Fuselage

Theme for the day: " Another Boogeyman bites the Dust"

My first task today was to work on a stiffener plate for the firewall, where the fuel line fitting penetrates the firewall. When I first installed this fitting back on April 2nd, I simply used two thick aluminum washers, like you use in other parts of the plane. But I haven't been comfortable with the washers used on this fitting as stiffeners. It just didn't seem adequate to me. The plans show a stiffener riveted to the firewall here for the fuel pump for a carburated engine installation. But I was in the dark about what to do in my case because the information I needed for a fuel-injected system isn't in any of the drawings I have at this point. Andair's drawings don't show a stiffener here either. So I wrote to Vans and sent them my pictures from April 2nd, and Joe Blank emailed me a copy of drawing number OP-32. It shows the details for an IO-360 fuel system. Thanks, Joe! He said I'm actually getting into the firewall forward part of the project, which explains why I don't have the drawings yet. Apparently this drawing comes with either the firewall forward kit, or the finish kit. But firewall forward or not, I don't see how I can accurately install fuel lines in the fuselage unless I have a starting point and an ending point. And I want this done right. So I followed the plans on drawing OP-32 and replaced the washer on the aft side of the firewall in the cabin. I made a stiffener from some .063 sheet and riveted it to the firewall. I still don't like the aluminum washer on the forward side of the firewall. But that seems to be standard practice. I'm going to see if I can find a steel one to replace it.

Here's the new stiffener as seen from inside the cabin. I feel much better now about this installation.

UPDATE: November 28, 2012 - In spite of the drawing, I still didn't get it. I didn't study the drawing long enough or carefully enough. This stiffener is supposed to go on the engine side of the firewall, and it gets riveted to some of the rivets on the vertical stiffener angle as well as to the firewall, making it very sturdy. I went back and studied OP-32. It doesn't say anywhere on the drawing that the doubler goes on the engine side. But you can figure that out if you study it long enough. But a little note on the drawing would have been nice. Anyway, check out my work from this link to see the doubler I fabricated and riveted on here.

While I was taking care of this, I went ahead with another idea I saw on a website somewhere. The stiffener angle that goes across the bottom of the firewall recess opening is loose right now. Rather than waiting until the firewall recess is riveted on, there's a good way to install this stiffener now using 2 small keeper rivets. So I drilled, countersunk the angle and dimpled the firewall, and riveted this piece in place.

The red arrows show the keeper rivets. Below is how it looks from inside the fuselage.

Installing The Fuel Lines, From The Fuel Valve Through The Sides Of The Fuselage:

Next, since I can't put it off any longer, I went to work to install the fuel lines, from the selector valve to the sidewalls of the fuselage. Honestly, I have been procrastinating on this for some time. The 3/8" tubing isn't easy to bend or work with, and I didn't know how I was going to get all those bends in the tube, get it in place, flare the ends and everything, and avoid messing it up. As anyone knows, bending any kind of metal back and forth enough times will weaken it and it will crack and break. So I'm wary of getting any kinks in the line, or overworking it and weakening it. So how do you go about this? Some builders have elected to put in a union here, or several unions. I'd like to avoid that if possible. Each connection you introduce in the system becomes another potential failure point, or a place for a leak to develop. (how much fuel do you want in your cabin?) So I can see the advantage of the single piece of tubing that Vans shows in the plans, going all the way from the fuel tank to the selector valve. Other builders have gone to companies like Bonaco and just purchased flexible fuel lines to install. Nothing wrong with that. But I decided that I should at least give it my best shot before going either of those routes.

Someone has been quoted as saying "there are a lot of boogeymen in this project" and I know exactly what he was talking about. Like a child having a bad dream about a boogeyman, only to wake up and find out it was just a stupid dream, today I learned that just like I have seen many times before in this project, something that intimidates you for a long time isn't so bad after all once you jump in and get started. So to help slay that boogeyman, here is a list of hints that I learned along the way, that helped me get this finished:

Don't be in a hurry. Take your time and really think through each move before you do anything. Sometimes I just sat there staring at it for a while before going forward. This is time well spent.

Here's the first step: Use a piece of wire to bend into the shape that the tubing needs to take, and use it as a template of sorts. This is especially helpful for short pieces and sharp curves. Pay particular attention to the inboard end near the fuel valve, and get this wire shaped as accurately as you can, especially on this end.

Then, cut a length of tubing about 35" long. It helps to leave it partially coiled up, so it will fit in the fuselage when you're ready to start installing it in place. But unroll and straighten out the inboard end. Then, using the wire template you just made as a guide and your tubing bender tools, put in the bends that you need under the fuel valve. You want to put the bends that are necessary under the fuel valve in place first, before installing the tube. This allows you to put the fittings on the tube and flare the end, and do all this work on the workbench, rather than trying to do it bent over the side of the fuselage, contorted in some uncomfortable position. Using the wire template, you can get it very close before you ever put it in the plane.

Now you're ready to begin installing the tubing. You want to start in the center of the fuselage with each piece and work toward the side of the fuselage, not the other way around. You're not gonna believe how easy this is.

Here's where I started installing the tube for the right side. In the picture above, it's through the first grommet. You can also see the left side tubing, that I had installed previously, with the bends in place that you need under the fuel valve. I removed the fuel valve temporarily at this point so I could see better. You have to leave the tubing coiled or bent just a little just to get the tubing to fit in the cabin and the end to go in this first grommet. The piece of tubing I used was about 35" long, which turned out to be plenty long. I trimmed about 3" off the end when I was done. Final trimming will be done later when the wings are on.

Here the tubing is pushed through two grommets and on into the gear leg weldment area. If you're building an "A" model RV, the gear leg weldment presents no problem at all. You'll be amazed to find out that there are holes in the gear leg weldment in just the right place for this tubing to pass through. Thanks, Vans! Amazing.

Next, you remove the two rubber grommets from the side of the fuselage and insert a tube bending spring from the outside, through the hole in the gear leg weldment. This serves as a guide to push the tubing through without kinking or overworking it. I wouldn't attempt this without this spring. If you don't have a set of these springs, you can find them in Home Depot's aviation isle for less than $10 bucks. For this task alone, it's money very well spent.

I received an email from a fellow builder who wanted to know more about these tube bending springs, and where you get them. So I thought I would post a picture here. I found them at Home Depot in the plumbing department. I'm sure you could also find them at Lowe's or other home-improvement stores or plumbing stores. They're used for, you guessed it, bending soft copper tubing for plumbing purposes. The bag of all four springs cost less than $10. Get some! It's the best money you'll spend for all your tubing work on the RV.

Working carefully, you continue to push the tube through the spring, bending gently as necessary as you go. Next thing you know, here it is. Even though the exit angle needs to be adjusted, it's in place! And it wasn't hard at all. This whole process probably took about 5 to 10 minutes. Easy!

Now, put the fuel valve back in place and do the final tweaking and adjusting to get this end attached and screwed in place. Finger tight is fine for now. This took me a little while, but it anchors the tube in place, which greatly helps finish the rest of the installation.

This is probably the hardest part, but the bending spring really helps here. The final bending of the tube to the shape you see above was accomplished by using a round wood dowel as a lever to bend the tubing and push it toward the corner. Do this gently and don't do this without the bending spring in place or you'll kink the tube! The shorter, tighter curve near the hole was finished using a smaller dowel or screwdriver handle in between the tube and the side skin to sort of wrap the tubing around to bend it just right so it exits the hole at a 90° angle. Also make sure that where the tubing passes through the hole in the gear leg weldment, it's centered in the hole and not rubbing on it. A little inspection mirror helps you see under here. Then take the spring off and see how good it looks! You're almost finished! I noticed later that this gentle S-curve will allow for a bit of adjustment to the length of the tubing, in or out, for final connection to the fuel tank.

Some final tweaking will position the tube in the middle of the hole and straighten it out. Then it's time to put the rubber grommets back on.

The interior rubber grommet goes on first. It takes some persuasion to get this on, but a small flatblade screwdriver used gently to push it on really helps. Obviously, you have to push it on from the outside, through the hole, and then fit it in place.

Then the exterior one goes on. A bit of lubricant on the interior face of the grommet where it rubs on the other one helps it slide into place much easier. All done! I spent over 2 hours on the left side fuel line. But the right side took me less than an hour from start to finish. And this was my first attempt at these fuel lines. I didn't end up throwing any tubing in the scrap pile (other than the short ends I trimmed off), nor did I have to order any additional material from Vans. I'm not bragging, I'm just so happy to find out how easy this was. I'm sure you can do it, too. I don't have a picture, but at this point I trimmed off about 3", which still left more than enough to reach the fuel tank when the wings are on.

UPDATE: October 23, 2010. I'm posting a later update here. After mating the wings I did the final measuring and trimming. As it turns out, the exact length of this fuel line, from the side skin behind the black grommet to the end of the flare, is exactly 3-5/8". I would have liked to know this measurement at this point. Perhaps this will help someone at this same stage of the build.

Here's the fuel valve with all 3 tubings and fittings in place, just to double-check the fit of everything. Turned out great. You want to leave clearance underneath these lines, if you can, for wiring runs to go through the snap bushings seen in the background in the bulkhead. Next, I'll be installing the brake lines. However, as you can see above, the soundproofing material I used when I first installed it was a bunch of leftover scraps pieced together. This looks shoddy to me, and I've decided I'm going to replace it. I'm ordering a new piece from Aircraft Spruce, and it needs to go down before I install brake lines, so I'm going to do some other things before putting in the brake lines.

So for now, I'm finished with plumbing, and it's time to move on. It feels good. This boogeyman will haunt me no more.

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