Fuel Tank Vent Modification

Released December 20, 2013, or the day after the second fuel tank service bulletin (13-12-12) was issued, this accessory kit is designed to overcome another one of the fuselage tank issues - namely the tendency of the tank to splash back upon refueling.  The tank can also push fuel out of the vented cap by virtue of rapid expansion of the fuel from a cool storage tank to a hot and/or warming fuselage fuel tank.

Either way, the engineers at Vans believe this is the answer to the problem of the fuel splash back problem.  It goes without saying that the key motivation behind this effort was an attempt to prevent the Lexan (polycarbonate) back windshield from cracking due to the exposure of gasoline. This malady has effected quite a number of owners, solely taking into account those that have posted on Vansairforce.net.

Since the tank was already torn apart for the installation of the doublers featured in the aforementioned service bulletin, it was obvious that this was the time to take on the additional task of installing the tank vent modification.  As an added bonus, I had not yet vented the fuel tank cap, which must effectively be undone, by plugging the vent hole with ProSeal.  Sometimes you just get lucky.

Shown below are a couple of pictures of the fuel tank with the new 1/2 inch hole, which was drilled adjacent to the tank filler neck, and then fitted with an AN 45 degree bulkhead fitting.  A thick aluminum washer and nut, inside the tank, secure the fitting.

An additional 9/16 inch hole for the aluminum vent line was drilled through the corner of the fuselage bulkhead as shown below.  There are another pair of holes, as yet undrilled, that will be for the vent lines exiting the "floor" of the tailcone.  There is also a plastic vent line that is installed in the aluminum vent line, which has a separate exit and thus the need for two exit holes.

The next shot is of the final preps for permanently sealing the bulkhead vent fitting in the tank top.  Specifically shown are the washer and nut that will be inside the tank.

All tightened down and the bulkhead fitting sealed with Proseal too.

YET ANOTHER FUEL TANK SERVICE BULLETIN!!!!

Service Bulletin 13-12-19, issued December 19, 2013.  Subject: Fuel Tank Attach Modification.

This is the second service bulletin issued for this ridiculous fuselage gas tank in just over two years - two years and 5 days to be exact.  Gee, Tom, tell us how you really feel about the tank.  Yet another of the "infinite" number of failure modes has emerged for the engineers at Vans to subdue.  They need just a bit more reinforcement of the forward attach points on the tank after another RV-12 had its tank breached.  Seems this failure mode was worse than the previous one.  Seems the frangible bolts weren't "frangible" enough.  So now, all RV-12 builders and pilots get to dismantle their tanks and insert some more doublers into the corners of the forward bulkhead of the tank and replace their existing frangible bolts with some new more frangible ones.

Quoting the last sentence of the 2013 SB's synopsis: "Adding more robust hardware in conjunction with doublers inside the tank will help the frangible head of BOLT-00002 to fail before significant distortion of the tank and make the tank more resistant to a breach."

And quoting the last sentence of the 2011 SB's synopsis: "While the severity of the impact was such that a breach of the fuel tank is not surprising, the tank can nonetheless be made more breach resistant by the addition of clips and by the use of frangible bolts."

Am I the only doubting Thomas out there?  I am so frustrated about the prospect of tearing up a perfectly good and tight tank.  If I had to do it all over again, I would definitely go with the group of EAB builders who have/are pioneering wet wings - where the fuel belongs in an airplane.  I know of at least 1 RV-12 currently flying with wet wings.  Not exactly a compelling statistic but the work I have seen on those in progress is stellar.

Okay, I am tired to griping so I'll get on with the start of my teardown saga....it is still very early in the process.  The first pictures show the T-1209 sender plate in surgery.  Below shows all but 2 of the sender plate screws removed.  The remaining 2 had to have their Phillips head converted with a Dremel tool into a deep slot configuration so I could get enough torque for their removal.

 After slotting the heads, I was able to remove the two problem screws and now the ProSeal removal debacle begins.  I had some success earlier in the project using some heavy duty stripper (methylene chloride-based product) for softening the ProSeal in cleaning up the tank after assembly and before painting.  That is what you see around the perimeter of the T-1209 below.

Now, I have to figure out how to break the seal without destroying the tank bulkhead and the sender plate.  I am having no success with anything plastic, so I will probably have to resort to something sharp and metallic...which will probably not end well.  More to come.

Fast forward a few hours.  I got some reassurances from others at VAF.com to go ahead and use a sharp metal tool, as shown below to pry apart the sender plate and bulkhead.  It actually worked okay.

Progressing nicely.

Victory!

Cleaned up the bulkhead and sender plate (not shown) with my drill and wire brush attachment.

Next, came removal of the rivets for the nutplates and then more rivets from the tank bulkhead where the doublers are to be installed.  Below is the attach bracket with the nutplate rivets and adjacent rivets removed and the area cleaned of the ProSeal and finish paint.

More rivets, nutplate, and paint removed from the other attach bracket.

Stay tuned...or just watch the photo's date stamp to get a feel for the duration/time lapse of the events.

The next step in the process is removal of the ProSeal from the interior of the tank, where the doublers are to be installed.  This is definitely hard, long work exacerbated by the long, blind reach into the tank to do the work.

And this is the objective: the two doublers that will strengthen the tank to the point that the frangible bolts will fail before the tank breaches.

I didn't take too many pictures during the final sealing of the tank.  In particular, I failed to snap pictures of the doublers, coated with Proseal going into the tank.  I think I lose part of my sanity when I am working with ProSeal, as all HE** seems to break loose as soon as I start applying it to aluminum!

The picture below also appears on the tank vent modification page, but gives a good perspective of the amount of ProSeal I applied to the doublers.

Spreading the "love" on the face of the tank bulkhead in preparation for the sender plate and its dozen screws.  All internal mods have been completed including re-connecting the vent line, which I was certain I would somehow forget to do!

Now comes the waiting game: letting the ProSeal setup for a week or two before conducting round 2 of the fuel tank leak testing.

Firewall Forward, Part 3

After enlarging one of the firewall openings from 1" to 1.375" for the d-sub connector on the engine wiring harness, it was time to fabricate a custom pass through. 

As previously mentioned, I am using the Alumiweld product (from Harbor Freight) to "braze" the tube stock to the sheet stock.

Shown below is a picture of my first attempt at the two part pass through assembly.  I ended up junking this one as the notch in the lower left corner of the male part just bugged me, so I made another one.

Version 2 of the pass through.

Final installation of the pass through with number 8 machine screws, washers, stop nuts and a new longer rivet (at the 6 o'clock position).

Another view, which also happens to show the existing throttle cable hole in the firewall to the lower left.

The next series of tasks involves finalizing the firewall for the Viking engine installation, which includes changing some of the Rotax "features".  Among them is this array of holes which allows the passage of warm air from the radiator of the Rotax installation.  Not needed for the Viking, I embarked upon the mission of covering it up with another piece of stainless steel.

I will also point out that I did remove the engine after finishing the preliminary installation (see Firewall Forward, Parts 1 & 2), so no, these pictures are not out of order, despite what it might seem.

Foreground picture of the fabricated stainless cover plate, drilled, deburred and ready to install in the firewall.

 

Riveting and goo-pucky complete.  The goo is the 3M Fire Barrier sealant, which I have previously used in other places on the firewall.  As I finish sealing the firewall, I will probably also use some of the ProSeal, as recommended by Vans.

Cleaned up and ready to go.

The next Rotax feature to amend was this fuel line (don't remember if it was a supply or return) hole in the firewall shelf.  New patch cut, drilled, deburred and ready to install with the Fire Barrier sealant.

All done, awaiting clean up.

Firewall Forward, Part 2

After the engine was secured to the airframe, the next series of tasks was/is to determine the firewall pass-throughs and fuel system configuration.

The pictures below shows an intial layout of the fuel system, firewall forward.  The layout features a stainless steel line emerging from below the firewall shelf at about mid-span.  That stainless steel tube takes an immediate right angle turn toward the pilot side as shown below.  The provided lines from the previous owner are not going to work out, but its inclusion here will give you an idea of my intentions.

As that steel line progresses outboard, it will terminate into the inlet of the high pressure, 10-micron fuel filter that will be mounted on the firewall, slightly beneath the brake fluid reservoir as shown below.  That location will hopefully provide good access to changing the filter's element at each annual as well as preserve some real estate on the firewall between the engine and brake reservoir.

The discharge side of the fuel filter will have an elbow and fuel pressure takeoff fitting (1/8 inch NPT female thread), which will tie into a teflon hose with AS 1072 firesleeve.  (By the way, that is NOT the hose that is pictured above.)  I will be using a Kavlico fuel pressure transducer mounted in the takeoff fitting, which will give the fuel pressure reading downstream of the high pressure filter and should give me an idea of the ongoing health of the filter, prior to the engine's injectors.

Shown below is another larger perspective of the stainless line emerging from the firewall shelf and proceeding toward the high pressure filter.

I am working with Tom Swearengen of TSFlightlines.com to spec out my fuel lines.  He is a great guy and very knowledgeable in the way of fuel, hydraulic, brake and just about any other line you will need on your aircraft. The picture below is another mockup, using 3/8 inch aluminum to get some measurements for the lines that Tom will be making for my installation.

Another view of the aluminum mock up.

Not completely happy with my aluminum mockup, I also purchased some thin-walled, 1/2 ID Tygon tubing to give another perspective to Tom of what I am trying to achieve with my plumbing.  After the Teflon line is firesleeved, it will be closer in size to the Tygon mockup than the aluminum one anyway.

The ball is now in Tom's court and I will have some new lines/hoses to mount up sometime in the next couple of weeks.  Talk to Tom Swearengen - you will not be disappointed!!!

The next picture illustrates what I wanted to point out about the initial phases of spec'ing out the firewall pass-throughs.  The hole in the firewall shown below was the "stock" grommeted 1-inch hole as it comes in the fuselage kit designed for the Rotax installation.  In the Viking installation, I plan on running the engine wiring harness through this hole and across the inside of the firewall toward the map box, where I plan on installing the ECU.  The terminus of the engine wiring harness is a 37 pin d-sub connector, which is almost 3 inches long.  With the bundle of wires attached to the connector, there is NO way that will fit through a 1-inch hole, lined with a thick rubber grommet...even after disassembling the connector...even after removing the grommet!

The solution was to employ a knock-out punch to enlarge the existing hole to 1-3/8 inches, about the minimum dimension to pass the "folded up" wire bundle and connector through.  But that creates a problem: there are no ready-made stainless steel pass throughs that large that I have been able to find.  The  plan now is to fabricate an aluminum pass through with the handy-dandy alumiweld rods shown below.

These test articles below were my first pass at a proof of concept, as ratty-looking and downright ugly as they are.  The nice feature is that the "brazed" joint is actually stronger than the aluminum itself - truly amazing stuff.  The downside is that it is aluminum and NOT stainless steel, so it's fireproof qualities will be lacking, relative to the stainless.  The only other alternative was the use of nylon pass throughs, which are large enough to pass this connector, but they are not really intended for high temp applications.  Stay tuned to see how this one turns out.  The 1-3/8 inch diameter tubing will arrive later this week and along with the .090 plate should make a pretty stout pass through for the engine's wiring harness.  I should also point out, that some other electrical wiring will also pass through this hole as well - all to be determined as I move further along this path.

There will also be two small pass-throughs on the passenger side of the aircraft, where the MAP hoses will run from the throttle body to the ECU.

Firewall Forward, Part 1

The last bare, naked firewall picture replete with a proposed fuel system plumbing configuration.  Fastforward one week later and that one is out the window.  I will have some additional mockups of the Part 2 installment of the blog.  So this is obviously the "before" picture and the one below gives some perspective of the "after".

Of note in the picture below is my use of the Harbor Freight chain hoist,suspended from the pair of 2x4's reinforcing the hard point attach.  The hoist has worked great, but an engine hoist would have been easier.

Front view, side views following...

 

I lost count of the number of times I went back and forth with the digital level trying to get everything perfect for the lower nosegear leg mounting.You are committed once your drill the two holes in the nosegear leg to establish the position of the lower mount, so everything has to be perfect.

The picture below illustrates the dilemma.  You will notice the lower engine mount's bracket is slightly canted with respect to the upper end of the nose gear leg.  Through a combination of shortening the interior red, rubber isolator "doughnut" and adding a couple of extra washers between the engine mount and the firewall, I was able to increase the distance between the upper and lower ends of this lower engine mount such that the angle was almost perfect...or close enough.

 

 Below is the after picture of the adjustments to the doughnut and engine mount (extra washers).

Below is a picture of the lower firewall mount and the extra washers required to produce the offset needed for the nosegear engine mount.

Every builder needs a cute gearhead neighbor friend to help with the tough jobs.  Debbie is just one such friend.  She's a great friend...and has more tools than I'll ever dream of owning.  In the end, it was her little box store right angle drill attachment that got the job done on drilling the passenger side holes for the nosegear engine mount....once we got everything locked down into position.

Quite the milestone when the engine puts its full weight on the airframe for the first time....I guess that could be my first RV-12 grin...no, actually my second.  The first was when I sat in the cockpit for the first time a couple of weeks ago.