Category Archives: Aeronautical

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

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.


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:

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.


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:

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:

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

No it wasn’t.  

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:

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

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:

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 Aeron with passengers in Perth Amboy, NJ.

Additional resources on the Phoenix UAV

Additional resources on Solomon Andrews and the Aereon

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


The firm Orbital ATK (formerly 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 /

You can watch a 2015 video celebrating 25 years of Orbital ATK’s Pegasus air-launched rocket at the following link:

Paul Allen’s firm Stratolaunch Systems Corporation ( 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). Following is a series of photos from Stratolaunch Systems showing the Stratolaunch aircraft during its first flight.

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:

What is the future for Stratolaunch?

With only the Pegasus XL as a launch vehicle, and Northrop Grumman having their own Stargazer carrier aircraft for the Pegasus XL, the business case for the Stratolaunch aircraft has been greatly weakened.  Air launch certainly offers a great deal of flexibility for launching small satellites. However, it appears that the newest generation of small orbital launch vehicles, like Electron (Rocket Lab, New Zealand) and Prime (Orbix, UK) will be able to offer similar launch services at lower cost.  Electron is operational now, and Prime is expected to enter service in 2021.  

In a 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.

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

Preliminary Design of an Experimental World-Circling Spaceship

The title of this post also is the title of the first RAND report, SM-11827, which was issued on 5 May 1946 when Project RAND still was part of the Douglas Aircraft Company. The basic concept for an oxygen-alcohol fueled multi-stage world-circling spaceship is shown below.

Source: RAND

Source: RAND

Now, more than 70 years later, it’s very interesting to read this report to gain an appreciation of the state of the art of rocketry in the U.S. in 1946, which already was benefiting from German experience with the V-2 and other rocket programs during WW II.

RAND offers the following abstract for SM-11827:

“More than eleven years before the orbiting of Sputnik, history’s first artificial space satellite, Project RAND — then active within Douglas Aircraft Company’s Engineering Division — released its first report: Preliminary Design of an Experimental World-Circling Spaceship (SM-11827), May 2, 1946. Interest in the feasibility of space satellites had surfaced somewhat earlier in a Navy proposal for an interservice space program (March 1946). Major General Curtis E. LeMay, then Deputy Chief of the Air Staff for Research and Development, considered space operations to be an extension of air operations. He tasked Project RAND to undertake a feasibility study of its own with a three-week deadline. The resulting report arrived two days before a critical review of the subject with the Navy. The central argument turns on the feasibility of such a space vehicle from an engineering standpoint, but alongside the curves and tabulations are visionary statements, such as that by Louis Ridenour on the significance of satellites to man’s store of knowledge, and that of Francis Clauser on the possibility of man in space. But the most riveting observation, one that deserves an honored place in the Central Premonitions Registry, was made by one of the contributors, Jimmy Lipp (head of Project RAND’s Missile Division), in a follow-on paper nine months later: ‘Since mastery of the elements is a reliable index of material progress, the nation which first makes significant achievements in space travel will be acknowledged as the world leader in both military and scientific techniques. To visualize the impact on the world, one can imagine the consternation and admiration that would be felt here if the United States were to discover suddenly that some other nation had already put up a successful satellite.’”

You can buy the book from several on-line sellers or directly from RAND. However you also can download the complete report for free in three pdf files that you’ll find on the RAND website at the following link:



Stratospheric Tourism Coming Soon

On 31 May 1931 Professor Auguste Piccard and Paul Kipfer made the first balloon flight into the stratosphere in a pressurized gondola. These aeronauts reached an altitude of 51,777 ft (15,782 m) above Augsburg, Germany in the balloon named FNRS (Belgian National Foundation for Scientific Research). At that time, a state-of-the-art high-altitude balloon was made of relatively heavy rubberized fabric. Several nations made stratospheric balloon flights in the 1930s, with the U.S. National Geographic Society’s Explorer II setting an altitude record of 72,395 ft (22,065 m) on 11 November 1935.

After World War II, very large, lightweight, polyethylene plastic balloons were developed in the U.S. by Jean Piccard (August Piccard’s twin brother) and Otto Winzen. These balloons were used primarily by the U.S. military to fly payloads to very high altitudes for a variety of research and other projects.

The Office of Naval Research (ONR) launched its first Project Skyhook balloon (a Piccard-Winzen balloon) on 25 September 1947, and launched more than 1,500 Skyhook balloons during the following decade. The first manned flight in a Skyhook balloon occurred in 1949.

The record for the highest unmanned balloon flight was set in 1972 by the Winzen Research Balloon, which achieved a record altitude of 170,000 ft (51,816 m) over Chico, CA.

USAF Project Man High & U.S. Navy Strato-Lab: 1956 – 1961

Manned stratospheric balloon flights became common in the 1950s and early 1960s under the U.S. Air Force’s Man High program and the U.S. Navy’s Strato-Lab program. One goal of these flights was to gather physiological data on humans in pressure suits exposed to near-space conditions at altitudes of about 20 miles (32.2 km) above the Earth. You’ll find an overview of these military programs at the following link:

Three Man High flights were conducted between June 1957 and October 1958. In August 1957, the Man High II balloon flight by Major David Simons reached the highest altitude of the program: 101,516 feet (30,942 m). The rather cramped Man High II gondola is shown in the following diagram.

Man High II gondola. Source: USAF.

The Man High II gondola is on display at the National Museum of the United States Air Force, Dayton, OH. You’ll find details on the Man High II mission at the following link:

Five Strato-Lab flights were made between August 1956 and May 1961, with some flights using a pressurized gondola and others an open, unpressurized gondola. The last mission, Strato-Lab High V, carrying Commander Malcolm Ross and scientist Victor Prather in an unpressurized gondola, reached a maximum altitude of 113,740 ft (34,575 meters) on the 4 May 1961. The main objective of this flight was to test the Navy’s Mark IV full-pressure flight suit.

Strato-Lab V open gondola. Source:

See the following link for details on Strato-Lab missions.

USAF Project Excelsior: 1959 – 60

To study the effects of high-altitude bailout on pilots, the USAF conducted Project Excelsior in 1959 and 1960, with USAF Capt. Joseph Kittinger making all three Excelsior balloon flights. In the Excelsior III flight on 16 August 1960, Capt. Kittinger bailed out from the unpressurized gondola at an altitude of 102,800 feet (31,330 m) and was in free-fall for 4 minutes 36 seconds. Thanks to lessons learned on the previous Excelsior flights, a small drogue stabilized Kittinger’s free-fall, during which he reached a maximum vertical velocity of 614 mph (988 km/h) before slowing to a typical skydiving velocity of 110 – 120 mph (177 – 193 kph) in the lower atmosphere. You’ll find Capt. Kittinger’s personal account of this record parachute jump at the following link:

Project Stargazer: 1960

Capt. Kittinger and astronomer William White performed 18 hours of astronomical observations from the open gondola of the Stargazer balloon. The flight, conducted on 13 – 14 December 1960, reached a maximum altitude of 82,200 feet (25,100 m).

Red Bull Stratos: 2012

On 14 October 2012, Felix Baumgartner exited the Red Bull Stratos balloon gondola at 128,100 feet (39,045 m) and broke Joe Kittinger’s 52-year old record for the highest parachute jump. Shortly after release, Baumgartner started gyrating uncontrollably due to asymmetric drag in the thin upper atmosphere and no means to stabilize his attitude until reaching denser atmosphere. During his perilous 4 minute 40 second free-fall to an altitude of about 8,200 ft (2,500 m), he went supersonic and reached a maximum vertical velocity of 833.9 mph (1,342.8 kph, Mach 1.263).

You’ll find details on Baumgartner’s mission at the following link:

Capt. Kittinger was an advisor to the Red Bull Stratos team. The gondola, Felix Baumgartner’s pressure suit and parachute are on display at the Smithsonian Air & Space Museum’s Udvar-Hazy Center in Chantilly, VA.

Red Bull Stratos gondola & pressure suit. Source: Smithsonian

Stratospheric Explorer: 2014

Baumgartner’s record was short-lived, being broken on 14 October 2014 when Alan Eustace jumped from the Stratospheric Explorer (StratEx) balloon at an altitude of 135,899 ft (41,422 meters).  Eustace used a drogue device to help maintain stability during the free-fall, before his main parachute opened. He fell 123,235 ft (37,623 meters) with the drogue and reached a maximum vertical velocity of 822 mph (1,320 km/h); faster than the speed of sound. You can read an interview of Alan Eustace, including his thoughts on stratosphere balloon tourism, at the following link:

More information of this record-setting parachute jump is at the following link:

World View® Voyager

If you’re not ready to sign up for a passenger rocket flight, and the idea of bailing out of a balloon high in the stratosphere isn’t your cup of tea, then perhaps you’d consider a less stressful flight into the stratosphere in the pressurized gondola of the Voyager passenger balloon being developed by World View Enterprises, Inc. They describe an ascent in the Voyager passenger balloon as follows:

“With World View®, you’ll discover what it’s like to leave the surface of the Earth behind. Every tree, every building, even the mountains themselves become smaller and smaller as you gently and effortlessly rise above. The world becomes a natural collage of magnificent beauty, one you can only appreciate from space. Floating up more than 100,000 feet within the layers of the atmosphere, you will be safely and securely sailing at the very threshold of the heavens, skimming the edge of space for hours. The breathtaking view unfolds before you—our home planet suspended in the deep, beckoning cosmos. Your world view will be forever changed.”

You can view an animated video of such a flight at the following link:

The following screenshots from this video show the very large balloon and the pressurized Voyager gondola, which is suspended beneath a pre-deployed parafoil parachute connected to the balloon. After reaching maximum altitude, the Voyager balloon will descend until appropriate conditions are met for releasing the parafoil and gondola, which will glide back to a predetermined landing point.

Source for five screenshots, above:  WorldView Enterprises, Inc.

In February 2017, World View opened a large facility at Spaceport Tucson to support its plans for developing and deploying unmanned balloons for a variety of missions as well as Voyager passenger balloons. World View announced plans to a fly a test vehicle named Explorer from Spaceport Tucson in early 2018, with edge-of-space passenger flights by the end of the decade.

For more information on World View Enterprises and the Voyager stratosphere balloon, visit their website at the following link:



Protocol for Reporting UFO Sightings

The United States Air Force began investigating unidentified flying objects (UFOs) in the fall of 1947 under a program called Project Sign, which later became Project Grudge, and in January 1952 became Project Blue Book. As you might expect, the USAF developed a reporting protocol for these projects.

Starting in 1951, the succession of Air Force documents that provided UFO reporting guidance is summarized below:

Headquarters USAF Letter AFOIN-C/CC-2

This letter, entitled, “Reporting of Information on Unidentified Flying Objects,” dated 19 December 1951, may be the original guidance document for UFO reporting. So far, I have been unable to find a copy of this document. The Project Blue Book archives contain examples of UFO reports from 1952 citing AFOIN-C/CC-2.

Air Force Letter AFL 200-5

The first reporting protocol I could find was Air Force Letter AFL 200-5, “Unidentified Flying Objects Reporting,” dated 29 April 1952, which was issued on behalf of the Secretary of the USAF by Hoyt S. Vandenberg, Chief of Staff of the USAF.

  • Defines UFOs as, “any airborne object which by performance, aerodynamic characteristics, or unusual features, does not conform to any presently known aircraft or missile type.”
  • UFO reporting is treated as an Intelligence activity (denoted by the 200-series document number)
  • Provides brief guidance on report content, which was to be submitted on AF Form 112, “Air Intelligence Information Report,” and not classified higher than RESTRICTED.
  • The local Commanding Officer is responsible for forwarding FLYOBRPTS to the appropriate agencies. FLYOBRPT is an acronym for FLYing OBject RePorT.
  • Responsibility for investigating UFOs was assigned to the Air Technical Intelligence Center (ATIC) at Wright Patterson Air Force Base, Ohio. ATIC was a field activity of the Directorate of Intelligence in USAF Headquarters.
  • AFL 200-5 does not indicate that it superseded any prior USAF UFO reporting guidance document, but it is likely that it replaced USAF letter AFOIN-C/CC-2, dated 19 December 1951.

Download AFL 200-5 at the following link:

How to Make FLYOBRPTs

In 1953, the AITC issued “How to Make FLYOBRPTs,” dated 25 July 1953, to help improve reporting required by AFL 200-5.

Figure 1 from How to Make a FLYOBRPT

Source: USAF

This guidance document provides an interesting narrative about UFOs through 1953, explains how to collect information on a UFO sighting, including interacting with the public during the investigation, and how to complete a FLYOBRPT using four detailed data collection forms.

  • Ground Observer’s Information Sheet (9 pages)
  • Electronics Data Sheet (radar) (5 pages)
  • Airborne Observer’s Data Sheet (9 pages) and,
  • Supporting Data form (8 pages)

This report showed that the USAF had a sense of humor about UFO reporting.

Figure 2 from How to Make a FLYOBRPTSource: USAF

Download “How to Make FLYOBRPTs” at the following link:

Air Force Regulation AFR 200-2

In 1953, the Secretary of the Air Force, Harold E. Talbott, issued the original Air Force Regulation AFR 200-2, “Unidentified Flying Objects Reporting”, dated 26 August 1953.

  • Superseded AFL 200-5, dated 29 April 1952
  • Defines procedures for reporting UFOs and restrictions on public discussion by Air Force personnel
  • Change 200-2A was issued on 2 November 1953
  • Between 1954 and 1962, the USAF issued several subsequent versions of AFR 200-2, as listed below.

AFR 200-2, “Unidentified Flying Objects Reporting (Short Title: FLYOBRPT)”, dated 12 August 1954.

  • Superseded AFR 200-2 dated 26 August 1953 and Change 200-2A
  • Identifies the USAF interest in UFOs as follows: “Air Force interest in unidentified flying objects is twofold: First as a possible threat to the security of the United States and its forces, and secondly, to determine technical aspects involved.”
  • Defines an expected report format that is less comprehensive than the guidance in “How to Make FLYOBRPTs.”
  • Clarifies that Headquarters USAF will release summaries of evaluated data to the public. Also notes that it is permissible to respond to local inquiries when the object is positively identified as a “familiar object” (not a UFO). In other cases, the only response is that ATIC will analyze the data.
  • Download this version of AFR 200-2 at the following link:

AFR 200-2, “Unidentified Flying Objects (UFO),” dated 5 February 1958

  • Supersedes the version dated 12 August 1954
  • Broadens the USAF interest in UFOs: “First as a possible threat to the security of the United States and its forces; second, to determine the technical or scientific characteristics of any such UFOs; third, to explain or identify all UFO sightings…”
  • Updates report formats and provides additional guidance on reporting
  • Download this version from the CIA website at the following link:

AFR 200-2, “Unidentified Flying Objects (UFO),” dated 14 September 1959

  • Supersedes the version dated 5 February 1958

AFR 200-2, “Unidentified Flying Objects (UFO),” dated 20 July 1962

  • Supersedes the version dated 14 September 1959
  • Superseded by AFR 80-17

Air Force Regulation AFR 80-17

In 1966, the USAF issued AFR 80-17, “Unidentified Flying Objects (UFO),” dated 19 September 1966

  • Supersedes AFR 200-2 dated 20 July 1962.
  • Two changes were issued:
    • AFR 80-17, Change 80-17A, dated 8 November 1966
    • AFR 80-17, Change 1, dated 26 October 1968, superseded AFR 80-17A, 8 November 1966
  • No longer considers UFO reporting as an intelligence activity, as denoted by the 80-series number assigned to the AFR
  • Places UFO reporting under the Research and Development Command. This is consistent with recasting ATIC into the Foreign Technology Division (FTD) of the Air Force Systems Command at Wright-Patterson AFB.
  • Broadly redefines UFO as “any aerial phenomenon which is unknown or appears out of the ordinary to the observer.”
  • Orders all Air Force bases to provide an investigative capability
  • Change 80-17A assigned University of Colorado to conduct an independent scientific investigation of UFOs. Physicist Edward U. Condon would direct this work.

Download AFR 80-17, with change 80-17A and change 1 here:

Project Blue Book’s final report

In late October 1968, the University of Colorado’s final report was completed and submitted for review by a panel of the National Academy of Sciences. The panel approved of the methodology and concurred with Edward Condon’s conclusion:

“That nothing has come from the study of UFOs in the past 21 years that has added to scientific knowledge. Careful consideration of the record as it is available to us leads us to conclude that further extensive study of UFOs probably cannot be justified in the expectation that science will be advanced thereby.”

In January 1969, a 965-page paperback version of the report was published under the title, “Scientific Study of Unidentified Flying Objects.”

On 17 December 1969, Air Force Secretary Robert C. Seamans, Jr., announced the termination of Project Blue Book.

Additional resources

You’ll find a good history by of the U.S. Air Force UFO programs written by Thomas Tulien at the following link:




The Mysterious Case of the Vanishing Electronics, and More

Announced on 29 January 2013, DARPA is conducting an intriguing program known as VAPR:

“The Vanishing Programmable Resources (VAPR) program seeks electronic systems capable of physically disappearing in a controlled, triggerable manner. These transient electronics should have performance comparable to commercial-off-the-shelf electronics, but with limited device persistence that can be programmed, adjusted in real-time, triggered, and/or be sensitive to the deployment environment.

VAPR aims to enable transient electronics as a deployable technology. To achieve this goal, researchers are pursuing new concepts and capabilities to enable the materials, components, integration and manufacturing that could together realize this new class of electronics.”

VAPR has been referred to as “Snapchat for hardware”. There’s more information on the VAPR program on the DARPA website at the following link:

Here are a few of the announced results of the VAPR program.

Disintegrating electronics

In December 2013, DARPA awarded a $2.5 million VAPR contract to the Honeywell Aerospace Microelectronics & Precision Sensors segment in Plymouth, MN for transient electronics.

In February 2014, IBM was awarded a $3.4 million VAPR contract to develop a radio-frequency based trigger to shatter a thin glass coating: “IBM plans is to utilize the property of strained glass substrates to shatter as the driving force to reduce attached CMOS chips into …. powder.” Read more at the following link:

Also in February 2014, DARPA awarded a $2.1 million VAPR contract to PARC, a Xerox company. In September 2015, PARC demonstrated an electronic chip built on “strained” Corning Gorilla Glass that will shatter within 10 seconds when remotely triggered. The “strained” glass is susceptible to heat. On command, a resistor heats the glass, causing it to shatter and destroy the embedded electronics. This transience technology is referred to as: Disintegration Upon Stress-release Trigger, or DUST. Read more on PARC’s demonstration and see a short video at the following link:

Disintegrating power source

In December 2013, USA Today reported that DARPA awarded a $4.7 million VAPR contract to SRI International, “to develop a transient power supply that, when triggered, becomes unobservable to the human eye.” The power source is the SPECTRE (Stressed Pillar-Engineered CMOS Technology Readied for Evanescence) silicon-air battery. Details are at the following link:

On 12 August 2016, the website Science Friday reported that Iowa State scientists have successfully developed a transient lithium-ion battery:

“They’ve developed the first self-destructing, lithium-ion battery capable of delivering 2.5 volts—enough to power a desktop calculator for about 15 minutes. The battery’s polyvinyl alcohol-based polymer casing dissolves in 30 minutes when dropped in water, and its nanoparticles disperse. “

You can read the complete post at:

ICARUS (Inbound, Controlled, Air-Releasable, Unrecoverable Systems)

On 9 October 2015, DARPA issued “a call for disappearing delivery vehicles,” which you can read at the following link:

In this announcement DARPA stated:

“Our partners in the VAPR program are developing a lot of structurally sound transient materials whose mechanical properties have exceeded our expectations,” said VAPR and ICARUS program manager Troy Olsson. Among the most eye-widening of these ephemeral materials so far have been small polymer panels that sublimate directly from a solid phase to a gas phase, and electronics-bearing glass strips with high-stress inner anatomies that can be readily triggered to shatter into ultra-fine particles after use. A goal of the VAPR program is electronics made of materials that can be made to vanish if they get left behind after battle, to prevent their retrieval by adversaries.”

With the progress made in VAPR, it became plausible to imagine building larger, more robust structures using these materials for an even wider array of applications. And that led to the question, ‘What sorts of things would be even more useful if they disappeared right after we used them?’”

This is how DARPA conceived the ICARUS single-use drone program described in October 2015 in Broad Area Announcement DARPA-BAA-16-03. The goal of this $8 million, 26-month DARPA program is to develop small drones with the following attributes

  • One-way, autonomous mission
  • 3 meter (9.8 feet) maximum span
  • Disintegrate in 4-hours after payload delivery, or within 30 minutes of exposure to sunlight
  • Fly a lateral distance of 150 km (93 miles) when released from an altitude of 35,000 feet (6.6 miles)
  • Navigate to and deliver various payloads up to 3 pounds (1.36 kg) within 10 meters (31 feet) of a GPS-designated target

The ICARUS mission profile is shown below.

ICARUS mission profileICARUS mission. Source: DARPA-BAA-16-03

More information on ICARUS is available on the DARPA website at:

On 14 June 2016, Military & Aerospace reported that two ICARUS contracts had been awarded:

  • PARC (Palo Alto, CA): $2.3 million Phase 1 + $1.9 million Phase 2 option
  • DZYNE Technologies, Inc. (Fairfax, VA): $2.9 million Phase 1 + $3.2 million Phase 2 option

You can watch a short video describing the ICARUS competition at the following link:

The firm Otherlab ( has been involved with several DARPA projects in recent years. While I haven’t seen a DARPA announcement that Otherlab is a funded ICARUS contractor, a recent post by April Glaser on the recode website indicates that the Otherlab has developed a one-way, cardboard glider capable of delivering a small cargo to a precise target.

“When transporting vaccines or other medical supplies, the more you can pack onto the drone, the more relief you can supply,” said Star Simpson, an aeronautics research engineer at Otherlab, the group that’s building the new paper drone. If you don’t haul batteries for a return trip, you can pack more onto the drone, says Simpson.

The autonomous disposable paper drone flies like a glider, meaning it has no motor on board. It does have a small computer, as well as sensors that are programed to adjust the aircraft’s control surfaces, like on its wings or rudder, that determine where the aircraft will travel and land.”

 Otherlab_SkyMachines_APSARA.0Sky machines. Source: Otherworld

Read the complete post on the Otherlab glider on the recode website at the following link:

The future

The general utility of vanishing electronics, power sources and delivery vehicles is clear in the context of military applications. It will be interesting to watch the future development and deployment of integrated systems using these vanishing resources.

The use of autonomous, air-releasable, one-way delivery vehicles (vanishing or not) also should have civilian applications for special situations such as emergency response in hazardous or inaccessible areas.



Airbus Delivers its 10,000th Aircraft

Airbus was founded on 18 December 1970 and delivered its first aircraft, an A300B2, to Air France on 10 May 1974. This was the world’s first twin-engine, wide body (two aisles) commercial airliner, beating Boeing’s 767, which was not introduced into commercial service until September 1982. The A300 was followed in the early 1980s by a shorter derivative, the A310, and then, later that decade, by the single-aisle A320. The A320 competed directly with the single-aisle Boeing 737 and developed into a very successful family of single-aisle commercial airliners: A318, A319, A320 and A321.

On 14 October 2016, Airbus announced the delivery of its 10,000th aircraft, which was an A350-900 destined for service with Singapore Airlines.

EVE-1236Source: Airbus

In their announcement, Airbus noted:

“The 10,000th Airbus delivery comes as the manufacturer achieves its highest level of production ever and is on track to deliver at least 650 aircraft this year from its extensive product line. These range from 100 to over 600 seats and efficiently meet every airline requirement, from high frequency short haul operations to the world’s longest intercontinental flights.”

You can read the complete Airbus press release at the following link:

As noted previously, Airbus beat Boeing to the market for twinjet, wide-body commercial airliners, which are the dominant airliner type on international and high-density routes today. Airbus also was an early adopter of fly-by-wire flight controls and a “glass cockpit”, which they first introduced in the A320 family.

In October 2007, the ultra-large A380 entered service, taking the honors from the venerable Boeing 747 as the largest commercial airliner.   Rather than compete head-to-head with the A380, Boeing opted for stretching its 777 and developing a smaller, more advanced and more efficient, all-composite new airliner, the 787, which was introduced in airline service 2011.

Airbus countered with the A350 XWB in 2013. This is the first Airbus with fuselage and wing structures made primarily of carbon fiber composite material, similar to the Boeing 787.

The current Airbus product line comprises a total of 16 models in four aircraft families: A320 (single aisle), A330 (two aisle wide body), A350 XWB (two aisle wide body) and A380 (twin deck, two aisle wide body). The following table summarizes Airbus commercial jet orders, deliveries and operational status as of 30 November 2016.

Airbus orders* Includes all models in this family. Source:

Boeing is the primary competitor to Airbus. Boeing’s first commercial jet airliner, the 707, began commercial service Pan American World Airways on 26 October 1958. The current Boeing product line comprises five airplane families: 737 (single-aisle), 747 (twin deck, two aisle wide body), 767 (wide body, freighter only), 777 (two aisle wide body) and 787 (two aisle wide body).

The following table summarizes Boeing’s commercial jet orders, deliveries and operational status as of 30 June 2016. In that table, note that the Boeing 717 started life in 1965 as the Douglas DC-9, which in 1980 became the McDonnell-Douglas MD-80 (series) / MD-90 (series) before Boeing acquired McDonnell-Douglas in 1997. Then the latest version, the MD-95, became the Boeing 717.

Boeing commercial order status 30Jun2016


Boeing’s official sales projections for 2016 are for 740 – 745 aircraft. Industry reports suggest a lower sales total is more likely because of weak worldwide sales of wide body aircraft.

Not including the earliest Boeing models (707, 720, 727) or the Douglas DC-9 derived 717, here’s how the modern competition stacks up between Airbus and Boeing.

Single-aisle twinjet:

  • 12,805 Airbus A320 family (A318, A319, A320 and A321)
  • 14,527 Boeing 737 and 757

Two-aisle twinjet:

  • 3,260 Airbus A300, A310, A330 and A350
  • 3,912 Boeing 767, 777 and 787

Twin aisle four jet heavy:

  • 696 Airbus A340 and A380
  • 1,543 Boeing 747

These simple metrics show how close the competition is between Airbus and Boeing. It will be interesting to see how these large airframe manufacturers fare in the next decade as they face more international competition, primarily at the lower end of their product range: the single-aisle twinjets. Former regional jet manufacturers Bombardier (Canada) and Embraer (Brazil) are now offering larger aircraft that can compete effectively in some markets. For example, the new Bombardier C Series is optimized for the 100 – 150 market segment. The Embraer E170/175/190/195 families offer capacities from 70 to 124 seats, and range up to 3,943 km (2,450 miles).  Other new manufacturers soon will be entering this market segment, including Russia’s Sukhoi Superjet 100 with about 108 seats, the Chinese Comac C919 with up to 168 seats, and Japan’s Mitsubishi Regional Jet with 70 – 80 seats.

At the upper end of the market, demand for four jet heavy aircraft is dwindling. Boeing is reducing the production rate of its 747-8, and some airlines are planning to not renew their leases on A380s currently in operation.

It will be interesting to watch how Airbus and Boeing respond to this increasing competition and to increasing pressure for controlling aircraft engine emissions after the Paris Agreement became effective in November 2016.

Status of Ukraine’s Giant Transport Aircraft: Antonov An-124 and An-225

Historically, the Antonov Design Bureau was responsible for the design and development of large military and civil transport aircraft for the former Soviet Union. With headquarters and production facilities in and around Kiev, this Ukrainian aircraft manufacturing and servicing firm is now known as Antonov State Company. The largest of the jet powered transport aircraft built by Antonov are the four-engine An-124 and the even larger six-engine An-225.

An-124 Ruslan (NATO name: Condor)

The An-124 made its first flight in December 1982 and entered operational service in 1986. This aircraft is a counterpart to the Lockheed C-5A, which is the largest U.S. military transport aircraft. A comparison of the basic parameters of these two aircraft is presented in the following table.

An-124 vs C-5A_AviatorjoedotnetSource:

As you can see in this comparison, the An-124 is somewhat larger than the C-5A, which has a longer range, but at a slower maximum speed.

The An-124 currently is operated by the Russian air force and also by two commercial cargo carriers: Ukraine’s Antonov Airlines and Russia’s Volga-Dnepr Airlines. The civil An-124-100 is a commercial derivative of the military An-124. The civil version was certified in 1992, and meets all current civil standards for noise limits and avionic systems.

In their commercial cargo role, these aircraft specialize in carrying outsized and/or very heavy cargo that cannot be carried by other aircraft. These heavy-lift aircraft serve civil and military customers worldwide, including NATO and the U.S. military. I’ve seen an An-124s twice on the tarmac at North Island Naval Station in San Diego. In both cases, it arrived in the afternoon and was gone before sunrise the next day. Loading and/or unloading occurred after dark.

An-124_RA-82028_09-May-2010An-124-100. Source: Wikimedia Commons

As shown in the following photo, the An-124 can retract its nose landing gear and “kneel” to facilitate cargo loading through the raised forward door.

An-124_ramp downAn-124-100. Source: Mike Young / Wikimedia Commons

The following diagram shows the geometry and large size of the cargo hold on the An-124. The built-in cargo handling equipment includes an overhead crane system capable of lifting and moving loads up to 30 metric tons (about 66,100 pounds) within the cargo hold. As shown in the diagram below, the cargo hold is about 36.5 meters (119.7 feet) long, 6.4 meters (21 feet) wide, and the clearance from the floor to the ceiling of the cargo hold is 4.4 meters (14.4 feet). The installed crane hoists may reduce overhead clearance to 3.51 meters (11.5 feet).

An-124-diagram_tcm87-4236An-124-100 cargo hold dimensions. Source:

An-124_takeoffAn-124-100. Source:

Production of the An-124 was suspended following the Russian annexation of Crimea in 2014 and the ongoing tensions between Russia and Ukraine. In spite of repeated attempts by Ukraine to restart the An-124 production line, it appears that Antonov may not have the resources to restart An-124 production. For more information on this matter, see the 22 June 2016 article on the Defense Industry Daily website at the following link:

An-225 Mriya

The An-225 was adapted from the An-124 and significantly enlarged to serve as the carrier aircraft for the Soviet space shuttle, the Buran. The relative sizes of the An-124 and An-225 are shown in the following diagram, with a more detailed comparison in the following table.

An-124 & 225 planform comparisonAn-124 & -225 comparison. Source:

An-124 & 225 comparisonAn-124 & -225 comparison. Source:

The only An-225 ever produced made its first flight in December 1988. It is shown carrying the Buran space shuttle in the following photo.

AN-225 & BuranAn-225 carrying Buran space shuttle. Source:

After the collapse of the Soviet Union in 1991 and the cancellation of the Buran space program, the An-225 was mothballed for eight years until Antonov Airlines reactivated the aircraft for use as a commercial heavy-lift transport. In this role, it can carry ultra-heavy / oversize cargo weighing up to 250 metric tons (551,000 pounds).

An-225 gear downAn-225 Mriya. Source: AntonovAn-225 gear up

Surprisingly, it appears that the giant An-225 is about to enter series production. Antonov and Aerospace Industry Corporation of China (AICC) signed a deal on 30 August 2016 that will result in An-225 production in China. The first new An-225 could be produced in China as early as in 2019.

When it enters service, this new version of the An-225 will modernize and greatly expand China’s military and civil airlift capabilities. While it isn’t clear how this airlift capability will be employed, it certainly will improve China ability to deliver heavy machinery, bulk material, and many personnel anywhere in the world, including any location in and around the South China Sea that has an adequate runway.

For more information on this Ukraine – China deal, see the 31 August 2016 article by Gareth Jennings entitled, “China and Ukraine agree to restart An-225 production,” on the IHS Jane’s 360 website at the following link:

You’ll find more general information on the An-124 and An-225 on the Airvectors website at the following link:





Modern Airships – Part 1

This post was updated on 1 May 2019.

  1. Introduction

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 serving remote and/or unimproved sites
  • Persistent optionally-manned surveillance platforms
  • Maritime surveillance / search and rescue
  • Disaster relief, particularly in areas not easily accessible by other means
  • Unmanned aerial vehicle (UAV) / unmanned air system (UAS) carrier
  • Commercial flying cruise liner
  • Airship yacht

In spite of the significant interest, actual military, commercial and other customers have been slow coming to the marketplace with firm orders, the airship manufacturers have been slow in developing and delivering advanced airships that meet their customer’s needs, and funding was prematurely curtailed for several ambitious projects.  This uncertain business climate seems likely to change by the early 2020s, when several different heavy-lift airships are expected to be certified by airworthiness authorities and ready for mass production and sale to interested customers.

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:

In this article, Boris Pasternak, CEO of airship manufacturer Worldwide Aeros Corp., commented:

“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, this matter of “load exchange” (i.e., 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 for external ballast handling, while others require no such infrastructure.  The solution chosen for accomplishing a load exchange strongly influences how an airship can be operationally employed and where it can deliver its payload.

  1. 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.

There are three main types of powered airships: conventional, hybrid, and variable buoyancy / fixed volume.  The basic characteristics of each airship type are described below.

Basic characteristics of conventional airships

Conventional airships are lighter-than-air (LTA) vehicles that operate at or near neutral buoyancy.  Airships of this type include non-rigid blimps, rigid zeppelins, and semi-rigid airships. The lifting gas (helium) generate 100% of the lift at low speed, thereby permitting vertical takeoff and landing (VTOL) operations and hovering.  Various types of propulsors may be used for cruise flight propulsion and for low-speed maneuvering and station keeping.

  • Non-rigid airships (blimps): These airships have a flexible envelope that defines the shape of the airship, contains the lifting gas cells and ballonets, and supports the load of a gondola, engines and payload.
  • 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 structural framework that supports loads. A flexible envelope is installed over the structural framework and contains the lifting gas cells and ballonets.

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

  • Ballast: 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 require a corresponding ballast adjustment. If an airship is heavy and the desired buoyancy can’t be restored with the ballonets, ballast can be dumped in flight to increase buoyancy.
  • Lifting gas: Normally, there is no significant loss of lifting gas during flight.  If an airship is light and the desired buoyancy cannot be restored with the ballonets, it is possible to vent some lifting gas to the atmosphere to decrease static lift.
  • Ballonets:In conventional airships, the gas envelope is divided into a sealed main helium gas volume and separate gas volumes called “ballonets” that contain ambient air at atmospheric pressure. The ballonets are used to compensate for change in the volume of lifting gas and to make small changes in buoyancy by expanding or contracting the air volume to change the gross weight or the fore-and-aft trim of the airship.

On the ground, the ballonets may be inflated with air to make the airship negatively buoyant to simplify ground handling. To takeoff, the ballonets would be vented to the atmosphere, reducing the mass of air carried by the airship, allowing the helium gas volume to expand, and increasing buoyant lift.

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.

To descend, a fan is used to inflate the ballonets with outside air, adding mass and slightly compressing the helium into a smaller volume. This action decreases buoyant lift. As the airship continues to descend into the denser atmosphere, the helium gas volume continues to compress and the ballonets become proportionately larger.  Ballonet inflation 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:

Basic characteristics of hybrid airships

These are heavier-than-air (HTA) vehicles that are “semi-buoyant.”  This 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, inflated hybrid airship. Source: DoD 2012

General 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 helium gas volumes and separate 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 to adjust the roll angle.  While these airships are heavier-than-air, they still 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.  In some respects, these are semi-buoyant aircraft, with less buoyancy than the semi-rigid hybrid airships.  In exchange for the reduced buoyancy, handling on the ground is more like a conventional fixed-wing aircraft and load exchanges do not require external ballast.

Basic characteristics of variably buoyancy / fixed volume airships

 These are rigid airships that can become LTA or HTA, as the circumstances require.  These airships become heavier by compressing the helium lifting gas or ambient air:

  • Compressing the helium lifting gas into smaller volume tanks aboard the airship reduces the total lift generated by helium.
  • Compressing ambient air into pressurized tanks aboard the airship adds weight to the airship and thus decreases the net lift.

These airships become lighter by venting gas from the pressurized tanks:

  • Compressed helium lifting gas is vented back into the helium lift cells, increasing their volume and increasing lift.
  • Compressed air is vented to the atmosphere, reducing the weight of the airship and thus increasing net lift.

This buoyancy control process is accomplished without taking on external ballast or venting the lifting gas to the atmosphere.

General characteristics of variable buoyancy airships include the following:

  • Variable lift airships are capable of VTOL operations and hovering with a full load.
  • The buoyancy control system enables in-flight load exchanges from a hovering airship without the need for external ballast.
  • On the ground, variable lift airships can make themselves heavier-than-air to facilitate load exchanges without external infrastructure or ballast.
  1. The scale of large cargo airships

Some of the advanced airship concepts being developed, especially for future heavy cargo carriers, will result in extremely large air vehicles on a scale we haven’t 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 required for various lift applications. Source: DoD 2012

  1. Specific airships

Details on the airships listed in the following tables are provided in individual sections.

Megalifter, CargoLifter CL160, Project Walrus and SkyCat are included because they are of historical interest as early, though unsuccessful, attempts to develop very large cargo airships.  Concepts and technologies developed on these airship projects have promoted the development of other modern airships.

Among the airships in the above list, the following have actually flown: 

  • Zeppelin NT 07
  • Skybus 80K
  • Aeroscraft Dragon Dream
  • Hybrid Air Vehicles HAV-304
  • Hybrid Air Vehicles Airlander 10 prototype
  • Lockheed Martin P-791

As of May 2019, the Zeppelin NT 07 is the only advanced airship in this list that is flying regularly in commercial service. The others in the list are under development or remain as concepts only.

By the early 2020s, we likely will see several advanced airships on this list completing their development cycle and airworthiness certification.  The leading candidates seem to be:

  • Aeroscraft ML866 / Aeroscraft Gen 2
  • Airlander 10
  • Lockheed Martin LMH-1

Here are the links to the individual airships descriptions:

Conventional airships:

Variable buoyancy, fixed volume airships: 

 Hybrid (semi-buoyant) airships:


Bio-fuel at Less Than Half the Price

1.  New process for manufacturing bio-fuel

The Joint BioEnergy Institute (JBEI) is a Department of Energy (DOE) bioenergy research center dedicated to developing advanced bio-fuels, which are liquid fuels derived from the solar energy stored in plant biomass. Such fuels currently are replacing gasoline, diesel and jet fuels in selected applications.

On 1 July 2016, a team of Lawrence Berkeley National Laboratory (LBNL) and Sandia National Laboratories (SNL) scientists working at JBEI published a paper entitled, “CO2 enabled process integration for the production of cellulosic ethanol using bionic liquids.” The new process reported in this paper greatly simplifies the industrial manufacturing of bio-fuel and significantly reduces waste stream volume and toxicity as well as manufacturing cost.

The abstract provides further information:

“There is a clear and unmet need for a robust and affordable biomass conversion technology that can process a wide range of biomass feedstocks and produce high yields of fermentable sugars and bio-fuels with minimal intervention between unit operations. The lower microbial toxicity of recently developed renewable ionic liquids (ILs), or bionic liquids (BILs), helps overcome the challenges associated with the integration of pretreatment with enzymatic saccharification and microbial fermentation. However, the most effective BILs known to date for biomass pretreatment form extremely basic pH solutions in the presence of water, and therefore require neutralization before the pH range is acceptable for the enzymes and microbes used to complete the biomass conversion process. Neutralization using acids creates unwanted secondary effects that are problematic for efficient and cost-effective biorefinery operations using either continuous or batch modes.

We demonstrate a novel approach that addresses these challenges through the use of gaseous carbon dioxide to reversibly control the pH mismatch. This approach enables the realization of an integrated biomass conversion process (i.e., “single pot”) that eliminates the need for intermediate washing and/or separation steps. A preliminary technoeconomic analysis indicates that this integrated approach could reduce production costs by 50–65% compared to previous IL biomass conversion methods studied.”

 Regarding the above abstract, here are a couple of useful definitions:

  • Ionic liquids: powerful solvents composed entirely of paired ions that can be used to dissolve cellulosic biomass into sugars for fermentation.
  • Enzymatic saccharification: breaking complex carbohydrates such as starch or cellulose into their monosaccharide (carbohydrate) components, which are the simplest carbohydrates, also known as single sugars.

The paper was published on-line in the journal, Energy and Environmental Sciences, which you can access via the following link:!divAbstract

Let’s hope they’re right about the significant cost reduction for bio-fuel production.

2.  Operational use of bio-fuel

One factor limiting the wide-scale use of bio-fuel is its higher price relative to the conventional fossil fuels it is intended to replace. The prospect for significantly lower bio-fuel prices comes at a time when operational use of bio-fuel is expanding, particularly in commercial airlines and in the U.S. Department of Defense (DoD). These bio-fuel users want advanced bio-fuels that are “drop-in” replacements to traditional gasoline, diesel, or jet fuel. This means that the advanced bio-fuels need to be compatible with the existing fuel distribution and storage infrastructure and run satisfactorily in the intended facilities and vehicles without introducing significant operational or maintenance / repair / overhaul (MRO) constraints.

You will find a fact sheet on the DoD bio-fuel program at the following link:

The “drop in” concept can be difficult to achieve because a bio-fuel may have different energy content and properties than the petroleum fuel it is intended to replace. You can find a Department of Energy (DOE) fuel properties comparison chart at the following link:

Another increasingly important factor affecting the deployment of bio-fuels is that the “water footprint” involved in growing the biomass needed for bio-fuel production and then producing the bio-fuel is considerably greater than the water footprint for conventional hydrocarbon fuel extraction and production.

 A.  Commercial airline use of bio-fuel:

Commercial airlines became increasingly interested in alternative fuels after worldwide oil prices peaked near $140 in 2008 and remained high until 2014.

A 2009 Rand Corporation technical report, “Near-term Feasibility of Alternative Jet Fuels,” provides a good overview of issues and timescales associated with employment of bio-fuels in the commercial aviation industry. Important findings included:

  • Drop-in” fuels have considerable advantages over other alternatives as practical replacements for petroleum-based aviation fuel.
  • Alcohols do not offer direct benefits to aviation, primarily because high vapor pressure poses problems for high-altitude flight and safe fuel handling. In addition, the reduced energy density of alcohols relative to petroleum-based aviation fuel would substantially reduced aircraft operating capabilities and would be less energy efficient.
  • Biodiesel and biokerosene, collectively known as FAMEs, are not appropriate for use in aviation, primarily because they leave deposits at the high temperatures found in aircraft engines, freeze at higher temperatures than petroleum-based fuel, and break down during storage

You can download this Rand report at the following link

After almost two years of collaboration with member airlines and strategic partners, the International Air Transport Association (IATA) published the report, “IATA Guidance Material for Biojet Fuel Management,” in November 2012. A key finding in this document is the following:

“To be acceptable to Civil Aviation Authorities, aviation turbine fuel must meet strict chemical and physical criteria. There exist several specifications that authorities refer to when describing acceptable conventional jet fuel such as ASTM D1655 and Def Stan 91-91. At the time of issue, blends of up to 50% biojet fuel produced through either the Fischer-Tropsch (FT) process or the hydroprocessing of oils and fats (HEFA – hydroprocessed esters and fatty acids) are acceptable for use under these specifications, but must first be certified under ASTM D7566. Once the blend has demonstrated compliance with the relevant product specifications, it may be regarded as equivalent to conventional jet fuel in most applications.“

You can download this IATA document at the following link:

In 2011, KLM flew the world’s first commercial bio-fuel flight, carrying passengers from Amsterdam to Paris. Also in 2011, Aeromexico flew the world’s first bio-fuel trans-Atlantic revenue passenger flight, from Mexico City to Madrid.

In March 2015, United Airlines (UA) inaugurated use of bio-fuel on flights between Los Angeles (LAX) and San Francisco (SFO). Eventually, UA plans to expand the use of bio-fuel to all flights operating from LAX. UA is the first U.S. airline to use renewable fuel for regular commercial operation.

Many other airlines worldwide are in various stages of bio-fuel testing and operational use.

B.  U.S. Navy use of bio-fuel:

The Navy is deploying bio-fuel in shore facilities, aircraft, and surface ships. Navy Secretary Ray Mabus has established a goal to replace half of the Navy’s conventional fuel supply with renewables by 2020.

In 2012, the Navy experimented with a 50:50 blend of traditional petroleum-based fuel and biofuel made from waste cooking oil and algae oil.   This blend was used successfully on about 40 U.S. surface ships that participated in the Rim of the Pacific (RIMPAC) exercise with ships of other nations. The cost of pure bio-fuel fuel for this demonstration was about $26.00 per gallon, compared to about $3.50 per gallon for conventional fuel at that time.

In 2016, the Navy established the “Great Green Fleet” (GGF) as a year-long initiative to demonstrate the Navy’s ability to transform its energy use.

Great Green Fleet logo          Source: U.S. Navy

The Navy described this initiative as follows:

“The centerpiece of the Great Green Fleet is a Carrier Strike Group (CSG) that deploys on alternative fuels, including nuclear power for the carrier and a blend of advanced bio-fuel made from beef fat and traditional petroleum for its escort ships. These bio-fuels have been procured by DON (Department of Navy) at prices that are on par with conventional fuels, as required by law, and are certified as “drop-in” replacements that require no engine modifications or changes to operational procedures.”

Deployment of the Great Green Fleet started in January 2016 with the deployment of Strike Group 3 and its flagship, the nuclear-powered aircraft carrier USS John C. Stennis. The conventionally-powered ships in the Strike Group are using a blend of 10% bio-fuel and 90% petroleum. The Navy originally aimed for a 50:50 ratio, but the cost was too high. The Navy purchased about 78 million gallons of blended bio-fuel for the Great Green Fleet at a price of $2.05 per gallon.

C.  U.S. Air Force use of bio-fuel:

The USAF has a goal of meeting half its domestic fuel needs with alternative sources by 2016, including aviation fuel.

The Air Force has been testing different blends of jet fuel and biofuels known generically as Hydrotreated Renewable Jet (HRJ). This class of fuel uses triglycerides and free fatty acids from plant oils and animal fats as the feedstock that is processed to create a hydrocarbon aviation fuel.

To meet its energy plan, the USAF plans to use a blend that combines military-grade fuel known as JP-8 with up to 50 percent HRJ. The Air Force also has certified a 50:50 blend of Fisher-Tropsch synthetic kerosene and conventional JP-8 jet fuel across its fleet.

The Air Force Civil Engineer Support Agency (AFCESA), headquartered at Tyndall Air Force Base, Florida is responsible for certifying the USAF aviation fuel infrastructure to ensure its readiness to deploy blended JP-8/bio-fuel.