The U.S. Marine Corps' sword gets a brand-new edge.
- By George C. Larson
- Air & Space magazine, November 1998
Only two hours or so after getting under way, the operation began to unravel. On the evening of April 24, 1980, eight U.S. Marine Corps Sikorsky RH-53D Sea Stallions departed the USS Nimitz for a point in the Iranian desert more than 500 miles away. At a remote location designated Desert One near the Iranian town of Tabas, they would meet their strike force and six C-130 transports, some carrying fuel for the helicopters' next leg. What happened next was the first in a series of mishaps that led to a nightmare.
Aboard each RH-53D was a system called the "blade inspection method," or BIM. Each rotor blade has a hollow spar containing pressurized nitrogen gas; the pressure is monitored by a gauge wired to a warning light. If a spar cracks, the gas leaks, and the BIM gauge warns the pilot that the rotor may fail. Now one of the pilots was staring at just such a warning light. Although others later second-guessed his decision, he put the Sea Stallion down and waited while another helicopter in the formation stopped to get him and his crew.
Then another RH-53 lost some of its instruments and turned back to the Nimitz. Now they were down to six helos, the minimum required to accomplish the mission. Unforecast dust storms scattered the flight, and when the helicopters arrived at Desert One, the ground commander of the operation, Colonel Charles Beckwith, noted (as he wrote in his book Delta Force) that they seemed to come in from all points of the compass. And they were over an hour late. As Beckwith ordered his force on to the helicopters for a flight to the outskirts of Tehran, he got a final piece of bad news: another RH-53 equipment failure, this time a hydraulic system. Beckwith aborted the mission, hoping to avert losses and get his people out. But in the darkness, a hovering RH-53 struck one of the C-130s, and Beckwith heard a muffled explosion. A fuel tank had ignited.
Eight people died before the rest could escape the carnage, and 52 Americans in the occupied embassy in Tehran spent another night with their captors. President Jimmy Carter faced the public on TV the next day and took personal responsibility for approving the plan to rescue the hostages. Perhaps it is just coincidence, but about a year later, the United States took the first steps toward developing an aircraft that would become the V-22 Osprey.
To this day, when the brass briefs on the V-22, they point out how the rescue in the Iranian desert might have gone if they'd had the right aircraft.
Because of the limitations of the RH-53's range and speed, they say, the rescue had to be performed in stages. Too many stages. The plan violated the KISS Rule: Keep It Simple, Stupid. Under cover of darkness, the helicopters were to meet the C-130s, refuel, board the troops, move to a hiding place (Desert Two), and wait through the daylight hours of the second day in concealment. At nightfall, the troops would move by truck to the embassy, execute the assault-and-rescue operation, meet the helicopters, reload, then fly to an airstrip to meet some C-141 jet transports, which would speed everyone to safety. Next slide, please.
Here's the same mission but with V-22s instead of RH-53s and C-130s. One: V-22s fly nonstop from Nimitz to assault staging area near embassy. Two: Team prepares for assault. Three: Team assaults embassy. Four: Team and hostages board V-22s and fly back to Nimitz. There may be glitches, but the V-22s' backup systems do their jobs. It's over in eight hours, and who knows? Maybe Jimmy Carter gets re-elected.
But in 1980 the concept of a tiltrotor airplane, or convertiplane, that could use twin rotors to lift off vertically and then rotate the rotors so they function as propellers while wings provide lift was nothing more than a 30-year-old idea. A number of similar machines had been developed for research, mainly to evaluate schemes for controlling such an unconventional machine.
The mid-1950s through mid-1960s saw hybrids like the British Fairey Rotodyne, which combined a traditional lift rotor and a wing with propellers for forward thrust. Bell's XV-3 and X-22A were tiltrotors, the latter with ducts around the blades, while Boeing's VZ-2 and the LTV-Hiller-Ryan XC-142 were tiltwings in which the entire wing, together with engines and propellers (four of them on the -142), rotated as a unit. All these machines were conceived because the helicopter, a machine designed to hover, has an irreparable flaw when it tries to fly forward at high speed.
Hovering in still air, the helicopter is happyeverything is balanced and symmetrical, with the rotor blades creating equal lift throughout the circle of their revolution. To move forward, the pilot pushes the cyclic control, or stick, toward the nose, which causes the swash plate in the rotor head to increase the pitch of the rotors when they are swinging through the aft portion of the circle. The effective lift of the rotor system tilts forward, and the helicopter gently begins to accelerate. As its airspeed increases, the air flowing over the rotor blades begins to create an imbalance. The rotor blade that is advancing into the relative wind encounters a net gain in lift due to higher speed over its airfoil. The retreating blade encounters a net loss, and this divergence eventually increases until the retreating blade can no longer create sufficient lift and the aircraft rolls off toward the retreating blade even if the pilot tries to counter the roll with the cyclic control. This phenomenon, retreating blade stall, limits the top speed of traditional helicopters like the RH-53.
The tiltrotor effectively trumps this effect by turning the rotor into a propeller. No more advancing blade, no more retreating blade, just simple thrust, and all of it moving the airplane forward, supported on its wings. As Bill Leonard, Bell Boeing senior test pilot for the integrated test team from all three services that will operate the Osprey, puts it: "Don't think of this thing as a helicopter. Think of it as an airplane that hovers."
It is also important to think of it as an invention and to recognize the V-22 as the first wholly new aircraft configuration in the sky since the Harrierthe British jet that can take off and land verticallywhich entered service in 1970. (Accordingly, last August, the Federal Aviation Administration issued its first powered-lift ratingsspecifically for tiltrotor aircraftto eight V-22 test pilots.) While much of the inventing was accomplished by research aircraft, most significantly Bell's XV-15 for NASA and the Army, the final design of the V-22 has benefited enormously from the march of technological development in the broader fields of materials, electronics, and computer software. In fact, the aircraft that will be fielded first to the Marines as the MV-22 (the Air Force version is the CV-22; the Navy's, the HV-22) represents a wiser design that has benefited from some of the delays that have affected the program. The first prototypes were all-composite, but the decision to mate advanced composite materials with more traditional aluminum in the production aircraft, to cite just one example, appears smart: The most recent engineering and manufacturing development (EMD) aircraft are lighter and cheaper to build than earlier prototypes.
After the XV-15 showed that a tilt rotor aircraft could evolve into something more than a research platform, the next step was to build and fly six full-scale development (FSD) prototypes of the V-22. Although the program began as the JVX in 1981 under management of the Army, the Navy and Marines took over early in the game, with the Air Force as an interested partner looking at a smaller number of a special long-range V-22 version for the U.S. Special Operations Command, a combined force that would be called upon if something like the Tehran situation arose today.
Bell and Boeing formed a joint venture to build the craft in 1982, and a year later received a contract. Peering into the future, the Marines were especially anxious to replace their medium-lift Boeing Vertol CH-46 Sea Knights, a large, tandem-rotor helicopter designed and built in the 1960s, battle-tested in Vietnam, and refurbished, renovated, and rebuilt more often than George Washington's hatchet. The average Sea Knight is about 30 years old.
Crashes claimed two of the FSD prototypes. Following uneventful first flights in 1989, initially as a helicopter and later as a fixed wing, the first loss occurred on June 11, 1991, when one aircraft crashed due to incorrect wiring in the flight control system. The loss of a second aircraft and its crew on July 20, 1992, dealt the project a severe setback. While on approach to Quantico, Virginia, a series of component failures in one engine nacelle ignited a fire. Testing was halted pending an investigation and a redesign of the failed parts.
The V-22 program hit another rough patch in 1989, when Secretary of Defense Richard Cheney canceled it during the budget balancing battles of the early Bush administration. While the Reagan administration had allocated almost $1.5 billion for research and production, Pentagon analyst David Chu convinced Cheney that the V-22 was unaffordable. Chu and Cheney wanted more helicopters instead.
In his first appearance before Congress as the civilian head of defense, Cheney was mindful of enormous changes in global politics. A new Soviet leader named Mikhail Gorbachev was charming Americans, who were beginning to see their former adversary in a new light, and a budget balancing law called Gramm-Rudman-Hollings was pressing Cheney to make cuts in defense. At a hearing before the House of Representatives' National Security Committee on April 25, 1989, he testified in part: "we opted to stay with established weapons programs where production lines are operating efficiently rather than pursue the development of unproven technology."
But Congress wouldn't allow the V-22 to die, perhaps because some members had not forgotten Tehran. Also, there were election districts and states that had a lot to lose if the project were terminated, and Congress ordered Cheney to restore funding. A timely independent study stated that the tiltrotor concept was the best solution for the future Marine mission. The V-22 was alive, but those charged with its care and nurturing would proceed with a degree of caution that prevails even today as aircraft numbers 7 through 10 undergo testing at Patuxent River Naval Air Station in Maryland. Though the budget now looks bulletproof and the first parts for production aircraft are coming off the line, there seems to be a common understanding among the test team on one point: no mistakes. "Just one drop of rain and they don't fly," say people in the test crew, and that's only partially an exaggeration: The instruments on the test aircraft can be ruined if they get wet.
Not that Ospreys are prone to crash; they're even difficult to shoot down, mainly because of inherent damage tolerance built into the aircraft and two or more of everything that you absolutely need to stay in the air, beginning with the engines. A pair of Rolls-RoyceAllison T406-AD-400 turboshaft engines rated at 6,150 (and capable of nearly 7,000) shaft horsepower powers the craft through a system of shafts and gearboxes that can provide power to both rotors if one engine is lost. The engines are offspring of the proven T-58 turboprop, and its cousins are flying in the C-130 Hercules. The Osprey cannot land as an airplane because its 38-foot-diameter rotor blades would strike the ground, but the designers have already thought about the unthinkable: If, for some reason, the rotors won't transition into helicopter mode for landing, the graphite-and-fiberglass rotor blades will not fragment on impact but instead will "broomstraw"reduce themselves to a bundle of fibers like a straw broom flailing harmlessly at the asphalt. In a crash, the wings are designed to fail and separate from the fuselage, and the nose has a tilted bulkhead that works like the upturned tip of a ski to keep the airplane from flipping over if the nose tries to dig in. The structure is designed to tolerate battle damage and keep flying, and critical parts as well as both pilot seats are armored.
The MV-22 is designed to hold 24 fully armed Marines (and there's a seat for the crew chief), equivalent to a reinforced rifle squad, but the airplane's size has been defined by the vessels from which it will operate: amphibious assault ships, which resemble traditional straight-deck aircraft carriers but with shorter stern portions that are high and square. John Buyers, an easygoing Texan who serves as V-22 program manager for Bell Boeing, says the 38-foot diameter of the rotor blades is mandatory, defined by a required blade tip clearance of 12 feet, eight inches in the vicinity of these ships' islands and five feet from the wheels to the edge of the deck. "If we could have, we'd have made the rotors bigger," he says. "Optimum would have been about 43 feet," adds Boeing senior manager Gregory McAdams. So where did they get 12 feet, eight inches? "That was the CH-53's actual blade tip clearance, and the Navy just didn't want to give up any more than that," says McAdams. While the rotors defined the overall size and weight of the Osprey, its cabin interior dimensions are almost the same as those of the CH-46, which it will completely replace by about 2010.
A ramp folds down at the rear to accommodate two utility vehicles, and the craft has two belly hooks so that it can carry cargo on a sling beneath it. Once aboard a carrier, the Osprey takes only 90 seconds to fold into a package slightly longer than its 57-foot, four-inch fuselage. Although the equipment for the stowing cycle exacts a penalty in weight and cost, self-stowage means that more aircraft can be carried, and all can be launched and recovered within minutes. The Osprey can be refueled in flight through a probe, and it carries a rescue hoist plus a "fast rope"the line commandos slide down when they arrive in their special way. With inflight refueling, the V-22's ultimate range depends only on having enough tankers and on how long the crew can stay awake. Fuel tanks are located in the sponsons and the wings (plus three that can be installed in the cabin for transoceanic trips). Should gearbox lubricant be lost, the craft can fly another 30 minutes.
The Osprey has three independent flight control systems, any one of which can fly the aircraft. All three use fly-by-wire technology that employs electronic signals rather than cables and pulleys to operate the controls. There are two mission computers and three inertial navigation systems to help you figure out where you are, and the displays in the glass cockpit can be routed to any of the video tubes in the event one of them fails. All information for a mission can be loaded in seconds from a cartridge that plugs into a computer system. In addition to the various alerts and warning lights, an audio annunciator tells you what kind of trouble you're in. (The disarmingly dulcet voice belongs to Barbara Smith, deputy to Colonel Nolan Schmidt, the Marines' program director for the V-22.)
There are four electrical generators, two located with the engines and two more in the upper fuselage, and a battery good for 20 minutes of flying if all else fails. An onboard generator extracts nitrogen gas out of the air and floods the fuel tanks, displacing oxygen and reducing the risk of fire. The outer skin has a fine copper mesh embedded in it to form a conductive path in the event of a lightning strike. The aircraft has three completely independent hydraulic systems, which operate at 5,000 pounds per square inch; out in the fleet, only the F/A-18 has such high hydraulic pressures. But the V-22's hydraulic lines are made of titanium, which is thinner and lighter and thus saves weight. "We had to invent the connectors for that system," Buyers says. The engineers also had to rewrite all the criteria for replacing a line that has been scratched or nicked.
A little less than half the airplane is manufactured of composite materials, which, while incredibly light, are also corrosion-resistant and strong. Should a bullet penetrate it, the composite fibers ensure that the hole won't expand or start to crack. Systems and controls are distributed and separated throughout the aircraft so that one bullet can't take out all of anything. When things fail, they fail "softly"only half a control surface at a time, for example.
If all of the systems, capabilities, protection, and toughness seem hard to believe, consider this: The V-22 is an aircraft of the '90s, and the aerospace industry never stands still. Things have changed. At the old Vertol (now part of Boeing) plant in Philadelphia, where workers are building the first parts, there's little of the old din of metalworking; all those industrial sounds have been replaced by the softer whirring of electric motors, fans, and the actuators in robots. The workers here behave as if they're working on the hottest project in aerospace. There's the razor-sharp young engineer, Ken Eland, who is revolutionizing the way the Osprey is built. The company saved $21 million by eliminating the traditional mockup and so far has cut the parts count by 36 percent, eliminating 18,000 fasteners by such simple steps as making the skins and their stiffeners as a single integrated part.
And there's Valorie Bring, a former IBM employee who says she sort of fell into her current job of designing displays and switches and controls that the pilots can understand and use easily. She uses the word "customer" a lot. She's in charge of the Osprey's cockpit environment and co-author of a paper on how the entire electronic system works on a hypothetical mission. But her biggest job is to listen. "Ask 10 pilots and you'll get nine opinions, and then that one guy will change his mind," she says. "The trick is to find the common thread in their words."
You find the same culture at Pax River. In the hangars where the V-22s are tended between flights, the test aircraft are helpless giants with their innards exposed and people crawling all over them. They remind you of patients in an intensive care ward, surrounded by scaffolding, lines, and service carts. The military officers in khakis and olive flightsuits and black shoes mix with civilians wearing Nikes and sporting the occasional tattoo or piercing, while out in the parking lot there are motorcycles scattered among the pickups and sports cars and imports. You wondered where the new generation was headed? They're hard at work on the V-22.
While the basic principle of tilting the props to create an airplane that can hover seems obvious, it is not easy to design and build a craft that can do it successfully, as testified by the long line of research aircraft that have led up to the Osprey. The V-22 succeeds in large part because of small, lightweight, powerful computers that can store complex control laws to guarantee success in the hands of an average pilot. When the first Marine service pilots begin flying the V-22, the airplane's flight control system won't let them get into trouble. Bell Boeing senior test pilot Bill Leonard puts it this way: "There are three computers and a pilot, and all of us get one vote. There have been many times when I have been outvoted."
The engine nacelles are controlled by a small knurled thumbswitch on the thrust control lever in the pilot's left hand. The nacelles can rotate from zero degreesstraight ahead in the propeller positionto plus 95 degreesslightly aft of straight up so that the lift force pulls toward the tail of the airplane to slow down and even back up. A huge screw drive rotates the nacelles at up to eight degrees per second, and conversion can take as little as 12 seconds. Leonard says, "From about 60 degrees nacelle to 95, it flies like a helicopter. From 30 degrees down to zero, it's an airplane." (In the transition, it's a little of both.) In helicopter mode, the prop-rotors have full cyclic and collective controls using the stick and thrust control lever (TCL), respectively. "You use your left hand [TCL] to control altitudethe verticaland your right hand [stick] to control your position in pitch and roll," Leonard says. The foot pedals control the yaw axis, which works in helicopter mode by diverging the lift axes of both rotors, just as it works on a tandem-rotor helicopter like the CH-46 (see "Yaw Control," p. 31).
At between 40 and 80 knots forward speed (the Osprey uses knots, which equal 1.15 statute miles per hour, for airspeed measurement), the wing begins to produce lift and the airplane control surfacesailerons (in this case, combined flaps and ailerons called "flaperons"), elevator, and ruddersbegin to have an effect. At the same time, the helicopter controls begin to phase out of the prop-rotors, and at about 100 to 120 knots, they become propellers. The airplane's genius is in phasing from one mode to the other based upon flight conditions, mixing the controls so that both are active in the region between about 40 and 120 knots. The pilot can rotate the nacelle forward with the thumbswitch or, while accelerating, let the computer do it. During deceleration the pilot must rotate the nacelles to the vertical with the thumbswitch; otherwise, with the power pulled back, the V-22 will slow and eventually stall.
Where Leonard and other pilots may occasionally get outvoted by the three computers is in a region called the "conversion corridor." The corridor is a programmed schedule of airspeed-nacelle angle combinations that prevent the rotors from being overloaded at high speeds. The computer won't allow the pilot to rotate the nacelles back toward upright until the airspeed drops below 220 knots, for example. It will also move the nacelles from five degrees to zero automatically in airplane mode.
In the V-22 simulator at Pax River, Major Kevin Gross, a U.S. Marine with the integrated test team of V-22 pilots, lets me have a go at it. The cyclic control in my right hand feels like any military control stick, with switches and buttons arranged around it and a four-way "coolie hat" switch near the top to trim out imbalance in pitch or roll. But the thrust control lever in my left hand is different, more massive than any throttle or collective I've ever gripped. Instead of moving up and down like a helicopter's traditional collective, the TCL moves fore and aft, like a throttle, yet it feels natural to pick up to a hover by pushing forward to add power.
Normal takeoffs are made not from a hover but with the nacelles at 60 degrees. The airplane rolls for a short distance, and once aloft, I begin pushing forward on the thumb switch to rotate the nacelles forward. The nose dips a bit during the transition, and with Gross coaching me, I add a little bit of back pressure. Within a few seconds we are in a cruise climb at 180 knots. At five degrees nacelle, I can let go of the button and the nacelle will continue automatically to zero. Push the button once more and the rotor slows to 84 percent rpm and we are a pure airplane.
"It doesn't do loops, and it really doesn't do aileron rolls very well. It'll do a wingover," Gross says. Then, with the nacelles set at 95 degrees, Gross flies up the runway's electronic glide path backward, just to show that backing up can be done with an added task like shooting an instrument approach. These are the simple pleasures of the test pilot life, and Gross is quick to add, trying to keep a straight face, "This will not be normal procedure."
Has he ever done an autorotation, the power-off maneuver in a helicopter in which the rotor blades freewheel in a descent to an emergency landing? His cautious answer: "Autorotation has been evaluated. Actually there are three phases to autorotative descent. The entry to the autorotation, the descent itself in a steady-state condition, and then there's the flare at the bottom. We have done the autorotative descent in flight test. The entry and the recovery still have yet to be done, and I don't know if we actually will in EMD or not. That's a pretty big decision above our pay grade." Gross explains that this rotor system is not like a helicopter's in that the system is not free-turning with power off and there is not the same collective power to flare with at the bottom by pulling the blades to abnormally high pitch angles.
On the way home from the simulator flight, it dawned on me that the test pilots are continuing the process of invention: They are inventing how to fly the thing. Someday soon, someone will have to sit down and write a pilot operating handbook. Gross and his colleagues on the test team talk frequently about the coming day when the "lieutenants" get the airplane"When the lieutenants fly it," "We wonder how the lieutenants will handle this."
They freely speculate about some of the things they've done with the V-22, exploiting its talent for hovering in a very stable manner while they use the nacelle switch to alter the deck angle of the fuselage, a condition in which both pilots are looking down at the runway, which fills the windshield at a startling angle. "No other aircraft can do this," they say. But they don't know how many of these capabilities will make it into the syllabus and be taught when they "take it to the schoolhouse"their term for flight training.
They are surely aware that Marines inevitably discover the unusual corners of any aircraft's flight envelope. The British invented the Harrier, but a U.S. Marine invented "viffing," or vectoring in flight. No one had thought to try moving the nozzles of the jets' engines at high speed. It turns out that the use of this peculiar talent can make the Harrier a very difficult target to hit in aerial combat. The service pilots on the V-22 test team tacitly accept that this aircraft will perform feats as extraordinary as its appearance.
Residents of the coastal Carolinas will soon start seeing the V-22 in the skies near Marine Corps Air Station New River near Camp Lejuene in North Carolina. They are likely to stop their cars, jump out, and stare. Switchboards will light up all over Onslow County with reports of alien craft that look like two windmills attached to a big gray schoolbus with a forked tail.
And perhaps someday, a lonely gunman walking guard on American captives in a besieged embassy will hear a soft whirring sound in the night that comes closer and closer until suddenly he is faced with an apparition that stares back as if to say, Hey, buddy, hostage THIS!