Matt's RV-7 Project » Wings

Fuel tank manometer test

Matt — Sun, 23 Sep 2007 03:00:40 +0000

John loaned me his fuel tank leak testing kit a couple weeks ago, and I've been using it to do some extended testing of my fuel tanks. It's a simple water manometer that plugs into the tank outlet – you cap off the vent line and then use a Schraeder valve threaded into the drain flange to pressurize the tank.

I filled the first tank to 27 inches of water, which is about 1 psi, and marked the height of the water column.

Then I left it alone for a week. The water level fluctuated up and down with local pressure and temperature changes, but at the end of a week the tank was still holding approximately the same amount of pressure. After that I did the other tank, and it tested fine too. Hooray!

You can buy the fittings to make one of these setups from Van's, but you have to supply the plumbing and yourself (or borrow a buddy's).

Wing insurance

Matt — Sun, 17 Sep 2006 22:02:17 +0000

After reading this story of how a guy knocked one of his wings off the stand and dented up the leading edge, I went out to the garage and stuck a couple of bolts (actually they are the drift pins I made earlier) through each spar at the root end:

This should keep the wings from sliding onto the floor if someone bumps them. Whew. One less thing to worry about in the middle of the night.

Decided not to hang the wings yet

Matt — Wed, 14 Jun 2006 00:00:07 +0000

Never mind what I said about planning to hang the wings this weekend – I changed my mind. It occurred to me that the main reason I was planning to fit the wings to the fuselage was to locate the points where the fuel plumbing and electrical wiring go through the fuselage sidewalls, and also because that's the next step in the instructions. But, there's really no need to do it now: the fuel plumbing passthroughs are marked with prepunched holes, and I can just measure where the electrical conduit needs to go. Just to be sure, I called Van's and they confirmed that I can wait to do this until the airplane is nearly complete and in the hangar. This is great news, because I wasn't really looking forward to having one of the wings sticking out into the driveway.

Sealed up the right fuel tank

Matt — Thu, 08 Jun 2006 02:00:44 +0000

Today's mission: Finish out the remaining fuel tank. First order of business: safety wire the fuel pickup tube. Oh wait – I put the safety wire on backwards! Arrgh.

Ahem. Here it is again, properly safetied this time.

Mary took a bunch of photos while I was doing the proseal part. First the fuel sender gets gooped in place:

…with a nice seal all the way around the hole, plus a blob of proseal on the back of each nutplate.

Then I laid down a bead all the way around the access plate opening:

…which I then spread out with a popsicle stick.

If you are referring to this website during your fuel tank construction, take note! The float on the fuel sender in the photo below is on backwards. I discovered my error after I got all the proseal applied and was about to seal up the tank, but luckily was able to reverse the float without having to re-bend the wire (by popping the plastic float out of the wire loop, flipping it, and snapping it back in). That was a small moment of panic. If I'd paid closer attention in the first place, I would have noticed that the float was hitting the stiffener inside the tank.

Done! Sticky fingerprints everywhere, but it looks like we got a good seal all the way around. I'll know in a week after this cures and I perform a leak test.

Installed right randing right rens

Matt — Sat, 03 Jun 2006 22:52:47 +0000

Mary helped me swap wings, and then I trimmed and installed the other landing light lens, same as this morning:

This one took a quarter of the time and fits even better.

Okay, so as soon as I get more proseal I can goop up the other fuel tank, and that's the last real task before mating the wings.

Installed left landing light lens

Matt — Sat, 03 Jun 2006 18:45:16 +0000

Since I had the left wing out and accessible, and the temperature in the garage is certainly high enough to work with plexiglass, I decided to put in the landing light lens. First step was to mark some guide lines for making the cuts:

I covered the outside surface of the lens with masking tape to protect it from scratches, then made the straight cuts on the bandsaw.

Then I smoothed the edges and rounded off the corners on the scotchbrite wheel. I didn't think it would do so well on plexiglass, but it worked just fine. Oh scotchbrite wheel, is there anything you can't do?

As suggested by the plans, I made from duct tape a "handle" with which to hold the lens firmly against the inside surface of the wing skin. Oh duct tape, is there anything you can't do?

#40 holes were drilled through the wing and into the lens…

Then I enlarged the holes in the lens with my special not-so-much-with-the-cracking-of-the-plexiglass drill bits. Here I deviated from the plans slightly… they call for you to drill the holes in the skin to #30 and dimple, then drill the holes in the lens to 5/32" to allow the screws to move around as the lens shrinks or expands with temperature. Okay, that's fine. The problem is that the 6-32 screws used to secure the lens in place won't fit flush in a #30 dimple. I've seen plenty of RV's where the builder followed the plans exactly and ended up with the screws around the landing light protruding above the skin, which looks dumb. So, I just drilled the skin holes to 5/32", which is the correct size for a #6 screw, and dimpled with my #6 screw dimple die. Then I drilled the holes in the lens to 5/32", countersunk to accept the skin dimples, and drilled them up to 3/16" to provide expansion room. Seems obvious to me.

I also trimmed another half inch or so from the lower lip in order to improve the fit.

The nutplate retainer strips are attached with double sided tape:

It's pretty hard to see here, but I put a narrow strip of foam tape all the way around the inside of the lens cutout, to seal against water leaks and to provide some additional cushioning for the lens.

Done! The lens fits the contour of the skin very well… and look how nice and flush the screws are.

Fuel tank update

Matt — Sat, 03 Jun 2006 17:00:20 +0000

Two days later and the balloons haven't lost any air. Hooray, that means the tank doesn't have any leaks.

Fuel tank leak test

Matt — Fri, 02 Jun 2006 02:00:09 +0000

I put a pipe plug into the drain hole, and used fuel lube and tie wraps to secure partially inflated party ballons over the fuel feed and vent fittings. I figure if the tank can hold positive air pressure for a couple days with this goofy setup, it can surely hold avgas.

Sealed up the left fuel tank

Matt — Mon, 29 May 2006 20:06:52 +0000

Today was tank sealing day! Even us quickbuilders have to go through the rite of passage that is Proseal. Imagine poisonous peanut butter that's dark grey and sticks tenaciously to everything it comes in contact with, and you've got the general idea. I had to remove and replace the tank cover plates on my other RV to make some plumbing changes, and I didn't like it much, but at least I already know I can do it.

The first step was to attach the fuel pickup tube to the bulkhead fitting that was already installed in the tank cover plate. I sprung for the fancy prefab pickup tubes with the filter screen on them to keep bits of trash out of the fuel lines.

I also complied with the recent service bulletin that mandates safety wiring the flare nut in place. A couple of 1/16" holes through the nut, some safety wire, and done. Now I'm glad I waited a bit to seal up the tanks – it would have been a pain in the butt to remove the cover plate in order to make this fix.

I bent the float arm for the fuel level sender as laid out in the plans, which turned out to be dead on this time. I clecoed the sender to the cover plate and temporarily put it on the tank, in order to verify (with the help of some tape to hold the arm in various positions) that the float arm travels freely from stop to stop and that the length is correct. The float almost touches the top tank skin at the "full" position, and almost touches the bottom skin at the "empty" positon.

I cleaned and scuffed all the mating surfaces so the proseal would stick:

I also washed all the screws in acetone and air-dried them, to make sure the proseal would stick to them too.

After the parts were all prepared, the tools laid out, grungy clothing donned, and plenty of rags and gloves placed at the ready, it was glue time. I used one of the pre-measured proseal cartridges that Van's sells. It's a bit pricey at fifteen bucks, but it makes mixing and cleanup a snap.

This photo also indirectly demonstrates one of the other important requirements of doing this job – a helper with clean hands who can take pictures, fetch fresh gloves and tools, and so forth. Once again Mary was drafted to perform airplane duties. She was a huge help, since this stuff doesn't give you a lot of extra working time and it gets absolutely everywhere.

First under the glue gun was the fuel level sender. It came with a rubber gasket but I decided to just use a ring of proseal instead, since I was worried about the gasket drying up and cracking or otherwise letting a leak happen. I think they're designed for top-mounting in an automotive application, in which instance you could remove and replace the gasket a lot more easily than you could with an aircraft wing tank.

I buttered up the mating surfaces and screwed them together, first putting some proseal on the screw threads to prevent fuel wicking out. You can see below that I got a nice fillet of proseal all the way around the hole, which is a good sign. I also blobbed some proseal on the ends of the nutplates and around the bulkhead fitting. It already had a bit of sealant on it from the quickbuild factory, but I figured why not add a little more? Then I snapped the float arm into place in preparation for attaching the cover plate to the tank.

As an aside, I wish Van's would use closed-end nutplates on the fuel tanks instead of generic K1000's. Something like a NAS1473 would do the trick, and would definitely reduce the chances of fuel seeping out along the screw threads. I'm not so dogmatic about it that I want to build my own fuel tanks, however! No thank you.

Then I buttered up the mating surfaces of the cover plate and fuel tank rib with delicious toxic sludge (it's low-carb too) and screwed it into place, again with extra proseal dabbed onto the screw threads. Popsicle sticks are useful for spreading the goop around.

See, it really does get everywhere you touch. I made sure to get a nice fillet all the way around the edge of the cover plate, along with a nice "proseal washer" gooping out underneath each screw head. I used MEK to clean off the bulkhead fitting and the screw terminal for the fuel sender, but I didn't bother cleaning up anywhere else. The last thing I wanted was to get solvent into the joints I was trying to stick together!

Experienced builders may notice that I didn't use the cork gasket supplied in the kit. I remembered how dried out the cork gaskets were when I unsealed the tanks on my last RV, so I decided to just proseal the cover plate directly to the tank, as many builders also do. Less chance of an eventual leak that way, if you ask me.

Mary was laughing at me for getting proseal smeared on the fuel tank plans sheet. I guess she took this photo to document it for posterity.

The last step when working with proseal is always to clean the black goo off all your tools. We went through a lot of gloves and shop towels today. My lawnmowing clothes are a little grungier now as well.

I'll let the tank cure for several days before leak testing it. Only then will I know if I got it sealed up successfully. After that, I'll put the left wing back in the rack and do this job over again for the other wing.

Meanwhile, my garage smells like a meth lab. I hope the neighbors don't notice.

Finished riveting wings

Matt — Sun, 21 May 2006 22:34:06 +0000

Mary came out and helped me rivet the last of the wing skin rivets in place. The wings are now officially riveted together. We put a couple dings in the skin (again) but it's nothing that paint won't hide.

Then I put the left wing onto sawhorses so I can work on getting the fuel tank cover plates finished:

More wing riveting

Matt — Mon, 08 May 2006 02:22:19 +0000

RV hopeful Dave Blair came to check out the project and help rivet on the left wing's outer bottom skin. He got the hang of the rivet gun pretty quickly. By dinnertime we were cranking the rivets out one after another.

Don't be fooled – this is a lot less comfortable than it looks:

We got it about three quarters finished. I'll pester Mary to help me drive the last few dozen rivets sometime this week.

We put about the same number of dings in this wing as the other one that got riveted last week. Meanwhile, the pre-riveted part of my quickbuild wings have exactly one small surface imperfection that I've been able to detect. How in the world do the quickbuild factory people do such a flawless job? Do they have some kind of ultra precise robotic rivet-driving laser beam out there in the Philippines?

Riveted one wing bottom skin

Matt — Mon, 01 May 2006 01:55:49 +0000

Fellow KC-area builder Scott came by this afternoon to help rivet the outer bottom skins onto the wings, which is a task I've been procrastinating on for a while.

I had the long skinny arms so I got to buck all the rivets. Long sleeves are a must for this job. Also, this picture makes me hungry for Cozy burgers.

We planned to get both wings done in a couple hours, but we ended up taking all afternoon to get only one wing finished. We'll do the other one some other weekend.

This one didn't turn out too bad, although there are some dings and smilies here and there (especially back by the rear spar where it's hard to buck). Paint will hide them though. We only had to drill out two rivets, both of which were due to us misreading the callouts and using rivets that were too short.

Autopilot work

Matt — Mon, 03 Apr 2006 01:46:37 +0000

I broke out the TruTrak pitch servo today. Here's a shot of the servo and its bracket, next to the skimpy instruction sheet.

I drilled out four of the rivets in the F-729 bellcrank rib, then back drilled the bracket in place. Once the position was fixed, I marked and drilled three more #30 holes in the upright part of the bracket and four #40 holes through the bottom flange and belly skin. The holes in the skin were dimpled using pop rivet dimple dies.

After priming the bracket, I riveted it in place. Four solid rivets to replace the ones I drilled out, three pop rivets below where the squeezer couldn't reach (i.e. I didn't feel like shooting and bucking while leaning into the tailcone). Then Mary helped me back rivet the four rivets through the bottom flange (because she is awesome). The bracket is very secure and sure as heck isn't going anywhere.

Here's the servo temporarily installed, to test how the linkage works. It looks like it will be fine. Even with a stack of washers for spacing, the short pushrod isn't completely straight, but apparently that's normal.

While I was messing around with autopilot stuff, I removed the roll servo from the wing, tightened the screws that keep the DB9 connector in place, and put everything back in. This would have been easier to do all at once the first time, but of course I wasn't thinking about the wiring when I installed the servo. I played around with some cool slide-lock connectors that I bought from Digi-Key, thinking that I'd be able to use them instead of screws, but they didn't fit. Oh well, there probably won't ever be a need to remove that connector, and if I really have to I can just pull the servo out again through the access hole.

AOA Drain

Matt — Thu, 02 Feb 2006 02:06:56 +0000

Tonight I fabricated a simple drain tube for the upper AOA port. It's intended to channel the drained water down and out of the wing, as well as helping to guide the pin to the drain plunger. I started with a VA-112 fuel tank drain flange, which is normally mounted on the exterior of the fuel tank skin. I drilled another set of mounting holes and countersunk them so I could mount it the other way around:

Here's the drain hole and the rivet pattern. These rivets will be flush, fulfilling my goal of having none of this stuff poking out in the breeze.

And here's a shot of the finished product. A piece of clear vinyl tubing from the aviation aisle at Lowe's is slipped over the drain, and feeds down to an AN816-6-2D pipe nipple that I had lying around. That's kind of an odd size for normal use, but it worked great for this application. The tubing is a tight enough fit on both ends that I didn't bother with hose clamps.

The angle between the two ends is a little funny because I didn't plan to do this whole thing originally – I just located the hole where it was a straight shot up to the drain plunger, which makes sense if you're just going to use the drain pin without a guide tube. The bend in the tubing is due to the fact that the upper and lower skins aren't parallel here, which I'll allow for next time. I'm pretty happy with how this first attempt turned out, though.

This was probably overkill from the point of view of draining out water – I'm given to understand that hardly any water ever enters the AOA port in the first place – but it does a dynamite job of guiding the pin to the plunger when you're poking it up into the wing without being able to see what you're doing.

Roll servo wiring

Matt — Mon, 30 Jan 2006 02:21:11 +0000

I was travelling or doing errands for most of the weekend, so I didn't get anything done on the plane besides running the wires for the autopilot roll servo. Two adel clamps and some tie wraps keep the wire bundle safely away from the moving parts. The only snafu is that there's no way to tighten the screws that hold the d-sub connectors together unless you take the servo completely out. I think I'll try to find some thumbscrews to use there instead.

I bought this cool label maker that can print directly onto shrink tubing. Now I won't forget that this connector at the wing root is for the "roll servo". Okay, maybe this didn't need to be labelled, but I had to test out my new toy.

Trimmed rear spars

Matt — Thu, 26 Jan 2006 02:50:07 +0000

The RV-7 and RV-8 share most of the wing parts in common, but if you're building an RV-7 you have to trim off some of the rear spar due to the different width of the fuselage between the two models. I'm sure Van's does this to save a few pennies, rather than just punching a couple buttons on the CNC machine and producing the correct parts for the kit in the first place. Anyway, the plans include a full-scale template of the area to trim, which I xeroxed and then transferred to the rear spar stubs:

Nothing gets the blood pumping like hacksawing through a quarter inch of aluminum and then filing and polishing it until it shines. Except doing it twice, I guess. Ignore those things that look like nicks, they're just reflections from the camera flash.

Various wing work

Matt — Sun, 22 Jan 2006 02:00:03 +0000

Today I installed the angle of attack ports in the left wing. Click here to read up on what AOA is all about. The first step involved a lot of careful measuring – the AOA plans are very particular about where the ports are located. The photo below is of the lower port, and the marked line is parallel to the spar.

Two #30 holes are dimpled for the 4-40 flush screws that hold each port in place. I used handy my pop-rivet dimple dies for this step.

Here's an identical-looking shot of the upper AOA port. I guess I probably didn't need to document this one too, but oh well. The left wing is now back in the cradle here.

Here are the port assemblies attached to the wing and sealed to the skin with blue (non-corrosive) RTV. The upper port has a drain valve on it so you can get rid of what small amount of water as might work its way in there. You can't tell from this photo, but the lower port is a couple inches further inboard than the upper port, again precisely located according to the plans.

You drill the actual hole for the AOA ports using a #60 drill – that's 0.040". Tiny.

Outside view of the finished product.

Another hole is drilled in the lower skin to accomodate this drain valve poker, so you can drain the water out before preflight. I have some doubts about how well this will work in practice – I may have to bond some kind of a guide tube in there.

The AOA tubing passes through a spar lightening hole (and is securely tie wrapped in place) then proceeds down the wing through the bushings in the tooling holes just aft of the spar.

AOA tubing and pitot heat wires are secured to the rigid pitot line to keep them from interfering with the bellcrank.

At the root end I left a pitot heat connector and a foot or two of extra AOA line. I've decided to make the wings removable by putting connectors in all the wires and lines – not because I expect to have to take the wings off, but to make the final plumbing/wiring job similar, logistically speaking. Since I won't have to wait until the wings are attached to finish the wiring and plumbing, I'll be able to finish more of the internal systems in the garage instead of at the airport. That's a long time from now though.

I finally received my wiring conduit from Van's, about a month after I ordered it. I got a length of it installed in the left wing, which took way longer than I planned – it's nearly impossible to get it through the wing walk ribs, so I spent several hours on this simple step. It's not going anywhere now that it's in, though.

It's too cold to work with the plexiglass landing light lenses, so on to the right wing's landing light cutout. Rough cut with Dremel:

Trimmed with snips and sanding drum:

Smoothed with files and scotchbrite wheel:

I was wearing a dust mask during all of the above metalwork, and I'll share with you a lesson I learned during this process: don't wear a dust mask right after you eat at India Palace unless you like the taste of recirculated curry. I guess it's true what John Lennon said: instant khorma is gonna get you.

End of the line for this sanding drum:

I got tired of my bench grinder walking all over the workbench, so I secured it with these bolts that I found in my junk box. I didn't have any bolts long enough to actually bolt the grinder to the bench, although that turned out to be a good thing: I used these shorter bolts as studs that keep the grinder from moving around but allow it to be easily lifted up and off if I need to for some reason.

Let there be landing light

Matt — Mon, 16 Jan 2006 02:27:14 +0000

With Mary's help, I lifted the left wing out of the cradle and onto a pair of padded sawhorses this morning. Then I cleaned the poor dirty wing with soapy water – the top side was still covered with the preservative oil that's applied to the Quickbuild kits at the assembly site. Now it's all nice and shiny on top where I couldn't reach before. There are also some light scuff marks where the wings rubbed against their straps in the truck – but since I plan to have this airplane painted eventually, no need to worry about polishing them out.

Then I got out one of the Duckworks landing light kits I bought last month. I popped for the HID xenon lamps, since I have the same type of headlights on my Toyota and I really like them. These lights are expensive, but I'll hopefully never have a problem with nighttime visibility at those dark country strips, and these bulbs will probably last longer than the airplane's engine.

Here's what you get for your money:

The first step is to measure and then tape the included template to the leading edge, over the outboard-most rib bay:

The shape of the landing light cutout is then traced onto the wing. Hacking a huge hole in the front of my beautiful wing was a little scary to think about, so I sort of stared at it for a while before continuing to the next step, doing a mental tally of my accumulated karma.

Well, no going back now! I'm going to have a landing light whether I like it or not. The initial cuts were made with a fiber cutoff wheel in my Dremel tool. This and subsequent steps produce a lot of airborne aluminum dust, so I had a dust mask on for all of this.

Next I enlarged the hole up to the lines with a 2" drum sander in my electric drill. This turned out to be an excellent way to do this job, since it made nice round corners and didn't take material off too fast to control.

After the basic cutout was there, I attacked it with files to finish off the shape, and went over it with a 1" Scotchbrite wheel to smooth up the edges. For all the worrying I did about getting this cutout to come out right, I think it turned out rather well.

The lens is held onto the wing with screws that go into two little retainer strips behind the plexiglass. Here I'm match drilling the retainer strips to the skin:

I went ahead and put the nutplates on without priming the strips. They are removable and non-structural, and they aren't in contact with anything but plexiglass, so I'm not worried about corrosion here.

The instructions leave it up to the builder as to where the HID ballast is installed. I elected to bolt it right to the mounting plate that holds the bulb, instead of trying to mount it to the rib somehow. The available space on the mounting plate is tight but it's doable. I oriented the connectors outboard so they can protrude through the lightening hole in the outboard rib. (I think this is actually the only orientation that will let everything fit)

The mounting plate then got primed, along with some pitot mounting hardware.

Two nutplates on each rib hold the light mounting plate. The holes in the plate are oversized so you can wiggle it around to aim the light.

Behold: bulb and ballast bolted beautifully.

I decided not to prime the light retainer ring either – the bare metal look makes the bulb seem shinier! Also note that the bolt heads for the ballast just clear the retainer ring's "ears".

It works! I hooked it up to my bench power supply to gauge the current draw, which started out at around 7 amps and dropped to 5 after a few seconds of running. And boy, is it ever buh-right. This picture doesn't do it justice. I had the garage door closed and all the lights turned off, and this sucker made it seem like the sun was shining. Awesome.

I secured the length of wire that goes between the bulb and ballast with an adel clamp and some tie wraps. I also put some cellophane over the lens to protect it from fingerprints during installation – fingerprints leads to hot spots leads to shortened bulb life. (which is why I had rubber gloves on when I installed the retainer ring)

Here it is mounted in the wing. The electrical connectors do indeed protrude through the lightening hole, just as I planned. Excellent.

I'm stuck on this mini-project until I can get ahold of some plexiglass drill bits from Avery, but that's okay because I'm not likely to have much time to work on it before next weekend anyway.

Parts update: Still waiting on replacement electrical conduit from Van's. Slowest shipping ever.

Finished prepping bottom skins

Matt — Sun, 15 Jan 2006 23:44:14 +0000

I finished deburring and dimpling the bottom wing skins, along with the corresponding rivet lines on the ribs. Here's a random shot of the ribs, all dimpled.

This whole series of steps took forever and was boring. I can't imagine doing a whole wing's worth of this – hooray for Quickbuild.

This time around I deburred the skin edges by going over them first with a vixen file to knock off the shear marks, then with an edge burnishing tool, then with a blue (fine) roloc pad on the die grinder. It worked pretty well and didn't take forever like sandpaper does.

Working on bottom wing skins

Matt — Mon, 09 Jan 2006 02:21:45 +0000

I remembered that I actually can get some work done on the wings while I'm waiting on the wiring conduit to show up – getting a headstart on the epic amount of drilling, deburring, dimpling, priming, and other grunt work that has to happen before the bottom wing skins get riveted in place. I got as far as getting the skins drilled and partially deburred before I had to go do other stuff (and also it was cold in the garage).

I also got the various spots where the skins overlap fixed up with a nice bevel, per the plans. I used a die grinder and put a scrap piece of aluminum between the inboard bottom skin (already riveted in place) and the rear spar, to keep from grinding into it by accident. That seemed like something that would be good to avoid.