Hello all, I couldn't find the average weight saved by installing a firewall mounted battery on a early model 182. Does anyone have a rough estimate of the amount of weight saved by moving the battery from the back of the plane to the firewall? Thanks and sorry if this has been gone over before.

It's about 30 lbs by the time you pull the cable and everything.

akaviator wrote:It's about 30 lbs by the time you pull the cable and everything.

Yup. On my 62 180 it was 35 lbs.

I can't vouch for it's accuracy, but the W&B revision for my 180 when the firewall Odyssey was installed shows:
battery -28# @ 114"
batt box, solenoid, drain -3 @ 114"
battery cable -2 @ 56"

battery box (early Burl's) +2 @ -2"
odyssey battery +14.8 @ -2"
solenoid +1 @ -1"
new cables +1.5 @ 0

Net change 13.7#.
On this airplane, it moved the CG forward about 1.92".
Hope this helps.

Wow, thanks guys for the responses. Those are some significant savings!

Great mod, but nothing is free. (CG)

Yes, the savings is nice, but I think 35 lbs might be a bit dreamy. The Concord bat I removed in the back was 29.8 lbs. The Odyssey is 14.5. Stock battery box removed was 2.43, FA Dodge I installed was 2. Shore power plug removed was 1, battery cables removed were 3.4, new cables installed were 1.2. Presumably you will also be removing the hat shelf, brackets, and cross bar which weigh 3.35 lbs together. I have installed 3 selkirk EB's so far, and my advice FWIW is to go with Hitchcock. Stronger, easier to install, better fit, MUCH better made, AND more than half the weight. Selkirk is 11 vs/ the 5 for the carbon fiber. Net weight savings for moving the rear bat and installing the CF baggage is just over -17, and as Hotrod says, be prepared for a CG move. Not uncommon to get the A/C out of the envelope... Make sure you have the correct size cables with correct ends made up. Some have talked about using 4g, but the book calls for thicker. Use 0 or 1. Bogart makes very nice cables and is worth it. A good time to replace the two solenoids also (keep one old as a spare in your tool kit. Hope that helps...

bigrenna wrote:Great mod, but nothing is free. (CG)

Yes, the savings is nice, but I think 35 lbs might be a bit dreamy. The Concord bat I removed in the back was 29.8 lbs. The Odyssey is 14.5. Stock battery box removed was 2.43, FA Dodge I installed was 2. Shore power plug removed was 1, battery cables removed were 3.4, new cables installed were 1.2. Presumably you will also be removing the hat shelf, brackets, and cross bar which weigh 3.35 lbs together. I have installed 3 selkirk EB's so far, and my advice FWIW is to go with Hitchcock. Stronger, easier to install, better fit, MUCH better made, AND more than half the weight. Selkirk is 11 vs/ the 5 for the carbon fiber. Net weight savings for moving the rear bat and installing the CF baggage is just over -17, and as Hotrod says, be prepared for a CG move. Not uncommon to get the A/C out of the envelope... Make sure you have the correct size cables with correct ends made up. Some have talked about using 4g, but the book calls for thicker. Use 0 or 1. Bogart makes very nice cables and is worth it. A good time to replace the two solenoids also (keep one old as a spare in your tool kit. Hope that helps...

Call me dreamy all you want. I started with my plane at 1760.5lbs @34.5in CG. I did the FWF odyssey battery in the FA Dodge box, replaced the ELT with a newer 406, threw out the rotten old 7.00x6s and put a set of 8.50x6s on. She now weighs 1725.7lbs @32.38in CG. I never did good in math, but this is pretty easy and works out to 34.8lbs. Pretty damn close to 35...

David

You guys convinced me to purchase the mount. I just got off the phone with Burl and ordered one of his Burl Firewall Battery Boxes. Should be here in the next week! Looking forward to the weight savings.

All I can comment on is my own personal experience. The numbers I posted are exact numbers as I weighed everything I removed and added. They were a pound for pound comparison on what was removed vs what was installed, not a net figure on the scales post augmentation. I too got rid of a legacy ELT and went with the ultra-light Kannad ELT. That savings was only 4 lbs, so I guess if I included that, the net savings for the work back there would be 21.

This is not directed towards you David in any way, but I can say from personal experience, that weight saving claims are easily tossed around the internet. The reality is usually half than the hyperbolic rhetoric. I have spent a lot of quarters and even more time trying to get my Skywagon as light as possible. There was what I wished, and there is what was. Pretty big difference for me.

Perhaps you did save 35lbs which is awesome. For me, in my 66 H model, I removed 36.63lbs (incl battery, battery box, shore pwr plug, fuse assy, and all cables to the starter solenoid.) In its place, I added 15.7 lbs of box, bat, and 6' of 1g cable. My savings was 20.93. Removing the hatshelf + brackets + canvas rear bulkhead was about a wash with the CF EB. Saved just under 4 with the Kannad.

(All comments made with love and are not meant to be confrontational)

I really appreciate the hard work you put into your wagon Greg. I wasnt meaning to be confrontational, just wanted to explain the numbers. Like you, I can only comment from personal experience. I didn't weigh every single piece. I figured 8.50s are heavier then 7.00, but called it a wash. The 4 lb ELT difference is more then I would have expected. So call it 30 in savings on the battery for my plane. I did not install an EB yet, but its high on my list. It's interesting to see how different it can be from one plane to the next. Looking forward to hear how much you save TX.

When doing this mod a year ago, I read as much as I could. Most are for and some are against, but I have been pleased with the results. Lots of people will make bold claims, but I think it is likely you will save somewhere between 15-20 lbs. (I was near the 20 lb mark.)

Most do the mod to install a "flat" extended baggage area, and the useful increase is an added bonus. Like BiggieR, I HIGHLY recommend the AirGlas carbon fiber kit from Hitchcock Aviation.

We did the same thing with the '54 180 and saved 19 pounds with that mod alone. To help the CG not to move forward as much we replace the old starter with a light weight sky tec. That alone saved another 10 pounds in the engine compartment. So we added 16 pounds to the firewall and lost 10 pounds so the net effect was only a 6 pound addition. The only other mods out there that can save you that kind of weight will cost some major $$$.

This is a great mod if your CG is not real far forward. I would do it again.

+1 on the Sky-Tec. Would do that again in a heartbeat.

Moving that bat really does adversely effect the CG so be prepared. FWIW, the starter is only around -7" so the savings there really doesnt change the CG very much at all. I also did the MT (not really for the perf, but to rectify the CG) For me, I found a net difference of 7lbs for the starter and 14 for the 2 blade prop. Changing both from stock moved the CG around 0.6" or so. My CG is still fwd, but def out of the red zone and now manageable.

Side note: You can also run w/out any oil. This will save you 22 lbs at -15. Short lived, but great mod for the real light weight freak.

That 35 lbs of weight that was back there should be replaced with 35 lbs of survival gear, etc. to get the CG moved back again.

This is a great option, but like others have said you will see/feel a significant cg move forward. Flying my 185 empty I now roll the trim all the way aft during landing to neutralize the yoke pressure. But. Having just come back from my trip to CA and back, with a week and a half of stuff for two people in the back, plus two sets of golf clubs, fishing rods, waders, boots, vest, survival kit, toolkit, tiedowns, etc - the balance was perfect at cruise and only rolled a little over half way aft during landing. Love it.

As far as new battery cable size is concerned check your aircraft model/year Service Manual wiring diagram. For instance on my 185 the wiring diagram calls for a 4 ga wire (R-PA1) from the battery to the battery contactor (located on/near the battery box), and a 2 ga wire (R-PA4) (because of the long run) from the battery contactor to the starter contactor, and 2 ga wire (R-KA2) from the starter contactor to the starter. Since we eliminated the long run of cable by mounting the battery on the firewall, and changed from the higher current draw Energizer to the lower current draw Hartzell M-Drive, we used 4 ga as that is the appropriate wire size in this case when current/length of run is calculated.

However, I have since replaced all the cables with 2 ga as part of trying to understand the new Hartzell M-Drive Starter random hot start problem. Our thinking was perhaps the 4 ga cable, once heat soaked, was loosing amperage. That ended up not being the case. 4 ga is ample, but since I've already replaced it with 2 ga, and I might end up putting the Energizer Starter back on, I'll just leave it be for now.

It is important that you only use wiring that is designed for aircraft. They have a much higher number of finer strands when compared to automobile wiring of the same gauge. This allows for a smaller gauge wire in aircraft to carry a higher current load then the same size automotive wire. Current travels on the outside of the strands, so the more strands you have in a wire the more current it can carry.

Barnstormer wrote:Current travels on the outside of the strands, so the more strands you have in a wire the more current it can carry.

I am nit-picking here, but the "skin effect" where current travels mainly along the outside of a conductor is only true for alternating current. DC current flows uniformly across the cross-section of the conductor. I'd suspect the primary advantage for more, finer conductors would be for flexibility and vibration resilience.

A1Skinner wrote: ... I started with my plane at 1760.5lbs @34.5in CG. I did the FWF odyssey battery in the FA Dodge box, replaced the ELT with a newer 406, threw out the rotten old 7.00x6s and put a set of 8.50x6s on. She now weighs 1725.7lbs @32.38in CG. .....

You've probably already done this, but I'd do a few sample load calc's based on a lightweight pilot and minimum fuel. My airplane came in at 1693# & 34.73" with 5 gallons unusable fuel (that's 1663 and 34.49" empty). With another 5 gallons & a 170# pilot on board, it's at 1893# & 35.05"-- just barely inside the 35" forward CG limit for my 1953 model. That 170# ship sailed on me a long time ago, and I don't plan to ever be down to 5 gallons usable, but it is something to think about. My airplane seems to fly just fine at that weight & CG, it even flares into a 3-point with flaps 40 which I've heard some people have trouble with.

As was pointed out on another thread, the CG envelope was expanded for later models to a 33.5" forward limit. So if you have one of those later model airplanes, you're probably golden. It just pays to check. Oh yeah, looking at the loading graph I'm reminded that as the weight goes up, at a certain point the forward CG limit moves aft. With my airplane, that point is 2050#.

My 66 Skylane is already very nose heavy with the Pponk and 3 blade so when I switched over to the small battery I left it in the stock location. Still saved 10 + lbs (ish) and didn't add any more weight to the nose. I did this a few years back and have had no issues.

I've made over 120 firewall mounted battery kits and installed 20-30 myself. Typical RG 35 battery comes in at around 30lbs. , box ,mount and battery senonid funds about 3.5 lbs. Old cable from aft battery box forward to starter is about 7-9 lbs. All together 41.5 or near about . Firewall mounted battery (SBS-J16 ) is 14 lbs. The EDM battery box and mount weight is 1 pound on the money,add another 2 lbs for #2 wire and senolid = difference of 24.5 lbs or about 6 gallons of fuel. Better starting / cranking to get that beast moving .

One of the things I've learned with my airplane's many modifications is that rounding figures and just plain mathematical errors can make a huge difference. Ultimately after so many modifications, my airplane's calculated weight and balance disagreed with its actual W&B when it was actually weighed. All that FWIW.

Cary