During initial Bell 430 flight testing it was discovered that in high speed forward flight excessive left cyclic was needed to maintain forward flight. On the 430 the fix was to re index the upper swashplate a few splines to couple lateral to longitudinal inputs. If you look at the 430 pitch links, you will notice they are angled like a helix.
During 407 flight testing, a similar characteristic was observed, however the affect was non linear compared to the 430. With increasing speed, increasing lateral cyclic input was required, however before reaching full forward cyclic the need for lateral cyclic became reduced. So just re indexing the swashplate was not a viable solution.
To add non linear lateral coupling to forward longitudinal input, Bell on the 407 incorporated a cam mechanism under the pilot seat. The cam profile adds minimal lateral input for aft cyclic, and maximum lateral input at approximately 65 to 75% max forward longitudinal input. By 100% almost all the lateral input is removed. If you remove the pilot seat, and examine the cam profile, you can see the magnitude of lateral input with longitudinal cyclic.
FYI if you box the 407 cyclic without hydraulic boost, you may hear a popping noise under the pilot seat. This noise is generated by a anti jam spring cartridge in the cam linkage.
Great explanation, CTR,,,
