Empennage Countersinking

[dnimigon]

Hi List. I'm a new builder and trying to get my head wrapped around the countersinking of the front & rear spars on the stab. I've read it over and over and just not sure the right way to countersink these spars. I understand the C/S of the #40 holes in the flanges. It's just the C/S holes on the foward side of HS-906, aft side of HS-903 & forward side of HS-907. For some reason I can't see the big picture here. If anyone has a pic of this. Also the direction that the rivets fit into these. Maybe I'm missing something here or miss read something. You know the old saying, a picture's worth a thousand words. I just don't want to do somethings that I'll regret and ruin.
Dave

 

[woxofswa]

I believe what you are referring to is the countersinking of the spars on the outside of the flanges to allow room for the depression of the dimples in the skins that will overlay the spars. In some places the spar flanges are dimpled, but in others where a flat surface is needed on the inside of the flange, the outside is c/s rather than dimpled.

 

[Robert M]

Empennage

Maybe this will help?..

The front spar doubler, HS-907, has 12 holes at the center of the doubler. Six of these holes go to the left front spar and 6 go to the right front spar. These 12 holes are right at the point where the fuselage connects to the HS. The four corner holes are left open for the bolts that attach the HS to the fuselage. The other 8 holes are countersunk on the front of the doubler so the countersunk rivets don?t interfere with the front spar fitting flush against the fuselage.

As for the rear spar doubler, HS-906, and HS-903?s, rear spars, there are 4 rivets that get countersunk. Two face forward and two face aft. The two rivets that get countersunk on the doubler are the two that sit out by themselves. At the very center section of the rear spar and spar doubler, all of the rivet holes are in vertical rows of three except the two rivet holes that are to be countersunk. These holes are countersunk on the forward facing side of the doubler.

The other two rivets that attach the doubler to the rear spar fit up under the elevator hinge bearing. These two rivets must be flush so you countersink those two holes on the rear facing part of the rear spar, HS-903.

I am on the road right now. I will be home tomorrow afternoon. If you still aren?t sure about this area and would like some photos, send me an email address and I will send you some detailed photos.

 

[dnimigon]

e-mail

Hi Myron & Rob
Thanks for the reply. I'll have a read on what you posted. I'm going away here next week, down where it's warm. I'll leave my e-mail if you could send some pics that would be great.
[email protected]
P.S. I should be right behind you on the build once I get some things sorted out. Maybe I do need this break from work to clear my head.
Dave

 

[pmccoy]

Maybe this photo will help

Here is a photo of my spar doubler plate. Not sure if these are the ones you are concerned about.

 

[Seattle]

I can't believe I did that

So...... Any of you folks countersink the aft face of the HS-906 by mistake? I highlighted the aft (should be on the spar) and forward (should be on the spar doubler) countersink locations with different colors on the blueprint. That didn't stop me one bit from incorporating both features on one part.

I may have a work-around. I'm thinking about fabricating a conical washer from the head of an MS20426AD4 rivet and installing these washers in the two countersinks that will be hidden in the stack-up. We used to do this down at Douglas when a repair doubler covered up an existing countersink. I'll call Vans on to make sure but thought I'd confess my sins to the group.

Just looking to see what those, who may have made this same error, did. Thanks.

Craig

 

[mike109g6]

Countersinking

Hi List. I'm a new builder and trying to get my head wrapped around the countersinking of the front & rear spars on the stab. I've read it over and over and just not sure the right way to countersink these spars. I understand the C/S of the #40 holes in the flanges. It's just the C/S holes on the foward side of HS-906, aft side of HS-903 & forward side of HS-907. For some reason I can't see the big picture here. If anyone has a pic of this. Also the direction that the rivets fit into these. Maybe I'm missing something here or miss read something. You know the old saying, a picture's worth a thousand words. I just don't want to do somethings that I'll regret and ruin.
Dave

Dave,
Everyone is in this boat in the beginning. It's trying to wrap your mind around what the designer is intending down the road. First-get yourself some different colored magic markers and mark your plans and manual to show specific variations. Second to see the big picture, in your manual if you look about midway at the rear where the small plans set is you will see some completely assembled plans. Like the plans that show the emp assembly being attached to the fuse. I used these a lot to help me figure out why something was being built a certain way. They help you 'see' the big picture. On the piece that you are talking about specifically, later you will have attachments to the fuse at the locations where the countersunk rivets are and they must be flush in order to allow attachment to the fuse and vertical stab to the HS.
Hope that this helps,
Mike H 9A/8A