The safe CG envelope (X% MAC to Y%MAC) as determined by the manufacturer must be such as to allow the airplane to rotate smoothly at VR rather than the VR needing change according to the CG position.
Hence, the CG envelope is taken (by the manufacturer) small enough to accomodate a whole range of VR' s. If the CG envelope were to be taken larger, then yes, you would have a problem and you may need to take CG position into account for Vr.
Before the flight you need to determine whether or not your CG is within the limits acceptable for taxiing, take-off roll, rotation, climb and flight. This includes all VR/Vmcg/Vmca speeds and combinations thereof. That' s what the loadsheet is for.
As a reference, if I'm not wrong CG data is not used on the FMS take-off reference page.
It is used in the perf init page for computation of cruise CG in order to calculate fuel efficiency. I don' t hink that cruise CG is used as reference for take-off performance data.
I can imagine that on certain smaller aircraft your CG could modify your VR because the CG spectrum is made to accommodate a larger range of CG positions. I have yet to see such an aircraft' s POH as most of the time the manufacturer will prefer to take safe limits with the CG rather than play around with airspeeds.
Last edited by fly_antonov; 24th February 2010 at 20:42.