Delta

Delta (pronounced del-tuh)

(1) The fourth letter of the Modern Greek alphabet (Δ, δ).

(2) The consonant sound represented by this letter.

(3) The fourth in a series of items.

(4) Anything triangular, an allusion to the Greek capital delta (Δ).

(5) In mathematics, an incremental change in a variable, as Δ or δ.

(6) A nearly flat plain of alluvial deposit between diverging branches of the mouth of a river, often, though not necessarily, triangular.

(7) A word used in communications to represent the letter D (usually initial capital letter); Used in the ICAO (International Civil Aviation Organization) radiotelephony spelling alphabet (usually known as the NATO phonetic alphabet).

(8) In astronomy, a star that is usually the fourth brightest of a constellation (initial capital letter).

(9) In computing, a small but noticeable effect or the set of differences between two versions of a file; in informal use, a small but noticeable effect.

(10) In surveying, the angle subtended at the centre of a circular arc.

(11) A type of cargo bike that has one wheel in front and two in back.

(12) In electrical engineering (often attributive), the closed figure produced by connecting three coils or circuits successively, end for end, especially in a three-phase system.

(13) In finance, the rate of change in an option value with respect to the underlying asset's price.

(14) In chemistry, a value in delta notation indicating the relative abundances of isotopes or relating to or characterizing a polypeptide chain that is one of five types of heavy chains present in immunoglobins.

(15) In aerodynamics, a type of wing.

(16) The NATO code name for a class of Soviet nuclear-powered ballistic missile submarine armed with sixteen multi-warhead missiles.

(17) In physics, of or characterizing the atom or radical group that is fourth in position from the functional group of atoms in an organic molecule.

(18) In US Space Force use, a unit, nominally headed by a colonel, equivalent to a USAF operations wing, or an army regiment.

(19)   In electrical engineering, the closed figure produced by connecting three coils or circuits successively, end for end, especially in a three-phase system.

Circa 1200: From the Middle English deltha from the Latin delta from the Ancient Greek δέλτα (délta), from the Phoenician dalet & daleth (tent door).  It was akin to the Hebrew dāleth.  It was the fourth letter of the Greek alphabet (equivalent to the Modern English D) and was shaped like a triangle (Δ).  The sense of a delta being a "triangular island or alluvial tract between the diverging branches of the mouth of a great river" is because the Ancient Greek writer Herodotus (circa 484–circa 425 BC) used it to describe the mouth of the Nile River (now known as the Nile Delta).  That was picked up in English during the 1550s and applied to other river mouths (often of quite different shapes) by 1790.  The related forms are deltaic and deltification.  In pre-modern medicine, the deltoid muscle (the large muscle of the shoulder; triangular, resembling the Greek letter delta) was described in 1758, the name from the Ancient Greek deltoeides (triangular, literally "shaped like the letter delta).  In modern use, the "deltoid muscle" gained the short-form “delts” in 1977.  The related form is deltoidal.

The delta-wing

Gloster Javelin (1951-1967).  The first twin-engined delta-wing in service, the Javelin was the UK’s long-term solution to its need for an all-weather interceptor, the post-war technology gap until then filled by the stop-gap Gloster Meteor and that most improbable cold-war fighter, the de Havilland Mosquito.  The Javelin was the last aircraft to bear the Gloster name, the company absorbed into the morass created by the mergers, acquisitions and nationalization that befell British industry between Attlee and Thatcher. 

In aviation, the delta shape pre-dated aircraft by centuries, triangular stabilizing fins for rockets described in the sixteenth and seventeenth centuries and the first lifting wing in delta form patented in 1867 for use by a dart-shaped, rocket-propelled airplane.  However, although there were prototypes and much theoretical work was done during the first half of the twentieth century, it wasn’t until the late-1940s when jet propulsion made possible high-speed subsonic and supersonic flight that it was possible to build airframes which could take advantages of the delta-wing’s unique properties.

Lockheed SR-71 Blackbird (1963-1999).  A product of Lockheed’s Skunk Works, although in development as a high-altitude interceptor since 1959, the US government didn’t admit the SR-71 existed until 1964 and decided ultimately to use it for reconnaissance and research into supersonic flight.  The SR-71 in 1976 set the world record for the fastest flight by an air-breathing manned aircraft and the mark still stands.

The delta form offers structural advantages and aerodynamic characteristics suited to the fluid dynamics of airflow in supersonic conditions.  To suit different applications, design variations have evolved, with and without additional stabilizing surfaces.  The long root chord of the delta wing and minimal structure outboard is inherently structurally efficient, able to be built stronger and stiffer yet lighter than a swept wing of equivalent lifting capability.  It’s thus simple and relatively inexpensive to build.

Avro Vulcan (1956-1984).

Until the UK adopted the submarine-launched Polaris missile system, the Vulcan was the platform for the UK’s independent nuclear deterrent and it remained in service long enough to be deployed for its only combat mission, a flight of five aircraft used for (conventional bombing) missions during the 1982 Falklands War.  Each aircraft flew almost 4000 miles  (6,500 km) from Ascension Island, Victor tankers used for the air-to-air refueling, almost 1.1 million gallons (5 million litres ) of fuel burned each mission.

The long root chord also allows a deeper structure for a given aerofoil section, providing more internal volume for fuel and other storage without a significant increase in drag although, on supersonic designs, designers often take the opportunity to use a thinner aerofoil instead, thereby further reducing drag.  Usefully, the large root chord also provides a large surface area which assists in reducing the minimum speed; a low landing speed being a design objective in most military and civil applications.  Delta wings can be designed to induce vortex lift, so flow separation can be turned into a means of increasing lift and the whole structure is naturally stable in pitch, therefore not requiring a separate tail surface.

Aérospatiale/BAC Concorde (1969-2003).

The Anglo-French supersonic passenger jet operated commercially between 1976-2003.  Flying at twice the speed of sound and carrying up to 128 passengers, it was the longest lasting of its time, the Soviet Tupolev Tu-144 in passenger service only for a few years during the 1970s after which it operated both as a freighter and a research platform and the American SST never progressed beyond engineering mock-ups.  The Americans worked out the economics were never going to make sense; the Soviets had a different relationship to money and the Concorde lasted as long as it did only because the French & British governments wrote-off the development costs.

There are drawbacks.  The large wing area creates more viscous drag for the same amount of lift compared to a high aspect ratio wing; swept wings have a better lift-to-drag ratio than deltas.  Also, high-lift devices like fowler flaps are hard to integrate into delta wings with the rearward location of the trailing edge producing intolerable pitching moments when such flaps would be deflected.  In short, delta wings are superior only in supersonic flight; their best known design probably the Anglo-French Concorde.

Lindsay Lohan in delta skirts.

A delta skirt is characterized by its triangular shape, an allusion to the Greek letter delta (Δ); almost always, a delta skirt is fitted at the waist, flaring out towards the hem, creating the triangular silhouette.  The concept is adaptable and can be made from just about any fabric, the most popular including cotton, taffeta, silk and a variety of other synthetics.  Delta skirts tend to be shorter because to produce the triangular effect as length increases either some sort of internal structure is required or additional material needs to be used, increasing bulk and weight.  Although most associated with younger women, they have been adopted by a number sub-sets from the anime aesthetic, Goths and bohemians to hippies.

Ogee

Ogee (pronounced oh-jee)

(1) A double curve, resembling the letter S, consisting of two arcs that curve in opposite directions so that the ends are parallel.   An ogee is a kind of sigmoid curve, technically formed by the union of a concave and a convex line.

(2) In architecture, a molding with such a curve for a profile; cyma, also called gula or talon.

(3) In fluid mechanics, a specific aerodynamic profile.

(4) In mathematics, an inflection point.

(5) In cosmetic surgery, a desired shape for the curve of the malar or cheekbone prominence transitioning into the mid-cheek hollow.

(6) In distillation, the bubble-shaped chamber of a pot still connecting the swan neck to the pot which allows distillate to expand, condense and fall back into the pot.

1275-1325: From the Middle English ogeus (plural oggez), ogeve, egeve & egeove, variants by assimilation from the French oggif (diagonal rib of a vault) from the Old French œgive, ogival, ogive & augive, from the Late Latin augiva of uncertain origin.  In the Late Latin there was ogis (a support, prop), thought derived from the Classical Latin augeō (to increase, strengthen) from which Spanish gained auge (highest point of power or fortune; apogee); a doublet of ogive.  The use in architecture to describe regular & irregular S-shaped moldings began in the 1670s, supplanting the earlier augive, from the Late Latin augiva of uncertain origin but perhaps related to the Latin via (way; road).  In the Middle English, the late thirteenth century ogif was "a stone for the diagonal rib of a vault", derived from the French and the Medieval Latin ogiva.

An Ogee arch.

An ogee is a curved shape vaguely like an “S”, consisting of two arcs that curve in opposite senses, so that the ends are tangential.  In architecture, it’s used to describe a molding with a profile made by a lower concave arc flowing into a convex arc.  Used first in Persian and Greek architecture from Antiquity, it’s most familiar now as a part of the Gothic style.  Because the upper curves of the ogee arch are reversed, it’s not suitable where the load-bearing rates are high and it’s thus used mostly in self-supporting structures exposed to their own weight and not subject to high external forces.

An inflection point.

In mathematics, an ogee is an inflection point, a point on a curve at which the sign of the curvature (ie the concavity) changes; inflection points may be stationary but are neither local maxima nor local minima.  Inflection Points merely mark the point on the curve where it changes from concave upward to concave downward (or vice versa), it is not a directional measure.  Calculus is needed to find where a curve goes from concave upward to concave downward and for this mathematicians use derivatives, one which determines the slope and a second which defines whether the slope increases or decreases.

The cosmetic surgeon's template.

When cosmetic surgeons speak of the ogee curve, they’re referring to the elongated S curve which, when looking at a patient’s face at a three-quarter aspect, describes the curve from the eye through the cheek down to below the cheek (technically the malar or cheekbone prominence transitioning into the mid-cheek hollow).  As people age, the face loses volume in our face and the ogee curve flattens out. With facelifts and related procedures, the cosmetic surgeon aims to create an ogee curve, restoring the chiseled refinement of youth.

Lindsay Lohan, Cosmopolitan, October 2022 edition (photographs by Ellen Von Unwerth (b 1954)).  The photographs illustrate the ideal ogee curve in the facial structure and Ms Lohan shows how a model's pout can be used to optimize the effect.  The car is a second generation AMC Javelin (1971-1974).

Shapes derived from the ogee curve are popular design motifs used for just about everything where they can be applied but it's most associated with large, flat surfaces because it's in such spaces the geometric repetition can be most effective, thus the prevalence in fabrics, wallpaper and floor-coverings.  The mind visualizes the shape as something like a two-headed onion and it's probably the association with the architectural style so often seen on mosques or other structures in the Arab world that in there's presumed to be some Islamic influence but ogee long pre-dates Islam.  There are few conventions of use except that the designs tend to be displayed in either a horizontal or vertical aspect; diagonal deployment is rare.

In fluid mechanics, the ogee describes the shape used to create certain aerodynamic profiles, the classic example being the delta wing of the Concorde airplane.  The ogee-type wing used on the Concorde one flavor of the compound delta (sometimes called double delta or cranked arrow) where the leading edge is not straight.  Typically the inboard section has increased sweepback, creating a controlled high-lift vortex without the need for a foreplane and the shape of the sweepback is defined by the parameters of the ogee.  On the Concorde, the two sections and cropped wingtip merge into a smooth ogee curve.

Diversity

Diversity (pronounced dih-vur-si-tee (U) or dahy-vur-si-tee (non-U))

(1) The state or fact of being diverse; difference; unlikeness; nonuniformity.

(2) The inclusion of individuals representing more than one national origin, color, religion, socioeconomic stratum, sexual orientation etc.

(3) In mathematical logic, the relation that holds between two entities when and only when they are not identical; the property of being numerically distinct.

(4) In politics, the social policy of encouraging tolerance for people of different cultural and racial backgrounds

(5) In politics as multiculturalism or more specific legislation mandating diversity, an attempt to redress historic discrimination.

(6) In biology, as biodiversity, the degree of variation of life forms within an ecosystem.

(7) In zoological taxidermy, as species diversity, the effective number of species represented in a data set.

(8) In genetics, as genetic diversity, the total number of genetic characteristics in the genetic makeup of a species.

(9) In agriculture, as crop diversity, the variance in genetic and phenotypic characteristics of plants used in agriculture.

(10) In electronic communications, the principle of the deployment of multiple channels or devices to improve reliability.

(11) In electrical engineering, as diversity factor, the ratio of the sum of the maximum demands of the various part of a system to the coincident maximum demand of the whole system.

(12) In law, a term often used in equal-opportunity legislation when codifying specific metrics.

1300–1350: From the Middle English diversite (originally "variety; range of differences" and by the late fourteenth century "quality of being diverse, fact of difference between two or more things or kinds; variety; separateness; that in which two or more things differ" (usually in a technical or neutral sense), from the Old French diversité (difference, diversity, unique feature, oddness (and when used in a degoratory sense "wickedness, perversity; contradiction") (which survives in the Modern French as the twelfth century diversité), from the Latin diversitatem (nominative dīversitās) (contrariety, wickedness, perversity, disagreement (and in a secondary sense "difference, diversity")), the construct being  diversus (past particle of divertere) (contradiction, difference; turned different ways (and in Late Latin "various") +‎ tas.  The Latin tas suffix was from the primitive Indo-European tehts, from the Ancient Greek της (tēs) and Sanskrit ताति (tāti).  In English, the construct uses the suffix ity which is used to form abstract nouns indicating a state of being.  Suffix is from the Middle English ite, a borrowing from the Old French ité and directly from the Latin itatem (nominative itas).  As used as a suffix denoting state or condition, in Latin it was built with a connective i + tas.  Fowler’s Modern English Usage (1926) notes that in English, a word with the ity suffix usually means the quality of being what the adjective describes, or concretely an instance of the quality, or collectively all the instances whereas a word with an ism appended means the disposition, or collectively all those who feel it.  Diversity is a noun, diverse is an adjective (and collective a noun) and diversely is an adverb; the noun plural is diversities.

Diversity: The path to DEI

Diversity had the distinct negative meaning "perverseness, being contrary to what is agreeable or right; conflict, strife; perversity, evil" in English from late fourteenth century but was obsolete after the seventeenth (although the twenty-first century critiques of wokeness and political correctness has seen "diversity" again used in this way in certain quarters).  Diversity as a virtue in the political construction of nation-states was an idea which grew as modern democracies developed in the decades after the French Revolution (1789) because it was thought essential to prevent one faction from arrogating all power (and discussed in The Federalist (now usually called The Federalist Papers) 85 essays published in 1788 and written by some of the Founding Fathers of the United States to advocate ratification of the constitution).  The word however was also used under the Raj where many of the British colonial "fixes" (at which they excelled) used existing divisiveness (which they encouraged and sometimes even created) as part of the principle of "divide & rule".  Diversity under the Raj was real, cross-cutting and multi-layered but for from the modern sense in which ethnicity, gender and sexual identity are the typical determinates, this use emerging as now understood in the early 1990s, the original purpose being to provide for the "inclusion and visibility of persons of previously under-represented minority identities".

Projecting diversity: Lindsay Lohan in rainbow T-shirt, the T-shirt of the T-shirt created through Yoshirt's portal.

Although the use of diversity (in a positive sense) as applies to race, gender etc. appears to date only from 1992, the term "affirmative action", as government policy designed to promote or achieve diversity in various aspects of life, was first used in an executive order signed by US President Kennedy in 1961.  That was a decree which required that government contractors "…take affirmative action to ensure applicants are employed, and employees are treated during employment, without regard to their race, creed, color, or national origin".  Such policies have become widespread, especially since the 1980s and, in the west, are applied exclusively for the benefit of groups or individuals thought disadvantaged.  Beyond the west, other countries have adopted such policies although sometimes they’re applied for the benefit of a defined majority.  Increasingly, in the US, affirmative action policies are being challenged, sometimes by groups themselves defined as "diverse".

To demonstrate a corporate commitment to workplace DEI (diversity, equity and inclusion), always include a brunette in photos. 

In the West, not all approve of diversity positive initiatives.  In March 2018, the University of Sydney Union issued a statement noting the application of an affirmative action policy to its debating team would promote diversity and prevent domination by “affluent, white, privately educated students”.  The union’s press release was prompted by a report in the Murdoch press that the new affirmative action policies will mean the university would be sending not necessarily its best team to the annual debating tournament, but one “…meeting quotas for women, people of colour, and others oppressed by the white male supremacy”.

Former senator Eric Abetz

Anxious always to expose conspiracies by communists, LGBTQQIAAOP agitators, Trotskyists, trade unionists and other malcontents, then Senator Eric Abetz (b 1958; senator for Tasmania (Liberal) 1994-2022) labelled the move “Stalinist dogma’’ dressed up as progressive thinking, adding the union’s move was evidence of “stifling political correctness’’ which threatened to “damage the future generations who are taught this nonsense as fact’’.  The former senator was perhaps not someone good at recognizing white privilege or understanding its implications for those from diverse backgrounds but he did take a Churchillian stand defending the nation when the Gay and Lesbian Kingdom of the Coral Sea Islands declared war on Australia so there's that.

The young ladies of Alpha Gamma Delta: ἐννέα κόραι, ἑπτὰ αὐτῶν ξανθαί (ennéa kórai, heptà autôn xanthai).

Alpha Gamma Delta (ΑΓΔ and clipped usually to "Alpha Gam") decided to adopt “DEI best practice” in choosing their webpage banner, including not one but three brunettes.  Dating from 1904 when the first chapter was founded at New York’s Syracuse University, AGD is an international women's fraternity and social organization with over 200,000 members, some 200 collegiate chapters and over 250 alumnae groups.  There is an on-line shop (Alpha Gam Boutique) with lines of hats, T-shirts, stoles, tank-tops & such and there's the helpful facility of "custom chapter orders".

Concord & Concorde

Concord or Concorde (pronounced kon-kawrd)

(1) Agreement between persons, groups, nations, etc.; concurrence in attitudes, feelings, etc; unanimity; accord; agreement between things; mutual fitness; harmony.

(2) In formal grammar, a technical rule about the agreement of words with one another (case, gender, number or person).

(3) A treaty; compact; covenant.

(4) In music, a stable, harmonious combination of tones; a chord requiring no resolution.

(5) As concordat, under Roman-Catholic canon law, a convention between the Holy See and a sovereign state that defines the relationship between the Church and the state in matters that concern both.

(6) In law, an agreement between the parties regarding land title in reference to the manner in which it should pass, being an acknowledgment that the land in question belonged to the complainant (obsolete).

(7) A popular name for locality, commercial operations and products such as ships, cars etc.

(8) In horticulture, a variety of sweet American grape, named circa 1853 after Concord, Massachusetts, where the variety was developed.

1250-1300: From the Middle English and twelfth century Old French concorde (harmony, agreement, treaty) & concorder, from the Latin concordare & concordia, (harmonious), from concors (of the same mine; being in agreement with) (genitive concordis (of the same mind, literally “hearts together”)).  The construct was an assimilated form of com (con-) (with; together) + cor (genitive cordis (heart) from the primitive Indo-European root kerd (heart)).  The "a compact or agreement" in the sense of something formal (usually in writing) dates from the late fifteenth century, an extension of use from the late fourteenth century transitive verb which carried the sense "reconcile, bring into harmony".  From circa 1400 it had been understood to mean "agree, cooperate, thus a transfer of sense from the Old French & Latin forms.  Concorde was the French spelling which eventually was adopted also by the British for the supersonic airliner after some years of linguistic squabble.  Concord is a noun & verb, concordance & concordat are nouns, concorded & concording are verbs and concordial & concordant are adjectives; the noun plural is concords.

The Concorde and other SSTs

Promotional rendering of Concorde in British Overseas Airways Corporation (BOAC) livery.  BOAC was the UK's national carrier between 1940-1974 when merged with British European Airways (BEA) to form British Airways (BA).

Concorde was an Anglo-French supersonic airliner that first flew in 1969 and operated commercially between 1976-2003.  It had a maximum speed over twice the speed of sound (Mach 2.04; 1,354 mph (2,180 km/h)) and seated 92-128 passengers.  Man breaking the sound barrier actually wasn’t modern; the cracking of a whip, known for thousands of years, is the tip passing through the sound barrier and engineers were well aware of the problems caused by propellers travelling that fast but it wasn’t until 1947 that a manned aircraft exceeded Mach 1 in controlled flight (although it had been achieved in deep dives though not without structural damage).  The military were of course immediately interested but so were those who built commercial airliners, intrigued at the notion of transporting passengers at supersonic speed, effectively shrinking the planet.  By the late 1950s, still recovering from the damage and costs of two world wars, France and the UK were never going to be in a position to be major players in the space-race which would play-out between the US and USSR but civil aviation did offer possibilities for both nations to return to the forefront of the industry.  France, in the early days of flight had been the preeminent power (a legacy of that being words like fuselage and aileron) and UK almost gained an early lead in passenger jets but the debacle of the de Havilland Comet (1949) had seen the Boeing 707 (1957) assume dominance.  The supersonic race was thought to be the next horizon and the UK’s Supersonic Transport Aircraft Committee (STAC) was in 1956 commissioned with the development of a Supersonic Transport (SST) for commercial use.

Concordes exist in a number of flight simulator programs; this is Colimata's Concorde v1.10 in BA livery.

The committee’s early research soon established it was going to be an expensive undertaking so the UK sought partners; the US declined but in 1962 the UK and France signed the Anglo-French Concorde agreement, a framework for cooperation in the building of the one SST.  The choice of name actually came some months after the engineering concord was signed, the manufacturers submitting to the UK cabinet the names Concord and Concorde, it being thought desirable to have something which sounded and meant the same in both languages (the French had already agreed it shouldn’t be called the Super-Caravelle the project name for a smaller SST on which some work had been done in 1960).  The other suggestions put to cabinet were Alliance or Europa.  In the cabinet discussions in London, Alliance was thought to be "too military" and Europa offended those Tories who still hankered for the "splendid isolation" which had been the British view on European matters in the previous century.  Even in the nineteenth century age of Pax Britannica splendid isolation had been somewhat illusory but in the Tory Party the words still exerted a powerful pull.  

The French-built Concorde 001's roll-out, Toulouse Blagnac airport, 11 December 1967.

There is some dispute about whether the cabinet ever formally agreed to use the French spelling but, like much in English-French relations over the centuries, the entente proved not always cordial and the name was officially changed to Concord by UK Prime Minister Harold Macmillan (later First Earl Stockton, 1894–1986; UK prime-minister 1957-1963) in response to him feeling slighted by Charles de Gaulle (1890-1970; President of France 1958-1969) when Le President vetoed the UK’s application to join the European Economic Community (the EEC which evolved into the present Day EU of which the UK was a member between 1973-2020).  However, the Labour party won office in the 1964 general election and by the time of the roll-out in Toulouse in 1967, the UK’s Minister for Technology, Tony Benn (Anthony Wedgwood Benn, 1925–2014, formerly the second Viscount Stansgate) announced he was changing the spelling back to Concorde.  There were not many eurosceptics in the (old) Labour Party back then.

Concorde taking off, 1973 Paris Air Show, the doomed Tupolev Tu-144 in the foreground.

The engineering challenges were overcome and in 1969, some months before the moon landing, Concorde made its maiden flight and, in 1973, a successful demonstration flight was performed at the same Paris air show at which its Soviet competitor Tupolev Tu-144 crashed.  Impressed, more than a dozen airlines placed orders but within months of the Paris show, the first oil shock hit and the world entered a severe recession; the long post-war boom was over.  A quadrupling in the oil price was quite a blow for a machine which burned 20% more fuel per mile than a Boeing 747 yet typically carried only a hundred passengers whereas the Jumbo could be configured for between four and five hundred.  That might still have been viable had have oil prices remained low and a mass-market existed of people willing to pay a premium but with jet fuel suddenly expensive and the world in recession, doubts existed and most orders were immediately cancelled.

Three of the greatest landmarks of the analogue era: Space shuttle Enterprise (OV-101, the first orbiter, used for atmospheric test flights and never flew in space) atop NASA 905 SCA (Shuttle Carrier Aircraft, one of two modified Boeing 747s used to ferry shuttles from landing sites back to the Kennedy Space Center in Florida and a BA (British Airways) Concorde taking off, Paris Air Show, 1983.

Concorde 002 on public display at BAC's (British Aircraft Corporation) airfield, Filton, Bristol, site of its construction.

Eventually, only twenty were built, operated only by BOAC (BEA/BA) and Air France, early hopes of mass-production never materialized; while orders were taken for over a hundred with dozens more optioned, the contracts were soon cancelled.  By 1976 only four nations remained as prospective buyers: Britain, France, China, and Iran; the latter two never took up their orders and by the time Concorde entered service, the US had cancelled their supersonic project and the Soviet programme was soon to follow.  Even without the oil shocks of the 1970s and the more compelling economics of wide-bodied airliners like the Boeing 747, there were problems, the noise of the sonic boom as the speed of sound was exceeded meaning it was impossible to secure agreement for it to operate over land at supersonic speed.  Accordingly, most of its time was spent overflying the Atlantic and Pacific and BA and Air France sometimes made profit from Concorde only because the British and French governments wrote off the development costs.  Concorde was an extraordinary technical achievement but existed only because the post-war years in the UK and France were characterised by national projects undertaken by nationalised industries.  Under orthodox modern (post Reagan cum Thatcher) economics, such a thing could never happen. 

Concorde F-BTSC (Air France Flight 4590), Charles de Gaulle Airport, Paris, France, 25 July 2000.

On 25 July 2000, Air France Flight 4590, bound for New York, crashed on take-off out of Paris, killing all 109 on board and a further four on the ground. It was the only fatal accident involving Concorde, the cause determined to be debris on the runway which entered an engine, causing catastrophic damage.  In April 2003, both Air France and British Airways announced that they would retire Concorde later that year citing low passenger numbers following the crash, the slump in air travel following the 9/11 attacks and rising maintenance costs.

Lindsay Lohan in The Parent Trap (1998)

Fictional works are usually constructed cognizant of physical reality and technological innovations have always influenced what's possible in plot-lines.  The cell phone for example offered many possibilities but also rendered some situations either impossible or improbable (although Hollywood has sometimes found either of those no obstacle in a screenplay).  The retirement of Concorde also had to be noted.  Not only had it long been used as a symbol of wealth but there was also the speed so plot-lines which included the relativities of the duration of commercial supersonic versus subsonic trans-Atlantic travel were suddenly no loner possible.  Lindsay Lohan's line in The Parent Trap (1998) since 2003 (and for the foreseeable future) is a "stranded relic" of the Concorde era.     

Tupolev Tu-144 (NATO reporting name: Charger).

The Tu-144 was the USSR’s SST and it was the first to fly, its maiden flight in 1968 some months before Concorde and sixteen were built.  It was also usually ahead of the Anglo-French development, attaining supersonic speed twelve weeks earlier and entering commercial service in 1975 but safety and reliability concerns doomed the project and its reputation never recovered from the 1973 crash.  The Soviet carrier Aeroflot introduced a regular Moscow-Almaty service but only a few dozen flights were ever completed, the Tu-144 withdrawn after a second crash in 1978 after which it was used only for cargo until 1983 when the remaining fleet was grounded.  It was later used to train Soviet cosmonauts and had a curious post-cold war career when chartered by NASA for high-altitude research.  The final flight was in 1999.

Boeing 2707.

While perfecting supersonic military aircraft during the early 1950s, Americans had explored the idea of SSTs as passenger aircraft and had concluded that while it was technically possible, in economic terms such a thing could never be made to work and that four-engined jets like the Boeing 707 and Douglas DC8 were the future of commercial aviation.  However, the announcement of the development of Concorde and the Soviet SST stirred the Kennedy White House into funding what was essentially a vanity project proving the technical superiority of US science and engineering.  Boeing won the competition to design an SST and, despite also working on the 747 and the space programme, it gained a high priority and the 2707 was projected to be the biggest, fastest and most advanced of all the SSTs, seating up to three-hundred, cruising at Mach 3 and configured with a swing-wing.  Cost, complexity and weight doomed that last feature and the design was revised to use a conventional delta shape.  But, however advanced US engineering and science might have been, US accountancy was better still and what was clearly an financially unviable programme was in 1971 cancelled even before the two prototypes had been completed.

Lockheed L-2000.

Lockheed also entered the government-funded competition to design a US SST.  Similar to the Boeing concept in size, speed and duration, it eschewed the swing-wing because, despite the aerodynamic advantages, the engineers concluded what Boeing would eventually admit: that the weight, cost and complexity acceptable in military airframes, couldn’t be justified in a civilian aircraft.  As the military-industrial complex well knew, the Pentagon was always more sanguine about spending other people's money (OPM) than those people were about parting with their own.  Lockheed instead used a slightly different compromise: the compound delta.  After the competition, Boeing and Lockheed were both selected to continue to the prototype stage but in 1966 Boeing’s swing-wing design was preferred because its performance was in most aspects superior and it was quieter; that it was going to be more expensive to produce wasn’t enough to sway the government, things being different in the 1960s.  Reality finally bit in 1971.

Depiction of a Boom Overture in United Airlines livery.

In mid-2021 US carrier United Airlines (UA) announced plans to acquire a fleet of fifteen new supersonic airliners which they expected to be in service by 2029.  It wasn’t clear from the press release what was the most ambitious aspect of the programme: (1) that Colorado-based Boom (which at the time had not achieved supersonic flight), would be able by 2029 to produce even one machine certified by regulatory authorities for use in commercial aviation, (2) that the aircraft would be delivered at close to the budgeted US$200 million unit cost, (3) that what United describe as “improvements in aircraft design since Concorde” will eliminate, reduce or mitigate (all three have at various times been suggested) the effects of the sonic boom, (4) that it won’t be “any louder than other modern passenger jets while taking off, flying over land and landing”, (5) that sufficient passengers will be prepared to pay a premium to fly at Mach 1.7 in a new and unproven airframe built by a company with no record in the industry or that (6) Greta Thunberg (b 2003) will believe Boom which says Overture will operate as a "net-zero carbon aircraft".

Looking sceptical: Greta Thunberg.

The suggestion was the Overture will run on "posh biodiesel", made from anything from waste cooking fat to specially grown high-energy crops although whether this industry can by 2029 be scaled-up to produce what will be required to service enough of the aviation industry to make either project viable isn’t known.  Still, if not, Boom claimed "power-to-liquid" processes by which renewable energy such as solar or wind power is used to produce liquid fuel will make up any shortfall.  Boom does seem a heroic operation: they expect the Overture to be profitable for airlines even if tickets are sold for the same price as a standard business-class ticket.  One way or another, the flight-path (figuratively and literally) of the Boom Overture follows is going to become a standard case-study in university departments although whether that's in marketing, engineering or accountancy might depend matters beyond Boom's control.

Boom XB-1 in subsonic flight.

Boom’s progress can’t however be denied because on 10 February, 2025, its XB-1 “proof of concept” test platform accomplished what orthodox physics once deemed impossible.  On that day if flew over California’s Mojave Desert at speeds beyond the sound barrier without generating a sonic boom, the announcement surprising some sceptics but doing little to quell the doubts among analysts unable to build models which show a sustained profitable life for the project.  What Boom did with the XB-1 was use an implementation of “Mach cut-off” technology which exploits atmospheric conditions by manipulation, redirecting shock waves upward rather than toward the ground.  This is achieved by operating the airframe in a certain four-dimensional envelope (a window created by specific atmospheric conditions within a certain height range up to a certain speed).  Flying within these parameters, the airframe minimizes the unwanted effects of pressure waves, dispersing them without forming the concentrated pressure front that creates the dreaded sonic booms.  Whatever the sceptical economic modelers may conclude, it was an impressive display of Boom’s technology and engineering with the ground-level impact eliminated, at least in the ideal, controlled conditions of a test flight.

Scripps Climate Physics explains Mach Cut-Off.

What the economists noted was the XB-1 was able to achieve the much vaunted “silent-supersonic” at around 1,200 km/h (750 mph) and the math indicates the means to implement Mach cut-off when travelling faster (certainly the 2,100 km/h (1300 mph; Mach 1.7) which apparently remains Boom’s target) doesn’t yet exist, even at the level of theory.  On land, sea or air, for centuries what has determined commercial viability is the speed-cost trade-off and notional profitability was for at least some of Concorde’s years of operation achieved because it offered a quicker trans-Atlantic flight-time (typically the Concorde at Mach 2.04 (1,350 mph, 2,180 km/h) would take 3 hours 30 minutes while at Mach 0.85 (565 mph, 910 km/h), a Boeing 747 would need 7-8 hours).  In truth that profitability was a fudge subsidized by taxpayers (a remarkably common phenomenon in modern capitalism) because the French & British governments “wrote off” the development costs (some Stg £1.3 billion by the late 1970s at a time when a billion pounds was still a lot of money and even that may have been a deliberate under-estimate to conceal the true cost which has been estimated (in 2023 Sterling value terms) as high as Stg£21 billion).

Boom XB-1 taking off.

Rich customers or those with tickets paid for by OPM (other people’s money) were prepared to pay the significant premium charged for a seat on Concorde just to avoid sitting an additional 4-5 hours on a wide-bodied subsonic aircraft and that’s the market Boom is interested in for a trans-continental (New York City (NYC) to Los Angeles (LA)) US service.  Subsonic flight times on the NYC-LA route are typically 5-6 hours while Boom will be able to achieve that in under two hours if their silent subsonic plans can be realized; that would mean the road transport components of a trip elements to and from the NYC & LA airports could be longer than the time in the air.  If able to offer a 3-4 hour reduction in NYC-LA travel time, genuinely that’s a marketing advantage but one which can be leveraged only if there are enough customers willing (with the required frequency) to spend somebody’s money to fill the seats of UA’s 15 silentsonics.  If, as Boom once indicated to venture capitalists (VC) and others (JAL (Japan Airlines has reportedly invested US$10 million), the tickets on the NYC-LA route would retail at around the subsonic business-class level, then few doubt their model will work but it remains to be seen whether what’s necessary can be achieved (1) by 2029 or (2) ever.  Hopefully, Boom does succeed so delta-winged supersonics can make a (quieter) return to the skies though it’ll be a shame if the marketing department insisted on changing the corporate name to something like “Boomless”, “No Boom”, “Boom-Free” or whatever.  “Boom” is a really good name for an aviation outfit has some history in the field, “Boom” the nickname of Marshal of the Royal Air Force Hugh Trenchard (First Viscount Trenchard, 1873–1956) who was instrumental in the formation of Britain’s RAF (Royal Air Force) although he gained the moniker because of the tone of his voice rather than anything to do with fluid dynamics.