The U.S. Marine Corps' sword gets a brand-new edge.
- By George C. Larson
- Air & Space magazine, November 1998
(Page 4 of 5)
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workers are building the first parts, there's little of the old din of metalworking; all those industrial sounds have been replaced by the softer whirring of electric motors, fans, and the actuators in robots.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.