More longeron bending - 3 hours

One of the benefits of working in an engineering office is that I can draft the longeron bending templates to perfect full scale and also mirror them to fit both the Left and Right sides. I scanned in my F-721B aft deck pieces and then drew out the correct bend in autoCAD to 1:1 scale.

And of course the continuous roll plotter comes in extra handy.I managed to print out a 72" long paper template.

I managed to make short work of the second longeron. It goes way more quick than the first one as you now have a feel for the correct pressure needed on the bending dies, and you are not so afraid of over bending. I managed to bend the send one to near correct in about an hour or so. Then came the not so fun tweaking. The bend of the two pieces is virtually perfect on the horizontal, but not on the vertical. this shows up when you clamp the two pieces together.
Looking great here....



But not so good here....

This is where things can get a little frustrating. Trying to flatten that unwanted separation between the longerons results in changing the bend that you want to have match the template. So lots of back and forth futzing. I spent an hour on it but was making little progress, but at least I was in the ball park.

Starting the big bend! - 9 hours

Again, I spent some time reading up on other build logs on bending the longerons before I started in. I figured out that I didn't really need to make the cuts at this exact time. But it was very important to mark things out. My reasoning is (that the fuselage up to this point is reminding me) that pieces are more exact when you can fit, check, and then cut rather than blindly cut....more so around the horizontal stabilizer. I So, I dug out my thin sharpie and went to work.





I then dug out my longeron bending dies that I have bought some time ago. One of the items everyone talks about is protecting the angle from marring so I used some gorrilla tape and lubed the dies with WD-40. That works well but a pain in the butt as it wants to remove your sharpie marks.

I drew a reference line on the dies

First pass, you will notice the gentle bend.

Second pass, Third pass. Ugh... I am being careful not to overbend as the longeron dies mention but this is painful. I've been at it for hours and only small steps. I decide I can then become a bit more aggressive with the bending. Yup, bends going well now, but there is a noticeable curl up in the longeron 90deg perpendicular to the bend i'm making, which is to be expected. I went to work taking that bend out and trying get it to lay flat on the table again. Interesting, by taking the vertical bend out is relaxes the horizontal bend i'm trying to get. Hmmm, You purposely want to overbend the longeron a bit on the horizontal. Well after a few hours, of working with the longeron. I had both the horizontal curve matching the plans and laying flat on the table.

I am the aluminum whisperer.

Now...next concern was bending the other longeron and matching it up to the plans.

Measuring longerons - 3 hours

It was time to start on the longerons. These have been sitting up on the garage shelf for quite some time. They collected a lot of dust. I spent some time getting the garage ready, putting saw horse out and leveling the run to aid in accurate measuring. I cleaned up the ends of the longerons and then clamped them together and began marking out the dimensions. After a good discussion with a local builder he offered a few tips and suggestions, using the bottom skin and the aft canopy deck pieces as a guide. He mentioned that he had to trim a bit of the front of the longeron to fit the bulkhead which got me thinking about if I could get myself into hot water with edge distance issues (as was the case with the F-728/729 angles)

 I spend a few hours researching and reading. Before I did anything I decided to research the whole longeron process. I was most curious about if I could run into any potential edge distance issues, seems that most folks trim about ¼” off the front of their longerons. After all my reading I decided to give myself some extra material to play with (½” extra to be exact). So I erased all my marks and drew a new reference line that would give me ½” extra. I clamped a piece of oak on the new datum point and re-measured all the dimensions out. 

 

 

 

 

 

Riveting F-712, F-706 (again) and F-707 & F-708 - 4 hours

I woke up this morning ready to go on riveting the bulkheads together. I started with the F-712 bulkhead. I back riveted the entire assembly it turned out so good.






Funny though that after I had it all riveted is when I figured out that the plans have you hold off this step. I did not read the manual for F-712, I just assumed. I started checking off steps in the manual and that's when I noticed it.

I began to dig into who, what, why and where. Took my hours to figure out if this is going to be a problem.  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. 

I suspect the plans are set up this way to accommodate the quick builds. Anyone with a quick build fuse (7 or 7A) gets the fuselage with nothing on the bulkhead. If you have a 7A you then have to fabricate the tie down bar and install it before you mount the vertical stabilizer. It would be reasonable that to avoid confusion they just have everyone do it later. 

After all my research, I am confident that my little oops has actually turned out to be the better method of installation.

Now that I could breath easy, I moved onto riveting the F-706 bulkhead...Again.
 




 Admittedly I struggled a bit with setting the left side rivets on the F-729 rib. On my first attempt a few weeks ago, I put the factory heads of the rivets forward, leaving shop heads aft on the web flange, the result is that it wanted to curl the web flange up. So on this attempt I put the factory heads aft to prevent the flange from curling. Much more difficult to squeeze those rivets and get them straight. After drilling them out, I decided to go for the bucking method a used the same technique as that used on setting the wing ribs. bending the rib slightly to the side and using a super long rivet set. Worked perfectly. 
 
I completed the F-706 bulkhead. Obviously I've not riveted the F-728 and 729 angles at this time. I will do that once I can confirm perfect alignment of the bellcrank axis. 

I then riveted the F-707 and F-708 bulkheads. Easy
 
 

Prep'd & Primed all bulkheads (except F-711) - 9 hours

Managed a huge day today in the garage. A very tedious process to prime that I have. Scuff parts, wash in soapy water, rinse, dry, wax & degrease, MEK, Prime. With setup and take down of the large containers for washing parts it takes a lot of time so its beneficial to prime all at once. Also I am motivated to get this done as I always like to have a full 24 hours dry time minimum to the primer before I assemble.

Since bulkheads F-706 and F-712 where ready to go, I started the priming process for those.

As those parts were drying, I needed to work on the F-710B angle. The fit of the angle wasn't the best for the tabs on the bulkhead where the longerons get installed. The sharp corner on the end of the angle needs to be rounded to allow the bulkhead, tab and angle all to sit flush.



I went to work rounding that corner. However one of the jobs I need to do is to round the top flange of the F-710B angle so it nests nicely inside of the longeron. The best way I believe I can do this is to round it once I have it all installed and can verify perfect fit. So I will hold off on riveting this part until later.

Once I finished rounding the angle for the bulkhead tabs, I moved on to prepping the F-707, F-708 and F-710 parts for priming. Lots of work to break all the edges, deburr and polish all the nooks and crannies. I opened the holes for the rudder cables (Did I ever mention I hate doing those?) and the static lines. Then it was through the long a tedious process of priming....

Preping F-706, F-712 bulkheads for priming - 3 hours

One of the big jobs that needs to be done is to prep the bulkhead parts for priming. Before I dive into that I was sure to open up the holes for the rubber cables and the static line.



Like the wing ribs these tend to be a little annoying as of all the corners and flanges. Going through each edge and notch is a bit tedious but it goes a bit quicker with the 3M on the dremmel and that does an excellent job on polishing.

When ever I have a stubborn hole that does not like to come clean with the debur tool, I buff the hole with the 1" 3M square on the dremmel and it cleans it up nicely. (I also found that doing this gives much better success of dimpling without cracks on the wing tanks back when I worked on that piece. So why not continue using the method?)

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.