Firewall Forward, Part 4

I am now moving into the electrical wiring phase of the firewall forward construction.  Before I get too deep into that I want to set up some of the basic electrical wiring procedures I am using for the power distribution system and its cabling: battery, contactor, alternator and starter.

First order of business is to show off the Harbor Freight tool of the month that I have used with great success in electrical cable construction.  Let me also add that for the firewall forward electrical, I am speaking of 10 AWG wire and smaller gauge (larger diameter) wire.  The first shot below shows the HF hydraulic crimper - its a bad boy!  Makes even my unskilled hands produce some nice professional looking crimped terminals.

I should also brag on my HF wire/cable cutter, shown in the lower right of the next picture.  It makes cutting the 6, 8 and 10 AWG cabling a breeze and leaves a nice clean end.  But I digress.  Of note is the stripped end of the 8 AWG wire in preparation for the ring terminal attachment.  I have done all of my wire stripping with attempted surgical precision utilizing a brand new razor sharp Exacto blade and knife.  I have had perfect results just scoring a ring around the insulation without breaking into the wire bundle and then carefully working it off, again, with the knife.

Next step is to place the shrink tubing and uninsulated ring terminal into position and grab the bad boy.

 Jig up the assembly perfectly centered in the appropriately-sized jaws of the crimper.

A nice view of the assembly being crimped onto a 8 AWG wire.

Removed from the crimper and immediately prior to heat shrinking...

And the finished product.  Terribly out of focus pictures as the camera was giving me some attitude that I could never resolve - sorry about that.  Suffice it say that I am very pleased with the results of the cabling.

 The next few shots are of the power distribution system and are not quite permanently in place as I am still "noodling" the layout.

Shown below is a shot of the contactor, alternator and coolant overflow tank, without the battery.  Of particular note is the shunt mounted along side the seafoam green (primer) doubler.

The next image shows the battery in place, but without its hold down strap.  You can also make out the battery and battery/alternator leads that will run to the power buss, along the upper edge of the firewall.  Yet to be installed in this space are the two 1/2 inch manifold pressure (MAP)  hoses from the throttle body that will penetrate the firewall and connect with the ECU.  I anticipate that the ECU will be mounted just about directly behind the contactor (backside of the firewall), which will be on top of the glove box.  Yes, it is crowded.

Top view of the same.

Also worth mentioning is the routing of the starter cable (6 AWG) through the unused engine mount hole, on its way to the 5/16 inch stud on the starter (not shown).  Another 8 AWG wire runs from the contactor down to the 50 amp fuse (little black box) then to the shunt and then up and over to the alternator and its 1/4 inch stud.  The small, white wire poking out from the loom is the alternator field wire that will run (from next to the stud on the alternator) to the master switch.

 Much more forthcoming in this Firewall Forward series of blogs...

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.