RV-8 CG with earthX battery

I have installed an Odyssey battery (15 pounds) in the engine compartment with a O-360-A1A and a Hartzell CS prop, that I think is a mistake for the CG location.
I will replace the Odyssey and I?ll install an earthX (4 pounds ).
My questions are?
1.- Do I still need some weight in the rear?. For example the Odyssey battery in its original rear position.
2.- How about using the Odyssey battery like a backup? I just need to install some "small" wires
Jose del Peso 80981
Madrid (Spain)

If you are going to use the lead acid battery as backup for the LiFe, be sure to have a separate contactor for each. Charging in parallel is no problem. Discharging in parallel is. The lower voltage of the lead acid battery will suck the juice out of the Lithium battery, so you don't want to have them both in the circuit with the alternator off. Instead, use one at a time.

Ed Holyoke

I just worked the W&B numbers. For an RV-8/8A with the 180hp IO-360 and Hartzell CS prop, one PC-625 battery mounted forward, and one PC-625 in the normal aft position yields a nice W&B. This is what I did on the new RV-8 project.

I mounted my forward PC-625 in the forward baggage well. I was never a fan of batteries mounted forward of the firewall.

In my first RV-8A I mounted one PC-625 in the forward baggage well, and one on the left side just aft of the firewall. The W&B was workable but 25 pounds of lead shot in the baggage compartment made solo flying better.

If you are interested I can provide photos on how I mountd each battery, and the power distribuion wiring instruction. Just PM me your email address.

Carl

Revival

Reviving an old thread.

Historically, with lead acid batteries that are 15-24lbs, battery location was important to CofG in the RV-8. With EarthX batteries that weigh 4lbs, that seems less important. I'm also planning two batteries. The primary battery being the ETX680c at 3.9lbs. For backup a ETX104 at 1.3lbs. That's only 5.2lbs total.

I'm planning a parallel valve engine, injected 360/370/375 with inverted oil and a constant speed prop, hopefully composite.

Are there concerns putting these batteries on the firewall? Does the battery circuitry care to live in a warm location? I know some put the battery on the forward baggage floor, but I'd rather use that for bags. Does moving 4 or 5lbs from the firewall to the aft battery location make a large enough difference to be worth the heavy cable runs?

Another thought is to put the 1.3lb backup battery in the rear location, as that would save some firewall penetrations.

Thoughts?

David Z said:

...
Are there concerns putting these batteries on the firewall? Does the battery circuitry care to live in a warm location? ...

Click to expand...

I have one 680c on the FW, Hartzell metal CS prop, no issues with W&B. I'm sure it gets warm in there but so far the battery seems happy.

No reason to put the backup battery FWF - just put it somewhere secure behind the panel - depending on what you are going to install there is plenty of space there, and I suppose it will be small. I used this one (IBBS-12V-3AH) which is behind the panel, works great, mounts and wires easily.

https://www.tcwtech.com/product/integrated-battery-back-up-system-ibbs/

I originally planned on having the battery in the tail before the earthx lifepo4 came along, and the change saved probably 20 lbs including all the wire, mounting HW, and the battery. Plus the wiring FWF is so much simpler.

Hold on...

This thread is driving me crazy! Why is anybody asking the forum to let them know it's OK to add or remove weight from their airplane? Every airplane should have a weight and balance computation completed after the first weighing of the airplane. If you move/add/subtract any weight it should only require a re-computation of the weight and balance to determine the new center of gravity (CG) of the airplane. You don't need to weigh the airplane again or ask your buddies if you did good! The only reason to re-weigh the airplane is if the original weight and balance is in question, such as a new owner of an airplane might suspect that the prior owner didn't keep up with the changes in weight and balance as equipment was changed over the years.

If you don't know how to compute weight and balance, learn. It's not complicated. Simple addition and multiplication skills are all that's required.

I spent over 2000 hours flying my RV-8 on the ragged edge of the flight envelope and I did so with confidence because I knew my takeoff weight and CG for every load and insured that I was within published parameters for normal operations or aerobatics. If you need to consult your virtual friends on VAF to determine if your RV is safe for flight... Well, good luck.

I think the thread is from people building
the airplane, so no W&B done, to people
that are flying, so W&B done, to decide the
battery configuration
Jose del Peso

Don’t go crazy

ronschreck said:

This thread is driving me crazy! Why is anybody asking the forum to let them know it's OK to add or remove weight from their airplane? Every airplane should have a weight and balance computation completed after the first weighing of the airplane. If you move/add/subtract any weight it should only require a re-computation of the weight and balance to determine the new center of gravity (CG) of the airplane. You don't need to weigh the airplane again or ask your buddies if you did good! The only reason to re-weigh the airplane is if the original weight and balance is in question, such as a new owner of an airplane might suspect that the prior owner didn't keep up with the changes in weight and balance as equipment was changed over the years.

If you don't know how to compute weight and balance, learn. It's not complicated. Simple addition and multiplication skills are all that's required.

I spent over 2000 hours flying my RV-8 on the ragged edge of the flight envelope and I did so with confidence because I knew my takeoff weight and CG for every load and insured that I was within published parameters for normal operations or aerobatics. If you need to consult your virtual friends on VAF to determine if your RV is safe for flight... Well, good luck.

Click to expand...

Don’t let it drive you crazy,.. I like this thread for planning purposes.. I plan on grove aluminum gear, berringer wheels, parallel valve engine and a composite CS prop.. I would love to hear where someone with a similar configuration ended up with their CG, so I don’t make a mistake and have to relocate after mounting the battery in the wrong location. It doesn’t relieve me from doing a W&B, but I would like a sneak peak...

Thanks Tom, that's exactly why I'm asking the questions. Most of my fuselage is still parts on the shelf.

With the wealth of knowledge on VAF, I'm seeking to learn from the experience of others.

I will be doing a careful and accurate weigh of the plane after it's built and doing the math to determine if it's loaded within the envelope before flight.

David Z said:

Reviving an old thread.

Historically, with lead acid batteries that are 15-24lbs, battery location was important to CofG in the RV-8. With EarthX batteries that weigh 4lbs, that seems less important. I'm also planning two batteries. The primary battery being the ETX680c at 3.9lbs. For backup a ETX104 at 1.3lbs. That's only 5.2lbs total.

I'm planning a parallel valve engine, injected 360/370/375 with inverted oil and a constant speed prop, hopefully composite.

Are there concerns putting these batteries on the firewall? Does the battery circuitry care to live in a warm location? I know some put the battery on the forward baggage floor, but I'd rather use that for bags. Does moving 4 or 5lbs from the firewall to the aft battery location make a large enough difference to be worth the heavy cable runs?

Another thought is to put the 1.3lb backup battery in the rear location, as that would save some firewall penetrations.

Thoughts?

Click to expand...

To your questions:
- I dislike mounting batteries on the firewall. I understand the necessity in some RVs (like the RV-14), but I consider the engine side of the firewall a very bad environment for a battery - any battery.
- As I already posted, on my first RV-8A I mounted both PC-625 batteries just aft of the firewall, one on each side of the cabin floor. For the parallel valve IO-360 and initial FP prop the W&B was fine. After I replaced the FP prop wiht a real one (the Hartzell BA CS prop) the ship was a little nose heavy.
- For the latest RV-8 (IO-360-M1B, same Hartzell prop, Grove Gear) I mounted one PC-625 in the forward baggage well, the second PC-625 in the normal aft location. The battery takes up little space in the forward baggage compartment.

Final W&B after a full base/clear coat paint job:
- Empty weight: 1118 lbs
- Empty CG: 78.18”

I’m happy with this CG result - running the numbers I can just about load the plane anyway I want and keep the CG in the envelope.

On using one or more EarthX type batteries, my thoughts:
- I would never consider mounting an EarthX in the cabin or behind the baggage area, vented or otherwise (others may be more tolerant than I on this). This leaves the firewall as a the only practical option.
- This leads to either spending a boatload of money on a composite prop, or adding weight aft to compensate for a nose heavy ship. I guess you can just install a FP prop as well.

Carl