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Battery Location

T

tjett

Member
I am getting ready to buy the Vans Wiring kit for my RV8. I need to decide on the fwd or aft battery wiring kit. I am putting in an IO 360 and Hartzell 72 inch "blended airfoil" constant speed prop. I talked to Van's, they recommend the fwd. They stated that with this engine prop combination it works best for the CG. Pilot is behind the CG in the 8 and with the pilot at 205 lbs. large passenger and the battery in the aft CG goes out aft. They did say that with the 200 hp engine the aft battery works best. Makes sense to me but wanted to here what you all think before I order the wiring kit. :)
 
Back

I'm putting mine in the back, I have an IO-360-A1A (200hp) with inverted oil and a hartzell. Lots of posts on this subject so you should find your answer.
 
Vans seem to concentrate on the engine as the main factor. Given the greater arm, the use of the (heavy) Hartzell v a FP or light CS I'd have thought a more significant factor?

We have 180HP IO and Hartzell and Battery in back. Ideal for us :) A search on this forum will give you lots more info / factors...

Andy
 
I have the same setup as Andy, and the back worked out best.

I think with a lighter prop, the firewall would be good, but not with the heavy hartzell.
 
Put it in the back. Danny King told me this after I put mine on the firewall. He was right...it works best in the back. I have a RV8 with your same combination and I weigh 175 pounds. I can carry a 237 pound passenger and just be within the rear CG envelope with no baggage.
 
I have always agreed with Danny on this - the aft mounted battery makes the most sense in an -8 with a Hartzell. The truth is that the Odyssey is just not that heavy of a battery , considering what you can carry in the baggage compartment. Louise and I throw our two travel bags back there, our two laptop backpacks in the forward, and hop in for more than a week's travel without an issue!

Of course, neither of us weighs 237 lbs....;)
 
Firewall

It's apples and oranges I know, but my previous experiences with C-185 in bush flying was the forward battery was best.

We had two 185's with back batteries and two with STC for firewall mount (which we did). Night and day as far as W&B. What you're dealing with is basic mechanics of leverage (arms).

I weigh 210 and tall. Most of my buds are over 170. Add a 20-40 lb weight in the back and the moment becomes quite large as I see it. Baggage?

Also I have a O-360 with FP as a consideration.

Plus remember you also have to run a long cable a long way with battery in back.

Not saying back battery is bad in an 8 (who am I to say such:), as this is by first 8 to build), but I am just relying on my previous hands on experiences.

I will be putting mine on the firewall.
 
I have a heavy engine, and went with the battery in back. I'm not done building, so no weight and ballance yet, but I do know one thing: That #2 welders cable reccomended for starting duty is heavy, and 6 feet of it adds up.
I'm not adverse to moving it forward if the W&B permit it later, but I think it was best to build it in back while it was easy. Pulling out the tray, cable, contactor and wire to move them forward won't be as hard as going the other way.
My .02
 
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a builders choice

My 1st RV8 had the 180 hp engine w/ CS prop, a smoke system in the front baggage area and the battery in the back.
My 2nd RV8, currently still being completed, same engine, prop & smoke system, has the battery in the front.
My thoughts are:
Initially the RV8 seemed a little tail heavy on final. (I ended up increasing the Horiz Stab incidence to fix that.)
Passengers in the back made the plane really sensitive on landing, requiring too much extra landing speed for good control.
Long #2 cables from battery to starter and bus.
The #2 cable had to go through the spar, along with everything else.
Had to penetrate the FW for the #2 wire to get it to the starter.
It was easier to go out the rear CG envelope.
Poor access to the battery.

With the battery in front:
Shorter battery wiring.
Fewer large firewall penetrations for cable. (Actually, none in my case. I modified the external shunt, from the volt meter, to have the main stud penetrate the FW so I could bolt on both sides for main power.)
All #2 wire is ahead of the FW.
Much easier access to the battery.

I really think it is a personal decision. I went through a bunch of W&B calculations, based on several planes W&B, and made the appropriate calculations to see the difference. Both ways work fine, but you may have operational preferences that point you one way or the other. (But, I agree that with the angle valve engine, the battery should go in the rear.)

In the future, I'll carry my tool kit in the back baggage when solo and move it, as appropriate, with passengers. For me, the battery on the FW is the way to go.
 
Thanks

Thank you all for sharing your thoughts, ideas and views. They all make sense. Also a thank you to Doug Reeves for putting the sight together. Building an RV without the site would be a bummer for me. I like to learn from folks who have been through it.

Tom Jett:)
 
Tom:

I have the "lighter" engine -- an O-360 A1A with Hartzell CS prop. I put the battery in back and I'm glad I did. Even with the battery back there, my -8 is a bit nose heavy. I'd hate to think what it would be like if the battery were forward. I weigh 165 and usually fly alone. With passenger the airplane flies better -- seems better balanced.

My vote is for battery in back.

Chris
 
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Some factors to consider re Battery Location:
  1. RV-8 difficult to 3 point with Fwd CG, especially fwd of 80.0" - so are you someone who likes/needs to do 3 pointers, and will fly solo fairly often? Wheelers clearly are happy with Fwd CG.
  2. RV-8 unpleasant (relatively!) to Aerobat with Fwd CG. Our Basic Wt/CG is 1106/78.59", and for solo display type stuff, I secure 55lbs in the rear baggage area, it is much easier/nicer, but still better 2 up.
  3. A colleague built an IO 180HP Hartzell VP prop with Fwd Battery and came out with 1102/75.86". With 190lbs in the front seat and nothing else he is out of Fwd CG limit unless he carries rear ballast/baggage :(
  4. I know 2 people (both IO 180HP / Hartzell) who have moved battery from front to rear. I know nobody (anyone here?) who has moved battery from Rear to Front. Not a direct comparison but see Randy's RV-3
  5. With our 1106/78.59, 180lb in front, I need a Pax weighing 265lb to get to aft CG at lowish fuel.
  6. Baggage is not a big factor, since if you were embarrassed for (rear) CG, you can redistribute the weight to the front baggage area.
  7. It is a "fact of life" that rear CG gives a nicer handling / more fun / less stable aeroplane to fly. Fwd CG gives a boring / stable IFR type platform - ideal for certain "missions", but not really what we want in the RV community :D
Andy
RV-8 G-HILZ
RV-8tors
 
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rear battery cable weight NOT an issue

When you pick up the #2 battery cable that runs from the rear battery location to the starter relay, you think, "Oh my, that's heavy". So I weighed mine.
It weighs just over 2 lbs. So I would not let that influence your choice.

I definitely would mount the battery in back with the Hartzell prop.
 
Andy, I think you have a typo in point #4

4.I know 2 people (both IO 180HP / Hartzell) who have moved battery from front to rear. I know nobody (anyone here?) who has moved battery from Front to Rear.
 
Lithium Battery's

Looks great it they work well and last long enough to make the price somewhat comparable to lead acid. What do you all think?:)
 
Check the charging system requirements

Sounds interesting to me, too; however, I'd like to know more about how it interacts with the charging system. From my experience with electric RC airplanes, the lithium batteries use a special charger to recharge them. Additionally, they hold their charge a lot longer, once charged. It could be that racing vehicles don't have a charging system and these batteries are used because of that. I don't know.
My assumption would be that these batteries are compatable with our alternator systems, but that wasn't stated on the site.
Worth some additional investigation before you plunk down the cash.
 
That's what I love about Homebuilts!
Imagine getting permission to put one of these in a certified plane??!
I have an Odyssey in my RV-8 project now, but I'd switch to a Lithium Ion in the future, if it favors the weight & ballance.
 
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