Archives for the month of: April, 2025

The Overture Alliance

April 25, 2025 //

The Past & The Present

Global GDP in 2003, the year Concorde retired was $38 Trillion. In 2024 the same was $105 Trillion. The total number of air passengers in 2003 was 1.7 billion and the same in 2024 was 9.5 billion. In 2003 routes over 10 hours were unheard of, Singapore Airlines launched its non stop to Los Angeles from Singapore in 2003. Today such routes are taken for granted.

The numbers above suggest the nature of air travel has changed over the last 22 years. More people are traveling longer, more frequently and more people have more money to spend on air travel.

The air travel landscape that Overture will inherit is very different from the one Concorde left behind.

The Alliance

The single biggest advantage of an alliance is synergy. Synergy across Network. Synergy across operations and synergy across product (fares, lounges, loyalty programs and much more). More on this later.

Globally there are three airline alliances The Star Alliance, Oneworld & SkyTeam..

The alliances have directly been responsible for stimulating air travel by offering seamless travel over longer distances to more people than ever before.

Range

Over the last 22 years ultra long haul aircraft have taken over several premier fleets of the World. These aircraft have reset travelers’ expectations to ‘ direct nonstop flights’.

During supersonic flight the rate of fuel burn is three times that of subsonic flight and the Overture’s range of 4250 nm (nautical miles) looks puny compared to the range of Over 9000 nm for most modern ultra long haul aircraft.

What the Overture might lack in range, it makes up in speed.

Passenger expectations however do not change, the speed becomes an added layer to the expectation.

Enter the Overture Alliance.

Concorde Pool History

Concorde production ceased in 1979 and a total of 14 were built, seven each for British Airways and Air France.

Both airlines entered into a parts pool program to keep costs down.

The pool program was responsible for keeping the aircraft flying until 2003, as parts became scarce in later years.

The Concorde alliance was localized as it involved two airlines belonging to neighboring countries in Europe.

The Overture will birth into a truly Global World and we can expect airlines from around the World to feature on the Overture probables list.

Overture Probables

The Overture currently has three confirmed airlines .The first two are American players, they are United and American Airlines. The third is Japanese, and it is Japan Airlines.

Who might the other probables be?

A tentative list might like this:

The Concorde operators:

British Airways – Low

Over the last twenty years British Airways has gone down the route of fleet optimization and post Concorde have turned away from SST. But you never know.

It bears mentioning that Qatar Airways (also on the probable list) owns 25% of IAG (International Airline Group) the parent company of British Airways and other airlines such as Iberia, Aer Lingus,LEVEL and Vueling

British Airways traditionally ran the New York and Barbados routes from London and both routes are well within the reach of the Overture. In addition to most of Continental North America.

Range in Nautical Miles from London Heathrow.

Air France – Moderate

Of the two Concorde operators Air France might be higher on the probable list. They have embarked on a fleet renewal strategy and the Overture might make sense as AIr France looks to differentiate itself on the European Business and Leisure market. In fact AF 4590 (the Concorde crash of 2000 at Paris) was a charter carrying passengers (most of them German) to New York, where they were to join a Cruise to Ecuador.

The Overture reach from Paris is similar to that from London.

The Concorde Marketer:

Singapore Airlines – Moderate

Between 1977 & 1980 Singapore Airlines entered into a partnership with British Airways to fly the SIN – BAH – LHR v v route. The aircraft was painted with both liveries one on each side and each airline was responsible for selling their own side. The partnership had several issues and died a natural death in 1980.

This partnership did highlight Singapore Airlines’ Supersonic aspirations and Overture presents exactly this.

The Overture range allows Singapore to have non stop routes across Australia, China and their traditional stronghold Japan, Korea and gives them non stop reach into the Middle East and slightly beyond into Eurasia.

The Wisher

Virgin Atlantic – High

Richard Branson the founder of Virgin Atlantic is a longtime admirer of Concorde. In 1996 he made a highly publicized attempt to lease Concordes from British Airways. His argument being the British Government had subsided the development of Concorde and British Airways should not have monopoly on it.

In 2003 as Concorde’s retirement was announced, Branson once again offered to lease / buy them and first offered one pound per aircraft going as high as five million pounds per aircraft. He even had Concorde models produced in Virgin livery and distributed globally.

In 2016 Virgin entered into an agreement with BOOM for the purchase of 10 Overture aircraft, however this agreement has since expired and Branson turned his attention to Virgin Galactic, sending tourists to space.

The probability of Virgin coming back remains high even though nothing has been announced.

The Virgin Atlantic range footprint for the Overture is the same as British Airways.

The ME3

Qatar Airways – High

Qatar Airway’s has been at Commercial Aviation’s forefront for the last twenty years. They have a diverse fleet that represents agility. Overture is a fresh ingredient to the Qatar Airways mix. Qatar has consistently presented itself as a high end destination and the Overture adds to this aura.

The Overture range gives Qatar Airways reach across Europe, Scandinavia, Africa and Asia.

Emirates – Moderate

Ever since the late 90s when Emirates began it’s meteoric growth to its current overwhelming scale. Emirates represents all that Dubai stands for and more. Dubai stands for the power of innovation as does Emirates, which has been very careful with its fleet choices. For an airline with over 250 aircraft (all long haul, widebodies) they have only two aircraft types, the A380 & B777 and only recently added a third type, the A350. However Emirates will always be a tempting choice.

The Overture range gives Emirates a similar footprint out of Dubai to that of Qatar Airways out of Doha.

Etihad- Low

Etihad made several poor choices with mergers and acquisitions (Jet Airways, Alitalia, Air Berlin)and most have gone bad. However they are on a path to recovery. They only turned profitable in 2024 and appear wiser for the experience. Overture is still 5 years away and you never know if a fresh spark might be ignited.

India & China

The fastest growing aviation markets in the World.

India has two dominant carriers Indigo and Air India.

Indigo – Low

Indigo is a LCC. They are growing at a phenomenal rate and Indigo is among the most valuable airlines in the World. They have begun offering a Hybrid product that includes a Stretch class.

Air India – Moderate

Air India is in the midst of a major turnaround after being taken over by the Tata group in 2022. Over fifty years of mismanagement have ensured that Tata is rebuilding an airline from scratch.

Singapore Airlines holds a 25.1% stake in Air India and shares a very close relationship with the Tatas. In the 1990s they tried to start an airline in India with the Tatas but ran into government related road blocks. When Singapore Airlines’ predecessor MSA (Malaysia Singapore Airlines) was formed in 1966, Air India which was founded and run by Tatas since 1932 trained the early batches of MSA’s crew.

Air India was nationalized in 1953 and stayed that way until 2022 when it reverted back to Tatas, who are turning the airline around with key stakeholder Singapore Airlines.

If Singapore Airlines has a go at the Overture Air India will probably be involved creating a tight double hub with a reach from Australia to Europe & Africa.

The reach of the double hub over Singapore & Mumbai.

China

China has the second largest GDP Globally at over $20 Trillion. They are one of the two fastest growing aviation markets in the World.

The current economic situation between China and the USA renders any conversation about the Overture moot. China has begun returning Boeing aeroplanes to the USA.

China is a very strong Supersonic market. Their premier airframe manufacturer COMAC (Commercial Aircraft Corporation of China) has expressed long term interest in SST and even has some concepts.

For now China will not be figuring in Overtures plans.

Bridging the Pacific

The Overture enters an increasingly globalized market. Currently a high percentage of Global economic power houses are in East, South & Southeast Asia.

With it’s range of 4,250 nm bridging the Pacific becomes a challenge where distances are double the range of the Overture.

Two points present themselves. The first is Honolulu in Hawaii and the second is Anchorage in Alaska.

There is no need to reinvent the wheel.

Honolulu

The approximate mid point of the Pacific Ocean. Honolulu has a history of being a logistical stopover and later tourist draw.

In the 1930s as Panam’s Clipper flying boats began to spread out across the World. Panam used Hawaii as a major refueling point as their flying boats bridged the Pacific.

Traffic to Hawaii kept increasing as planes got faster, and the tourism industry there exploded. Today Hawaii is considered a major tourist destination.

Honolulu has the ability to connect the US West coast to Australia, New Zealand, Japan and Korea on the Overture.

Anchorage

Anchorage emerged as a critical bridge on the East West Pacific route in the pre ETOPS ( Extended Range Twin Operations, applicable to aircraft with two engines) era. Right through the 1970s and 80s airlines used Anchorage as a critical technical refueling stop as they bridged the Pacific.

The arrival of aircraft such as the B777, B787 & A350 and ETOPS changed technical stops with their disruptive range efficiencies.

Since the 1990s Anchorage has exploded into a critical cargo hub, used by almost every major freight operator.

The Overture represents a return to Anchorage for passenger operations technical refueling stops. A stop in Anchorage opens up Continental North America from Tokyo or Seoul.

Note: The Concorde underwent extensive cold weather testing while based at Fairbanks through the early 1970s ending in 1974. Alaska is familiar was Supersonic Transports.

An Air France Concorde at Fairbanks Alaska in 1974.

Reach into Continental North America over Anchorage.

Range into North America over Anchorage.

The Overture Alliance

So what will the Overture Alliance look like?

Before we dive into the future, let’s examine two alliances that pre date todays mega alliances. These two stand out for their depth and synergy.

The KLM / Northwest Alliance from 1989
The British Airways / Qantas from 1995

The KLM / Northwest Alliance

This particular alliance started off the JV (Joint Venture) model in aviation. The two carriers found synergy across Schedules, revenue sharing (they pioneered the straight rate prorate model, a concept where airlines share revenue based at pre determined rates by route), frequent flyer programs and delivered a seamless passenger experience.

The synergies created by a strong double hub strategy on both sides of the Atlantic which would become the template for alliances moving ahead.

The KL/NW alliance would set the ground for the SkyTeam alliance.

The British Airways / Qantas Kangaroo Route

The JSA (Joint Services Agreement) on the Kangaroo Route was to create synergy across a midpoint hub at Singapore.

The JSA involved revenue sharing across flights, coordinated schedules, synergized pricing and shared costs ( Singapore as a hub was not a home base for either British Airways or Qantas). They went as far as aligning product across cabins.

What sets the JSA apart was coordinated crew layovers, aircraft maintenance and provisions stock at Singapore.

The JSA between BA/QF would become the basis for Oneworld.

The two examples highlight the synergies achieved across Men, Machines & Money.

The Morphing of Alliances

The JSA changed with the emergence of Emirates and Qantas realized in 2013 they had superior reach into Europe / UK / Africa / India and the Middle East by using Emirates based in Dubai than using the JSA over Singapore.

On a more recent note (2022) within the OneWorld alliance, British Airways which represented the AJB (Atlantic Joint Business) with American Airlines to Asia and Africa was replaced by Qatar Airways as the AJB partner to Asia and most of Africa.

The above examples highlight the emerging importance of the ME3 and more importantly future alliances need to be extremely flexible and agile to deal with ever changing Global dynamics.

With this knowledge how will the Overture Alliance look?

The Overture Alliance with definitely synergize Men , Machines & Money.

Men

Dedicated Overture teams at each hub
Each Overture airline responsible for their hub
Costs at Honolulu & Anchorage to be shared
Overture lounges at transit points
Common training facilities at dedicated hubs

Machines

For the most part airlines run the Overture as a p2p (point to point) operation
Honolulu & Anchorage provide a transit/transfer hub as necessary (there may be other hubs)
A common pool program at Anchorage & Honolulu. Each airline responsible for parts at their hub
Honolulu to Australia / New Zealand will be a side trip ( or a subsonic journey elsewhere)
Booking and back end systems to be aligned

Money

Deep synergy across revenue sharing
Hub costs each airline is responsible
Costs at Honolulu & Anchorage to be shared (as per use by airline)
Marketing expenditure can be shared across constituents

Notes:

By doing so airlines avoid the pitfall of spreading themselves too thin, and allows them to focus on key routes, much like the concept of the LCC (Low Cost Carriers). Such an operation opens up LCCs buying into this.

The Overture Alliance once again heralds the return of RTW ( Round The World) journeys like the previous century.
As observed in previous alliances, the constituents and business needs are constantly changing and scalability has to be built into the alliance model.
Since the aircraft is the BOOM Overture, BOOM will need to be a critical part of this alliance from a Machine perspective.

I have probably missed many perspectives and airlines during the course of writing this and I apologize to those I missed.

Disclaimer: This article has used images from multiple sources accessed through Google.

For more deep dive easy to read articles please go to https://theaviationevangelist.com do keep scrolling down, and do share

Follow me:

LinkedIn : https://www.linkedin.com/company/the-aviation-evangelist/

X : @ManiRayaprolu

Reddit : r/theaviationevangelist

Facebook : https://www.facebook.com/profile.php?id=61583497868441#

Tags Air India, American Airlines, BOOMSupersonic, Concorde, Emirates, Honolulu, Japan Airlines, Network, Overture, Qatar Airways, Singapore Airlines, United Airlines

Categories Uncategorized

Supersonic Shockwave

April 13, 2025 //

Prologue

At the end of my previous piece on the BOOM Symphony, more than a few questions were asked about the Sonic Boom, Sound Barrier, Boomless Cruise etc. This piece attempts to answer the questions. For that we need to go right to the very beginning.

History

Prehistoric Man might have taken the concept of sound for granted and not given it much thought. The first inflection point was the realization there was a relation between lighting and thunder i.e how thunder always followed lightning. Some intuition later they realized that both travelled through the space around and above them.

The Norse God Thor was attributed by the the Vikings for Lightning as his hammer, Mjölnir travelled across the sky followed by Thunder as Mjölnir struck his enemies.

Similarly the Indian God Indra’s Vajra representing a diamond (indestructible) and thunderbolt (irresistible force)caused lightning as it travelled through the sky . Indra’s domain included Lightning and Thunder among many others.

History is replete with such allusions to Lightning and Thunder. From these allusions it is clear that lightning was faster than Thunder.

The concept of speed is arrived at.

Science Timeline

Scientific rigor made its entry. Below is a timeline some of the milestones in understanding sound.

By 500 BC Pythagoras discovered that musical pitch depended on the percussion instruments string length
Aristotle around 350 BC believed that an object striking air caused sound, he still thought sound was instantaneous
Vitruvius in 50 BC Discovered the concept of the echo was in manmade architecture
Between the 9-12th centuries several Islamic scholars studied vibration & resonance and the concept of sound moving through air as a medium

The Middle Ages & Renaissance periods made strides in understanding sound as a wave.

In the early 1600s Galileo observed the concepts of vibration
Marin Mersenne in 1636 measured the speed of sound for the first time at 1380 ft/s (the first measurement of the speed of sound)
Issac Newton around 1687 applied his laws of motion to sound in air and calculated the speed of sound at 979 ft/s
During the 1740s Euler and Bernouli created the wave equation for sound

There were several further increments to Man’s understanding of the phenomenon of Sound and then came Ernst Mach.

Ernst Mach

Mach was the first person to describe and photograph shockwaves.

By the 1800s when bullets or projectiles were fired at high speeds a loud cracking sound was observed. While piquing curiosity nobody understood what was taking place.

Mach who prided himself as a multi dimensional scientist merged physics , photography and optics in a fresh new manner.

Mach’s explorations into supersonic fluid dynamics led him to team up with physics photographer Peter Salcher.

Together in 1887 they presented a paper that correctly described the sound effects of a supersonic bullet in motion. They determined the existence of a shockwave with the bullet as the apex of the shockwave.

The photography technique used was Schlieren Photography, a relatively new technique. The principle of this technique is light bends when it passes through air with a slightly different density.

Schlieren photos use mirrors, a lens, a bright light and a sharp edge to detect light refractions through the air. He then fired bullets through this set up and captured the shockwave! A first…

Pic 1. The 1887 Schlieren image present by Mach & Salcher. Pic 2 the Schlieren setup with a bullet and shockwaves passing through it.

It was August Toepler who developed this technique in the 1860s to capture heat and density differences in air. This was developed specifically for thermodynamics and gas flow. Mach innovated on this technique to capture bullets in supersonic flight.

A Schlieren image of BOOM’s XB-1 in supersonic flight. Note the shockwave off the nose.

Man finally began to grasp what the sound barrier was about….pictorially!

The speed of sound or Mach is named after Ernst Mach.

Transonic Adventures

The term transonic was coined around 1945 by NACA director (the NASA precursor) Hugh Dryden while referring to speeds that were close to the speed of sound. The speed range is between Mach 0.8 – 1.2.

In dogfights during WW2 P-38 Lightnings, Spitfires & Thunderbolts accidentally approached Mach 0.8 – 1 in steep power dives.

As these speeds were hit pilots experienced locked controls and violent shaking of the aircraft also known as compressibility buffeting. In some cases the aircraft broke apart or just stopped responding to control surface inputs.

The phenomenon was experienced for the first time and terrified pilots, who were the guys in the hot seat. They felt like they hit a wall and described it as a barrier. The term sound barrier originated here.

Experiential research later scientists replicated these effects and understood that as airflow over the wings and airframe approached the speed of sound, shock waves formed and disrupted known flight rules. This was the compressibility effect.

The fix was dive recovery flaps under the wings to be deployed early in the dive. The flaps helped bring the nose up and recover the aircraft. Engineers had managed to fix an issue they had scant understanding of.

The swept wings courtesy the Germans were coming.

Glamorous Glennis

Post WW2 a large number of documents and scientists on aeronautical research were seized from the Germans and transported to the United States as part of Operation Paperclip.. The documents were on wing design, shockwave research from the Me-262 (the first Jet aircraft) and airframe design among many others.

Glamorous Glennis was piloted by Gen Chuck Yeager(had the privilege of interacting with him a couple of times on X)and named after his wife. The Bell X-1 was an all American aircraft purpose built aircraft designed to break the sound barrier. Among the many innovations it had was an airframe shaped like a .50 Calibre bullet (a shape known to handle supersonic speeds).

The wings were unswept (straight) and extremely thin with a thickness to wing chord (distance between the leading and trailing edges of the wing) ratio of 8%.

Pic1. A cutaway of the Glamorous Glennis. Pic.2 image of Glamorous Glennis from Gen Chuck Yeager’s profile on X

The tail plane was all moving to handle speeds in excess of Mach 1 and powered by a four chamber XLR-11 rocket engine that developed 6000lbs of thrust.

On 14 October 1947, Glamorous Glennis piloted by Gen Chuck Yeager after dropping from a B-29 Superfortress at 25,000 feet, ignited its rocket and flew into history as the first aircraft to go through the sound barrier in level flight.

The Bell X-1 flew over eighty flights and contributed greatly to our understanding of Supersonic flight.

The Golden Decade

The next decade and half would be the golden age of Supersonic flight.

Using the German WW2 research along with their own the US and Russia developed several firsts for aircraft.

Swept back wings (typically about 35 degrees) became the norm for the next generation of transonic/supersonic aircraft.

The US F-86 Sabre and Russian MIG-15 were the first aircraft to maintain high transonic level flight with stable handling.

The F-100 Supersabre and the MIG-19 Farmer the first aircraft to consistently maintain Mach 1+ speeds in level flight.

The F104 Starfighter the first fighter to hit Mach 2 and the big boy, the B-58 Hustler the first strategic bomber to hit Mach 2+.

The Human Facor

The decade of the 1960s ushered in a SST competition between the Concorde(UK & France), the TU-144(Soviet Union) and the Boeing 2707(USA). Supersonic transport stood for national superiority and attention turned to transporting people at Supersonic speeds across continents.

A mockup of the B2707. The aircraft never made it past the concept stage.

Supersonic speed always has the shadow of the sonic boom following it. The Boom itself is a sudden sharp booming sound or a double boom that follows the aircraft and the sound decibels range of 110 – 140 dB. The best analogy is the waves off the prow of a boat as ploughs through water.

The Oklahoma City Experiment

Starting Feb’64 for eight months Oklahoma City was subjected to 1253 sonic booms @ eight booms a day.

The FAA wanted to study the effects of sonic booms on the local population and chose Oklahoma City as the test subject.

Initially the population was enthusiastic about these tests, but soon realized the booms were everything and more than they were cut out to be.

The people of Oklahoma experienced the following:

Disrupted sleep cycles that induced anxiety
Physical damage to property
Pets were frightened and stressed
Sensitive instruments being disrupted

Oklahoma City felt like a guinea pig and a $25 compensation per household for damage caused, only added insult to injury. The experiments drew over 15000 complaints.

The Oklahoma experience snowballed into a national anti supersonic travel movement. Congress cut funding to the B-2707 program and by 1973 supersonic travel over land was banned in the United States, the rest of the World followed suit.

This was a body blow to the Concorde and TU-144 which were in advanced stages of development. They would fly Supersonic only over water (Concorde) and the TU-144 with its limited range only over the Soviet Union.

Supersonic Travel would be on the backburner for the next 25 years.

QueSST

Psychoacoustic , a word that pique’s interest

By the 1990s NASA and the United States after exiting the Supersonic race had data across fluid dynamics, community response and shockwave shaping. Technological and material improvements improved aircraft airframe and engine efficiencies, the time had arrived to realign Supersonic research from creating new aircraft to better understanding the shockwave and creating designer shockwaves!

Psychoacoustic is how a sound comes across to people. The factors that contribute to it are things like startle factor (suddenness and loudness), frequency (low or muffled sounds are more accepted by the human ear) and timing of the day.

NASA already knew that repeated sound over 100 dB drew complaints, while a decibel level of 75dB was more acceptable to people.

The QueSST ( Quiet Supersonic Transport)program is about laying down the guidelines on the future of Supersonic transport across airframes, flight paths, speeds, altitudes and many more parameters, hopefully overcoming the 1973 ban.

During the 1990s NASA used a T-38 Talon to fly controlled supersonic passes over microphone arrays to understand boom propagation over different terrains and study boom carpet (the impacted ground area of a sonic boom)patterns.

In 2003 a F-5E Tiger with a reshaped nose was used to demonstrate that shockwaves can be manipulated. This test proved that boom intensity can be reduced by at a third.

Between 2011-2016 there were several acoustic simulation studies conducted which arrived at the 75 dB target.

Between 2016-2021 NASA used a F-15B in conjunction with advanced ground sensor arrays to measure shockwave propagation and help tune future computational models. These tests were run over unpopulated desert.

There were several sonic boom carpet models used to test and control sonic boom impact area. Some of the tests included F/A-18 Hornets dive maneuvers to narrow the boom carpet.

The X-59

The Lockheed Skunk Works is NASA’s low boom flight demonstrator aircraft, designed to fly at Mach 1.4 over land.

The X-59 is a specially designed airframe to control, break and reduce sonic booms. The aircraft will be used to confirm the sonic boom carpet, identify shockwave interaction with different parts of the aircraft and further fine tune computational models.

The design innovations include a long tapered nose that is over a third of the length of the aircraft at thirty feet. The nose stretches the shockwave formation at the very start. Due to the nose design, the aircraft uses 4K cameras for forward vision. The design of the wings in relation to the nose need the use of canards (small wing shaped appendages forward of the wings) for stable flight. The all moving tail plane is designed to handle supersonic speeds with minimum shockwave. Lastly the GE F414 engine is mounted on top of the fuselage to direct shockwaves away from the ground.

The X-59 on the apron at Skunks Works, Lockheed Martin.

The aircraft uses area rule shaping to reduce drag (and mitigate shockwaves) at and around the speed of sound. Simply put, the rule states the shape of the aircraft should transition as smoothly as possible, also called the coke bottle shape.

The X-59 will be flown over multiple cities and communities across the United States and surveys will be taken of these communities to study their response to the shockwave characteristics of the X-59 in multiple flight profiles.

NASA’s goal is to prove to regulators that designed booms are acceptable to communities and pave the path to overturning the Supersonic ban over the Continental United States.

The Boom Connection

BOOM with the XB-1 did achieve Boomless cruise although they used a different approach.

The XB-1s use of atmospheric refraction to keep the sonic boom away from the ground.

BOOM used atmospheric refraction from a high altitude (over 35,000 feet) to use the atmosphere to bend the waves upward and keep away from the ground. They used area rule shaping to optimize shockwave generation. Furthermore BOOM limited the speed to Mach 1.1 to control shockwaves.

BOOM is part of the ecosystem NASA is looking to create. The X-59 tests are expected to initiate a Supersonic standards conversation and BOOMs Overture will benefit from these tests.

The Final Word

Finding innovative solutions to overcome physical limitations is the path forward. At the heart of the solution is managing human behavior and attitudes towards Supersonic Shockwaves.

Disclaimer: This article has used images from multiple sources accessed through Google.

For more deep dive easy to read articles please go to https://theaviationevangelist.com do keep scrolling down, and do share

Follow me:

LinkedIn : https://www.linkedin.com/company/the-aviation-evangelist/

X : @ManiRayaprolu

Reddit : r/theaviationevangelist

Facebook : https://www.facebook.com/profile.php?id=61583497868441#

Categories Uncategorized

Supersonic Symphony by BOOM

April 5, 2025 //

Overture

On January 28 2025 the BOOM XB -1 demonstrator aircraft broke the speed of sound three times and achieved ‘Boomless ‘ supersonic cruise hitting speeds of Mach 1.1 . The Mojave supersonic corridor used by XB-1 was the same as the one used by the X-15 program. The XB-1 was flying in the footprints of history.

A screen grab of the tri engine XB-1 demonstrator with the speed indicator showing Mach 1.11.

Boomless cruise was a concept first pioneered by NASA with their Quiet Supersonic Transport (QueSST) program in the 1990s. Lockheed Martin is in advanced stages of building the experimental X-59 aircraft to demonstrate low boom technology.

Before the X-59 program Northrop Grumman showed this is possible with a modified T-38/F-5E Tiger dating back to the 1950s. The F-5E Tiger had a reshaped nose and fuselage in an early attempt to control the sonic boom that follows supersonic flight.

A ChatGPT generated image of a comparison of low boom aircraft

BOOM supersonic is now using data from the tests to design the BOOM Overture. While airframe aerodymanics are key to achieving sustained Boomless supersonic cruise, there is one aspect that is just as important and that is the engines.

SST History

To suitably know the present we first need to understand and acknowledge the past. Aviation history has two SSTs to use as a reference point. The first is the legendary Concorde and the second, the fabled TU-144 both developed in the 1960s , a decade that gave us several aircraft that helped shape the future of air travel. The B747 (Jumbo) & the B737 among them, not to mention the grand daddy of High Supersonic (Mach 2-5) aircraft technology the XB-70 Valkyrie and the B-58 Hustler (first flight 1956) with which the Overture shares some similarity.

A side of the B-58 Hustler with and without the parasite tank. Two engines under the wing clearly visible.

This piece focuses on supersonic transport engines and their evolution.

Turbojet v/s Turbofan

Before we dive into the BOOM Symphony we first need to understand the difference between a Turbojet and a Turbofan. What separates the two is a concept called Bypass. Turbojets have what is called a bypass ratio of 0. This means that all the air that goes in through the engine nacelle also goes through the compression stages of the jet before being pushed out the back. Hot exhaust gasses can be loud because of exhaust gas velocity and in several cases the use of afterburners at various stages of flight be it take-off, climb or cruise.

The turbofan was an evolution of the Turbojet and has a bypass ratio of greater than 0. Engineers soon discovered that not all air needs to pass through the engine combustion chamber all the time. Infact, this is not only inefficient and noisy, but leads to high operating temperatures and this often resulted in structural failures both on the engine and airframe.

A comparison between a turbojet and turbofan.

Turbofans can be generally divided into three broad categories, low(LBR), medium (MBR) and high (HBR) bypass ratio. The TU-144 used a LBR engine, the Symphony is a MBR and most subsonic airliners of today use HBR. Turbofans may also use afterburners.

What are Afterburners?

Afterburners are an extra combustion chamber located at the end of the turbine sections of a Jet engine. Afterburners inject and combust additional fuel into the hot exhaust gasses passing out of the turbine section of a jet engine.They generate incremental thrust in engines that use them.

The Concorde’s Olympus 593 engines increased thrust from 32,000lbs to 38,050lbs with afterburners. On the TU-144s initial NK-144 Kuznetsov engines the thrust increased from 22,500lbs to 33,000 lbs. The later RD-36-51 Kolesov engines increased from 20,000lbs to 44,115lbs. (These engines came in too late in the TU-144 program and could do little to avoid the closure of the program. In any case the Kolesov engines too used afterburners during cruise, which meant the TU-144 was always short on range).

Afterburners might increase thrust substantially but the engines get thirty and range gets impacted negatively.

The Concorde & TU-144

The TU-144 won the first to flight race against the Concorde by 61 days.

The placement and size (diameter) of the engine types was dictated by aerodynamic performance across the speed spectrum from zero to Mach 2+.

The rectangular engine pod of the Concorde and TU-144.

The choice for both these aircraft were engines embedded under the wings in squarish shaped pods. Since the nacelle diameter could not be large (due to supersonic aerodynamic concerns) the width on the Concorde was 1.8m, and the TU-144 was 1.7m per engine and the total width under each wing was 3.7 & 3.5m respectively The length of each of the pods were 9.2m on the Concorde and 8.5m on the TU-144. The height of the pods on both the aircraft was 2m. From these figures we see the engines were similar in size , the magic was what happened inside.

The Olympus 593 engineers of the Concorde opted for a Turbojet and the NK-144 engineers of the TU-144 opted for a very low bypass Turbofan ( BPR 0.6:1 ). Very low bypass turbofans have operating characteristics very similar to a Turbojet.

One of the key pieces inside a jet engine is its compressor. Every compressor has low pressure and high pressure stages each driven by coaxial shafts (twin spool)that drive the various stages of compression as air is driven through the engine and ignited.

The Concorde’s Olympus 593 had seven low pressure and seven high pressure compression stages. Alternatively the the TU-144’s, NK-144 had 6 low pressure and 7 high pressure compression stages. The overall compression ratio of the Olympus 593 was 15:1 and the NK-144 was 11:1 . These numbers look low by today’s standards but history acknowledges these were the limitations of the engines given the materials and technology of the time.

Compressors operate in a very narrow range. An engine compressor on the Concorde spun between 3,500 – 7,000 r.p.m and that on the TU – 144 spun between 3,000 – 7,000 r.p.m. These were the compressor rotations across the entire speed range . Maintaining a stable flow of air through the compressor at all times was one of the secrets of maintaining stable supersonic flight. Disruptions can result in either a compressor stall that is loss of compression and engine performance or Compressor Surge where airflow reverses direction, leading to a flame out.

On the Concorde this was done with innovative use of a series of ramps and bleed valves.The initial TU-144 was much simpler and had immovable fixed inlets and this led to compressor stalls and surges which were difficult to reverse. Later TU-144 models had ramps similar to the Concorde.

The Concorde ramps at work. Image from Heritage Concorde.

The use of afterburners on both aircraft only added to compressor demands. The Concorde used afterburn for takeoff and climb only. The TU-144 used it all times.

The use of afterburn at take off and climb added to severe sound pollution. The Concorde takeoff decibels was approx 120 – 125 dB and reduced a bit during climb. Landing was approx 100dB . The TU-144 had a take off sound level getting toward 140dB and climb at 120dB, landing was similar to the Concorde at approx 100dB. These figures show both aircraft were loud, the TU-144 more than the Concorde. For comparison a very loud night club is rarely over 110dB. Anything over 130dB is painful.

Such sound was unacceptable even over 50 years ago and definitely not today. The Concorde which flew the daily route out of JFK to London / Paris had a specially designed route out of JFK to minimize noise impact on residential areas.

Enter the Symphony

Creating a supersonic (airliner) engine has many issues specific only to Supersonic travel.

The first is sound at take off, climb and cruise. The second is fuel burn. Supersonic travel burns three times the amount of fuel a normal sub sonic engines burn. ( BOOM plans to use Sustainable Aviation Fuel/SAF to reduce carbon footprint). The third is the biggest enemy, air resistance also known as drag. Lastly the use of afterburners needed to be avoided for reasons stated above.

A cross section of the BOOM Symphony engine.

The lessons learnt from Concorde/TU-144 was that having engines embedded in the wings/airframe created turbulence and drag related efficiencies ,there were other inefficiencies related to maintenance and safety that needed to be overcome.

BOOM has decided to go with engines slung below the wing much like the B-58 Hustler from 1956.

We are now in the realm of efficiency dictating form.

BOOM decided to go with a medium bypass ( MBR 1.5:1 ) turbofan for reasons of overall efficiency in the areas of noise, fuel consumption and eliminating afterburners. The Symphony will generate 35,000lbs of thrust ( compression ratio of 25:1)without Afterburn and this requires a great deal of optimization.

Initially BOOM decided on a three engine Overture, but this needed a much larger diameter turbofan which increased sound and reduced redundancy , BOOM decided to go with the traditional four turbofan layout . The current jets have 72in (6 ft) diameter engines. Rough back of the hand math shows the three jet config to be approx 96in (8ft) in diameter leading to inefficiencies mentioned earlier all round.

The engine design of an underslung engine is necessarily different from an embedded engine especially entry and exit.

The air nacelles are axis symmetric on the Symphony v/s levered ramps on earlier SSTs. The intake is engineered to manage airflow through the speed spectrum.

An excellent example of this kind of an intake is the system on the SR-71 a.k.a Blackbird/Habu. The inlet spike moved back 26 inches as speed increased to control the shockwave position and maintain compressor pressure. The engine had bypass doors and bleed slots to further manage internal pressure. In the case of the SR-71 80% of all thrust came from compression inside the intake. This clearly suggests a sophisticated yet simple design.

The Symphony has three low pressure (LP) and six high pressure (HP) compressor stages. Having much fewer LP stages is offset by having a bypass of 1.5:1 which neither the Concorde nor the TU-144 ( bypass 0.6:1 ) had. The HP stages work at optimizing the engine as it moves through sub, trans and supersonic speeds. Having fewer LP stages and more HP stages highlights technology improvement across aerodynamics and materials.

The 787 with chevron nozzles represents a fresh look at managing exhaust gasses. The chevron nozzles are effective in damping sound by managing the mixing of the hot exhaust gasses with the ambient cooler air. The Concorde with it’s variable geometry buckets showed how supersonic airliners can optimize exhaust gasses. In the case of the Symphony we can expect to see variable geometry chevron nozzles?

The Chevron nozzles on a Cargolux 747-8 engine exhaust.

The last bit is Artificial Intelligence ( AI ). When Honda created the VTEC engine, it took the world by storm. It had effectively created two engines in one. One engine for pottering around the city and the second for zipping down expressways. When the iVTEC came out it added efficiency to this exciting mix and created the modern Honda engines of today. The i stands for intelligent, AI that manages engine requirements through the rev range. AI effectively developed fresh efficiencies.Honda has further used a twin scroll turbo (independent exhaust gas streams through one turbo two scrolls), effectively cutting turbo lag without the need for two turbos (compound not twin turbos) and still being relatively compact. The Acura TLX Type S is an exciting mix of VTEC technology and raw instantaneous power response . Much like what BOOM is attempting to do with the Symphony.

A cross section of the twin scroll turbo.

Postlude

BOOM appears to have learnt the lessons from Overture’s Supersonic siblings well. They are leveraging the efficiencies new materials and technologies to create a fresh new tomorrow.

During the course of the writing of the piece I once again realized what great aircraft the Concorde and the TU-144 were, a doff of the hat to the scores of engineers who built and worked these birds.

Disclaimer: This article has used images from multiple sources accessed through Google. No plagiarism intended. This article is for recreational / educational purposes only and of no monetary value.

For more deep dive easy to read articles please go to https://theaviationevangelist.com do keep scrolling down, and do share

Follow me:

LinkedIn : https://www.linkedin.com/company/the-aviation-evangelist/

X : @ManiRayaprolu

Reddit : r/theaviationevangelist

Facebook : https://www.facebook.com/profile.php?id=61583497868441#

Tags BOOMSupersonic BOOMSymphony Supersonic SST

Categories Uncategorized

The Overture Alliance

Supersonic Shockwave

Supersonic Symphony by BOOM

Recent Posts

Archives

Categories

Meta