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.

 

Canopy Installation, Part 6

Forward with the alternate canopy fiberglass trim piece....almost per Van's instructions, but with a few of the EAB/I'd rather do it my way deviations.

One of the first tasks was to cut out the full size templates provided with the plans to create the components of the trim piece.  I elected (deviation) to mount the templates on poster board to give a firm foundation upon which to lay up the fiberglass.  One of the problems many builders experience is the sag in the whetted fiberglass over the non-uniform surface of the forward canopy frame where it mates to the forward fuselage.  The stiffened templates are an effort to minimize/eliminate the sag and the requisite filler required to make it "all purdy."  The first shot below shows the right side with the template taped into place.  There is electrical tape trimming the intersection of the template with the canopy bubble and clear shipping tape covering every square inch of the template.  Finally, there is some butcher paper masked onto the surround area to minimize the effects of any accidental spills of the epoxy resin.

And speaking of resin, I am continuing to use West Systems epoxy, the 105 resin and the 209 (extra slow) hardener.  It is very nice stuff and very simple to work with and I do not even perceive any fumes.

Up next was the cutting of the fiberglass cloth into the 5 layers as prescribed by Vans.  The use of a rotary cutter and straight edge simplifies and makes short work of a somewhat tedious task.

Five plys of fiberglass all trimmed to size and ready to go.

 Mix up the epoxy resin (3.7 parts resin to 1 part hardener, by weight) and we're off to the races.  In the heat of the battle, I did not take any photos.  The shot below is of the glassed 5 plys and a layer of peel ply or dacron fabric.  Use of the peel ply makes a huge difference in the quality of the finish.  I will still need to do some heavy resin/micro slurry build up of the low spots, but the surface is so nice to work with after the peel ply.

The next picture shows the peel ply coming up off the cured resin.

 
And the finished work prior to filling...

I forgot to mention the last of the prep work required before laying up the fiberglass.  That involves spreading some good quality car wax (I used Turtle Wax) over the areas to be glassed to facilitate easy removal when the part is cured.  I used 3 heavy coats prior to applying the glass and resin.  I will have to comment on the success of my procedure later as the fiberglass fairing is still resting in place.  I will perform the resin/micro filling of the fairing where it sits in place for an easier approach to the sanding.

 The second piece of the fairing, on the pilot side of the fuselage.

The last piece of the fairing is the long straight piece that connects to the sides.  Below, the area is taped and waxed prior to glassing.

Again, no pix from the glassing process, but the third of three pieces of the fairing is now drying with the peel ply on top.  The micro "cake frosting" process will happen next...when the microballoons arrive in the mail.

Landing Gear, Part 2

Next up is the wheel and brake installation upon the main gear legs.  The pictures below show only the axle and the spacer plate attached to the gear leg as I don't plan on installing the calipers until later.  I just want to get the forward fuselage on its gear to better facilitate the upcoming fiberglass fairing construction.  The entire fuselage is currently on a table and really is too high for the fiberglass work...to make matters worse, I cannot fully extend the canopy to its upright position without hitting the overhead garage (hangar) rafters!

The next process is a tricky one....namely, assessing the amount of correction for toe-in or toe-out.  The Van's prescribed method of using a thread and wooden block seems like a reasonable approach, but it has given me the "fits."  My best guess is that I have about 1+ degree of toe-out on the pilot side gear leg.  I believe that the passenger side wheel/leg assembly is about true.  After being tempted to shim the axle to the gear leg with washers, I gave in to the more precise and structurally (for the bolts) superior method of using a shim.  Those buggers are expensive at $25 each...especially when it really is almost impossible to measure the exact angle that the leg and axle make with the aircraft centerline.  I imagine that with some lasers you could nail it right on the money.  The poor quality pictures below document my best efforts at quantifying the toe-in/out.  More to come when the shim arrives, gets installed and I see the result.  I'm not too thrilled about this process.

Back to the brakes momentarily to document the installation of the blue AN fluid fittings with the requisite pipe thread sealant to secure the connection.

Next process will be to install the nose gear leg and fork and then the wheel.  The first task is to install a couple of anti-rotation plates to constrain the nosewheel axle.  The shot below shows the plates after priming and solid riveted to the fork with AN426 rivets

The front end of the fork has two holes that must be tapped with 5/16-24 threads so accommodate the cap screws that serve as the the stops for the swiveling nosewheel.  Do you see the error?  Yep, I threaded the holes in the bottom of the fork - not the top.  I fixed that pretty quick and reinstalled  the cap screws to their correct location.

Some more substantial fun awaits: affixing the nose gear leg and the lower Viking engine mount to the firewall.  The picture below actually shows the upper mount as well as the lower mount.  The Viking mounts are installed with 3/8 inch bolts with Nordlock washers on both sides of the firewall.  The fitment was excellent and required very little work to get everything lined up and installed.

Now, its time for the first landing from about 6 inches of altitude from where the little beast has lived for past several months.  One note prior to the next ground-based pictures:  putting the legs on the RV-12 does come with a cost.  The fuselage will no longer be able to be placed on its side for ease of installation of any sub-systems.  I hope I have done my homework and do not regret the timing of the landing gear installation.

This is also a pretty good shot of the Viking engine mounts.

And we have a smooth landing...