PC680 vs PC925 in RV-8

[N941WR]

Originally Posted by Airzen

I got

- IO-parallel valve (180 hp)
- Sky-Tec Light Weight Starter (7.8lbs)
- Plane-n-power altrenator (6.5 lbs)

PS Chris: Not sure I can shave more off the nose without going to automotive starter as you mention (and I am not confident myself to do those kinds of mods As for alternator, I think at 6.5 lbs its already pretty light.

PS Andy: you might be right, thats why I am seeking info.

The Sky-Tec is essentially an automotive starter.

One way to drop a little more weight is to go with P-mags. They are 1.5 lbs lighter than a standard mag. Install two and you drop another 3 lbs.

[DanH]

Originally Posted by Saville

When you say "mounted on it's side" which direction did you have the lugs face?

Aft.......

[Neal@F14]

I replaced a Concorde RG-25XC with a PC-925 in my RV-6. I needed the extra weight on the nose to help out my CG. I had to trim some metal off the battery box cover to give some clearance near the positive terminal, and fabricate new spacers inside the cover to properly secure the different outer dimensions of the PC-925. With the Skytec starter, this battery cranks the O-320 engine super fast.

[SHIPCHIEF]

Although you said you 'will have' a rear mounted battery, indulge me for a moment...
I have an RV-8, which I mounted the battery in the rear. It offset my Mazda turbo rotary well, and my CG was just right.
I flew the rotary for 16 hours, it was powerful, it never failed, but it wasn't for me.
I installed a parallel valve IO-360, and used a Skytec lightweight starter, a Superior front induction sump, Airflow performance fuel injection and my own direct induction chin scoop. I installed a CATTO 3 blade prop. The engine is conical mount and I use one P-mag. I use a Denso mini alternator with the small diameter belt pulley type flywheel.
In short, I did everything I could to reduce weight.
So I moved the PC-680 battery to the firewall. The CG is still aft of the previous CG with the rotary engine, and I removed 3.2 pounds of battery cable!
Best of all, I don't have to fish around in the back to access the battery. I prefer having it on the firewall for ease of access.
A side note: Many of use build our planes, then do the weight & balance and hope for the best. If your EAA chapter has a set of scales, you should weigh & balance the aircraft at some progress milestones, like with wing & engine on, and do a few calculations. Then decide where to put your battery, strobe power supply and ELT?

[ColoRv]

Another data point for your consideration:

Angle valve
Pmags
Whirlwind CS
Grove gear
PC680 in rear

The last thing in the world I want is more weight aft. As it is there is literally no way to load my plane and get to the front of the CG envelope. Overload the front baggage with 75 lbs and leave the rear seat and baggage empty and I'm still not there but I can go off the back end quite easily. My thought was the "heavy" angle valve needed the weight in the rear. The Grove gear, light prop, pmags and crank without counterweights pretty much negated that I guess.

I've never felt I needed more battery, despite 10:1 Pistons.

[Bevan]

Weight is the enemy. You may want to save even more with one of the Lithium batteries. I saved over 12 lb with a Shorai and havn't looked back.

Bevan

[ColoRv]

Originally Posted by Bevan

Weight is the enemy. You may want to save even more with one of the Lithium batteries. I saved over 12 lb with a Shorai and havn't looked back.

Bevan

The weight savings appeals to me....but the failure mode does not. Especially with my battery inside with me. I know the new ones have electronics in them to prevent meltdown fires but one thing keeps coming to mind. My Dynon D6 was working well until the electronics failed. My Pmag was also working quite well until its electronics failed. Both of those pieces have a lot more expensive electronics in them than the new batteries...but neither of them burst into flames when the electrons got confused.

I'm going to let some of the braver in here life test that tech for a while longer before I jump on the wagon. Probably quite a while longer. Still, I agree with you.....weight is the enemy so I am tempted.

[Bevan]

I'm not sure about the normal location for the battery on the RV8 but I would think the logical place for a very light battery is forward of the firewall. Shorter cables also equals less weight. My firewall is well sealed from the cabin. The failure mode of LiFePo batteries is rather benign compared to the earlier flavours of lithium batteries as I recall. Do your own research.

I had trouble getting fuel to the engine one day cause the lines had been pumped dry for W & B. Forgot to prime them. My hangar neighbor thought I could taxi away on the battery power alone.

Bevan

My opinions only. Do your own research.