Why the V-22 Osprey is Unsafe

     G2mil has attempted to expose the largest scandal in US military history for several years.  A total of eight articles about the unsafe and costly V-22 Osprey have appeared, one in the last issue while the others can be read by following this link: V-22 articles.  In early 2004, an outside aviation expert briefed top Generals at Headquarters Marine Corps about lingering safety concerns over the V-22.  This copy was provided by a concerned former Marine Corps officer:

Lingering Safety Concerns Over V-22

by XXXXXXXXXXX

from XXXXXXXXXXXXXXXXXXXXXX

12 December 2003

After three years of careful study and analysis of the V-22 following the tragic crash at Marana, Arizona in March 2000, several safety-related issues continue to concern me about the safety of flight of V-22 within a combat or hostile environment. The significant mission advantages V-22 offers have been addressed elsewhere; the focus of this paper is limited to safety concerns that remain after completion of all modifications implemented since the last mishap at New River.

From my point of view, there are six critical issues whose operational consequences need to be understood by decision-makers as these may affect the future operational safety of this aircraft and the survivability of aircrews in a combat environment. The six issues are:

  1. The V-22’s lack of an autorotation capability, or even a demonstrated all engine inoperative safe landing capability, remains cause for concern.  V-22 fails to meet the ORD threshold requirement for a survivable emergency landing with all engines inoperative from a large portion of its operating envelope.
  2. V-22 flight characteristics in VRS (vortex ring state) are problematic for roll control and the aircraft is susceptible to un-commanded rolling as a result of saturation in the roll channel of the flight control system when the aircraft is operated into VRS. This aircraft response to VRS phenomenon is drastically different than that of any conventional helicopter.
  3. The V-22 is prone to roll PIO (pilot-induced oscillation) in helicopter mode during high gain pilot tasks such as shipboard operations, precision hover in confined areas, or precision hover/landing in obscured visibility.
  4. The V-22’s high vibratory loads, coupled with a very flexible structural design and complex hydraulic system, is problematic for hydraulic, electrical, and mechanical systems and is likely to lead to high failure rates for these systems. Many such failures have safety implications.
  5. The V-22’s susceptibility to wake or tip vortices from other aircraft is problematic for roll control and can result in un-commanded rolling of the aircraft. At low altitude, this could lead to a loss of an aircraft.
  6. The V-22’s high downwash velocity field has the potential to produce significant detrimental effects on hovering operations in desert environments or over water.

The six issues are discussed in the body of this paper. These should be closely monitored in future operational testing and evaluation, and corrective actions taken where possible through equipment changes, training, and changes in tactics, procedures and techniques. Many of these concerns, however, are inherent in the V-22 design and may be difficult to extenuate. Understanding the substance of the issues is key to understanding the operational consequences.

1. LACK OF AUTOROTATION CAPABILITY

Although it was initially believed that V-22 would have a full autorotation capability, it is now generally agreed that the V-22 cannot autorotate in any practical sense. Although the V-22 has performed an autorotation in a technical sense, the test procedure was carefully structured to allow for a safe entry (the engine power was slowly removed to allow the aircraft to establish a stable autorotation.) In a practical autorotation, the aircraft must be able to enter a stable autorotative state following an abrupt power interruption. Although an abrupt removal of engine power in V-22 has never been done, such an event would probably result in loss of control because of the inability to maintain rotor RPM. This is especially true if the failure occurs in transition mode  (60 deg nacelles)[1], the common configuration used for “slinging” external loads.

The single autorotation test in V-22 also demonstrated that the attempt to recover from autorotation to a safe landing by using stored rotor energy to arrest the rate of descent failed markedly. The test data indicate that the aircraft would have impacted the ground at a rate of descent of about 3700 ft/min (61.7 ft/sec) ¾ a fatal rate-of-descent.  Authoritative proponents, e.g., the NASA Review Team, have argued that autorotation is not a needed capability for the V-22 due to the low probability of a two-engine failure. My analysis of Navy safety data shows that the Navy/USMC experiences a dual engine failure in a helicopter about once every 3 to 4 years due to fuel contamination onboard a ship. Historically, such accidents have usually been survivable because the helicopter autorotates into the water and the crew and passengers quickly scramble out.  If such an event were to occur in V-22, it will probably be fatal to crew and passengers because the aircraft will not smoothly enter autorotation, but most probably depart from controlled flight, and because the cabin is too cramped for a rapid egress.

We know from the combat record in Vietnam[2] that many ground fire hits on a helicopter result in a need for an immediate autorotation. Of the 3,000 or so helicopters lost during the Vietnamese conflict, fully 80 to 90 percent were lost on approach to landing (i.e., where V-22 would be operating in helicopter mode), approximately half safely autorotated to the ground, thereby saving the crews. Even though the V-22 rotors are interconnected, some combat fire hits can be expected to result in loss of both an engine and the rotor interconnection. Such combat events in V-22 would be fatal.

Autorotation is to a helicopter pilot (and his passengers) what an ejection seat is to a fighter pilot. When everything goes wrong, as it often does in a combat environment, autorotation is all a helicopter pilot has to save his and his passenger’s lives. As good as the V-22’s survivability features may be (and they are very good), there will still be times when everything does go wrong; at those times autorotation could be the difference between a chance for survival and a fatal outcome. The lack of autorotation capability in V-22 is inherent in this tilt-rotor design given current technology options. The mission advantages provided by the tilt-rotor design, such as long range and high speed, afford survivability advantages during the ingress portion of a mission, but for landings into a hot zone, the lack of autorotation capability is an important factor whose consequences should be clearly understood.

In my view, V-22 fails to meet the ORD threshold requirement to be able conduct a “survivable emergency landing with all engines inoperative” over a large portion of its operational envelope – helicopter mode flight below about 2000 above ground level. From higher altitudes, or when operating in airplane it is generally believed that V-22 is capable of conducting a survivable, all engines-inoperative emergency landing, although considerable risk is incurred in such a maneuver because of the very high sink rate of V-22 and the high airspeed needed for the maneuver.

2. OPERATION INTO Vortex Ring State

Background

Following the Marana mishap in March 2000, with the realization that VRS may have been implicated in a new manifestation termed “asymmetric VRS,” I began researching the technical literature in an attempt to understand the causative factors and the possible implications for future V-22 operations. I quickly realized that little historical data existed on the subject in the technical literature, and more importantly, that the critical testing of the effects of this phenomenon on V-22 had not been conducted.  The Navy and the contractor, Bell/Boeing, to their credit immediately initiated plans to conduct extensive wind tunnel testing and flight testing to fill this void.

During this effort, I noted that, because of the side-by-side rotor configuration of V-22, the effects of VRS on this aircraft would not depend on rate of descent, airspeed, and pitch attitude alone (the traditional VRS parameters), but also on roll and yaw rates. In this regard, V-22 is inherently different from conventional helicopters because roll and yaw rates alone can change the position of a rotor within the VRS parameter space. Furthermore, the change is always in opposite directions for the two rotors, raising concerns about asymmetric VRS conditions during maneuvering. As a rough estimate, I performed simple calculations of the possible magnitude of this effect and concluded that near the maximum roll and yaw rates capable with the aircraft, it might indeed be possible for the two rotors to enter VRS conditions in an unsymmetrical way, resulting in a departure from controlled flight. Since maximum roll and yaw rates could be used during combat evasive maneuvering, I was immediately concerned over the safety of such maneuvering in the V-22.

To support the conclusions of the rough calculations, consistent with my responsibilities, I solicited the support of the Rotorcraft Center of Excellence at the University of Maryland – one the preeminent centers of such research in the world – where a new form of numerical rotor simulation was being developed. Professor Gordon Leishman agreed to assist. In order to modify their numerical codes for V-22 use, it was necessary to have accurate physical parameters for the V-22 rotors (airfoil section, mass distribution, chord distribution, etc.). I requested these data from the V-22 Program Office through the DOT&E action officer. The required data were never made available. The needed parameters, or reasonable estimates for them were ultimately gleaned from the open rotorcraft literature and the Maryland codes were modified for V-22 use. Dozens of runs were made at varying initial conditions, including conditions where large yaw and roll rates were input. While the numerical methodology necessarily incorporates a simplified model of the V-22, Professor Leishman and I believe that the modeling does capture the basic phenomenology. The results of these numerical calculations confirmed my rough calculations and raised my concern level, which I communicated to DOT&E. Pursuant to this issue, in mid-2001, XXX, through DOT&E, requested the Program to conduct flight testing with V-22 to include three evasive maneuvers that I believe pilots might resort to in combat to avoid enemy fire[3].

In a subsequent technical interchange meeting in late 2002, the Bell/Boeing-NAVAIR team agreed, in principle, that the maneuvers should be done and embarked on an flight test program to include these maneuvers. To date these maneuvers have not been accomplished because the V-22 rotor control system repeatedly exceeded rotor disk flapping limits while approaching the requested conditions. The inability to maneuver V-22 in this fashion without exceeding rotor flapping limits is a serious safety concern in itself and argues against the ability of V-22 to safely perform evasive maneuvering in a combat environment.

Summary of the VRS Phenomenon and its Consequences for V-22

Vortex ring state is a flight condition in rotorcraft that manifests as rotor thrust fluctuations without any flight controls inputs. This happens only at slow-speed and in descending flight, during aggressive maneuvering such as may occur in combat, or in unusual wind conditions where the winds are coming vertically from below (e.g. turbulent conditions in mountainous environment or in the vicinity of a ship). Unlike conventional helicopters, such thrust fluctuations are particularly problematic for V-22 because of the side-by-side placement of the rotors, which responds to these fluctuations by creating a rolling moment. In attempting to compensate for these rolling moments, the flight control system of V-22 can reach a saturation point at which the pilot no longer has any control authority. If this occurs at low altitude, the situation could result in a crash.

The very limited maneuvering flight test data given to DOT&E recently clearly show that flight control saturation, as a result of maneuvering, is possible. I believe that this potential for flight control saturation should be viewed with serious concern unless flight-testing shows that such experiences are truly rare. The V-22 Program Office has recently stated that all problems of controllability linked to VRS have been resolved, but The bulk of the flight test data needed to fully assess this phenomenology has not yet been released for independent analysis.

Bell/Boeing has now clearly documented, through flight testing, that V-22’s VRS phenomenology is the same as that for conventional helicopters; however, the consequences of experiencing VRS in V-22 are drastically different than those in conventional helicopters because of the possibility of encountering asymmetric VRS conditions.  Whereas a conventional helicopter upon entering VRS conditions may shudder, shake, and become “sluggish” at the controls, a V-22 may experience an un-commanded roll. This would have profound consequences at low altitude. This conclusion and the associated concern were shared by the accident investigators of the Marana crash, who state in their final report:

. . . a V-22 entering a Vortex Ring State and/or blade stall condition is not peculiar to tilt-rotors. However, the end result, departure from controlled flight, is more extreme than results experienced in most helicopters to date.

The concern over VRS entry in V-22 can only be understood in the context of historical helicopter accident rates. My review of mishap data[4] shows that in normal peacetime operations, a military helicopter crashes, on average, once every 50,000 hours of flying, a rate of 2 accidents per 100,000 flight hours. In combat situations this accident rate typically rises drastically because pilots under stress make mistakes. The accident rate for the UH-1 in 1964 was about 2 per 100,000 flight hours; in 1969, at the height of the Vietnamese conflict, it had risen to 36. And, this figure is likely to be greatly under-reported because many accidents during the war were attributed to hostile fire. Many of these accidents were classified as “hard landings”; in my view, such hard landings can be directly attributable to the common pilot error of placing the aircraft into VRS conditions from which recovery was not possible. 

During the recent Afghanistan operations, the press reported that the U.S. lost 12 helicopters; most of them were classified as “hard landing.” Exact flying hours for US helicopter operations in Afghanistan have not yet been available, but a reasonable estimate can be made based on the number of units deployed, the duration of the conflict, and the assumption of 700 hours per month, per unit. Such an estimate yields numbers ranging from 10,000 to 20,000 hours of cumulative flying and the accident rate for these operations between 60 and 120 per 100,000 flight hours.

What may not be appreciated is that for every crash experienced as a result of this common pilot error, there was likely a much larger number of “close calls” that did not result in a crash because the pilot was able to recognize and correct the error. Statistics on these numbers are not available, but my experience as a pilot tells me that the ratio may be as high as 10 to 1. The issue here is that in V-22, a number of the “close calls” would become casualties because the V-22’s response to this common pilot error can be an un-commanded roll, which makes recovery at low altitude improbable.

3. Tendency to PIO

The fundamental characteristics of V-22, which include a very high roll moment of inertia and roll control implemented through differential rotor thrust (differential control power) results in a rotorcraft with a tendency to PIO. Significant flight control software improvements since the early days of the program (late 1980s) have significantly decreased this tendency, but some concerns remain. 

In 1999, a V-22 operating from the deck of the USS Saipan narrowly avoided a catastrophic accident when the pilot initiated a PIO resulting in the aircraft’s prop-rotors nearly contacting the deck of the ship. The pilot was highly experienced and the wind and sea conditions were benign at the time. With a lesser skilled pilot, or more demanding environmental conditions, this event could have easily ended tragically. During the operational evaluation (OPEVAL) in 1999-2000, at least one pilot reported a distinct susceptibility to PIO and commented on the consequences for less than highly experienced pilots:

The aircraft is somewhat unstable in the lateral axis during wave-off. Pilots who are high gain will have trouble flying this aircraft. Extreme attention must be paid to preventing over-controlling this aircraft in the roll channel.

This same susceptibility has also resulted in the inability of V-22 to conduct air-to-air refueling operations when configured in conversion mode (60° nacelle angle).

Examination of the V-22’s frequency response plots (Bode plots) in 2000 showed that the aircraft failed to meet the basic stability requirements mandated for rotorcraft[5] and was indeed PIO-prone. Since 2000, the Navy and Bell/Boeing have stated that the frequency response of the aircraft has been modified to remove this tendency. Updated Bode plots have not been made available to date.

The tendency to PIO could, in rare, but not negligible, circumstances, could result in the loss of an aircraft.  These circumstances include: shipboard operations, attempting a precision landing in confined areas, and attempting to land in limited visibility such as a desert environment at night. Although such events will be rare, they are likely to be more frequent than they historically have been for conventional helicopters, which exhibit no such tendency.

4. EFFECTS OF VIBRATORY LOADS

            The forces that drive vibrations in V-22 are not much different than those that drive vibrations in conventional helicopters; however, the characteristics of the V-22 structure are such that the deformations involved in these vibrations are much larger. This is because V-22 is a much more flexible structure than a conventional helicopter – a conventional helicopter is typically a prolate spheroid (football) shaped structure while V-22 is a large “U”-shaped structure with two very large masses at the ends (the engines). The result is the need for long and flexible runs of hydraulic, electrical, and mechanical lines that are more susceptible to tensile loads, bending loads, abrasions, and deformations than conventional helicopter designs. Furthermore, because of V-22’s mechanical complexity, there are many more lines and connections between lines than there are in conventional helicopters. For example, V-22 has a total of 48 hydraulic line segments within the engine nacelles that are “downstream” of leak isolation circuits. A leak in any one of these 48 lines will put a V-22 into a dual hydraulic failure situation. This is a serious situation for V-22 because under this condition, the rotor blade pitch rate will be different on the two rotors resulting in large rolling and/or yawing moments when the flight controls are moved.

This susceptibility of the principal aircraft systems is likely to lead to higher failure rate of these systems. Failure of these components can be expected, albeit in infrequent occasions, to contribute to catastrophic accidents. Experience with the aircraft and component redesign will certainly improve the situation over time, but the root cause will remain. Suitability data will need to be watched closely in future operational testing (OT IIF, OT IIG)  as to safety implications.

5. SUSCEPTIBILITY TO WAKE AND TIP VORTICES

            There is considerable flight evidence to indicate that V-22 response to the interception of a wake or wing-tip vortex by one of the prop-rotors can be an un-commanded roll[6]. There have been at least three cases where an un-commanded roll was experienced in a V-22 as a direct result of flying in proximity to another aircraft.  NAVAIR and Bell/Boeing have addressed this problem by placing strict operating limitations on the allowed proximity to other aircraft – currently 250 feet laterally with at least 50 feet vertically. There are two concerns here: First, both wake and wing-tip vortices are known to persist for a very long time and for long distances depending on wind conditions. The FAA guidelines are to remain at least 2,000 feet from other aircraft to avoid intercepting such vortices. Second, in situations of low visibility or confined landing areas, pilots are likely to ignore this limitation to some degree. Flight testing to quantify the degree and extent to which this is a real problem in V-22 (TR-65) is planned but as of now remains to be conducted. Given that air assault, one of the V-22’s primary missions, is by definition many aircraft landing in the same general location at the same time, there is cause for concerns.

6. HIGH DOWNWASH VELOCITY

Because of the high disk-loading of V-22, the downwash velocity is about twice that of any conventional helicopter, and because of the side-by-side placement of the prop-rotors there are two distinct downwash wakes that are transverse to the flight direction. This has several operational implications that bear on safety issues. The most critical one, I believe, is the effects of downwash on landings at night in a desert environment – a challenge in any helicopter, but more difficult, and potentially dangerous, in the V-22.

We have seen a limited number of operations under these conditions, and the experience has not been good. Aircrew comments from the OPEVAL are best for summarizing the concerns:

“During CALS it was extremely difficult to safely clear the aircraft in and out of the zone.  . . . we are going to big landing zones right now and smaller landing zones will greatly increase risk of prop-rotor or fuselage contact with obstacles.”   (Flight Engineer)

“Poor visibility from aircraft under NVG’s do not allow proper separation from terrain/trees etc. and are a high risk item.”   (Flight Engineer)

“ Landing in the desert will prove to be a challenge to aircrew. . . . Brownouts will be a common occurrence.”   (Pilot)

“Could not land the majority of time because the rotor wash created a brown out condition.”   (Cabin Crewmember)

“High velocity rotor wash does not enable the V-22 to operate in the same environment as the aircraft it is replacing (CH-46E/CH-53D)”   (Cabin Crewmember)

“Excessive dirt and sand intrusion is evident during desert landings. Numerous failures and faults post landing (DSIU, NIU, RAPS). Most problems can be cleared by restetting the circuit breaker, but dirt and sand is having negative effects on any system.”   (Pilot)

“Sand/desert landings were not possible this evening.”    (Pilot)

“Dust cloud was made even when hovering 150’ up.”   (Pilot)

“Dust generated up to a 200’ AGL hover – reduces vision significantly and also clogs the nacelle oil coolers causing PRGB/TAGB hot cautions.”    (Royal Navy OTD)

“True desert is extremely challenging to land in the V-22.”   (Pilot)

“The best way to fly this airplane is on a sunny day about 70 degrees, no humidity to a paved landing strip, this is from a maintainers point of view because this aircraft ingests all of the above and it ruins parts.”  (Crew Chief)

In a similar vein, I witnessed the first set of operational water operations during OPEVAL. On the first pass, while attempting to reach “10 and 10” (10 feet above the water at 10 knots ground speed) the pilot clearly lost visual contact with the water surface and plunged the belly of the aircraft into the water. In this case, recovery was possible and immediate; in future similar events, things could go differently.

As additional V-22 experience is gained, pilots may develop techniques to reduce the impact of V-22 downwash upon the ability to conduct desert landings.  However, unless such techniques prove successful, the ability to land in the desert at night will remain cause for safety concern.

FINAL COMMENTS

In addition to the problems described above there are other V-22 idiosyncrasies to confront the careless or fatigued pilot, pitch-up with sideslip and over-modulation of nacelles being two of the most significant.

The bottom line is that all of the these concerns argue that V-22 is likely to have a larger accident rate when operating within a combat or hostile environment than any conventional helicopter simply because the aircraft has many more ways of getting into trouble than does a conventional helicopter. Unfortunately, all of these issues are the result of basic design features in the V-22 and cannot be changed – the side-by-side rotor configuration, the high disk-loading, and the roll/yaw control implementation through differential thrust. There is not much that can, physically, be done about it. Extensive education and training of aircrews and better warning systems will certainly help, but will not remove the fundamental susceptibility.

[1]  With a sudden power loss with the nacelles at 60 degrees, the relative wind is approximately in the plane of the rotors, thereby acting to stop the rotors.

[2] SEA After Action Report, Rand Corp, 1976

[3] These maneuvers consisted essentially of maximum rate course reversals and landing zone aborts and are consistent with the definition of “aggressive agility” as required for utility rotorcraft in ADS-33E,  Performance Specification, Handling Qualities Requirements for Milirary Rotorcraft, 21 Mar 2000.

[4] USN, USAF and USA mishap statistics supplied to IDA by the Services safety centers.

[5]  I recognize that the V-22 is a tilt-rotor rather than a conventional rotorcraft.

[6] Two DRs (deficiency reports) and one comment in the OPEVAL database between 1998 and 2000.

                                                                  Name Withheld

G2mil Comments

Operation in Vortex Ring State

     Examples of helicopter pilots entering VRS are provided by Marine Colonel R. E. Joslin in his June 2003 article in Approach magazine.  Note that these experienced pilots entered VRS despite their training which resulted in "hard landings."  If these pilots were flying V-22s, the aircraft would have rolled over.  While in the helicopter mode with rotors up, anytime a V-22 hits turbulence caused by weather, nearby aircraft, or its own wake, each rotor encounters different conditions.  The rotor with the most solid air underneath produces more thrust causing the V-22 to instantly roll in the other direction.  Rotor thrust imbalances can also occur because of mechanical problems, damage from enemy fire, or when one rotor is suddenly closer to the deck, like the edge of a ship, building, or cliff.

     A snap roll can usually be averted if the pilots recognize it immediately and have sufficient ground clearance to make a correction by tilting the nacelles forward until they get "new" stable air under their rotors.  If not, the V-22 will roll over and kill everyone aboard, as it has done in every fatal V-22 crash.  This is not a problem with helicopters as their rotors are attached directly to the fuselage near the aircraft's center of gravity.  When helicopter pilots encounter problems, they remain upright  and can focus attention on the emergency, and if they hit the ground, it is usually on their sturdy landing gear which minimizes damage.  In contrast, V-22s wobble with roller coaster type G forces as pilots struggle to keep upright.  Although the V-22 is designed so that one engine can turn both rotors should the other fail, enemy fire or mechanical damage to a rotor or gearbox can cause an instant loss of thrust to one rotor allowing the other rotor to instantly flip the V-22 over.  A cart wheeling V-22 will not only destroy itself and passengers, but nearby aircraft and people on the ground or on ship.

Tendency to PIO - Susceptibility to Wake and Tip Vortices

    In September 2004, a V-22 pilot attempted to reassure aviators that VRS was no longer an issue with an article in Naval Proceedings magazine.  He didn't claim the problem has been solved, but that it is better understood.  The V-22 test program had conducted several VRS tests at high altitude.  He noted:  

"During our testing, we experienced 12 roll-off events, 8 to the right and 4 to the left. The direction of roll off was not predictable from the cockpit. In fact, the cockpit characteristics approaching VRS were not as well defined as in single-rotor helicopters. We noticed a slight increase in vibration, rotor noise, and flight control loosening that would not in every instance foretell of an impending roll off. Each roll off, however, was characterized by a sudden sharp reduction of lift on one of the two proprotors, resulting in an uncommanded roll in that direction. We also noted that roll offs required nearly steady-state conditions to trigger them. Any dynamic maneuvering tended to delay or prevent a roll off from occurring. On many occasions, we entered the VRS boundary during dynamic maneuvers and then exited the boundary without encountering a roll off."

    Warning systems have been designed to help pilots stay out of VRS, but pilots may ignore such devices in combat.  Although pilots testing VRS easily regained control, they had plenty of altitude and focused exclusively on VRS.  However, pilots flying operational missions will have a dozen other things on their mind and may not respond to VRS warnings for several seconds.  And there will be no VRS warning from ground effect imbalances, high winds or wake and wing tip vortices from nearby aircraft.  As a simple example, if you are driving a test car to see how it handles during a tire blow out while rounding a corner, you will be prepared to handle that emergency and can "prove" it is not a problem.  Yet if you are driving in the rain while looking at a map as children play in the backseat and a tire unexpectedly blows out while rounding a corner, you may lose control. 

     As that V-22 test pilot noted: "We noticed a slight increase in vibration, rotor noise, and flight control loosening that would not in every instance foretell of an impending roll off. Each roll off, however, was characterized by a sudden sharp reduction of lift on one of the two proprotors, resulting in an uncommanded roll in that direction."  Once again, this problem is unique to the V-22, and is mostly likely to occur while pilots are focused on complex tasks related to approaching a landing zone or ship.  Moreover, they may not have enough altitude to tilt their rotors forward to regain control should VRS warnings sound.  Lastly, transport helicopters often fly in close formation.  Suddenly tilting rotors forward to avoid VRS is likely to cause a collision with an aircraft in front, or possibly a building or mountain.

Effects of Vibratory Loads

     The author noted the effects of vibratory loads because of the V-22's unusual U-shape design along with lengthy hydraulic lines needed to tilt the wing-tip engines.  The V-22 has a very poor vertical lift capability.  It can only lift one-third as much as modern helicopters of its size, like the CH-53X, despite the fact that it is made with the lightest weight materials available.  It is mostly a composite (plastic) aircraft which vibrates much more than traditional aluminum or fiberglass airframes.  In addition, its small blades are much more rigid to also act as propellers in the aircraft mode.  Helicopters have long, flexible blades which act as shock absorbers.  As a result, stresses from air turbulence and maneuvering encountered by the V-22's more rigid rotors are transmitted directly into the rotorhub and aircraft; imagine a car without shock absorbers.

      Because of this lack of blade flexibility, sharp maneuvers have caused new lightweight composite parts in V-22s to break during testing, so further tests were recently cancelled. The Fort Worth Star-Telegram published an investigative report on September 26, 2004 by Bob Cox on recent V-22 testing which noted: 

Some testing was done. But a series involving specific, sharp defensive maneuvers was skipped after Bell engineers warned that it would severely damage the rotors, according to a source within the testing program who asked not to be identified for fear of losing his job.

Several people told the Star-Telegram that the canceled tests are important.

Program officials feared the maneuvers would damage the aircraft.

Tom Christie, the chief weapons tester for the Pentagon, acknowledged to the Star-Telegram that the "most severe maneuvers" were not conducted during recent testing. When asked whether the skipped tests signal shortcomings that could affect the V-22's performance in combat, he did not answer directly.

"The tactical implications of this limitation have been carefully considered and will continue to be reviewed," he said.

     Another problem is the V-22 uses a unique lightweight 5000 psi hydraulic system that caused many problems in the past, spouting leaks 171 times during operational testing in 2000 and was the primary cause of the last fatal crash.  Helicopters use larger and heavier 3000psi systems with stainless steel lines.  While titanium is stronger than stainless steel, it is more brittle, more costly, and more difficult to manufacture.  This is documented in a June 24, 2002 Department of Defense Inspector General Report which shows the hydraulic lines on the first dozen V-22 production aircraft were failing after less than 10% of their expected service life.  A hydraulic line leaked somewhere on a  V-22 after every five hours of flight time, and every twenty hours it was a line used for flight control.  V-22 program managers claimed that leaks weren't important because the hydraulics system is triply redundant.  However, on page 1 of the DOD IG report it notes: "The design results in a triply redundant hydraulic system, provided there are no failures in the common hydraulic lines of the three subsystems."   

     There are 24 "common" hydraulic lines that provide power for three subsystems that tilt the nacelles/rotors.  There is no back-up or way to isolate these lines should damage occur from enemy fire, a leak due to chafing or fatigue, or from accidental damage during ground maintenance.  Should this occur, as it did during the December 2000 crash, sensors should detect the problem and inform the computerized flight control system.  However, the tilting nacelles that contain the rotors are not physically aligned, they move independently and must be kept in sync by the flight control computer that is reliant on sensors to relay the position of each nacelle/rotor.  Should the sensors fail to accurately report because they are damaged themselves, or should the flight control computer become confused by unusual input as all hydraulic fluid squirts out at 5000 psi in a manner of minutes, the V-22 will begin to wobble and crash, unless the pilots land very quickly.  

     If a leak from a common hydraulic line disables all three systems used to tilt the nacelle, it should freeze in place, and the flight control computer should identify this emergency and freeze the other nacelle in place.  While the pilots can fly with frozen nacelles, a controlled crash landing may be in order depending on their tilt position and if a large hard surface runway is within range.  This is not an issue with helicopters as their rotors do not tilt.

     Because of these problems, many people assumed the V-22 would adopt traditional hydraulic systems as part of its 2001 redesign, adding yet another thousand pounds of weight to an already overweight aircraft.  Instead, the program made fixing the leaky titanium lines its primary focus during the 17-month stand down, adding coatings and stronger fasteners.  However, ten months after resuming testing, the V-22 program announced that all test V-22s would be grounded for ten days to replace defective titanium hydraulic lines.  According to the V-22 program office, these new hydraulic lines leaked during a V-22 assembly test at Fort Worth on December 6, 2002.   They inspected lines and learned they were so thin in places they would only last 10% of their promised service life. This was truly embarrassing because they had selected the world's best titanium manufacturer to produce this key item.  Choosing a new manufacturer to produce new lines would take months, and there was no guarantee anyone could make them to specs.  So they kept word of the defective titanium lines secret until new ones were delivered in March 2003 from two new contractors.  It is unclear why V-22s were not grounded when this safety problem was uncovered on December 6th.

      Luckily, no V-22 crashed during this time.  After a ten day stand down to replace the 20 flight critical lines in the V-22s undergoing testing, Ward Carroll, the V-22 Public Affairs official, explained that replacing all the defective lines, like those that control the ramp and doors, would be too expensive.  Only the 20 critical lines were replaced, while the other 780 defective lines remain in each V-22. So current plans are to deliver the first 60 V-22s with known defective hydraulic lines to the Marines and let them replace them as they begin to leak.

     On August 6th, 2003, even one of the newly replaced titanium hydraulic lines sprung a leak after just a few hours of use during a pilot training flight.  The back up system worked and the V-22 made a safe emergency landing.  The program immediately announced there would be an investigation into the cause, but stated that it was not caused by chaffing or defective lines.  Of course they didn't know the cause, but would never admit the problem had still not been fixed.  The preliminary report was that one of the fasteners had worked itself loose because of normal vibration, which caused a line to leak.  This is not surprising since lighter titanium hydraulic lines with fluid at 5000psi are subject to much greater forces than heavier 3000psi stainless steel lines used by helicopters.  

     Last March, Philip Coyle, a former undersecretary of defense who ran the Pentagon's weapons testing programs throughout the 1990s said: "It's not a question of whether they will leak, but when they will leak."  After this emergency landing, he told "Aerospace Daily":  "How is it after 2.5 years of work here that we're still having this problem? That, I think, is the most important question. What does it say about the developmental work?"  The V-22 program has accumulated over 2000 flying hours since its return to flight in 2002, but these hours have been spread among a dozen new V-22s, and most all these hours were safe, smooth flying in the aircraft mode.  The durability of these composite parts and titanium lines stressed by less flexible rotors remains to be seen.

Lack of Autorotative Capability.

     The ability to autorotate was a requirement for the V-22 as Marine helicopter pilots felt it was essential.  However, testing showed that the V-22 cannot safely autorotate, so waivers were granted and this "JORD" requirement was eventually deleted.  If any helicopter loses all engine power, its large rotors spin rapidly as it descends, then the pilot can "flare" to land safely. This is called "autorotation".  After years of evasion, the V-22 program now admits the V-22 rotors are too small for autorotation to allow a safe vertical landing should both engines fail.  They point out that losing both engines would be extremely rare, so they claim autorotation is not an issue. However, it will be an issue in combat where enemy fire may damage both engines.  As the author noted, problems with fuel gauges, fuel pumps, fuel contamination, aircraft fire, or plain pilot error can starve both engines of fuel and cause them to shut down.  Here is an example from the Navy Safety Center where autorotation allowed a crew to safely exit a helicopter which lost both engines due to a fuel pump malfunction.

      During peacetime, losing power to just one engine is not uncommon, known as One Engine Inoperative (OEI).  If this occurs in a loaded helicopter, most lack the power to stay airborne and begin a controlled descent.  Helicopters can land safely at half power if the pilot descends rapidly enough to flare before landing, just like with autorotation.  But what happens to a loaded V-22 which loses one engine while its rotors are upright?  While the segmented cross-shaft should ensure power to both rotors, its rotors cannot allow the V-22 to flare, so it will hit the ground very hard. 

      This is a key issue, yet the program has refused to test a one engine out vertical landing of a loaded V-22.  They say a V-22 can convert to the airplane mode and land safely at an airfield with a rolling landing with just one engine.  However, a V-22 with rotors up may be too close to the ground to allow conversion to the airplane mode as it falls.  This also assumes that a friendly airfield is in range, which is rarely the case while operating from ships at sea.  

     During sea trials last year, all the oil in one engine leaked out so it shut down. This happened on the deck of a ship, so an unplanned one-engine out test did not occur.  However, one V-22 team member admitted to Aviation Week that a one-engine vertical landing would damage a V-22, although the crew should escape serious injury.  Since engine failures are not unusual, the Marines can expect to have a few $115 million V-22s suffer serious damage from hard emergency landings each year.

     The chief test pilot for the V-22 program, Tom MacDonald, was asked by Rotorhead magazine how a V-22 with one engine out would land aboard ship.  MacDonald said it would be the same procedure for a helicopter; clear the flight deck and perform a rolling landing.  Yet a helicopter would flare just prior to landing and roll just a few feet afterwards.  A V-22 cannot flare and has no tailhook, so it may not be able to stop before rolling off the side of the ship.  This is why the program has no plans to test a one engine out vertical landing aboard ship.

     V-22 apologists use their imagination to dismiss the value of autorotation.  They point out the fixed-wing aircraft cannot autorotate.  However, fixed-wing aircraft are not expected to fly low and slow and land under enemy fire.  In addition, they will always operate within range of an airfield, while a V-22 is expected to operate from ships and remote sites out of range of an airstrip.  As a result, a prudent safety restriction on the V-22 is that it cannot fly unless it has fuel to reach an airfield in the event of an engine loss.  The FAA requires that the flight plan for two-engine passenger aircraft allow it to reach an airfield should one engine fail. This was an issue with the big two-engine 777s flying across the Pacific, which have lost an engine of four occasions.  Unless a loaded V-22 can demonstrate that it can safely land on a ship and grassy field with one-engine out, it must not fly unless in range of a divert airfield, especially since this is a passenger aircraft, not a fighter with an ejection seat.  Of course Marine ground commanders would never accept the V-22 with this limitation, which is why this issue is ignored.

Final Comments

     The author noted: "The oft-quoted mantra of the V-22 supporters: “twice the speed, three times the load, five times the range” is a pure fiction, a fiction that has become dogma through mindless repetition." The most direct comparison is with the new CH-53X which is the same size of the V-22 (empty weight).  It costs one-third of a V-22, has the same range, and can carry three times the payload.  This comparison enrages V-22 supporters who argue that the CH-53X comparison is flawed because it is a heavy lift helicopter, while the V-22 is designed to replace the Marines medium lift helicopter-- the CH-46E.  The V-22 weighs twice as much as the old CH-46E, burns twice as much fuel, but can only carry the same payload and number of passengers as that 40-year old design, and this according to Boeing.  In short, the V-22 is heavy weight size helicopter with poor medium lift performance.  

      The V-22 program spin is to say comparisons to other modern helicopters is wrong, it can only be compared to a 40-year CH-46E which has been safety restricted to half its original payload.  Imagine going to a Toyota dealership and the salesman telling you not to compare a 2005 Toyota to a 2005 Ford or 2005 Honda. He insists you can only compare it to your 1965 Chevy, which is only running on four cylinders, because "that is what you are replacing." I know this sounds silly, but that argument is routinely made by the V-22 program office.  Compared to two modern medium lift helicopters (the US-101 and VH-92), the V-22 is around 40% faster and has the same range, but has 30% less payload, a 25% smaller cabin, costs five times more, cannot autorotate, cannot safely land vertically with one engine out, cannot mount a defensive machine gun, and cannot fit inside a C-17.

      On a final note, why isn't Boeing offering the V-22 for the civilian market?  The answer is because they attempted to gain FAA certification several years ago and failed.  The FAA considers the V-22 unsafe for passengers.  Meanwhile, the Navy is about to award a contract for 23 medium-lift helicopters for the President's fleet.  The battle is between the US-101 and VH-92; both these helicopters use more modern systems than the 20-year old V-22 design.  So why has the White House ignored the V-22?  A White House spokesmen recently dodged the question, but stated that safety was the primary consideration in choosing a design.

                                           Carlton Meyer  editor@G2mil.com

©2004 www.G2mil.com

Letters

V-22 Unsafe?

Just in case you haven't heard I thought I'd pass along a little tidbit from Canada.  A V-22 has been undergoing cold weather testing at the Canadian naval air base Shearwater in Halifax, Nova Scotia.  Last week it  had to declare an emergency while on a test flight off the coast when a 15cm section of one of its rotor blades came off in flight. It terminated the test and managed to make it safely back to the base.  The pilots first indication of trouble were warning lights in de-icing system and vibrations in flight systems. Cause, is of course under investigation but the section of blade came off while the AC was shedding ice.

 
Garry P.Burke
Operations Officer/Officier des opérations
Regional Operations Centre/Centre des opérations régionales
Canadian Coast Guard/Garde côtière canadienne
Maritimes Region/Région des maritimes


Many More V-22 Problems

The V-22 was supposed to be designed as a Troop Carrier Transport to replace what is cleverly called in PC language a "Legacy"; such as the Vertol H-46 (and Sikorsky H-3) which have been flying since the early 1960's. (Note: the "legacy" troop transport helicopters (H-46, H-3) have troop transport cabins which are about 20% larger than the V-22 troop cabin!)  After wasting over $14 Billion of taxpayer funding and the unnecessary death of some 27 crew members, it appears that the V-22 is severely lacking Safety and Human Factor Engineering capabilities - which had been successfully incorporated in the past.

A review of a few items and capabilities of what, after 18-20 years of waste include the following: 

Cabin size:  Was supposed to carry 24 fully equipped troops.  GAO and IG determined that it can safely carry 18 troops! The cabin size as noted is about 20% smaller than the helos 30-40 years ago. This is NOT progress.

Environmental Controls: Supposed to be designed for a wide range of temperature control!  It is actually limited to a temperature of only + - 10 Degrees!   At altitudes with temps of  - 30 deg, the cabin can only generated temps of  - 20 degree and at temps of 130 deg, can only cool down to 120 deg.

Pressurized Cabin: The design and added weight was found to add too much for the Empty Weight of the aircraft and was deleted from the contract Requirements and Specifications.  Virtually all aircraft certified by the FAA and Military for flight above 10,000 feet are pressurized! 

Nuclear Biological Chemical: These were basic requirements for all transports; but the sealing of doors and lack of pressurization caused this capability to be deleted. With this lack, crews must have special suits, masks and helmets which are time consuming and awkward for emergency NBC situations.

Oxygen: Again, because of weight and power requirements, there are only FOUR O2 outlets for the crew! This restriction makes the V-22 unable to carry Troops above 8-10,000 ft altitudes and restricts the Troop carrier to longer ranges and higher altitudes WITHOUT troops on board.

No Windows or Handholds: There are NO windows or Handholds for troops which severely decrease their environmental awareness and stability. With some flight conditions, the troops can become nauseous and sick because of  loss of situational awareness and potential of vertigo.

Baggage and Storage: The need for troop equipment for 'ruck sacks', weapons and other gear are nonexistent!

When 24 troops are jammed into the cabin area; the narrow width of the cabin requires gear to be stacked between each others knees and legs!  This further causes problems similar to the nausea experienced in WWII when prisoners were stacked into train boxcars - on the way to Dachau?

Vehicle Transport: Originally required capability to carry a "jeep" or equivalent. Because of the lack of use of standard cabin decks (replaced by new technology plastics);  the solution used for testing (maybe once?) was to have several troops carry two 20 foot extruded aluminum 'load spreaders' for the cabin and two 10 foot spreaders of the same for the dropdown ramp. When finally in to the narrow cabin, the crew chief has to go around to the aircraft entrance, because of lack of space to move from to back of cabin.

Radar Signature: The radar reflectivity of the two 38ft diameter propellers is such that the V-22 from distance of 150-200 miles looks like a pair of Boeing 707s in formation.  

Autorotation: For some 18 years, everyone involved in the V-22 -- Congress, Contractors, USMC, Navy, etc  - have all claimed that the V-22 would be easily capable of  conducting a SAFE auto rotation. We have been telling DOD and others that the V-22 cannot do an autorotation - which is a standard for ALL helicopters. Recently they DELETED this capability as UNSAFE. In all of this time, the test pilots actually attempted (ONCE ONLY) to accomplish a full autorotation and almost loss total control.

Effect of Vibration Loads:  The structural characteristics of the V-22 are such that the deformations are much larger than that of helicopters because of the shape of the structure and the very large weight of nacelles (engine, gearing, etc). The bending and tensile loads are such that the susceptibility is certain to lead to a much higher failure rate of components  - which can lead to catastrophic accidents.

Go-NoGo:  All civilian and military Twin Engine  certifications, require a Go-NoGo check before take off to determine the airspeed/torque vs takeoff distance in order to shut down and stop when necessary to avoid a forced landing before takeoff. The only decision in the NATOPS manual is that of "Pilots Discretion" !!  

Flap Exceedence:  Whereas virtually ALL helicopter rotors have a limit of 28-30 Degree Blade Flapping capability, the V-22 Propellers are limited to 10 Degrees - to avoid damage to the rotor, rotor swash plates  and rotor hubs. The result of exceeding these limits can result in rotor failure or breakage, leading to aircraft control failures. This has been a big problem for the V-22 design and is very seldom ever involved in normal helicopter rotors.

Tendency of PIO: The tendency of PIO (Pilot Induced Operation)  is a direct result of design features, which include a very high roll moment of inertia and roll control differential rotor thrust.

Susceptibility to Wake and Tip Vortices: There is  considerable flight evidence that the V-22 response to the interception of a wake and wing-tip vortex by ONE of the proprotors is that of an uncontrolled rollover. That is yet another problem with the side by side rotors.  Helicopter rotors blow FOD away, yet the two outboard V-22 rotors blow FOD back toward the aircraft.  When they open the rear ramp in a sandy, snowy, or debris areas, everyone is pelted with incoming.

Conclusion

Ignoring other problems with aerodynamics, maintenance and low reliability, it is easily determined that the V-22 is NOT a Safe Troop Aircraft, and is totally lacking any evidence of Human Factor Engineering/Safety Design.  Congress, GAO, IG, FAA and NTSB should immediately initiate an Investigation and Audit of the V-22, for the significantly defective Safety and Human Factor shortfalls and other problems such as the 5-6 emergency landings required during the last 6 months, because of other failures.

                                                                                   Col Harry P Dunn USAF ret.

Your the Hanger Queen!

Lies, Lies, Lies, Lies ,Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies, Lies.                   

The V-22 will be a Success you suc as.

                                                                                          Richard Word

                                                                                  Bell Helicopter-Textron

Ed: Thanks for the input.  I'll make corrections based upon your expert response.

V-22 Safety

I do not think the impact of ultra high air downwash should be neglected either.  I know of one helicopter incident where downwash blew a piece of snow fence into a tail rotor leaving the helo resting on its side.  I am sure there are a lot of examples.   The downwash associated with the V-22 will greatly limit operation to prepared sites and brings another vulnerability into play.  You could not use over sand,  water, loose dirt etc  - you no longer have a helicopter or helicopter utility - and can only use between FOD free prepared sites etc.  This problem with Helo ops in Iraq is already a formidable one with actions to wet the sand in LZ often required etc.  Some form of simple STOL airplane would be far more practical useful -  a Cessna "super"  STOL caravan, Dehaviland Otter or such.  Use what UPS uses.

I also think there should be a high emphasis on the probable (and somewhat proven) correlation of fatalities to accidents - almost certain to be a direct ratio as the typical loss of control impact circumstance for the V-22 will almost never be survivable (either roll over or excessive sink as you discuss).  At least the sole occupant AV-8 has an ejection seat.  It is just not survivable. 

It would seem the supports either have a $ or status stake in this.  Most practical people simply can see that it will never work.  Dick Cheney should stick his nose in this again.  He was right the first time: "It will not do what it was supposed to do and if it could, it would be too expensive."  That succinct position was right on.  If it is necessary to support a welfare program, two could be provided to NASA for ongoing testing and the true believers could go work there.  The project will undoubtedly die at OPEVAL or shortly after,  as the true circumstance of it will come to the front stage.   Probably sooner is better as delay will not make it healthy as the fundamentals are lacking. 

                                                                                                  Name Withheld

Ed: The program often notes that downwash from a V-22 is no worse than a CH-53E when standing near the landing site.  That may be true, but the V-22's smaller and faster turning rotors have three times the disc loading, which means their downwash is three times more concentrated at the landing site.  This matters little on a hard deck like a ship or airfield, but acts like a huge sandblaster at unimproved sites.

They did desert testing at the Marine base in Yuma a couple years ago.  The outboard rotors tossed FOD back toward the aircraft, breaking a window and filling the cabin with debris.  They decided to repeat the testing last year, but at Nellis AFB near Las Vegas.  I'm not sure why.  Perhaps because area around Nellis has finer sand with fewer small rocks, and of course Las Vegas is more fun than Yuma.

Vortex Ring State

     As an Army two tour Vietnam helicopter pilot with over 4,000 flying hours I am puzzled over that assertion (estimate) that 1/3 of all helicopter accidents were a result of VRS.  In the early years 1965-1967 the majority of accidents on approach were due to a lack of engine power because of the high load factors and the pilots wanting to accomplish the mission. In later years with higher engine power this type of accident was significantly reduced.

     I do agree that helicopters can perform the mission better than the V-22. Not just the CH-53 but the CH-47 which can also out perform the V-22. Do not think that any opposition to the V-22 will succeed, because politically President Bush will not cancel such a high profile project from his state.

                                                                                                Gary

Ed: Those assertions by a rotorcraft expert seem high to me as well.  VRS was probably just a contributing factor, yet enough to cause the accident.  If you note that link to an article by a Marine Colonel about VRS, there is a graph which shows VRS regions which reduce performance.

Tiltrotors Have Failed 

I served two Vietnam tours.  One as a HH-3E Air Rescue Crew Commander and the second as the director of the 3rd Air Rescue Group Plans Officer in the 7th Air Force Hq. Saigon.  The latter had me again fighting against establishing a South East Asia Operational Requirement for the Tilt-Rotor aircraft.  Even before that while serving as the Long Range Plans Officer for the Air Rescue Service in 1962-1965 I fought tooth and nail against the validation of the Tilt-Rotor to fulfill an outstanding operational requirement for a specified Combat Aircrew Recovery Aircraft (CARA).

Among the stated requirements was a downwash velocity limitation of not more than 15psf - and a complete power loss autorotational capability.  Noteworthy is that neither then nor now does the V22 Osprey meet those requirements.  The inherent design flaws leading to dynamic instability at low speeds and inability to safely execute combat maneuvers associated with the Air Rescue Mission eliminated the V22 as a candidate to meet the requirement as early as 1952 (XV-15).  After eighteen years and $14 Billion dollars--not one of the limited production V22s produced has met the Joint Operational Requirements Directives (JORDs). 

Recent near catastrophic uncommented in-flight aircraft oscillations have again delayed programmed V22 Operational testing.  The aircraft are now produced at the rate of one per month and then put in storage at a cost of $124 million per aircraft!  I had some limited success with publication of these facts in the San Antonio Express News --i.e... Letters,  following announcement of axing the Comanche Helicopter.  You published some material addressing the revolving door Marine Corp Generals whose support for this albatross is either born of a dangerous ignorance or total loss of integrity born of self-serving greed.  The charge also applies to Air Force General Charles Holland (SOC) who ought to know better -he's an aero-engineer and has been briefed on the inherent design flaws of this aircraft  I seek a compilation of Senior General Officers and Executive Level DOD Civilians over the past eighteen years who have influenced the continued life of this tar-baby - and have acted so as to seemingly work a fraud upon the United States and cause the wrongful deaths of 30 unwary young Marines.

                                                                             LT COL John H. McLeaish, USAF (ret) 

V-22 Scandal Homepage