Tilt Rotor Autorotation performance IS a risky business.
One source of information:
https://fas.org/man/dod-101/sys/ac/v22-report.pdf
A Quote from the USMC Osprey Fact Book found at DTIC.
Myth: The V-22 is unsafe because it can’t autorotate
Fact: The V-22 is a tiltrotor and does not rely on autorotation for
a survivable power-out landing. The wide separation of the engines and the ability to drive both rotors with one engine make a power-out landing extremely unlikely. However, if required, the V-22 can glide for a predictable run-on landing in airplane mode, much like a turboprop.
From a "Vertical" Article:
If Things Go Bad
Nearly every system in the Osprey is triple-redundant. There are three flight control computers, three lightweight inertial navigation systems, three hydraulic systems and four generators. The V-22 only requires one of these systems to safely continue flying; the others exist for safety purposes, yet have identical functionality. This doesnt mean that things cant go wrong as with any aircraft, there are obvious emergencies that require learned procedures to overcome.
Stalling the Osprey is a definite possibility when youre flying in the low end of the airplane-mode flight envelope. Typical stall speeds occur around 105 to 110 KCAS, depending upon aircraft conditions; fortunately, its rare to be flying that slow without having converted. One situation that can be encountered, however, is an accelerated stall, because the stall speeds can increase upwards of 140 KCAS as the bank angle increases.
Normal stall characteristics in the V-22 are very benign: about the only indication that the airplane is stalled is the increase in descent rate on the display. Because the Osprey exhibits blown wing characteristics, it is very difficult to develop a full stall, thereby making the effects less dramatic. Continuing into a full stall will result in a nose-down pitching moment, but the effect is not nearly as dramatic as with some airplanes. Recovery is the same as with any airplane: reduce the control stick backpressure and apply full power: the Osprey will break the stall almost immediately. On the primary flight display, a stall meter is displayed below a 35-degree nacelle setting, showing a dynamic percentage of the stall to assist the pilot.
Probably the most discussed issue with the Osprey is the lack of autorotational ability. Of course, the Osprey spends the overwhelming majority of time flying as an airplane, so its easy to see that the need for autorotation is pretty minor but as Murphys Law states, when you least expect it, things can indeed go bad very quickly.
Technically, the Osprey can actually enter autorotation, although the flight characteristics are extremely poor. Reduce the TCL to the full aft position with the nacelles full aft and the rotor system is being powered solely by the upward flow of air through the rotors. The greatest detriment to the autorotational capability of the Osprey is the very-low-inertia rotor system, which doesnt store as much energy as a traditional helicopter rotor system. Rotor r.p.m. will bleed off very quickly if the autorotation is not entered almost immediately, and it is very difficult to recover lost r.p.m. Stopping the nacelles at the full aft position is also critical, because any edgewise airflow over the rotor will rapidly decay r.p.m. This also corresponds to very poor qualities during the flare and touchdown portions of an autorotation. The autorotational descent rate is quite large about 5,000 feet a minute and an aggressive and rapid flare is necessary to arrest that rate. An increase in r.p.m. will be briefly noticed here; but, again, due to the low inertia of the rotor system, that gained r.p.m. will very quickly start to decay.
Autorotations are taught and practiced in simulators with varying degrees of success. The simulators are designed to indicate a crash if any structural load limitations are exceeded; most autorotations end in a red screen. The truth of whether an autorotation is survivable, though, is hard to define. Chances are that an autorotation in an Osprey would be an extremely difficult maneuver, with survival owed more to luck than skill.
The loss of both engines in airplane mode requires very similar emergency techniques as utilized in a twin-engine airplane. However, as mentioned earlier, unlike an airplane it is impossible to feather the proprotors. The glide ratio of the Osprey is about 4.5 to 1 and the rate of descent while windmilling is about 3,500 feet a minute at 170 KCAS. Landing speeds vary with aircraft weight, but a middle-of-the-envelope speed is 130 KCAS. Unfortunately, the proprotors will definitely impact the ground, and converting the nacelles is not recommended. A safety design feature of the proprotors, however, is for them to broomstraw and throw the resulting fibers away from the fuselage to minimize damage to the occupants. Unfortunately, this characteristic has been tested in accidents; fortunately, it works as advertised.