Do nothing, follow the plans, leave battery location alone
joeboisselle said:
I've heard if you've got an o-360 with CS prop on an rv-4, the battery can be placed in the baggage compartment for better weight and balance. Could anyone with this configuration point me in the right direction? That's a lot of extra wire I'd rather not install if I don't have to. Thanks in advance!
I had a RV-4, O320 with a Hartzell and solo it was towards the fwd CG range, but it actually the empty CG was very nice with passenger and bags. I could load up to gross Wt., passenger (girlfriend 110lbs?) and fill the baggage area to the gills with backpacking / camping gear and full fuel. My battery was is the stock location between the feet.
I suggest you don't anything with the battery. Running large "0" gage or "2" gage battery cables to the baggage area is a pain and adds overall weight. Plus builders that do this (mostly on RV-8's) usually use two heavy batteries to make it worth their while to move the battery location. Moving one light PC680 would do little. So they are adding a lot of weight.
As per the Gent above the new PC680 is light weight and is really quite reasonable to place in the stock location. Just remember any chage you make from the plans usually adds weight, cost and build time. Van did a good job to start with.
Lets say you have a CG issue:
You could use temporary ballast in the baggage compartment. You can take ballast out when not needed. I know a few factory planes like this, namely the Piper Seneca II (light twin). I flew it with a few cases of oil in the aft baggage, unless flying passengers or cargo. That might be OK on a RV-8 with a Gross of 1,800 lbs, but the RV-4 is only 1,500 lbs gross. You can't afford adding weight all over.
If you HAD TO make a permanent CG adjustment, you could put some weight (lead) in Vert/Horz stabilizer area under the fairing tail fairing. Think about this, to make a rear mounted battery you need to add a lot of extra weight (long heavy battery cables and heavy battery or batteries). If you would leave the battery alone and that weight savings and put it under the the tail, you can affect the CG more with less weight. Remember moment is Wt x ARM.
And just for the record, the expensive solution would be replacing the heavy Hartzell (55 lbs), if that is what you have, and use a WW151 (28 lbs) or other light (expensive) composite prop. I think the Hartzell BA prop is the best choice but it does weigh more.
Leave the battery alone if at all possible.
