What is “supersonic”?

Sep 17, 2019 · 4 min readWhat is “Supersonic”?

Flying at high speeds is a dream that millions of people around the world share.

Not only is it a thrill to imagine traveling at supersonic speeds or even hypersonic speeds, it’s also tempting to imagine arriving at your destination faster. How fast can you fly — exactly? Here’s a look at how the aerospace industry categorizes the speeds of flight and the type of aircraft capable of achieving those speeds.

Typically, we measure the speed of an aircraft by its Mach number, which is a velocity relative to the speed of sound (approximately 770 mph or 1,239 kmh at sea level). Mach 1 is the speed of sound.

Four general categories define the speed of flight: subsonic, transonic, supersonic and hypersonic. Each is relative to a Mach number.

Subsonic

At this speed, an aircraft is traveling slower than the speed of sound — less than about Mach 0.8. Subsonic aircraft include everything that flies slowly, including all general aviation aircraft, such as the Cessna 172, ultralights, and even paragliders.

Commercial aircraft, such as the Boeing 777 and Airbus 330, and smaller regional jets that have less than 100 seats, are subsonic as well. Most older military jets also fall into the subsonic category. Examples include the F-100 Super Sabre, which was developed in the 1950s and flown by the U.S. Air Force for 25 years.

Transonic

At this speed, an aircraft is approaching the speed of sound but hasn’t yet reached and surpassed Mach 1. At some places on the aircraft the speed will exceed Mach 1, while at others it will be less than Mach 1. There are a handful of aircraft that fly deep in the transonic regime, including the Cessna Citation X and the Gulfstream G650.

The line between subsonic and transonic is blurry. There are even transonic flows on both of the subsonic commercial airliner examples mentioned above. In some cases, you can even see the shadow of the shocks on the upper wing. Click here to watch the shock wave formation on a Boeing 737 in transonic flight.

Supersonic

At this speed, the entire aircraft is experiencing supersonic airflow and traveling at speeds faster than Mach 1. Generally, supersonic speeds range from Mach 1.2 to Mach 5. Boom’s Overture will fly comfortably in the supersonic regime at Mach 2.2.

What is “Supersonic”?

Rockets, such as the Space Shuttle, fly at supersonic speeds immediately after liftoff and for about 45 seconds until about two minutes after launch. During this time, the shuttle accelerates from Mach 1 to Mach 5.

Many types of military aircraft are also capable of supersonic flight. For example, the F-4 Phantom II first took to the skies in 1960 and exceeded Mach 2. Nicknamed the “Flying Footlocker,” it was retired in 2013.

Hypersonic

At this speed, an aircraft is traveling faster than Mach 5.

The hypersonic X-15, a joint venture that NASA conducted with the Air Force, the Navy, and North American Aviation, Inc., flew at Mach 6.7. The X-15 flew from 1958 to 1969 and provided insights that later contributed to the Mercury, Gemini, and Apollo piloted spaceflight programs.

It also helped inform the Space Shuttle, which flies at hypersonic speeds while in the earth’s upper atmosphere. (It slows down to supersonic speeds as it re-enters the lower part of the earth’s atmosphere.) Most recently, China launched its experimental “waverider” Starry Sky-2 hypersonic aircraft, which soared at about Mach-5.

5 for 400 seconds (after being carried by a rocket to an altitude of 18 miles or 30km).

The reason for the distinction between supersonic and hypersonic is due to temperature changes. At speeds above Mach 5, most metals will melt or become so soft that they can’t be used for any type of structure.

As a result, hypersonic aircraft must go to extreme measures for heat protection (such as the tiles and blankets protecting the space shuttle).

While it’s challenging to imagine what happens to an aircraft at such temperatures, here are two examples: aluminum will melt at approximately 1,200° F or 648° C and steel will melt at approximately 2,500° F or 1,371° C.

To learn more about speed versus temperature, click here for a great blog about why air is hot when you fly fast and why there’s no such thing as “cooling air” once you’ve achieved Mach 1.

In pictures: Here are the planes being built to bring back supersonic travel

It's been over 15 years since Concorde was up in our skies flying faster than the speed of sound but there are some working to bring supersonic transport back for commercial use.

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CNBC takes a look at the companies currently developing supersonic passenger jets:

  • PLANE: OVERTURE
  • CRUISING SPEED: MACH 2.2
  • FIRST SCHEDULED FLIGHT: 2023

Boom's founders hope its 55-seater plane will be 30 percent more efficient and 30 times quieter than the Concorde.

In early January, the Colorado based company Boom Supersonic reportedly closed a $100 million series-B investment round to support the development of its mach 2.2 airliner, Overture. Total funding for Boom now stands at $141 million.

Boom says that it's supersonic demonstrator plane, the XB-1, will break the sound barrier in 2019 for the first time and will reach Mach 2.2 shortly thereafter in subsequent testing.

  1. PLANE: AS2
  2. CRUISING SPEED: MACH 1.4
  3. FIRST SCHEDULED FLIGHT: 2023

Aerion is developing a 12-seater business jet that has the capability of flying direct from New York to Sao Paulo and London to Beijing.

It's planning to develop bigger and faster variants of the AS2, including potential commercial models.

The preliminary design phase is expected to conclude in 2020. Aerion are working in partnership with American aero and defense company Lockheed Martin to develop the AS2.

Lockheed is also working with Nasa on creating a quieter supersonic commercial plane called the X59 QueSST and is attempting to reshape the conventional design of a fixed-wing aircraft to solve the issue.

  • PLANE: SPIKE S-512
  • CRUISING SPEED: MACH 1.6
  • FIRST SCHEDULED FLIGHT: 2023
  1. Boston based Spike Aerospace claim the S-512 will be the fastest civilian aircraft available.
  2. It's developing a 12 to 18 person quiet supersonic jet that is aiming to fly Dubai to New York non-stop in nearly half the time it currently takes a subsonic aircraft.
  3. They are developing the $125 million plane with the help of Greenpoint Technologies and Siemens.
  4. But if supersonic's not fast enough …
  5. Boeing have released a model of a hypersonic plane.

PLANE: UNKNOWN

CRUISING SPEED: MACH 5

FIRST FLIGHT: ???

Boeing hypersonic plane design concept

Hypersonic planes will be traveling at Mach 5. Five times the speed of sound. That's 3,836 miles per hour. Meaning the plane would take just under two hours to complete the Sydney to San Francisco journey.

Correction: This article has been amended to remove a comparison between supersonic and hypersonic flight times.

Definition of supersonic

First recorded in 1915–20; super- + sonicsu·per·son·i·cal·ly, adverbsupersensual, superserviceable, supersession, supersex, supersize, supersonic, supersonic transport, supersonics, superspeed, superstar, superstateDictionary.

com Unabridged
Based on the Random House Unabridged Dictionary, © Random House, Inc.

2020rapid, prompt, hasty, brisk, immediate, hurried, expeditious, swift, unexpected, nimble, sudden, abrupt, quick, speedy, agile, hot, airplane, plane, short, flying

  • Within a week, they had determined there was indeed a broad range of supersonic frequencies capable of precipitating the dust.The Year When Stardust Fell|Raymond F. Jones
  • It coughed once, sending a beam of supersonic energy into the bodies of both men.The Penal Cluster|Ivar Jorgensen (AKA Randall Garrett)
  • A wave of some sort—probably subsonic or supersonic—continuously filled the Vininese atmosphere.The Instant of Now|Irving E. Cox, Jr.
  • Flying at supersonic speed, they reached the area of the lost missile in the South Atlantic soon after lunch.Tom Swift and the Electronic Hydrolung|Victor Appleton
  • During the next two days, events moved with supersonic speed for the Cubs.Dan Carter Cub Scout|Mildred A. Wirt

being, having, or capable of reaching a speed in excess of the speed of soundsupersonic aircraftCollins English Dictionary – Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012Having, caused by, or relating to a speed greater than the speed of sound in a given medium, especially air.Of or relating to sound waves beyond human audibility.The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.Having a speed greater than that of sound in a designated medium, usually air; having a speed greater than Mach 1. Compare hypersonic subsonic transonic.The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

WORD OF THE DAY

osmaticadjective | [oz-mat-ik]SEE DEFINITION

What Is "Supersonic"?

Scientific American presents Everyday Einstein by Quick & Dirty Tips. Scientific American and Quick & Dirty Tips are both Macmillan companies.

Every so often, you might hear somebody mention that something or other has reached supersonic speeds. Obviously that must be pretty fast, but exactly how fast is it?

Speed Vocabulary

Let’s start with same basic terminology. Most people use the word “speed” to describe how fast something is moving. However, in physics, speed is just part of the story. The direction of movement is also crucial in most physics calculations. Scientists use the term “velocity” to describe both the magnitude (or speed) of your movement combined with the direction.

The final term we need to understand to talk about supersonic speed is something called the Mach number. The Mach number is the ratio of the velocity of an object relative to some medium and the speed of sound in that medium.

Let’s look at an example. According to the IAAF, world record holder Usain Bolt can run at a maximum velocity of 12.27 meters per second (m/s). The speed of sound is around 340.

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3 m/s (technically the speed of sound varies somewhat with temperature, but we’ll just stick with this number to make things easier). If you take the ratio of these two numbers, 12.27 m/s divided by 340.3 m/s, you get 0.036.

In other words, Usain Bolt can run at Mach 0.036.

Those of you who have been listening to the Math Dude podcast and are good with fractions will notice that as Usain’s velocity increases, the ratio of his velocity to the speed of sound approaches 1. If he were able to run at 340.3 m/s, he would reach Mach 1.

> Continue reading on QuickAndDirtyTips.com

Commercial supersonic aircraft could return to the skies

Flying faster than the speed of sound still sounds futuristic for regular people, more than 15 years after the last commercial supersonic flights ended.

The planes that made those journeys, the 14 aircraft collectively known as the Concorde, flew from 1976 to 2003.

It traveled three times faster than regular passenger aircraft, but the airlines that flew it couldn’t make a profit on its trips.

The reason the Concorde was unprofitable was, in fact, a side effect of its speed.

When the plane sped up past the speed of sound – about 760 mph – it created shock waves in the air that would hit the ground with a loud and sudden thud: a sonic “boom.

” It is so alarming for people on the ground that U.S. federal regulations ban all commercial aircraft from flying faster than the speed of sound over land.

Those rules, and the amount of fuel the plane could carry, effectively limited the Concorde to trans-Atlantic flights. Operating the plane was still so expensive that a one-way ticket between London and New York could cost over US$5,000. And the Concorde often flew with half its seats empty.

The main benefit of supersonic travel is the reduction in flight time. A three-hour flight across the Atlantic could make a day trip possible from the U.S. to London or Paris, essentially saving one whole work day.

As an aerospace engineer studying high-speed air vehicles, I believe that recent advances in technology and new trends in commercial air travel could make supersonic flight economically viable.

But regulations will have to change before civilians can zip through the skies faster than sound.

Fact Sheet – Supersonic Flight

FAA Home ▸ News ▸ Fact Sheets

March 30, 2020 Contact: Henry J. Price

Phone: 202-267-3883

BackgroundThe Supersonic Transport (SST) Concorde aircraft was introduced in the early 1970s. At that time, many in the aviation community thought that the time had arrived for regular supersonic air travel for passengers.

However, the Concorde was retired nearly two decades ago because of the high cost of meeting the environmental restrictions on sonic booms, inefficient fuel consumption, and other factors. Ultimately, the Concorde’s future as a viable transportation vehicle was limited.

Companies in the United States and abroad are now taking a new look at supersonic air travel. Lighter and more efficient composite materials, combined with new engine and airframe designs, may offer the potential for introduction of a viable SST. 

In the area of supersonic aircraft noise, the Federal Aviation Administration (FAA) continually works to ensure the United States keeps pace with latest scientific, technological, and environmental advancements to maintain the safest, most efficient, and advanced airspace system in the world.

Supersonic Aircraft Noise Standards DevelopmentAs part of the Department of Transportation’s (DOT’s) priority on innovation in transportation, the DOT and the FAA are taking steps to advance the development of civil supersonic aircraft.

In line with this, the FAA is initiating two rulemaking activities on civil supersonic aircraft noise.

The first activity is a proposed rule for noise certification of supersonic aircraft, and the second is a proposed rule to streamline and clarify the procedures to obtain special flight authorization for conducting supersonic flight-testing in the United States.

The subsonic noise certification regulations of 14 Code of Federal Regulations (CFR) Part 36 do not apply to supersonic aircraft. The current rulemaking activity related to noise certification of supersonic aircraft will determine the technological and economic basis that supports noise level requirements that are appropriate for supersonic aircraft.

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There is support in Congress for the advancement of new supersonic aircraft. Section 181 of the FAA Reauthorization Act of 2018 specifies that the FAA administrator exercise leadership in the creation of federal and international policies, regulations, and standards relating to the certification and safe and efficient operation of civil supersonic aircraft.

The publication of proposed rules will depend on the ongoing data and information gathering process being conducted. This is necessary in order for the FAA to fulfill its obligations under 49 U.S. Code (USC) 44715.

The FAA anticipates meeting the statutory deadlines for the remaining proposed rule.

The deadline to publish in the Federal Register a Notice of Proposed Rulemaking (NPRM) for noise certification of supersonic aircraft is March 31, 2020.

On June 17, 2019, Acting FAA Administrator Dan Elwell announced the imminent publication of the NPRM to streamline the process for obtaining approval for flight testing of new supersonic aircraft. The NPRM was published in the Federal Register on June 28, 2019.

Existing Supersonic Overland RestrictionsConsiderations of the impact of sonic booms from supersonic flight preceded the development of the Concorde aircraft.

The Aircraft Noise Abatement Act of 1968 directed the FAA, after consultation with the DOT, to “prescribe and amend standards for the measurement of aircraft noise and sonic boom,” and, “… such rules and regulations as the (administrator of the FAA) may find necessary to provide for the control and abatement of aircraft noise and sonic boom.” In 1970, acting under this authority, the FAA proposed a regulation that would restrict operation of civil aircraft at speeds greater than Mach 1, unless authorized by the FAA. The regulation was finalized with minor changes on March 28, 1973 and codified at (now) 14 CFR 91.817 and Appendix B to Part 91.

The FAA’s existing restrictions can be found at 14 CFR Part 91.817.

 In essence, that regulation prohibits anyone from operating a civil aircraft at a true flight Mach number greater than 1 over land in the United States and from a certain distance off shore where a boom could reach U.S. shores.

There is a procedure that allows supersonic operation under certain conditions granted on an individual basis. In addition, any new aircraft would need to meet current airworthiness and noise certification requirements.

The two supersonic rulemaking activities would not rescind the prohibition of flight in excess of Mach 1 over land. At the same time, the FAA is working within the existing statutory and regulatory authority to consider the range of permissible supersonic operations.

In addition, the FAA is assessing the current state of supersonic aircraft technology in terms of mitigating the noise impacts associated with supersonic overland flight.

To this end, Section 181 also requires a biennial review of aircraft noise and performance data beginning on December 31, 2020 to determine whether to amend the current ban on supersonic flight by civil aircraft over land in the United States.

Supersonic Aircraft International ActivitiesSince the FAA expects any new supersonic aircraft to operate internationally, we are collaborating with other national aviation authorities and working within the International Civil Aviation Organization (ICAO) Committee on Aviation Environmental Protection (CAEP) to develop international noise and emissions standards appropriate for future supersonic aircraft and the engines that power them.

SummaryAs part of the DOT’s priority on innovation in transportation, the DOT and the FAA are taking steps to advance the development of civil supersonic aircraft.

In line with this, FAA is initiating two rulemaking activities on civil supersonic aircraft noise.

The first activity is a proposed rule for noise certification of supersonic aircraft, and the second is a proposed rule to streamline and clarify the procedures to obtain special flight authorization for conducting supersonic flight-testing in the United States.

There is support in Congress for the advancement of new supersonic aircraft.  Section 181 of the FAA Reauthorization Act of 2018 specifies that FAA administrator exercise leadership in the creation of federal and international policies, regulations, and standards relating to the certification and safe and efficient operation of civil supersonic aircraft. 

Currently, U.S. law prohibits flight in excess of Mach 1 over land unless specifically authorized by the FAA for purposes stated in the regulations. The two supersonic rulemaking activities would not rescind the prohibition of flight in excess of Mach 1 over land. 

This page was originally published at: https://www.faa.gov/news/fact_sheets/news_story.cfm?newsId=22754

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