Ref using the tip weights for track control.
Nearly all of the Bell model helicopters employ what they term Product Balance using front and rear pockets on the upper surface of the blade near the tip
Product balance on the M412 is used to control the track pattern change between the ground and hover test conditions and thereby prevent lateral vibration readings on opposing sides of the polar plot for the two conditions.
With around 1000 G acting on the mass at this span location any chordwise changes of mass distribution have a profound influence on controlling the “noodle” (nice term Nick!) torsionally when the disk is coned. For this reason it is most important that the aircraft is flown at the correct AUM for the RTB flights as the response sensitivities for product balance are only good for a narrow range of AUM.
The RTB in flight test conditions use climb and let-down (hi power low power) to further expose Chord-wise tip CofG mismatches in the pack that would point to a need for a product balance correction.
With regard to the procedure for using it, it is well documented in the MM and most effective, I personally wish more manufacturers would use it
Wunper
P.S.
By the by the M412 has a heavily reflexed asymmetric aerofoil section, and just how relevant that is to using Product Balance vs a symmetrical section I’ll leave to the egg heads…