Flying The Osprey Is Not Dangerous, Just Different: Veteran PilotsAn
[Vous devez être inscrit et connecté pour voir ce lien] that the pilot caused the June 13 crash of a CV-22B Osprey at Eglin Air Force Base, Fla., in which all five crew on board were injured, marks the second time within weeks a major accident involving the helicopter-airplane hybrid transport has been blamed on the human at the controls, not the machine. Some AOL Defense readers think they see a pattern there that points to a larger conclusion.
"The Osprey is an inherently dangerous and unforgiving aircraft to fly," a reader who identified himself only as "Robert" declared in a comment posted after
[Vous devez être inscrit et connecté pour voir ce lien] that a Marine Corps pilot's errors caused an MV-22B to crash during an exercise in Morocco last April. Two crew chiefs died in that accident and both pilots were severely injured.
Robert, whose view echoes those of other critics who have posted their opinions of the Osprey on AOL Defense, added that the V-22's "quirks are numerous and I feel pose an exceedingly dangerous risk when compared to other aircraft."
Against the backdrop of the Morocco and Florida crashes, such comments raise a fair question, Osprey pilots interviewed by AOL Defense agreed: Does the V-22 being a tiltrotor make it dangerously tricky to fly? Nine out of 10 interviewed -- the notable exception being the test pilot who suffered the Osprey's first crash in 1991 - said the opposite is true.
"The first thing I'd ask Robert is, what's his flight experience?" said Bill Leonard, who from 1993-2006 was principal Osprey test pilot for Bell Helicopter Textron Inc., which makes the V-22 in a 50-50 partnership with Boeing Co. Leonard estimates he logged a bit more than 1,000 hours flying succeeding generations of the Osprey, from the 10 prototypes to the fourth-generation Block B. He added that in a 40-year career in which he was shot down four times as a UH-1 Huey helicopter pilot in the Vietnam War, continued to fly as an Army special operations aviator, then served as a military and commercial test pilot, he flew about 200 different types of aircraft, from Boeing 747 jumbo jets to gliders.
"Every airplane has its quirks," said Leonard, now an independent contractor who teaches a two-day aerodynamics course to incoming Marine and Air Force Osprey pilots at Marine Corps Air Station New River, N.C. "The Osprey is no different from any other aircraft, whether it's an airplane, a helicopter, a glider, a balloon - whatever it is that goes up and gets away from the surly bonds of Earth," Leonard said. "If you misapply the controls, you'll have a problem."
Leonard and other Osprey pilots generally agreed, though, that because the V-22 is a tiltrotor, it has peculiarities that require pilots to keep in mind they're flying a hybrid, not a conventional helicopter or fixed-wing airplane.
"I don't believe the Osprey is inherently difficult to fly," said Tom Macdonald, who as a Boeing test pilot and later chief of the combined Bell-Boeing-military V-22 test pilot team logged more than 1,150 hours in the tiltrotor from 1991 until he left the program in 2007. Macdonald no longer flies the Osprey but in 2003 won an award from the Society of Experimental Test Pilots for flying dangerous tests to find out when a V-22's rotors might go into a treacherous aerodynamic condition called "vortex ring state," in which a rotor can suddenly lose lift. Vortex ring state was blamed for the Osprey's worst crash, in which 19 Marines died during an operational test at Marana, Ariz., on April 8, 2000.
"There are handling characteristics in flying the Osprey that are starkly different from other aircraft, but those different characteristics are not necessarily bad, they're just different," Macdonald said.
The chief reason the Osprey is different from other aircraft is that it can take off and land like a helicopter by pointing two large rotors housed in swiveling wingtip pods called "nacelles" straight up to 90 degrees or even backward to 97.5 degrees. Once airborne, and after gaining sufficient forward speed flying like a helicopter to produce lift with its wings, the pilot can turn the V-22 into a fixed-wing airplane by pushing a small thumbwheel on the throttle, or Thrust Control Lever (TCL), to tilt the nacelles and rotors forward to angles as low as zero degrees.
The pilot can also stop the nacelles at angles between 60 and roughly 30 degrees above horizontal to make the Osprey fly neither like a pure airplane nor a pure helicopter but something in between.
To accomplish all this, the Osprey has computerized flight controls - known as "fly by wire" - that make the pilot's manual controls - stick, TCL and pedals -- perform differently depending on the mode of flight. The flight control computer mixes helicopter and airplane controls in different proportions as the angles of the nacelles change:
- When the Osprey is in helicopter mode, with its nacelles vertical or nearly so - 97.5 to 60 degrees -- and its rotors providing all lift, the pilot's stick, TCL and pedals perform the way helicopter controls do. Pushing the stick forward or pulling it back makes the aircraft move forward or backward. Pushing the stick to either side makes the aircraft move laterally. Adding or removing power with the TCL makes the Osprey gain or lose altitude by collectively changing the angle at which all three blades on each rotor meet the air as they rotate. Pushing the left or right pedal makes the aircraft turn in that direction by altering the angle of the rotor blades cyclically - higher on one side, lower on the other -- as they rotate through the arc they describe.
- When the Osprey is flying like an airplane, with nacelles tilted forward between 30 and zero degrees and with the roughly 120 knots of forward airspeed needed to generate all lift from the wings in level flight, the stick, TCL and pedals perform as a fixed-wing aircraft's controls do. Pushing the stick forward or pulling it back will make the aircraft dive or climb by moving the control surface on the tail known as the "elevator." Adding or reducing power with the TCL will make the Osprey fly faster or slower. Pushing the stick sideways will move control surfaces on the wings called "flaperons" in opposite directions to roll or bank the aircraft, and pushing the foot pedals will move the tail rudder to make the Osprey turn.
"The one difference between our aircraft and everybody else's aircraft is the changing controls," said Capt. Justin "Moon" McKinney, a 17-year Marine Corps veteran who flew in the Osprey's first combat deployment to Iraq in 2007 and recently completed two-and-a-half years as an MV-22 operational test pilot. McKinney, who recently rejoined an operational squadron, said that with the nacelles between 30 and 60 degrees, "If you hit power, you're going to go up
and forward. All the controls do a little bit of everything."
This is one reason McKinney says flying the Osprey can be a "thinking man's game." But the ability to combine helicopter and airplane functions gives the Osprey unique capabilities, he noted, such as executing what pilots call an "80 Jump" takeoff by tilting the nacelles forward to 80 degrees and applying power. The 80 Jump "gets you out of the dust and gets wind over wings" in a hurry, McKinney said, allowing a quick departure from a landing zone that might come under hostile fire.
In addition to such unique capabilities, the Osprey's large nacelles and rotors create special characteristics a pilot has to take into account, and which underlay the two recent crashes.
The wingtip nacelles each contain an engine, rotor system, driveshafts, a gear box and other elements that weigh a total of about 5,500 lbs. and shift the aircraft's center of gravity as they move forward and back. Osprey pilots are taught in training that the aircraft's nose must be held level or pitched up when the nacelles are being tilted forward. Swinging that much weight forward can shift the aircraft's center of gravity so far the controls can't prevent it from diving.
Failure to keep that in mind contributed to the
[Vous devez être inscrit et connecté pour voir ce lien], which occurred when a pilot with 160 hours in the MV-22B lifted into a hover, turned to head in the other direction, let the nose pitch down as he did, then tilted the nacelles farther forward than allowed with less than 40 knots of airspeed, and with a tail wind impinging on the elevator.
"Helicopters lower the nose and pull pitch to accelerate," observed retired Marine Lt. Col. Jim "Trigger" Schafer, who, as a member of a Marine Corps/Air Force Multiservice Operational Test Team (MOTT),flew operational tests of the Osprey in 1995-2000. "You can't fly the V-22 like a helicopter."
Schafer, who lost close friends in the Osprey's crashes during development, added that the V-22 "is one of the easiest aircraft I've flown" in helicopter or airplane mode. However, he said, "All that conversion/transition stuff in between is a unique V-22 skill set that must be taught with repetition and building seat time." In Morocco, he said, "It appears the aircraft was flown beyond its capability. Take a perfectly good Cessna 172 and take off and pull back on the nose and not support the pitch attitude with airspeed, the aircraft will stall."
Another Osprey characteristic is the powerful downwash of its rotors, a function of their size compared to the thrust they need to produce. Designed to fit on the deck of an amphibious assault ship, the Osprey's rotors are 38 feet in diameter -- about five feet less than would have been optimum for an aircraft designed to carry 24 Marines and take off vertically at a maximum gross weight of 52,600 lbs., according to engineers who helped design it. The V-22's rotor blades are also twisted far more than a helicopter's because they have to grab the air like propellers when flying in airplane mode. This combination of relatively small diameter and high twist creates the Osprey's strong downwash, a feature known as "high disk loading."
The Osprey's rotor wash is powerful enough that pilots are instructed to keep at least 250 feet separation between their cockpit and that of a V-22 flying ahead when flying in formation and in helicopter mode so as to avoid the lead aircraft's rotor wake. Marine Corps and Air Force flight manuals also admonish pilots to avoid the lead aircraft's 5 to 7 o'clock position, fly at least 25 feet higher, and increase that separation to 50 feet when forced to cross the lead's wake.
Failure to follow those rules runs the risk that the turbulence from the lead V-22's rotor wake will knock the lift out from under one of the trailing aircraft's rotors, causing a snap roll that may be unrecoverable - the cause of the June 13 CV-22B crash, the Air Force accident report found. The Air Force report on the accident, however, said that while the pilots failed to see that they were flying through another Osprey's wake, "CV-22 wake modeling is inadequate for a trailing aircraft to make accurate estimations of safe separation from the preceding aircraft."
The high disk loading of the Osprey's rotors also causes a V-22 phenomenon called "lateral darting." When hovering 10 or 15 feet above the ground or over a ship's deck, the Osprey is subject to slipping quickly to one side or the other as turbulence created by its rotors disturbs the air beneath it. Numerous modifications to the flight control software over the years have helped with that problem, current Osprey pilots said, but lateral darting is one reason former V-22 test pilot Grady Wilson recalls the aircraft as "squirrely."
"It puts out a gale force wind underneath it," Wilson said. "So you hover at 50 feet, because as you start to come down ... it wobbles around." Current Osprey pilots said the tactic used to avoid lateral darting is to "fly the aircraft to the deck" rather than hover at low levels. Wilson, who joined Boeing to fly the Osprey in late 1990 after flying Hueys in Vietnam and serving as an Army and NASA test pilot, added that the V-22 "was a tricky aircraft to fly from the time I got into it."
Wilson was piloting Osprey prototype No. 5 at Greater Wilmington Airport in Delaware on June 11, 1991, when the aircraft went haywire at takeoff and pirouetted nose-first into a runway from low altitude. As it turned out, a worker had inadvertently reverse-wired part of the flight controls, making them malfunction. Wilson and his copilot walked away from the crash, but Wilson quit the next year after another Boeing test pilot, three other company employees and three Marines were killed in Osprey prototype No. 4, which plunged into the Potomac River at Quantico Marine Base after a fire in its right nacelle crippled the engine and rotor on that side.
"It's tricky because you have two opposing mindsets as a pilot to operate under," said Wilson, who flew the Osprey a bit less than 90 hours in all. "One is go fast; the other is hover and precision. They're counter to each other." Wilson added that, in his view, "You need a fairly experienced helicopter guy to handle this thing."
Former test pilot and aerodynamics instructor Leonard said he respected Wilson's views but found them out of date.
"One of the biggest problems we've had in the community is getting past the idea that it's a helicopter that flies fast," Leonard said. "It's not. It's an airplane that hovers. And if you fly the airplane like a helicopter, yes, it's very difficult to fly as a helicopter. And if you do that, you have a very good chance of having a problem with controllability because of the way the aircraft operates. If you fly it like an airplane and you are willing to take the time to understand the capabilities of it in helicopter, it's a very, very easy airplane to fly."
One active duty V-22 pilot, speaking on condition of anonymity because he hadn't been authorized to comment, cited himself as a prime example of what Leonard meant. Originally a fighter jet pilot, this officer transferred to the Osprey, became an operational pilot and has flown combat missions in the V-22 without ever touching the controls of a helicopter - as have a small number of other current Osprey pilots. Helicopter experience has proven unnecessary, this pilot said, because today's Osprey has an Automated Flight Control System that has been refined so much since the prototypes Wilson flew that it makes it easy to hover the aircraft.
"I still have never flown a helicopter, don't have a single minute of helicopter flying time, but if I can come from a (fighter jet) and have no problems hovering this airplane, then it's a pretty darn stable airplane," this pilot said. "Fixed wing pilots almost have an easier time coming in because in a helicopter you're always working, always working. This is all (helicopter pilots) know. We (fixed-wing pilots) actually hover (in the Osprey) better than a lot of helicopter pilots because the helicopter pilots have it ingrained in them, 'I'm in a hover; I've got to be making corrections.' So they're constantly moving the controls when they don't necessarily need to."
Thanks to the automated flight controls, this pilot added, "I'll tell you this: if you ever get to the point where you're hovering and you're working too hard, let go of the controls, and that airplane will hover just fine - better than you, because it has an automatic flight control system that's constantly, every nanosecond, making inputs based on what the pilot's doing, based on what all the flight control computers and those airborne sensors outside are taking in."
Arthur "Rex" Rivolo, an Air Force F-4 Phantom fighter jet pilot in Vietnam who later flew helicopters in the Air National Guard and in the 1990s monitored the Osprey's development program for a federally funded think tank said he remained convinced that, "The V-22 is indeed a slippery aircraft."
"It is prone to small pilot errors and those small errors have catastrophic results," Rivolo said in an email. "The additional degree of freedom [nacelle angle], along with the side-by-side differential control for roll and yaw greatly increases the complexity of the 'decision space' for the pilot. The flight envelope is of a much higher dimensionality and much more complex that any conventional helo or a fixed-wing aircraft. Training does not address these issues well."
Macdonald, who heatedly debated the V-22's merits with Rivolo more than a decade ago, when the Osprey was being redesigned and retested following two crashes in the year 2000, said he believed the aircraft's record since then simply hasn't borne out Rivolo's views.
Since the Osprey's first flight in 1989, there have been six V-22 crashes, three during its development prior to 2000, in which four Boeing employees and 26 Marines perished, and three since it was redesigned and retested between 2001-2005, then put into service with the Marines and Air Force. In the three Osprey crashes since 2001, a total of six persons have died. Since Oct. 1, 2001, the U.S. military has lost 416 helicopters - mostly to accidents - at a cost of 623 American lives.
Retired Air Force Col. Jim Shaffer, a former special operations helicopter pilot who from 1997-2000 commanded his service's contingent of the MOTT, agreed with Macdonald. "I flew (MH-53) Pave Low helicopters for a couple of decades," Shaffer emailed, "and as much as I love that machine [now in the boneyard], it tried to kill me many times." Shaffer added that a "quick look at the mishap rate" shows that the Osprey is "well above some other machines" in safety.
Two of the three Osprey crashes since 2001 have been Air Force CV-22Bs, including one that made a hard landing while carrying Army Rangers on a night raid in Afghanistan in 2010, then flipped onto its back after its nose gear hit a ditch, killing four of 20 persons on board. After the recent crash at Eglin, said retired Maj. Paul Alexander, who between 2004-2009 was one of the Air Force's first four CV-22 instructors, the service is discussing whether to hire experienced hands such as himself to help train new pilots. The Army's 160
th Special Operations Aviation Regiment (SOAR) uses such an arrangement with retired 160
th SOAR pilots, Alexander said, which allows experienced active duty pilots to focus on operations.
"The experience level in the Air Force in the Osprey community is starting to diminish because they picked, initially, many pilots who had the experience to help the program get off the ground, and many of those pilots have been promoted or have retired like myself and are moving on to other jobs," said Alexander, who flew MH-47 Chinooks for the 160
th SOAR for 15 years before transferring to the Air Force to fly the Osprey. "This is an aircraft that, being rather new still, you don't have that experience depth or that base to work with."
Heavy operational demand for AFSOC's two dozen CV-22Bs, meanwhile, has made it hard for Air Force Osprey pilots to get as much training time as they would like. AFSOC's Osprey pilots had been doing very little training in formation flying prior to the Eglin crash. After initial training with the Marines, incoming AFSOC pilots have been required to do only two formation flights in their Air Force CV-22B training, one in daytime and one at night, and they were given the option to waive the daytime flight, one AFSOC pilot said. Since the Eglin crash, however, CV-22B pilots are getting more copilot training hours, this pilot added, and formation flying is getting new emphasis.
AFSOC spokeswoman Capt. Kristen Duncan disputed the pilot's unauthorized description of CV-22B formation flight training. "Air Force aircrews learn formation skills in undergraduate pilot
training, and much of that is transferrable to any aircraft type," Duncan said by email. "During
CV-22 Mission Qualification training our aircrews have 10 formation flights. Continuation training requires four NVG (Night Vision Goggle) formation flights per semi-annual period. In reality, since Air Commandos train as they fight, a large percent of continuation training flights are scheduled as formation flights."
Asked to respond to that statement, the AFSOC pilot said that "to say that flying formation in one aircraft is akin to flying formation in another is absurd. Each aircraft obviously exhibits different flight characteristics and pilots fly different lateral and vertical spacing between aircraft utilizing unique sight pictures." Some jet fighters are separated by distances of as little as three feet when flying formation, this pilot noted, and short distances are much easier to judge than the near football field lengths of separation required in the V-22. "The UH-1 Huey is the aircraft most often used in Undergraduate Pilot Training to prepare future V-22 pilots," this pilot added. "It also exhibits much different rotor wash characteristics than the V-22. At the most fundamental level, formation flying between one aircraft and another is not a transferrable skillset." Finally, this pilot added, while 10 formation flights are part of the plan for AFSOC CV-22 training, pilots are able to graduate with as little as two.
Maj. Frank Lazzara, who as an Army warrant officer flew OH-58D Kiowa Warrior scout helicopters for seven years before transferring into the Air Force in 2005 to fly MH-53s and later CV-22s, said all AFSOC pilots would welcome more time to train.
"Do all Osprey pilots in our squadrons get to fly enough? They certainly don't get the time that I got as a young 53 pilot or as an initial Osprey cadre guy," said Lazzara, who in addition to flying operational missions for AFSOC serves as a CV-22B instructor. "When people are not trained properly or don't follow their training," he added, "there is a vulnerability there. But that's true for any aircraft."
Or, as former Osprey test pilot Bill Leonard put it, "What we do is risky."
Accueil
Dernières images
S'enregistrer
Connexion
Bell Boeing V 22 Osprey
par Patts Jeu 02 Juil 2009, 22:11
contract by the U.S. Naval Air Systems Command (NAVAIR). Under the eleven-month contract, which includes four option years, logistics support will be provided for the Rolls-Royce AE 1107C-Liberty engines that power the U.S. Marine Corps’ MV-22 Osprey and U.S. Air Force Special Operations Command’s CV-22 Osprey. The total contract has a potential value exceeding $600 million.