavy bar for the cary throughs.

Just to be sure I asked more specifically:

Ok. That sounds good. I want to be more specific in regard to my first question. The bulkheads are F904A and F904B which are the center section ones. Maybe somewhere near the midpoint near the fuel selector valve maybe. Of course heading your comments on hole size, edge distance, and nearer the bottom.

Vans response was:

As long as you have proper edge distances and by all means do not nick the
through bar on the bottom of that assembly you will be fine.

I have not drilled any additional holes yet but wanted to know whether it was Ok once I get to that point.

Getting different advice from the same company is not something that should be happening. I think it is one reason taking an airplane from start to completion is not for everyone.
 
Hole in center section web

The plate you are pointing to with your Sharpie is the web of the center section beam, not a bulkhead. I draw the distinction because of the loads in the beam. The top and bottom flanges (in this case the aluminum bars top and bottom) react most of the tension (bottom) and compression (top) loads under positive Gs. The web reacts the shear.

My suggestion would be to note the hole spacing of the two holes on either side of the aircraft centerline shown on the plans picture. The holes are on 2-3/4" centers. Then I would measure 2-3/4" from the outboard hole to where you want the new hole. This puts it almost in the center between the adjacent seat ribs. Be especially careful to debur all of these holes as they are stress concentration locations in the web.
 
terrye said:
The plate you are pointing to with your Sharpie is the web of the center section beam, not a bulkhead.
Click to expand...

I had the same thought, but the plans shown in the first post clearly identify it as a bulkhead, so that terminology is apparently correct.
erich
 
Maybe it was my wording

dbaflyer said:
Odd. I asked what I thought would be a similar question not too long ago.

"On DW16 there is a Note 2 which talks about optional SB625-8 snap bushing for additional wiring runs. Where can this "extra" hole be put since it has to go through the fore and after center section? And this is a very important structure in the plane."

Vans response was:

If you need to add holes for wires in the center section or rear spar carry through areas you need keep in mind normal edge distances for the size of hole, no larger than 5/8. Also it is best to have the hole as low as possible without drilling into the heavy bar for the cary throughs.

Just to be sure I asked more specifically:

Ok. That sounds good. I want to be more specific in regard to my first question. The bulkheads are F904A and F904B which are the center section ones. Maybe somewhere near the midpoint near the fuel selector valve maybe. Of course heading your comments on hole size, edge distance, and nearer the bottom.

Vans response was:

As long as you have proper edge distances and by all means do not nick the
through bar on the bottom of that assembly you will be fine.

I have not drilled any additional holes yet but wanted to know whether it was Ok once I get to that point.

Getting different advice from the same company is not something that should be happening. I think it is one reason taking an airplane from start to completion is not for everyone.
Click to expand...

Sir,
Thank you for your response. I though the response from vans was rather to cover their bases but I think it might have been the way I worded my question as I asked for "approval". Anyways, I appreciate you response and I am thankful to get a sanity check from the group. When I drill the hole I will follow the general rules of spacing and edge distance and take extra care not to nick the bars!
 
Last edited by a moderator:
RV7AJeremy said:
Sir,
Thank you for your response. I though the response from vans was rather to cover their bases but I think it might have been the way I worded my question as I asked for "approval". Anyways, I appreciate you response and I am thankful to get a sanity check from the group. When I drill the hole I will follow the general rules of spacing and edge distance and take extra care not to nick the bars!
Click to expand...

I thought I remember seeing a note on the RV-8 plans that allow for an additional hole in the carry through spar WEB for routing. Don't know if its different for the -7.
 
Only you can answer this question, but do you really need another hole in the center section? Usually when I find myself asking a question that no one can answer with any definitiveness, I realize that I maybe I'm asking the wrong question. There are already four holes that Van's designed into the center section. Could you perhaps eliminate your desire to add a fifth by some creative re-routing of stuff? You may (and probably do) have more wires to run than me, since I'm a relatively simple VFR plane, but it might be worth thinking more on. Good luck.
 
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