http://www.dau.mil/educdept/mm_dept_resources/reports/v22-final-report.pdf"2.5 AUTOROTATION
The JORD states that the V-22 must be capable of performing a survivable emergency
landing with all engines inoperative, and identifies the requirement for the aircraft to be
capable of conducting a power-off glide/autorotation. The Panel members heard from the
Director of Operational Test and Evaluation that,
“Basic rotorcraft engineering analysis
indicates that the V-22 will have a difficult time achieving a stable autorotation following
a sudden power failure at high power settings, and that the probability of a successful
autorotational landing from a stable autorotative descent is very low.” According to a
white paper provided by the V-22 Program Office, the capability of the V-22 to perform
autorotations was examined during the developmental phase of testing. “V-22
developmental testing included autorotative descents in the aircraft and autorotations to
landing in the simulator…The V-22 has demonstrated stable autorotative descents as
described above in flight test and offers enough control to the pilot to touchdown at a
survivable rate of descent,
but evaluations in the simulator have shown limited
repeatability of making a safe landing at the touchdown phase. This is largely due to the
small amount of energy in the rotor system available to the pilot for managing descent
rate and speed at touchdown.
The proprotor disc of the V-22 is relatively small when compared with those of
helicopters. The size of the disc was defined in large part by the requirement to
accommodate shipboard operations. The twisted proprotor blades were designed as a
compromise that would permit hover performance in the helicopter mode and turboprop
cruise performance in the fixed-wing mode. From an autorotative perspective, these
designs
result in higher rates of descent, higher airspeeds, and less rotor energy at the
bottom of an autorotation available to convert to lift. This necessitates run-on landings
at
higher airspeeds (60kts) than helicopters at the bottom of the autorotative descent.
NATOPS contains preliminary procedures (currently being revised) for autorotation.
While
not fully tested in Developmental Test (DT), the intent is to give the pilot the
procedures that would maximize the probability of a favorable outcome should an
autorotation occur.
FMF pilots are not cleared to conduct autorotations except in
emergencies; practice autorotative descents also are not allowed. All pilot training for
autorotation and airplane mode power-off glide
is via simulator. (i.e. it's too damned dangerous to practice!)
While autorotations may be problematic for the V-22, development test pilots have
concluded from simulation and high altitude tests that an airplane mode glide landing can
be performed with repeated success to
a hard surface runway.WHAT RUNWAY???
They believe its performance will be similar to other fixed-wing aircraft with
similar glide characteristics. 4.6:1 glide ratio, 110 lb/ft^2 wing loading and 90knot stall speed? What "similar" aircraft do they mean? Only the space shuttle has a worse glide ratio of any similar sized airplane that I know of...
V-22 pilots receive simulator training in the proper techniques for unpowered airplane
mode landings, but as with autorotations, they
do not yet practice them in the aircraft.(Why not?)
The probability of the V-22 being forced to execute an autorotation vice a power-off
glide is low. The combination of high engine reliability, large separation between
engines, lower vulnerability to ground fire than CH-46/53 predecessors, and the lack of a
tail-rotor make the chances of an autorotation lower for the V-22 than for a typical
helicopter. It also must be stated that the V-22 is a hybrid aircraft designed to an
employment concept requiring 70 percent of its airborne life to be spent in airplane mode
and only 30 percent of its airborne time spent in conversion or helicopter mode. To
further reduce the possibility that the aircraft would be forced to perform an autorotation,
V-22 pilots are trained to transition to (or stay in) airplane mode after a single engine
failure. Helicopter and conversion modes are allowed to accommodate land ing, but this
proactive strategy places the aircraft into the safest possible posture should the second
engine or interconnect drive shaft (ICDS) fail. One note of concern, however, is that
according to the NATOPS emergency procedure for single engine flight, at the
conclusion of the airplane mode flight, aircraft should be landed vertically. According to
the Bell Boeing test pilot,
this discontinuity is probably due to the lack of experience
among the V-22 community with glide landings, and the lack of sufficient developmental
test in this area."(This whole paragraph is a bureaucratic excercise in rationalizing away a real risk as "unlikely" but in reality it is highly likely if the insurgents understand anything at all about the V22, they will take advantage of this weakness to bring it down by shooting at both engines simultaneously.)
Conclusion: The V-22 has less autorotative capability than most helicopters and more
than any fixed-wing aircraft.
(This is an idiotic statement - fixed wing aircraft don't have a need to "autorotate" because they don't hover near the ground in the first place. They maintain a decent altitude and have a high enough lift to drag ratio that they can actually glide somewhere SAFE to land.)
Conclusion: The high disc loading of the V-22 limits the potential for improvement to its
autorotative capability.
(i.e. Polite way of saying (disk loading is the helicopter equivalent of wing loading for a fixed wing aircraft) that this thing can't be autorotated.)
Conclusion: The V-22 has less power-off glide capability than most fixed-wing transport aircraft and more than any helicopter.
Recommendation: Reassess the requirement for autorotative flight in view of the low
need, low probability of improvement and the existence of alternatives.
(Translation: When you can't meet the specification, just find an excuse to waive the specification instead.)
Conclusion: The V-22 community does not appear to place enough emphasis on the
glide- landing capability of the aircraft as an alternative to autorotation, especially in the
one-engine-out procedures.
(No joke Sherlock...)
Recommendation: Reassess the capability of the V-22 to conduct power-off glides.
Explore design and operational techniques to optimize power-off glide capability (e.g.,
minimize proprotor drag commensurate with auxiliary power requirements).
(Again..what was I saying earlier in the original thread???)
Recommendation: Ensure that the full flight simulator used by pilots at Marine Corps
Air Station, New River accurately emulates both autorotative and power-off glide
simulations to the degree required for effective pilot training.
(Translation: It's SO dangerous to practice autorotation or power off glide in the V22 that it MUST be simulated and only ever attempted in an emergency. This begs the question, "how accurate will the simulation be?" if they can't really practice it in actual flight.)
Some more from the same report:
"V-22 Autorotation Characteristics * Relatively high disc loading makes autorotation more problematic than for equivalent weight helicopter
* Autorotation and power settling per se are not unique tiltrotor risks, but depending on altitude, once in
autorotation or power settling situation, tiltrotor configuration lends itself to
a potentially worse outcome
than for equivalent helicopter configuration."Hmmm....just what I stated in the original thread... the damn thing will perform worse than a helicopter in engine-out.. they are being amazingly polite in glossing it over with "potentially worse outcome"...
"The ability to transition to airplane mode after an engine failure and perform a precautionary landing
on a runway means there should rarely be a need for two engine-out autorotation."
Again WHAT runway are they talking about? If the thing is hovering or loitering in an urban area at low altitudes the runway will far out of glide range. 1,000 foot of altitude will equal, at best 4600 feet of glide range. What are they going to use it for? Perimeter patrol of the Baghdad airport? That's the only way it will be able to "glide" to a landing -i.e. if it is already in the traffic pattern at the airport.
This thing is dangerous and it's going to get Marines killed in combat.
Doug De Clue
Orlando, FL
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