I have sent these photos with a brief email to Van's and awaiting on reply but I'd like to get thoughts from brain trust here. We found cracks in aft bulkhead on 1995 RV6 with 1700 hours. The bulkhead appears to be two identical bulkheads sandwiched back to back. Thoughts on proper procedure?
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Proper repair procedure for cracks in aft bulkhead.
- Thread starter Fugitive
- Start date
I would be curious what Vans says.
The bulkheads on early RV kits 3,4,6, never fit very well. It took a lot of manipulation and sometimes shimming to get the flanges to lay flat without stress. It’s obvious to me that these were riveted under stress.
I do not believe there is a lot going on structurally with this part of the lower bulkhead. Vans or a more knowledgeable person should chime in.
Had this been caught earlier, stop drilling may have prevented propagation. That time has passed. I do not believe, with the sandwiched bulkhead, that repairing the flanges will be possible as you would be drilling through both bulkheads, but maybe. Replacing that bulkhead isn’t as big of a job as replacing the tailwheel stinger weldment and folks tackle that job.
Wait for Vans and others here to comment , but at first glance, I see two ready options: replace the bulkhead, or leave it as is.
I would thoroughly inspect the inner bulkhead and especially those securing the tailwheel weldment.
The bulkheads on early RV kits 3,4,6, never fit very well. It took a lot of manipulation and sometimes shimming to get the flanges to lay flat without stress. It’s obvious to me that these were riveted under stress.
I do not believe there is a lot going on structurally with this part of the lower bulkhead. Vans or a more knowledgeable person should chime in.
Had this been caught earlier, stop drilling may have prevented propagation. That time has passed. I do not believe, with the sandwiched bulkhead, that repairing the flanges will be possible as you would be drilling through both bulkheads, but maybe. Replacing that bulkhead isn’t as big of a job as replacing the tailwheel stinger weldment and folks tackle that job.
Wait for Vans and others here to comment , but at first glance, I see two ready options: replace the bulkhead, or leave it as is.
I would thoroughly inspect the inner bulkhead and especially those securing the tailwheel weldment.
Original poster here...just if anyone was interested, I spoke with Van's yesterday and their recommendation was to replace the aft bulkhead which, on the tail wheel version, is two F-612's back to back. They also suggested adding a brace outlined in Service Letter 00014 which oddly enough is for the 7/8/9 but not the 6. The tech wasn't sure why but recommended adding it anyway. I've ordered the parts and will start removing tailwheel weldment and bulkhead soon.
Sounds like they’re taking a conservative approach. Nothing wrong with that.
I suspect the 6 isn’t included as none have ever been reported. The 6 fuselage is quite a bit shorter than the 7 which may be a factor. Looks easy enough to do, but if they don’t know why they are recommending it ? Not much legacy experience left at Vans would be my guess.
Good luck in your repair and good catch.
Would be very interesting if the other sandwiched bulkhead panel has same cracks.
Also the next bulkhead forward should be inspected for similar cracks as the tail wheel mount would transmit same stress loads there too.
Also the next bulkhead forward should be inspected for similar cracks as the tail wheel mount would transmit same stress loads there too.
Difference being that the forward bulkhead stress would be primarily in tension as opposed to the aft bulkhead being primarily in compression.
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Definitely not an engineer here. I picture the possible front to back motion of the t/w mount transmitting (in addition to the vertical forces) to the two bulkheads, the rear bulkhead taking the majority of the loads but the forward (single thickness) bulkhead still carried some of it. Who knows how much rough taxi surfaces an older RV has seen over the decades of use.
Just saying, if it’s apart, good idea to inspect adjacent areas too.
I remember taxiing across Reno Stead’s ramps & thinking I’d rip off my tail wheel in one of their ramp’s 3” expansion cracks & that would definitely be front/back loads in that case… maybe I should have looked for cracks then!
The FWD end of the weldment for the tailwheel is attached to a bulkhead as well. On my -4 build, I recall making sure the weldment and the bulkheads were fitted together before anything was permanently affixed. If in this case, the weldment had large gaps, the bulkhead would be pretty well loaded up when the 3 bolts are tightened, which may put some significant stress on that area. Also, the vertical fin rear spar attaches there, which I don't see in the picture. Was it preloaded?
You get this repaired yet?
Both f612 bulkheads were cracked. Vans had one and the next batch wasn’t expected to be produced for 6 months. I attempted to make a duplicate f612 bulkhead and failed miserably. I visited nearby airports and found an accomplished sheet metal A&P. He built, primed and installed them. I, then, took it to paint shop at my home field for touchup. It’s a tight area to work on. Not a repair for a novice in my opinion…but it’s finally done.
I am in the middle of replacing mine. vans got the f612s back in stock last month
If I had to hazard a guess, i'd say they didn't recommend it because many (most?) 6s have lighter-weight fixed pitch propellers and therefore aft-ish CGs. Adding more weight that far back is not going to improve handing on your typical Rv-6, and would, ironically, make it easier to end up with the sort of stresses that may cause those bulkhead cracks in the first place.
--Ron
