Jonnyb

Jonnyb

Well Known Member
So I’m getting to the point where I have to decide on battery location, and this feeds into so many variables that it’s difficult to come to a definitive position. Although I might be over thinking this. I would appreciate any information from people who have gone down this route.
My current plan is for an IO-360M1B with a Hartzell 2 blade Aluminium CS prop, and an EarthX EXT680C.
With this configuration Im thinking the Fwd battery location would be ok. If I go with an MT composite prop, this is lighter so the fwd battery is still ok. What about the IO-360-A1B6 engine with the Hartzell prop and a fwd battery?
Can I ask what others have done?
 
If you use the EXT680X the battery has little impact. This WAS a big deal with lead batteries but isn’t with lithium once.

Even if you need weight in the back you are better of saving the weight of the long and heavy wire to the battery and put a little bit of lead in the tail. The lead will weigh less than the wire for the same CG effect of moving the battery back. So your empty weight will be less for the same CG.

Hope that helps.

Oliver
 
I have an IO-360 M1B in my RV-8 and wanted to upgrade the prop to a 3 blade composite. I did the wt & bal comparing my Hartzell 2 blade C/S to the 3 blade MT with a big honking 24 lb Acft battery the original builder installed just behind the aft baggage area. Didn’t exactly like the CG numbers so ran the numbers for the MT with a 15 lb Odyssey PC 680 instead and the numbers worked out great. I weighed the airplane and swapped out the odyssey with the equivalent weight of an EarthX 3.9 lb battery and the Odyssey is just a bit better for wt & bal and the EarthX at a whopping $400 with shipping was hard to justify anyway. Been using the PC680 and wt & bal always works out. With a high torque Skytec NL starter I have ample starting power and never an issue even with my 9:5:1 pistons.
 
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olyolson said:
Been using the PC680 and wt & bal always works out
Click to expand...
well, we have more or less the same config on the -8, but it ain't that good as in being quite nose heavy. With that IO-360-M1B, the 3 bladed MT, the lightweight starter and alternator, and a PC680 firewall mounted, I (74kg ops weight) have to carry at least 10kg (22 lbs) in the rearmost cargo for the aircraft to feel comfy during landings. I flew it initially without ballast, but initiating a proper flare on a shortish runway was no real pleasure as the aircraft was very slightly out of forward CG.
Another thing, don't cut your stick too short...
 
Dan 57 said:
well, we have more or less the same config on the -8, but it ain't that good as in being quite nose heavy. With that IO-360-M1B, the 3 bladed MT, the lightweight starter and alternator, and a PC680 firewall mounted, I (74kg ops weight) have to carry at least 10kg (22 lbs) in the rearmost cargo for the aircraft to feel comfy during landings. I flew it initially without ballast, but initiating a proper flare on a shortish runway was no real pleasure as the aircraft was very slightly out of forward CG.
Another thing, don't cut your stick too short...
Click to expand...

My PC680 is behind the aft baggage area under the shelf sheet metal cover and wt & bal is always good and I don’t fly with any ballast. My -8 may be configured slightly different than yours with more weight aft because of the where things were installed. I weighed the airplane with the Odyssey battery installed and then removed it and put the weight of the EarthX battery in its place to compare.

Good point- I just installed a new standard RV-8 straight stick with a Tosten military grip and it’s as high as it can be and still clear the bottom of the panel.
 
Yep - decisions to make. I took a good friend’s RV-8 W&B as a starting point (I had confidence in the accuracy of his data). This plane had a similar 180hp parrallel valve engine, two PC-625 batteries located just aft of the firewall, and the same Grove gear I‘m using.

I corrected his W&B data to reflect my two blade Hartzell BA prop instead of his three blade MT prop. This yielded my expected result of nose heavy (not horrible, but not what I wanted).

I left one PC-625 mounted forward in the baggage well and moved (on paper) one of the forward PC-625 batteries to the normal aft location. This calculated out to a much better W&B and is what I’m flying with now.

I suggest you find an RV-8 close to what your plane will be. Here mostly the engine is the critical factor as props and such you can calculate out.

The other suggestion is to decide now what you want the plane to do as in mostly solo, mostly with passenger (and how big), full baggage or not, etc. Run the numbers. Here the rule is to error on the side of nose heavy versus tail heavy.

For me, loaded out with passenger and bags to gross I will move the heavy bags to the forward baggage compartment. Landings are more three point than not. For solo and some bags I do wheelies.

With the pilot seat forward of the passenger, the RV-8 configuration will alway be a compromise WRT W&B.

Carl
 
My Rv8 has the exact configuration you suggest - io360-M1B, Hartzell CS 2 blade prop and Earthx 680m with the Earthx is mounted upfront.

I fly solo with 10kg-20kg ballast in the back. Empty CG is at 1965mm.

Hope this helps.

Dov
 
I’m with Oliver. My only disappointment with the RV8‘s performance is the stick and trim force required solo. Even with 180hp and a composite CS prop. If you want total performance from a -8 it needs counterweight . The aft battery location helped when batteries were 25 pounds but with the modern ones it only moves the CG a small fraction of an inch. If I did it again I would use an EarthX up front and install one of the clever removable counterweight ideas at the tail.
 
EarthX on the FW, 2-blade metal Hartzell, PV IO-360, Grove gear, and I like it. If my alternator dies, I'll probably replace with a Monkworx to save even more weight, although I could lose 5kg from my mid-section much cheaper and easier. I usually fly with my sleeping bag and tent in the back, and often with my little tool bag. It does make the flair a bit deeper. Totally empty, it will be a wheel landing.
 
My 8 is still under construction, hopefully completed later this year. PV IO-360 M1B, WW 300 series CS prop, PC680 on the firewall to save on the heavy cable, light weight starter and alt, stock gear. Hoping the W&B will work out ok with the 36lb WW up front. Maybe need an extra coat of paint on the tail :unsure:
 
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