Moving the battery to firewall

I am thinking about an Atlee Dodge mod moving the battery to the firewall. I like the idea of removing the long cables, reducing weight. What is the downside? I thing Odyssey battery is the right choice. Plane is a ‘68 180H.


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Be careful of over heating the battery with exhaust heat or an engine preheater. Otherwise it's a good move, functionally speaking. And if you don't already have one, install a master relay on the battery box.

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5CT7 said:

I am thinking about an Atlee Dodge mod moving the battery to the firewall. I like the idea of removing the long cables, reducing weight. What is the downside? Plane is a ‘68 180H.

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The downside is moving the CG forward. This is particularly important when lightly loaded. Cessna put the battery back there for a reason.

My 180’s battery has been on the firewall for over 20 years. I'd owned the plane for 3-4 years before the change. There’s no down side that I’ve found.

Before you buy the Dodge box you may want to call MLJ Aircraft at Birchwood Airport in Alaska. They used to make the best box going, and it uses a PC625 battery instead of the PC680/SBS-J. MLJ’s longtime owner retired so I don’t know if they still make their battery box but if they do it’s the one to get. If you want an Odyssey battery, that is. When my current battery gives up I’d like to go with an EarthX ETX-900. I’m not sure what the field approval attitude is. It should be doable with the TSO version.

skywagon8a said:

The downside is moving the CG forward. This is particularly important when lightly loaded. Cessna put the battery back there for a reason.

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A firewall mounted Odyssey was installed on my 180 by a previous owner close to 20 years ago.
They did some other stuff at the same time, but when I crunch the numbers from their W&B revision,
it looks like the battery mod resulted in 14 pounds less weight and moved the CG forward 1.9".
This 180 has had a fairly forward CG since I've owned it (currently at 34.6" empty),
it's the only one I have any time in to speak of, but it flies fine.
No problem flaring, even with full flaps, which I've heard is sometimes a problem.
A more aft CG might give it snappier handling, and would probably result in slightly higher cruise speed & slightly lower stall speed--
but on the positive side, the forward CG allows you to carry more gear in back while still staying in the CG envelope.
I like that there's not several feet of battery cable to add weight & voltage loss.
All in all, I'd say the pluses outweigh the minuses.

In fact these aircraft were designed to carry loads, not to fly around solo. If you’re worried about CG, install an extended baggage compartment, and carry your survival gear back aft, till you need to load up. I spent quite a few hours flying these things at work, and a fed CG when empty was a good thing, and easy to deal with.

Aft CG on the other hand, CAN kill you.

Forward is manageable, even when empty.

MTV

I do not think there is a downside.

The first 185 I flew had a mid-aft CG when empty, and we always struggled to load it within CG limits. I thought that was normal.

The next 185 I flew was with a private owner. I jumped in for a quick flight with the owner after annual and it planted the mains all by itself on wheel landings. It turned out we were ahead of the forward CG - we picked it up at the maintenance hangar, but the survival gear that was normally in the extended baggage was sitting in the owner's hangar. The survival gear was only 25 lbs, but it was enough to bring the CG behind the forward CG limit with two guys in the front. A firewall battery would have required some more weight back there, I imagine. It hauled 1000+ lbs with full fuel, though, and was very easy to keep ahead of the aft CG limit.

Two Cubs I flew benefitted from the battery moving forward.

A third, nearly identical, Cub had a CG so far forward that I struggled to get the CG behind the forward limit when solo. Retaining the aft battery would have been nice.

Point being, do a weight and balance! Shorter cables and less weight are good, but see how it affects your plane specifically.

As MTV said, forward CG is normally easy to deal with, just carry (more) survival gear, tools, oil, water, etc. There is not a whole lot you can do about aft CG when the plane is full, except take stuff out.