Work and family stuff have been getting first priority over the last few days, but I’ve continued on the slow and steady path to getting the right longeron bent.
How do you know that the longeron is bent correctly? By comparing it to the template included in the plans. I cut out the template and glued it to some cardboard…easy enough. Just gotta continue the bend-and-compare process…
Today was the day to start bending the longerons. To RV builders, particularly those of us building the side-by-side airplanes (RV-6, -7, -9 and -10) where the fuselage side curve is more pronounced, this is one of those sort-of-dreaded tasks that we really don’t want to screw up. It’s kinda like the elevator trim tab and the fuel tanks. Fortunately, by this point I’m pretty much over the mental hurdle of working with the longerons…
Making the bend isn’t terribly difficult…it’s just “fiddly”, meaning that it takes a lot of tweaks and adjustment to get the longerons to fit the template that’s included in the plans. The basic process is to clamp the longeron at a spot just behind where the bend should occur, preload it by pulling the free end in the direction of the bend, and finally apply a moderate whack with a dead-blow hammer right next to the vise to “set” the bend. Do that a couple dozen times, moving the longeron an inch or so in the clamp before each whack, and the bend gets done.
Making the bend isn’t terribly difficult…it’s just “fiddly”, meaning that it takes a lot of tweaks and adjustment to get the longerons to fit the template that’s included in the plans. The basic process is to clamp the longeron at a spot just behind where the bend should occur, preload it by pulling the free end in the direction of the bend, and finally apply a moderate whack with a dead-blow hammer right next to the vise to “set” the bend. Do that a couple dozen times, moving the longeron an inch or so in the clamp before each whack, and the bend gets done – and at some point you end up with something like this…
But like many other things in this project, it’s not quite as simple as it looks. Whacking the longeron to bake the big bend tends to give it some unwanted twist…
…and that takes a bit of twist with a wrench to remove. But removing that twist also takes out some of the bend you wanted to make in the first place, and you gotta keep the bend where you want it. Like I said…it’s “fiddly”.
I found some good advice on the web, and that’s to not try to do the entire bend in one session. An hour or so a day for the next few days… I don’t want to be ordering any more longeron material!
Finished the J-channels today…woohoo!
The next step in the plans was to start bending the longerons. I really didn’t feel like messing with that yet, so I clecoed the F-711 and F-712 bulkheads in place on the F-779 lower tailcone skin.
The fit of these parts is notoriously bad, and I’d read a lot of gripes about this area on the usual websites. Those tabs on the bulkheads have to be bent correctly to match the angle of the F-779 skin, and the skin itself is very thick (0.040″) so it requires some wrestling to get several of those clecoes in place.
Once I started looking at this area and how the tailwheel mount fits between the F-711 and F-712, I realized that there are a couple of rivets in the F-712 that shoudln’t have been done yet…so I get to drill them out.
Got the new longerons clamped, measured and trimmed. Looks just like they did the last time I did this, so look back a couple of entries to see what it looks like.
I also continued trimming the J-channel ends…sorry, no pictures.
I’m back from Oshkosh and my batteries are definitley recharged. One big boost came from seeing my friend Mike fly his RV-7 to Oshkosh for the first time. Mike overcame more than his share of hurdles to get to this point, so it’s really motivational to me to see his airplane at the Big Show.
The new longerons arrived today, shipped in a long piece of PVC pipe. Thanks to careful handling by UPS (NOT!), one end of the pipe was pretty badly damaged – but fortunately the longeron material only had a few minor scuffs on one end – and that can be trimmed away. Cool!
I’m off to Oskhosh next week to get my RV building batteries recharged…
Started measuring and trimming the J-channel material that’s used for auxiliary longerons in the fuselage tailcone. There are three sets of two J-channels that must be made from stock. I measured them using the same method I used on the longerons, and double-checked the measurements before cutting. Came out great! The ends need to be shaped to accomodate the bulkheads, but that will come later. Sorry, no pictures…
I purchased a new, extremely heavy vise from Sears with jaws that are designed to be removed. I fabricated a new set of oak jaws, this time a lot thicker so that they can’t possibly hurt the yet-to-be delivered longerons. Since I now have a lot of spare longeron material, I cut off a piece and made some trial bends with no damage to the longeron.
I also re-evaluated my bending technique and decided to abandon the Orndorff method and go back to Vans’ instructions. When in doubt, RTFM!
After a little bit of irritation, I realized once again that just about any mistake on the project can be fixed with a call to Vans for new parts. No, new longerons aren’t cheap – shipping alone is more than the cost of the parts. They should be here in a couple of weeks.
Today I hit a new low in the project.
If you look at the picture above, you’ll see that my vise has oak jaws. I removed the vise’s original steel jaws and replaced them with the oak ones I fabricated to protect the longerons during the bending process, during which the longeron is clamped in place and bent using a dead-blow hammer.
Well, it turns out that oak compresses more than I thought, and about halfway through the bending process oak jaws compressed sufficiently to expose the steel screws that hold them in place. I didn’t notice this was happening, and as I tightened down the vise, those screws left these nasty gouges on the longerons…
This was a real demoralizer. I’m gonna have to figure out what to do next.