The Perlan 2 glider, an engineless aircraft designed to fly in the stratosphere, made its first flight on September 23 above Redmond Municipal Airport, Oregon. During the test sortie, it reached 5,000 feet, a first step towards a planned 90,000 feet next year and eventually 100,000 feet. The objective of the Airbus Group-sponsored project is scientific–mainly about weather, climate and the ozone layer.
In Argentina in 2016, the Perlan 2 will begin riding air currents that, in certain mountainous regions near the north and south poles, can reach into the stratosphere. Next year’s flights are expected to reach 90,000 feet, exceeding even the altitudes achieved by the U-2 and the SR-71 spyplanes.
The Perlan 2 can also be envisioned as a spacecraft with glider wings. The lack of an engine avoids polluting the atmosphere it will study. Design engineers are free of the complexity of designing an engine that can operate in stratospheric conditions, where air density is only 2 percent of sea-level values and temperatures dip to -70C.
Despite having no engine, the glider’s true airspeed at that altitude will be more than 360 knots. The two-pilot crew will breathe pure oxygen provided by a rebreather system, similar to what astronauts use in space.
The promoters of the project believe it will help scientists to understand the weather. “What happens at the highest levels of the stratosphere impacts weather around the globe, and Perlan 2 will be able to observe directly important atmospheric phenomena that previously have only been speculated about,” they said.
With respect to climate change, Perlan 2 will collect and share data with atmospheric scientists worldwide to improve models. As for the ozone layer, Perlan 2 can take untainted air samples from the stratosphere to measure the levels of ozone-damaging chemicals and assess whether the ozone layer is replenishing or still depleting.
Perlan 2 could even provide an insight into how wing-borne aircraft could operate above the Martian surface, as Perlan 2 will operate in atmospheric conditions roughly similar to those on Mars.
At the headwaters of the project were NASA test pilot Einar Enevoldson, billionaire adventurer Steve Fossett and meteorologist Elizabeth Austin. In the 1990s, Enevoldson saw evidence that in regions closer to the poles, in winter, air waves could extend above the troposphere and well into the stratosphere. Stratospheric mountain waves, like huge ocean waves, are kicked off by strong winds blowing over the tops of high mountain ranges, such as the Andes. As long as the wind above the ridge blows constantly at a higher and higher velocity with increased altitude, the wave will propagate upward. As a pilot, Einar quickly figured out that a glider could ride those waves all the way up to near space.
In 1998, Austin joined Einar’s search to understand stratospheric mountain waves. She expanded upon his findings, proving that it is the stratospheric polar night jet (existing only in winter) and the polar vortex that are factors in sustaining these mountain waves up to 130,000 feet. The Perlan Project was formed to explore these waves.
Fossett and Enevoldson went ahead with Perlan 1 in 1999, modifying a conventional sailplane. They flew it in 2006 to greater than 50,000 feet–this was Phase 1. They quickly determined they needed a custom aircraft to go higher and started designing it. Fossett’s death in an unrelated 2007 flying accident stalled the project until 2014, when Airbus Group became the title sponsor. The non-profit effort has other sponsors–Weather Extreme Ltd., United Technologies and BRS Aerospace.
Perlan 2 has a maximum gross weight of 1,800 pounds and a wingspan of 84 feet. Due to its relatively low aspect ratio, the wing makes Perlan 2 a mediocre performer at low altitudes, but the excess wing area is most welcome in the thin air encountered at 90,000 feet. The cabin will be pressurized to provide a maximum cabin altitude of 14,500 feet (much higher than the Boeing 787’s 6,000-foot cabin altitude, for instance).
Phase 3 is scheduled for May 2019 when the aircraft will be prepared to explore the polar vortex in the northern hemisphere. Traveling in the stratosphere at up to 100,000 feet, Perlan’s speed will increase to the point where it will need new transonic wings.