30 November 2023

High-altitude electric aircraft development – a high-level view

If you are an avid reader of Inside IP, you may remember a previous article that looked into electric aircraft. Well, time flies, and there have been some exciting developments in this technological field. With this in mind, we will look at recent developments related to High-Altitude Electric Aircraft (HAEA).

The aviation industry is in a state of flux, with revolution possibly just around the corner. The pursuit of sustainable aviation solutions to reduce adverse environmental effects has shifted development focus onto new propulsion systems and even new fuels. Earlier this year, an Airbus A321 was flown with both engines using 100% sustainable aviation fuel. But there has been a lot of development in the electric propulsion sector too.

High-Altitude Electric Aircraft (HAEA) can be viewed as the proof of concept and starting point for the future of air travel and have the possibility to revolutionise a wide spectrum of applications. HAEA offer a broad array of advantages that pave the way for a leaner, quieter, and more efficient mode of air transportation.

HAEA include electrical aircraft that operate at high altitudes, often above 60,000 feet (18,300 metres), comprise a lightweight airframe, solar panels, batteries, and an electric propulsion system. The solar panels convert sunlight into energy that is stored in the batteries and can be used to power the aircraft throughout the night. In testing, HAEA have proved that they can fly for weeks or even months at a time.

Environmental benefits

The environmental benefits of HAEA go a long way in addressing the concerns surrounding climate change and air pollution. Their electric propulsion systems eliminate harmful aircraft emissions, which significantly reduces their environmental footprint and contributes to global decarbonisation efforts. HAEA also produce much less noise that traditional counterparts, enabling a more harmonious coexistence between aviation and the environment, including communities near airports and under flight paths.

The zero-emission flight of HAEA shows promise for mitigating the aviation industry’s contribution to climate change. It is thought that conventional aircraft account for approximately 2%  of global greenhouse gas emissions, with this figure projected to increase with the increased demand for air travel. HAEA zero-emission propulsion systems show that electric propulsion could be a viable solution to reducing the aviation industry’s carbon footprint and could provide a more sustainable future for air travel. Although it must be accepted that there are still significant obstacles to overcome before large commercial aircraft can be converted to electrical propulsion systems.

However, the environmental advantages of HAEA extend beyond zero-emissions. The electric motors used on HAEA exhibit improved efficiency at high altitudes, which increases range and reduces power consumption compared with traditional aircraft. In addition, their lightweight batteries and aerodynamically optimised designs further enhance performance. Developments in each of these technology sectors are enabling payloads of HAEA to become heavier and allowing HAEA to operate over longer distances all whilst minimising energy consumption. As these performance metrics improve year on year, the possibility of electric powered flight becoming common place edges closer.


HAEA have the potential to transform a diverse range of aircraft applications. Just some of the applications in the diverse range include telecommunications, surveillance, and logistics.


Telecommunications applications include providing high-speed reliable internet connectivity to underserved regions. The HAEA can operate from high altitudes providing coverage to vast areas; particularly useful for remote and mountainous regions where terrestrial infrastructure may be limited or non-existent. Due to their ability to move slowly and for long periods of time, HAEA could serve as aerial stations that provide continuous connectivity to remote communities, enabling access to essential online services and helping to bridge the digital divide in poorer communities to foster economic growth.


Surveillance applications include border security, law enforcement, and environmental monitoring. The ability of HAEA to operate at high altitudes provide a vantage point for wide-area surveillance. In addition, HAEA can be equipped with advanced sensors and cameras that enable the provision of real-time data for detecting and intercepting illegal or military activity, monitoring environmental conditions, and tracking wildlife populations.


HAEA could also be utilised to revolutionise logistics by transporting goods and supplies to remote locations. This would improve supply chain efficiency and reduce transportation costs. The ability of HAEA to fly over harsh terrain and reach remote areas may make them a valuable asset for disaster relief, delivering humanitarian aid, and resource exploration.


Over the last decade, significant progress has been made in improving technologies implemented in HAEA. Developments have been made and patents filed in a broad spectrum of technology areas including battery systems, propulsion systems, airframe design, control systems, and lightweight and durable airframes and materials.

Battery Systems

The development of high-energy density and lightweight batteries is and will continue to be essential for the success of HAEA. Breakthroughs on novel battery chemistries, electrode materials, and cell designs will improve battery performance and reduce weight.

In fact, over the past decade, battery energy density has increased by an average of around 5% per year, leading to lighter and smaller batteries for the same amount of energy storage. Continuing success in this area is crucial for extending the range of HAEA and enabling them to carry heavier payloads. Battery specific energy has also increased by a similar amount enabling the reduction in weight of powertrains, improving overall efficiency, and extending flight duration.

For example, earlier this year, CATL, a Chinese battery producer, announced their new “Condensed Battery”, which according to CATL will have an energy density of 500 Wh/kg, and state that they plan on entering mass production this year. Although the battery could be used in many applications, CATL are said to be working with partners in the aviation industry. The larger energy density is said to be achieved by focusing on a new high-energy cathode and anode, improved isolation files, and a micron-scale adaptive structure mesh able to regulate the chemical reactions within the battery. The are very few details on the Condensed Battery as of yet, but if you’re interested, CATL recently had a PCT application published related to a method for preparing and an electrolyte containing the lithium bisfluorosulfonyl imide, and a secondary battery thereof; WO 2023/142026.

Propulsion systems

Improvements in relation to the propulsion systems are essential in increasing the efficiency, reliability, and capability of operating at high altitudes. Patents in this area tend to focus on the enhancement of electric motors, power electronics, and propellers.

Over the last decade it is estimated that electric motor efficiency and electric motor power density have increase by an average of around 2% to 3% per year. The increase in efficiency of conversion of electrical energy into mechanical energy if important for reducing losses in the system to maximise the range of HAEA and minimise their energy consumption. The boost in power density has resulted in more powerful motors for their size and weight. Thus, enabling HAEA’s to achieve higher speeds and operate at higher altitudes or increase payload capabilities.

Companies like YASA Motors have developed efficient and powerful electric motors and lightweight power converters that are crucial for reducing the weight of HAEA powertrains.

Control systems

HAEA require advanced control systems to ensure stability, manoeuvrability, and flight safety at high altitudes. Companies like Honeywell have developed novel control algorithms and integrated flight control systems that enhance the stability, manoeuvrability, and autonomous flight capabilities of HAEA.

Real-world applications

The discussion around HAEA’s is not just a theoretical one. Companies such as Airbus and BAe Systems have produced and tested their own HAEA that prove the concept works. Examples such as BAe’s Phasa-35 and Airbus’ Zephyr have been flown at high altitudes for days on end and governments are deliberating on how to use such aircraft a satellite substitutes.

Companies who have invested resources into developing electric powered aircraft have been protecting their inventions by obtaining intellectual property rights. In  the last three years alone, 174,000 patent applications have been filed in the aerospace and defence sector. Although this large figure is not a reflection of innovations solely relating to HAEA, HAEA technology does form a growing portion of this sector. In fact, since 2010, Airbus along with Boeing have filed the most patents related to solar powered aircraft technology sector.

Taking the example of Airbus’ Zephyr programme, the real-world application of the technology actually began back in the early 2000’s with a test flight for Zephyr 3 being planned in 2003 when the programme was owned by Qinetiq. Zephyr 6 test flights followed in 2008. At the time Qinetiq filed three patent applications in relation to the Zephyr, one example being WO 2009/066073.

However, the patent landscape in this technology sector is now not only occupied by global aerospace companies. Other companies focussed on specific components for solar powered aircraft also invest heavily in protecting their intellectual property. For example, Sunlight Photonics, which develops autonomous UAVs and wireless systems,  holds 57 US patents and as of spring 2023 had 15 pending PCT applications. Other companies that focus on solar panel technology or battery technology that can be used in HAEAs similarly protect their innovations using intellectual property rights.

Thus, although the concepts relating to electric aircraft and HAEA is not new, with some of the larger aerospace companies having pursued electric powered flight for some time, the entrance of some smaller companies with expertise in specific areas is accelerating innovation in this technology area.


Based on the current trajectory of technological progress and the growing demand for sustainable aviation solutions, HAEA are likely to play an increasingly important role in the future of air travel.

Some leaders in the aviation sector expect HAEA to achieve commercialization within the next decade, with initial applications in telecommunications, surveillance, and logistics, providing the services previously discussed.

However, commercialisation is likely to be dependent upon achieving significant improvements in range and payload capacity, enabling HAEA to transport larger payloads over longer distances, and in operational efficiency.

As HAEA technology continues to mature and the demand for sustainable aviation solutions intensifies, the future of air travel could be poised for a transformative shift. HAEA, with their zero-emission operation, superior efficiency, and versatile applications, hold promise for shaping a cleaner, quieter, and more sustainable future for air transportation, not just for HAEA but also for the improvement of aviation in general.


The development of HAEA is a complex and multifaceted endeavour. It requires collaboration among various stakeholders, including researchers, industry leaders, and government agencies. The past decade of development gives hope that electric aircraft will one day be the norm and so it can be understood that by addressing the remaining challenges, HAEA have the potential to revolutionize aviation offering sustainable and efficient solutions for a wide range of applications.