jferraro17

jferraro17

Opulence, I has it...
I've come to the point where I need to make a fore/aft decision on the battery. I've searched multiple ways in these forums. I've also played with a few cg calculators...unfortunately, I have very little GA experience, and even less dealing with CG scenarios in a light airlplane. So the call goes out to trusty 'ol VAF ...


-8A
0-360/180HP
Catto 3 Blade
Glass panel
230# pilot

I'm concerned about aft CG scenarios...wife (135#, don't tell her I posted that) in back for aerobatics, or loaded up for x-country and burning fuel off. However, I *think* most flying will be solo, local aero type stuff.

Which location gives me the best options? Anyone with that exact setup?

Thanks to the knowledge pool, as always!

Joe
 
no worries

our planes are very similar. am using 180hp O360, single dynon, 220 pounds of nordic dynamite (me), metal prop, PC680 on the firewall. doing the math reveals no drama. have noticed that the pitch response is quite different with varying CG.
 
Joe,

Pilot weight isn't goiign to make much difference. Other than that, I have the same engine as you do, but the heavier Hartzell Prop. At any rate - aft mounted battery, and I've had 280 pounders in the back - not doing Acro of course!

The truth is, the odyssey battery is pretty light - I like mine in the back, and would do it again - keeps a clean firewall, and the CG aft.


Paul
 
CG

Ironflight said:
Joe,

Pilot weight isn't goiign to make much difference. Other than that, I have the same engine as you do, but the heavier Hartzell Prop. At any rate - aft mounted battery, and I've had 280 pounders in the back - not doing Acro of course!

The truth is, the odyssey battery is pretty light - I like mine in the back, and would do it again - keeps a clean firewall, and the CG aft.


Paul
Click to expand...

Joe:

I ended up with an angle valve lycoming up front which adds about 40lbs at the engine CG. I put an Odyssey 680 aft. which works well in my situation. My wife and I are "standard+" on the FAA scale. (Hope she doesn't see this post too!).

We can load the plane (1120lbs EW) with full fuel, us and 125 lbs of baggage and only go slightly out the top of the envelope. I've never done this of course.:rolleyes:

I think that if I were you, I would put the battery in the most convenient place and adjust the baggage load to suit.

If you're solo, full fuel at your weight, you may want to add ballast in the rear. Isn't this confusing???????????????
 
Thanks guys. It is confusing for my little brain...sure miss the Loadmaster!

I know Paul and Mannan are TWs, but even though (or because?) I'm an -8A, I still think the aft location is going to work for me...certainly for the day to day flying.

Guess I could always move it, down the road, if it proves troublesome. Besides, I really want to do that aft baggage floor mod;)


Joe
 
Joe
Just to echo what others have said, I have an 8A with:

O-360
Hartzell
Aft PC-680
Empty wt. 1123#

When I am solo with no baggage my CG is right at 80" and the forward limit is 78.7 so if I had mounted the battery on the firewalll I would have probably had to carry ballast to fly solo. Also working on the back of the engine would be a PITA with the battery box in the way.

Installing the aft battery and running the 2 ga. wire under the floor is more work initally but worth the effort.

Paul Danclovic
Jamestown NC
 
There are always going to be many opinions on this issue. You can go either way you want. In the end you can't go wrong if you simply accept on faith the advice Van's offers. They designed the airplane, they know best what the proper battery and battery mounting location is for your particular engine/prop combo. I contacted, then heeded Van's truly informed advice and am glad I did. Van's own sample weight & balance sheet assumes 44 pounds on the RV-8 tailwheel. With the Odyssey battery mounted on the firewall per Van's suggestion, my airplane enjoys 66 pounds back there and a very short battery cable run in the bargain.

n4tijm.jpg
 
FWIW, I bought a wrecked 8a with a 180 HP and a hartzell 2 blade. It had the battery on the firewall. It must not have worked out too well, because the builder had bolted a chunk of 1" thick steel on the deck where the horizontal stab is attached, most likely to correct the cg. (I can't imagine any reason to add weight to an airplane other than that)

I would go for the rear setup--keep the weight off the nosewheel.
 
I contacted, then heeded Van's truly informed advice and am glad I did.
Click to expand...
I do not like to disagree with Rick... ;) but!

Van's makes some generic advice about "where" to put the battery, but it is not, in my opinion, intended to override the CG limits they provide.

As a few posts above have indicated, there are lots of issues / differences between each RV... and even 2 builders with the same equipment state may see a CG variation on "how" they built their RV-8(A).

We were lucky... someone a year ahead of us followed Van's advice, and with an IO-360 18-HP and Hartzell, put the battery on the firewall. After weighing, he found he had to ballast the aircraft to fly solo. We changed our build therefore (same eqpt) to rear battery (we still have the front battery tray present!), and moved the Basic CG aft by 2.1". When built we were another 0.6" aft than that... (1106/78.59").

Someone else now building similarly, but light FP rather than Hartzell C/S, and moving the battery to the firewall almost exactly compensates, in theory.

What priority are Dual Aerobatics to you? That will limit how far aft you can go... Solo aerobatics with fwd CG are hard work, but easily dealt with by ballast. Baggage not really an issue since you have 2 areas.

The RV-8A I suggest needs to be looked at carefully due to the nosewheel issues. Vans made comments about weight on the nosewheel, and the tandem RV-8A will vary CG far more significantly dual/solo than the SBS.

The battery is the easiest tool you have to affect CG late on... and anything you can do to be able to "postpone" or even "reverse" that decision if necessary will help.

There would be no substitute for you contacting RV-8A flyers, and establishing as best you can what fit they did, and then work the figures for your fit.

Andy
 
Andy Hill said:
There would be no substitute for you contacting RV-8A flyers, and establishing as best you can what fit they did, and then work the figures for your fit.

Andy
Click to expand...




I thought that is what I was trying to do? :)

Thanks for all the input-
Joe
 
jferraro16 said:
I thought that is what I was trying to do? :)
Click to expand...
When you do decide how to proceed partly based upon data collection from RV-8A builders, here is another information source you may want to consider. Van's flatly rejects the idea of aft mounting an Odyssey battery. According to them, only the Concord battery is approved for the aft mounting location. Perhaps that explains why the battery tray is designed in the shape it is, but I'm just guessing.

I really do not know why Van's does not approve of an Odyssey back there, we did not get into the technical aspects of it during a telephone call for tech help to discuss CG matters.

That said, we know (as indicated on this thread alone) that many builders do aft mount the Odyssey and report success doing so. Now I am not challenging anyone's decision to do so, not at all. In my case, I heeded Van's advice and am merely passing along what was said to me. Perhaps someone better informed can explain why Van's might adopt such a position.
 
Thanks Rick,

Add another thing to look into to my list. Concord vs. Odyssey..both gel? So much to learn :eek:

I'm still trying to figure out why the manual tells me to put the fuel and brakes lines in before the forward side skins, but I can't find the line stock anywhere in the fuse kit...


Still having fun!

Joe
 
The Odyssey is not a gel cell, but rather an AGM (Absorbed Glass Mat) technology. Don't know about the Concorde. AGM batteries tend to have minimal self discharge, and low internal resistance, which allows the tiny battery to offer a lot of cranking current.
 
Fuel and brake line

jferraro16 said:
Thanks Rick,

Add another thing to look into to my list. Concord vs. Odyssey..both gel? So much to learn :eek:

I'm still trying to figure out why the manual tells me to put the fuel and brakes lines in before the forward side skins, but I can't find the line stock anywhere in the fuse kit...


Still having fun!

Joe
Click to expand...

Joe,

I had to get Van's to send me the 3/8 fuel line as it was not in my kit (QB) some things just get overlooked. I ordered even more line and have gone though that. I think doing the line with the side skins off will make life much easier but with the QB that is not an option and the line that goes from the right tank under the weld mount to the selecter has given me fits. I have one in but I think I am going to give it another try.

Cheers
 
Mod to tray for odyssey

Rick6a said:
When you do decide how to proceed partly based upon data collection from RV-8A builders, here is another information source you may want to consider. Van's flatly rejects the idea of aft mounting an Odyssey battery. According to them, only the Concord battery is approved for the aft mounting location. Perhaps that explains why the battery tray is designed in the shape it is, but I'm just guessing.

I really do not know why Van's does not approve of an Odyssey back there, we did not get into the technical aspects of it during a telephone call for tech help to discuss CG matters.

That said, we know (as indicated on this thread alone) that many builders do aft mount the Odyssey and report success doing so. Now I am not challenging anyone's decision to do so, not at all. In my case, I heeded Van's advice and am merely passing along what was said to me. Perhaps someone better informed can explain why Van's might adopt such a position.
Click to expand...

Rick,

Did you use the odyssey or the concord in back. I am planning on using the odyssey but have not looked at the tray yet. I wonder if the tray will need modificaton. Will it fit two odyssey batteries?

Cheers
 
RVG8tor said:
Rick,

Did you use the odyssey or the concord in back. I am planning on using the odyssey but have not looked at the tray yet. I wonder if the tray will need modificaton. Will it fit two odyssey batteries?

Cheers
Click to expand...
Mike,

As I indicated in post #8, per Van's recommendation I installed an Odyssey battery on the firewall. My RV-8 is equipped with an IO-360 and Hartzell prop. Some significant and additional weight savings was achieved by going with Grove gear.
 
2 locations?

Many years ago I flew Cobra Attack helicopters. We had two battery locations. the crew chiefs would move the battery to the tail boom or the nose depending on armament load. Has anyone built an -8 with a setup for the battery aft AND on the firewall?
 
Rick6a said:
There are always going to be many opinions on this issue. You can go either way you want. In the end you can't go wrong if you simply accept on faith the advice Van's offers. They designed the airplane, they know best what the proper battery and battery mounting location is for your particular engine/prop combo. I contacted, then heeded Van's truly informed advice and am glad I did. Van's own sample weight & balance sheet assumes 44 pounds on the RV-8 tailwheel. With the Odyssey battery mounted on the firewall per Van's suggestion, my airplane enjoys 66 pounds back there and a very short battery cable run in the bargain.
Click to expand...

Listers,
Rick is correct that Vans wants you to use the larger, heavier Concord battery in the rear. You should understand that Vans only recommends rear battery placement for the 200 HP angle valve 360 engines with C/S props. With that very heavy engine/prop combination, the extra weight of the heavier battery is a plus.
There have been many threads on weight/balance on the 8 and 8A on the various lists. Most posters like the rear mounted battery with a 360 engine or C/S prop. The advantage is that they don't run out of elevator trim authority during short final when flying solo. The downside of the rear battery is the weight of the extra #2 cable running to it.
Charlie Kuss
 
lancef53 said:
What model Concorde battery is recommended? Anybody have the dimensions?
Click to expand...

Lance,
I think the recommended rear battery is Concorde RG25. not the Odyssey PC680 battery that most builders use. It weighs about 50% more and takes up most of the battery tray. See

http://www.aircraftspruce.com/catalog/pdf/RG-25.pdf

http://www.aircraftspruce.com/catalog/elpages/concordebatt.php

Rick, please correct me if I'm wrong here.

You can see the specs for the Odyssey PC680 here

http://www.enersysreservepower.com/ody_b.asp?routine=ody_spec&brandID=5

Charlie Kuss
 
I'm still not clear on specifically why Van's does not recommend an aft mounted Odyssey, I merely heeded their advice.

Assuming an at least 7 pound weight advantage an Odyssey battery (15 lbs.) enjoys over a Concorde battery (22 lbs.) any aft mounted battery installation must also include that very weighty #2 battery cable and an expected loss of efficiency to be expected over its comparatively longer run. I will hazard a ballpark guesstimate that additional cable length and its weight including supporting hardware comes in at an additional 5 lbs. regardless of battery type. Right or wrong?

For CG purposes, I am very glad I aft mounted, far aft.....that frigging ELT with it's 8 "D" cell batteries serving double duty as ballast. :)
 
Rick6a said:
I'm still not clear on specifically why Van's does not recommend an aft mounted Odyssey, I merely heeded their advice.

Assuming an at least 7 pound weight advantage an Odyssey battery (15 lbs.) enjoys over a Concorde battery (22 lbs.) any aft mounted battery installation must also include that very weighty #2 battery cable and an expected loss of efficiency to be expected over its comparatively longer run. I will hazard a ballpark guesstimate that additional cable length and its weight including supporting hardware comes in at an additional 5 lbs. regardless of battery type. Right or wrong?

For CG purposes, I am very glad I aft mounted, far aft.....that frigging ELT with it's 8 "D" cell batteries serving double duty as ballast. :)
Click to expand...

Rick,
I'd say your guesstimate of 5 pounds for the added length of battery cable is about right. The forward mounted battery uses #4 cable, due to the short length of the cables. Lots of folks with the lighter parallel valve engines use the lighter Odyssey battery, in the rear location, with good results. It's really up to each builder to decide for himself the pros and cons of C/G issues and battery only operations endurance time.
Charlie
 
Aft mounted batter

I just bought the wiring kit for an aft mounted battery from Vans this past month. I am planning on the Odyssey battery but now you guys have me worried. When I read the instructions (I will have to read them again) I recall if you were IO-360 with C/S prop the recommendation was for an aft mounted battery, it did not say size or type of battery. I have read many reports of those that like the aft mounted battery. One friend of mine wishes he had mounted his aft (RV-8). So anyone flying with an aft mounted Odyssey? What CG issues do you have if any? If the battery up in the baggage area is a better fit CG wise I don?t want to mount it aft, I don?t want it on the fire wall just for battery life.

FYI: I weighed the long cable from my kit (pre-cut with connectors) that goes to the firewall with the short cable to the batter contactor that also goes aft and it weighed in at 2.4 lbs, which is about 50% less than the guesses.

Thanks for any help and advice.

Charlie one of these days when I get out to see my parents I still hope to come see your project.
 
In my RV-8A, EW was 1124 @ 77.15". Flying solo I carry 23 lbs of ballast in the baggage compartment and my CG is 80.40. The ballast is a Oxy bottle and a tool bag (with a couple of quarts of oil for extra weight).

I spent many hours playing with weight and balance using a friends 8A that was equiped like i had planned mine (O-360 w/CS). My thought process was I'd rather have a forward CG, controlable with ballast solo, and have less issues with a passanger and baggage. I put the battery on the firewall. One reason I built the 8A was because of its loading possibilities having a front and rear baggage compartment.

I will forward my simple excel spread sheet if you want to experiment with it.
Just send me an e-mail. [email protected]
 
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jferraro16 said:
Thanks Rick,

Add another thing to look into to my list. Concord vs. Odyssey..both gel? So much to learn :eek:

I'm still trying to figure out why the manual tells me to put the fuel and brakes lines in before the forward side skins, but I can't find the line stock anywhere in the fuse kit...


Still having fun!

Joe
Click to expand...

Joe,
Both batteries I listed links to at the top of page 3 are AGM batteries. Gel batteries are a slightly outdated technology. Concorde makes both AGM and flooded (wet) acid batteries. Stay away from those. You don't want battery tray corrosion issues.
Your tubing line stock should be in a coil about 15 inches in diameter. I dislike the 3003 Versitube that Vans supplies, but that's just me. Lots of folks have built their planes with it, so you know it works. The German (anal) in me just hates how easily Versitube nicks and scratches when you try to make tight compound bends. It's also hard to get it to look nice (cosmetic) since it comes coiled. I used the Versitube to make prototypes (practice tubes), then made the final products out of 5052 I purchased from ACS. The 5052 comes in 6 foot straight lengths. ACS ships it on wooden sticks. This protects the tubing and keeps the shipping costs down.
Charlie Kuss
 
jferraro16 said:
Thanks Rick,

Add another thing to look into to my list. Concord vs. Odyssey..both gel? So much to learn :eek:

I'm still trying to figure out why the manual tells me to put the fuel and brakes lines in before the forward side skins, but I can't find the line stock anywhere in the fuse kit...


Still having fun!

Joe
Click to expand...

Joe,
I did the tubing on my 8A after the fuselage was completely riveted together and upright. I had no real problems doing it that way. I don't see how you could do the fuel vent tubes without the vertical parts of the F-802s on anyway??? Having the left side skin off, might have made doing the fuel lines around the fuel selector easier. I used the Andair selector, which limits space even more. I just made a mod to the mid cabin cover to ease access there. I felt this was better, because for future maintenance/repairs I won't be able to remove the side skin! :eek: I also made a mod for the vent lines for the same reason.
Send me an email if you want photos of what I did.
Charlie Kuss
 
Charlie--

Not sure when you started your kit, but, on the new -1 fuse kit, the 802s are installed--permanently--before you even cleco the forward side skin on for riveting. One could end up at a point where all the skins are done, except the forward side skins and the junction with the mid side skins.

I would LOVE to see any/all of the pics of your fuel set-up... I'm going Andair too.

jferraro16 at yahoo.com

Joe
 
Joe
What I'm doing on my -8 is building a battery tray that I'm going to mount just behind the firewall on the floor in place of the front baggage well that will be held in with bolts. I'm also going to install a plastic conduit that I got at Van's under the floor and the nut plates under the rear baggage for a rear mount battery. I'm planing to use the PC 680 battery. When I weigh the plane and find out where the CG is, that will tell me where to put it. If it says I can put it in front, that is where I will put it. However, when I fly it and IF I run out of trim on final then I will put it in the back.
 
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