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What is the battery moment arm on an RV-10?

Flying again!

Flying again!

Well Known Member
I am going to replace the battery my -10 came with with a much lighter Shorai LFX36L3. Current battery (Odyssey 1200) is fine but limits me due to aft CG with 4 people and luggage. Example: currently with my family on board and 80 pounds of baggage I am the aft CG limit when I reach 30 pounds of fuel remaining.

Preliminary calculations show a 33.5 pound saving swapping out the battery! I measured from the rear seat to the battery and came up with an arm of 196.94 but do not know if this is correct.

Anyway, with weight savings and my estimated moment arm I have no aft CG issue. With my family and 100 pounds of luggage I can go to zero fuel remaining and still be within the CG range. With just me and full fuel my CG is at the forward CG but not an issue but I may swap batteries if I am only flying with 1 or 2 passengers and wanted the moment arm so I can account for the change.

I will weigh the -10 next month after the condition inspection since a couple of other things are being installed and I want a new measured W&B.

Thanks -- TJ
 
Bust me if I,m wrong, maybe Mike knows. I thought CG on the 10 moved forward as you burn fuel.
 
Fuel is forward of the C/G-------so the C/G moves aft as you burn off fuel. 360 pounds of fuel..............

It is possible to take off with C/G just fine, but burn enough to land with the C/G out of the envelop to the rear.
 
aerhed said:
Bust me if I,m wrong, maybe Mike knows. I thought CG on the 10 moved forward as you burn fuel.
Click to expand...

With 360# in front seat, 280# in back, 80# of luggage, at full fuel, CG on my a/c is 115.76. At zero fuel it moves aft to 116.8 (aft CG limit is 116.24)

However, solo with 190# in front seat, no luggage or pax, full fuel CG is 109.25 and moves aft to 109.32 with zero fuel.

The strange thing is that with the new battery, 360# in front seat, 280# in back, 80# of luggage, at full fuel,the CG is 114.76 and moves aft to 115.66 with zero fuel. However, solo with 190# pilot, fuel fuel CG is 107.91 and moves forward to 107.71 at zero fuel (ahead of the fwd CG limit of 107.84).

This is due to the fuel moment arm of 108.9 which is behind the CG solo with the Shorai battery so the CG moves forward as it burns down.

Fun with math :)
 
not rocket science

Hey guys, this isn't rocket science.
As already pointed out, Van's numbers are:
Forward cg limit: 107.8"
fuel moment arm: 108.9"
Aft cg limit: 116.2"

So most of the time, your cg is between 108.9" and 116.2", and it will move aft as you burn gas.

But if you are solo (and have short legs, and don't weigh too much) your cg can be between 107.8" and 108.9". In that case the cg moves further forward as you burn gas.

e.g., IF you are right at either limit, then burning any more gas will put you out of limit!
 
Flying again! said:
I am going to replace the battery my -10 came with with a much lighter Shorai LFX36L3. Current battery (Odyssey 1200) is fine but limits me due to aft CG with 4 people and luggage. Example: currently with my family on board and 80 pounds of baggage I am the aft CG limit when I reach 30 pounds of fuel remaining.

Preliminary calculations show a 33.5 pound saving swapping out the battery! I measured from the rear seat to the battery and came up with an arm of 196.94 but do not know if this is correct.
Thanks -- TJ
Click to expand...

I don't know the answer to your question, but try measuring from the center of the battery to the leading edge of the wing (somehow sight thru the fuselage). The datum that Vans uses is 99.44" in front of the leading edge.

EDIT: I looked up my W&B spreadsheet and I have the aft end of the baggage space at 189"; I think the battery center may be a bit more than 8" (197-189) behind the bulkhead.(?) But your number seems to be close.

BTW, 30 lbs of gas is 5 gallons. In an emergency where you need that last 5 gallons, you could always have a passenger reach back and pull a suitcase forward, and put it under their feet.
 
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It sounds to me that your idea will work fine, as long as you are within Max Gross Weight. The Odyssey PC1200 is probably overkill, anyway.
I'm amazed at the light weight of the Shorai LFX36L3, but the price reflects that.
By the way, I've got a heavy nose, so I always have ballast in the baggage compartment when I fly alone - that would be a lot better than changing out batteries in your case. I use pennies in $25 boxes from the bank. Comes out to about $2 a pound and they are easy to move forward, or leave with the ramp guy.

John
 
On the RV10 that I worked on a few years ago the owners mission was cross country flight with his family. With that in mind we moved the 680 battery from the aft position in the fuse to the forward face of the firewall. This move saved us a total of 17 lbs of weight and greatly reduced the wiring complexity.
A standard 680 metal box was used for the firewall.
What this meant was that when flying solo, in a worst case situation, the aircraft was placarded with a need for 50 lbs in the baggage compartment. Aside from the total reduction in empty weight it meant that more useful load could be carried, especially the important back seat and baggage load.
I have about 25 hours on the aircraft and it flew very nicely solo with the proper weight in the baggage area.
I do believe that this is an excellent modification for others to consider.
YMMV.
 
How did you save 17 pounds? Is that all wire weight?

John - I too need to carry 20 lbs of ballast when solo. I have a plastic 2 1/2 gallon jug of water. Doubles as emergency supply, and if I pick up passengers it's easy and cheap to dump on the ramp.
 
Tom Martin said:
On the RV10 that I worked on a few years ago the owners mission was cross country flight with his family. With that in mind we moved the 680 battery from the aft position in the fuse to the forward face of the firewall. This move saved us a total of 17 lbs of weight and greatly reduced the wiring complexity.
A standard 680 metal box was used for the firewall.
What this meant was that when flying solo, in a worst case situation, the aircraft was placarded with a need for 50 lbs in the baggage compartment. Aside from the total reduction in empty weight it meant that more useful load could be carried, especially the important back seat and baggage load.
I have about 25 hours on the aircraft and it flew very nicely solo with the proper weight in the baggage area.
I do believe that this is an excellent modification for others to consider.
YMMV.
Click to expand...

Perhaps one could do the same thing, only with a lighter LiPo battery. It would seem that this scenario wouldn't require as much ballast when flying solo...?
 
Flying again! said:
I am going to replace the battery my -10 came with with a much lighter Shorai LFX36L3. Current battery (Odyssey 1200) is fine but limits me due to aft CG with 4 people and luggage. Example: currently with my family on board and 80 pounds of baggage I am the aft CG limit when I reach 30 pounds of fuel remaining.

Preliminary calculations show a 33.5 pound saving swapping out the battery! I measured from the rear seat to the battery and came up with an arm of 196.94 but do not know if this is correct.

Anyway, with weight savings and my estimated moment arm I have no aft CG issue. With my family and 100 pounds of luggage I can go to zero fuel remaining and still be within the CG range. With just me and full fuel my CG is at the forward CG but not an issue but I may swap batteries if I am only flying with 1 or 2 passengers and wanted the moment arm so I can account for the change.

I will weigh the -10 next month after the condition inspection since a couple of other things are being installed and I want a new measured W&B.

Thanks -- TJ
Click to expand...

Let me know how that battery works out. I have a 925/680 in the back and run into similar loading issues.
 
I am going to put the OD 925 In the back and a 680 up on the fwd firewall for a emergency back up battery. A lot cheaper then the TCW products and i can use itr if the 925 is dead for engine start.
 
Hi TJ,
FWIW, I just removed my Shorai LFX36L3 from my RV-10 and replaced with a PC680. The Shorai worked great for about 6 months then slowly starting losing the ability to crank the IO540. I was always have to cross tie to the 680 to start. I tried charging the Shorai but the charger cut out after only about 20 mins saying it was fully charged I gave up and installed a second 680.

Jim Faber
 
jimfaber said:
Hi TJ,
FWIW, I just removed my Shorai LFX36L3 from my RV-10 and replaced with a PC680. The Shorai worked great for about 6 months then slowly starting losing the ability to crank the IO540. I was always have to cross tie to the 680 to start. I tried charging the Shorai but the charger cut out after only about 20 mins saying it was fully charged I gave up and installed a second 680.

Jim Faber
Click to expand...

Hi Jim,

Sorry to hear that. The LFX batteries used by others in the -6, -7, and -8 have not reported the same problem. Did you use a trickle charger between flights?

I saw an LFX36 on Amazon for $262 but want it to work longer than 6 months for that type of money! Dual 680's only save 8 pounds over my 1200 and I don't think a single 680 would give the reserve I want.

Need to do more research.....
 
Flying again! said:
Hi Jim,

Sorry to hear that. The LFX batteries used by others in the -6, -7, and -8 have not reported the same problem. Did you use a trickle charger between flights?

I saw an LFX36 on Amazon for $262 but want it to work longer than 6 months for that type of money! Dual 680's only save 8 pounds over my 1200 and I don't think a single 680 would give the reserve I want.

Need to do more research.....
Click to expand...

No I did not, however I flew almost 30 hrs on a long cross country trip for over a 7 day period. I would think that be enough to fully charge the battery. At the end of the trip, it would not crank the engine by itself.

My battery could be bad one. Hope you have better luck than I did.

Jim
 
I got 194"

I was running the numbers to move the battery forward of the firewall in my 10 same as someone else mentioned, and I figured a 194" arm, think I measured from the leading edge. Would definitely measure again to check before doing it though. FYI- I figured the CG change from moving the battery to be 2.5".

Dwight
 
Space Cadet said:
I was running the numbers to move the battery forward of the firewall in my 10 same as someone else mentioned, and I figured a 194" arm, think I measured from the leading edge. Would definitely measure again to check before doing it though. FYI- I figured the CG change from moving the battery to be 2.5".

Dwight
Click to expand...

Dwight,

Did you move your battery? If so, where did you mount it? Any weight savings in cable? I assume you did this to help offset the weight of the AC unit...? I hope you've been flying lately. We need to catch up. Call me sometime and we'll go hang out at Centennial.

Mike
 
jimfaber said:
I flew almost 30 hrs on a long cross country trip for over a 7 day period. I would think that be enough to fully charge the [Shorai] battery. At the end of the trip, it would not crank the engine by itself.
Click to expand...

Jim etal,

It does sound like a bad battery or charging system as it is not normal from my experience.

As a counter point, I left my aircraft sitting in the hangar for 65 days, pulled it out and off for a 3 day 25 flight hour trip. Back in the hangar for 5 days. Then a 2-day 11 hour trip. Back in in the hangar for 22 days. Then a 5 hr day trip. No battery tender, trickle charger, etc.
 
I think a bad Shorai battery is a definite possibility. Don't think it is the charging system. It reads good volts and amps when running and the Odyssey battery is always charged and ready to go.

The problem is that the Shorai battery was in the plane when I bought it and the builder can't remember where he bought it. Shorai will only give a 30% credit off the full retail price on a new one without a receipt and you have to pay shipping to return the old one and the new one. I decided to replace it with a PC680. $88 delivered.
 
Completed swap to Shorai LFX36L3 and did W&B

Got delayed some but just completed the swap of my Odyssey 1200 with the Shorai LFX36L3 and weighed the RV-10 again.

First, in 2.5 years the RV-10 gained 12 pounds. I weighed the plane after I imported it to the US and before Mel did the airworthiness inspection. Since then I installed HID lights, a rear strobe light, rudder trim, a Flap Positioning System, an anti splat air oil separator, 12 inch vinyl N numbers, a control head for a soon to be installed ADS-B system, interior lights, repaired 2 wheel fairings, and a bunch of other misc stuff. So 12 pound increase seems right.

Installing the Shorai LiFePro was straight forward and only needed the use of some of the pads that come with the battery and some balsa wood spacers. No battery box mod was required.

The result:

Empty weight and CG before: 1668 pounds and 108.0216
Empty weight and CG after: 1638 pounds and 106.2668

Saved 30 pounds and moved the CG 1.755 inches fwd. It turns out the battery moment arm on my -10 calculates as 203.83 inches.

Real world, I can carry my family (365# front seat, 270# rear seat, 130# in baggage) and be within aft CG at zero fuel. In comparison, before with the same passengers I could only carry 84# of baggage and be within CG at 0 fuel. So I gained 46 pounds of baggage capacity which is very useful with 2 women!

The only drawback is fwd CG solo cured by putting 20# in the luggage area.

So far battery is strong cranking the engine. More to follow as I get time on it.

TJ
 
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