Preparations for a test flight of the Airbus Zephyr, one of several new solar-powered, high-altitude, long-endurance systems under development.

HIGH-ALTITUDE long-endurance (HALE) platforms are not new. More than 30 years ago, Boeing’s Condor flew to an altitude of more than 67,000ft and achieved over 50 hours’ sustained flight.

The 1990s saw the emergence of Northrop Grumman’s RQ-4 Global Hawk and the General Atomics-Aeronautical Systems Inc ALTUS, and AeroVironment Inc develop a series of prototype solarpowered HALE aircraft for NASA under the agency’s Environmental Research Aircraft and Sensor Technology programme, resulting in the Pathfinder, Pathfinder Plus, Centurion and Helios.

In August 2001, Helios reached an altitude of 96,863ft, a world record for sustained horizontal flight by a winged aircraft that still stands 18 years later. More recently, Boeing’s Phantom Works division produced the Phantom Eye, while AeroVironment Inc developed a system called Global Observer.

Adding to this lineage of solar-powered HALE aircraft just now is a new crop of designs, also referred to as HAPS (highaltitude pseudo-satellite) systems.

These are very slim, almost fragile-looking vehicles made from lightweight materials such as carbon fibre and use highly efficient aerodynamic profiles and photovoltaic technologies. They are designed to push the HALE envelope for winged aircraft, their solar technologies offering an ability to remain airborne for long periods of time (not just days or weeks, but months) and operate high in the stratosphere, far above weather systems and conventional air traffic.

The Airbus Zephyr is one of the highest-profile of these new solarpowered HALE/HAPS systems.

The UK company QinetiQ first developed the Zephyr concept in the early 2000s, the Zephyr 7 variant going on in 2010 to claim the official endurance record for an aircraft by remaining airborne for two weeks.

Airbus acquired the Zephyr programme in 2013 and, last year, the latest Zephyr S variant broke its predecessor’s record on a test flight in Yuma, Arizona by remaining airborne for 25 days, 23 hours and 56 minutes. Also in 2018, Airbus opened a dedicated testing site for the Zephyr S at Wyndham in Western Australia. In April 2019, it was reported a Zephyr S had crashed on a test flight from that location.

The UK MoD has ordered three Zephyrs, interest that reflects the obvious military utility provided by solar-powered HALE/ HAPS systems for intelligence, surveillance and reconnaissance and serving as a communications relay, their endurance allowing them to remain on station for very long periods and their operating altitude letting them fill gaps in coverage and connectivity in between satellites and other manned and unmanned assets.

The characteristics of solar-powered HALE/HAPS systems mean they have applications in the civilian sphere, too. Their persistence gives an ability to provide constant, all-encompassing telecommunications connectivity. Google and Facebook were interested in developing HAPS systems to provide broadband connectivity, although both have abandoned those projects.

However, as reported in the news pages of this issue, a separate joint venture between AeroVironment Inc and the Japanese company SoftBank called HAPSMobile, is developing a system called the HAWK30 to deliver telecommunications connectivity for unserved locations such as mountainous terrain, remote islands and developing countries.

Developers see uses for solarpowered HALE/HAPS systems in the commercial sector beyond comms relay. Aurora Flight Sciences says its Odysseus system, due to fly this year, is designed for climate and weather research, measuring vegetation, ice coverage and soil moisture, and monitoring weather and storms.

The Ordnance Survey (OS) is working on a system called Astigan, intended as a cost-effective, reliable and reusable platform for collecting geospatial mapping, climate and environmental data. Astigan is designed to have interchangeable Earth observation instruments, such as atmospheric monitoring systems, high-precision cameras and multispectral sensors. The system will also provide comms support for natural disasters and supporting land management and urbanisation challenges. The OS is planning to undertake what it calls “endurance testing” of Astigan later in 2019, before undertaking a high-altitude test.

Another solar-powered HALE/ HAPS system in the works in the UK is the Prismatic PHASA-35, which its developers say will be suitable for remote sensing, environmental monitoring, disaster support, widearea surveying of agricultural yields and early warning for forest fires.

Last year, Prismatic announced BAE Systems was collaborating with the company to develop the aircraft, BAE providing, “expertise in aerospace technology and project management to progress the PHASA-35 programme through to a marketable offering”. Prismatic plans to test-fly the PHASA-35 this year, a quarter-scale model called PHASE-8 having flown in 2017.

How do all these systems compare in size and performance?

The current iteration of the Airbus Zephyr is a comparative baby, with a 25m (82ft) wingspan and a 65kg (77lb) weight. The PHASA-35 will have a 115ft (35m) wingspan and 150kg (330lb) weight, and Astigan a 124ft (38m) wingspan and a 328lb (149kg) weight.

Both the Odysseus and HAWK30 will be considerably larger.

Odysseus will reportedly have a 242ft (74m) wingspan, while the span on the ten-engine Hawk 30 will be 256ft (78m) wide, according to information released by its developer in April 2019.

Aurora Flight Sciences has so far provided little detail about the size of the payload Odysseus will be able to carry, but the company promises it will have, “the biggest payload capacity available in persistent, solar aviation”.

Mark Broadbent

E195-E2 certified


THE SECOND member of the Embraer E-Jets E2 family, the E195-E2, has received its type certification from three regulatory agencies: ANAC (the Brazilian Civil Aviation Agency), the US Federal Aviation Administration and the European Aviation Safety Agency.

The E195-E2 is the biggest E-Jets E2 variant, the baseline E190-E2 having entered service in 2018 and the smaller E175-E2 due to undertake its first flight this year ahead of service entry in 2021.

Embraer used two E195-E2s in the certification testing campaign for the variant, one for aerodynamic and performance tests and the other for the interior and validation of maintenance tasks.

The company said the testing confirmed the E195-E2 was “better than its original specification”, reporting fuel consumption was 1.4% lower than expected, which it said means the aircraft burns 25.4% less fuel per seat compared to the firstgeneration E195.

The E195-E2 will enter service in the second half of 2019 with Azul in Brazil, which has ordered 51 examples. Binter Air Canarias will also receive the first of the three it has ordered later this year.

Mark Broadbent

Design challenge


EACH YEAR there is a design challenge issued by NASA and the DLR (German Aerospace Centre) to aerospace engineering students to come up with new ideas for aeronautics technology.

This year, the focus is on concepts for small aircraft with low fixed and operating costs for the regional aviation market.

The challenge is to come up with a design that is flexible for both passenger and freight transport, economical and environmentally friendly for areas with low passenger volumes, and for unmanned operating scenarios.

In Germany, approximately 40 students have registered for the challenge from five universities and there will be a double-digit number of participating teams from various universities across the United States. One winning team will be selected from each country, with the winners chosen later this year.

NASA and the DLR have worked closely in aeronautics research for many years in areas such as air traffic management, low-noise aircraft and low fuel consumption flight. Mark Broadbent