Monday, September 28, 2015

How Perlan 2 glider will soar to 90000 feet without an engine

 Jamie Darcy|Airbus
After completing its maiden flight on Sept 23, the Airbus Perlan 2 pressurized glider designed to fly at the edge of space will attempt to fly to 90,000 ft next year, where the air density is less than 2% of what it is at sea level.

Only aircraft to beat the altitude is the Soviet designed MIG-25 Foxbat supersonic interceptor-reconnaissance fighter, which has reached over 120,000 ft.

But Perlan 2 will beat the altitude records set by the Lockheed Martin U-2 and SR-71 Blackbird reconnaissance aircraft, 72000 ft and 85000 ft respectively.

The Perlan 2 will explore the science of giant mountain waves that help create the ozone hole and change global climate models. This require the engineering of a spacecraft with glider wings that can fly in less than 3% of normal air density and at temperatures of minus 70 degrees C, conditions approximating the surface of Mars.

It carries a crew of two and scientific instruments needed to explore the stratospheric mountain waves.

The aircraft has a gross weight of 1,800 pounds and a wing span of 84 feet. Its true flight speed at 90,000 will be 350 knots (403 mph). The cabin will be pressurized to 8.5 psi (14,500 feet). The crew will breathe pure oxygen provided by a rebreather system.

The Perlan 2 is designed to fly the most efficiently at 50,000 feet but fly acceptably at sea level and at 90,000 feet.

But how can a glider soar to 90,000 feet without an engine.

Steve Fossett and Einar Enevoldson soared the Perlan 1 glider to 50,722 feet on August 30, 2006 using “stratospheric mountain waves.”

Mountain waves form when winds of at least 15 knots cross over a mountain range perpendicularly and the atmosphere is “stable” waves will form on the lee side of the mountains. A glider uses the upward moving part of this wave system to climb.

What sets the Perlan Mission apart from just gliding on mountain waves is that it require one critical additional element to enable us to soar into the stratosphere: The Polar Vortex.

The maximum altitude of mountain is usually at the boundary between the troposphere and the stratosphere. This is because the cold air of the mountain wave encounters warmer air at the boundary and cannot rise further.


Winds in the Polar Vortex can reach speeds of 260+ knots allowing the mountain waves to propagate upwards into the stratosphere. These are called “stratospheric mountain waves.”

Gliders fly in harmony with the atmosphere rather than using engines to overcome gravity and weather. The glider harnesses the natural flow and poser of a complex atmosphere and gains height by finding “lift” or air rising faster than the natural sink rate of the glider.

Like any glider, the Perlan 2 will be towed to a predetermined height by another tow plane.

Thereafter, the crew will use piloting techniques that are commonly used by wave soaring pilots. These techniques were shown to work at high altitude by Perlan 1. Using clouds and instruments, the pilot will fly the Perlan 2 to areas of rising air. When in the rising air, the pilot will maneuver the Perlan 2 to remain in the area of the strongest up draft. When there are no clouds to mark the area of lift positioning will be done with the aid of a GPS based moving map.

There are three main types of rising air, or lift, used by glider pilots to soar above the earth:

Wave Lift

Wave lift is similar to ridge lift in that it is created when wind meets a mountain. Wave lift, however, is created on the leeward side of the peak by winds passing over the mountain instead of up one side. Wave lift requires a good wind over the ridge and stable air. As long as the wind above the ridge blows constantly at a higher and higher velocity with increased altitude the wave will propagate upward. The Perlan 2 will use wave lift to reach 90,000 feet.

Thermals

Thermals are columns of rising air created by the heating of the Earth's surface. As the air near the ground is heated by the sun, it expands and rises. Pilots keep an eye out for clouds that mark the rising air and terrain that absorbs the sun more rapidly than surrounding areas and “kick off” thermals. Gliders can soar these spiraling columns of air up the base of the clouds.

Ridge Lift

Ridge lift is created by winds blowing over mountains, hills or other ridges. As the air goes over the ridge, it is deflected upward and forms a band of lift along the windward side of the slope. Gliders flying ridge lift stay close to the ridge.

The Perlan 2 will use these waves to soar to the edge of space. Benefiting from the lessons learned on Perlan 1’s ascent, the pressurized cabin will allow its pilots to enjoy unencumbered flight, with full control over stick and rudder, and many small switches.

During the Perlan 1 mission, due to lack of pressurized cabin, the pressure suits that they wore for protection inflated too much in the cramped cockpit, hindering them to control the sailplane properly.

With an empty weight of 1,100 pounds, and a wing area of 262 square feet, the 84-foot span machine is amazingly light for the structural strength required for stratospheric flight.

With more wing area than a conventional sailplane, it would stay aloft, but never compete with such craft at lower altitudes. But in the thin air at 90,000 feet, with 98 percent of the earth’s atmosphere beneath it, it will be unrivalled.

In the event of an emergency, the crew can deploy a drogue parachute from the tail for rapid vertical descent. At low altitude, the crew can deploy a BRS ballistic recovery parachute that can safely lower the entire aircraft to the ground.

To do scientific research at the edge of space while keeping the crew safe the Perlan 2 has been equipped with:
  • Cabin pressure regulator and air bottle
  • dual-redundant re-breather system for life support
  • Tail drogue parachute and BRS parachute
  • High altitude radar transponder by Sandia Aerospace
  • Instrumentation and lighting to fly at night by Whelen Engineering
  • Data loggers to validate world record, LX-9000
  • Scientific instrumentation
  • Cameras to record meteorological conditions
  • Lithium-ion rechargeable batteries
  • Telemetry to communicate with mission control and scientists on the ground

PHASE 1 : SEPT 2012
Steve Fossett and Einar Enevoldson soared the Perlan I research glider to a new record altitude for gliders of 50,722 feet in the mountain waves at El Calafate, Argentina on 08.30.06. The Perlan I is now on permanent display at the Seattle Museum of Flight.

PHASE 2 : JULY 2016
The Airbus Perlan Mission 2 will design and construct a pressurized glider to soar to the edge of space at 90,000 feet. This phase of our research will set a new world altitude record for wing-borne flight exceeding the records claimed by the U-2 and the SR-71.

PHASE 3 : MAY 2019
This phase will set a goal of exploring the stratosphere up to 100,000 feet. Flight speeds will increase to the point where the glider will need new transonic wings. Flight operations will be extended to exploring the Polar Vortex in the northern hemisphere.

The Perlan team will next take the Perlan 2 to San Diego for more ground testing before heading to Nevada later in the year for higher altitude flights.