F-412 repair

THe RV-4 I am working on was shipped from the US to Uk without any bolts to hold the WD-409 tailspring weldment to the F-412 bulkhead. THe result can be seen here:




So if anyone is tempted to transport their pride and joy from home to the hangar without putting these bolts in - DON'T!!

My concern now is how best to effect the repair. AS you can see above, the F-412 is well and truyly knackered and needs to be replaced. Removing it was an interesting procedure because of the numerous rivets that were hidden along the top and bottom longerons - eventually solved witha aa die grinder. The overall finish wasn't too good so I have a bit of filing and polishing to do to get rid of sharp coners, hacksaw arks and so on.

The big problem is that the F-411 is not vertical WRT to the top longeron. If I put in the new F-412 properly, normal to the longeron, it is about 3/16-1/4" out WRT to the aft plate of the weldment. I don't want to have to remove the F-411 as well and anyway, as the skin is already drilled, any attempt to true it up will lead to edge distance issues on the F-411 flanges. Putting the F-412 in at the same angle as the F-411 leads to some interesting problems at the bottom, with insufficient room to get the rivet into the flange. I suspect that the weldment never butted up to the F-412 properly....

My preferred solution would be to mount the F-412 correctly ie normal to the longeron, and put some shims under the weldment mounts - say 1/8' at each end. Here's a couple more pictures.



Here the strip of aluminum is clamped along the line that would be parallel to the back side of F-411

Finally, I have new bulkhead parts from Vans but the fit is not brilliant. I wondered about riveting a flange in place at the correct location and making a new bulkhead that would have a better fit, then to rivet to the flange, then riveting a second bulkhead over the first with another flange, to emulate the original Van's design with a double flange.


I hope all is clear. Any suggestions guys?

Thanks as always for help and comments.

Chris Mitchell

RV-8 - built, flown, sold
RV-4 - in remediation

Not AGAIN!!

I have seen this mistake too many times. Ugh.

I doubt you can fix the 411, nor would it need replacing. Yes, the side skins would need splicing at some point fwd of the 411 if you were to do this, along with the aft belly skin.

The kits I have assembled all needed some re-shaping of both the 411 and 412 parts before the aft fuselage could be assembled.

The new flange/new bulkhead centersection is not really the best plan for a secure attachment of the Fin aft spar...

As for the 412, I have had a number of F1 sets made up (for the same sort of repair) - these are of better quality, and just might fit better. I can ship a set (front and back) for you to try if you would like. Send 'em back if you can't use 'em, or fwd to a pal in Linthwaite Yorkshire if that is easier.

f 1 boss (at) gmail dot com

Carry on!
Mark

New weldment

Hi Chris
How about fabricating (or get made) a new weldment to accommodate the angle change and length in respect to 412. Leave the rest as is.

Chris

Getting there slowly....

Thanks for the replies and for the offer of parts Mark. I had wondered about getting anew weldment made up but in the end got a new one from Vans, which is about 3/32 longer than the old one....! THAT has taken up most of the slack.

I made a new bulkhead from 0.040, made separate flanges to hold it in place - to ease location. Then I have riveted a Vans bulkhead with the bent up flanges in place on the aft side to finish it all off. I have added a piece of angle at the underside of the junction of the F-412 and F-419 (rear deck) to tie the parts together. The piece of angle extends under the top longerons. Spacer on top to fill the gap. The angle on top to hold the VS will go on later.

Its been a real pain altogether, but I am finally satisfied that everything is where it ought to be and is securely attached. I will add some photos later.

Now I am off to re-rivet the f-411 but getting the rivet heads properly countersunk - something that was not done by the previous builder. Getting there slowly - I am so looking forward to starting the wiring and plumbing!

Chris

I'm working on a repair in this area too, would be interested in photos of what you did.
thanks

Here are a few photos of work in progress. I'll add some more later when the garage has warmed up a bit!!

Chris

Everything removed except the WD-409 - took a lot of drilling and some grinding because of concealed keeper rivets between longeron and the wrecked F-412.



Flanges made from 0.040 material bent up and riveted in place - careful to check location and that they are at right angles to the longerons, so as to ensure that the new bulkhead is vertical WRT the centre-line of the aircraft:





You have to have the WD-409 weldment in place before the bottom flanges. I used the bottom 1/3 of a Van's part for this area, partly because it was difficult to get clearance all the way round the aft face of the weldment if I made them separately. However, it is difficult to impossible to rivet buck the bottom rivets so I used pulled rivets here:



Then I made up a bulkhead from 0.040 material - here it is laid in place, held by a piece of angle and a spacer across the top, prior to putting in a couple of keeper rivets. Note that I have removed the top deck (previous builder had not installed it properly and had cut some in appropriate holes in it, necessitating replacement):





The angle and spacer are not called for on the plans but will help lpocate everything correctly - the string is me checking that everything is set squarely to the centreline.

I don't have any photos of the finished work yet - I'll add the tomorrow. Basically I have used a Van's part for the aft face of this double bulkhead. AS I am still fixing various other problems I won't have any photos of the finished deal with the VS in place for a while yet. My next chore is to fix the skin under the baggage floor which has suffered from being rested on a trestle and so is no longer quite the shape that Van's intended!

Chris

Kudos to your handiwork Chris!!

Thanks - that's kind! I didn't post a photo of all the parts I made but discarded as unsatisfactory for one reason or another. This repair has been a real pain in... well most of my anatomy. I kinda think Van's should make the risk of damage clear in the instruction books or even on the plans. A couple of countersunk rivets in place would be adequate protection. I originally only learned about the problem from this site (which alone has made it worth several years of subscriptions to Doug).


Chris
RV8 - built, flown and sold
RV4 - ongoing repair, rebuild and remediation...... Flying by March 2014??