Chapter Log

Step 0 - Materials
Status: Completed 
Est Time: 0.00, Actual: 0.00
Est Cost: $ 856.85, Actual: $ 856.85
Date Completed: 01/12/2009

Step 1 - Fabrication of Parts
Status: Completed 
Est Time: 3.00, Actual: 4.00
Est Cost: $ 0.00, Actual: $ 0.00
Date Completed: 01/12/2009

I didn't think to get good pictures of this step. Basically, I followed the CozyGirrls' method to make the strake ribs. It's not hard. You just edge-glue two sheets of foam into one large sheet, glass both sides, then trace and cut out the various strake rib pieces. A band saw followed by some light sanding made quick work of this step.

The only complicated part is that it turns the process into a REALLY big layup - I mean, you're stretching very large pieces of fabric out and wetting out/stippling into the center of a large sheet of foam. It really helps to have an assistant for this step, and to use a slower hardener mix.

I actually completed this step over a year ago, but hadn't cut all the pieces out until I moved to the hangar. I marked it complete on this date only because on this date both strakes are officially sealed, which means the parts must be done. =D

Step 2 - Jigging and Assembly of Parts
Status: Completed 
Est Time: 14.00, Actual: 30.00
Est Cost: $ 0.00, Actual: $ 0.00
Date Completed: 01/12/2009

I screwed this step up pretty good, and John's help was immeasurably valuable in catching and fixing the mistake.

Basically, I started off OK. I rigged a table under the left strake area using plywood and 2x4s to rig up a relatively stiff and sturdy (and perfectly level) jig table. I didn't know at the time that I could really have just skipped this step, but c'est la vie.

Using the table as a guide turns out to not be as convenient as using the string-line method to align the rib leading edges, so I ended up doing that. My case was a little complicated because I'm also doing the extended strake modification, so there are actually two important lines to deal with. But it sure is an easy method to do.

Sort of.

I must have either been tired or rushed when I set this up because when John double-checked the left and right sides they didn't match. He ended up having to redo a fair bit of the layout work. It all worked out OK in the end, but this does underscore the importance of taking it slow and having as many eyes on a project as possible to catch mistakes. I'm sure I would have caught it, too - it wasn't exactly a subtle mistake. But it could have been avoided if I hadn't been in such a rush.

Step 3 - Inside Layups
Status: Completed 
Est Time: 20.00, Actual: 20.00
Est Cost: $ 0.00, Actual: $ 0.00
Date Completed: 01/12/2009

The inside layups went more or less according to plan. However, because I'll have ethanol in my fuel, I paid the extra bucks (lots of extra bucks) for ProSeal, which is supposedly proof against a range of alcohols and fuels. We'll see. It sure is expensive. It's also a hell of a mess - it's very thick, hard to mix, and hard to spread, even when heated. It's definitely not like micro - it doesn't spread smoothly and you end up with lots of little icicles and frosting tips. It cures to a rubber-like coating. We'll see!

Step 4 - Vent, Screen, and Drain
Status: Completed 
Est Time: 6.00, Actual: 10.00
Est Cost: $ 0.00, Actual: $ 0.00
Date Completed: 01/12/2009

Some of these pictures are dark because it's winter, the hangar doors are closed, and lighting is pretty poor in the hangar right now.

Here you can see here one of the fuel sump screens. It's a sink strainer, obviously, but hey, that's what the plans call for and it does the job very well. You can also see the vent and grounding lines, with the recommended additional vent holes near the back corner of the strake drilled into it. The water drains are also installed - I'll try to dig up some better pictures of them later.

Step 5 - Top Skin Cores
Status: Completed 
Est Time: 14.00, Actual: 20.00
Est Cost: $ 0.00, Actual: $ 0.00
Date Completed: 01/12/2009

I haven't had as much hangar time as I'd like, and had a bunch of dental work to recover from on top of it all, so John gets credit for the strakes. I just helped hold the skins as final assembly was completed. In these pictures you can see the dark ProSeal. It goes on VERY thick and stiff, but looks like it does a good job of forming a solid barrier. Between that and the hat method for installing the top skin, I think there's a good chance of either getting a seal on the first try, or coming very close. We'll see!

These pictures are very dark because the hangar is very dark. It's winter right now, and we're having to use two propane heaters to get the hangar warm enough to do any work at all. John asked me to get some electric blankets to help the strakes stay warm enough to cure. I wasn't able to find any, but it worked out OK anyway. The 50-50 Fast/Slow mix we are using for our MGS managed to cure rock-hard overnight.

Step 6 - End Rib and Outlet Piping
Status: Completed 
Est Time: 6.00, Actual: 1.00
Est Cost: $ 0.00, Actual: $ 0.00
Date Completed: 01/12/2009

My "end rib" step is a little weird because I followed the CozyGirrrls' technique and installed the rib with the rest of the strake parts. This was done while the wings were attached, then scribed and cut to the profile of the inboard edges of the wings. This will produce a very good match to the wing profile, and, ideally, minimize the finishing work in this area.

This area is normally filled with foam but I left it open for now. The plan is to put storage compartments in here for spare bulbs, tire tubes, etc.

Step 7 - Bottom Outside Skin and Sump
Status: Completed 
Est Time: 14.00, Actual: 16.00
Est Cost: $ 0.00, Actual: $ 0.00
Date Completed: 03/22/2009

My sump blisters contain an added accessory, a liquid level sensor designed for fuel tank installation. It's made of polysulfone, which is both fuel and ethanol resistant, and has a 1/4" NPT tap so it's easily installed and completely accessible from outside the tank in case it ever needs to be serviced or replaced.

I actually installed a series of these sensors at even spacing up the tank wall (which was a bit of doing, actually - John saved my wrists by doing all the tapping in the aluminum plates installed in the tank walls, and I owe him - it was a lot of work doing that tapping!

The idea here is that people have had a lot of trouble with tank level sensors, especially when ethanol is in the fuel (as it will be in mine). But a mechanical sensor has fewer failure modes if it's properly installed. These units add an additional safety factor in that they use magnetic switches, so there is no risk of spark inside the tank. They're not cheap, at about $11 per, but they work very well and I'm looking forward to using them. I'll hook them up to a simple LED bar graph indicator, with an additional annunciator warning on the lowest tank sensor, and the sensor in the sump.

Step 8 - Top Skin
Status: Completed 
Est Time: 16.00, Actual: 20.00
Est Cost: $ 0.00, Actual: $ 0.00
Date Completed: 03/22/2009

My top skin is more or less to plans, but there are a few things to note from this step. First, there is an access hole in the outboard rib, normally an area filled with foam. After some discussion, John and I decided to leave this area open, and fill it later. For now it will provide an easy access point to one of the common sources of fuel tank leaks. After the tanks are fully sealed we'll discuss what to do with it.

Second, you can now see the accessories installed in my tank. In addition to the usual fuel line elbow in the sump, there is a return at the top of the tank. I'll use a solenoid to switch the return, which is the same thing John does. There has been a LOT of discussion of how to do this - I've agonized over it for THREE YEARS, and discussed various solutions with all the experts. My final conclusion has been that there IS no "perfect" way - every method has pros and cons. I chose this method because it seems the most natural to me, and thus I believe that during a failure I will be more likely to intuitively select the right response than if I'm relying on a system that makes less sense to me in the first place. Designed for Humans.

You can also see the plates installed for the level sensors. There are five in each tank - four in the tank itself, and one in the sump. The original Cozy just has sight gauges. Many builders install level sensors, but there are accuracy problems, especially with ethanol-based fuels. I chose a middle ground.

In case you're curious, the part I used is a Cynergy 3 RSF86Y100R. Digikey carries them for $14.83 apiece, with a bit of a discount if you buy 10. But apparently Digikey won't be carrying them much longer. If they run out, both Allied Electronics and Newark show stock for similar prices.

I'll measure the weight next time I think of it. But as for that, they feel pretty light, and capacitive senders aren't exactly feathers anyway. The cost is probably comparable, if a bit more because I used five sensors.

Step 9 - Pressure Check
Status: Completed 
Est Time: 5.00, Actual: 11.00
Est Cost: $ 0.00, Actual: $ 0.00
Date Completed: 04/05/2009

Summary
This is a long section because it took many steps. However, I believe the overall method for finding and fixing the leaks was sound, and I'd like to repeat it here for other builders:

1. Connect a hose barb fitting to an air compressor with a good (easily turned) pressure valve. Close the valve all the way. Hook a line up to a T fitting with one leg to an altimeter and the other to a tank vent line.
2. Break apart a standard butane BBQ lighter, the kind with the long nose. This will yield a largish butane cylinder and a tiny plastic hose. Just before hooking up the lines above, insert this hose into the tank's vent line and pull the cylinder's valve up for 3 seconds to release a shot of butane into the tank. You don't need much!
3. Turn on the air compressor and slowly pressurize the tank until the altimeter reads -1500 to -1800 ft. (We found -1800 was safe and made it easier to find the leaks.) Be patient. You have to FILL the tank with air, and the vent pipe is not large. Go slowly and let the tank settle every few seconds until you get it stable.
4. Use a gas sniffer around all joints, the leading edge, the end rib, the sump, the baggage compartment, and all fittings. Pay particular attention to seams, but don't assume the seam IS the leak. Do NOT throw soap liquid around yet! We found out the hard way that the gas sniffer is sensitive to the soap! (Try sticking the sensor of your gas sniffer into your soap bottle.)
5. If you think you've found a leak in bare glass, you can use soap to confirm it. This is useful around the sump. But if it's near the leading edge or ribs, it's probably a pinhole that's escaping through one of the kerfs in the leading edge curve. Drill small pilot holes through the TOP glass (don't go all the way through!) and use the gas sniffer to home in on the exact location. Then dremel away the likely area and use the sniffer and/or soap to confirm.

2009-04-02 (2 hours):
John and I played with an altimeter for a while, checking out both tanks. He managed to rig an air compressor to JUST BARELY pressurize the tank. There's definitely a leak somewhere in both tanks - a slow one, but worth finding. I had the great idea to duct tape plastic wrap loosely around all the typical leak spots - sump, outboard rib, inside wall, etc. My hope was that the leak would gradually inflate the area, effectively making a visible "balloon". My hopes were dashed! Either the leak isn't enough to noticeably inflate the plastic wrap, the idea itself is flawed (the tape around the wrap is leaking), or we just didn't tape the right areas. Whatever the reason, we ditched that idea.

I have two more ideas I intend to pursue. This weekend I'll be bringing a leak detector - a professional model my neighbor used in Navy housing to find gas leaks. My plan is to inject a tracer gas like butane into each tank and look for each leak. Yes, I know, I will have to be VERY careful once this is done. But the leak detector is extremely sensitive, and even a tiny bit of gas will set it off, so I don't need to inject enough to reach explosive levels!

My second idea is similar to finding A/C leaks. I have a canister of UV dye. Injecting that will show any leaks under black light (and the leak detector will sense this dye, as well). It's relatively inert and safe for fuel systems, but it's my second choice because I'm not sure the dye will properly aerosolize enough, and STAY aerosolized enough, to trace. Still, it's good to have a backup plan. Worst case this dye could be mixed with a light machine oil and it would definitely work then, it's just that I'd need like 25 gallons of it! I guess I could put it into fuel, but that's no cleaner than just using fuel and your nose to find the leaks. The one nice thing about this dye, though, is that it marks whatever it leaks into, so with a black light you can search around for even tiny, slow leaks that would otherwise escape notice. It's conceivable you could leave the tanks sitting for a week to try to get even the slightest leaks to show up.

2009-04-05 (4 hours):
Today we followed up on the pressure check. The UV dye was basically worthless - it didn't aerosolize enough to make it useful. I do think if it was added to fuel it might be handy if you were planning to fill the tank. It permanently marks anything it touches and glows bright yellow under a black light.

What did the trick was the butane and the gas leak detector. This is an expensive, professional unit - I don't know if a cheap, off-the-shelf device would work. I scavenged a tank of butane from a disposable grill lighter, which was nice because it included a handy plastic tube that fit over its nozzle. I ran this a few inches into the vent tube, got John to douse his cigarette, then pulled on the little nozzle until I could feel the gas come out (it gets quite cold). We quickly attached the air compressor, ran a bit of pressure in (about -1500ft on the altimeter), then started checking for leaks.

The left strake was a bit tricky. One leak showed up right away - it was a pinhole in the sump, which the leak detector localized then we found with soap bubbles. (The soap for kids' blowing bubbles worked great - it's specifically designed to produce large bubbles with minimal pressure. Dish soap is fine too but it helps if you dilute it.)

The second hole was more difficult to find. As noted above, we had previously duct-taped large sheets of saran wrap over various common leak areas. The leak detector was confirming that the hidey hole between the left two outboard ribs was filling slowly with the butane/air mix. But though we both tried (for almost two hours, I think), we couldn't find the area with the soap bubbles.

Switching to the right strake, we found that leak very quickly. If you're going to use this method, it helps to have fresh air coming in, but not a breeze. The detector is VERY sensitive, and it can pick up on the CO in human breath, smoke from a burning cigarette, or even fumes outgassing from your hangar mate's gas tank. Or anything else that might emit a vapor. Since it's basically a particle counter, even slight contaminants in the air can make it react, which forces you to turn down the sensitivity, which makes it harder to find the leaks. The right strake was coming up blank until we opened the hangar doors. (We hadn't done that before because it's still quite cold and windy here - fortunately, we were blessed with a sunny and relatively still evening.)

Bingo. As soon as we did that, and let the air clear out and settle a bit, I found a strong leak around the forward drain port. John tweaked the teflon compound around the screw in there, and eventually switched to teflon tape, and the tank is now sealed. We left an altimeter on it, pressurized, and we'll check it in a few days.

Back to the left tank, I think I just got lucky. John had suggested that many leaks creep along the strake skin kerfs - he'd had that problem himself. And the way the butane was filling the hidey hole made it seem like it had some expansion room ALONG the leak point. That is, it wasn't reacting the way the pinhole in the sump was. With that one, every time we pressurized the tank a bit more, the leak detector immediately went into overdrive. In the hidey hole, the buildup was much slower. It seemed like it had a delayed reaction - like it was creeping along something. I did finally notice with the leak detector that the leak was strongest along the leading edge - not against the tank wall, as I had intuitively been probing, but actually halfway OUTBOARD from that rib.

John suggested a binary search by drilling holes along the leading edge. Bingo. At the first hole he drilled, the leak detector went nuts. We then drilled additional holes at various intervals, noting that whenever we drilled a hole closer to the source, that hole had a stronger emission, but farther holes were reduced. As we zeroed in, we began using the Dremel to open up sections of the upper skin until we found what we were looking for - a hole in the inner side of the upper strake skin. This opened up very near one of the kerf lines, and was allowing the leak to follow that line. Incidentally, this was VERY near the outboard tank rib, which was why the ProSeal hadn't helped - there wasn't any there because we had to allow a space for the flox on the T-hats to adhere!

The fix is easy. I stuffed a tiny bit of flox into this hole and the one in the sump, then put a very wet 2-BID patch on top, with some plastic to help eliminate pinholes, and worked the epoxy carefully with a hair dryer to remove all traces of bubbles. On Thursday when I go back out we'll recheck the tank pressure.

Despite the work involved, we were both pretty pleased. The right tank sealed on the first try - we don't really count the drain hole as a "leak" since it wasn't a problem in a layup, we just had to tighten the drain plug. The left tank only had two small issues, and both were easily fixed once we hit on the right combination to find the leaks. In any case, it was a 1-day effort. The big deal here is the ProSeal, which let us eliminate 95% of the bottom skin as leak sources. That's VERY helpful to know!

2009-04-07 (1 hour):
So the pressure went up! The secret, of course, is the temperature change, and also outside air pressure changing the pressure on the outside skin of the tank and the test tubing. This is amazingly important - even pressing on or squeezing slightly the strake skin or tubing makes a big jump in the altimeter. The right tank is sealed!

The left tank, not so much. I tested it again and was sad to see the leak was just as bad as before, despite fixing two big holes. Well, nothing for it. I started drilling holes again, this time starting at the kerf line that caused so much trouble before. It took a LOT more holes to find it this time, but it was right where I predicted - within an inch of a kerf line. Those kerfs are trouble. If you're reading this, and you haven't yet done your strake skin layups, make sure there's plenty of micro in there!

Anyway, this leak turned out to be a weak point in the skin that was letting air bleed out, find its way to a kerf line, then progress along the leading edge that way. Another patch, and I'll test again in a few days when I get back out. What I SHOULD have done is duct-taped the hole so I could test for any MORE leaks, but I stupidly didn't think about that. Oh well.

By the way: This leak testing system is working very well. The dye was a total waste of time, but the gas leak detector is so sensitive that it picks up even a tiny amount of butane. I'm injecting only a small amount - about equivalent to holding a butane lighter open for 3 seconds - in the entire 25-gallon tank. I've cautiously tested it to see if it will burn. It doesn't. But the leak detector definitely finds it, and screams its head off when you're right at the source of the leak. The only frustrating part has been adjusting the sensitivity of the unit to tolerate the other hydrocarbons we have in the hangar. John is working on his fuel tanks, and we're still heating with propane heaters, so those things are throwing the detector off a lot.

To make this system work we're pressurizing the tank to between 1500-1800ft (altimeter reads negative). At sea level (which we're at) that's about 1psi - not a lot of pressure to get from an air compressor. To achieve it we're just BARELY cracking the valve open. The air compressor helps maintain the pressure despite the leak, which is helpful for finding it. Unfortunately, what it also does is kick in every few seconds (because there IS a leak). The leak detector isn't loud enough to hear over the air compressor, so it slows down the detection a bit. If you can, get a detector with headphones!

Also, pay CLOSE attention to your pressure! It tends to creep up or down. Down and your leak goes away, which is not so good if you're trying very hard to find it! At least it's not harmful. But up, and you'll eventually crack something open elsewhere, just making more leaks. Not good!

04-09-2009 (2 hours):
I'm not sure exactly how tightly sealed these tanks need to be. I'm finding a number of leaks in the left tank, but they're all pinholes in the top skin. Only a very small amount of air is escaping, and only because I'm digging along the skin to find them... giving them an escape hatch as I do so. At least I'm getting faster at this.

04-12-2009 (1 hour):
The leaks continue. I managed to find and seal three more upper-skin pinholes. There's a pattern here - they're almost all along the middle tank rib, where there was no proseal (because it had to be bare glass for the flox to stick). The good news is the tank is definitely leaking a lot more slowly - as I find and fix each one, I can tell it's working.

One lesson I learned the hard way is the gas sniffer detects soap! I never would have thought this, but it does. DAMHIKT.

04-16-2009 (1 hour):
Finished! Both tanks now hold a seal. Onward!

Step 10 - Leading Edge and Outboard Fairing Blocks
Status: Completed 
Est Time: 14.00, Actual: 8.00
Est Cost: $ 0.00, Actual: $ 0.00
Date Completed: 04/16/2009

04/02/2009 (3 hours):
With my strakes swept forward, their leading edges fall just past the instrument panel. This was too good of a coincidence to pass up. Along the leading edge, just under where the foam blocks will be, I installed electrical channels made of shower curtain rod covers. These are great - wires slide very easily along them. I carefully tucked them inside one another at the joints (where the sweep of the strakes changes), and duct-taped over them wherever there were holes to prevent micro from getting in when the leading edge foam blocks are attached.

In each channel I installed two pairs of 16ga wires (one each for NAV and strobe lights), and an antenna wire for the wing COM antenna. If I run into trouble with the strobe disrupting antenna signals I can always move one of the wire pairs, but I'll wait and see before I make any changes.

04/09/2009 (1 hour):
Tonight I installed SOME of the leading-edge fairing blocks. I've left two off so I can do any fixes required if the left tank fails its next pressure check.

04-16-2009 (4 hours):
The rest of the blocks went on tonight. Fairing into the fuselage was a little tricky but they look like the match, as near as we could tell. The leading edge layup was extended to cover the holes drilled to find the tank leaks.

Step 11 - Fuel Valve, Electric Pump, and Gascolator
Status: In Progress 
Est Time: 20.00, Actual: 5.00
Est Cost: $ 0.00, Actual: $ 0.00
Date Completed: 04/03/2009

My engine will be a Mazda rotary, which uses a high-pressure fuel injection system with a return. After much debate, I'm following in John's footsteps. Each tank will have a pump underneath each rear seat, which will be tied together at the fuel rail. A return will feed a solenoid that will pass the return fuel to the selected tank. Only one pump will be on at a time.

This is a useful setup with some interesting side effects. First, its controls can be simplified to the point that feed and return are switched together, so there is no need for the pilot to manage both devices, and accidental cross-feed is prevented. However, deliberate cross-feed can be engaged when desired. This is a nice feature if you're on the ground and about to refuel. You know the fuel you have remaining is good, so you can pump it all into one tank (which is now a "known good" tank) and refuel ONLY the other tank. You can then take off and perform critical maneuvers on known-good fuel, and only use the new fuel when it is safe to make the switch. If there is contamination, this gives you a response option. You can also use this technique to empty a tank for inspection.

In the first picture below you can see several of the components in my fuel system, including the pump, tank fittings, and sump level sensor.