Firewall - Part I

The partially completed fuselage kit I bought already had the firewall roughed out, along with all the brackets that tie the firewall to the fuselage.  Step 1 was to see how it fits...

Luckily, it fits very nicely :-)

Because I am not going with a 'standard' engine, I need to do a lot of stuff that is not in the book.  So I have been planning out where I am going to put everything.

Stuff to fit:

• Batteries (including capacitors needed for UL install)
• Voltage regulator (50A)
• Gascolator
• Fuel pumps / filters
• Primary fuel feed / fuel injection return
• Air / oil separator
• Cabin heat box
• Throttle, and cabin heat controls
• Master relay(s) (do not need starter relay, as it is on the engine)
• MAP sensor
• Fuel pressure sensor (which is fitting to output of fine fuel filter, via banjo fitting)
• 
  

In order to 'fit' everything, I had a local plexiglass shop make me a Plexiglas firewall.  They cut the outside profile of the firewall, and the slots that go around the nose gear mount.

I am not comfortable with the limited amount of hard points on the cage for attaching accessories.  So during this process, I am going to add a number of additional hard points.

My kit did not come with the material needed for the angle structure that goes on the firewall, so I ordered a bunch of 1.25 x 1.25 x 0.125 6061 T6 angle.

The Glasair documentation for anything firewall forward is very lacking... once I got over that and figured I am on my own, it started moving much quicker.  A lot of hunting and frustration was involved trying to figure out what to do.

Firewall Framework:  Glasair uses an aluminum angle structure (attached to hard points on the cage) to mount all accessories.  In a 'usual' Sportsman, this would include battery, oil cooler, engine transducers, firewall pass throughs for wiring, cabin heat box, etc.

Goal:  Have ZERO firewall penetrations that need to be removed.  Example:  Battery mounting - the goal will be to be able to remove the battery without having to remove a firewall penetration.  This will apply to everything.  Coils, fuel filters, regulator, etc.  Once the firewall and framework is mounted, nothing will need to be removed EVER.

With using a UL Power Engine, my needs are a bit different:

1. (Electric) Fuel pumps (qty 2 - primary and backup, controlled by the ECU)
2. Fuel filters (course and fine)
3. Air / oil separator
4. Gascolator
5. Batteries (qty 2 - EarthX ETX900)
6. Coil packs (qty 2)
7. Master relays (qty 2 - one for each battery)
8. Cabin heat box (stainless - Canadian requirement)
9. Main fuel line (output from either pumps or header)
10. Fuel injector return

Fuel Pumps / Fine Filters - Location (Note - also see Fuel System post for more details (add link)):  Option 1 will be to put the pumps on the forward tunnel inside the cockpit.  Option 2 is on the firewall.  Honestly, I don't like either option, but they have to go somewhere.  All of the hardware is ordered to adapt the standard UL pumps / filters to inline input and output rather than side entry.  With all this, it should fit in the tunnel.  If that doesn't work, then I will come back to putting all this stuff on the firewall.

I am pushing ahead with plan A - filters / pumps under the header, on top of the forward tunnel.  Something like this:

Tentative tank placement:

The firewall framework has been proceeding well.  Mounts made for coil packs, regulator, fuel filter, batteries, gascolator, etc.

Once the pump and filters are complete, then I can proceed to putting in the Plexiglas template and fitting the cabin heat box, cable passthroughs, air deflector, etc.  Hopefully then I can really start moving.

Plexi firewall in place.  Main fuel line drilled, as well as return.  Cabin heat airbox next.  Battery box clamped in place.

A lot of the above did not work out:

• Battery box too wide and too low - hit engine mount (I finally had the brainwave I had better put it on and check for clearance issues...)
• Gascolator not low enough.  Hit exit ramp that transitions between the bottom of the fuselage and firewall.

So I changed my mind on the battery box.  Decided to go stainless, and cover it in a reflective mat.  From reading on the forum, this seems to be a good option.  I will also put a 1" cooling flange on the front.

Redesigned the gascolator mount to be similar to the Glasair design (I am using the same Gascolator they use).

5 pieces to the battery box.  

1. Floor the rivets from the bottom
2. Back mount that will tie into the firewall structure on both sides.
3. Front cover that wraps around to tie the back mount and floor together
4. Strap that hold the batteries in.

To pull the batteries will require taking the box off, but it will only be 5 bolts (plus the wires) and the entire box comes out.

Firewall frame below removed for drilling / finishing.  The back is flush riveted so it won't interfere with the firewall.

Firewall frame all primed, relays temporarily mounted, gasolator fit checked, cabin heat box drilled.

Parts getting their grey coating to match the engine mount (and everything else)

Exit air ramp drilled.  The bottom is held in with captive fasteners on the bottom of the firewall stainless.  Screws will go through the fiberglass, air ramp, and then into the firewall structure.

Everything completed to date installed.  (New) plan is to finish all the cockpit / avionics wiring with the firewall out.  Real firewall will not be installed until after engine / engine mount has been test fit.

The firewall template has been out of the fuselage for a month or more while working on other things.  Its pretty much going to stay in this state until I have an engine.  Part II will cover the next phase of the firewall later in 2022.