May 2, 2010

Working in Miniature - 5.0 Hrs.

Over the last two weeks, I've made additional very slow progress on the fuel pump installation. This has been much more of a challenge than I thought it would be. But first, an order came in from Avery Tools for a few items I ordered recently. It still feels good to get packages in the mail related to the airplane. I still feel like a kid on Christmas morning, opening up the package to look at all the goodies!

Shown above are a pair of clippers used to clip the ends of zip-ties off flush so you don't have any sharp edges protruding. I tried them out. Nice! A lot of wiring is coming up in the near future, and I figured these will come in very handy. Next, a set of 1/8" pop-rivet dimplers. I've used the 3/32" size since starting the empennage way back at the beginning, but I'm just now getting around to getting a pair for 1/8" flush rivets. I haven't really missed them but I know at least one place I'll need them in the near future, so I picked up a pair. Avery even gives you a starter batch of nails to use with your rivet puller. Finally, I ordered a set of ruddle cable fairings. I want to get these installed in the near future as well. Okay... on to the continuing work with this fuel pump...

This has been an exercise "working in miniature" as I would call it. The installation of the Andair Fuel pump is bringing some new challenges my way. It looks so simple but there's more to it than meets the eye.

These two crossbeams made of 3/4 x 3/4 angle go under the F-782C cover between the two center floor rib stiffeners in the cabin. The bracket that holds the fuel pump and controller is held to these angles with screws going into the 4 nutplates that will be installed, as you can see above.. The F-782C cover is thin and flimsy, so I can see the need to have something more substantial to hold such an important component as the fuel pump. The 4 short angle brackets shown above will be riveted to these crossbeams and then drilled to the floor rib stiffeners. They will have nutplates installed as well. Machine screws will hold the F-782C cover in place to the floor ribs and these crossbeams. Below, all the pieces after being fitted, primed, and nutplates installed on the crossbeams. There are a couple of shims, too, which I'll explain in a moment.

Above, I have the 4 nutplates installed in the crossbeams that will hold the fuel pump bracket. Now this is where it starts to get more interesting. A while back, when I fitted the F-782C cover, I drilled it to the floor ribs according to Vans plans. I did not know at that time about the group buy on the Andair fuel pump system and that I would be going this route. So I already had a hole drilled in the 782C cover and in the floor rib that was in very close proximity to where you're supposed to drill the hole for this crossbeam attach bracket. My options were to either drill another hole very close to the existing one, which would look unsightly and I didn't like the idea of drilling a structural component like a floor stiffener full of unnecessary holes, or I could somehow modify the crossbeams' brackets to make it fit in place where it's supposed to go using the existing hole. I fiddled around quite a bit until I developed a solution unique to my installation.

Here's the working in miniature part of this whole operation. These little angle brackets are a lot of work! They will be riveted to the crossbeams and then bolted to the floor stiffeners using these miniature nutplates. These are special-order nutplates that don't come in the kit. I ordered them from Aircraft Spruce. Getting them to fit just right, drilling and countersinking for the rivets that hold them in place, and finally the riveting itself, all tested my skills. You don't have much material here to work with for doing things like clamping down for drilling. When you're deburring them on the scotchbrite wheel, they get hot quickly and burn your fingers. The countersinking cage is too big to fit on the part, so countersinking for the rivets has to be done carefully by hand. Finally, after priming them, you can't just rivet these nutplates on as usual. My squeezer easily installed one rivet, the one furthest from the vertical part of the angle. But that inside rivet was a challenge. Look at it. None of my rivet sets or squeezer sets will fit in between the center of the nutplate and the wall of the angle. So how are you going to set that rivet? In addition, the nutplate itself ran into the radius curvature on the inside of the angle. In order to place it where it needed to be, I had to file away some of the radius until the nutplate would lie flat. So all in all, these parts were a lot of work. I messed up several of them and had to start over.

Here's my secret weapon for setting those nutplate rivets. A long time ago when I bought my used rivet gun on eBay, it came with an odd assortment of rivet sets including this one. It's a long pin type of rivet set. I have no idea what its' original purpose was or what it was designed for. All I know is, as I was scratching my head looking for a way to set these nutplate rivets, this looked like a workable solution. I was able to use it to backrivet those rivets against my backriveting plate. Using low air pressure and holding it very carefully, it worked great the first time!

So, moving on, you have to think ahead and plan a strategy very carefully to put all this together and make it all fit correctly. Let me explain the picture above. I riveted those little nutplates on the aft pair of brackets only, for now, and riveted those brackets to the aft crossbeam (on the right in the pic above). Because of the location of the existing holes in the floor ribs, as I explained earlier, the solution for me was to rivet the brackets to the forward side (inside the angle) of the crossbeam. It also required using some shims to push the brackets forward far enough to fit the existing hole in the floor rib. The aft crossbeam can then be screwed in place without the F-782C cover for now (you can see the screw through the floor rib on the right). With the fuel pump bracket bolted in place on the crossbeams, this locates the position of the forward crossbeam. The angle brackets on the forward crossbeam have been riveted in place and drilled for the nutplates but the nutplates are not installed yet. This allows you to use a right-angle drill to drill the hole through the floor rib as you can see above. There's no way you'll install this without a right-angle drill, as far as I can see. Once these holes are drilled in the floor ribs, those special little nutplates can be installed in the brackets. Oh, one other thing. You have to compensate for the thickness of the F-782C cover when riveting these brackets to the crossbeams, and allow room for the cover to slip in place between the floor rib and the crossbeams. I used some scrap metal shims when I fitted the brackets to the crossbeams before drilling and riveting.

Next, the crossbeams are removed from the floor and everything cleaned up. Now, they are reinstalled under the F-782C cover and the bracket screwed down in place. With the aft crossbeam screwed in place, it locates the position of the forward one, so the forward holes can be drilled in the cover. Below is a shot of the underside of the F-782C cover with the crossbeams and bracket bolted in place.

You can see all the holes I drilled in the cover, to allow the bolts, nuts and washers to protrude safely through so the bracket will lie flat on the cover. You can also see how I riveted the clips on the aft crossbeam on the forward side of the angle using shims, in order to position the holes as I already described.

Now, finally, it's time to drill the forward pair of holes in the cover using the holes in the brackets as drilling guides. Then, finally, I will rivet those little nutplates to the forward brackets. Then, hopefully, everything can be test-fitted in place in the fuselage. I hope it all fits. It should.

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