Perhaps enough water has flowed under the bridge since the USMC MV-22 tragedy for us to be able to see the simple issues at the core of the accident.
Regardless of which organisation’s hat one is wearing I believe there is no arguing with the premise that IF asymmetric vortex ring (VR) is allowed to develop on an MV-22 when flying at low level in the helicopter mode, a high rate of roll will develop with catastrophic results.
From the purely pilot’s perspective, a similar situation can happen to a Harrier fitted with the original metal wing during a transition to or from the hover. Because the Harrier is directionally unstable at these speeds the pilot is responsible for keeping it pointing the way it is going by use of his feet. If he does not do this, or worse still actually tries to use his feet to control heading or track over the ground (instead of banking) then the aircraft’s dihedral effect will have it on its back in a trice.
The way the manufacturer tackled this lethal threat (sadly, as is the way of the world, only after the first fatal) was to develop warning systems that announced the ONSET of the problem while any lateral out of trim was still small and still being contained instinctively by the pilot using his lateral controls.
Now forget Harrier and think Osprey.
The prevention of roll induced by asymmetric VR needs two things:
1 An early warning that the flow on either proprotor is TENDING towards VR
2 A rapid AUTOMATIC configuration change to the aircraft to take it away from the detected incipient VR conditions.
Some years ago the Aerodynamic Research Flight at RAE Bedford carried out trials with a helicopter fitted with instrumented rotor blades so they could measure aerodynamic pressures at 2% chord. I rang the (now retired) scientist in charge of that research and he explained how they could detect the spread of VR as it developed along the blade. From this I
conjecture that perhaps a couple of such sensors (optimally positioned) on each Osprey blade might just produce the necessary error signal of DIFFERENT aerodynamic circumstances on parts of the SAME blade, to satisfy a solution to the warning system requirement. Given that each rotor has three blades the triple redundancy of such a system also appeals to me.
If early warning IS shown to be possible by whatever technique (but please leave the pilot out of this as he is more than busy enough doing a demanding military task) then I think the battle is won because I don’t see para 2 above as being difficult to sort out.
VR is by all accounts not a very stable state of affairs (as the RAE found when trying to stay in it for the trials I mentioned earlier) so I have a gut feel that a quick AUTO nudge forward
(5 deg?) of the engine nacelle tilt angle might be sufficient to kill the build-up of VR before it spreads to the whole blade.
If all this is allied with a unique and unmistakable warning to the pilot to initiate a go-around then perhaps the job of avoiding the accident might be completed.