Wow Crab
That's a really quaint peice of history, Britain at it's best etc
Interesting to note:
1 that there was such a violent nose down tendancy in those earlier types and since no horizontal tail surfaces then one presumes (i think you can see it) that the Center of Pressure from the Arm and Area of the tail boom is way aft of the rotorhead. (they describe running out of aft cyclic to stay in VR)
2 they still describe roughness, even though a really good vortex ring state can be hyper smooth, maybe the slipstream of around the boom? Or not fully formed.
3 the center of the phenomenon is centered symetrically around the zero airspeed axis in the Brit version. UNLIKE the center of the phenomenon shown in Rotorbees graph (Origin US Military?) which seems to show a maximum at about 65degrees angle of incidence (VERY SURPRISING THAT, maybe not true, see Brit version below)
On reflection the US MIL version that Rotorbee shows would be the right zone for VIBRATION but is not showing where VR is. It is effectively showing where the vibration zone is, on the edge of VR, rather than the VR itself. Whereas the Brit version is showing where you would find VR.
By using 'Vi' in the graph you can see that it is possible to sustain VR to higher ROD by adding power (more Vi) and increasing the ROD than you can stay in VR to. Hard to stay in FDVR, never seen any evidence that it is hard to get out of, only hearsay.
