Magnesium or Alum Sump on RV-9a?

Getting ready to order engine and was offered an option of a Magnesium or Aluminum sump. The Magnesium is 7lb lighter and $350 more expensive.

Would this be worth it for an RV-9A with recent glass avionics? Note that I am also going to be running a WW-GA200L prop, which I understand is already rather light.

That's a question only you can answer - it comes down to trading dollars for pounds. Each of us will have their own point of happiness on that scale.

I'm more concerned along the lines of CG. Am I getting too light up front? Is there a way to calculate this without knowing all the numbers?

$50 a pound for weight saved is a bargain. And seven pounds saved is huge.

Sounds like a great deal to me!

Dave

What engine?

My 9A with a 320 and WW C/S prop required 2 lbs in the tail until it was painted. I would recommend the lighter option.

gfb said:

I'm more concerned along the lines of CG. Am I getting too light up front? Is there a way to calculate this without knowing all the numbers?

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It is best to build as light as you can. Then you can add weight where you need it, if you need it.

I have thought about buying the sump and installing it on my O-360, just to drop a few pounds, maybe some day. Now if I could get a magnesium belly replacement for me!

If the engine is a 360, then I'd say go for the lighter sump. If a 320 engine, then you might need the extra weight up front.

Who supplies the Magnesium sump?

It seems to me that a lot of 9A's with 320s & FP props (especially composite ones) end up needing more nose weight for optimal cg. Nearing the weighing stage on mine, I'm really curious to see where the cg lands...a little tail-biased for me is not a big issue as I don't anticipate having to carry much baggage. I'd save the $350 and lose bragging rights for having the exotic sump.

Don't know who the supplier is but Titan is the manufacturer/assembler I am working with that has it.

gfb said:

Don't know who the supplier is but Titan is the manufacturer/assembler I am working with that has it.

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I originally had a Lycoming O-320 E2D on my 9A, and decided to placard a lower than advertised baggage weight limit because it would've been possible in multiple scenarios to load out of aft CG range. Granted, Vans has conflicting information in various places about the 9's baggage weight limit to begin with - I found 75 lbs, 80 lbs, and 100 lbs all advertised in different spots.

Anyway, with the E2D, I had to limit to 80 lbs or less. Last year I ordered and installed a Titan OX-340 stroker and opted for the heavier aluminum sump. After the new weight & balance, I could remove the placard and fly with 100 lbs in baggage if I wished. If the engine weighed 7 lbs less I think I might be back to placarding the baggage area again.

Not a huge issue either way, really. 80 lbs is still a lot of baggage, and everyone's choice of panel, interior, prop, and accessories can have more influence on balance than that sump.