Originally Posted by
SansAnhedral
Its hard to take what's clearly a quarter century old crusade (written in comic sans, no less) very seriously when the subject matter of VRS/AVRS was absolutely thoroughly
tested,
studied, and
addressed to the point where tiltrotors have proven that they are actually less hazardous when it comes to VRS due to the ability to very simply recover without a complex maneuver like Vuichard. Versus helicopters, the tiltrotor ability to positively control pylon angle allows a hugely effective thrust vector shift and shedding of circular wake.
VRS is a tired old V-22 boogeyman and red herring that deserves to be left in the past where it belongs.
There are over 70 reports and papers on this area of activity to date, yet there is always value in better operational awareness. For the V-22, roll is a symptom not a principle cause, the rates involved in roll initially move the disk away from the boundary, however the anti roll input may deepen the location in the boundary. The NATOPS boundary is conservative, and also operationally adequate for the tactical employment of the aircraft; if the crew need to exceed the published limit, they are in an odd place. Wind effects are not a major factor if the aircraft sink rate is managed. The recovery by nacelle tilt is very fast. These are well established conditions, and VRS is not a major factor for the V-22, however, the same research also shows the models by Onera, Leishman, Drees, Peters, Xin & Gao, Betzina, Washizu, Newman, and by Wolkovich, all place a boundary that is less than the small thrust fluctuations, large fluctuations, asymmetries, and even roll off, as indicated by the collaborative review by Onera and Georgia Tech. To that end, it appears we still have benefit in better understanding. But, is VRS a factor in normal V-22 operations? No. Is the recovery from VRS in a V-22 rapid, far more so than the conventional helicopter, it is immediate (1sec) on tilting the nacelle.
Does VRS have a place as a discussion item in a departure accident of a V-22? Hard to see how that would be a condition that would be encountered in the normal state of affairs, and the V-22 boundary is benign, the recovery is straightforward, but the consequences of not applying recovery is pretty drastic. Time to put to bed? Not yet, some of the models show bifurcations as is to be expected, but most do not, the models remain useful but not completely accurate at this time.