Category Archives: Commercial aviation

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

Background

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 / 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). 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:

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

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

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:

http://www.airbus.com/presscentre/pressreleases/press-release-detail/detail/-9b32c4364a/

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: https://en.wikipedia.org/wiki/Airbus

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

Source: https://en.wikipedia.org/wiki/Boeing_Commercial_Airplanes

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: aviatorjoe.net

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: aircharterservice.com

An-124_takeoffAn-124-100. Source: aircharterservice.com

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:

http://www.defenseindustrydaily.com/more-an124s-on-the-way-antonov-signs-agreement-with-key-customers-02913/?utm_source=Sailthru&utm_medium=email&utm_campaign=Military%20EBB%206-22-16&utm_term=Editorial%20-%20Military%20-%20Early%20Bird%20Brief

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: Airvectors.com

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

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: fcba.tumblr.com

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:

http://www.janes.com/article/63341/china-and-ukraine-agree-to-restart-an-225-production

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

http://www.airvectors.net/avantgt.html

 

 

 

 

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:

https://www.newyorker.com/magazine/2016/02/29/a-new-generation-of-airships-is-born

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:  zeppelinfan.de

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:

 

How Long Does it Take to Certify a Commercial Airliner?

After designing, developing, and manufacturing a new commercial airliner, I’m sure the airframe manufacturer has a big celebration on the occasion of the first flight. The ensuing flight test and ground static test programs are intended to validate the design, operating envelope, and maintenance practices and satisfy these and other requirements of the national certifying body, which in the U.S. is the Federal Aviation Administration (FAA). Meanwhile, airlines that have ordered the new aircraft are planning for its timely delivery and introduction into scheduled revenue service.

The time between first flight and first delivery of a new commercial airliner is not a set period of time. As you can see in the following chart, which was prepared by Brian Bostick (http://aviationweek.com/thingswithwings), there is great variability in the time it takes to get an airliner certified and delivered.

Time to certify an airliner

In this chart, the Douglas DC-9 has the record for the shortest certification period (205 days) with certification in November 1965. The technologically advanced supersonic Concorde had one of the longest certification periods (almost 2,500 days), with authorization in February 1976 to conduct a 16-month demonstration period with flights between Europe and the U.S. before starting regular commercial service.

The record for the longest certification period goes to the Chinese Comac ARJ21 twin-jet airliner, which is the first indigenous airliner produced in China. The first ARJ21 was delivered to a Chinese airline in November 2015. The ARJ is based on the DC-9 and reuses tooling provided by McDonnell Douglas for the licensed production of the MD-80 (a DC-9 variant) in China. I suspect that the very long certification period is a measure of the difficulty in establishing the complete aeronautical infrastructure needed to deliver an indigenous commercial airliner with an indigenous jet engine.

In the chart, compare the certification times for the following similar commercial airliners:

  • Four-engine, single aisle, long-range airliners: Boeing 707 (shortest), Douglas DC-8, Convair CV-880, Vickers VC-10, De Havilland Comet (longest)
  • Three-engine, single aisle, medium range airliners: Boeing 727 (shorter), Hawker Siddeley Trident (longer)
  • Two-engine, single aisle airliners: Douglas DC-9 (shortest), Boeing 737, Boeing 757, Airbus A320, British Aircraft Corporation BAC 1-11, Dassault Mercure, Caravelle (longest)
  • Two-engine, single aisle, short range regional jets: Embraer ERJ 145 (shortest), Bombardier CRJ-100, BAe 146, Fokker F-28, ERJ 170, Bombardier CS Series, Mitsubishi MRJ, Sukhoi Superjet, VFW-614, Comac ARJ21 (longest)
  • Four-engine, wide-body, long-range airliners: Boeing 747, Airbus A340, Airbus A380 (longest)
  • Three-engine, wide-body, long-range airliners: Douglas DC-10 (shorter), Lockheed L-1011 (longer)
  • Two-engine, wide-body airliners: Boeing 767 (shortest), Boeing 777, Airbus 350, Airbus A300, Boeing 787 (longest)

Time is money, so there is tremendous economic value in minimizing the time between first flight and first delivery. The first 16 aircraft at the top of the chart all enjoyed relatively short certification periods. This group, which includes many aircraft that appeared in the 1960s – 70, averaged about 400 days between first flight and first delivery.

More modern aircraft (blue bars in the chart representing aircraft appearing in 2000 or later) have been averaging about 800 days between first flight and first delivery (excluding ARJ21).