Category Archives: Aeronautical

The Giant Air-Launch Mothership, Roc, Makes its Second Flight

Peter Lobner

After Paul Allen’s death on 15 October 2018, the Stratolaunch Systems company he founded lost the broad air launch business vision it had under his leadership. A year later, on October 2019, the private equity firm Cerberus Capital Management became the new owner of the firm renamed Stratolaunch, LLC.  Another year later, in November 2021, Stratolaunch LLC announced its new air launch business vision with an initial focus on missions involving a prototype reusable hypersonic rocket plane called the Talon-A. Stratolaunch has engaged the aerospace firm Calspan (https://www.calspan.com/stratolaunch-testing/) to build and test models of the Talon-A.  As described on the Stratolaunch LLC website (https://www.stratolaunch.com), Talon-A is only the first of a family of air-launched vehicles that will be developed to establish “a complete air-launch vehicle ecosystem.”  It looks like Paul Allen’s broad air launch business vision still may be alive and well under new leadership.

In an important milestone for Stratolaunch LLC, their giant carrier aircraft, Roc, returned to the air for the second time from the Mojave Air and Space Port in southern California on 29 April 2021, more than two years after its first flight on 13 April 2019.

Stratolaunch’s Roc carrier plane during its second test flight
on 29 April 2021.  Source: Stratolaunch
Stratolaunch’s Roc carrier plane during its second test flight
on 29 April 2021.  Source: Stratolaunch
The Roc on its landing approach at Mojave Air and Space Port at the end of its second flight. Source: AP Photo/Matt Hartman

During its second flight on 29 April 2021, the Roc reached a maximum altitude of 14,000 feet (4,267 m) and a top speed of 199 mph (320 kph).  The 28-wheel undercarriage remained extended for the whole flight.

At some point in the future, the Roc carrier aircraft test flight program will transition to captive carry flights with a Talon-A vehicle, followed by drop tests and finally actual flight tests of the hypersonic vehicle.  

Stratolaunch explains that its Mach 6-class Talon-A vehicle is designed to make hypersonic testing more routine. They describe the Talon-A as follows:

“The Talon-A features a length of 28 feet (8.5 m), a wingspan of 11.3 feet (3.4 m), and a launch weight of approximately 6,000 pounds (2,722 Kg). It will conduct long duration flight at high Mach, and glide back for an autonomous, horizontal landing on a conventional runway. It will also be capable of autonomous takeoff, under its own power, via a conventional runway.”

Rendering of the Mach-6 Talon-A hypersonic vehicle in flight. 
Source: Stratolaunch

Beyond Talon-A, Stratolaunch is developing a larger hypersonic vehicle named Talon-Z.  A longer-term objective is to develop the Black Ice fully reusable space plane that will be able to fly payloads and crew to orbit and return them to Earth for a landing at a conventional airport. The initial design will be optimized for unmanned cargo launch and return missions. A follow-on manned version will be optimized for transporting crews and cargo to and from orbit. 

Stratolaunch’s planned family of aerospace vehicles is shown in the following graphic.

The Stratolaunch carrier vehicle, Roc, is shown with three hypersonic vehicles ready for launch.  Below (L to R) are the Talon-Z and Talon-A hypersonic vehicles and the
Black Ice orbital space plane.  Source: Stratolaunch

If you’re interested, you can subscribe to the Stratolaunch newsletter on their website.

For more information:

Phileas Fogg, Grab Your Hat! The World Sky Race® is Coming in 2023.

Peter Lobner, 11 February 2021

The World Air League is the organizer for a monumental airship race around the globe that will be held between September 2023 and May 2024.  The World Air League describes their mission as follows:

“The mission and vision of the World Air League are to promote the advancement of lighter-than-air aviation for a sustainable future. The World Air League is creating the World Sky Race as an epic challenge to inspire inventors to invent and adventurers to compete. For strategic impact and purpose, the World Air League in embedding the World Sky Race®  to be included in the global educational system to provide the world’s next-generation with a path to explore with their destination an alternate greener, cleaner future.”

You’ll find the World Sky Race® website here:  www.worldskyrace.com/

Source: World Air League

The upcoming World Sky Race® will launch in September 2023 when the competing airships cross the Prime Meridian heading east over Greenwich, London, and will end eight months later in Paris in May 2024, after the competitors have circumnavigated the globe. During the eight-month race, the airships will be flying over 130+ UNESCO World Heritage Sites and cities. Hopefully this flying caravan will inspire people worldwide to the green transportation opportunities represented by modern airships. The following map shows the proposed route. 

Source: World Air League

The following travel poster images provide inspiring views of some of the destinations that will be visited during the upcoming World Sky Race®.

Source: World Air League

The World Air League previously attempted to organize the inaugural World Sky Race® in 2010.  That race didn’t occur. Hopefully the planned 2023 – 2024 race will become a reality and will be a rousing success.

For more information:

Videos:

Competition is Growing in the Air-Launch Route to Orbit

Peter Lobner, 18 January 2021

Virgin Orbit Cosmic Girl and LauncherOne

On 17 January 2021, Virgin Orbit conducted an airborne launch from their modified Boeing 747-400 “mothership,” Cosmic Girl, and their LauncherOne rocket boosted a payload of 10 small CubeSats into low Earth orbit.  This marks the first commercial orbital mission for Virgin Orbit.

Cosmic Girl carrying a LauncherOne rocket takes off from Mojave Air and Space Port. Source: Virgin Orbit (above), AP Photo/Matt Hartman (below)
Cosmic Girl performs the pre-launch pitch-up maneuver 
at an altitude of about 35,000 ft (10,688 m) during a test flight test
on 12 April 2020. Source: Virgin Orbit
Launch 17 January 2021. Source: Virgin Orbit

You can watch a short video of the launch here: https://www.youtube.com/watch?v=DU1YQWfhb4c

LauncherOne is a 70 foot long (21.34 meter), liquid fueled, two stage booster rocket that can deliver a 300 to 500 kg (661 to 1,102 lb) satellite payload  to orbit. Due to the flexibility of using an airborne launch platform, the satellite can be placed into an orbit at any inclination between 0° (equatorial) to 120° (30° retrograde).

NASA sponsored the 10 CubeSats launched on 17 January under their Educational Launch of Nanosatellites (ELaNa) program. NASA also funded the launch under its Venture Class Launch Services (VCLS) program.

This was Virgin Orbit’s second attempt to launch satellites into orbit with LauncherOne.  The first flight on 25 May 2020 failed due to a break in a propellant line for the first stage engine.

You’ll find more information on the Virgin Orbit website here: https://virginorbit.com

Stratolaunch Roc

In my 15 April 2019 post, you’ll find details on the giant Roc airborne launch platform developed by Paul Allen’s firm Stratolaunch Systems Corporation and flown for the first time on 13 April 2019: https://lynceans.org/all-posts/paul-allens-stratolaunch-aircraft-makes-its-first-flight-but-with-an-uncertain-business-plan/

After Paul Allen’s death on 15 October 2018, the focus of Stratolaunch changed dramatically and Roc has remained grounded at the Mojave Air and Space Port since its first flight.

Roc on its first flight.  Source:  REUTERS/Gene Blevins/File Photo

It appears that, on 11 October 2019,  Stratolaunch Systems was sold by its original holding company, Vulcan Inc., to an undisclosed new owner.  Since then, Stratolaunch has put increased emphasis on using the Roc as an airborne launch platform for testing hypersonic vehicles.  On 10 November 2020, Alan Boyle, writing for GeekWire , reported, “Today, Stratolaunch announced that it’s partnering with an aerospace research and development company called Calspan to build and test models of its Talon-A hypersonic vehicle, a reusable prototype rocket plane.”

The Stratolaunch website is here:  https://www.stratolaunch.com

Northrop Grumman Stargazer and Pegasus

Since 1990, Northrop Grumman Innovation Systems (formerly Orbital ATK and before that Orbital Sciences Corporation) has offered airborne launch services with their converted Stargazer L-1011 mothership and Pegasus booster rocket. From a launch altitude of about 40,000 ft (12,192 m), a three-stage Pegasus XL can carry satellites weighing up to 1,000 pounds (453.59 kg) into low-Earth orbit.

The L-1011 Stargazer carrying a Pegasus XL rocket.
Source: Northrop Grumman

The Northrop Grumman webpage for their Pegasus launch vehicle is here:  https://www.northropgrumman.com/space/pegasus-rocket/

For more information:

Virgin Orbit:

Stratolaunch:

Northrop Grumman:

Festo’s SmartBird and BionicSwift – A Decade of Progress in Deciphering How Birds Fly

Peter Lobner

1. Background on Festo

Festo is a German multinational industrial control and automation company based in Esslingen am Neckar, near Stuttgart. The Festo website is here: https://www.festo.com/group/en/cms/10054.htm

Festo reports that they invest about 8% of their revenues in research and development.  Festo’s draws inspiration for some of its control and automation technology products from the natural world. To help facilitate this, Festo established the Bionic Learning Network, which is a research network linking Festo to universities, institutes, development companies and private inventors.  A key goal of this network is to learn from nature and develop “new insights for technology and industrial applications”…. “in various fields, from safe automation and intelligent mechatronic solutions up to new drive and handling technologies, energy efficiency and lightweight construction.”

One of the challenges taken on by the Bionic Learning Network was to decipher how birds fly and then develop robotic devices that can implement that knowledge and fly like a bird. Their first product was the 2011 SmartBird and their newest product is the 2020 BionicSwift.  In this article we’ll take a look at these two bionic birds and the significant advancements that Festo has made in just nine years.

2. SmartBird

On 24 March 2011, Festo issued a press release introducing their SmartBird flying bionic robot, which was one of their 2011 Bionic Learning Network projects. Festo reported:

  • “The research team from the family enterprise Festo has now, in 2011, succeeded in unraveling the mystery of bird flight. The key to its understanding is a unique movement that distinguishes SmartBird from all previous mechanical flapping wing constructions and allows the ultra-lightweight, powerful flight model to take off, fly and land autonomously.”
  • “SmartBird flies, glides and sails through the air just like its natural model – the Herring Gull – with no additional drive mechanism. Its wings not only beat up and down, but also twist at specific angles. This is made possible by an active articulated torsional drive unit, which in combination with a complex control system makes for unprecedented efficiency in flight operation. Festo has thus succeeded for the first time in attaining an energy-efficient technical adaptation of this model from nature.”

SmartBird measures 1.07 meters (42 in) long with a wingspan of 2.0 meters (79 in) and a weigh of 450 grams (16 ounces, 1 pound).  This is about a 1.6X scale-up in the length and span of an actual Herring Gull, but at about one-third the weight. It is capable of autonomous takeoff, flight, and landing using just its wings, and it controls itself the same way birds do, by twisting its body, wings, and tail.  SmartBird’s propulsion system has a power requirement of 23 watts.

Source:  All three SmartBird photos from Festo

More information on SmartBird is on the Festo website here:  https://www.festo.com/group/en/cms/10238.htm

You can watch a 2011 Festo video, “Festo – SmartBird,” (1:47 minutes) on YouTube here:  https://www.youtube.com/watch?v=nnR8fDW3Ilo

3. Bionic Swift

On 1 July 2020, Festo introduced the BionicSwift as their latest ultra light flying bionic robot that mimics how actual birds fly. 

The BionicSwift, inspired by a Common Swift, measures 44.5 cm (17.5 in) long with a wingspan of 68 cm (26.7 in) and a weight of just 42 grams (1.5 ounces). It’s approximately a 2X scale-up of a Common Swift, but still a remarkably compact, yet complex flying machine with aerodynamic plumage that closely replicates the flight feathers on an actual Swift.  The 2011 SmartBird was more than twice the physical size and ten times heavier.

The BionicSwift is agile, nimble and can even fly loops and tight turns.  Festo reports: “Due to this close-to-nature replica of the wings, the BionicSwifts have a better flight profile than previous wing-beating drives.”  Compare the complex, feathered wing structure in the following Festo photos of the BionicSwift with the previous photos showing the simpler, solid wing structure of the 2011 SmartBird.

Source:  All three BionicSwift photos from Festo

A BionicSwift can fly singly or in coordinated flight with a group of other BionicSwifts.  Festo describes how this works: “Radio-based indoor GPS with ultra wideband technology (UWB) enables the coordinated and safe flying of the BionicSwifts. For this purpose, several radio modules are installed in one room. These anchors then locate each other and define the controlled airspace. Each robotic bird is also equipped with a radio marker. This sends signals to the anchors, which can then locate the exact position of the bird and send the collected data to a central master computer, which acts as a navigation system.”  Flying time is about seven minutes per battery charge.

More information on the Bionic Swift is on the Festo website here:  https://www.festo.com/group/en/cms/13787.htm

You also can watch a 2020 Festo video, “Festo – BionicSwift,” (1:45 minutes) on YouTube here: https://www.youtube.com/watch?v=v8fgc77dwwg

4. For more information about other Festo bionic creations: 

I encourage you to visit the Festo BionIc Learning Network webpage at the following link and browse the resources available for the many intriguing projects. https://www.festo.com/group/en/cms/10156.htm

On this webpage you’ll find a series of links listed under the heading  “More Projects,” which will introduce you to the wide range of Bionic Learning Network projects since 2006.

You also can watch the following YouTube short videos of Festo’s many bionic creations:

Modern Airships – Part 1

Peter Lobner, Updated 3 April 2021

1. Introduction

Modern Airships is a three-part document that contains an overview of modern airship technology in Part 1 and links in Parts 1, 2 and 3 to more than 130 individual articles on historic and advanced airship designs.  This is Part 1.  Here are the links to the other two parts:

You’ll find a consolidated Table of Contents for all three parts at the following link.  This should help you navigate the large volume of material in the three documents.

Modern Airships – Part 1 begins with an overview of modern airship technology, continues with a summary table identifying the airships addressed in this part, and concludes by providing links to 38 individual articles on these airships. A downloadable copy of Part 1 is available here:

If you have any comments or wish to identify errors in this document, please send me an e-mail to:  PL31416@cox.net.

I hope you’ll find the Modern Airships series to be informative, useful, and different from any other single document on this subject.

Best regards,

Peter Lobner

3 April 2021

2.  Well-established benefits and opportunities, but a risk-averse market

For more than two decades, there has been significant interest in the use of modern lighter-than-air craft and hybrid airships in a variety of military, commercial and other roles, including:

  • Heavy cargo carriers operating point-to-point between manufacturer and end-user, eliminating inter-modal load transfers enroute
  • Heavy cargo carriers serving remote and/or unimproved sites not adequately served by other modes of transportation
  • Disaster relief, particularly in areas not easily accessible by other means
  • Persistent optionally-manned surveillance platforms for maritime surveillance / border patrol / search and rescue
  • Passenger airships
  • Commercial flying cruise liner / flying hotel
  • Airship yacht
  • Personal airship
  • Drone carrier
  • High altitude regional communications node

One of the very significant factors driving interest in modern airships is that they offer the potential to link isolated regions with the rest of the world while doing so in a way that should have lower environmental impacts than other transportation alternatives for those regions. This target market for airships exists in more than two-thirds of the world’s land area where more than half the world’s population live without direct access to paved roads and reliable ground transportation.

This matter is described well in a 21 February 2016 article by Jeanne Marie Laskas, “Helium Dreams – A new generation of airships is born,” which is posted on The New Yorker website at the following link: https://www.newyorker.com/magazine/2016/02/29/a-new-generation-of-airships-is-born

In spite of the significant interest and the development of many promising airship designs, an actual worldwide airship cargo and passenger transportation industry has been very slow in developing.  To give you an example of how slow:

  • As of December 2020, the Zeppelin NT 07 is the only advanced airship that has been certified and is flying regularly in commercial passenger service. 
  • At the March 2019 Aviation Innovations Conference – Cargo Airshipsin Toronto, Canada, Solar Ship CEO Jay Godsall proposed an industry-wide challenge to actually demonstrate by July 2021 airships that can move a 3 metric ton (6,614 lb) standard 20 foot intermodal container configured as a mobile medical lab 300 km (186 mi) to a remote location. Godsall noted that this capability would be of great value if it did exist, for example, in support of relief efforts in Africa and other regions of the world.

So in spite of the airship industry having developed many designs capable of transporting 10 to 100 tons of cargo thousands of miles, today there is not a single airship that can transport a 3 metric ton (6,614 lb) payload 300 km (186 mi).

Why has the airship industry been so slow to develop? The bottom line has been a persistent lack of funding.  With many manufacturers having invested in developing advanced, detailed designs, the first to secure adequate funding will be able to take the next steps to build a manufacturing facility and a full-scale prototype airship, complete the airship certification process, and start offering a certified airship for sale.

There are a some significant roadblocks in the way:

  • No full-scale prototypes are flying:  The airship firms currently have little more than slide presentations to show to potential investors and customers.  There are few sub-scale airship demonstrators, but no full-scale prototypes.  The airship firms are depending on potential investors and customers making a “leap of faith” that the “paper” airship actually can be delivered.
  • Immature manufacturing capability:  While the airship industry has been good at developing many advanced designs, some existing as construction-ready plans, few airship firms are in the process of building an airship factory. The industrial scale-up factor for an airship firm to go from the design and engineering facilities existing today to the facilities needed for series production of full-scale airships is huge.  Several years ago, Russian airship manufacturer Augur RosAeroSystems proposed building a new factory to manufacture up to 10 ATLANT airships per year.  The funding requirement for that factory was estimated at $157 million.  The exact amount isn’t important.  No matter how you look at it, it’s a big number.  Large investments are needed for any airship firm to become a viable manufacturer.
  • Significant financial risk:The amount of funding needed by airship firms to make the next steps toward becoming a viable manufacturer exceeds the amount available from venture capitalists who are willing to accept significant risk. Private equity sources typically are risk averse. Public sources, or public-private partnerships, have been slow to develop an interest in the airship industry. The French airship firm Flying Whales appears to be the first to have gained access to significant funding from public institutions.  
  • Significant regulatory risk:Current US, Canadian and European airship regulations were developed for non-rigid blimps and they fail to address how to certify most of the advanced airships currently under development.  This means that the first airship manufacturers seeking type certificates for advanced airships will face uphill battles as they have to deal with aviation regulatory authorities struggling to fill in the big gaps in their regulatory framework and set precedents for later applicants.  It is incumbent on the aviation regulatory authorities to get updated regulations in place in a timely manner and make the regulatory process predictable for existing and future applicants.  
  • No airship operational infrastructure:  There is nothing existing today that is intended to support the operation of new commercial airships tomorrow.  The early airship operators will need to develop operating bases, hanger facilities, maintenance facilities, airship routes, and commercial arrangements for cargo and passengers.  While many airship manufacturers boast that their designs can operate from unimproved sites without most or all of the traditional ground infrastructure required by zeppelins and blimps, the fact of the matter is that not all advanced airships will be operating from dirt fields and parked outside when not flying.  There is real infrastructure to be built, and this will require a significant investment by the airship operators.
  • Steep learning curve for potential customers: Only the operators of the Zeppelin NT have experience in operating a modern airship today.  The process for integrating airship operations and maintenance into a customer’s business work flow has more than a few unknowns.  With the lack of modern airship operational experience, there are no testimonials or help lines to support a new customer. They’ll have to work out the details with only limited support.  Ten years from now, the situation should be vastly improved, but for the first operators, it will be a challenge.
  • Few qualified pilots and crew:  The airship manufacturers will need to work with the aviation regulatory authorities and develop programs for training and licensing new pilots and crew.  The British airship manufacturer Varialift has stated that one of the roles of their ARH-PT prototype will be to train future pilots.  

This uncertain business climate for airships seems likely to change in the early 2020s, when several different heavy-lift airships are expected to be certified by airworthiness authorities and ready for series production and sale to interested customers.  If customers step up and place significant orders, we may be able to realize the promise of airship travel and its potential to change our world in many positive ways.

3. Status of current aviation regulations for airships

As noted previously, current aviation regulations have not kept pace with the development of modern airship technology. In this section, we’ll take a look at the current regulations.

In the US, the Federal Aviation Administration’s (FAA) current requirements for airships are defined in the document FAA-P-8110-2, Change 2, “Airship Design Criteria (ADC),” dated 6 February 1995, which is available here: https://www.faa.gov/aircraft/air_cert/design_approvals/airships/airships_regs/media/aceAirshipDesignCriteria.pdf

The ADC applies to non-rigid, near-equilibrium, conventional airships with seating for nine passengers or less, excluding the pilot, and it serves as the basis for issuing the type certificate required before a particular airship type can enter commercial service in the US.  The limited scope of this current regulation is highlighted by the following definitions contained in the ADC:

  • Airship:  an engine-driven, lighter-than-air aircraft, than can be steered.
  • Non-rigid: an airship whose structural integrity and shape is maintained by the pressure of the gas contained within the envelope.
  • Near-equilibrium: an airship that is capable of achieving zero static heaviness during normal flight operations.

Supplementary guidance for non-rigid, near-equilibrium, conventional airships is provided in FAA Advisory Circular (AC) No. 21.17-1A, “Type Certification – Airships,” dated 25 September 1992, which is available here: https://www.faa.gov/documentlibrary/media/advisory_circular/ac_21-17-1a.pdf

The FAA’s ADC and the associated AC were written for blimps, not for the range of modern airships under development today.  For example, aerostatic lift is only one component of lift in modern hybrid airships, which also depend on powered lift from engines and aerodynamic lift during forward flight.  Hybrid airships are not “lighter-than-air” and cannot achieve zero static heaviness during normal operations, yet they are an important class of airships being developed in several countries.  In addition, almost all modern airships, except blimps, have rigid or semi-rigid structures that enable them to carry heavy loads and mount powerful engines that cannot possibly be handled by a non-rigid airship.

Recognizing the absence of an adequate regulatory framework for modern airships, civil aviation authorities of Germany and Netherlands developed supplementary guidance to the European Joint Aviation Requirements (JAR-25) and the FAA’s ADC for a category of airships called “Transport Airships,” which they define as follows:

“The transport category is defined for multi-engined propeller driven airships that have a capacity of 20 or more passengers (excluding crew), or a maximum take-off mass of 15,000 kg or more, or a design lifting gas volume of 20,000 m3or more, whichever is greater.”

These supplementary requirements are contained in the document “Transport Airship Requirements” (TAR), dated March 2000, which you will find at the following link: https://www.faa.gov/aircraft/air_cert/design_approvals/airships/airships_regs/media/aceAirshipTARIssue1.pdf

So, this is the status of US and European airship regulations today.  

In the US, Lockheed-Martin currently is in the process of working with the FAA to get a type certificate for their semi-buoyant, hybrid airship, the LMH-1.  Clearly, they are dealing with great regulatory uncertainty.  Hopefully, the LMH-1 type certification effort will be successful and serve as a precedent for later applicants. 

4. Lifting gas

In the US, Canada and Europe, aviation regulations only allow the use of non-flammable lifting gas:

  • FAA ADC:  “The lifting gas must be non-flammable.” (4.48)
  • TAR: “The lifting gas must be non-flammable, non-toxic and non-irritant” (TAR 893)
  • Canadian Air Regulations:  “Hydrogen is not an acceptable lifting gas for use in airships.” (541.7)

Without hydrogen, the remaining practical choices for lifting gas are  helium and hot air. A given volume of hot air can lift only about one-third as much as the same volume of helium, making helium the near-universal choice, with hot air being relegated to a few, small thermal airships.

The current high price of helium is a factor in the renewed interest in hydrogen as a lifting gas.  It’s also a key selling point for thermal airships.  Most helium is produced as a byproduct from natural gas production. Helium is not “rare.” Only a very small fraction of helium available in natural gas currently is recovered, on the order of 1.25%.  The remainder is released to the atmosphere. The helium recovery rate could be higher, but is not warranted by the current market for helium.  Helium is difficult to store.  The cost of transportation to end-users is a big fraction of the market price of helium.

Hydrogen provides 10% more lift than helium.  It can be manufactured easily at low cost and can be stored.  If needed, hydrogen can be produced with simple equipment in the field.  This could be an important capability for recovering an airship damaged and grounded in a remote region.  One airship concept described in Modern Airships – Part 3, the Aeromodeller II, is designed for using hydrogen as the lifting gas and as a clean fuel (zero greenhouse gases produced) for its propulsion engines.  A unique feature of this airship concept is an on-board system to generate more hydrogen when needed from the electrolysis of water ballast.

A technique for preventing hydrogen flammability is described in Russian patent RU2441685C2, “Gas compound used to prevent inflammation and explosion of hydrogen-air mixtures,” which was submitted in 2010 and posted in 2012. This technique appears to be applicable to an airship using hydrogen as its lifting gas.  You can read the patent at the following link: https://patents.google.com/patent/RU2441685C2/en

The Canadian airship firm Buoyant Aircraft Systems International (BASI) is a proponent of using hydrogen lifting gas.  Anticipating a future opportunity to use hydrogen, they have designed their lifting gas cells to be able to operate with either helium or hydrogen.  BASI claims that lifting gas cells designed originally for helium lifting gas cannot later be used with hydrogen lifting gas.

Regulatory changes will be required to permit the general use of hydrogen lifting gas in commercial airships.  Time will tell if that change ever occurs.

Even with the needed regulatory changes, the insurance industry will have to deal with the matter of insuring a hydrogen-filled airship. 

5.  Types of modern airships

The term “aerostat” broadly includes all lighter than air vehicles that gain lift through the use of a buoyant gas. Aerostats include unpowered balloons (tethered or free-flying) and powered airships. 

The following types of powered airships are described in this section:  

  • Conventional airships
  • Semi-buoyant hybrid airships and aircraft
  • Variable buoyancy airships
  • Helistats (airship – helicopter hybrid)  
  • Stratospheric airships
  • Thermal (hot air) airships
  • Hybrid thermal (Rozier) airships

5.1  Conventional airships

Conventional airships are lighter-than-air (LTA) vehicles that operate at or near neutral buoyancy. The lifting gas (helium) generates approximately 100% of the lift at low speed, thereby permitting vertical takeoff and landing (VTOL) operations and hovering with little or no lift contribution from the propulsion / maneuvering system.  Various types of propulsors may be used for cruise flight propulsion and for low-speed maneuvering and station keeping. 

Airships of this type include rigid zeppelins, semi-rigid airships and non-rigid blimps.

  • Rigid airships (zeppelins): These airships have a lightweight, rigid airframe that defines their exterior shape.  The rigid airframe supports the gondola, engines and payload.  Lifting gas cells and ballonets are located within the rigid airframe.
  • Semi-rigid airships:  These airships have a rigid internal spine or structural framework that supports loads. A flexible envelope is installed over the structural framework and contains the lifting gas cells and ballonets.
  • Non-rigid airships (blimps): These airships have a flexible envelope that defines the shape of the airship, contains the lifting gas cells and ballonets for buoyancy management, and supports the load of a gondola, engines and payload.

The Euro Airship DGPAtt and the Flying Whales LCA60T are examples of conventional rigid airships.

The Zeppelin NT and the SkyLifter are examples of conventional semi-rigid airships.

The Aeros 40D Sky Dragon and the SAIC Skybus 80K are examples of conventional non-rigid airships.

After being loaded and ballasted before flight, conventional airships have various means to control the in-flight buoyancy of the airship. Control can be exercised over ballast, lifting gas and the ballonets as described below.

Controlling buoyancy with ballast:  

Many conventional airships require adjustable ballast (i.e., typically water or sand) that can be added or removed as needed to establish a desired net buoyancy before flight.  Load exchanges (i.e., taking on / discharging cargo or passengers) can change the overall mass of an airship and may require a corresponding ballast adjustment. If an airship is heavy and the desired buoyancy can’t be restored with the ballonets or other means, ballast can be removed on the ground or may need to be dumped in flight to increase buoyancy.

Controlling buoyancy with lifting gas:  

However, temperature differentials between the lifting gas and the ambient air will affect the aerostatic lift produced by the lifting gas.  To exploit this behavior, some airships can control buoyancy using lifting gas heaters / coolers to manage gas temperature.  

The lifting gas inside an airship’s gas cells is at atmospheric pressure.  Normally, there is no significant loss (leakage) of lifting gas to the environment.  A given mass of lifting gas will create a constant lift force, regardless of pressure or altitude, when the lifting gas is at equal pressure and temperature with the surrounding air. Therefore, a change in altitude will not change the aerostatic lift.  

The lifting gas heaters are important for operation in the Arctic, where a cold-soak in nighttime temperatures may result in the lifting gas temperature lagging behind daytime ambient air temperature.  This temperature differential would result in a loss of lift until lifting gas and ambient air temperatures were equal.

Conversely, operating an airship in hot regions can result in the lifting gas temperature rising above ambient air temperature (the lifting gas becomes “superheated”), thereby increasing buoyancy. To restore buoyancy in this case, some airships have coolers (i.e., helium-to-air heat exchangers) in the lifting gas cells to remove heat from the lifting gas.

As described by Boyle’s Law, pressure (P) and gas volume (V) are inversely proportional at a constant temperature according to the following relationship:  PV = K, where K is a constant.  As an airship ascends, atmospheric pressure decreases.  This means that a fixed mass of lifting gas will expand within the lifting gas cells during ascent, and will contract within the lifting gas cells during descent.  As described previously, this lifting gas expansion and contraction does not affect the magnitude of the aerostatic lift as long as the lifting gas is at equal pressure and temperature with the surrounding air.

If an airship is light and the desired buoyancy cannot be restored with the ballonets or lifting gas coolers, it is possible to vent some lifting gas to the atmosphere to decrease aerostatic lift. 

Controlling buoyancy with ballonets:

The airship hull / envelope is divided into sealed lifting gas volumes and separate gas volumes called “ballonets” that contain ambient air. The ballonets are used to compensate for modest changes in buoyancy by inflating them with small fans or venting them to the atmosphere to change the gross weight of the airship.  Fore and aft ballonets can be operated individually to adjust the trim (pitch angle) of the airship. 

As the airship gains altitude, external air pressure decreases, allowing the helium gas volume to expand within the gas envelope, into space previously occupied by the air in the ballonets, which vent a portion of their air content overboard. The airship reaches its maximum altitude, known as its “pressure height,” when the helium gas volume has expanded to fill the gas envelope and the ballonets are empty.  At this point, the airship’s mass is at a minimum and the helium lifting gas can expand no further.

On the ground, the ballonets may be inflated with air to make the airship negatively buoyant (heavier-than-air) to simplify ground handling. To takeoff, the ballonets would be vented to the atmosphere, reducing the mass of air carried by the airship.

To descend, a low-pressure fan is used to inflate the ballonets with outside air, adding mass. As the airship continues to descend into the denser atmosphere, the helium gas volume continues to contract and the ballonets become proportionately larger, carrying a larger mass of air.  Ballonet inflation / venting is controlled to manage buoyancy as the airship approaches the ground for a landing.

In flight, inflating only the fore or aft ballonet, and allowing the opposite ballonet to deflate, will make the bow or stern of the airship heavier and change the pitch of the airship.  These operating principles are shown in the following diagrams of a blimp with two ballonets, which are shown in blue.

Blimp with ballonets (blue).  Source: zeppelinfan.de

5.2  Semi-buoyant hybrid airships

Hybrid airships are heavier-than-air (HTA) vehicles. The term “semi-buoyant” means that the lifting gas provides only a fraction of the needed lift (typically 60 – 80%) and the balance of the lift needed for flight is generated by other means, such as vectored thrust engines and aerodynamic lift from the fuselage and wings during forward flight.

Sources of lift for a semi-rigid, hybrid airship.  Source: DoD 2012

Basic characteristics of hybrid airships include the following:

  • This type of airship requires some airspeed to generate aerodynamic lift. Therefore, it typically makes a short takeoff and landing (STOL).  
  • Some hybrid airships may be capable of limited VTOL operations (i.e., when lightly loaded, or when equipped with powerful vectored thrust engines).
  • Like conventional airships, the gas envelope in hybrid airship is divided into lifting gas volumes and separate ballonet volumes containing ambient air. 
  • Hybrid airships are heavier-than-air and are easier to control on the ground than conventional airships.

There are two types of hybrid airships:  semi-rigid and rigid.  

  • Semi-rigid hybrid airships:  These airships have a structural keel or spine to carry loads, and a large, lifting-body shaped inflated fuselage containing the lifting gas cells and ballonets.  Operation of the ballonets to adjust net buoyancy and pitch angle is similar to their use on conventional airships.  These wide hybrid airships may have separate ballonets on each side of the inflated envelope that can be used to adjust the roll angle.  While these airships are heavier-than-air, they generally require adjustable ballast to handle a load exchange involving a heavy load.
  • Rigid hybrid airships:  These airships have a more substantial structure that defines the shape of the exterior aeroshell. The “hard” skin of the airship may be better suited for operation in Arctic conditions, where snow loads and high winds might challenge the integrity of an inflated fuselage of a semi-rigid airship. Otherwise, the rigid hybrid airship behavior is similar to a semi-rigid airship. 

The Lockheed-Martin LMH-1 is an example of a semi-rigid hybrid airship.  The AeroTruck being developed by Russian firm Airship GP is an example of a rigid hybrid airship.

5.3  Semi-buoyant hybrid aircraft

Semi-buoyant aircraft are heavier-than-air, rigid, winged aircraft that carry a large helium volume to significantly reduce the weight of the aircraft and improve its load-carrying capability.  Aerostatic lift provides a smaller fraction of total lift for a semi-buoyant aircraft, like a Dynalifter, than it does for a semi-buoyant, hybrid airship.

A semi-buoyant aircraft behaves much like a conventional aircraft in the air and on the ground, and is less affected by wind gusts and changing wind direction on the ground than a hybrid airship.

The semi-buoyant aircraft has some flexibility for loading and discharging cargo without having to be immediately concerned about exchanging ballast, except in windy conditions.

The Aereon Corporation’s Dynairship and the Ohio Airships Dynalifter are examples of semi-buoyant aircraft.

5.4  Variable buoyancy airships

Variable buoyancy airships can change their net lift, or “static heaviness,” to become LTA or HTA as the circumstances require.  Basic characteristics of variable buoyancy airships include the following:

  • Variable buoyancy airships are capable of VTOL operations and hovering, usually with a full load.
  • The buoyancy control system may enable in-flight load exchanges from a hovering airship without the need for external ballast.
  • On the ground, variable buoyancy airships can make themselves heavier-than-air to facilitate load exchanges without the need for external infrastructure or ballast.
  • It is not necessary for a “light” airship to vent the lifting gas to the atmosphere.

Variable buoyancy / fixed volume airships

Variable buoyancy commonly is implemented by adjusting the net lift of a fixed volume airship.  For example, a variable buoyancy / fixed volume airship can become heavier by compressing the helium lifting gas or ambient air:

  • Compressing some of the helium lifting gas into smaller volume tanks aboard the airship reduces the total mass of helium available to generate aerostatic lift.
  • Compressing ambient air into pressurized tanks aboard the airship adds mass (ballast) to the airship and thus decreases the net lift.

The airship becomes lighter by venting the pressurized tanks:

  • Compressed helium lifting gas is vented back into the helium lift cells, increasing the mass of helium available to generate aerostatic lift.
  • Compressed air is vented to the atmosphere, reducing the mass of the airship and thus increasing net lift.

The Aeros Aeroscraft Dragon Dream and the Varilift ARH-50 are examples of variable buoyancy / fixed volume airships.

Variable buoyancy / variable volume airships

Variable buoyancy also can be implemented by adjusting the total  volume of the helium envelope without changing the mass of helium in the envelope. 

  • As the size of the helium envelope increases, the airship displaces more air and the buoyant force of the atmosphere acting on the airship increases. Static heaviness decreases.
  • Likewise, as the size of the helium envelope decreases, the airship displaces less air and the buoyant force of the atmosphere acting on the airship decreases. Static heaviness increases.

The concept for a variable buoyancy / variable volume airship seems to have originated in the mid-1970s with inventor Arthur Clyde Davenport and the firm Dynapods, Inc. The tri-lobe Voliris airships and the EADS Tropospheric Airship are modern examples of variable buoyancy / variable volume airships.

Variable buoyancy propulsion airships / aircraft

Back in the 1860s, Dr. Solomon Andrews invented the directionally maneuverable, hydrogen-filled airship named Aereon that used variable buoyancy (VB) and airflow around the airship’s gas envelope to provide propulsion without an engine. 

VB propulsion airships / aircraft fly a repeating sinusoidal flight profile in which they gain altitude as positively buoyant hybrid airships, then decrease their buoyancy at some maximum altitude and continue to fly under the influence of gravity as a semi-buoyant glider. After gradually losing altitude during a long glide, the pilot increases buoyancy and starts the climb back to higher altitude in the next cycle.

The UK’s Phoenix and Michael Walden’s HY-SOAR BAT concept are two examples of variable buoyancy propulsion airships / aircraft.

5.5 Helistats (airship / helicopter hybrid)

There have been many different designs of airship / helicopter hybrid aircraft (a helistat) in which the airship part of the hybrid aircraft carries the weight of the aircraft itself and helicopter rotors deployed around the base of the airship work in concert to propel the aircraft and to lift and deliver heavy payloads without the need for an exchange of ballast.

The Piasecki PA-97 and the Boeing  / Skyhook International SkyHook JLH-40 are examples of helistats.

5.6 Stratospheric airships

Stratospheric airships are designed to operate at very high altitudes, well above the jet stream and in a region of relatively low prevailing winds typically found at altitudes of 60,000 to 75,000 feet (11.4 to 14.2 miles / 18.3 to 22.9 km).  This is a harsh environment where airship materials are exposed to the damaging effects of ultraviolet radiation and corrosive ozone.  These airships are designed as unmanned vehicles.

Applications for stratospheric airships include military intelligence, surveillance and reconnaissance (ISR) missions, civil environmental monitoring / resource management missions, military / civil telecommunications / data relay functions, and research missions such as high-altitude astronomy.  All of these can be long term missions that can last weeks, months or even years.

Typically, the stratospheric airship will operate as a “pseudo-satellite” from an assigned geo-stationary position.  Station keeping 24/7 is a unique challenge.  Using a hybrid electric power system, these airships can be solar-powered during the day and then operate from an energy storage source (i.e., a battery or regenerative fuel cell) at night.  Some propulsion systems, such as propellers that work well at lower altitudes, may have difficulty providing the needed propulsion for station keeping or transit in the very low atmospheric pressure at operating altitude.

The DARPA ISIS airship and the ATG StratSat are two examples for stratospheric airships.

5.7 Thermal (hot air) airships

Thermal airships use hot air as the lifting gas in place of helium or hydrogen. A given volume of hot air can lift only about one-third as much as the same volume of helium.  Therefore, the gas envelope on a thermal airship is proportionally larger than it would be on a comparable airship using helium as the lifting gas. 

The non-rigid GEFA-Flug four-seat AS-105GD/4 and six-seat AS-105GD/6 and the semi-rigid, two-seat Skyacht Personal Blimp are examples of current thermal airships that use propane burners to produce the hot air for lift.  Pitch can be controlled with fore and aft burners.  There are no ballonets.

5.8  Hybrid thermal (Rozier) airships

This buoyancy control concept was developed and applied in the 1700s in hybrid balloons designed by Jean-François Pilâtre de Rozier.  Such “Rozier” balloons have separate chambers for a non-heated lift gas (hydrogen or helium) and a heated lift gas (air).  This concept has been carried over into airships. With helium alone the airship is semi-buoyant (heavier-than-air).  Buoyancy is managed by controlling the heating and cooling of the air in a separate “thermal volume.”

Examples of hybrid thermal (Rozier) airships are the British Thermo-Skyship (circa 1970s to early 1980s), Russian Thermoplane ALA-40 (circa 1980s to early 1990s), and the heavy-lift Aerosmena (AIDBA) “aeroplatform” currently being developed in Russia. All were lenticular (lens-shaped) airships.

6. How does an airship pick up and deliver a heavy load? 

The term “load exchange” refers to the pickup and delivery of cargo by an airship, with or without an exchange of external ballast to compensate for the mass of cargo being moved on or off the airship.  This isn’t a simple problem to solve.

The problem of buoyancy control

In Jeanne Marie Laskas’ article, Igor Pasternak, CEO of airship manufacturer Worldwide Aeros Corp. (Aeros), commented on the common problem facing all airships when a heavy load is delivered:

“The biggest challenge in using lighter-than-air technology to lift hundreds of tons of cargo is not with the lifting itself—the larger the envelope of gas, the more you can lift—but with what occurs after you let the stuff go. ‘When I drop the cargo, what happens to the airship?’ Pasternak said. ‘It’s flying to the moon.’ An airship must take on ballast to compensate for the lost weight of the unloaded cargo, or a ground crew must hold it down with ropes.”

Among the many current designers and manufacturers of large airships, the matter of maintaining the airship’s net buoyancy within certain limits while loading and unloading cargo and passengers is handled in several different ways depending on the type of airship involved.  Some load exchange solutions require ground infrastructure at fixed bases and/or temporary field sites for external ballast handling, while others require no external ballasting infrastructure and instead use systems aboard the airship to adjust buoyancy to match current needs or provide vectored thrust (or suction) to temporarily counteract the excess buoyancy.  The solution chosen for managing airship buoyancy during a load exchange strongly influences how an airship can be operationally employed and where it can pickup and deliver its payload.

Additional problems for airborne load exchanges

Several current designers and manufacturers of large airships report that their airships will have the ability to conduct airborne load exchanges of cargo from a hovering airship.  Jeremy Fitton, the Director of SkyLifter, Ltd., described the key issues affecting a precision load exchange executed by a hovering airship as follows:

“The buoyancy management element of (an airborne) load-exchange is not the main control problem for airships. Keeping the aircraft in a geo-stationary position – in relation to the payload on the ground – is the main problem, of which buoyancy is a component.”

The matters of precisely maintaining the airship’s geo-stationary position throughout an airborne load exchange and controlling the heading of the airship and the suspended load are handled in different ways depending on the type of airship involved.  The time required to accomplish the airborne load exchange can be many minutes or much longer, depending on the weight of the cargo being picked up or delivered and the time it takes for the airship to adjust its buoyancy for its new loaded or unloaded condition. Most of the airships offering an airborne load exchange capability are asymmetrical (i.e., conventional “cigar shaped” or hybrid aerobody-shaped) and must point their nose into the wind during an airborne load exchange.  Their asymmetrical shape makes these airships vulnerable to wind shifts during the load exchange. The changing cross-sectional area exposed to the wind complicates the matter of maintaining a precise geo-position with an array of vectoring thrusters. 

During such a delivery in variable winds, even with precise geo-positioning over the destination, the variable wind direction may require the hovering airship to change its heading slightly to point into the wind. This can create a significant hazard on the ground, especially when long items, such as a wind turbine blade or long pipe segment are being delivered.  For example, the longest wind turbine blade currently in production is the GE Haliade-X intended for off-shore wind turbine installations.  This one-piece blade is 107 meter (351 ft) long.  A two degree change in airship heading could sweep the long end of the blade more than three meters (10 feet), which could be hazardous to people and structures on the ground.

Regulatory requirements pertaining to load exchanges

The German / Netherlands “Transport Airship Requirements” (TAR), includes the following requirement for load exchanges in TAR 80, “Loading / Unloading”:

(c) During any cargo exchange…the airship must be capable of achieving a safe free flight condition within a time period short enough to recover from a potentially hazardous condition.”

This requirement will be a particular challenge for airships designed to execute an airborne load exchange from a hovering airship.

The CargoLifter approach to an airborne load exchange

One early approach for delivering a load from a hovering airship was developed for the CargoLifter CL160.  As described on the Aviation Technology website (https://www.aerospace-technology.com/projects/cargolifter/), the CL160 would have performed an in-flight delivery of cargo as follows:

“The airship hovers at about 100 m above the ground and a special loading frame, which is fixed during flight to the keel of the airship, is then rigged with four cable winches to the ground, a procedure which is to assure that the airship’s lifting gear stays exactly above the desired position. Ballast water is then pumped into tanks on the frame and the payload can be unloaded. The anchor lines are released and the frame is pulled back into the payload bay of the airship.”

In a 2002 test using a heavy-lift CargoLifter CL75 aerostat as an airship surrogate, a 55 metric ton German mine-clearing tank was loaded, lifted and discharged from the loading frame as water ballast was unloaded and later reloaded in approximately the same time it took to secure the tank in the carriage (several minutes).  In this test, the 55 metric tons cargo was exchanged with about 55 cubic meters (1,766 cubic feet, 14,530 US gallons) of water ballast.

The SkyLifter approach to an airborne load exchange

One airship design, the SkyLifter, addresses the airborne load exchange issues with a symmetrical, disc-shaped hull that presents the same effective cross-sectional area to a wind coming from any direction. This airship is designed to move equally well in any direction (omni-directional), simplifying airship controls in changing wind conditions, and likely giving the SkyLifter an advantage over other designs in conducting a precision airborne load exchange.

You’ll find more information on airship load exchange issues in a December 2017 paper by Charles Luffman, entitled, “A Dissertation on Buoyancy and Load Exchange for Heavy Airships (Rev. B)”, which is available at the following link:  https://www.luffships.com/wp-content/uploads/2018/02/buoyancy_and_load_exchange.pdf

7. The scale of large cargo airships

Some of the advanced airship concepts being developed, especially for future heavy-lift cargo carriers, will result in extremely large air vehicles on a scale not seen since the heyday of the giant zeppelins in the 1930s.  Consider the following semi-rigid hybrid airships shown to scale with contemporary fixed-wing cargo aircraft.

Size comparison for hybrid airships sized for various lift applications.  
Source: DoD 2012

8. Specific airships in Part 1

The airships reviewed in Modern Airships – Part 1 are summarized in the following set of graphic tables that are organized into the categories listed below: 

  • Conventional, rigid and semi-rigid airships
  • Conventional, non-rigid airships (blimps)
  • Variable buoyancy, fixed volume airships
  • Variable buoyancy, variable volume airships
  • Helistats (airship / helicopter hybrids)
  • Semi-buoyant hybrid aircraft
  • Semi-buoyant hybrid airships
  • Stratospheric airships
  • Thermal (hot air) airships

Within each category, each page of the table is titled with the name of the category and is numbered (P1.x), where P1 = Modern Airships – Part 1 and x = the sequential number of the page in that category.  For example, “Stratospheric airships (P1.2)” is the page title for the second page in the “Stratospheric airships” category in Part 1.  There also are stratospheric airships addressed in Modern Airships – Parts 2 and 3.

Links to the individual Part 1 articles on these airships are provided in Section 9.  Some individual articles cover more than one particular airship.

Among the airships in the above tables, the following have flown: 

 Conventional airships:

  • Cargolifter Joey
  • Zeppelin NT 07 

Conventional airships:

  • Skybus 80K
  • Voliris 900

Variable buoyancy, fixed volume airships:

  • Aeros Aeroscraft Dragon Dream

Variable buoyancy, variable volume airships:

  • Voliris 901 & 902

Helistats (airship / helicopter hybrid):

  • Piasecki PA-97-34J

Semi-buoyant hybrid aircraft:

  • Dynalifter DL-100
  • Aereon 26 (only as a heavier-than-air craft)

Semi-buoyant hybrid airships:

  • ATG SkyKitten
  • Lockheed Martin P-791
  • Hybrid Air Vehicles HAV-3 & HAV-304
  • Hybrid Air Vehicles Airlander 10

Stratospheric airships:

  • SwRI HiSentinel
  • Lockheed Martin HALE-D

Thermal (hot air) airships:

  • GEFA-Flug AS-105GD/4 & AS-105GD/6 
  • Skyacht Personal Blimp

As of April 2021, the Zeppelin NT 07 is the only advanced airship that has been certified and is flying regularly in commercial passenger service.  The simpler GEFA-Flug and Skyacht thermal (hot air) airships also are flying regularly.  Among the others that have flown, most have been retired and a few were damaged or destroyed.  The remaining airships in the Part 1 tables are under development or remain as concepts only.

Among the airships in the above tables, the following cargo airships seem likely to receive their airworthiness certification in the next several years. The leading candidates identified in Part 1 are:

  • Lockheed Martin: LMH-1 hybrid airship
  • Hybrid Air Vehicles (HAV): Airlander 10 hybrid airship
  • Voliris V932 NATAC

These airships will be competing in the worldwide airship market with the leading candidates identified in Part 2, which may enter the market in the same time frame:

  • Flying Whales: LCA60T rigid airship
  • Millennium Airship: SkyFreighter
  • Varialift:  ARH-PT variable buoyancy airship prototype and the larger ARH 50
  • Euro Airship:  Corsair & DGPAtt variable buoyancy airships
  • Solar Ship: 24-meter Caracal light cargo semi-buoyant airship and the Wolverine medium cargo semi-buoyant aircraft
  • Egan Airships:  The PLIMP drone and Model J plane / blimp hybrids

All of these candidates depend on a source of funding to bring their advanced designs to market.  At the present time, Flying Whales appears to have the have the best funding from diverse sources in France, Canada China and Morocco.

The 2020s will be an exciting time for the airship industry.  We’ll finally get to see if the availability of several different heavy-lift airships with commercial type certificates will be enough to open a new era in airship transportation. Aviation regulatory agencies need to help reduce investment risk by reducing regulatory uncertainty and putting in place an adequate regulatory framework for the wide variety of advanced airships being developed.  Customers with business cases for airship applications need to step up, place firm orders, and then begin the pioneering task of employing their airships and building a worldwide airship transportation network with associated ground infrastructure.  This will require consistent investment over the next decade or more before a basic worldwide airship transportation network is in place to support the significant use of commercial airships in cargo and passenger transportation and other applications. Perhaps then we’ll start seeing the benefits of airships as a lower environmental impact mode of transportation and a realistic alternative to fixed-wing aircraft, seaborne cargo vessels and heavy, long-haul trucks.

9. Links to the individual articles

The following links will take you to the 38 individual Modern Airships – Part 1 articles.  

Conventional, rigid and semi-rigid airships:

Conventional, non-rigid airships (blimps):

Variable buoyancy, fixed volume airships:

Variable buoyancy, variable volume airships:

Helistats (airship / helicopter hybrid):

Semi-buoyant hybrid aircraft:

Semi-buoyant hybrid airships:

Stratospheric airships:

Thermal (hot air) airships:

Aerostats:

Modern Airships – Part 3

Peter Lobner

1. Introduction

“Modern Airships” is a three-part document that contains an overview of modern airship technology in Part 1 and links in Parts 1, 2 and 3 to 95 individual articles on historic and advanced airship designs. This is Part 3.  Here are the links to the other two parts:

You’ll find a consolidated Table of Contents for all three parts at the following link.  This should help you navigate the large volume of material in the three documents.

Modern Airships – Part 3 begins with a summary table identifying the airship concepts addressed in this part, and concludes by providing links to 32 individual articles on these airship concepts. A downloadable copy of Part 3 is available here:

If you have any comments or wish to identify errors in this document, please send me an e-mail to:  PL31416@cox.net.

I hope you’ll find the Modern Airships series to be informative, useful, and different from any other single document on this subject.

Best regards,

Peter Lobner

August 2019

2. Specific airship concepts in Part 3

The airships described in Part 3 are relatively exotic concepts in comparison to the heavy-lift cargo airships that dominate Parts 1 and 2.  Many of the airship concepts in Part 3 are designed for operation with very low or no carbon emissions.  I’ve grouped these airship concepts based on their applications rather than on their design / type because sometimes those details are difficult to determine when few graphics and limited descriptions are available.  A few of these airships look good as concepts, but may be impossible to build.  Nonetheless, all of these relatively exotic concepts point toward an airship future that will benefit from the great creativity expressed by these designers.

The airship design concepts reviewed in Part 3 are summarized in the following set of tables.  Except for a few sub-scale models, none of these airship concepts have flown.  Links to individual articles on these airships are provided at the end of this document.

3. Links to the individual articles

The following links will take you to 32 individual articles.  Note that the Avalon Airships article addresses all three of their airship design concepts, which are listed separately in the above tables and in the following index.

Cargo & multi-purpose airships

Mass transportation airships:

Flying hotel airships:

Touring airships:

Flying yacht airships:

Remotely-piloted special purpose airship:

Personal airships:

Thermal (hot air) airships:

Other novel designs:

Modern Airships – Part 2

Peter Lobner, Updated 3 April 2021

1. Introduction

Modern Airships is a three-part document that contains an overview of modern airship technology in Part 1 and links in Parts 1, 2 and 3 to more than 130 individual articles on historic and advanced airship designs.  This is Part 2.  Here are the links to the other two parts:

You’ll find a consolidated Table of Contents for all three parts at the following link.  This should help you navigate the large volume of material in the three documents.

Modern Airships – Part 2 begins with a summary graphic table identifying the airships addressed in this part, and concludes by providing links to 64 individual articles on those airships. A downloadable copy of Part 2 is available here:

If you have any comments or wish to identify errors in these documents, please send me an e-mail to:  PL31416@cox.net.

I hope you’ll find the Modern Airships series to be informative, useful, and different from any other single document on this subject.

Best regards,

Peter Lobner

 April 2021

2. Specific airships in Part 2

The airships reviewed in Modern Airships – Part 2 are summarized in the following set of graphic tables that are organized into the 11 categories listed below: 

  • Conventional, rigid and semi-rigid airships
  • Conventional, non-rigid airships (blimps)
  • Hybrid (semi-buoyant) airships
  • Hybrid thermal (Rozier) airships
  • Variable buoyancy, fixed volume airships
  • Variable buoyancy, variable volume airships
  • Variable buoyancy propelled airships
  • Stratospheric airships
  • Semi-buoyant plane / airship hybrids
  • Electro-kinetically (EK) propelled airships
  • Small LTA drones

Within each category, each page of the table is titled with the name of the category and is numbered (P2.x), where P2 = Modern Airships – Part 2 and x = the sequential number of the page in that category.  For example, “Stratospheric airships (P2.2)” is the page title for the second page in the “Stratospheric airships” category in Part 2.  There also are stratospheric airships addressed in Modern Airships – Parts 1 and 3.

Links to the individual Part 2 articles on these airships are provided in Section 3.  Some individual articles cover more than one particular airship.

Among the airships included in the above tables, more than 35 have flown.

Several airships that have not yet flown have well-established designs and their manufacturers seem to be poised to start building their full-scale prototype(s) and engaging aviation regulatory authorities in the long process leading to a type certificate for their production airships.  Several manufacturers have received orders that are conditional on having a type certificate.  Almost all are limited by a lack of funding to get from Point A (today) to Point B (having a type certificate).

The most promising new heavy-lift airship manufacturers identified in Part 2 are:

  • Flying Whales (France): The firm appears to have solid funding from diverse sources in France, China, Canada and Morocco, which should be adequate to fund the construction and flight testing of a prototype LCA60T airship.  Full-scale production facilities are planned in France, China and Canada and commercial airship operating infrastructure is being planned. In 2019, the LCA60T prototype maiden flight was expected to take place in 2021.  That date has slipped to 2024.
  • Varialift (UK):  The factory in France and the ARH-PT prototype are under construction, but the schedule for completing the prototype has slipped, perhaps by three years to 2022, primarily because of tenuous funding. Without a stronger funding stream, the future schedule is unpredictable.
  • Euro Airship (France): The firm claims that production-ready drawings exist for their Corsair and the larger DGPAtt.  When funding becomes available, it seems that they’re ready to go.
  • BASI (Canada): The firm has a well developed design in the MB-30T and a fixed-base operating infrastructure design that seems to be well suited for their primary market in the Arctic. When funding becomes available, it seems that they’re ready to go.
  • Millennium Airship (USA & Canada): The firm has well developed designs for their SF20T and SF50T SkyFreighters, has identified its industrial team for manufacturing, and has a business arrangement with SkyFreighter Canada, Ltd., which would become a future operator of SkyFreighter airships in Canada.  In addition, a development plan defines the work needed to build and certify a prototype and a larger production airship. When funding becomes available, it seems that they’re ready to go.
  • Aerosmena (AIDBA, Russia): The firm offers the latest designs for heavy-lift hybrid thermal (Rozier) “aeroplatforms,” which use two lift gases: helium and heated air.  The A20 will be the prototype for the entire family of Aerosmena aeroplatform. When funding becomes available, it seems that they’re ready to go.
  • Atlas LTA Advanced Technology (Israel): After acquiring the Russian firm Augur RosAeroSystems in 2018, Atlas is continuing to develop the ATLANT variable buoyancy, fixed volume heavy lift airship.  They also are developing a new family of non-rigid manned and unmanned blimps.  However, the development plans and schedules have not yet been made public.

These heavy-lift airships will be competing in the worldwide airship market with the leading candidates identified in Modern Airships – Part 1, which could enter the market in the same time frame if they get adequate funding:

  • Lockheed Martin (USA): LMH-1 hybrid airship
  • Hybrid Air Vehicles (UK): Airlander 10 hybrid airship
  • Aeros (USA): Aeroscraft ML866 / Aeroscraft Gen 2 variable buoyancy / fixed volume airship
  • Voliris (France): V932 NATAC & SeaBird semi-buoyant, inflated wing airships

For decades, there have been many ambitious projects that intended to operate an airship as a pseudo-satellite, carrying a heavy payload while maintaining a geo-stationary position in the stratosphere on a long-duration mission (days, weeks, to a year or more).  None were successful.  This led NASA in 2014 to plan the 20-20-20 airship challenge: 20 km altitude, 20 hour flight, 20 kg payload.  The challenge never occurred, but it highlighted the difficulty of developing an airship as a persistent pseudo-satellite.  The most promising new stratospheric airship manufacturers identified in Part 2 are:

  • Sceye Inc. (USA):  This small firm is developing and, since 2017, has been flight testing mid-size, multi-mission stratospheric airships. The firm also is building a new headquarters and manufacturing facility in New Mexico. Plans for stratospheric communications system flight tests in 2021 have been filed with the Federal Communications Commission. 
  • Thales Alenia Space (France): The firm is developing the multi-mission Stratobus.  Their latest round of funding from France’s defense procurement agency calls for a full-scale, autonomous Stratobus demonstrator airship to fly by the end of 2023, five years later than another demonstrator that was ordered in the original 2016 Stratobus contract, but not built.

China remains an outlier after the 2015 flight of the Yuanmeng stratospheric airship developed by         Beijing Aerospace Technology Co. & BeiHang.  The current status of the Chinese stratospheric airship development program is not described in public documents.

Among the many smaller airships identified in Part 2, the following manufacturers could have their airships flying in the early-to-mid 2020s if adequate funding becomes available.

  • Dirisolar (France): The firm has a well developed design for their five passenger DS 1500, which is intended initially for local air tourism, but can be configured for other missions.  When funding becomes available, it seems that they’re ready to go.
  • A-NSE (France):  The firm offers a range of aerostat and small airships, several with a novel tri-lobe, variable volume hull design.  Such aerostats are operational now, and a tri-lobe airship could be flying in the early 2020s.
  • Egan Airships (USA):  The PLIMP Model J drone has already flown and the Model J plane / blimp hybrid is the likely candidate for FAA type certification. When funding becomes available, it seems that they’re ready to go.
  • Solar Ship (Canada): The firm’s 24-meter Caracal semi-buoyant, inflated wing airship has already flown successfully.  However, that basic design did not scale up successfully. Hence, the larger Wolverine has been redesigned as a significantly different semi-buoyant aircraft.  Solar Ship has not described their current development and certification schedules.

There seems to be a proliferation of small LTA drone blimps and other small LTA drone vehicles.  Some were developed initially for military surveillance applications, but all are configurable and could be deployed in a range of interesting applications. 

The 2020s will be an exciting time for the airship industry.  We’ll finally get to see if the availability of several different heavy-lift airships with commercial type certificates will be enough to open a new era in airship transportation. Aviation regulatory agencies need to help reduce investment risk by reducing regulatory uncertainty and putting in place an adequate regulatory framework for the wide variety of advanced airships being developed.  Customers with business cases for airship applications need to step up, place firm orders, and then begin the pioneering task of employing their airships and building a worldwide airship transportation network with associated ground infrastructure.  This will require consistent investment over the next decade or more before a basic worldwide airship transportation network is in place to support the significant use of commercial airships in cargo and passenger transportation and other applications. Perhaps then we’ll start seeing the benefits of airships as a lower environmental impact mode of transportation and a realistic alternative to fixed-wing aircraft, seaborne cargo vessels and heavy, long-haul trucks.

3. Links to the individual articles

The following links will take you to 64 individual articles that address all of the airships identified in the preceding graphic table.

Conventional, rigid and semi-rigid airships:

Conventional, non-rigid airships (blimps):

Hybrid (semi-buoyant) airships:

Hybrid thermal (Rozier) airships:

Variable buoyancy, fixed volume airships:

Variable buoyancy, variable volume airships:

Variable buoyancy propulsion airships:

Stratospheric airships:

Semi-buoyant plane / airship hybrids:

Electro-kinetically (EK) propelled airships:

Small LTA drones:

Riding the Phantom Zephyr

Peter Lobner, updated 21 February 2021

1.  Background

When charged molecules in the air are subjected to an electric field, they are accelerated. When these charged molecules collide with neutral ones, they transfer part of their momentum, leading to air movement known as an “ionic wind.”  This basic process is shown in the following diagram, which depicts a strong electric field between a discharge electrode (left) and a ground electrode (right), and the motion of negative ions toward the ground electrode where they are collected.  The neutral molecules pass through the ground electrode and generate the thrust called the ionic wind.

This post summarizes work that has been done to develop ionic wind propulsion systems for aircraft.  The particular projects summarized are the following:

  • Major Alexander de Seversky’s Ionocraft vertical lifter (1964)
  • Michael Walden / LTAS lighter-than-air XEM-1 (1977)
  • Michael Walden / LTAS lighter-than-air EK-1 (2003)
  • The Festo b-IONIC Airfish airship (2005)
  • NASA ionic wind study (2009)
  • The MIT electroaerodynamic (EAD) heaver-than-air, fixed wing aircraft (2018)

In addition, we’ll take a look at recent ionic propulsion work being done by Electrofluidsystems Ltd., Electron Air LLC and the University of Florida’s Applied Physics Research Group.

2.  Scale model of ion-propelled Ionocraft vertical takeoff lifter flew in 1964

Major Alexander de Seversky developed the design concept for a novel aircraft concept called the “Ionocraft,” which was capable of hovering or moving in any direction at high altitudes by means of ionic discharge. His design for the Ionocraft is described in US Patent 3,130,945, “Ionocraft,” dated 28 April 1964.  You can read this patent here: https://patents.google.com/patent/US3130945A/en

The operating principle of de Seversky’s Ionocraft propulsion system is depicted in the following graphic.

Ion propulsion scheme implemented in the de Seversky Ionocraft. 
Source: Popular Mechanics, August 1964

In 1964, de Seversky built a two-ounce (57 gram) Ionocraft scale model and demonstrated its ability to fly while powered from an external 90 watt power conversion system (30,000 volts at 3 mA), significantly higher that conventional aircraft and helicopters.  This translated into a power-to-weight ratio of about 0.96 hp/pound.  You can watch a short 1964 video of a scale model Ionocraft test flight here: 

Screenshot showing Ionocraft scale model in flight
Screenshot showing ionic wind downdraft under an Ionocraft scale model in flight

De Seversky’s Ionocraft and its test program are described in an article in the August 1964 Popular Mechanics magazine, which is available at the following link:  https://books.google.com/books?id=ROMDAAAAMBAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false

Alexander de Seversky’s one-man Ionocraft concept.
Source: Popular Mechanics Archive, August 1964
Alexander de Seversky’s Ionocraft commuter concept.
Source: Popular Mechanics Archive, August 1964
1969 Soviet concepts for passenger carrying Ionocraft.
Technology for Youth magazine, 1969, Issue 7.

In the 1960s, engineers found that Ionocraft technology did not scale up well and they were unable to build a vehicle that could generate enough lift to carry the equipment needed to produce the electricity needed to drive it.

3.  The first free-flying, ion-propelled, lighter-than-air craft flew in 1977:  Michael Walden / LTAS XEM-1

The subscale XEM-1 proof-of-concept demonstrator was designed by Michael Walden and built in 1974 by his firm, Lighter Than Air Solar (LTAS) in Nevada.  After leaving LTAS in 2005, Michael Walden founded Walden Aerospace where he is the President and CTO, building on the creative legacy of his work with the former LTAS firms.  The Walden Aerospace website is here: http://walden-aerospace.com/HOME.html 

The basic configuration of this small airship is shown in the following photo.  The MK-1 ionic airflow (IAF) hybrid EK drives are mounted on the sides of the airship’s rigid hull.

Source: Walden Aerospace.
Basic configuration of the MK-1 ionic airflow (IAF)
hybrid EK drive. Source: Walden Aerospace.

XEM-1 originally was tethered by cable to an external control unit and later was modified for wireless remote control operation. In this latter configuration, XEM-1 demonstrated the use of a hybrid EK propulsion system in a self-powered, free-flying vehicle.  

Walden described the MK-1 IAF EK drive as follows:  “The duct included a 10 inch ‘bent tip’ 3-bladed prop running on an electric motor to create higher pressures through the duct, making it a ‘modified pressure lifter’…. The duct also had a circular wire emitter, a dielectric separator and a toroidal collector making it a ‘toroid lifter’.”

The later MK-2 and MK-3 IAF EK drives had a similar duct configuration.  In all of these EK drives, the flow of ions from emitter to collector imparts momentum to neutral air molecules, creating usable thrust for propulsion.  You’ll find more information on the MK-1 IAF EK drive and later versions on the Walden Aerospace website here:  http://walden-aerospace.com/Waldens_Patents_files/Walden%20Aerospace%20Advanced%20Technologies%2011092013-2.pdf

The XEM-1 was demonstrated to the Department of Defense (DoD) and Department of Energy (DOE) in 1977 at Nellis Air Force Base in Nevada.  Walden reported:  “We flew the first fully solar powered rigid airship in 1974, followed by a US Department of Defense and Department of Energy flight demonstration in August 1977”…. “ DoD was interested in this work to the extent that some of it is still classified despite requests for the information to become freely available.”

Walden credits the XEM-1 with being the first fully self-contained air vehicle to fly with a hybrid ionic airflow electro-kinetic propulsion system. This small airship also demonstrated the feasibility of a rigid, composite, monocoque aeroshell, which became a common feature on many later Walden / LTAS airships.

4.  The second free-flying, ion-propelled, lighter-than-air craft flew in 2003:  Michael Walden / LTAS EK-1

Michael Walden designed the next-generation EK-1, which was a remotely controlled, self-powered, subscale model of a lenticular airship with a skin-integrated EK drive that was part of the outer surface of the hull.  The drive was electronically steered to provide propulsion in any direction with no external aerodynamic surfaces and no moving parts.

EK-1 aloft in the hanger.  Source: LTAS / Walden Aerospace
EK-1 with a skin-integrated propulsion system moving during hanger test flight in 2003.Source: LTAS / Walden Aerospace
 

In June 2003, LTAS rented a hangar at the Boulder City, NV airport to build and fly the EK-1.  Testing the EK-1 was concluded in early August 2003 after demonstrating the technology to National Institute for Discovery Science (NIDS) board members.

Based on the EK-1 design, a full-scale EK airship would have a rigid, aeroshell comprised largely of LTAS MK-4 lithographic integrated thruster / structure hull panels.  As with other contemporary Walden / LTAS airship designs, the MK-4 panel airship likely would have implemented density controlled buoyancy (DCB) active aerostatic lift control and would have had a thin film solar array on the top of the aeroshell.

Artist’s concept of a MK-4 panel airship.
Source: Walden Aerospace

5.  The third free-flying, ion-propelled, lighter-than-air craft flew in 2005: the Festo b-IONIC Airfish

The Festo b-IONIC Airfish airship was developed at the Technical University of Berlinwith guidance of the firm Festo AG & Co. KG.  This small, non-rigid airship is notable because, in 2005, it became the first aircraft to fly with a solid state propulsion system.  The neutrally-buoyant Airfish only flew indoors, in a controlled environment, at a very slow speed, but it flew.

Airfish. Source:  Festo AG & Co. KG

Some of the technical characteristics of the Airfish are listed below:

  • Length:  7.5 meters (24.6 ft)
  • Span: 3.0 meters (9.8 ft)
  • Shell diameter: 1.83 meters (6 ft)
  • Helium volume:  9.0 m3(318 ft3)
  • Total weight:  9.04 kg (19.9 lb)
  • Power source in tail: 12 x 1,500 mAh lithium-ion polymer cells (18 Ah total)
  • Power source per wing (two wings): 9 x 3,200 mAh lithium-ion polymer cells (28.8 Ah total)
  • High voltage: 20,000 to 30,000 volts
  • Buoyancy:  9.0 – 9.3 kg (19.8 – 20.5 lb)
  • Total thrust:  8 – 10 grams (0.018 – 0.022 pounds) 
  • Maximum velocity: 0.7 meters/sec (2.5 kph; 1.6 mph)

The b-IONIC Airfish employed two solid state propulsion systems, an electrostatic ionic jet and a plasma ray, which Festo describes as follows:

  • Electrostatic ionic jet:  “At the tail end Airfish uses the classic principle of an electrostatic ionic jet propulsion engine. High-voltage DC-fields (20-30 kV) along thin copper wires tear electrons away from air molecules. The positive ions thus created are then accelerated towards the negatively charged counter electrodes (ring-shaped aluminum foils) at high speeds (300-400 m/s), pulling along additional neutral air molecules. This creates an effective ion stream with speeds of up to 10 m/s.”
  • Plasma-ray:  “The side wings of Airfish are equipped with a new bionic plasma-ray propulsion system, which mimics the wing based stroke principle used by birds, such as penguins, without actually applying movable mechanical parts. As is the case with the natural role model, the plasma-ray system accelerates air in a wavelike pattern while it is moving across the wings.”
Airfish.  Source: Festo AG & Co. KG
Airfish.  Source: Festo AG & Co

The Festo b-IONIC Airfish demonstrated that a solid state propulsion system was possible.  The tests also demonstrated that the solid state propulsion systems also reduced drag, raising the intriguing possibility that it may be possible to significantly reduce drag if an entire vessel could be enclosed in a ionized plasma bubble.You’ll find more information on the Festo b-IONIC Airfish, its solid state propulsion system and implications for drag reduction in the the Festo brochure here: https://www.festo.com/net/SupportPortal/Files/344798/b_IONIC_Airfish_en.pdf

You can watch a 2005 short video on the Festo b-IONIC Airfish flight here:

6.  NASA ionic wind study – 2009

A corona discharge device generates an ionic wind, and thrust, when a high voltage corona discharge is struck between sharply pointed electrodes and larger radius ground electrodes.

In 2009, National Aeronautics & Space Administration (NASA) researchers Jack Wilson, Hugh Perkins and William Thompson conducted a study to examine whether the thrust of corona discharge systems could be scaled to values of interest for aircraft propulsion.  Their results are reported in report NASA/TM-2009-215822, which you’ll find at the following link: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100000021.pdf

Key points of the study included:

  • Different types of high voltage electrodes were tried, including wires, knife-edges, and arrays of pins. A pin array was found to be optimum. 
  • Parametric experiments, and theory, showed that the thrust per unit power could be raised from early values of 5 N/kW to values approaching 50 N/kW, but only by lowering the thrust produced, and raising the voltage applied. 
  • In addition to using DC voltage, pulsed excitation, with and without a DC bias, was examined. The results were inconclusive as to whether this was advantageous. 
  • It was concluded that the use of a corona discharge for aircraft propulsion did not seem very practical.”

7.  The first heavier-than-air, fixed-wing, ion-propelled aircraft flew in 2018

On 21 November 2018, MIT researchers reported successfully flying the world’s first heavier-than-air, fixed-wing, ion-propelled (electroaerodynamic, EAD) aircraft.  You can read the paper by Haofeng Xu, et al., “Flight of an aeroplane with solid-state propulsion,” on the Nature website here: https://www.nature.com/articles/s41586-018-0707-9

The design of the MIT EAD aircraft is shown below:

a, Computer-generated rendering of the EAD airplane. 
b, Photograph of actual EAD airplane (after multiple flight trials).

Some of the technical characteristics of this MIT aircraft are listed below:

  • Wingspan: 4.9 meters (16 ft)
  • Total weight: 2.45 kg (5.4 lb)
  • Power source: powered by 54 x 3.7 volt 150 mAh lithium-ion polymer cells (8.1 Ah total)
  • High voltage: 40,000 volts (+ 20,000 volts / – 20,000 volts)
  • Total thrust: 3.2 N, 326 grams (0.718 pounds) 
  • Maximum velocity: 4.8 meters/sec (17.3 kph; 10.7 mph)

In their paper, the MIT researchers reported:

  • “We performed ten flights with the full-scale experimental aircraft at the MIT Johnson Indoor Track…. Owing to the limited length of the indoor space (60 m), we used a bungeed launch system to accelerate the aircraft from stationary to a steady flight velocity of 5 meters/sec within 5 meters, and performed free flight in the remaining 55 meters of flight space. We also performed ten unpowered glides with the thrusters turned off, in which the airplane flew for less than 10 meters. We used cameras and a computer vision algorithm to track the aircraft position and determine the flight trajectory.”
  • “All flights gained height over the 8–9 second segment of steady flight, which covered a distance of 40–45 meters…. The average physical height gain of all flights was 0.47 meters…. However, for some of the flights, the aircraft velocity decreased during the flight. An adjustment for this loss of kinetic energy…. results in an energy equivalent height gain, which is the height gain that would have been achieved had the velocity remained constant. This was positive for seven of the ten flights, showing that better than steady-level flight had been achieved in those cases.”
  • “In this proof of concept for this method of propulsion, the realized thrust-to-power ratio was 5 N/kW1, which is of the order of conventional airplane propulsion methods such as the jet engine.”  Overall efficiency was estimated to be 2.56%.

The propulsion principles of the MIT EAD aircraft are explained in relation to the following diagram in the November 2018 article by Franck Plouraboué, “Flying With Ionic Wind,” which you can read on the Nature website at the following link:  https://www.nature.com/articles/d41586-018-07411-z

The following diagram and explanatory text are reproduced from that article.

  • In Figure a, above: …an electric field (not shown) is applied to the region surrounding a fine wire called the emitter (shown in cross-section). The field induces electron cascades, whereby free electrons collide with air molecules (not shown in the cascades) and consequently free up more electrons. This process produces charged air molecules in the vicinity of the emitter — a corona discharge. Depending on the electric field, negatively or positively charged molecules drift away (red arrows) from the emitter. These molecules collide with neutral air molecules, generating an ionic wind (black arrows). 
  • In Figure b, above: The aircraft uses a series of emitters and devices called collectors, the longitudinal directions of which are perpendicular to the ionic wind. The flow of charged air molecules occurs mainly along the directions (red arrows) joining emitters and collectors. Consequently, the ionic wind is accelerated (black arrows) predominantly in these regions. 

You can view a short video of the MIT EAD aircraft test flights here:  

8.  The future of ionic propulsion for aerospace applications.

If it can be successfully developed to much larger scales, ionic propulsion offers the potential for aircraft to fly in the atmosphere on a variety of practical missions using only ionized air for propulsion.  Using other ionized fluid media, ionic propulsion could develop into a means to fly directly from the surface of the earth into the vacuum of space and then operate in that environment. The following organizations have been developing such systems.

Electrofluidsystems Ltd.

In 2006, the Technical University of Berlin’s Airfish project manager, Berkant Göksel, founded the firm Electrofluidsystems Ltd., which in 2012 was rebranded as IB Göksel Electrofluidsystems.  This firm presently is developing a new third generation of plasma-driven airships with highly reduced ozone and nitrogen oxide (NOx) emissions, magneto-plasma actuators for plasma flow control, and the company’s own blended wing type flying wing products.  You’ll find their website here:  https://www.electrofluidsystems.com

Source: Electrofluidsystems TU Berlin
Advanced plasma-driven aircraft concept. Source:  Electrofluidsystems TU Berlin

MIT researchers are developing designs for high-performance aircraft using ionic propulsion.  Theoretically, efficiency improves with speed, with an efficiency of 50% possible at a speed of about 1,000 kph (621 mph).  You can watch a short video on MIT work to develop a Star Trek-like ion drive aircraft here:  

Electron Air LLC

Another firm active in the field of ionic propulsion is Electron Air LLC (https://electronairllc.org), which, on 6 November 2018, was granted patent US10119527B2 for their design for a self-contained ion powered craft.  Their grid shaped craft is described as follows:

“The aircraft assembly includes a collector assembly, an emitter assembly, and a control circuit operatively connected to at least the emitter and collector assemblies and comprising a power supply configured to provide voltage to the emitter and collector assemblies. The assembly is configured, such that, when the voltage is provided from an on board power supply, the aircraft provides sufficient thrust to lift each of the collector assembly, the emitter assembly, and the entire power supply against gravity.”

The device, as shown in patent Figure 3, consists of a two-layer grid structure with a collector assembly (50), an emitter assembly (70) and peripheral supports (33 to 37).

You can read patent US10119527B2 here: https://patents.google.com/patent/US10119527B2/en?oq=10119527

This patent cites Alexander de Seversky’s Patent 3130945, “Ionocraft.”

You can watch a short (1:22 minute) video of an outdoor tethered test flight of a remotely controlled, self-contained, ion powered, heavier-than-air craft with onboard power at the following link: https://www.youtube.com/watch?v=aX21HCHlgKo

University of Florida, Applied Physics Research Group

In the early 2000s, a Wingless Electromagnetic Air Vehicle (WEAV) was invented by Dr. Subrata Roy, a plasma physicist and aerospace engineering professor at the University of Florida. WEAV is described as a heavier-than-air flight system that can self-lift, hover, and fly using plasma propulsion with no moving components. The laboratory-scale device is six inch (15.2 cm) in diameter.  The basic configuration of the disc-shaped craft is shown in patent 8960595B2 Figure 1.

This research project has been supported by the US Air Force Office of Scientific Research. You’ll find details on WEAV technology in the University of Florida’s 2011 final report at the following (very slow loading) link: https://apps.dtic.mil/dtic/tr/fulltext/u2/a564120.pdf

In this report, the authors describe the technology: “This revolutionary concept is based on the use of an electro-(or magneto) hydrodynamic (EHD/MHD) thrust generation surface that is coated with multiple layers of dielectric polymers with exposed and/or embedded electrodes for propulsion and dynamic control. This technology has the unique capability of imparting an accurate amount of thrust into the surrounding fluid enabling the vehicle to move and react. Thrust is instantaneously and accurately controlled by the applied power, its waveform, duty cycle, phase lag and other electrical parameters. Once the applied power is removed the thrust vanishes.”

The following patents related to WEAV technology have been filed and assigned to the University of Florida Research Foundation Inc.:

These patents do not cite Alexander de Seversky’s Patent 3130945, “Ionocraft.”

9.  More reading on electrodynamic propulsion for aircraft

General

MIT electroaerodynamic aircraft

Ionocraft lifters

WEAV

Phoenix Makes Its First Flight With Variable Buoyancy Propulsion. What’s Old is New Again!

Peter Lobner

Updated 18 July 2019

1. Phoenix

The Phoenix Unmanned Aerial Vehicle (UAV) is a small, autonomous airship designed to serve as a very long endurance, high-altitude “atmospheric satellite” that is capable of station keeping using an innovative variable buoyancy propulsion system.  The UAV is intended for use in telecommunications and a range of other civil and military applications.

Phoenix development is being lead by a consortium of UK universities, businesses, and innovation centers, with a distribution of roles and responsibilities as shown in the following graphic.

Source:  https://phoenixuas.co.uk

This project runs for three years. It is one of several projects supported the UK’s Department for Business, Energy & Industrial Strategy (BEIS), through the Aerospace Technology Institute (ATI) and Innovate UK, to invest in “research and technology projects to deliver world leading aerospace technologies in the UK.”

The Phoenix project website is here: https://phoenixuas.co.uk

The Phoenix UAV is a small, variable buoyancy airship measuring 15 meters (49 feet) long, with a wingspan of 10.5 meters (34 feet).  The UAV’s teardrop-shaped fuselage is constructed from a Vectran fabric, with short wings and a cruciform tail made of carbon fiber composite material. Thin film solar panels on the wing and horizontal stabilizer surfaces generate electric power for the UAV’s systems and to charge an onboard battery that provides continuous power at night and during inclement weather.

Source:  https://phoenixuas.co.uk
Source:  https://phoenixuas.co.uk

The fuselage contains 120 cubic meters (4,238 cubic feet) of helium lifting gas (hydrogen is an alternative), a supply of lifting gas, and a separate inflatable 6 cubic meter (212 cubic feet) cell containing heavier air.  I would expect that the Phoenix is ballasted for near neutral buoyancy so that the control span of the buoyancy control system can produce both positive and negative buoyancy.

To increase buoyancy, air in the inflatable cell is released to the atmosphere via a vent in the tail.  If needed, lifting gas can be released to the gas envelope to gain positive buoyancy.  As the lighter-than-air Phoenix gains altitude, the aerodynamic surfaces generate forward momentum, propelling the UAV forward during the unpowered climb.  

At the top of the climb, buoyancy is decreased by pumping outside air into the inflatable cell, increasing the gross weight of the UAV. As the now heavier-than-air Phoenix enters an unpowered dive, the aerodynamic surfaces continue generating forward momentum to propel the UAV.

During an extended mission, the climb-dive cycle is repeated as often as needed to provide propulsion for controlling the position of the UAV.

First indoor flight.  Source: https://phoenixuas.co.uk

On 21 March 2019, the Phoenix UAV made its first successful flight indoors, covering about 120 meters (394 feet) and becoming the world’s first large variable buoyancy powered autonomous UAV. Outdoor tests will be conducted after the UK Civil Aviation Authority certifies the UAV.  As currently configured the developers expect that Phoenix can operate at altitudes up to about 914 meters (3,000 feet).

You can watch a short video of the first flight here:

https://www.youtube.com/watch?v=jcqPvKfZjac

But was it the first ever flight of an airship using variable buoyancy propulsion?

No, it wasn’t.  First there was Aereon in the 1860s and then there was AHAB in the early 2000s.

2. Aereon

Back in the 1860s, Dr. Solomon Andrews invented the directionally maneuverable, hydrogen-filled airship named Aereonthat used variable buoyancy and airflow around the airship’s gas envelope to provide propulsion without an engine.  The gas envelope on the original Aereon airship consisted of three side-by-side, cigar-shaped balloons, each with seven internal cells containing the hydrogen lifting gas. The balloons formed a gas envelope measuring 80 feet (24.4 meters) long and 13 feet (4 meters) wide. 

  • Buoyancy of the airship was controlled by venting some hydrogen lift gas or dropping some sand ballast.  
  • The angle-of-attack (pitch angle) of the gas envelope was controlled by moving the center of gravity of the gondola (i.e., by moving people in the gondola fore and aft as needed)
  • Propulsive force was generated by alternating between positive buoyancy (lighter-than-air) flight and negative buoyancy (heavier-than-air) flight, and by coordinating the pitch angle of the gas envelope. 
    • During a buoyant ascent, the pitch angle was adjusted to as much as 15 degrees up.  Air flow along the top surface of the envelope moved from bow to stern and drove the airship forward.   The airship can continue to ascend until it reaches its “pressure altitude” where the decreasing atmospheric air density reduces airship buoyancy from positive to neutral.
    • During a semi-buoyant descent, the pitch angle was adjusted to as much as 15 degrees down.  Air flow along the bottom surface of the envelope moved from bow to stern and continued to drive the airship forward.
  • Direction was controlled by a rudder at the stern of the airship
Source:  Popular Science Monthly, January 1932

Andrews first flew Aereon over Perth Amboy, NJ on 1 June 1863 and flew at least three times more.  With Aereon, he demonstrated the ability to fly in any direction, including against the wind, make broad 360 degree turns, and navigate back to and land at his starting point.  Aereon’s gondola could carry the pilot and three passengers.

On 5 July 1864, the US Patent Office issued Patent # 43,449 to Solomon Andrews for his invention of a balloon that was capable of directed flight and could even be flown against the wind.  You can read the patent here: https://patents.google.com/patent/US43449

Lithograph of Solomon Andrews’s first airship “Aereon”
Source: United States Library of Congress’s Prints and Photographs division,
digital ID cph.3b01438.

Andrews’ second airship, Aereon 2, had a different gas envelope design, described as “a flattened lemon, sharply pointed at both ends.”  Aereon 2 also used a different approach for controlling buoyancy.  The new approach used a complex set of ropes and pulleys to squeeze or release external pressure on the hydrogen gas bags, thereby changing their volume and how much air was being displaced.  Aereon 2 flew over New York City on 25 May and 5 June 1866. The second trip ended up about 30 miles away with a landing in Oyster Bay, Long Island. This was Andrews’ last flight. 

Source: Skinner Auctioneers

Andrews organized the Aerial Navigation Company, which was chartered in November 1865 for “the transportation of passengers, merchandise and other matter from place to place.”  The firm intended to build commercial airships and establish regular airship service between New York and Philadelphia.  During the post-Civil War economic crisis, many banks failed and Aerial Navigation Co. went bankrupt, ending the plans for the first commercial passenger and freight air service in the world.

Source: Worthpoint

3. Advanced High-Altitude Aerobody (AHAB)

In the early 2000s, the Physical Science Lab at New Mexico State University was developing the Advanced High-Altitude Aerobody (AHAB), which consisted of a large, solar-powered, non-rigid, winged aerobody with the payload suspended below on several retractable cables. Changing the length of the cables moved the center of gravity and thereby controlled the attitude of the aerobody. Changing the buoyancy of the aerobody caused it to climb or descend. As with the Phoenix UAV and Solomon Andrews’  Aereon, a forward propulsive force was generated during each climb or descent maneuver.  With this modest propulsion capability, AHAB was designed for station-keeping operations in near-space (very high altitude) where propellers would be ineffective.

In 2004, Mary Ann Stewart, et al., reported, “This superpressure balloon incorporates wing-like devices to give it a sleek aerodynamic shape. AHAB is designed to offset the effects of light winds by using a porpoising technique as necessary, trading altitude for horizontal motion. The craft is made up of a series of individual cells, and helium is pumped between cells to effect movement.”

Lt. Col Ed Tomme and Sigfred Dahl provided additional performance information, noting that such vehicles “will use a variety of unconventional buoyancy-modification schemes that allow vehicles to propel themselves by porpoising through the air at about 30 to 50 knots, enabling them to overcome all but the most unusual near-space winds.”

The AHAB airship.  Source: adapted from Air & Space Power Journal, Winter 2005, Volume XIX, No. 4, p. 47

In the 1-14 July 2019 issue of Aviation Week & Space Technology magazine, former AHAB program manager, Mike Fisher, commenting on the new Phoenix UAV, provided the following historical insights on AHAB: 

“The Aerobody was a solar-powered lighter-than-air vehicle (non-rigid rather than semi-rigid, as in the Phoenix) that pioneered the idea of using a ballonet to cause buoyancy and changes in center of gravity to enable propeller-less forward flight.

We took the concept far enough to demonstrate the validity of the underlying physics by building a subscale prototype that we successfully tested in indoor flight tests. Ultimately, the then-existing limits to photovoltaic cell and battery technology kept us from going past the prototype stage.”

What’s old is new again!

In the past two decades, winged underwater gliders implementing Andrews’ basic variable buoyance propulsion principle have been developed.  See the 2001 article, “Autonomous Buoyancy-driven Underwater Gliders,” which you can read here:

https://pdfs.semanticscholar.org/8b21/111dee323c13a57079767b4973ce30bc6c24.pdf

Now, the UK Phoenix team has demonstrated variable buoyancy propulsion in a small, unmanned airship, 156 years after Solomon Andrews first flew the much larger Aereon with passengers in Perth Amboy, NJ, and almost two decades after the indoor test flight of the subscale AHAB prototype at New Mexico State University.

Best wishes to the UK Phoenix team in their efforts to develop an operational variable buoyancy propulsion system for a modern airship.

Additional resources on the Phoenix UAV

Additional resources on Solomon Andrews and the Aereon

Additional resources on the Advanced High-Altitude Aerobody (AHAB)

Additional resources on buoyancy-driven airships

Paul Allen’s Stratolaunch Aircraft Makes its First Flight, but With an Uncertain Business Plan

Updated 19 March 2020

Peter Lobner

Background

The firm Northrop Grumman Innovation Systems (formerly Orbital ATK, and before that, Orbital Sciences Corporation)  was the first to develop a commercial, air-launched rocket capable of placing payloads into Earth orbit.  Initial tests of their modest-size Pegasus launch vehicle were made in 1990 from the NASA B-52 that previously had been used as the “mothership” for the X-15 experimental manned space plane and many other experimental vehicles.

Since 1994, Orbital ATK has been using a specially modified civilian Lockheed L-1011 TriStar, a former airliner renamed Stargazer, as a mothership to carry a Pegasus launch vehicle to high altitude, where the rocket is released to fly a variety of missions, including carrying satellites into orbit.  With a Pegasus XL  as its payload (launch vehicle + satellite), Stargazer is lifting up to 23,130 kg (50,990 pounds) to a launch point at an altitude of about 12.2 km (40,000 feet).

Orbital ATK’s Pegasus XL rocket released from Stargazer.  
Source: NASA / http://mediaarchive.ksc.nasa.gov

You can watch a 2015 video celebrating 25 years of Orbital ATK’s Pegasus air-launched rocket at the following link: https://www.youtube.com/watch?v=0L47cpXTzQU

Paul Allen’s firm Stratolaunch Systems Corporation (https://www.stratolaunch.com) was founded in 2011 to take this air-launch concept to a new level with their giant, twin-fuselage, six-engine Stratolaunch carrier aircraft.  The aircraft has a wingspan of 385 feet (117 m), which is the greatest of any aircraft ever built, a length of 238 feet (72.5 m), and a height of 50 feet (15.2 m) to the top of the vertical tails. The empty weight of the aircraft is about 500,000 pounds (226,796 kg).  It is designed for a maximum takeoff weight of 1,300,000 pounds (589,670 kg), leaving about 550,000 pounds (249,486 kg) for its payload and the balance for fuel and crew.  It will be able to carry multiple launch vehicles on a single mission to a launch point at an altitude of about 35,000 feet (10,700 m).  A mission profile for the Stratolaunch aircraft is shown in the following diagram.

Typical air-launch mission profile. Source: Stratolaunch Systems

Stratolaunch rollout – 2017

Built by Scaled Composites, the Stratolaunch aircraft was unveiled on 31 May 2017 when it was rolled out at the Mojave Air and Space Port in Mojave, CA.  Following is a series of photos from Stratolaunch Systems showing the rollout.

Stratolaunch ground tests – 2017 to 2019

Ground testing of the aircraft systems started after rollout. By mid-September 2017, the first phase of engine testing was completed, with all six Pratt & Whitney PW4000 turbofan engines operating for the first time.  The first low-speed ground tests conducted in December 2017 reached a modest speed of 25 knot (46 kph).  By January 2019, the high-speed taxi tests had reached a speed of about 119 knots (220 kph) with the nose wheel was off the runway, almost ready for lift off. Following is a series of photos from Stratolaunch Systems showing the taxi tests.

Stratolaunch first flight

The Stratolaunch aircraft, named Roc, made an unannounced first flight from the Mojave Air & Space Port on 13 April 2019.  The aircraft stayed aloft for 2.5 hours, reached a peak altitude of 17,000 feet (5,180 m) and a top speed of 189 mph (304 kph). The following series of photos show the Stratolaunch aircraft during its first flight.

Source, above two photos:  Stratolaunch Systems
Source:  REUTERS/Gene Blevins/File Photo
Landing at the conclusion of the first flight.   Source:  Stratolaunch Systems

Stratolaunch posted an impressive short video of the first flight, which you can view here:

Stratolaunch family of launch vehicles: ambitious plans, but subject to change

In August 2018, Stratolaunch announced its ambitious launch vehicle development plans, which included the family of launch vehicles shown in the following graphic:

  • Up to three Pegasus XL launch vehicles from Northrop Grumman Innovation Systems (formerly Orbital ATK) can be carried on a single Stratolaunch flight. Each Pegasus XL is capable of placing up to 370 kg (816 lb) into a low Earth orbit (LEO, 400 km / 249 mile circular orbit).
  • Medium Launch Vehicle (MLV) capable of placing up to 3,400 kg (7,496 lb) into LEO and intended for short satellite integration timelines, affordable launch and flexible launch profiles.  MLV was under development and first flight was planned for 2022.
  • Medium Launch Vehicle – Heavy, which uses three MLV cores in its first stage. That vehicle would be able to place 6,000 kg (13,228 lb) into LEO.  MLV-Heavy was in the early development stage.
  • A fully reusable space plane named Black Ice, initially intended for orbital cargo delivery and return, with a possible follow-on variant for transporting astronauts to and from orbit.  The space plane was a design study.

Stratolaunch was developing a 200,000 pound thrust, high-performance, liquid fuel hydrogen-oxygen rocket engine, known as the “PGA engine”, for use in their family of launch vehicles.  Additive manufacturing was being widely used to enable rapid prototyping, development and manufacturing.   Successful tests of a 100% additive manufactured major subsystem called the hydrogen preburner were conducted in November 2018.

Stratolaunch Systems planned family of launch vehicles announced in August 2018.
Source: Stratolaunch Systems

After Paul Allen’s death on 15 October 2018, the focus of Stratolaunch Corp was greatly revised. On 18 January 2019, the company announced that it was ending work on its own family of launch vehicles and the PGA rocket engine. The firm announced, “We are streamlining operations, focusing on the aircraft and our ability to support a demonstration launch of the Northrop Grumman Pegasus XL air-launch vehicle.”    

You’ll find an article describing Stratolaunch Systems’ frequently changing launch vehicle plans in an article on the SpaceNews website here:

https://spacenews.com/stratolaunch-abandons-launch-vehicle-program/

What is the future for Stratolaunch?

Air launch offers a great deal of flexibility for launching a range of small-to-medium sized satellites and other aerospace vehicles. With only the Pegasus XL as a launch vehicle, and with Northrop Grumman having their own Stargazer carrier aircraft for launching the Pegasus XL, the business case for the Stratolaunch aircraft has been greatly weakened.    

Stratolaunch’s main competition:  The Northrop Grumman Stargazer at the Mojave Air and Space Port in January 2019, available for its next Pegasus XL launch mission.  Source: Author’s photo

Additional competition in the airborne launch services business will come in 2020 from Richard Branson’s firm Virgin Orbit, with its airborne launch platform Cosmic Girl, a highly-modified Boeing 747, and its own launch vehicle, known as LauncherOne.  Successful drop tests of LauncherOne were conducted in 2019.  The first launch to orbit is expected to occur in 2020.  You’ll find more information on the Virgin Orbit website here: https://virginorbit.com

An inert LauncherOne rocket falls away from its 747 carrier aircraft in a July 2019 drop test.  Source: Virgin Orbit

Additional competition for small satellite launch services comes from the newest generation of small orbital launch vehicles, like Electron (Rocket Lab, New Zealand) and Prime (Orbix, UK), which are expected to offer low price launch services from fixed land-based launch sites.  Electron is operational now, and achieved six successful launches in six attempts in 2019. Prime is expected to enter service in 2021.  

In the cost competitive launch services market, Stratolaunch does not seem to have an advantage with only the Pegasus XL in its launch vehicle inventory.  Hopefully, they have something else up their sleeve that will take advantage of the remarkable capabilities of the Stratolaunch carrier aircraft.

19 March 2020 Update:  Stratolaunch change of ownership

Several sources reported on 11 October 2019 that Stratolaunch Systems had been sold by its original holding company, Vulcan Inc., to an undisclosed new owner. Two months later, Mark Harris, writing for GeekWire, broke the news that the private equity firm Cerberus Capital Management was the new owner.  It appears that Jean Floyd, Stratolaunch’s president and CEO since 2015, remains in his roles for now. Michael Palmer, Cerberus’ managing director, was named Stratolaunch’s executive vice president. You can read Mark Harris’ report here: https://www.geekwire.com/2019/exclusive-buyer-paul-allens-stratolaunch-space-venture-secretive-trump-ally/

It will be interesting to watch as the new owners reinvent Stratolaunch Systems for the increasingly competitive market for airborne launch services.