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AeroVironment Helios Prototype

The Helios Prototype was the fourth and final 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 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.[1] It was developed from the NASA Pathfinder and NASA Centurion aircraft.

Helios Prototype
Helios Prototype in flight
Role Unmanned aerial vehicle
Manufacturer AeroVironment
First flight September 8, 1999
Status Destroyed in 2003
Primary user NASA ERAST Program
Number built 1
Developed from NASA Pathfinder, Pathfinder Plus and NASA Centurion

Helios Prototype edit

 
Pathfinder Plus (left) and Helios Prototype (right) on the Dryden ramp
 
AeroVironment Chairman Paul MacCready shows a cross section of the AeroVironment/Helios Prototype wing spar.

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 the sun-powered development flights that followed.[1] The aircraft's maiden flight was on September 8, 1999.[2]

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 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.[3]

Using the traditional incremental or stairstep approach to flight testing, 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.[1]

Aircraft description edit

 
Helios Prototype flying wing moments after takeoff, beginning its first test flight on solar power from the U.S. Navy's Pacific Missile Range Facility on Kauai, Hawaii, July 14, 2001.

The Helios Prototype is an ultra-lightweight flying wing aircraft with 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 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 the entire wing.[1]

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 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 m2)., 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.[1]

The all-wing aircraft 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 the fixed landing gear—rugged mountain bike wheels on the rear and smaller scooter wheels on the front.[1]

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 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 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.[1]

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 the upper wing surface.[3] 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.

Records edit

 
Helios with very high wing dihedral just before breaking up
 
Helios disintegrates as it falls towards the Pacific
 
Wreckage of Helios in the Pacific

On August 13, 2001,[1] 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.[4] The altitude reached 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).[1]

Crash edit

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 a remotely piloted systems checkout flight in preparation for an endurance test scheduled for the following month.[5]

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 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 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 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 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."[3]

The investigation report identified a two-part root cause of the accident:

  1. "Lack of adequate analysis methods led to an inaccurate risk assessment of the effects of configuration changes leading to an inappropriate decision to fly an aircraft configuration highly sensitive to disturbances."
  2. "Configuration changes to the aircraft, driven by programmatic and technological constraints, altered the aircraft from a spanloader to a highly point-loaded mass distribution on the same structure significantly reducing design robustness and margins of safety."[3]

Specifications edit

 
Solar Aircraft Evolution through the ERAST Program
 
Schematic of Helios HP03 Hydrogen-Air Fuel Cell Configuration
Specifications[1][3][6][7]
  Pathfinder Pathfinder-Plus Centurion Helios HP01 Helios HP03
Length ft (m) 12 (3.6) 12 (3.6) 12 (3.6) 12 (3.6) 16.5 (5.0)
Chord ft (m) 8 (2.4)
Wingspan ft (m) 98.4 (29.5) 121 (36.3) 206 (61.8) 247 (75.3)
Aspect ratio 12 to 1 15 to 1 26 to 1 30.9 to 1
Glide ratio 18 to 1 21 to 1 ? ? ?
Airspeed kts (km/h) 15–18 (27–33) 16.5–23.5 (30.6–43.5) ?
Max altitude ft (m) 71,530 (21,802) 80,201 (24,445) n/a 96,863 (29,523) 65,000 (19,812)
Empty Wt lb (kg) ? ? ? 1,322 (600) ?
Max. weight lb (kg) 560 (252) 700 (315) 1,900 (862) 2,048 (929) 2,320 (1,052)
Payload lb (kg) 100 (45) 150 (67,5) 100–600 (45–270) 726 (329) ?
Engines electric, 2 hp (1.5 kW) each
No. of engines 6 8 14 14 10
Solar pwr output (kW) 7.5 12.5 31 ? 18.5
Supplemental power batteries batteries batteries Li batteries Li batteries, fuel cell

See also edit

The footage shows the Helios in the air

References edit

This article contains material that originally came from the web article by Greg Goebel, which exists in the Public Domain.   This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration.

  1. ^ a b c d e f g h i j NASA Armstrong Fact Sheet: Helios Prototype
  2. ^
  3. ^ a b c d e Investigation of the Helios Prototype Aircraft Mishap – Volume 1, T.E. Noll et al., January 2004
  4. ^ . Fédération Aéronautique Internationale. Archived from the original on 16 October 2013. Retrieved 14 October 2013.
  5. ^ "Helios Prototype Solar Aircraft Lost In Flight Mishap", ScienceDaily, July 1, 2003, accessed September 8, 2003
  6. ^
  7. ^
  • "Photovoltaic Finesse: Better Solar Cells—with Wires Where the Sun Don't Shine", an article by Daniel Cho on page thirty-three of the September, 2003 issue of Scientific American

External links edit

  • NASA's Helios Prototype Solar-Powered Aircraft
  • Helios for kids
  • Helios model by DesignsbyALX 2011-05-19 at the Wayback Machine.
  • "3G Tested at 65,000 feet (20,000 m) in the stratosphere" 3G news release July 23, 2002
  • Science Daily article on Pathfinder Plus altitude record
  • Pathfinder Plus at NASM
  • NASA-AeroVironment contract for followon projects[permanent dead link]
  • Helios record attempt article
  • NASA image collections:

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The Helios Prototype was the fourth and final 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 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 1 It was developed from the NASA Pathfinder and NASA Centurion aircraft Helios Prototype Helios Prototype in flight Role Unmanned aerial vehicle Manufacturer AeroVironment First flight September 8 1999 Status Destroyed in 2003 Primary user NASA ERAST Program Number built 1 Developed from NASA Pathfinder Pathfinder Plus and NASA Centurion Contents 1 Helios Prototype 1 1 Aircraft description 1 2 Records 1 3 Crash 2 Specifications 3 See also 4 References 5 External linksHelios Prototype edit nbsp Pathfinder Plus left and Helios Prototype right on the Dryden ramp nbsp AeroVironment Chairman Paul MacCready shows a cross section of the AeroVironment Helios Prototype wing spar 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 the sun powered development flights that followed 1 The aircraft s maiden flight was on September 8 1999 2 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 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 3 Using the traditional incremental or stairstep approach to flight testing 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 1 Aircraft description edit nbsp Helios Prototype flying wing moments after takeoff beginning its first test flight on solar power from the U S Navy s Pacific Missile Range Facility on Kauai Hawaii July 14 2001 The Helios Prototype is an ultra lightweight flying wing aircraft with 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 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 the entire wing 1 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 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 m2 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 1 The all wing aircraft 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 the fixed landing gear rugged mountain bike wheels on the rear and smaller scooter wheels on the front 1 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 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 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 1 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 the upper wing surface 3 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 Records edit nbsp Helios with very high wing dihedral just before breaking up nbsp Helios disintegrates as it falls towards the Pacific nbsp Wreckage of Helios in the Pacific On August 13 2001 1 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 4 The altitude reached 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 1 Crash edit 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 a remotely piloted systems checkout flight in preparation for an endurance test scheduled for the following month 5 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 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 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 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 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 3 The investigation report identified a two part root cause of the accident Lack of adequate analysis methods led to an inaccurate risk assessment of the effects of configuration changes leading to an inappropriate decision to fly an aircraft configuration highly sensitive to disturbances Configuration changes to the aircraft driven by programmatic and technological constraints altered the aircraft from a spanloader to a highly point loaded mass distribution on the same structure significantly reducing design robustness and margins of safety 3 Specifications edit nbsp Solar Aircraft Evolution through the ERAST Program nbsp Schematic of Helios HP03 Hydrogen Air Fuel Cell Configuration Specifications 1 3 6 7 Pathfinder Pathfinder Plus Centurion Helios HP01 Helios HP03 Length ft m 12 3 6 12 3 6 12 3 6 12 3 6 16 5 5 0 Chord ft m 8 2 4 Wingspan ft m 98 4 29 5 121 36 3 206 61 8 247 75 3 Aspect ratio 12 to 1 15 to 1 26 to 1 30 9 to 1 Glide ratio 18 to 1 21 to 1 Airspeed kts km h 15 18 27 33 16 5 23 5 30 6 43 5 Max altitude ft m 71 530 21 802 80 201 24 445 n a 96 863 29 523 65 000 19 812 Empty Wt lb kg 1 322 600 Max weight lb kg 560 252 700 315 1 900 862 2 048 929 2 320 1 052 Payload lb kg 100 45 150 67 5 100 600 45 270 726 329 Engines electric 2 hp 1 5 kW each No of engines 6 8 14 14 10 Solar pwr output kW 7 5 12 5 31 18 5 Supplemental power batteries batteries batteries Li batteries Li batteries fuel cellSee also edit source source source source The footage shows the Helios in the air History of unmanned aerial vehicles Electric aircraft Regenerative fuel cell NASA Pathfinder First flew in June 1983 NASA Centurion First flight 10 November 1998 QinetiQ Airbus Zephyr First flight in 2008 Facebook Aquila First flight28 June 2016 SoftBank AeroVironment HAPSMobile First flight 11 September 2019 BAE Systems PHASA 35 First flight 17 February 2020 References editThis article contains material that originally came from the web article Unmanned Aerial Vehicles by Greg Goebel which exists in the Public Domain nbsp This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration a b c d e f g h i j NASA Armstrong Fact Sheet Helios Prototype Helios Prototype fact sheet old edition archived at archive org a b c d e Investigation of the Helios Prototype Aircraft Mishap Volume 1 T E Noll et al January 2004 Aviation and Space World Records Federation Aeronautique Internationale Archived from the original on 16 October 2013 Retrieved 14 October 2013 Helios Prototype Solar Aircraft Lost In Flight Mishap ScienceDaily July 1 2003 accessed September 8 2003 NASA Pathfinder fact sheet archived at archive org NASA Centurion Fact Sheet archived at archive org Photovoltaic Finesse Better Solar Cells with Wires Where the Sun Don t Shine an article by Daniel Cho on page thirty three of the September 2003 issue of Scientific AmericanExternal links edit nbsp Wikimedia Commons has media related to AeroVironment Helios Prototype NASA s Helios Prototype Solar Powered Aircraft Helios for kids Helios model by DesignsbyALX Archived 2011 05 19 at the Wayback Machine 3G Tested at 65 000 feet 20 000 m in the stratosphere 3G news release July 23 2002 Science Daily article on Pathfinder Plus altitude record Telecom relay achievements at Airport International Space com article History of solar powered UAVs at The Future of Things Pathfinder Plus at NASM NASA AeroVironment contract for followon projects permanent dead link Helios record attempt article NASA image collections Pathfinder Pathfinder Plus Archived 2013 02 17 at the Wayback Machine Centurion Archived 2013 04 15 at the Wayback Machine Helios Prototype videos Retrieved from https en wikipedia org w index php title AeroVironment Helios Prototype amp oldid 1174391701, wikipedia, wiki, book, books, library,

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