Are V22 flight envelope restrictions relevent to a completely different aircraft with purported lower downwash (and therefore disc loading)?
Bell claimed that lower disc loading on the BA609 incresed max RoD before VRS. Seems like they planned on a 800ft/min "normal operation limit" based on some sort of safety factor, since VRS occured 2000-5000ft/min. This is an old article, so I wonder if flight testing has since expanded the "normal" RoD limits.
Staying flexible - and safe
The issue of vortex ring state highlighted by the V-22 crash will be tackled mainly by training pilots to stay within the proper flight envelope, says Barbour, and by teaching them how to recognise and escape the condition. A form of rotary-wing stall, vortex ring state occurs when the aircraft catches up with the wake ejected by the rotor. "That will require a very high rate of descent in this aircraft because of our disc loading, and this is desirable for us," he says.
The normal rate of descent in the BA609 will be 300-500ft/min. At 800ft/min the pilot will receive an indication that descent rate has reached the limit of normal operations. This is well below the 2,000-5,000ft/min rate required to enter vortex ring state, says Barbour. And if the pilot does encounter vortex ring, escape will be a matter of tilting the nacelles down and applying power to accelerate out of the proprotor wake, he says.