More Fuel & Brake System

Finished the brake lines (Section 36) including the parking brake valve today! I ordered a 3' long control cable from McMaster (P/N 3125K44) along with a clevis and control knob, and fabricated a mounting bracket for it to attach to the tunnel wall and actuate the parking brake lever. Everything lined up as planned and it seems to work perfectly! I secured all the brake lines in place and tightened the brake valve mounts and took a few pics of the brake system:

Brake lines and brake valve in tunnel

Brake lines terminated on firewall

Parking brake valve with control cable mounted in place.

Demonstrating the clearance between the elevator/aileron controls and the brake valve/control assembly. In a worst-case scenario with the aileron control rod touching the bottom of its cutout, there is still about 1/4" between it and the clevis for the parking brake, which itself is in a "parking brake ON aka on-ground-only" position. The elevator control passes over the top of the valve with at least an inch or so of clearance.

This location for the parking brake valve should work fine... at least that's what I'm thinking so far. Next up was to start making components for the fuel system in Section 37. Since I'm "rolling my own" boost pump and return line, and also moving the fuel selector forward about 6" to make room for the armrest throttle quadrant, the fuel line measurements in the plans will be of little use other than to use as a general guide. The first thing to do is actually build the boost pump module, which I did by making two U-shaped pieces of 5052-O 3/8" aluminum tube:

Check valve (left) and boost pump (right) connected via two U-shaped tubes and fittings. Inlet is at the bottom tee, outlet is at the top.

The black jacket over the pump is an insulation sleeve I found online for fuel pumps, and it should help the pump run both cooler and quieter. Next, I started with the task of mounting the pump assembly and the pressure relief valve into the tunnel. Sarah and I riveted the two little pump mount brackets to the forward fuse bottom skin (deferred from way back in Section 28) in their normal locations. We had held off on riveting these before because we wanted to make sure we could make use of them and wouldn't have to relocate them or make a custom bracket. It turns out the standard locations work great, and we can put the boost pump module in the aft and center location, with the pressure relief valve in the forward location. This means the "send" line will exit the firewall on the L side of the firewall, and the "return" line will enter the firewall on the R side. So, with this plan in mind, I got to work getting it all installed.

Boost pump module installed in tunnel. Pump is secured via the standard hose clamp mounting method, and the check valve is secured to the L tunnel side with an adel clamp and #8 flush screw.

Larger view of the forward tunnel area, with both fuel Send (L) and Return (R) fittings visible below the heater outlets.

Next, more 3/8" 5052-O tubing had to be bent and installed between the firewall and the modules, as well as one run going back to a fitting on the rear R tunnel wall that will be the aux tank fill inlet. This line will be plumbed to a small panel in the rear seat area accompanied by a vent line and electrical connection. When an aux tank is installed, we'll be able to flip a switch on the panel to turn on a transfer pump inside the aux tank which will feed fuel to the fuel return line downstream of the pressure relief valve, allowing fuel to be fed into either the R or L fuel tanks, depending on the fuel selector.

Aux fuel inlet line visible above the rest of the fittings, with line swooping aft and then below the rest of the brake and fuel fittings. Also visible: tunnel entry points for fuel return and brake lines.

Aft tunnel area with everything installed

Forward tunnel area with everything installed

Boost pump module and pressure relief valve assembly close-ups. The taped-off fitting on the upper left side of the photo is the fuel inlet (from fuel selector send outlet), and on the bottom center is the fuel return outlet (to fuel selector return inlet).

Overview of the tunnel area from the firewall looking aft

That's pretty much it for today! Lots of good progress. The astute observer may notice a lack of pipe thread sealant on the exit side of the pressure relief valve, where there is a reducer and tee fitting for the fuel return and aux feed lines. I'll need to pressurize the system once and double-check the pressure setting for the relief valve, as it can be adjusted via a hex key inserted through this end of the valve. I figured it would be worth it to not seal these threads yet since they will likely be coming back off again anyway.

Other than that, I took some measurements for the stainless braided lines I'll need to buy to go from the tunnel entry points in the rear of the tunnel and up to the fuel selector, and also the two lines coming from the selector to the send and return lines. Until I can get them ordered and delivered, it's on to something else... maybe priming and assembling the back seats? We'll see!

Brakes, Fuel, Flaps, and Panel!

Big day, lots of little stuff. Oh yeah, and Happy Halloween! It was nice to get back to building after the whole ordeal of unpacking the finish kit. We started this morning by flaring and installing the remaining two brake lines, and then final-attached the -AN fittings to the parking brake valve for a first installation. I've decided to use Loctite 567 as a thread sealant, which seemed to get the best reviews on its performance overall. It smells pretty good too... Sarah claimed it smells like a "hotel lobby with a swimming pool nearby." I would have never made that association, but, yes once she said that, that's EXACTLY what it smells like.

Attaching the AN fittings to the parking brake valve using Loctite 567

The completed fitting installation

We then test-fitted the parking brake valve with all four lines connected to it for the first time. It fits perfectly! Now the only thing left with the parking brake valve is to figure out a control mechanism and get the necessary hardware for it. We'll get to that at some point eventually.

In the meantime, it was time to get started assembling the fuel system. I had ordered a number of fittings necessary to put everything together, but I quickly discovered I was in need of just a couple more. No worries, I'll tack them on to the next order from Spruce. Until then, since I had the Loctite 567 out, I could still install a few fittings into the various fuel system components.

The 100-micron fuel prefilters with AN-6 fittings installed

Walbro fuel pump with AN-6 fittings installed

I then made two brackets to attach the fuel prefilters to the landing gear mounts under each seat out of angle aluminum. It went pretty smoothly, and I think I have the finalized fuel system routing/layout figured out. I'll make a diagram here in the next couple days and post on here.

Moving on to see what I could work on, I got back into Section 40 and made 4 little spacers used to attach the flap actuator to its brackets:

The four spacers placed next to their respective steps in the plans

Those spacers were kind of a PITA to make! They are quite small, and it's really hard to hold them square against the bandsaw and belt sander, but with a bit of patience and burnt fingertips we got them made! The dial caliper works really well here to check measurements and end up with a perfectly-sized piece.

The last thing today before calling it quits was to get back to Section 31, Upper Forward Fuselage. We're basically done with that section except for some dimpling and riveting, but I don't want to do too much more until I really finalize my panel layout. So, I clecoed the assembly back together and started with one of my all-time favorite pastimes, avionics daydreaming.

Initial proposed general panel layout

2x Garmin GDU 46x displays, Garmin GMC 307 control panel, and GRT Mini-X backup EFIS

Still LOTS more planning needed for this panel, and even more money to spend on it. The main thing I wanted to do now though is see if I can figure out which parts of the underlying structure will need cutouts and modifications to support the layout I have in mind. I do want to have my autopilot control high and centered, which may require some modifications to the center rib for clearance. I'll need to get some final measurements and start making those cuts. I also need to figure out how I want all the switches laid out. I'd like to keep the panel as symmetrical as possible, and allow for PIC'ing from either the left or right side with minimal difference in usability of the panel. Like I said, lots more to figure out here, but I thought I'd at least share my current thoughts of what I'd like out of this panel.

That's pretty much it for now! I think the plan for tomorrow is to finish up the rear seats, and maybe some other miscellaneous shenanigans... stay tuned!

Brake Lines - More Fuel System Planning

Almost done with Section 36! Tonight I bent the remaining two brake lines using the same techniques I did for the first two lines, and after flaring them and temporarily laying them into place, I was finally able to take a picture of the parking brake valve mount:

Matco parking brake valve mount

The valve will have two 45-degree fittings on the front side, and two 90-degree fittings on the back side, allowing the lines to come straight out from the tunnel into the under-seat areas. I chose the forward-most of the three holes to do this so that there would be more room behind for the fuel send and return lines.

With that, I realized I couldn't go any further on the brake system without thread sealant (I thought I had ordered some already but I hadn't). A quick trip to Home Depot left me with the realization that Loctite 567 is not sold locally and must be ordered online... bummer. No big deal, plenty left to do! On to the fuel system...

For the fuel system, you may remember a while back I had some some initial planning and procuring of parts. I've received my Walbro pump, check valves, pressure relief valve, and a handful of AN fittings. Now it's time to lay things out and actually figure out how this is all going to go together.

Parker 665-2-3/8D2 Relief Valve, Walbro GSL393 pump, Parker 2625 Check Valve

2x Aeromotive 12319 100-micron fuel prefilters, one under each seat

Newton SPRL Duplex Fuel Selector, Model V4-3-P-C

Underside of the fuel valve... lots of connections to make here!

Now that these parts are here in-hand and I have "most" of the fittings I need, it's time to get back to diagram-drawing and come up with a finalized version of the fuel system layout. Should get to that this weekend in between cleaning up in preparation for the finish kit's arrival!

Brake Lines - Rear Seat Backs

Productive night tonight! Now that the parking brake valve mount has been made, we can start with actually fabricating the brake lines. There are a total of four brake lines to make: One under each front seat going from the landing gear mount to the tunnel (where the parking brake valve is), and then one on each side of the tunnel going forward from the valve and up the firewall, terminating at a bracket on the upper left area of the firewall. I'll be making these runs out of 5052-O aluminum tubing, which is a stronger material than the provided 3003 alloy in the kit (3003 is not used on brake lines in production aircraft). This is a common upgrade that I decided to go for and had previously ordered the necessary lengths from Aircraft Spruce.

Meanwhile, Sarah came out and first helped rivet the parking brake valve brackets to the bottom fuse skin in the tunnel, and then decided to start working on the rear seats (Section 42). We're going to try a small modification here and make the back seat more of a 60/40 bench-style seat as opposed to individual buckets. Cleaveland sells a kit to do something similar (with headrests and all), but we're going to try to keep it simpler and just extend the left-side seatback using an extra F-637A seatback panel which I added to my finish kit order. So in the meantime, Sarah can still make many of the supporting bits needed to assemble the seats. No pics yet of these parts, but she made a number of parts out of aluminum angle to form the structure of the seat backs.

Back in Section 36, I got started on bending brake lines. The first ones to make are the ones that go under the front seats. They are relatively straightforward, and I began using a technique I read about on the forums, where you take a piece of solid-core copper house wire and bend it to the desired length and shape, and then use that as a template to make the actual brake line.

Copper wire cut and formed to desired shape for brake line

Using the wire as a template, I got out the 1/4" 5052 tubing and used my OTC 6515 tubing bender to make the same part out of brake line:

5052 tubing bent to shape from wire template

In this way, I made both brake lines that go under the seats, and decided that was enough for tonight. It turns out Sarah finished making her brackets but didn't feel like busting out the drill, and I had finished my two brake lines but didn't feel like busting out the flaring tool. Still a very productive evening, and with a few more nights like this we might have two more sections crossed off the to-do list!

Section 36 Begin - Finish Kit on its way!

Finally! Time to start working on the brake and fuel lines... just in time to get notification that the finish kit will be here on Monday next week... aaaah! It will definitely be here too soon, but that's ok. It's hard to predict when to place the order for the next kit, because with lead times and such it's a decision you're making several months ahead of time, and the desire is to not be too late. In the end, no complaints on our end, will just be another day or two away from building while we sort and inventory all the new parts that come in the finish kit. We should have room for everything... hopefully.

In any event, the first order of business in Section 36 is to do something that isn't even in Section 36, or Van's plans at all... mount the aftermarket Matco parking brake valve. Derek came over tonight and we set out to figure out the best placement for it. As I've said in earlier posts, I'm going to try and mount it in the tunnel, underneath the control column elevator linkage area. I've done the measurements and checked them twice, and I see no reason that the valve won't fit here. In my mind, it will work better in this location because it will be easier to get to, and it is a location that already involves a junction in the brake lines per the standard plans. I'll need to reorder which brake or fuel line goes where through the three pre-drilled holes between the under-seat areas and tunnel, which I think we can handle. Otherwise I really don't think there will be much heartache over putting it in this location. That's the hope, anyway.

Somehow I made it all night without taking a single picture, but really there wasn't much to photograph except for a lot of Derek and I scratching our heads and holding valves, brackets and control linkages in place and moving things around so that I could be absolutely sure this was going to work. Eventually I said alright let's do this, and in short order a few mounting brackets were made out of angle aluminum . Since I don't have pics yet, basically the mount is made of four 1.5" long pieces of AA6-063x3/4x3/4 made into two "Z" brackets. One end of the Z will rivet to the tunnel floor, and the other end will have a K1000-3 nutplate to bolt the valve to. Since there are two bolts on the valve, two of these Z brackets were made.

Everything got drilled, deburred, dimpled, and countersunk, including match-drilling the holes in the tunnel floor. Then a quick primer session, followed by squeeze-riveting the brackets together put a close to this first night back to building... more to come!

Brake/Fuel System Design - Initial Plan

<<<I apologize in advance, this is going to be a long thread filled with lots of theories, ramblings and thoughts.>>>

So tonight instead of doing any actual "work" on the plane, I did some major research and planning on the brake and fuel systems. The brake system is fairly straightforward--at least the part in Section 36--which essentially runs two lines from the firewall area to the landing gear mount area. If you want to include the Matco parking brake, then it's a simple insertion into the lines "somewhere." Most folks install their parking brake valve on the firewall, but after reading a pretty descriptive (and hilarious) description from builder Myron Nelson about how difficult it is to reach the valve should it ever need servicing, I will be locating mine at the rear of the tunnel, where the brake lines diverge to go to the R and L sides. While unconventional, this location should be a lot easier to access in the future, and make for an easy control cable run in the tunnel. Pics and diagrams to follow.

Next, on to the fuel system. By far, this is the more complex, expensive, and thought-provoking system between the two. It is also a system that has been over-engineered and/or over-complicated by more than one builder, and sadly it is has also been at least a contributing cause for a number of fatalities in the experimental aircraft world, including the infamous accident that killed John Denver. There has even been one or two accidents involving RV-10's and poor fuel system design, although both of the ones I am aware of also involved highly modified automotive engine installations, which of course kind of throws all the usual stuff out the window to begin with. That's not what we're going for here.

What we ARE going for here though is what I'm going to call a "minor variation" on a tried-and-true system design, for two very specific reasons: (1) I am installing a fuel return line for future compatibility reasons, should I decide to install an electronic fuel injection system (e.g. EFII); (2) I will have provisions to connect a removable auxiliary fuel tank in the backseat or cargo area when extra endurance is required. Nothing too crazy, but any kind of modification needs to be considered very (and I mean VERY) carefully. So, we need to start with a standard RV-10 fuel system, analyze the crap out of it, and then (did I say carefully?) make our tweaks. So... keeping all this in mind, let's get started. Here is a diagram I made of a relatively standard, tried-and-true fuel system design to start with as a reference point.

"Standard" RV-10 fuel system design, IO-540 w/ Mechanical Injection

So I'm starting with this diagram above and calling it "Standard", but really there are already a few modifications depicted here. Notably, the check valves on each of the R/L vent systems, and individual pre-filters instead of the single filter at the boost pump module. The vent check valves are installed in each wing root and serve as a secondary vent, should the primary vent become clogged with ice (or a very unlucky bee). The individual prefilters simply separate the R/L fuel tanks a bit more, so that in the event one tank coughs up some really nasty gunk in the fuel and clogs the filter, you can still switch to the other tank and have unobstructed flow. These are two very common modifications that are pretty well documented already on other builders' sites, and I feel that they are both accepted pretty openly as safety improvements for protection against icing and fuel contamination.

So now, let's analyze the system a bit and look at the individual components, particularly the boost pump module. In the diagram above, the boost pump module is shown as three individual parts above the fuel selector: The check valve, the boost pump, and the regulator (or pressure relief valve). The way it works is best understood if we split into two distinct modes of operation: boost pump off and boost pump on.

• Boost pump off: Suction from the engine's mechanical fuel pump pulls fuel through the check valve and forward through the system. Fuel can technically also flow through the pump and its internal check valve (if present) but we will consider that a path of more resistance. Fuel does not flow through the regulator.
• Boost pump on: The pump pressurizes fuel going toward the engine, "forcing" fuel through the engine's mechanical pump and increasing system pressure, particularly at the inlet side of the mechanical pump, which is where vapor lock can occasionally occur. Due to this change in pressure, the check valve closes and prevents fuel from flowing backwards. Lastly, because the boost pump is capable of producing higher than desired pressure, the regulator opens for any excess of ~30psi and allows some fuel to return to the pump inlet.

Looking at the different boost pump modules available out there, I came across three different brands: The Van's-endorsed Airflow system, the Andair system, and the EFII system.

The ironically-named Airflow fuel pump module seems to have a number of happy customers, and it is Van's choice (always a plus), but it uses an Airtex fuel pump which is a brand I have quite a bit of personal experience with in the automotive world and regard them as inferior to just about any other kind out there. Furthermore, you can go buy the Airtex E2351 fuel pump used in that module for around $60, so I'm a little hard-pressed to cough up $500 to buy it.

The Andair pump looked awesome at first glance. Less external lines and fittings to go wrong, an internal regulator, and oh wow a BRUSHLESS motor! I've always wondered why brushless fuel pump motors haven't really caught on, it seems like they would be vastly superior to the traditional brushed motors in terms of both noise and longevity. Well, it turns out after reading a number of articles online about this particular pump that it is actually *louder* than others and there have been a number of failures, particularly early on due to some early design flaws. A rather disgruntled early-adopter made a video highlighting all the design flaws of this pump and posted it to Youtube, visible here. To be fair, it appears that the company has made improvements to the design since this time, and I am not aware of any recent failures of this pump. Even so, that was enough to make me move on, especially since this is the most expensive of the three options... the FPK-540 is priced at $850!

Finally we have the EFII module. This thing seems great-- it uses a Walbro brand pump (MUCH better than the Airtex in my opinion) and it has a custom check valve/regulator that boasts the lowest "cracking pressure" of the three available models. This means that the mechanical pump doesn't have to "pull" as hard to get fuel when the boost pump is off, which is a good thing especially at high altitudes or hot temperatures. And, it's very competitively priced at $649.

Between the three choices, to me the clear winner is the EFII module. There's just one thing left to consider though: the fuel return line that I have available on my system. If we take a second look at how these boost pump modules work, we can introduce an additional benefit that a true return line can provide. The way these modules are designed (in the absence of a return line) is that the regulator's return path is cut very short, sending fuel back only a few inches and re-introducing it at the inlet of the boost pump. With low demand from the engine (e.g. on descent), the majority of fuel follows this small circular path, absorbing heat from both the pumping process and the warm environment of the tunnel. Since we want our fuel to be as cool as possible for a number of reasons, this is not an ideal situation.

So, what if we pieced our system together instead of buying a pre-made module, using exactly the same kinds of parts as above, but allowed for the regulator to send fuel all the way back to the tanks? I spent hours online tonight, searching for pumps, check valves, and regulators, and I believe I have found a winning combination:

• Walbro GSL393 fuel pump ($98.18). This is (I believe) the exact same model of pump used in the EFII boost pump setup. It has exactly the right spread of pressures and flows to exceed the demands of a 260HP IO-540 engine without going way overboard. The larger GSL392 pump is somewhat more popular in the automotive world but it has significantly higher output, which really is unnecessary here. The GSL393's performance chart can be seen here:

Walbro GSL393 Pump Performance

• McMaster-Carr 47715K21 check valve ($30.07). This valve has 0.5psi cracking pressure (VERY low) and PTFE seals that work well with all kinds of fuels and in a wide range of temperatures. I had originally considered some other valves with Buna-N (nitrile) or Viton seals, but nitrile doesn't hold up to certain kinds of fuel additives, and Viton doesn't perform well in cold temperatures (below around +10 deg F). I actually spent considerably more time than I thought I would looking at check valves, there are a lot of different options out there and care must be taken to choose the right one.
  (EDIT 9/2/15: After further research, I've selected the Parker 2625 "Swing-type" check valve, price TBD. This valve is aluminum instead of brass, and has a fluorocarbon seal with even greater temperature range, and is designed specifically for fuel systems like this)
• Aeromotive 13301 Fuel Pressure Regulator ($131.94). This regulator is adjustable between 3-65psi (30psi desired here), and will work perfectly to send excess fuel back to the tanks. It is also rebuildable and seems to have a strong history of reliability.
  (EDIT 9/2/15: A simpler method may be to use a standard relief valve with 25 or 30psi rated pressure. I'm torn between the two options and will keep searching on this.)

Cool! The same and/or equivalent parts for less than $300... I like it. So that's it, you say? Well, almost. There is one more thing to consider. Now that we have a standalone regulator, what if we move it to the head of the line and "tee" it off the entry to the fuel injection servo? This way, we eliminate any potential over-pressurization issues along the whole fuel system, and we now have the ability to run cooler fuel all the way to the servo. This should pretty much eliminate any hot-start issues and/or occurrences of vapor lock. This isn't a wild or crazy idea of mine, either... it's been the standard for how automotive fuel injection systems have worked for at least the past 30 years (which is of course about 40 years *after* these Lycosaurs were designed). So, after all that, I present you with my first draft of the fuel system diagram:

N165MJ Fuel System Design - First Draft

(EDIT: To see post with Second Draft, click here)

If you've been following along from the previous diagram, you'll see that really not much has changed except for the "duplex" fuel selector, the location of the pressure regulator, and the path of the returned fuel. I'm going to stew on this design for a little while and figure out the number of connectors, tees, fittings, etc etc that will be necessary to make this all work, and go from there. In the meantime, please feel free to comment (or email me) your ideas or opinions on this design! I welcome all feedback.

One other thing left to cover is the aux tank connections, but that is fairly simple in design. My plan there is to have two fittings and an electrical connector hidden somewhere in the R interior side wall that I will connect to a custom ~20gal fuel cell that can be placed in the rear seat floor or baggage compartment. Fuel will be burned from both main tanks as normal, and then when a tank has enough room in it to accomodate the fuel from the cell, an electric transfer pump inside the cell will be activated to refill the selected tank (either right or left) through the return line. It should work pretty slick... or at least that's the hope.

Whew! Sorry for such a long post tonight. Hopefully I've been able to document my current thoughts in a clear way. Excited to see how this all plays out!