I've read quite a number of posts about firewall mounted batteries to allow for flat floor extended baggage, and I'm quickly approaching the acquisition of an extended baggage kit myself.

The one thing I'm worried about is the shift in CG. Has anyone done this modification, and wished they would have just lived with the battery box in the extended baggage due to the 2" forward shift in CG that many have reported?

The flat floor baggage looks cool and may be advantageous if you sleep in your plane a lot, but other than that, the "regular" extended baggage that allows the battery to stay in the rear is the best option IMHO....and for reasons you just mentioned. If you fly around solo most of the time like I do, the more weight you keep back there, the better.

If you want a compromise to offset the added weight of the baggage compartment install, you can just put the Oddessey SBS-J16 battery inside the stock box. You still lose a little bit of weight, but your not going too far the wrong way on the CG.

Also, I've never used the flat floor baggage mod, but it seems to me its only flat while you're on the ground...in flight the floor is angled forward and things must be migrating forward?!?! I dunno, like I said, never used one...

I don’t regret it from a W&B perspective. I regret it because now I don’t have a battery that will satisfy the STC requirements to install the Surefly electronic ignition. Still trying to think of a way to keep the battery forward, and still install the ignition at some point.

On the CG front, I installed a MT prop, an Aerocet hydraulic pump in the tail, and moved the battery forward. It all roughly balanced out. I also fly heavily loaded most of the time. If you're trying to fly empty and light, that’s harder to manage, but manageable.

I really like the flat floor. Much easier to load. There’s a 2” lip to get across when sliding stuff to the rear. It’s about an 8-10” threshold in factory configuration. Very awkward to load an item through the door, then get your arms, head, and shoulders through the door to lift it to the rear. Of course these aren’t heavy items, but they’re clumsy. I load sleeping bags, pillows, laundry, etc. I can still fill the volume without exceeding the 50 lb. limit even with the increase in space given by the flat floor.

I do. With my 2650 gross weight and a ~1,770 airplane I almost always have 100# in the back to keep me inside the envelope. I thought was going to be doing different flying when I moved the battery forward, and it made sense. Now I have 200# of lead shot in 25# bags that are used as ballast for various configurations. The carbon fiber extended baggage is super nice though and it is awesome to stuff it full of light things and put the cargo net over them, out of the way.

I was modeling what removing my Horton cuff and doing a Sportsman cuff would look like for W&B, and it’s not pretty, I almost need to do the Wing-x to get the upgross. Then the wind blows constantly here, and most people report the wing-x is a handful in x-winds. About to just get a 185 so I don’t have to worry about it anymore... ( almost, then I look at my savings account and realize that upgrade is a long way off)


Rod

No regrets whatsoever. In Alaska we carry survival gear and there's always enough stuff to put back there to move the CG. During hunting/camping season I can put my entire Arctic Oven Igloo back in the extended baggage area staying well below the weight limit. Carrying ballast messes with me cause there's always enough mission essential "stuff" back there.

Another big plus is when you hit the starter button that baby spins! And the battery is warmed when blanketed and using my preheat.

On another subject, I know everyone loves the Sportsman kit but removing a Horton to install one is kind of hard to justify in my simple mind. A Horton equipped 180 has won Valdez numerous times as well as many other STOL competitions up here.

Gunny wrote a great series on modding the wing on his 180 and spoke of getting back a lot of roll authority on his bird after the Wing X by adding VGs.

Akaviator makes several good points. Less battery cable means far stronger cranking, and heat the engine room, and battery gets warm too. Aft battery in cold climate is really hard on batteries. Battery never gets very warm in winter, thus holds less charge. Eventually that can bite.

To compensate for doing so on my 175, I installed an MT prop. W & B came out nice, pulls like a tugboat and smoooooth.

I’d do it again, battery belongs on firewall.

Proper survival gear/tool kit takes care of empty cg.

MTV

Wa180 wrote:...With my 2650 gross weight and a ~1,770 airplane I almost always have 100# in the back to keep me inside the envelope. ….. Now I have 200# of lead shot in 25# bags that are used as ballast for various configurations.....

My 53 model (with a firewall mounted Odyssey) is about 1650 empty.
CG crowds the forward end of the envelope--
in fact, when empty it's just out of the envelope.
But since everything I put in is aft of the empty CG,
it's in (barely) even with only 10 gallons of fuel & a 170# pilot.
It handles just fine when lightly loaded & just me aboard,
and I have no problem landing 3 point even with full flaps.
A more-aft CG should make it cruise faster & stall slower,
but this way I have extreme flexibility when loading it up.

Thanks for the feedback everyone, this is excellent information to chew on. I fly solo most of the time, I try to fly light.

If I was to go flat floor it would be for the weight savings of the lighter battery and reduced battery cable length, which can be considerable according to what I've read. I do fly with survival/safety gear, but probably nothing like with what the Alaska guys fly with. I already fly with a bag of tube sand up against the rear bulkhead all the time, I'm afraid the modification would actually cost me weight because I would have to offset the forward placement of the battery with more ballast.

Related question - in this mod does the Oddessey battery go on the engine or cockpit side of the firewall?

Engine side.

So, it appears you’re reluctant for reasons you’ve noted, to move the battery. But, you’d like an extended baggage.

Why not leave the battery where it is, roughly, replace the existing battery with an Odyssey battery, AND install an extended baggage?

Seems to me that any mechanic worth his salt could figure a way to get that done. When I installed extended baggage in a 170, we put the ELT UNDER the baggage floor, with an access door. The Odyssey battery, laid on its side (it’s sealed) is no thicker than an ELT.

So, why not stop worrying about fwd CG and innovate?

MTV

Thanks for the input, MTV,

The question isn't whether or not to install extended baggage, but whether or not to relocate the battery. Extended baggage kits are available in both versions for my aircraft so that's not a major concern.

I moved the battery forward on a 1958 182 that I used to own and loved the result -- more and flat storage area, elimination of energy robbing cables, warmer battery for cranking, etc. I did notice that my CG was so far forward that I needed to make an adjustment. My mechanic installed a 10 pound lead weight in my tail cone. Combined with the long moment arm, this more than compensated for the forward shift in CG resulting from the battery relocation. I strongly advocate moving the battery to the firewall.

CParker wrote:Thanks for the input, MTV,

The question isn't whether or not to install extended baggage, but whether or not to relocate the battery. Extended baggage kits are available in both versions for my aircraft so that's not a major concern.

I’m totally in favor of moving the battery as I noted earlier. But your latest post seemed to me to suggest that you had already decided against moving it.

We replaced aft (crappy) batteries in Huskys with Odyssey’s in same place. Worked fine and didn’t change CG.

And, with the Odyssey, you could probably mount under extended bag, and have flat floor. I hate adding lead for ballast.

MTV

CParker wrote:Thanks for the input, MTV,

The question isn't whether or not to install extended baggage, but whether or not to relocate the battery. Extended baggage kits are available in both versions for my aircraft so that's not a major concern.

Have you calculated the new W&B with the firewall battery?

The cranking performance is so much better it's crazy.

I haven't, I'm at 35.2" @ 1761 empty. That's with 10 lbs of lead in the tailcone already. I'll run some numbers to simulate and see where it comes up. I was at 34.1" before the lead. Forward limit is 33," if my memory serves me right. I'll also run it with my standard kit of tools and survival gear at the extended baggage arm to see what the balance is.

I'm definitely not an expert on any of this, and I don't intend to seem combative by any means, I'm just skeptical of the benefit of moving that weight forward and making an already nose heavy airplane even more so, but at the same time the extra cranking power and weight savings look awfully nice. I'm just the kind of guy that likes to know all the data to make an informed decision.

There is a lengthy post on this site, I forget who wrote it, I read it a couple days ago and it talks a lot about moving the W&B further forward as a result of reducing weight and how it's a fool's errand. The post made a lot of sense to me. I was planning on rebuilding my front seats to reduce weight since they need attention anyways, and replace engine accessories with lightweight versions as they come due, but it doesn't seem like many other modifications for weight reduction are worth it. My instrument panel is already pretty clean.

Add a MT prop to the equation and see if that helps...

I would wonder whether the Oddessy has the power to crank from the extended baggage (original battery location). Mine is under the copilots seat, and it's not that energetic. That said, the cables are light.

I am keen to move it to the firewall, once its possible. Innovate, when paperwork allows.............

Battson wrote:I would wonder whether the Oddessy has the power to crank from the extended baggage (original battery location). Mine is under the copilots seat, and it's not that energetic. That said, the cables are light.

I am keen to move it to the firewall, once its possible. Innovate, when paperwork allows.............

I'd be curious about that as well. On a Citabria with an 0-320 it works, but not a ton of extra cranking power. A big 470 might be a touch crank.

Nizina wrote:My mechanic installed a 10 pound lead weight in my tail cone.

Is this legal? I’d love to do this - would happily give up 10# in UL for a more reasonable empty CG.