Airways Top 10 Never-built Commercial Aircraft

The second half of the 20th century saw aircraft manufacturers design airliners with extreme characteristics.



February 2, 2023

DALLAS — From the 1950s to the early 2000s, the airline industry was in a race for supremacy. This was due to the trend of the growing hub-and-spoke model at the time. The idea was that there would be many little airports with airplanes transporting people to big super-airports connected by jumbo jets.

Due to the limited capacity of airports to accommodate more planes departing at the same time, aircraft manufacturers began developing larger planes to fit more passengers, allowing for more planes to depart without overcrowding the airports.

The following list is not ranked in any particular order, so we'll begin with the Tupolev Tu-404, which is an example of an extremely large jet project that has been built and abandoned due to the limited capacity of airports to accommodate more planes departing at the same time.

Tupolev Tu-404

The Tupolev Tu-404, an astronomically large Russian project from the early 1990s, is what you get when you quadruple the size of the Airbus A380 and add Aeroflot livery. It came from a school of thought that praised the development of massive double-decker aircraft.

As we all know, the lone offspring of this theory, the magnificent A380, flew less amid the pandemic, with the last superjumbo rolling out of the Airbus plant last year, and those ideas went nowhere. However, the bright models and plans that are marveled at and then forgotten at air shows contain a large number of others.

The large jet airliner designed by the Tupolev Design Bureau in the late 1970s was intended to be a flagship aircraft for Soviet airlines, providing seating for up to 350 passengers. However, the project was eventually abandoned due to the high cost of development and the limited capacity of airports to accommodate more planes departing at the same time. As a result, the Tupolev Tu-404 never entered production, and only a few prototypes were ever built.

Although the majority of Tupolev's civil aircraft were military derivatives—the Tu-114, Tu-124, and Tu-104 and their modifications—the desire to compete in Western markets necessitated the development of airliners from the ground up. The Tu-154, a marginally successful rival to the Boeing 727, emerged in this manner.

The type would be obsolete by the early 1980s, prompting the development of the Tu-204, the first and only example of the final generation of Soviet planes.

Saab 107 wind tunnel model, courtesy of TDL 2016. Photo: Giru-XX - Own work, CC BY-SA 4.0

Saab 107

The Saab 107 was a series of small aircraft designed by Saab AB of Sweden but never produced. The SAAB 1071 and SAAB 1073 were two feeder liner types that Svenska Aeroplan AB was working on from 1966 to 1968, with a planned maiden flight date of 1973.

The design goals for both concepts were to reduce production and operating costs, as well as airport turnaround times. SAAB decided to compete with terrestrial transit in both areas after conducting extensive market research.

A model of the SAAB 1071 was displayed at the Hannover air show in April 1968, and model images and illustrations of both concepts appeared in the specialized press around the same time. Project 10 was canceled because Saab needed international partners to help with development costs, but none were forthcoming.

The SAAB 1071 was designed to fly between domestic hub airports and minor domestic airfields over extremely short distances. The proposition included the aircraft having a high wing with a rectangular shape, a pressurized circular fuselage with room for 40 passengers, and four turboprop engines with an 800 horsepower rating.

The expected development expenses were 100 million SEK, while the maximum unit sales prices were 5 million SEK. For future use, it would be simple and inexpensive to lengthen the wings and fuselage. Simple, single-pivoted slot flaps were installed on the wing to provide maximum lift for short takeoffs within an 800 m runway. Reversing the thrust of the propellers was meant to shorten the landing distance.

The second SAAB 1073 project was designed for passenger and freight transportation on slightly longer domestic routes between airports with 1200 m or longer runways. Because of this, the STOL requirement was less stringent, and the design had two turbofans in nacelles beneath the high wing's moderate wing sweep. The elevator was maintained away from the exhaust jets by the T-tail.

The proposed turbofans, a pair of Rolls-Royce Trent engines with a thrust rating of 10,000 lb, could carry up to 80 passengers. The final sales price was set at a maximum of SEK15m, with development costs estimated at SEK300m. This concept would have required both public support and collaboration with a major foreign aircraft manufacturer.

Wind tunnel at the Fábrica Militar de Aviones (FMA), Córdoba. Photo: S/D -, Public Domain

FMA IA 36 Cóndor

Kurt Tank created the IA 36 Cóndor for the "Fábrica Militar de Aviones" in the early 1950s as an Argentine jet-powered mid-range aircraft. No prototypes were built, and only a full-size wooden mockup remained. 

In late 1951, a team led by German engineer Kurt Tank began work on the IA 36 Cóndor project, which included the construction of a 1:1 scale wooden fuselage mock-up and a 1:34 scale wind tunnel model. The project would be abandoned in 1958 by the Pedro Eugenio Aramburu-led administration.

The FMA IA Cóndor was intended to be replaced in later versions with lighter and more powerful engines. Five Rolls-Royce "Nene II" turbojets arranged in an annular configuration around the rear fuselage, as in the Messerschmitt P.1110 and Heinkel He 211, would have powered the proposed aircraft.

The aircraft's top speed was expected to be 950 km/h (590 mph), while the top speed of the de Havilland Comet 3 at the time was 780 km/h. The design would have accommodated 32 to 40 passengers (480 mph).

The IA 36 had sweeping wings, similar to Tank's Pulqui II fighter prototype, which increased aerodynamic effectiveness. The range was predicted to be 5,000 kilometers, and the wingspan was 34 meters (112 feet) (3,100 mi; 2,700 NMI).

Sukhoi KR-860. Images: From the site, Fair use,

Sukhoi KR-860

The Sukhoi KR-860 "Wings of Russia," formerly known as the SKD-717, was a double-decker wide-body superjumbo jet that Sukhoi, a Russian aerospace manufacturer, wanted to build. At the 2000 Paris Air Show, a model on a 1/24th scale was displayed. 

The design had a payload capacity of roughly 300 metric tons, a maximum weight of about 650 metric tons, 12 seats with three aisles on the main deck, and 9 abreast seats with two aisles on the top deck. It was designed to accommodate between 860 and 1000 people.

Conventional fuselage doors or the forward and aft ventral escalators would be used for entry. Winglets and a fold-outboard of the outer engine were features of the wing design. The Antonov An-225 had a payload capacity of 250 tonnes and a maximum weight of 640 tonnes. At the 1999 Paris Air Show, a model on a 1/24 scale was displayed. The plane would have been the biggest, widest, and heaviest airliner in the entire world if it had been built. 

The first design for the aircraft was developed in the 1990s, with a projected program cost of US$10bn (earlier published figures were US$4-5.5bn) and a target delivery date of 2000 for the first aircraft.

The market was predicted to support a total of 300 aircraft with an estimated cost per unit of between US$160m and US$200m (an earlier estimate was US$150m), with manufacture set to take place at the Kazan Aircraft Production Association facility. A KR-860T (T stands for Tanker) version, which was later proposed for use as an airborne liquefied natural gas (LNG) tanker for far-north locations, was originally created for the carriage of passengers.

The concept suggested using LNG to fuel the turbines rather than normal jet fuel, like on the Tupolev Tu-206, to take advantage of the presence of LNG on the aircraft. 

The project did not move past the marketing model stage.

3-view line drawing of a Boeing Sonic Cruiser, redrawn from Fig. 15 of US Patent 6,575,406 B2 (granted June 10, 2003). Image: Mliu92 - Own work, CC BY-SA 4.0

Boeing Sonic Cruiser 

The Boeing Sonic Cruiser was a proposed jet airliner with a delta wing-canard arrangement. Because of its delta wing and a high subsonic cruising speed of up to Mach 0.98, it stood out from ordinary airliners. When Boeing first proposed the Sonic Cruiser in 2001, airlines favored lower operational costs over faster travel.

The purpose of many preliminary research and development programs that started in the 1990s at Boeing was to examine prospective designs for a possible new near-sonic or supersonic airliner. On March 29, 2001, the Sonic Cruiser was made public shortly after rival Airbus' A380 went on sale.

When not enough airlines expressed interest, Boeing's idea of the 747X derivative as a competitor to the A380 was abandoned, instead offering the Sonic Cruiser as an entirely different strategy.

The Sonic Cruiser was built for quick point-to-point connections for 200 to 250 people rather than the A380's enormous capacity, which necessitates a hub and spoke model of operation. Critics said that Boeing timed their announcement in an effort to divert attention from the A380's takeoff.

Smaller supersonic and subsonic business jets, various tail and engine locations, inlet and outlet configurations, and what Boeing called a "modular" system where the cruise speed could be changed from supersonic to near-sonic by an interchangeable nose—the "Sonic Cruiser" was a near-sonic variant—were all included in the range of delta wing-canard concepts studied in detail in Boeing's 2001 patent.

Boeing would abandon the Sonic Cruiser project in December 2002 in favor of the 7E7, a slower (Mach 0.85) and more fuel-efficient airliner that would ultimately be known as the 787 Dreamliner. 

Aerocon Dash-1.6 wingship

The Aerocon Dash-1.6 wingship was a ground-effect vehicle designed in the United States that could travel enormous distances at near-aircraft speeds while transporting massive loads and thousands of passengers.

The vehicle was advertised as carrying 2,000 passengers and 1,500 short tons of cargo (3,000,000 lb; 1,400,000 kg) over a distance of 11,500 miles (18,500 km; 10,000 NMI) at commercial aircraft speeds.

The US Defense Advanced Research Projects Agency (DARPA) conducted a preliminary analysis of the concept in the 1990s to determine the viability of a $1 billion program to develop a wingship for military applications. The Aerocon design was evaluated alongside submissions from a number of other manufacturers as part of this analysis.

The Department of Defense stopped providing funds for the design at the end of 1994 after determining it to be too risky.

Lockheed A380

Before the A380, Lockheed Martin had a concept for a double-decker super transport aircraft. In 1996, a crazy plane was developed that was larger than a 747, could carry more people than an A380, and would have ruled the skies.

Boeing had established the pattern with the 747, and Airbus was following suit with the A340 series. Lockheed Martin decided to consider the next logical step in aircraft development after abandoning the L1011 trijet design. They devised the Large Subsonic Transport scheme, a collection of drawings for a plane that would be the logical next step after the Boeing 747.

In addition to addressing the issue of restricted airport capacity, this aircraft would naturally meet growing demand in countries like China and serve as the US air force's next military aircraft as its fleets of transport vehicles near retirement. 

For long-haul flights, they aimed for a passenger capacity of about 800 people, with the option of turning it into a freighter.

It had a takeoff weight of 1.4 million pounds, or 635 metric tonnes, and four powerful engines. Similar to the Boeing 777X of today, it had foldable wingtips that reduced its wingspan from 282 feet (85 m) to 211 feet (64 m), the same as a Boeing 747. With a length of 262 feet, it was one of the longest planes in existence at the time (79 meters).

Later, Lockheed Martin admitted that it lacked the resources and expertise required to build the plane. It implies that bringing it to market would necessitate a collaboration between Boeing and Airbus, with a total development cost of US$18bn.

MD-12. Image: Anynobody - Own work, CC BY-SA 4.0

McDonnell Douglas MD-12

In the 1990s, McDonnell Douglas created the MD-12, a large wide-body airplane concept. It was designed as a quad-jet airliner at first but was later expanded to be a trijet larger than the MD-11. The MD-12 was designed to carry more passengers than the Boeing 747 due to its two full-length passenger decks.

McDonnell Douglas looked into improved, stretched variants of the MD-11 trijet under the moniker MD-12X, which may have a lower front passenger deck with panoramic windows. The MDC board of directors decided to make the MD-12X design available for airlines in October 1991. The MD-12X measured 237 feet 11 inches (72.5 meters) long and 212 feet 6 inches wide (64.8 m).

A Memorandum of Understanding to establish a business to build the new design was signed in November 1991 between Taiwan Aerospace Corporation and McDonnell Douglas.

The biggest shareholder in the new corporation would be McDonnell Douglas (51%), followed by Taiwan Aerospace (40%) and other Asian businesses (9%).

However, no orders were placed for the MD-12, so the project was canceled.

Boeing 747X

With two decks down the length of the aircraft and seating for more than 650 passengers, this proposed Boeing 747X from the 1990s would not only be the largest passenger aircraft in the sky, but it would also put an end to Airbus' ambitions to create its own double-decker.

Although Boeing never produced the 747X, the legend of the aircraft served as the basis for rumors about the company's upcoming new massive aircraft for many years.

Boeing chose to build a single-deck 747 with a hump-shaped cockpit on a second level primarily to allow for the addition of a front cargo door for potential freighter conversions; passengers on a second deck were an afterthought.

Boeing would review the double-deck design concept in 1993. The American manufacturer witnessed not only the development of double-deckers by Airbus and its competitor MD, but also the global expansion of air travel. Airlines needed aircraft that could transport as many passengers as possible because increased air travel meant increased airport congestion and a shortage of landing slots.

Boeing predicted that this market would require 2,500 airlines with more than 350 seats between 1990 and 2005, and they already had the order book to do so. Their 747-400 had received an astounding 382 orders in just five years, including 130 in 1990.

A promotional model of the Hawker Siddeley HS.141 airliner project is on display at the de Havilland Heritage Centre. Photo: Nimbus227 - Own work, Public Domain

Hawker Siddeley HS.141

The Hawker Siddeley HS.141 came about from a design study and submission for a British V/STOL aircraft, which is an airplane able to take off or land vertically or on short runways, in the 1970s. Neither a prototype nor a finished aircraft was made after Hawker Siddeley Aviation's design and wind tunnel testing. 

Calculations demonstrated that a typical take-off and landing flight profile covered a "noise footprint" of 20 square miles (50 km2) along an airport's runway using a limit of 90 decibels. With V/STOL aircraft, this footprint could be reduced to three square miles by using an approach path of six degrees (double the usual angle) and a climb-out path of fifteen degrees (8 km2).

By the late 1970s, it was anticipated that this type of STOL operation would be available at British metropolitan airports. VTOL operations were anticipated to start in the early 1980s, with the goal of further reducing the noise footprint to a circle with a circumference of just 3,000 ft. 

It was recommended for the HS.141 to climb vertically to a height of 250 feet (76 meters), then reduce power to 83% to continue climbing to a height of 1,000 feet (300 m). After converting to forward flight at this altitude using vectored thrust from the lift engines, the aircraft would accelerate and rise to 2,000 ft (600 m) using increasing thrust from the cruise engines.

The aircraft would be entirely supported by its wings alone at this point, having reached an airspeed of 168 knots (310 km/h), with the lift engines shut off and concealed by hinged doors. The technique was essentially inverted for an approach to a vertical landing, with the approach starting at 2,000 feet (600 meters) and 4 miles (6.4 km) from the landing location. 

Despite Hawker Siddeley's investment of time and money, the project was doomed by a lack of interest in civil VTOL operations and the abandonment of lift engine development.

Featured image: Artist's impression of the MD-12. Image: Anynobody - Own work, CC BY-SA 4.0