F-605C Rear Spar Bar Doubler extra hole

[High_Flyer]

Hi everyone,

I'm at working on the fuselage rear spar bulkhead, and here is a question regarding a mistake on the F-605C Rear Spar Doubler.

There is place on F-605C that does not have a hole at the same place as the F-605B.
Of course when drilling F-605C I didn't pay enough attention and started drilling before realising my mistake. I stopped just before the drill bit went all the way through:







Is that extra hole a problem? This is a place with a lot of stress...

Thanks,

Alain.

[krw5927]

Originally Posted by High_Flyer

Hi everyone,

I'm at working on the fuselage rear spar bulkhead, and here is a question regarding a mistake on the F-605C Rear Spar Doubler.

There is place on F-605C that does not have a hole at the same place as the F-605B.
Of course when drilling F-605C I didn't pay enough attention and started drilling before realising my mistake. I stopped just before the drill bit went all the way through:

Is that extra hole a problem? This is a place with a lot of stress...

Thanks,

Alain.

The usual "call Vans to be sure" advice applies.

If it were me, however, and if there were to be no hole within 1/2" on either side of the discrepant hole (drill start), I would drill it all the way through, deburr both sides as per usual, and drive/squeeze a solid AN470 rivet to fill the hole.

If a universal head rivet would interfere with another part in this area, it could alternatively be countersunk on one side for an AN426 rivet.

This is the repair that would be authorized in the large certified aircraft world.

[JonJay]

Originally Posted by krw5927

The usual "call Vans to be sure" advice applies.

If it were me, however, and if there were to be no hole within 1/2" on either side of the discrepant hole (drill start), I would drill it all the way through, deburr both sides as per usual, and drive/squeeze a solid AN470 rivet to fill the hole.

If a universal head rivet would interfere with another part in this area, it could alternatively be countersunk on one side for an AN426 rivet.

This is the repair that would be authorized in the large certified aircraft world.

Anytime your dealing with a spar, in my opinion, it is a Van's call as Kurt suggests.
Kurt, I am curious though. None of my airframe manuals show filling a hole with anything. If the hole is in an area where an acceptable repair can be made it is either dressed and left or, depending on the extent of damage, patched. I see folks recommend putting a rivet in an abondoned hole, but I do not understand what that rivet does for us. Any thoughts?

[JurgenRoeland]

I made exactly the same mistake some weeks ago. Looking at your picture, you didn't really drill through. I actually drilled all the way through and have an extra hole that will not be used.
I contacted vans support by email with the following question:

>> I accidentally drilled through F-605C at the point indicated in the picture.
>> So the F605-C has an extra "lightening hole" of #30 in the curve bent near the end.
>> I missed the note on the plan that you should only drill through
>> F705-A and F-705B I will install with rivet only through A and B and
>> leave C open. But it will leave a #30 hole in C.

Here is the answer of Sterling Langrell <sterling@vansaircraft.com> at vans support

"After talking to engineering they don't see this as a problem but would recommend you fill this hole with a rivet."

So the good old quote applies, put a rivet in and 'build on'

[JonJay]

Originally Posted by JurgenRoeland

Here is the answer of Sterling Langrell <sterling@vansaircraft.com> at vans support

"After talking to engineering they don't see this as a problem but would recommend you fill this hole with a rivet."

Ok, two smart people saying to put a rivet in an empty hole. I really want to know why.

[seattleworm]

Filling holes with solid rivet is really to reduce the fatigue damage around the holes, even it also improves the ultimate tension load capability slightly. Believe it or not, for a hole under tension, a properly deburred and filled hole will last 4 times longer than a unfilled, undeburred hole under the same fatigue load condition.

The hole in question here is not at high stress area, the high stress due to bending is really at top and bottom of the bar. Shear stress will be low as well. But nevertheless, filling the hole is always a good thing to do.

[JonJay]

Originally Posted by seattleworm

Filling holes with solid rivet is really to reduce the fatigue damage around the holes, even it also improves the ultimate tension load capability slightly. Believe it or not, for a hole under tension, a properly deburred and filled hole will last 4 times longer than a unfilled, undeburred hole under the same fatigue load condition.

The hole in question here is not at high stress area, the high stress due to bending is really at top and bottom of the bar. Shear stress will be low as well. But nevertheless, filling the hole is always a good thing to do.

Thanks Shawn.

[High_Flyer]

Thank you all for the replies.

I've also sent an email to Vans, waiting for their advice.
If I have any doubt I'll just re-order one F-605C.

Very good info about the reason to fill unused holes with rivets... I had no idea!

Jurgen, can you confirm you had to use a AN426 rivet (flush head) in order to have no interference with F-605B?

Good day to everyone.

Alain.

[JurgenRoeland]

I haven't put it in yet as I didn't prime yet but I think there will be enough space for a AN470. In any case, I want to avoid to take out even more material by countersinking.
In worst case, I'll squeeze it quite flat on the inside. It's not really going to hold anything together.

[High_Flyer]

Here is the reply from Sterling Langrell at the mother ship:

"You will need to finish drilling the hole and then fill it with the appropriate rivet."

Well, I guess that's what I'll do.