From a helo newsgroup:
http://yarchive.net/air/vortex_ring.html
"Vortex ring is the fancy term for the rotor eating its own downwash. Simply
said, when you descend near vertically at the same speed as your downwash, you
invite the rotor to simply push around the same old air, instead of making
mayhem on fresh stuff. If the rotor eats its own downwash, the net effect is
on the power you must use to prevent rapid descent. Basically, the rotor
wastes so much power just churning air that there isn't any left over to break
your fall ( we could describe powered flight as the clever use of fuel and
noise to temporarily prevent falling). The magic descent rate depends on the
disk loading (pounds of gross weight per square foot of rotor disk). The
lighter the disk loading (like in typical recip trainers) the easier it is to
find Vortex Ring state in a normal approach. <b>Typical downwash (induced)
velocities for light recips might be about 10 knots (17 ft per second, 1000 ft
per minute). If you steeply descend near that rate, you will nibble at Vortex
Ring.</b>"
http://www.globalsecurity.org/military/ ... 22-vrs.htm
"...Recovery from VRS in conventional helicopters, altitude permitting, is generally to reduce power and lower the nose attitude of the aircraft, regaining forward airspeed and permitting reapplication of power to stop or limit the rate of descent and minimize altitude loss. In the V-22, upon recognition of entry into VRS, the pilot must also respond immediately, in this case by reducing the nacelle incidence to below approximately 80 degrees <b>(a much more powerful anti-VRS input than lowering the nose)</b> while at least momentarily reducing power. When forward airspeed begins increasing, reapplication of power is possible to minimize altitude loss."
http://usmilitary.about.com/cs/weapons/a/osprey.htm
"“The V-22 is much less susceptible to vortex ring state,” Schultz said. “It takes a lot more to get a V-22 into the vortex ring state than any other helicopter.”
The tilt rotor technology even allows for a quicker recovery from this problem by tilting the rotor forward from the helicopter mode and flying out of the vortex ring state, said Lt. Col. Kevin Gross, the chief test pilot from the Marine Corps for the program. To further safeguard against the problem, a device was installed that gives pilots 18 seconds of warning that they might be entering vortex ring state."
http://www.aviationtoday.com/cgi/rw/sho ... tebook.htm
"Experts agree that any rotorcraft is vulnerable to vortex ring state. (Macdonald's flight test work, therefore, may help advance the safety of all helicopters eventually.) Relative to the phenomenon, though, the V-22's side-by-side rotor design poses a unique problem. The likelihood is that one rotor will enter vortex ring state before the other, resulting in the kind of severe roll-over seen in the Marana crash sequence. The recovery procedure that Macdonald developed and demonstrated is impressive. <b>By rotating the nacelles and rotors forward for just 2 sec., enough forward thrust is generated to dissipate the vortex ring state and allow the aircraft to fly away safely</b>"
http://www.helicopterpage.com/html/tiltrotor.html
"One VERY IMPORTANT thing to point out here is that the V-22, once it has encountered Settling With Power (Army) or Power Settling (Navy), has a unique ability to get out of it. It does so without aggravation of the situation that <b>normal helicopters do not have</b>. The nacelles have a control switch which can be "Beeped" (Quick pressing of the switch to make small movements) up or down to change the angle of the nacelle. This can increase forward airspeed quickly without changing the pitch of the prop-rotors. Increasing airspeed and flying into clean air is the way to get out of the Vortex Ring State which is responsible for the "Settling" issues. <b>The V-22 has the unique ability to increase airspeed without changing rotor pitch and can accomplish the airspeed increase much faster than any normal rotary wing aircraft.</b>"
A 45 has a muzzle.
A 9mm has a bullet vent.