Firewall accessory mount layout

[Zzz]

This seems like one of those things where it's better to have everything in hand before even trying, but I'm at a point where I've got the remote brake fluid reservoir and the parking brake valve to hang. It sure would be nice to get those mounted so I can route my final lines, but the list of "what ifs" is long. Heater control box? Battery? Oil cooler? Fuel line routing?

Is there any strategy to relegating electrical oriented items to one side, and oil/fuel/brake items to the other? Curious to see how others have laid theirs out.

Thanks.

[jaredyates]

Haven't you been taking pictures of everyone's firewall when you have gone to Oshkosh? I would think your engine choice would make a big impact on where things need to go. I'd suggest looking for a Bearhawk with a common engine first.

[alaskabearhawk]

FWIW, I took lots of pics and saved even more from sites online. Tailor yours to what you want. Even non-BH installations are useful. To insure correct placement of components, cables and whatnot make a firewall out of Plexiglas. Mount components and route other items as necessary for a good fit. Then you can take that and use it as a template for the real thing.

[Zzz]

To insure correct placement of components, cables and whatnot make a firewall out of Plexiglas. Mount components and route other items as necessary for a good fit. Then you can take that and use it as a template for the real thing.

That is a brilliant idea!!! Thanks.

Jared, I have yet to make my first trip to Oshkosh...

[Battson]

I've said it before, but there is MILES of room back there compared to most aircraft. You are spoiled for choice.

You can plan it out on paper taped to the firewall, and if you dont end up using something e.g. a heater box, that spot just ends up blank. No big deal!

Ideally, you would locate items based upon their proximity to the engine hook-up points, to minimise the length (weight) of connections and keep the install 'tidy'. E.g. put the oil cooler on the side of the firewall the oil outlet from the accessory case is on (port for the -540). If you get this wrong - no biggie - you just need to use a little more hose. There is plenty of room for that.

Having been in your position, and then learned a few things the hard way, here is my advice:

1. Decide on your design, and make a list of things that go on either side of the firewall, or pass through it.

2. Plan for the 'hard to move' constraints first e.g. control cables are fairly inflexible over the short distance behind the panel, and need to go straight through somewhere in the middle in the direction of your routing, fuel lines come from under the floor, typically on the port side for the fuel pump if using IO-540 etc.

3. Then start with the largest items - you have the fewest options for locating them, so they come first. Battery case is biggest, or EI if applicable, firewall mounted oil cooler (maybe?) - mine is mounted on the engine mount, the remote oil filter - which needs easy access without removing the cowling, then move to smaller items like the cabin heater box which is much more flexible.

4. Small things are best mounted in tight corners where big stuff wont fit anyway, near the engine mount attachment points, or near the edges of the firewall. That way they don't take up space which would be useful for a larger item. Small things include the through-bolts for the park brake, the brake fluid reservoir, the transducers for oil and fuel pressure, etc.

5. Penetrations for things like sensor wire looms, electrical cables, the starpoint earth, P leads, manifold pressure hose(?) - these can fit between other items and you needn't worry about them until the end. All I would say, is keep the electrically noisy things like the alternator cable and P leads away from your radio stack and associated antenna / headset wiring. Do not forget to shield all your radio related wires and your P leads, earth P leads at both ends.


Don't forget: Easy unobstructed access to your oil filter, mags / EI, battery, fluid reservoir, and sensors for maintenance without removing the cowling (in that order, based on my experience).