Battery on Firewall?

[NunavutPA-12]

I’ve been thinking I’d like to extend the baggage area on my Experimental PA-12-160 or …..create a second baggage compartment with access only from the outside. This would involve moving the battery, and probably the ELT.

Are there any concerns with moving the battery (PC-680) to the firewall? I’m thinking it would shorten up the wiring, make the battery more accessible and if I ever get the ‘plane on skis the battery would be in a nice warm area while the engine is heating.

I might move the ELT to a position under the pilot’s seat, unless that’s not a good idea (?)

I figure the weight of the new baggage compartment floor, rear bulkhead and external door would probably balance the relocated battery and ELT, and if not I could always stow the survival kit and tools in the aft area.

Comments from the experts?

 

[NunavutPA-12]

Delete

 

[cubunltd]

First thing i would do is calculate your weight and balance and determine from there where the best place would be for the battery. Are you using a standard battery? or an odyssey? standard battery on firewall may be too much. depends on the weight and balance of your 12. odyssey or similar battery may be best under front or rear seat or on firewall depending on YOUR weight and balance.

john

 

[NunavutPA-12]

Thanks John. Yes, I'll do the calculation. For now I'm just wondering if, other than W & B, there are any good reasons NOT to put the battery on the firewall or the ELT under the pilot seat.

I got rid of the Gill last year and replaced it with the smaller and lighter Oddysey.

I think there would be plenty of room on the firewall since I don't have a muffler. Also, I have metal belly panels so it shouldn't be too hard to create the aft baggage compartment and door.

 

[NimpoCub]

+1 for what John said.
Moving your battery (~10'?) forward will really change your W&B. Even the 680.
I moved mine (680) from behind the bulkhead to under the seat, put on the lightweight starter & alternator, stowed all my "permanent baggage" back with the ELT & I'm still on the forward side of W&B. Good for hauling loads, but when empty/light, my horiz.stab is trying to pull the tail down (bit of extra drag).

 

[cubunltd]

Other than weight and balance i see no harm in mounting the battery on the firewall. After all cessna does it. As far as the ELT put it somewhere where it won't get dammaged in an accident.

John

 

[Aviator]

Personally, I like the ELT easily accessible with quick disconnects so I can grab it on my out in a hurry. Don't know what the odyssey's environmental limitations are, but if the max exposure temp is less than about 350* you might have to box it. (Don't neglect exhaust stack radiation). Other than that and the W&B thing it's a win-win move. Stress the mounting for about 150# in all 3 axes.

 

[sierra bravo]

My Oyssey has partial enclosure in close proximity to a TCM 520 and it's exhaust in a C180 and it's never dislayed the slightest indication of heat stress. For all things other than CG the engine compartment is the ideal place for a battery. If it breaks loose in an accident I couldn't care less as long as it's in front of me.

Who produces a 406 ELT with a carry-along antenna? If anyone here read the reports of last week's 170B accident at Puntiila Lake did you catch the part where they reported the Air Guard got the 406 signal and validated it before the many ground-based witnesses called for help? Pretty cool stuff. Enjoy those 121.5s that so many of you keep in your planes. Alaska is turning off DF steer equipment. 121.5 just got even more obsolete than it already was.

 

[Aviator]

Who produces a 406 ELT with a carry-along antenna?

Here's 1 ameri-king.com AK-451

 

[Aviator]

I wish. Still on 121.5/243

 

[jk]

EBC makes one that is BNC connected with a rat tail mounted on the side for portable ops.

 

[mike mcs repair]

there is TONS of room in the sides of the boot cowl for the battery....

 

[NunavutPA-12]

Thanks all for the advice.

Looks like I may have to look into using one of these to avoid C of G problems

http://earthxmotorsports.com/products-page/etx-batteries/etx36d/

 

[Crash]

I’ve been thinking I’d like to extend the baggage area on my Experimental PA-12-160 or …..create a second baggage compartment with access only from the outside. This would involve moving the battery, and probably the ELT.

Are there any concerns with moving the battery (PC-680) to the firewall? I’m thinking it would shorten up the wiring, make the battery more accessible and if I ever get the ‘plane on skis the battery would be in a nice warm area while the engine is heating.

I might move the ELT to a position under the pilot’s seat, unless that’s not a good idea (?)

I figure the weight of the new baggage compartment floor, rear bulkhead and external door would probably balance the relocated battery and ELT, and if not I could always stow the survival kit and tools in the aft area.

Comments from the experts?

Might want to read this thread. http://www.supercub.org/forum/showthread.php?44024-Another-Light-Weight-Battery-Option

I don't think I'd want the mount a 15lb block of lead that far forward in the CG. Your extended baggage will not effect the rear CG enough to offset it.

I know in my current Cub, when I changed to an O-360, it made it real easy to go over on the nose with nothing in the extended baggage. Some situations don't allow for having "move-able ballast" on board to keep in the aft baggage, or you just forget. An example is when hauling a moose out and you take everything out of the plane (short take off area) to load the moose in. When coming back (now empty) it gets real interesting.....

Take care,

Greg

 

[PerryB]

What engine mount are you using? If its a stock length mount I would NOT put the battery up front. I have a Kenmore-12 (stock length) with ext. baggage and an under-seat battery, and I have put a 7.5 lb ballast weight in the aft empenage to get the c.g back where I like it. My ELT is at the rear of the ext baggage area. With an adult male in the back seat and a duffel bag in the ext baggage its perfect. The plane just went in for teardown/rebuild and is most likely going to get a Crosswinds STOL short mount put on it. I think under the seat is the best place for the battery. Nose heavy Cubs are self-defeating because you run out of elevator while the wing is still producing good lift. What is your empty C.G. using the leading edge as the datum point? A nice flying 12 (or any Cub for that matter) will be at least 12", if not more.

 

[aviationinfo]

Perry---

I assume you have the '18 horizontal stabilizer and elevator? My EWCG is about 10.5 and even with only myself in the airplane I never run out of elevator in the flare. I do however run out of nose up elevator trim in that case but the stick force is easily manageable.

 

[Gordon Misch]

I have the short mount on my 12, with O-320, Borer prop, Skytec starter, Plane-power Alternator and Sutton exh. Odyssey battery under rear seat.

My EWCG is 12.6, and I wouldn't mind it being a little farther aft. I load it as far aft as I can in the extended baggage, to reduce the drag-inducing tail-down trim setting. I do have sufficient elevator without messing with the trim, even completely empty and minimum fuel.

It's pretty darn tough to load the plane such that the loaded CG approaches the aft limit. Loading as far aft as I can (and still be practical) there is good pitch stability (as evidenced by stick force). If I were to do it again, I might well move the battery farther aft, though it's very convenient where it is.

With 30 gal of gas, me in the front, an "FAA person" in the back, 50 lb in fwd baggage and 40 lb in aft baggage, my spreadsheet computes CG at 18" (aft limit is 18.6"). This hypothetical loading would be a little overgross though.

With minimum gas (<10 gal) and just me in the plane, my spreadsheet puts the CG at 12.0.

 

[Larry G]

there is TONS of room in the sides of the boot cowl for the battery....