For Harry Dunn, Rivolo was a source of information and advice. On July 2, 2002, Dunn e-mailed Rivolo asking if he could suggest expert witnesses to testify in an Osprey lawsuit filed by an attorney Dunn was trying to help. Rivolo replied that he would try to think of some. He also told Dunn that Aldridge had asked for a briefing from IDA on the Osprey’s testing and Rivolo was going to deliver it. “I intend to get the maneuvering issue squarely on the table,” Rivolo assured.
When he briefed Aldridge, Rivolo told me, the undersecretary seemed sincere and concerned about Rivolo’s conclusion that the Osprey was unable to do the yank-and-bank maneuvers helicopters did in combat. Not long afterward, on August 8, 2002, Aldridge told the Defense Writers Group, a regular breakfast of military reporters in Washington, that he was “probably the most skeptical person in the Department of Defense” on the Osprey. “I’ve got some real problems with the airplane,” Aldridge said. “It’s a compromise between a helicopter, which wants very big [rotor] blades, and an airplane, which wants relatively small blades.” Aldridge said vortex ring state was a real hazard for the Osprey. “When this happens on this airplane, you lose control,” he said. “Once it starts to roll, you can’t correct it.” Those were Rex Rivolo’s views. The Osprey could be flown to avoid vortex ring state, Aldridge said, but “is it operationally useful in that event? That’s what the flight test program has to prove.” He was going to visit Pax River on September 6 to see how things were shaping up, Aldridge told the reporters. In the meantime, the Pentagon was studying what aircraft the Marine Corps might buy instead if the Osprey failed its flight tests.
* * *
About noon on September 6, Aldridge was at the Patuxent River airfield, peering across a football-field-sized expanse of grass toward an Osprey at the distant end of a runway. Nearby was Colonel Dan Schultz, the program manager, feeling antsier than he had the day the Osprey returned to flight three months earlier. Aldridge, energetic and often cheerful, was poker-faced as he watched the Osprey prepare to take off. He was standing between chief test pilot Macdonald and another test pilot, who were telling the undersecretary of defense what the flight he was about to see was meant to demonstrate. Macdonald loved to talk, but he found it hard to get a conversation going with Aldridge, and that left Macdonald edgy.
Macdonald and Schultz weren’t the only ones nervous about Aldridge’s visit. The Osprey staff at Pax River had spent weeks getting ready, for they knew today could be a turning point for the Osprey— especially if it went badly. Politically, the Osprey was hanging by a thread. Aldridge had made that clear in private, and in his recent remarks to the Defense Writers Group. The goal today was to persuade him that Navair’s flight test plans were going to address all his concerns.
Before coming out to the flight line, they had given Aldridge a two-hour briefing that already was making him reconsider what he had thought he knew about the Osprey.
Bell engineer Ronald Kisor told Aldridge the data collected so far indicated the Osprey actually was less vulnerable to vortex ring state than a helicopter. The reason was a feature the Osprey’s critics saw as a weakness—the high disk loading of its rotors. Their literally hurricane-force downwash meant the Osprey would have to descend far faster at low forward speeds than a helicopter would for the flow of air from beneath its rotors to equal the flow of air the rotors created—the recipe for vortex ring state. The critics were right in saying the Osprey would roll sharply if one of its rotors went into vortex ring state, Kisor conceded, but a pilot could regain control quickly simply by tilting the Osprey’s nacelles forward a few degrees and flying into clean air. The pilot who would fly for Aldridge today, Steve Grohsmeyer of Boeing, had been copiloting an Osprey that demonstrated the recovery method two years earlier, after vortex ring state was pinpointed as the cause of the crash at Marana. The test technique was to go up to 10,000 feet or so, ensuring plenty of altitude to recover, then slow the Osprey to a target speed in the danger area and descend rapidly. These High Rate of Descent tests, abbreviated HROD and pronounced “aitch-rod,” had been interrupted by the Osprey’s grounding since December 2000, but if Aldridge approved, they would resume soon.
Aldridge expressed no opinions, but Macdonald thought he seemed impressed with Kisor’s explanations. Macdonald thought the next briefing went even better.
Tom Wood, Bell’s chief aerodynamicist, had been assigned to talk about the Osprey’s maneuverability at low airspeeds. Wood had a succinct way of talking that seemed to appeal to fellow engineer Aldridge. As Wood offered data to rebut the idea the Osprey was too clumsy to avoid hostile fire in a landing zone, Aldridge began asking questions. Soon the two were talking as if no one else were in the room. As they finished, Aldridge again offered no opinions, but Macdonald was sure Wood had knocked the ball out of the park.
Macdonald had assigned Grohsmeyer and Marine Major Paul Ryan to fly a fifteen-minute demonstration for Aldridge. All they needed to do, Macdonald told them, was show Aldridge that anyone who said the Osprey wasn’t agile enough for combat was wrong.
Shortly after noon, their Osprey began rolling down the runway with its nacelles tilted at 60 degrees, then lifted off. Within seconds, Grohs-meyer took it to 150 feet, tilting the rotors all the way forward as he climbed, then came flying straight down the runway in airplane mode. Boy, that airplane is quiet, Aldridge thought as the Osprey zoomed toward him. Grohsmeyer banked and flew around the hangar, then returned, tilting the rotors up to 85 degrees as he and Ryan approached the grassy area in front of Aldridge. The Osprey slowed to 60 knots, apparently preparing to land helicopter-style. Instead, as if escaping ground fire, Grohsmeyer suddenly tilted the rotors forward and climbed away steeply, accelerating as he went. He brought the Osprey back around and landed on the grass about a hundred yards from Aldridge, then took off again straight up, hovered over the grass, turned the Osprey in a full circle, edged it sideways in each direction, then backward and forward. Finally, Grohsmeyer flew a series of figure eights in tight turns one hundred feet over the grass, flying at 40 to 80 knots with the rotors tilted between 70 and 80 degrees. Then he landed.
Macdonald asked Aldridge what he thought.
“I had no idea of the low airspeed agility,” Aldridge said.
Aldridge’s hosts took him to look inside a redesigned nacelle on another Osprey. He was impressed with how much cleaner the routing of the wire bundles and hydraulic lines was. He had been impressed with the briefings and the flight demonstration, too. He was no longer so worried about the Osprey’s side-by-side rotors or its agility. He still wanted to see if what the engineers had told him could be proven in flight tests, and he still wasn’t sure the Osprey was going to be worth its hefty price tag, but he was no longer inclined to cancel it. Aldridge told Schultz to proceed with the flight tests.
* * *
Once upon a time, test pilots like the famed Chuck Yeager tugged on a helmet and squeezed into a flight suit, strapped on an X-model aircraft, then bet their lives they could find the edge of its envelope without having to punch out or ride the experimental machine into the ground. Those days are long gone. Today’s test pilots still fly to the edge of the envelope. They still need “the right stuff ”—steady nerves, quick reflexes, maybe a little swagger in their walk. They still climb into new or modified aircraft and try things no one else has ever done with them. Today’s test pilots, though, no longer routinely fly into the unknown. They don’t even fly as often as they work on the ground. A test pilot today is more likely to be found manipulating a keyboard and mouse than a stick and throttle. He—they are still mostly men—is less likely to be sitting in a cockpit than in a meeting with engineers or at a desk, analyzing data and planning flight tests in meticulous detail.
Each step in a modern test flight is scripted on a “test card,” which is carried on a clipboard strapped to the pilot’s knee for easy reference while airborne. After a flight, the pilot writes a detailed report, which he and the engineers will go over in yet another meeting. The
report may rely in part on tape recordings of observations the pilot spoke into a microphone as he flew. It will certainly rely on data gathered during the flight by onboard instruments that instantly and constantly record not only the machine’s altitude, speed, pitch, yaw, roll, and other motions but its every moan and groan. The instruments radio the data in “real time” to a platoon of engineers on the ground whose job is to assess the results as they come in and watch for signs of danger. The engineers will warn the pilot to knock it off if they see him flirting with trouble. The era when the military was willing to risk a pilot’s life or a multi-million-dollar aircraft in a test faded into history with the advent of computerized flight simulators. Today, pilots “fly” dangerous tests first in SUV-sized machines that mimic real flight with astounding fidelity, yet without ever leaving the ground. Equipped with the same cockpit as the aircraft to be flown, the best of such computerized simulators can project on a screen beyond a mock windshield a virtual-reality display of nearly any geographic location as seen from any altitude. Runways, buildings, mountains, rivers, and trees are depicted faithfully, in living color, the way they would appear from an aircraft in a climb, a bank, a dive. Some simulators ape the motions of flight faithfully enough to induce vertigo and airsickness. Based on calculations fed into their computers, simulators can be programmed to replicate how an aircraft will behave in almost any circumstance. Flying the aircraft itself is the only way to prove the calculations were correct, but as a rule, test pilots today aren’t betting their lives when they go out and fly.
The Osprey’s High Rate of Descent tests were an exception to that rule. The pilots who flew them would venture into that region on the map marked “Here Be Dragons.” You could die there.
The HROD tests would be dangerous because vortex ring state was largely a mystery. The phenomenon was hard to describe, much less predict, partly because so little research had been done on it in the six-decade history of the helicopter. Beyond that, no one had ever devised an entirely reliable way to predict all the air flows created by rotors. Like the weather, there was a nearly infinite number of variables that could affect them—the configuration of the aircraft, the speed and direction of the wind, the aircraft’s altitude, the rotor’s angle of attack. The flows around an airplane wing, which moves into clean air constantly, can be predicted with great accuracy. The flows around a rotor, which moves in a circle but might be stationary or moving forward or backward or sideways as it rotates, are devilishly more complex. This makes engineering rotorcraft an art as well as a science. The pilots and engineers in the Osprey program were certain the aircraft’s high disk loading made it far less likely to go into vortex ring state than critics assumed. The only way to prove it, though, was to take an Osprey aloft and go find its vortex ring state boundary. Based on calculations and the tests done in 2000, the engineers and pilots were confident an Osprey could get out of vortex ring state simply by tilting its rotors into clean air. If they were wrong, though, someone could die trying.
Tom Macdonald, as the Osprey program’s chief test pilot, decided he should be the pilot in command for each of the dozens of flights planned in the second series of HROD tests. His copilot most often would be Steve Grohsmeyer of Boeing or Bill Leonard of Bell, though Macdonald always would have the controls. Only the two pilots would be aboard; there was no reason to risk more lives by having engineers or crew chiefs in the back.
Born and raised near Boston, Macdonald had become a test pilot during a twenty-one-year career in the Navy flying helicopters and jets. Since 1991, when he got out of the Navy, he had flown the Osprey for Boeing. He and Grady Wilson, the pilot who survived the first Osprey crash in 1991, were flying the chase plane in July 1992, when four Boeing employees and three Marines died in the second Osprey crash at Quantico. Macdonald had known all seven victims; some were close friends. He had lost other friends among the Marine Corps pilots and crew chiefs who died in the other Osprey crashes as well. Macdonald knew there were ways the Osprey could kill you—there were ways any aircraft could. He was equally sure the Osprey wasn’t unsafe—and certainly not the death trap its harshest critics called it. Macdonald never looked at it that way, but he was betting his life on that when the HROD tests began on November 25, 2002.
The tests began only six months after the Osprey’s return to flight partly because engineers had to come up with a piece of hardware to accurately measure the Osprey’s forward speed at less than 40 knots. Then, from November 2002 to July 2003, Macdonald and his copilots did sixty-two HROD tests, flying a total of 104 hours over a restricted flight range between the towns of Cambridge and Salisbury on Maryland’s eastern shore. Macdonald would climb to 10,000 feet, then tilt the rotors up into helicopter mode and slow to a target airspeed. As Macdonald held it there for a bit, a challenge in itself, the copilot would put his hands on his own set of controls, just in case. To duplicate the way the Osprey that crashed at Marana had been flying, Macdonald would lower the landing gear, tilt the nacelles back to 95 degrees, and start reducing power. The Osprey would begin to drop. Macdonald would let it fall until they hit a target rate of descent, then adjust the power to hold the Osprey at a steady sink rate. At that point, still descending, Macdonald and his copilot would talk into their microphones about the Osprey’s stability and handling, the quality of the ride, and whether they heard anything unusual. They were looking for ways a pilot might detect the onset of vortex ring state before getting into it. They repeated the flight profile over and over during those months, taking their measurements at every 500-foot increment of sink rate at a series of ever slower airspeeds.
As predicted, they found it hard to put the Osprey into vortex ring state. The boundary for a helicopter was a sink rate somewhere around 800 feet per minute at 40 knots or less of forward speed. Macdonald had to let the Osprey sink at least 2,500 to 2,600 feet a minute at 40 knots before it would near vortex ring state. Even at slower forward speeds, the boundary was a sink rate of around 1,700 feet per minute. He and his copilots weren’t actually trying to lose control of the Osprey, they were just trying to find the edge of the envelope, the point where they felt vortex ring state coming on. They got there a number of times without incident. “The thrust would begin to oscillate,” Macdonald told me. “A little up-and-down motion would settle into the aircraft that we weren’t commanding.” The Osprey would rock a little bit in some cases, and at the lowest speeds they tested, as slow as 10 knots forward speed while plunging toward the ground, the pilots would hear “this eerie howling and audio sound of the air rush,” Macdonald said. “We’d just get really silent and quiet.” Eleven times during the tests Macdonald flew, one of the rotors went into vortex ring state and the Osprey did a sudden, uncommanded roll—seven times to the right, four times to the left. Each time, Macdonald was able to recover by pushing the thumbwheel switch to tilt the nacelles forward and put the rotors into undisturbed air. Two seconds was usually all it took. Those seconds, though, gave Macdonald and his copilots some hairy moments.
The hairiest was on July 17, 2003. The tests already had achieved their primary goal—charting the Osprey’s envelope for vortex ring state—a couple of months earlier. Based on that envelope, the program had developed warning devices for the Osprey to alert pilots when they were flirting with vortex ring state. One was visual, a red light on the control panel in front of each pilot that would flash sink, sink if an Osprey exceeded a safe rate of descent. The other was a recording of a woman—a device that pilots call a “bitching Betty”—who would be heard in the pilot’s headset saying “sink rate, sink rate” in an urgent monotone if the limit were exceeded. The HROD tests were continuing, though, because Navair was trying to satisfy Institute for Defense Analyses expert Rex Rivolo that the tests had been adequate. That July 17, Macdonald and Grohsmeyer were flying 7–10 knots and descending at more than 2,300 feet per minute, well beyond the vortex ring state envelope already established. They were dropping like a rock while a special test device alternated th
e lateral tilt of each rotor to see if that would prevent vortex ring state. Macdonald was on the radio with an engineer on the ground when the Osprey suddenly snap-rolled right more violently than Macdonald had ever seen it do. Instinctively, he pushed the stick left as the roll began but the Osprey didn’t respond. By the time Macdonald recognized what was happening, the Osprey was flying on its side, left wing up and right wing down, and spiraling toward the ground ever faster. Macdonald pushed the thumbwheel to tilt the nacelles forward as fast as they would go, all the way to airplane mode. The seconds it took seemed like minutes, but finally he regained control and straightened the Osprey out. For a moment, there was silence in the cockpit and over the radio. Macdonald, Grohsmeyer, and the engineers on the ground knew the pilots had just had a close call. If the Osprey had rolled all the way upside down in helicopter mode, there was no telling what damage they might have done to the aircraft—or whether they could have regained control at all.
After Macdonald and Grohsmeyer landed, the program office and the pilots decided they had taken the HROD testing of the Osprey far enough. The Osprey’s boundary for vortex ring state had been established beyond any doubt, and studied more than that of any rotorcraft in the world.
Three months later, at a dinner in Los Angeles, the Society of Experimental Test Pilots gave Macdonald its highest honor, the Iven C. Kincheloe Award for “outstanding professional accomplishment.” The citation said Macdonald had flown “every flight in a test program where no test pilot has been before.” Chuck Yeager was in the audience that evening. He shook Macdonald’s hand.
The Dream Machine Page 46
