Lowering fuel consumption, reducing emissions and causing less noise are the targets for the future of aviation as the standard means of transport over longer than regional distances, available and affordable to a growing part of mankind. A continuous advance in aerodynamics, aircraft’s structure, engine development and air traffic management (see the chapter The Flight/ Safety+ATM) is essential. However, some proposals were surprising and the fanciful pictures are not published here. In 1983 a book has praised a study for NASA of a twin-fuselage plane for 2,000 passengers. But if twin-fuselage is so advantageous, why do the birds not have two bodies? Another study showed a plane, the wing being replaced by a ring, expected by experts flying in the year 2000. They waited in vain. Another surprising proposal was published by Air & Space in 2015: A helicopter-like body should be driven by some 16 fans, electrically-powered by batteries for short-distance flights. It reminds us of some media’s science fiction, seeing already flying motorcars falling out of the skies. By contrast, electric high-speed trains are successful. In 2015 Aerospace America has reported simulator trials by the German Aerospace Center and NLR of Amsterdam, studying midair refueling of airliners. The report commented that it “may seem like a fanciful notion.” Indeed, who would board such an airliner?

Concerning the engines, an increase in bypass ratio was envisioned with the open rotor development, but being noisy, it was considered doubtful for standard airliners. In 2012 Flight Intl informed about General Electric tests, hoping that around 2030 an open-rotor narrowbody fulfilling the noise criteria could be possible. A drawing showed a plane with two engines placed in a U-shaped tailfin. A realistic target for lowering fuel consumption has become the geared turbofan, enabling “the turbine in the core engine to run efficiently at high speed while the fan runs efficiently and quietly at low speed”, as Aerospace America reported it. In Jan 2016 it informed: “Pratt & Whitney’s PW1100-JM engine is the first of the new breed….”

A structure that gives high stiffness at low weight is a target. After composite materials, nanotechnology had become a magic word and Wikipedia (2012) explained: “Nanotechnology is the manipulation of matter on an atomic and molecular scale (…).” Reducing drag by reducing the size of aircraft surfaces is another NASA target. Also a reduction in skin friction drag by laminar flow has become a target. The Airbus A340-300 F-WWAI was prepared as “Breakthrough Laminar Aircraft Demonstrator in Europe”. A study in a Mach0.75 short-to-medium range plane for 180 passengers by Northrop-Grumman under the title SELECT has shown a conventionally shaped plane, not sensational, but nice. A NASA/ MIT study showed a ‘double bubble’ design concept with a very wide fuselage to provide extra lift, the engines being placed in the rear. Another MIT study is the H-Series hybrid wing body, the embedded engines in the rear. Other studies for subsonics showed a much larger wingspan than conventional aircraft, e.g. the ‘Stratolaunch’, to be powered by 6 engines – surprising in an epoch when the A380 and the B.747-8 programs had to struggle for survival.

A fuel-efficient revolution? This was a headline of Aerospace America in January 2013, describing NASA’s FWP (formerly Subsonic Fixed Wing Program) goal of reducing energy consumption by at least 60%, for entering service in 2035-2040. NASA engineer James Felder noted that larger fans “yield higher propulsive efficiency”, but underwing-mounted they would increase aircraft’s weight. Felder’s team focused on the propulsion TeDP, using turbine engines “to drive the rotating parts of superconducting generators, which would be mounted on each wingtip (…). This DC current would be cross-fed to an array of superconducting motors (…) on top of the rear fuselage” of the N3-X hybrid wing body. “Felder’s team says the N3-X TeDP configuration would be at least 20% more fuel-efficient than the N3-A HWB design …” On the other hand, with Boeing’s N3-A version after all 50% fuel-burn savings became targeted, without any uncertainty.

NASA N3-X study (NASA, via Wikipedia)

X-43A anticipation (courtesy NASA)

Supersonic?
When NASA and Tupolev decided for tests with the Tu-144 RA-77114, development of the “Hyperjet” for Mach2 and 300 passengers was announced, but the project was considered economically unrealistic. A 1998 NASA study showed a beautiful delta-winged aircraft with a conventional tailfin, the four engines in individual pods placed beneath the wing, maintenance-friendly. In 1995 the magazine ‘Airways’ had published a statement by renowned R.E.G. Davies, considering that the development cost of a supersonic passenger jet at the technological level of the 90s would be around $20 billion, with estimated 1st-class tariffs resulting in a need of only 9, theoretically 36 aircraft, far-away from the break-even point. In 2008 NASA issued contracts for its next generation of aircraft, the so-called N+1, N+2 and N+3. A beautiful delta-winged Boeing Icon II with a V-shaped tail, for Mach1.6 to 1.8 and 120 passengers was described (by Periodico K, August8, 2010) being envisioned for 2035. NASA set goals to reduce the effective perceived loudness (PLdb) in decibels from over 110 to around 70, but there is the problem that a decrease in sonic boom is increasing the drag. On the engine sector, variable-cycle engines with bypass burner would be an advance compared to the 2707-300 project decades ago. According to Aerospace America (Feb 2011), “TEAL Group and NASA agree the most likely market, at least through the next two decades, is for (supersonic) business jets” – not a matter of this survey.

Hypersonic US Defense Studies
After President George W. Bush had announced in 2004 his vision of a Mars exploration, development of air-breathing hypersonics subsequently was confined more or less to defense projects. For the legendary X-15, which has reached an altitude of more than 100km already in 1963, see the main chapter To Space. NASA’s X-43 “Hyper-X” program became a scaled-down successor of earlier space plane projects. In 2004 Mach9.8 was achieved. The USA has obtained superiority in scramjet propulsion with the X-43A program and its successor, the Boeing X-51 scramjet engine demonstrator, known as the WaveRider, scaled-down unmanned scramjet test vehicles. Another matter of the U.S. Air Force is the unmanned Space Plane X-37B, which was launched by an Atlas V rocket in April 2010 and returned after 220 days. The HTV-3X for Mach6 was to be powered by a turbine engine and scramjet, an “all-in-one powerplant”, as Wikipedia reported it. In contrast to those NASA, DARPA and Air Force experiments, hypersonics for commercial use – at present unrealistic - must be submitted to ecological considerations.

A Soviet hypersonic design (official sources)

Boeing Icon II (courtesy NASA, Boeing)

Hyper in Russia?
A revelation by a Soviet Marshal of Aviation in a Bulgarian military newspaper in 1988 was commented by Aerospace America (Jan 1989): “He showed interest in hypersonic aircraft for surveillance and interception (…) this caused Ward and others at General Dynamics to evaluate a hypersonic wind tunnel model seen at the 1987 Paris Air Show to assess Soviet high speed technology. The Tupolev design was for a Mach5-6 transport that (…) could carry 300 passengers over 4,500 miles (…). The configuration points to methane fuel since not enough volume is available for hydrogen with the large passenger cabin”. The book ‘Russian Aircraft’ of 1995 by Bratukhin has described a two-stage aerospace project “Burlak”, consisting of a Tu-160 bomber and “a solid-propellant missile, created by the ‘Raduga’ Design Bureau.” Another system “being currently developed is a multi-purpose aviation-space system (MASS …). The first stage comprises the An-225 aircraft and the second stage the ‘Buran’ orbital craft and an expendable external fuel tank.” This project, MAKC in Russian orthography, should have got a one-stage successor: “In Russia the research conducted in this line is aimed at designing a Tu-2000 experimental nonexpendable aviation-space (…) tailless aircraft, having a delta wing (…), powered by ramjet engines operating on liquid hydrogen (…). The Tu-2000 can be used as a basic aircraft for the creation of a hypersonic passenger aircraft.” It was compared to America’s NASP project – which already was cancelled, like the Tu-2000 being too ambitious for the time.

Studies in Europe
In Europe, LAPCAT (Long-term Advanced Propulsion Concepts and Technologies) was funded under the European Commission’s Framework programs. The LAPCAT A2 proposal for a Mach3-5 jet for 300 passengers was published in 2008, showing a plane of twice the length compared to an Airbus A380, delta-winged with the 4 engines in an under-wing position. The turbine-based combined cycle (TBCC) Scimitar engines use gas turbine technology with incorporation of heat exchangers in the main thermodynamic circle and scramjet bypass burner. For the next generation, LAPCAT focused on reaction engines researches using hydrogen fuel. Hydrogen would make any project independent on limited crude oil or on biofuel attempts, but since the “Hindenburg” explosion, caused by gaseous hydrogen, reports have spread anxiety.

In any case, if the necessary fuel efficiency can be achieved, it’s by subsonic, not by supersonic or hypersonic technology, as long as completely new energetics are not available. Years ago the well-known Teal Group senior analyst Richard Aboulafia has commented (quoted from Aerospace America, Feb 2011): “Mass supersonic transport is brain dead; the only way to make it happen is a fully socialistic environment, which is why the U.S. stepped away when NASA canceled its program in the 1960s.”

X-30 anticipation (courtesy NASA, via Wikimedia)

X-30 inspiration (McDonnell Douglas)

“Orient Express” and Ambitions
In 1986 U.S. President Reagan had announced the “Orient Express” – a transatmospheric vehicle (TAV) that could “by the end of the next decade take off from Dulles Airport and accelerate up to 25 times the speed of sound, attaining low-earth orbit or flying to Tokyo within 2 hours” (The Wall Street Journal, Feb13, 1986). In that year NASA and the industry joined in the X-30 program. McDonnell Douglas was advertising: “Kid’s stuff, because it’s your kids, and ours, who will gain most of the advances in material technology required to build the X-30 National AeroSpacePlane, forerunner of the Orient Express.” In 1994 the Congress canceled the NASP program.

Since 1952 American taxpayers have spent more than a billion dollar for SST projects, stopped on economic reasons. The competing Concorde could not cover the development cost, despite fares up to $20,000. Nevertheless supersonic dreams continued and a report by Sueddeutsche Zeitung (Dec10, 2016) listed a multitude of studies, from newcomer ‘Boom’ to a 120-seater of Lockheed-Martin and a 150-seater of Boeing, whereupon Volker Gollnick of Deutsches Zentrum fuer Luft- und Raumfahrt (DLR) was quoted: “It is not at all discernible that such a large supersonic plane would now have a market chance.” So the AS2 project of Aerion shows a Mach1.5 private jet for only 12 passengers. Spike Aerospace published the S-512 project for only 18 passengers, described by SZ: “Instead of looking out of a window, passengers in the Spike cabin are staring at monitors, installed all round.” Boom Technology presented the project of a nice Mach2.2 55-seater, delta-winged and twin-engined, optimistically announced for 2023, ordered already by daring Sir Richard Branson. Surprisingly, Japan Airlines showed interest.

Astronauts see earth, moon and stars from the upper stratosphere – other than hypersonic business travelers. Airbus cast doubts with a study of a Mach4.5 plane for 20 passengers, in 5km altitude to be shot upward, vertically. The still more daring DLR Spaceliner, to be coupled to a detachable recoverable booster, “would launch from Frankfurt vertically, like an ICBM. Its 50 passengers would experience several minutes of weightlessness, after which the vehicle would glide down to land horizontally in Sydney” (after 90 minutes), informed the Air & Space report of September 2009. A nice drawing showed it even with windows. However, why go to Australia with its 20 million inhabitants and not to the powerhouse China with more than 1.4 billion people? The other above-mentioned report informed that a ‘Skreemr’ should be “catapulted by a so-called Railgun …” It reminds us of Jules Verne’s ‘Columbiade’ canon, shooting Man to the Moon…

Supersonic, not to speak of hypersonic, was considered by R.E.G. Davies, the late curator of the National Air & Space Museum, being merely an episode – compare his last book ‘Airlines of the Jet Age’ (Smithsonian, 2011). Nobody knows when the oil reserves will be exhausted, nevertheless researches in other chemical fuels had started already decades ago – see the chapter Ecology + Energy. Nuclear fission is too hazardous for Earth and atmosphere. “Big plans for compact fusion”, that was another headline – see the main chapter To Space. At the beginning of the 21st century, analyst James Halstead of Aviation Financial Consulting (quoted by the Business Time Singapore) had summarized the progress during the 20th century since invention of the jet aircraft: “Historically the industry has been able to develop because the equipment has got faster, more efficient and larger, so unit costs of carrying the average passenger fell.” The beauty of the classic jetliner, based on the principle of the Boeing 707, is a result of all the development. Nevertheless revolutions in science could give birth to the icon of future …


Airbus A340, Lufthansa, Munich 2015 (WS)


Airbus A340-642, South African Airways, Cape Town 2004 (WS)


Flying over the Mediterranean (WS)