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WD-409 Tailspring weldment Fit Problem

mfleming

Well Known Member
Patron
The WD-409 tail spring weldment on my Quick Build fuselage is not fitting very well.

Having to shim the WD-409 seems to be a common solution to having a gap between the bulkheads and the weldment.

My fit problem doesn't seem to be able to be fixed with a shim (maybe).

What I'm seeing is that the F-712 aft most bulkhead is concave.

The weldment flange fits up hard against the aft bulkhead in the center of the flange but there is a significant gap on either side of center. I checked the flatness of the F-712 bulkhead with a straightedge and sure enough, its off by the same amount as the gaps.

I suppose I could remove the bulkhead and try and flatten it out somehow and then add a shim.

Any thoughts would be appreciated.

Here's a photo of the situation:

wd409.jpg
 
I have almost exactly the same problem! Mine is slow build, but the problem (at least for me) seems to actually be the WD-409 and not the bulkhead or aft fuselage geometry. Try carefully measuring the weldment and check that the aft face is parallel to the forward face. In my case, it isn't and the problem is with the aft face (twisted about 3/64"). It is also rotated slightly so that when the vertical hole through the weldment is exactly vertical the aft face isn't quite vertical (again the error seems to be about 3/64" measured on the top edge).

I have exchanged some emails with Van's and my current plan is to get the weldment straightened by a local welder, although Van's said it was ok to use shims at the aft end to make it fit correctly.
 
Shim!

Looks like the aft bulkhead is not flat - might take it off and make sure it is, then shim as required. I ask folks to add a permanent fastener in the middle of the aft bulkhead fastener pattern - use a c/s head #10 screw so the fin spar still lays flat on the bulkhead when attached. If the ship is moved without the fin being fastened in place, the aft fuselage can be damaged, and this extra fastener will keep the damage from happening.

Looks like good work to me - keep it up!
 
yes

I ask folks to add a permanent fastener in the middle of the aft bulkhead fastener pattern - use a c/s head #10 screw so the fin spar still lays flat on the bulkhead when attached. If the ship is moved without the fin being fastened in place, the aft fuselage can be damaged, and this extra fastener will keep the damage from happening.
I had this exact thing happen to me....had to replace the rear bulkheads!! Should be part of the plans.
 
.......... add a permanent fastener in the middle of the aft bulkhead fastener pattern - use a c/s head #10 screw so the fin spar still lays flat on the bulkhead when attached. If the ship is moved without the fin being fastened in place, the aft fuselage can be damaged, and this extra fastener will keep the damage from happening.

Interesting...not sure I understand exactly what you mean? Could you explain further or post a photo?
 
As an aside...
I have seen builders adding shims between the WD-409 and the F-712 aft bulkhead.
The plans say to add a shim, if needed, between the WD-409 and the F-711 bulkhead.
Any real reason to put the shim in one place or the other?
 
Interesting...not sure I understand exactly what you mean? Could you explain further or post a photo?

"If the ship is moved without the fin being fastened in place, the aft fuselage can be damaged, and this extra fastener will keep the damage from happening."

Think ahead: Once the plane is completed. If you removed the VS. The bolts holding the tailspring weldmont to the rear bulkhead are also removed. At that point the weldmont is carrying the weight of the tail and is pushing up on the hole cutout in the rear bulkhead, a point load! and the rear bulkhead will tear/deform/fail, while sitting in your hangar!
Now, if you remember to reinstall the bolts back into the bulkhead through the weldmont, that will also keep the problem from occuring. But it is easy to forget or not see the problem coming...ask me how I know :(
What Mark is saying, is to preemptivly install a screw through the rear bulkhead into the weldmont to possibly save yourself a future problem.
 
"If the ship is moved without the fin being fastened in place, the aft fuselage can be damaged, and this extra fastener will keep the damage from happening."

Think ahead: Once the plane is completed. If you removed the VS. The bolts holding the tailspring weldmont to the rear bulkhead are also removed. At that point the weldmont is carrying the weight of the tail and is pushing up on the hole cutout in the rear bulkhead, a point load! and the rear bulkhead will tear/deform/fail, while sitting in your hangar!
Now, if you remember to reinstall the bolts back into the bulkhead through the weldmont, that will also keep the problem from occuring. But it is easy to forget or not see the problem coming...ask me how I know :(
What Mark is saying, is to preemptivly install a screw through the rear bulkhead into the weldmont to possibly save yourself a future problem.

Very clear now! That IS a gotcha.

That's an easy enough fix at this stage of construction.

Thanks for the tip.
 
I made a shim...

Here's how I shimmed my bracket in my -8.

Using several different thicknesses and individual sheets, you might be able to fill the unsymmetrical void.
I had a void that varied from top to bottom, so I made one thick "baseplate", and then added successively smaller and thinner shims to form a "wedge".

http://websites.expercraft.com/dbw/index.php?q=log_entry&log_id=73213

Hope this helps,
 
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Here's how I shimmed my bracket in my -8.

Using several different thicknesses and individual sheets, you might be able to fill the unsymmetrical void.
I had a void that varied from top to bottom, so I made one thick "baseplate", and then added successively smaller and thinner shims to form a "wedge".

http://websites.expercraft.com/dbw/index.php?q=log_entry&log_id=73213

Hope this helps,

Nice!

I'm headed out to the shop to see if I can make the F-712 aft bulkheadit a bit flatter.

If not, then maybe I'll use your method.
 
New information from Van's

Just to bring everyone up to speed.

The WD-409 tail spring weldment was removed and the flanges proved to be perfectly aligned in pitch and yaw.

The F-712 aft bulkhead when removed proved to be flat with no signs of being concave.

The F-712 is being pinched when installed and this causes the concave shape.

Van's, after looking at the photo shown in post 1, said I must measure the gap and fashion a shim of the proper thickness and reinstall everything. They also said that getting the aft bulkhead installed was going to be tough but (I paraphrase) that I needed to buck up and do it :- ) )

Soooo...I made a shim and decided to install it between the forward F-711 bulkhead and the forward WD-409 flange (that's what the manual say's to do anyway).

Everything is installed but the F-712 aft bulkhead...I'll try that in the morning when I have some help.

Here's a photo with the shims installed.

409.jpg
 
All Over But The Riveting

Here's a photo of the WD-409 installed with the F-712 aft bulkhead in place.

Another shim had to be added to the aft WD-409 flange to make it meet Van's spec's.

409f.jpg
 
Michael,
How far down does the aft flange spacer go? Does it go as far down as the keeper rivets? Also, does it taper in thickness? Thick at the top, thinner at the bottom? Thanks for the details. I?m going to have to do something similar.
 
Michael,
How far down does the aft flange spacer go? Does it go as far down as the keeper rivets? Also, does it taper in thickness? Thick at the top, thinner at the bottom? Thanks for the details. I’m going to have to do something similar.

The shim is .025" (not tapered) and is 1⅜" deep and not quite as wide as the rear flange.

The shim does not make it to the keeper rivets. (From just above the keeper rivets to the bottom of the aft flange, the flange fits tight up against the F-712 bulkhead)

The plan is the shim will be captured when the vertical stabilizer bolt holes are drilled.

When sizing the shim I pushed some .025 stock into the gap until it would not go any further...marked it and fashioned a shim of that depth. Then I inserted the shim into the gap and drove it down until it was flush with the top of the WD-409 rear flange.

The problem with my installation was the Quick Build fuselage F-712 aft bulkhead would turn concave when installed...removed, it was flat.

I had already installed a .064" shim between the forward WD-409 flange and F-711 bulkhead.

The F-712 aft bulkhead was so difficult to install after adding the forward shims I really did not want to take everything apart. Ergo - the aft shim being driven in without disassembly.

You can see the concave F-712 aft bulkhead in the photo below (this was taken before adding any shims). After adding the forward shim the aft flange still looked like this photo but not as severe.

wd409.jpg
 
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