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26-525: The NASA Centurion was modified into the Helios Prototype configuration by adding a sixth 41 feet (12 m) wing section and a fifth landing gear and systems pod, becoming the fourth configuration in the series of solar-powered flying wing demonstrator aircraft developed by AeroVironment under the ERAST project. The larger wing on the Helios Prototype accommodated more solar arrays to provide adequate power for

52-407: A built-in 10-degree dihedral to give the aircraft more lateral stability. A slight upward twist at the tips of the trailing edge helped prevent wing tip stalls during the slow landings and turns. The wing area was 1,976 sq ft (183.6 m)., which gave the craft a maximum wing loading of only 0.81 lb./sq. ft. when flying at a gross weight of 1,600 lb. The all-wing aircraft

78-418: A delayed take off, due to the failure of the winds to shift as predicted, Helios spent more time than expected flying through a zone of low-level turbulence on the lee side of Kauai, because it was climbing more slowly than normal, since it had to contend with cloud shadows and the resultant reduction in solar power. As the aircraft climbed through 2,800 feet (850 m) 30 minutes into the flight, according to

104-570: A redesigned high-altitude airfoil and the span was increased to 206 feet (63 m). The number of motors was increased to 14 and the number of underwing pods to carry batteries, flight control system components, ballast, and landing gear rose to four. This article contains material that originally came from the web article "Unmanned Aerial Vehicles" by Greg Goebel, which exists in the Public Domain. [REDACTED]  This article incorporates public domain material from websites or documents of

130-420: A remotely piloted systems checkout flight in preparation for an endurance test scheduled for the following month. On the morning of the accident, weather forecasts indicated that conditions were inside the acceptable envelope, although during the preflight go/no-go review, the weather forecaster gave it a "very marginal GO." One of the primary concerns was a pair of wind shear zones off the island's coast. After

156-418: A thin, transparent plastic skin. The main tubular wing spar was made of carbon fiber. The spar, which was thicker on the top and bottom to absorb the constant bending motions that occur during flight, was also wrapped with Nomex and Kevlar for additional strength. The wing ribs were also made of epoxy and carbon fiber. Shaped Styrofoam was used for the wing's leading edge and a durable clear plastic film covered

182-413: A total of 1 hr and 24 minutes. At the time, it weighed in at 1,385 pounds (628.2 kg) (including a 150 pounds (68.0 kg) steel anvil hanging on its centerline to simulate a payload) for its first flight. The flight was nearly flawless and was followed by a second similar performance on November 19, this time before a crowd of VIPs and Media. It lasted 1 hr and 29 minutes. The third and final flight of

208-525: A wingspan of 247 feet (75 m), longer than the wingspans of the U.S. Air Force C-5 military transport (222 feet (68 m) or the Boeing 747 (195 or 224 feet (59 or 68 m), depending on the model), the two largest operational aircraft built in the United States. The electrically powered Helios was constructed mostly of composite materials such as carbon fiber , graphite epoxy, Kevlar , Styrofoam , and

234-705: The ERAST project, was the third generation aircraft in the NASA Pathfinder series of electrical-powered flying wing unmanned aircraft. The ERAST program managers had determined that an aircraft based on the Pathfinder/Pathfinder Plus concept would be the lowest risk approach of achieving the altitude goal. Initially, a quarter-scale model of the Centurion was test flown at El Mirage Dry Lake on March 4, 1997. The full-size Centurion's maiden flight took place at Rogers Dry Lake on November 10, 1998, and lasted

260-441: The Helios Prototype was first flown in a series of battery-powered development flights in late 1999 to validate the longer wing's performance and the aircraft's handling qualities. Instrumentation that was used for the follow-on solar-powered altitude and endurance flights was also checked out and calibrated during the initial low-altitude flights at NASA Dryden . The Helios Prototype is an ultra-lightweight flying wing aircraft with

286-580: The Public Domain. [REDACTED]  This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration . NASA Centurion The NASA Centurion was the third aircraft developed as part of an evolutionary series of solar - and fuel-cell -system-powered unmanned aerial vehicles . AeroVironment, Inc. developed the vehicles under NASA's Environmental Research Aircraft and Sensor Technology (ERAST) program. They were built to develop

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312-605: The aircraft into the Helios Prototype , with work starting in January, 1999. The design of Centurion resulted in an aircraft that looked very much like the Pathfinder, but with a much longer wingspan of 206 feet (63 m). Although the Centurion shape resembled the Pathfinder, the structure was designed to be stronger and capable of carrying numerous payloads (up to 600 pounds (272.2 kg)) more efficiently. Its wing incorporated

338-427: The altitude goals and powered the aircraft with batteries and solar cells. The second configuration, HP03, optimized the aircraft for endurance, and used a combination of solar cells, storage batteries and a modified commercial hydrogen–air fuel cell system for power at night. In this configuration, the number of motors was reduced from 14 to ten. Using the traditional incremental or stairstep approach to flight testing,

364-425: The entire wing. The Helios Prototype shared the same 8-foot (2.4 m) wing chord (distance from leading to trailing edge) as its Pathfinder and Centurion predecessors. The 247-foot (75 m) wingspan gave the Helios Prototype an aspect ratio of almost 31 to 1. The wing thickness was the same from tip to tip, 11.5 inches (29 cm) or 12 percent of the chord, and it had no taper or sweep . The outer panels had

390-433: The fixed landing gear—rugged mountain bike wheels on the rear and smaller scooter wheels on the front. The only flight control surfaces used on the Helios Prototype were 72 trailing-edge elevators that provided pitch control. Spanning the entire wing, they were operated by tiny servomotors linked to the aircraft's flight control computer. To turn the aircraft in flight, yaw control was applied using differential power on

416-508: The low altitude test series took place on December 3. On this flight the vehicle was loaded down to its maximum gross weight of 1,806 pounds (819.2 kg) to test its weight carrying capability. Total flight time on this flight was 30 minutes, as it was shortened because high winds were anticipated by mid-morning. All of these flights took place on battery power and verified the design's handling qualities , performance, and structural integrity. Following these three flights, NASA decided to expand

442-546: The motors on the outer wing panels higher than the motors on the center panels. Speeding up the outer-panel motors caused the aircraft to pitch down and begin a descent. Conversely, applying additional power to the motors in the center panels caused Helios to pitch up and begin climbing. From 2000 to 2001, the HP01 received a number of upgrades, including new avionics, high-altitude environmental control systems and SunPower solar array composed of more than 62,000 solar cells installed on

468-421: The motors — speeding up the motors on one outer wing panel while slowing down motors on the other outer panel. A major test during the initial flight series was the evaluation of differential motor power as a means of pitch control. During normal cruise the outer wing panels of Helios were arched upward and give the aircraft the shape of a shallow crescent when viewed from the front or rear. This configuration placed

494-523: The ocean within the confines of the Pacific Missile Range Facility test range and was destroyed. Most of the vehicle structure was recovered except the hydrogen–air fuel cell pod and two of the ten motors, which sank into the ocean." The investigation report identified a two-part root cause of the accident: This article contains material that originally came from the web article "Unmanned Aerial Vehicles" by Greg Goebel, which exists in

520-416: The pilot turned off the airspeed hold loop instead of executing the correct emergency procedure and increasing the airspeed hold loop gain. The aircraft’s design airspeed was subsequently exceeded and the resulting high dynamic pressures caused the wing leading edge secondary structure on the outer wing panels to fail and the solar cells and skin on the upper surface of the wing to rip off. The aircraft impacted

546-417: The subsequent mishap investigation report, "the aircraft encountered turbulence and morphed into an unexpected, persistent, high dihedral configuration. As a result of the persistent high dihedral, the aircraft became unstable in a very divergent pitch mode in which the airspeed excursions from the nominal flight speed about doubled every cycle of the oscillation . The over-speed condition was exacerbated when

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572-540: The sun-powered development flights that followed. The aircraft's maiden flight was on September 8, 1999. The ERAST program had two goals when developing the Helios Prototype: 1) sustained flight at altitudes near 100,000 feet (30,000 m) and 2) endurance of at least 24 hours, including at least 14 of those hours above 50,000 feet (15,000 m). To this end, the Helios Prototype could be configured in two different ways. The first, designated HP01, focused on achieving

598-519: The technologies that would allow long-term, high-altitude aircraft to serve as atmospheric satellites , to perform atmospheric research tasks as well as serve as communications platforms. It was developed from the NASA Pathfinder Plus aircraft and was developed into the NASA Helios . Centurion, originally built for the 100,000 feet (30,000 m) altitude on solar power milestone specified by

624-404: The upper wing surface. These cells featured a rear-contact cell design that placed wires on the underside of the cells, so as not to obstruct the cells' exposure to solar radiation . On August 13, 2001, the Helios Prototype piloted remotely by Greg Kendall reached an altitude of 96,863 feet (29,524 m), a world record for sustained horizontal flight by a winged aircraft. The altitude reached

650-402: Was assembled in six sections, each about 41 feet (12 m) long. An underwing pod was attached at each panel joint to carry the landing gear, the battery power system, flight control computers, and data instrumentation. The five aerodynamically shaped pods were made mostly of the same materials as the wing itself, with the exception of the transparent wing covering. Two wheels on each pod made up

676-520: Was more than 11,000 feet (3,400 m) — or more than 2 miles (3.2 km) — above the previous altitude record for sustained flight by a winged aircraft. In addition, the aircraft spent more than 40 minutes above 96,000 feet (29,000 m). On June 26, 2003, the Helios Prototype broke up and fell into the Pacific Ocean about ten miles (16 km) west of the Hawaiian Island Kauai during

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