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?
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