My C170B has a TCM IO-360 with the McCauley constant speed prop (XP Mods STC) and thus the CG is a bit more forward than I would like it to be. At the time I did the engine STC, I also moved the battery to the tailcone using the Del-Air STC. That helped. We also added a lead brick at STA 200. Worked out OK for the last 15 years.

Moving forward to 2015 I want to add an extended baggage to the airplane. Best choice seems to be the carbon fiber Air glas floor which is now available for the 170 under an STC. Problem is the battery box intersects the floor of the extended baggage and the STC paperwork specifiys that the STC is for 170s that still have the battery on the firewall. The Odyssey dry cell battery would fit under this extended baggage floor, laying on its side.

After a careful reading of AC 43.13-2B, Chapter 1 (structural data) and Chapter 10 (aircraft battery installations) it seems that I can fabricate a battery mount for the Odyssey dry cell battery, run a static load test on it to the Ultimate Loads per Ch 1 sections 103 to 105, and follow the battery installation checklist in Ch.10 and get this approved as a minor alteration.

AC 43.13-2B states in the first paragraph that 'this data generally pertains to minor alterations, however the alteration data herein may be used as approved data for major alterations when the AC chapter, page and paragraph are listed in block 8 of the 337'

My questions for the group:

Has anyone successfully done this (odyssey batt in the tailcone) as either a minor or major alteration on a C-170?

Am I out of my mind thinking it can be approved? As a minor alteration I should only need approval from my IA, right?

Note - there is virtually no weight or CG change when I do the battery and the extended baggage together as the lighter battery is offset by the added extended baggage floor. (again, I have the lead acid battery back there already)

Thoughts??

Cheers,

Pete

I'm planning to do the 360 conversion to my 170 as well so I'm interested in how this goes down.
Already have FWF set up. The only delay is, I found another 170 to restore and Im going to hang the motor on that one.

Is the CG that far forward after the conversion?

Pete,

This is likely to open a can of worms but believe me when I say I have thoroughly researched and confirmed this nine ways from Sunday. Because the Type Certificate Data Sheet for the Cessna 170, 170A, and 170B stipulates the weight of the battery, the only battery that can be used is one within (I can't remember the exact numbers but can find them) a couple of pounds either way. Unless of course a STC exists THAT INCLUDES THE BATTERY as part of the STC (not just suggests one to use), or you get a field approval. I'm not a 170 guy so don't know if a STC that includes the battery exists. Others will. Just remember the STC has to include the battery, just mentioning one in the instructions isn't enough.

Assuming there isn't a STC that includes the battery you'll need a Field Approval for the Odyssey if for no other reason then because the weight doesn't fall with the weight range allowed by the FAA for a replacement battery for the 170, 170A, 170B (because the TCDS specifies a weight).

How do I know this? Because my Stearman's TCDS specifies a 41lbs 12v battery, of which none are produced even close to that weight. So my Stearman, like nearly all others out there, needs a Field Approval for ANY battery install. I doubt very many have field approvals, but Stearmans are 70+ years old and aren't falling out of the sky so the FAA probably could care less.

The 180/185 TCDS does not stipulate battery weight so one can install any 12v aircraft battery of any weight (of like type) without a Field Approval.

In closing I will mention that the FAA has given us a very powerful tool for maintaining our certificated aircraft called "Owner Produced Part". Of course one has to adhere to one of the definitions of "Owner Produced Part" for it to be an "Owner Produced Part". And then assemble, document and log per the regs. Worth reading about and REALLY understanding the regs.

Sorry for not answering your ACTUAL question. Good luck and have fun.

I don't see how original battery weight makes a bit of difference since the battery is no longer in the original location. I don't think I'd even mention TCDS battery weights when talking to the Feds about this.

My Concord battery certainly doesn't weigh 23 pounds and that went in with a log book entry.

Okay, I'll say it.....get rid of that heavy propeller out front, and install an MT prop. You'll get better thrust, MUCH better CG, a lot less weight overall, and you can get rid of useless ballast weight.

Hell, it's only money.

MTV

mtv wrote:Okay, I'll say it.....get rid of that heavy propeller out front, and install an MT prop. You'll get better thrust, MUCH better CG, a lot less weight overall, and you can get rid of useless ballast weight.

Hell, it's only money.

MTV

I don't believe there is an MT prop STC'd for the Continental IO-360.

mtv wrote:
Hell, it's only money.

MTV

That's an argument that doesnt work that well with my wife.

robw56 wrote:
I don't believe there is an MT prop STC'd for the Continental IO-360.

You're right. Not yet anyway. And that would cost 10-15X what I am spending for ext baggage.

Not a 170, but I got a field approval to replace the G25 battery in the back of my C150/150TD with an Odyssey a few years ago. Like your XP Mods-converted 170, the engine upgrade STC on the 150 called for the battery be moved aft for CG purposes. If the extended baggage floor & battery change offset each other weight wise so your CG is still OK , sounds like it oughta work just fine. I sold my 150 a year or so ago, but if you want a copy of the paperwork you can get the aircraft records CD from the FAA for ten bucks. N4430U. Or PM me & I can give you the contact info for the current owner, he might be willing to just photocopy it off for you.

Re approval, I think the new mount will be more of an issue than the battery change itself. I don't know what you mean by "static load test", but I suspect that's electrical load. I know someone who aft-mounted an odyssey in a hot-rodded champ & had to do a g-load test on the battery mount-- which consisted of putting a fish scale on it and pulling it 3 g's worth (45 pounds or so, as I recall), to make sure the mount would hold it in a 3-g crash.

No, I meant static mechanical load. paraphrased below.

Pull on it from center of mass with a fish scale/load cell, etc forward, up and sideways at the specified loads. 3g up and sideways, 18 g forward for 'objects of mass within the cabin' which would be about 270 pounds. Must hold load for 3 seconds without permanent deformation of structure.

Would love to see that paperwork Hotrod180. PM sent.