CG datum for prop

agent4573 · #1 10-11-2020, 03:07 PM

Anyone know how far aft the prop is from the 0 datum? Vans lists the wing leading edge as 70" but my wings aren't on yet so I can't go measure. Hoping for the numbers for a 360 on the standard mount.

Were debating between the MT MTV-9 and the Whirlwind 300 series prop. There's 20 lbs difference between the two and I wanted to get an idea of cg effect. We're also running the sam james long cowl so I'll have a 2.5" prop extension on there for even greater moment arm. I know we're gonna be heavy to start with, and knocking 20lbs off is huge if we don't push the cg too far aft.

scsmith · #2 10-11-2020, 04:43 PM

Don't forget that the engine mounts for the 320 and 360 are different length, so depending on who answers you, you may get different answers.

In fact, if you have not fitted your cowl yet, and not purchased your engine mount yet, you might consider using the O-320 mount with an O-360 to get your engine c.g. a bit more forward. Then you can use the lighter, faster prop and still not be too tail heavy.

agent4573 · #3 10-11-2020, 05:35 PM

I looked into the 320 mount and decided against it. We want to do entry level IAC competition with this plane, and hanging everything further forward didn't seem like a good idea for extended periods of elevated g. Just a lot more stress on the firewall and mounts. We decided to go with the standard 360 mount and just push the prop forward. Both the engine manufacturer and at least MT has said that the there's no additional limits if used with a 2.5" extension.