Scott -

 

I wasn't suggesting that you were hung up on CG as percent MAC.  Your revelation that the POH expresses allowable CG range this way caught me by surprise.  I'm still building and the builders manual expresses CG as inches aft of datum.  So I don't really read the POH yet.  (My bad.)  Plus, in my work I'm used to CG being expressed as a Station Number (also inches aft of datum).  But if the POH uses %MAC then that's how we should talk about it, I suppose.

 

What's truly amazing, however, is that there are two different limits in the same handbook!  I'll take your word on this because my POH is in the hangar.  I am aware that there were two forward limits established for the 320 series.  As I understand it, the forward CG was revised to "allow" a more forward CG after Orin Riddell turbocharged his 360 and had a CG well forward of the previous limit.  When it turned out that it was just fine, the factory revised the forward limit to match.  I don't know if that farther forward CG is limited to large tails only -- that would make sense if it were.  I think I have the factory newsletter that addresses this.  I'll look for it.

 

Per your flight test comment, yes, I agree that we should verify the aft limit of our individual airplanes as part of our initial flight testing.  The factory limit may not be comfortable for all of us, and the time to find this out is in a controlled VFR flight test -- not flying home in hard IFR with a passenger.  (I have flown a sailplane at the aft limit and I was NOT a happy camper.  It was controllable but it took considerable pilot compensation.  All future flights were ballasted for a less aft CG.)

- Rob Wolf