The Tacit Blue in flight above Nevada. Long rumored to be a flying wing, it was, in fact, one of the strangest looking aircraft ever built. Its odd shape was to accommodate a specialized radar able to track armor units. The design also provided "all-aspect" stealth. The Tacit Blue first flew in February 1982, but was not declassified until April 30, 1996.
Artist's conception of a flock of Auroras. From top to bottom, the original "Black Diamond," the "North Sea" Aurora, and finally, the XB-70 Aurora. The stories about the Aurora began to spread in the late 1980s and reached their peak in 1994.
CHAPTER 9
The Return of Black Reconnaissance
HALSOL and the GNAT-750
With many calculations, one can win; with few one cannot… By this means I examine the situation and the outcome will be clearly apparent.
Sun Tzu ca. 400 B.C.
Despite the end of the Model 147 and 154 reconnaissance drone programs, interest remained in what were now called unmanned aerial vehicles (UAV).
Most of these were short-range, battlefield-support UAVs. But, just as stealth changed both tactical and strategic aircraft, it also caused a resurgence of interest in strategic reconnaissance UAVs. Two very different systems would emerge during the 1980s and early 1990s. They would also highlight the changing shades of Black.
One advantage of a UAV over a manned aircraft was that of flight duration. This had not been realized when the Model 147 and 154 drones were flown, but was central to the mission of the first of these new Black UAVs.
Its planned flight time would not be measured in hours or even days but in months. The technology to build the first of these Dark Eagles did not come from an exotic development program but from a contest.
GOSSAMER DREAMS
In the myth of Icarus, a man had flown by flapping wings attached to his arms. Even with the achievement of heavier-than-air flight, the dream remained: to fly with only the power of one's own body. In 1959, British industrialist Henry Kremer offered a 50,000-pound prize for the first successful man-powered flight. It was to cover a figure-eight course around two markers a half mile apart. The aircraft had to start and finish the course at an altitude over ten feet.
During the 1960s and early 1970s, a number of man-powered aircraft tried for the Kremer Prize, but all were doomed to failure. They were of conventional design, fitted with chain-driven propellers. Principally made of wood, they were too heavy and incapable of turning.
One man realized what was needed. Dr. Paul B. MacCready of AeroVironment Incorporated understood that neither a conventional design nor conventional thinking would work. The Kremer Prize would take an innovative aircraft, designed with no preconceived notions.
The result was the Gossamer Condor. It had a long, tapered wing. Like the Wright Flier, it had a canard and wing warping to provide control. The pilot rode in a gondola suspended below the wing. The Gossamer Condor was designed to fly at extremely low airspeeds. Dozens of times the plane crashed, once as it was approaching the second pylon and victory. Finally, on August 23, 1977, Bryan Allen peddled the Gossamer Condor around the course. Man had flown.[562]
With the Kremer Prize won, other frontiers beckoned. In 1980, AeroVironment was sponsored by DuPont to develop a solar-powered aircraft able to fly from Paris, France, to England. The first test aircraft, the Gossamer Penguin, was so fragile and unstable that it could be flown only in the early morning when the air was calm. Based on the results of these tests, the Solar Challenger was designed. This was a much smaller and more rugged aircraft. It could reach altitudes of over 12,000 feet. Power came from 16,128 solar cells, which covered the entire upper surface of the wing and stabilizer. Despite the large surface area, the array provided a maximum of only 2,600 watts — enough to power two hair driers. The Solar Challenger had a wingspan of 47 feet, but weighed just over 200 pounds. In July 1981, the Solar Challenger successfully completed a 163-mile flight from Paris to RAF Mansion, England, averaging a speed of about forty miles per hour at just over 11,000 feet.
THE ETERNAL AIRCRAFT
With the success of the Solar Challenger, AeroVironment began studying the possibility of a high-altitude, solar-powered UAV. If provided with some type of energy storage system, it could fly "eternally" and remain at altitudes above 65,000 feet. Flight duration would ultimately be limited only by such factors as mechanical systems wear.[563]
The design of a solar-powered Gossamer-type aircraft flying at these altitudes faced a number of problems. One peculiarity was engine performance. At takeoff, the Solar Challenger could barely climb; at 11,000 feet, however, it could equal a Cessna light plane. A piston engine loses power as it climbs, due to the thinner air. In contrast, a solar-powered aircraft's climb performance increases as the solar cells "see" a brighter sun, and the colder air improves efficiency. Above 30,000 feet, however, problems start to appear. The air temperature becomes constant, so there is not a continued improvement in efficiency. At the same time, the plane faces an increasing power requirement. Because of the thinner air, the plane must fly faster for its wings to generate the same amount of lift.
Another demand was the need to store power. More than half the current generated by the solar cells would have to be stored in some type of battery to keep the plane aloft during darkness. The "eternal" solar-powered aircraft would need twice the collection area, with no increase in weight, over the Solar Challenger.[564]
The design would have to be extraordinarily light — one-half pound per square foot of wing area, the same weight as foam art board. In contrast, an eagle has a wing loading of four to six pounds per square foot of wing. The eternal aircraft would need a wing loading half that of the Solar Challenger (including the pilot). The Gossamer Penguin's structure was light enough, but was too fragile. Despite these problems, theoretical calculations convinced Ray Morgan, vice president at AeroVironment's Design Development Center, that such an airplane could be built.[565] This also opened Black possibilities.
HALSOL
By 1983, AeroVironment was able to attract government sponsorship from a "classified customer" to build a proof-of-concept test aircraft.
(Among the possible "customers" that have been suggested are the National Reconnaissance Office, the CIA, and the Naval Research Laboratory.) It was called "HALSOL," for high altitude solar. Unlike the other Gossamer-type aircraft, this was to be a Black airplane in the classic sense. The HALSOL was developed and flown in secret. Its existence was not to be revealed for another decade.[566]
The HALSOL design was a pure flying wing, with no rudders or canard.
It had a span of 98.4 feet. From front to back, the wing was eight feet wide; it was made of five, 20-foot-long segments joined together. The main wing spar was made of thin wall carbon fiber tubes. Attached to this were ribs of Styrofoam reinforced with Kevlar and spruce. The wing was covered with Mylar plastic. Despite what one might think, the wing was far from being weak. It was stressed for a +5/-3g load factor (greater than the U-2). The center segment had two gondolas that enclosed the landing gear.
The aircraft was powered by eight electric motors — two mounted on the center of the wing, two on each inboard wing segment, and one on each outer wing segment. Spreading them out along the full span of the wing distributed the load. The HALSOL propellers had a variable pitch to match the available load on the power source, in order to permit the maximum efficiency. For the test flights, they were powered by silver-zinc batteries.
The HALSOL was controlled by radio from the ground. To pitch up or down, an elevator on the center wing section's trailing edge was used. To make a turn, the outermost motor on one side was sped up, while the opposite motors were slowed down.
HALSOL could hardly be called a high-performance aircraft. It flew at twelve knots and had a never-exceed speed at low altitude of twenty-seven or twenty-eight knots. Above this speed, it would go into a nose-down tuck.
It was estimated a climb to 70,000 feet would take about six hours. Because it was a test vehicle,
the HALSOL was designed to climb, rather than to remain at high altitudes.[567]
Total gross weight of the aircraft was about 410 pounds, with a payload of about 40 pounds.[568] The efforts to control weight led to creative thinking and some unusual solutions. The front wheel assembly on the two gondolas used dual baby-buggy wheels, while the main landing gear assembly had a sixteen-inch bicycle wheel.[569]
The HALSOL made its first flight in June of 1983.[570] Over the next two months, a total of nine flights were completed at Groom Lake. These lasted for thirty to sixty minutes and reached an altitude of 8,000 feet. Although the aircraft was proven to be aerodynamically and structurally sound, studies indicated that 1983-vintage solar cell technology was not efficient enough to permit very long, high-altitude flight. In particular, the solar technology lacked sufficient "power-density," the energy available per pound of the components. The HALSOL program was discontinued, and the aircraft was placed in storage.[571]
PATHFINDER
AeroVironment remained active in solar-energy research. In 1987 (four years after the HALSOL project ended), General Motors (GM) selected AeroVironment to develop the Sun Raycer car, which won. the first trans-Australia race for solar-powered vehicles. The following year, GM selected AeroVironment to develop the Impact, a battery-powered commuter car suitable for mass production. Both these electric car projects would have a major effect on the discontinued HALSOL project: by the end of the 1980s, lightweight solar cells, electric motors, and power-storage technology had advanced to the point that the original HALSOL concept became practical.[572]
A mission for such an eternal aircraft had also appeared. An aircraft like the HALSOL could be used to detect missile launches, such as the Scud ballistic missiles Iraq fired against Israel and Saudi Arabia during the Gulf War. This was seen as a preview of future regional conflicts. Scud missiles had been exported and were in production throughout the Third World.
Both Iran and North Korea were active in this area, as well as having ongoing chemical, biological, and nuclear-weapons programs.[573]
With the technology now available and a military need, the HALSOL was taken out of storage in early 1992. Under the direction of the Ballistic Missile Defense Organization (BMDO), the successor to the Strategic Defense Initiative, AeroVironment began a modification program. The basic airframe was retained, with the addition of new systems. One example was the motor-propeller system. The original variable pitch props were replaced with fixed props, with an electronic "peak-power tracker." Removing the original propeller system reduced the number of parts and increased reliability.[574] The original rare-earth DC motors were replaced with brushless AC motors, which also improved reliability and efficiency. The motors also had new custom-designed inverters to improve efficiency. Rows of cooling fins were added behind the propellers to radiate heat. Keeping the motor's temperature within limits while flying at high altitude was a problem due to the thin air. The complete motor and propeller assembly weighed only thirteen pounds.
In addition, the control surfaces were modified. The original HALSOL had only one elevator powered by four servos. In the new version, twenty-six elevators ran the full span of the wing's trailing edge.[575]
The biggest change was in the plane's power source. The original HALSOL was battery powered. (Only a few solar cells had been carried on the HALSOL to test the effect of wing flexing.) The modified aircraft would carry some two hundred square feet of new lighter-weight solar cells. They would cover about one-third of the wing and provide about 3.8 kilowatts of power. This was enough to fly on solar power alone after 9:30 A.M. In practice, however, the aircraft would fly on dual solar-battery power.[576]
The modification work was completed in the late summer of 1993 — a full decade after the HALSOL's last flight. Because of the extensive modifications, a new name was given to the aircraft. It was now called "Pathfinder."
OUT OF THE BLACK
It is important to note that, up to this time, there had been no hint that there was a Black Gossamer-type UAV or that it had been flown a decade before. The HALSOL-Pathfinder finally came out of the Black with an October 1, 1993, air force press release, which announced the aircraft's existence and described its history. It stated that the Pathfinder would make a series of low-altitude test flights at Edwards Air Force Base in October-November 1993. It was explained that the project had been declassified to allow use of commercially available technology and open discussion of technical ideas. At the same time, a photo of the original HALSOL was released.[577]
The Pathfinder's first flight was made on October 20, 1993. It lasted forty-one minutes and involved six trips around a 1.2-mile racetrack course on the Edwards lake bed. The top speed was sixteen knots, and the plane's altitude was limited to 200 feet. The Pathfinder was a majestic sight as it flew slowly above the tan lake bed like some huge transparent bird. As it flew, the wing tips arched up, forming a U-shape. The propellers made a humming noise as they spun. At least 60 percent of the Pathfinder's power was provided by the solar cells. The Pathfinder was controlled from the ground by Ray Morgan, who originally conceived of the project.[578]
The Pathfinder's public debut came on November 23, 1993, at the Edwards Air Force Base Air Show. Six weeks before, even its existence had been a secret; now, more than 200,000 people saw it on display. Never before had a Black airplane's first public showing come so soon after its existence had been revealed. The Pathfinder was in a roped-off area of the main hangar, and there were armed guards nearby. This was not due to any secrecy about the plane — people were kept back because the light in the hangar was enough to start the motors, and a spinning propeller might injure a spectator. The guards were to protect the other plane in the enclosure, a B-2 Spirit.[579]
The October-November flight-test series pushed the Pathfinder to the edge of its low-altitude flight envelope and measured the stability and performance of the modified aircraft. The data collected was used to develop autopilot software to allow the aircraft to operate independently of constant ground control.[580]
Following the first flight tests, the Pathfinder was returned to AeroVironment for modifications that would enable it to undertake high-altitude flights. Control of the program was also transferred from BMDO to NASA due to budget reasons. Rather than detecting Scud launches, it would be used for atmospheric research.[581]
While at AeroVironment, about 70 percent of the wing surface was covered with solar cells. (For aerodynamic reasons, the wing's leading edge cannot be covered.) These cells were lighter than those used for the first flights.
The high-altitude flights were seen as critical to demonstrate the feasibility of the Pathfinder concept. It was planned that the tests would run from late August through mid-October 1994 at Edwards.[582] The addition of the solar cells and the structural modifications took longer than expected, however, and by the time the Pathfinder was ready, it was late in the flight season. With the sun lower in the sky, it was felt it would be better to wait for more favorable conditions.[583]
The high-altitude tests were rescheduled for April-July 1995. As the Pathfinder lacks an energy-storage system, the flights would be made during daylight hours. The plane would take off at dawn and climb all day.
Peak altitude would be between 60,000 and 65,000 feet. The Pathfinder's flight characteristics at high altitudes are very different than the heavier and faster-flying U-2s. At altitude, the U-2s' minimum and maximum speeds, limited by wing flutter, provide only a small margin for flight. With the lighter and slower Pathfinder, both speeds are considerably slower and therefore much less susceptible to structural failure. This is important, as tight limits would be very demanding for the automatic control system.
The estimated cruising speed at altitude would be around 100 knots.[584] At sunset, electrical power would be lost from the solar cells, and the Pathfinder would start down. Due to the plane's high glide ratio, it would not land until about 2:00 A.M.
Following the high-altitude tests, long-durati
on flights could be attempted. The Pathfinder could take off from Alaska and fly over the North Pole for weeks at a time to measure ozone levels. During the summer, there is nearly continuous sunlight over the pole, so the Pathfinder would not need any energy storage system. The continuous flight time could be 2,000 to 3,000 hours, or 80 to 120 days aloft.[585] The Pathfinder's solar array would be equipped with double-sided cells. These would use the light reflected from clouds, the ice cap, and the atmosphere to produce power during the evening hours, when the sun is low. The plane would also have a set of small computers, gyroscopes, and a four-antenna satellite navigation system to allow automatic flight.[586]
HELIOS
The HALSOL-Pathfinder was designed to act as a technology demonstrator for the eternal aircraft, which would be a much larger and heavier aircraft. Currently called "Helios" or solar rechargeable aircraft (SRA), it would have a wingspan of 200 feet, made up of five, 40-foot-long segments.
There would be four landing gear gondolas. The solar array would produce 21.6 kilowatts, powering the eight motors — the same motors as were used on Pathfinder. The Helios-SRA would weigh about 1,100 to 1,200 pounds, and have a payload of 150 to 200 pounds. Its operational ceiling is planned to be about 60,000 to 65,000 feet; top speed would be around 100 knots.
Unlike the HALSOL-Pathfinder, the Helios-SRA would be optimized for high-altitude cruise, rather than climb.[587]
To allow around-the-clock flights, the Helios-SRA required an energy-storage system — a proton-exchange membrane fuel cell. Excess electrical current from the solar array would electrolyze water into hydrogen and […] and stored separately in the wing spar. At night, the hydrogen and oxygen would be allowed to recombine into water. The energy released would be converted back into electrical power for the motors. These fuel cells would be carried in the wing leading edge. The system has less than half the weight of rechargeable batteries.[588] Low-level research is currently under way on the fuel cells. This is a two- to three-year program. Although the technology is understood, the problem is putting it into a lightweight package. The Helios-SRA could be ready in 1997 or 1998.
Dark Eagles: A History of the Top Secret U.S. Aircraft Page 29