Rebuilding F-712 and F-706 Bulkheads - 7 hours

Admittedly I am a bit all over the place today on the build. I felt like working on the F-712 bulkhead and tie down bar. I had previously wrecked the last piece when my drill press caught the aluminum and oblonged one of the holes. I wasn’t going to let that happen again....I hope. I started off simply by marking out centrelines and then clamping on the AEX tie down bar onto the F-712 Bulkhead.

Next I was ready to drill the rivet holes into the bulkhead. Luckily the drill press was nice this go round (thanks to new drill bits I ordered)

Super happy with how everything lined up. No sloppy work here.

Next I did a little homework on which holes needed to be dimpled in the bulkhead. I see that from some build logs many have dimpled all the holes in the tie-down bar, which I suspect isn’t correct. Took me a little time but found out that the set of four holes towards the bottom aren’t dimpled/countersunk as they will be bolted later.



Here is everything sorted. Most holes are dimpled in the bulkhead, and just 4 holes are countersunk.

Fortunately my buddy Mike had a gift for me. Another....Yes Another one. 0.063x3/4x3/4 angle so I could resolve my dump edge distance issue that I had the other day. This time, I threw Van’s dimensions out and cut the piece 24.5” to fit it perfectly in the web.







Next I drew the radius of the flange on the angle and shaped the end of the angle. This allowed the maximum edge distance possible for all holes. I’m not going to run into this issue again...

Once I had the fitting of the new angle done. I clamped the F-729C angle on top and re-checked the top most rivet hole to ensure that I wasnt going to have edge distance issues on this one.

Tons of room!

I then drilled the new F-729B angle to the web.

I'm now ready to cleco everything together and check the alignment of the elevator bellcrank axis. From what I can tell (and its not easy to check things at this point) the holes only seem off about 1/16". Way better than my first attempt. However, I'm shy about drilling both those 1/4" holes right now because the alignment has much to do about the final positioning of the bulkhead. What I'm thinking of doing is avoiding drilling the 1/4" holes in the angles/webs until the Fuselage is more assembled (Just before I have to rivet in the F-728 assembly) My thinking is this scenario will help ensure that the axis bolt can be drilled perpendicular to building lines with certainty. I've been thinking pots on how I can do this and reached out on the forums to see if anyone else has done this.
I think I will end up making an oak drilling block/guide once I can ensure everything is square once the fuse is all cleco'd up. that's the best way I see to ensure it is drilled the best way possible

Next I cleco'd the assembly and match drilled the holes.

Once I had everything together. I noticed how the F-730 pate and the flanges on the webs seem to interfere with the one legged nutplates that get installed at a later time. It looks like the interference can make mounting the nutplates fairly difficult later, so I decided to make some relief cuts. On the left side, its just the flange that interferes with the nutplate. A round chainsaw file and some buffing with 3M made short work of this.





However the right side is a bit more problematic. I filed F-730 down for the nutplate, however it occured to me after that the lower most #40 hole is shifted to the right slighty preventing proper edge distance for a dimpled hole. Well there is some confusion as to what the correct edge distance is as I describe below. But the edge distance I have to work with is now 0.184".  Worst case is that I re-make or reorder F-730 which is super simple to do. Another option if I can't use the hole is to make another #40 hole just below it with proper edge distance.





If I reference the MIL-R-47196A spec on Van's FAQ page, then I am all good as it states minimum edge distance is 0.154". However if I reference the original 1977 version then I have an edge distance issue at it states that the edge distance is actually 0.219". I'm a bit worried that maybe there was an error when they reproduced the MILSpec and mislabeled the "A & B" "C & D" measurements. I've reached out on the forums, but got little response. I'll see what Van's says. 



Update: Vans says its all good and build on.

Rebuilding F-711 and F-712 bulkheads - 4 hours

I have to laugh now. I'm just making silly mistake after silly mistake. I cut the first F-111C horizontal attach bar too sort. I had 11 3/4" on my brain and not the required 14 3/4"/. So dumb.
Well, I'll forge on with making one F-711C horizontal stabilizer attach bars.

Other than this morning, nothing when awry and things turned out nicely. As usual I started drilling with the palm drill to get a pilot hole in the correct location but finished drilling on the drill press.

I'll trim the center material on F-711 once I get another piece of flat bar to make the second F-711C.
I moved on to the F-712 bulkhead. I measured up, cut and drilled the AEX tie down bar. I placed the bar in the vice and tapped the threads. By the way I use WD-40 for cutting threads on aluminum. I apply liberally and go slow. Quarter turn forward, back an eighth, over and over till I advanced the tap just past 1-1/4"

New parts arrived, remaking the F-706 bulkhead - 3 hours

Today all of the new parts arrived from Vans, All new F-706 bulkhead parts (Since the bell crank axis hole is not perpendicular to the longitudinal axis of the plane), New horizontal stab attach bars, flap bearings, and new tie down.

I drove straight away into drilling the bushing holes in the F-706B lower bulkhead. Again like last time I opted for smaller bushings than the plans call for to help preserve edge distance. I went with 7/16" diameter as I just need to worry about wiring and not a manual trim cable. The holes cutting came out extremely nice again with excellent edge distance.

I managed to cut both the web flanges and the F-730 reinforcing plate before I went to far, again turned out fantastic.



I set up the assembly to check the perpendicular alignment of the bellcrank axis and it looks to be more favorable than the first F-706 I built. But it is a bit difficult to tell because I haven't drilled the angles yet for those holes.

I cut and drilled the F-729B but this time the 1/8" diameter hole that I drilled per the plans was used to locate the forward most cleco in the F-729A rib as once could reason this is what the plans intend. (Why do you drill that same hole in F-728B, as the only hole it can be is for the lower most cleco in the F-728A rib).

This is where things get a bit dumb and a "Gotcha". If you follow Vans dimension for angle length on F-729B and use the 1/8" hole for the top of the angle where it meets F-729C, you will have edge distance issues on the aft most cleco hole on the F-729B angle...the angle won't be long enough. I had this happen on my first attempt.

If you follow Vans dimension for angle length on F-729B and use the 1/8" hole for the forward most cleco hole to attach you will have proper edge distance on the aft most cleco hole on the F-729B angle, however you will have edge distance issues for the rivet on top of the F-729B angle where it meets F-729C. This is what happened on today's attempt.

I clamped on the F-729C angle and drew a hole before I drilled to make sure all was ok, and sure enough....edge distance issue.


I looked at re-doing the F-729C angle but repositioning the hole that connects F-729C/F-729B. Its tricky, But I could make it work as I can center the hole between the 17/32" distance I have to work with as a centered hole will give good edge distance. I'll think about this for a bit. I'm likely going to just re-do the F-729B angle as per my recommendation below.

I realize now that the best method to ensure proper edge distances is to cut F-729 long enough to fin inside the F-729A rib, and round the ends of the angle to fit the curves on the rib flange. Do not drill a 1/8" hole at this time. clamp the angle to the rib in its entirety and mark the forward most and aft most cleco holes, Then cleco the assembly together, clamp the F-729C angle on and mark that hole.
You know can disassemble and you have all critical holes marked and can identify the minimum required edge distances. Drill the holes needed to attach the angle to the rib. Then vert last step....trim the excess material on each end of the angle, careful to not exceed good edge distances on all three end most holes.

Started the F-712 Bulkhead - 2 hours

A while ago I threaded and cut the AEX tie down when I had the bandsaw out cutting other things.

All I needed to do was mark center on the F-712 bulkhead, dimension it and fit it for drilling. Quite straight forward. Or so I thought.
I marked the holes and drilled them on the drill press.

Drew a center line on the bulkhead.
 
Lined up the piece and clamped it.


UPDATE - Just a heads up that the plans/manual don't actually have you install the tie down bar to the F-712 bulkhead at this point. The instructions actually have you install this part much later when you install the vertical stabilizer to the fuselage. I figured this out after priming and riveting the tie-down bar onto the F-712 bulkhead and spent much time researching if it was going to cause problems. I finally came to the conclusion after talking to a local builder friend (and also noticed that this was done on a few other build logs - John's RV7A project, Bruce Swayze's RV7A project) that this was totally ok to leave riveted on and did not cause issues later. An angle drill is used to start the #1/8" holes into the vertical stabilizer, and of course I plan on using the drill press anyway to finish the job. 

Started drilling the holes to 1/8" and clecoing. Last hole that needed to be drilled, the drill bit in the drill press grabbed the assembly and sucked it up, resulting in the hole becoming oblong and destroying the piece.

I think I've come to a brick wall. I've screwed up almost every bulkhead. Of course I realize now that my 1/8" drillbit was the culprit. It has a different twist than the other cobalt # bits that I have. It must be only for wood and me using it on aluminum is causing it to ruin holes when it grabs. I'm so frustrated at this point.

Started F-711C hoz stab bars - 4 hours

I started the day with a renewed sense of desire to get building. Even though The F-706 bulkhead didn't turn out the way I had hoped. I ordered the new parts and I will try again. It can only get better right?



I started off with re-making the F-729C angle as I have lots of 0.063 x 3/4x 3/4" angle now. I quickly turned that one out.

Next I started on the F-711C horizontal stabilizer bars. I drew the line down the center, and then marked half so I could cut two equal length pieces.

 
I then began drawing out all the measurements and started drilling the required holes at #40. I took the assembly apart and rechecked all dimensions and cleaned up ends on the sanding station. Once I was happy with everything I re-cleco'd the pieces together and started to open up the holes to 1/8". Then it all fell apart. The drillbit sucked the material up into the drill press and ruined the holes in both pieces. I am numb.....and in shock. I just can't seem to do anything right.


I decided to take a break and have lunch, No sense jumping into another piece being rattled. After a couple of hours, I decided to work a little bit more, a "get back up on the horse". I fabricated the F-710B angle.  

I managed to get it back drilled to the F-710 bulkhead. Looks like I will need to fine tune the angle to get it radius'd to fit the tabs on the 710 bulkhead.
 
 One item of note, the part quality from vans on the F-710 bulkhead isn't that great. Looks as if the punch press almost took another round out of the piece and put some gouges on the metal. Being this area takes some structural load, I'm not so comfortable using the piece.

Finished the F-706 Bulkhead....Or so I thought - 4 hours

Yesterday I had cleaned and primed the pieces and tonight I will assemble them.

I started riveting the F-730 plate to the F-706B bulkhead using the back rivet method for the flush rivets, then used a squeezer for the innermost rivets. Then I fitted the F-729 rib.


Then I riveted the F-729C angle thinking it would be easier to set the innermost rivet now.

Then I was ready to squeeze all the rest of the rivets. I was thinking more about aesthetics than I was about placing the shop heads on the thicker material. Slight curling of the webs...not horrible, but not great.


I then squared up the F-729C and final drilled it to the F-729B angle. Then I squeezed the rivet.

I finished the evening by riveting the F-706B bulkheads to the F-706A bulkheads halves. Once everything was together I double checked square on everything and noticed that the holes for the Elevator Bellcrank bolt, were not perpendicular to the webs. Something looked off. So I started in on figuring out why the holes were not aligned. I cleco'd the assembly to the bottom fuselage skin and things started to look better. However I was still out. I disassembled it and measured the holes for the mounting bolt and sure enough they measured 1/8" different from the aft side of the web flange to the hole. I was floored. I was so careful to open up the factory punched holes to 1/4" and it really seems like they were not aligned from the factory. 

I'll send an email to Van's to see what's up and go from there.

Update - I received an email back from Van's and in a nut shell they gave instructions on how to install doublers and re-drill the holes so they are perpendicular. I wasn't too keen on doing that at this stage (pre-fuse assembly). I checked the prices for a new F-706 bulkhead assembly and its only $110 so i'll just bit the bullet and do the piece over again. This time making absolutely sure that the holes from the factory are aligned and not the 1/8" out. I sat and stared and measured, and scratched my head for an hour trying to figure out where things went wrong, and All I can come up with is one of the F-728/729 ribs must have had a hole in the wrong spot? Well, If I rebuild it I can double check everything.