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.