By Mark Schauer, ATECFebruary 12, 2019
YUMA PROVING GROUND, Ariz. -- Humanity's first powered flight in 1903 lasted for 12 seconds.
In 2010, the Zephyr unmanned aircraft stayed aloft for two straight weeks high in the airspace above U.S. Army Yuma Proving Ground (YPG), setting a world record.
Last summer, an upgraded Zephyr returned to YPG and flew continuously for 25 days, 23 hours, and 57 minutes. Perhaps more significantly, the craft was able to spend its entire flight well above the altitudes normally achieved by commercial airplanes.
"Unlike previous flights when the aircraft had to come down to between 25,000 and 35,000 feet at night, this time we were able to stay above the weather," said Lori Slaughter, test officer. "Our lowest altitude during the flight itself was 55,000 feet."
The Zephyr's intended purpose is to serve as a low-cost, more-capable alternative to a spy satellite, able to loiter over the same vicinity for hours or days at a time. It still has the same name and mission as its original iteration, but boasts a slew of upgrades.
"We have brand new avionics that are a lot more efficient and better-controlled," said Sarah Bassett, project manager. "We have also updated all the solar panels and batteries with increased performance. We've also lightened the airframe."
The construction of the Zephyr is minimalist. Built of composite carbon fiber, the craft weighs a feather-light 100 pounds and has no wheels or landing gear--it is launched off of the shoulders and from the hands of five running individuals. Virtually every square inch of the 80-foot wingspan is covered by lightweight solar cells that charge batteries that power twin electric motors.
Also onboard are sophisticated electronics that allow the craft to be monitored and steered from a ground control station. All of this runs on the electrical power equivalent to that needed to light a single commercial light bulb.
The Zephyr's ability to fly at extremely high altitudes means it can safely evade bad weather while aloft. However, it is vital for the aircraft to perform its ascent and descent in favorable conditions. An unexpected deviation in the jet stream had forced testers to land the craft after 48 hours during a test at YPG in 2013, and all concerned were keen to avoid the same thing this time around.
When the team finally achieved a favorable window on July 11, the craft was run down the runway by Airbus personnel and began its slow and steady ascent into a record-breaking flight. All was going smoothly until the weather situation deteriorated in Phoenix, about 175 miles away. Though this weather pattern had no direct impact on Yuma Proving Ground, Phoenix's Sky Harbor Airport was closed for landings and had multiple commercial airliners circling in the skies above.
The Federal Aviation Administration asked for permission to use some of YPG's restricted airspace to help alleviate the aerial traffic jam that was accumulating in the skies above Phoenix, and YPG readily agreed to help. To accommodate this, the Zephyr's ascent path had to be moved to the extreme southern border of YPG's 2,000 square mile of restricted airspace, and the craft was confined to a small box to continue its climb. The deviation in the plan was completely unexpected, but testers took it in stride, ultimately seeing it as another positive test data point.
"We proved that we could stay away from commercial aircraft," said Bassett. "We managed quite easily to stay in a very small strip of air space and avoid the storms as we gained altitude."
Though YPG averages 360 days of clear weather annually and boasts stable air that is perfect for aircraft testing, testers had to cope with other effects of the intense summer heat.
To achieve optimal performance for a test baseline, the Zephyr's batteries had to be kept at a constant cool temperature prior to flight, which meant YPG personnel had to maintain a portable conditioning chamber at all times. YPG personnel also erected targets across YPG's desert ranges to give the Zephyr's optics suite things to seek while aloft. Even erecting the aircraft's ground control station prior to the flight took place in extreme temperatures.
"Our ground control system has a lot of dishes and antennas that need to be assembled on top," said Bassett. "You can't do it at night because it's dangerous. Even early in the morning, it is very hot outside."
While aloft, YPG personnel monitored the craft's flight at all hours of the day and night, and the Zephyr may have been stay aloft for an astonishing three months had other commitments not forced the crew to land and transport it for other testing elsewhere.
Making the test successful took the efforts of a multitude of YPG offices and shops, and the seamless interaction to achieve the mission impressed both the customer and the test officer.
"It's phenomenal how everyone works together," said Slaughter. "Everyone just comes together for the mission."