## How Fast is Mach One?

Within the realm of physics, there are certain barriers that human beings have come to recognize. The most well-known is the speed of light, the maximum speed at which all conventional matter and all forms of information in the Universe can travel. This is a barrier that humanity may never be able to push past, mainly because doing so violate one of the most fundamental laws of physics – Einstein’s Theory of General Relativity.

But what about the speed of sound? This is another barrier in physics, but one which humanity has been able to break (several times over in fact). And when it comes to breaking this barrier, scientists use what is known as a Mach Number to represent the flow boundary past the local speed of sound. In other words, pushing past the sound barrier is defined as Mach 1. So how fast do you have to be going to do that?

## Definition:

When we hear the term Mach 1 it is easy to assume it is the speed of sound through Earth’s atmosphere. However this term is more loaded than you might think. The truth is that a Mach Number is a ratio rather than an actual direct measurement of speed. And this ratio is due to the fact that the speed of sound varies from one location to the next, owing to differences in temperature and air density.

Mathematically, this can be defined as M = u/c, where M is the Mach number, u is the local flow velocity with respect to the boundaries (i.e. the speed of the object moving through the medium), and c is the speed of sound in that particular medium (i.e. local atmosphere, water, etc).

When the speed of sound is broken, this results in what is known as a “sonic boom”. This is the loud, cracking sound that is associated with the shock waves that are created by an object traveling faster than the local speed of sound. Examples range an aircraft breaking the sound barrier to miniature booms caused by bullets flying by, or the crack of a bullwhip.

## Speed of Sound:

Basically, the speed of sound is the distance traveled in a certain amount of time by a sound wave as it propagates through an elastic medium. As already noted, this is not a universal value, but comes down to the composition of the medium and the conditions of that medium.  When we talk of the speed of sound, we refer to the speed of sound in Earth’s atmosphere. But even that is subject to variation.

However, scientists tend to rely on the speed of sound as measured in dry air (i.e. low humidity) and at a temperature of 20 °C (68 °F) as the standard. Under these conditions, the local speed of sound is 343 meters per second (1,235 km/h; 767 mph) – or 1 kilometer in 2.91 s and 1 mile in 4.69 s.

## Classifications:

As with most ratios, there are approximations and categories that are used to measure the speed of the object in relation to the sound barrier. This gives us the categories of subsonic, transonic, supersonic, and hypersonic. This categorization system is often used to classify aircraft or spacecraft, the minimum requirement being that most of the craft classified have the ability to approach or exceed the speed of sound.

For aircraft or any object that flies at a speed below the sound barrier, the classification of subsonic applies. This category includes most commuter jets and small commercial aircraft, though some exceptions have been noted (i.e. supersonic commercial jets like the Concorde).

Since these craft never meet or exceed the speed of sound, they will have a Mach number that is less than one and therefore expressed in decimal form – i.e. less than Mach 0.8 (273 m/s; 980 km/h; 609 mph). Typically, these aircraft are propeller-driven and tend to have high aspect-ratio (slender) wings and rounded features.

The designation of transonic applies to a condition of flight where a range of airflow velocities exist around and past the aircraft. These speeds are concurrently below, at, and above the speed of sound, ranging from Mach 0.8 to 1.2 (273-409 m/s; 980-1,470 km/h; 609-914 mph). Transonic aircraft nearly always have swept wings, causing the delay of drag-divergence, and are driven by jet engines.

The next category is supersonic aircraft. These are craft that can move beyond the compression of air that is the “sound barrier.” These craft generally have a Mach number of between 1 and 5 (410–1,702 m/s; 1,470–6,126 km/h; 915-3,806 mph). Aircraft designed to fly at supersonic speeds show large differences in their aerodynamic design because of the radical differences in the behavior of flows above Mach 1.

These include sharp edges, thin wing sections, and tail stabilizers (aka. fins) or canards (forewings) that are capable of adjusting. Craft that typically have this designation include modern fighter jets, spy planes (like the SR-71 Blackbird) and the aforementioned Concorde.

The last category is hypersonic, which applies to aircraft that can exceed the speed of Mach 5 and can achieve speeds as high as Mach 10 (1,702–3,403 m/s; 6,126–12,251 km/h; 3,806–7,680 mph). Very few aircraft can move at such speeds, and tend to be rocket-powered (like the X-15), scramjets (like the X-43, or HyperX), or spacecraft that are in the process of leaving Earth’s atmosphere.

Another example is objects entering the Earth’s atmosphere. These can take the form of spacecraft performing re-entry, or meteorites that have passed through and broken up in Earth’s atmosphere. For example, the meteor that entered the skies above the above the small town of Chelyabinsk, Russia, in February of 2013 was traveling at a speed of about 19.16 ± 0.15 km/s (68,436 – 69,516 km/h; 42,524 – 43,195 mph).

In other words, the meteorite was traveling between Mach 55 and 56 when it hit our atmosphere! Given its tremendous speed, when the meteor reached the skies above Chelyabinsk, it created a sonic boom so powerful that it caused extensive damage to thousand of building in six cities across the region. This damage, which included a lot of exploding windows, resulted in 1,500 people being injured.

So how fast is Mach One? The short answer is that it depends on where you are. But in general, it is a speed that exceeds about 1200 km/h or 750 mph. If you’re capable of going this fast, you will be breaking the sound barrier, and people for miles around will be hearing about it!

We have written many interesting articles about sound here Universe Today. Here’s What is Sound?, What is the Fastest Jet in the World?, What is Air Resistance?, and What Does NASA Sound Like?

We’ve recorded an episode of Astronomy Cast all about the space shuttle. Listen here, Episode 127: The US Space Shuttle.

Sources:

## NASA’s New X-Plane Program to Bring Quiet Supersonic Flight

NASA has plans to develop new supersonic passenger aircraft that are not only quieter, but also greener and less expensive to operate. If NASA’s 2017 budget is approved, the agency will re-start their X-Plane program, the same program which was responsible for the first supersonic flight almost 70 years ago. And if all goes according to plan, the first test-model could be flying as soon as 2020.

The problem with supersonic flight—and the reason it’s banned— is the uber-loud boom that it creates. When an aircraft passes the speed of sound, a shockwave is created in the air it passes through. This shockwave can travel up to 40 kilometres (25 miles), and can even break windows. NASA thinks new aircraft designs can prevent this, and it starts with abandoning the ‘tube and wings’ model that current passenger aircraft design adheres to. It’s hoped that new designs will avoid the sonic booms that cause so much disturbance, and instead produce more of a soft thump, or supersonic ‘heartbeat.’

The image above shows what a hybrid wing-body aircraft might look like. Rather than a tube with wings attached, this design uses a unified body and wings built together. It’s powered by turbofan engines, and has vertical fins on the rear to direct sound up and away from the ground. (Just don’t ask for a window seat.)

Lockheed Martin Aeronautics has been chosen to complete a preliminary design for Quiet Supersonic Technology (QueSST.) They will have about 17 months to produce a design, which will then lead to a more detailed designing, building, and testing of a new QueSST jet, about half the size of a production aircraft. This aircraft will then have to undergo analytical testing and wind-tunnel validation.

After the design and build of QueSST will come the Low Boom Flight Demonstration (LBFD) phase. During the LBFD phase, NASA will seek community input on the aircraft’s performance and noise factor.

But noise reduction is not the only goal of NASA’s new X-Plane program. NASA administrator Charles Bolden acknowledged this when he said, “NASA is working hard to make flight greener, safer and quieter—all while developing aircraft that travel faster, and building an aviation system that operates more efficiently.”

NASA has been working in recent years to reduce aircraft fuel consumption by 15%, and engine nitrogen oxide emissions by 75%. These goals are part of their Environmentally Responsible Aviation (ERA) project, which began in 2009. Other goals of ERA include reducing aircraft drag by 8% and aircraft weight by 10%. These goals dovetail nicely with their revamped X-Plane initiative.

It’s hard to bet against NASA. They’re one of the most effective organizations on Earth, and when they set goals, they tend to meet them. If their X-Plane program can achieve its goals, it will be a win for aircraft design, for paying customers, and for the environment.

For a look at the history of the X-Plane project, look here.

## X-51 Waverider ‘Scramjet’ Test Flight Fails

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A highly anticipated test flight of the X-51A Waverider scramjet ended abruptly after the experimental aircraft suffered a control failure and broke apart during an attempt to fly at six times the speed of sound. The test flight took place off the coast of California and the X-51A was dropped from a B-52 bomber, but an US Air Force spokesman said that a faulty control fin prevented it from starting its unique “airbreathing” scramjet engine.

The X-51 Waverider program is a cooperative effort of the Air Force, DARPA, NASA, Boeing and Pratt & Whitney Rocketdyne. The Air Force is hoping this type of technology would be successful enough to eventually be used for more efficient transport of payloads into orbit and the Pentagon has touted its ability to deliver strikes around the globe within minutes.

The craft was carried to about 15,240 meters (50,000 ft.) by a B-52 from Edwards Air Force Base in California, and was dropped over the Pacific Ocean. Designers were hoping the Waverider would reach Mach 6 or more.

The scramjet (short for “supersonic combustion ramjet”) is an air-breathing engine, where intake air blows through its combustion chamber at supersonic speeds. The engine has no moving parts, and the oxygen needed by the engine to combust is taken from the atmosphere passing through the vehicle, instead of from a tank onboard, making the craft smaller, lighter and faster. Some designers have predicted it could reach speeds of anywhere from Mach 12 to Mach 24. Mach 24 is more than 29,000 km/hour (18,000 miles per hour.) This could cut an 18-hour trip to Tokyo from New York City to less than 2 hours.

But the concept has had limited success.

In May 2010, the first test of the vehicle had sort of a “successful” flight of 200 seconds of autonomous flight, which set a duration record for an aircraft powered by a scramjet engine. However, another test in 2011 failed, which was attributed to another design flaw.

A statement put out by the Air force said officials will conduct a rigorous evaluation of the test to assess all the factors behind the failure.

## How High Do Planes Fly

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Have you ever asked how high do planes fly? The answer is easy to understand when you remember how flight for aircraft works. The first thing to know is that air is a fluid just like water. So it works under the same rules. Any object that moves in a fluid is under the influence of four forces, drag, lift, weight, and thrust. The net total has to be positive so that the influence of thrust and lift keeps a plane in the air. Thrust and lift depend on the density of the air. So it is easier to achieve the ideal lift and thrust at higher elevations than lower elevations. So how high a plane flies is not fixed except for the limit of the vacuum of space of where the atmosphere becomes too thin for aerodynamics to work.

Lift and thrust are the main forces that make flight possible. As long as they are greater than weight or drag, plane will fly. Thrust is the forward acceleration produced by a plane’s engine. The less dense the air the more thrust a plane must produce to create the needed lift. The full explanation is pretty complicated but the best way to put is that every plane has a maximum condition it achieves to fly. This maximum is the best possible combination of density, speed, and lift to fly the plane. That is why the height a plane can fly can vary so much. It depends on the needs of the plane.

A good example is commercial turbo jets. Turbo jets fly below the speed of sound. The also weigh a lot. In order to reach optimal flight conditions and fly at speeds convenient enough to make air travel profitable, most commercial planes fly at 30,000 feet. This is high enough that a plane has the least amount of drag and can reach the top speed its engines can produce safely. Supersonic craft like fighter jets and spy planes can fly much higher. This is because they design of the plane makes it easier for the plane to resist drag and produce greater thrust to compensate for the thinner air.

So we see that how high a plane can fly is determined by its use, the drag, the lift, thrust, and weight. We also know that a planes absolute limit will be where air becomes too thin to act like a fluid which is the uppermost level of the atmosphere. Right now scientist are looking to take advantage of this upper level of the atmosphere to help planes fly even faster. However there are still barriers such as friction and engine design.

We have written many articles about airplanes for Universe Today. Here’s an article about the largest airplane, and here’s an article about pictures of airplanes.

If you’d like more info on airplanes, check out these articles from How Stuff Works. Here’s an article about How Airplanes Fly.

We’ve also recorded an entire episode of Astronomy Cast all GPS Navigation. Listen here, Episode 212: GPS Navigation.

Sources:
NASA
How Stuff Works

## What Will Airplanes of the Future Look Like?

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Will aircraft of the future look something like this? Project NACRE (New Aircraft Concepts Research) has this wide-body aircraft in mind for future flyers, designed for long-haul flights and able to accommodate up to 750 passengers. Measuring 65 meters long, 19 meters high with a wingspan of nearly 100 meters, the maximum take-off weight of the simulated flying wing is roughly 700 tons. The German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) has been performing flight tests to simulate and study the flight characteristics of large ‘flying wing’ configurations to prepare for future aircraft designs, using special airplane called ATTAS (Advanced Technologies Testing Aircraft System) research aircraft that has special software and hardware that can mimic the flight characteristics and performance of an entirely different aircraft.

What are some other future airplane concepts?

Airbus has this concept in mind – called a fantasy plane – that could be more fuel efficient because of its long, curled wings, a U-shaped tail, and a lightweight body. This could be the way planes look in 2030, Airbus says, and will have advanced interior systems, and be much quieter than current aircraft.

This supersonic aircraft concept by Boeing is nicknamed Icon II has V-tails and upper surface engines, and can carry 120 passengers in a two-class, single-aisle interior, and can cruise at Mach 1.6 to Mach 1.8 with a range of about 5,000 nautical miles.

Another concept from Boeing is the SUGAR Volt – which includes an electric battery gas turbine hybrid propulsion system – can reduce fuel burn by more than 70 percent and total energy use by 55 percent. This fuel burn reduction and the “greening” of the electrical power grid can greatly reduce emissions of life cycle carbon dioxide and nitrous oxide. Hybrid electric propulsion also has the potential to shorten takeoff distance and reduce noise.

This one is called the SmartFish, and utilizes a “lifting body” design, which means that the entire aircraft works to provide lift, rather than just the wings. The concept for this plane is a slender shape and composite material construction, which means less drag, and thus less thrust required for flight. The wing and fuselage form one integrated, futuristic-looking design. This plane can fly without slats, flaps, or spoilers, meaning increased fuel efficiency. See more on the SmartFish website.

Those are just a few concepts being tested and designed for the future of flight. You can read more about NASA’s work on the future of aeronautics here.

## Experimental Scramjet Aircraft Set for Test Flight

The X-51A Waverider hypersonic scramjet project is set for its second test flight today, and the U.S. Air Force hopes it will demonstrate technology that can eventually be used for more efficient transport of payloads into orbit. The craft will be carried to 15,240 meters (50,000 ft.) by a B-52 from Edwards Air Force Base in California, and be dropped over the Pacific Ocean. A booster rocket will fire, getting the Waverider to Mach 4.5; then the scramjet will kick in, and designers hope it will reach Mach 6 or more.

The X-51 Waverider program is a cooperative effort of the Air Force, DARPA, NASA, Boeing and Pratt & Whitney Rocketdyne.

In May 2010, the first test of the vehicle had sort of a “successful” flight of 200 seconds of autonomous flight, which set a duration record for an aircraft powered by a scramjet (short for “supersonic combustion ramjet”) engine. However, it was hoped that the X-51A would fly for as long as 300 seconds (or 5 minutes) and reach Mach 6. But during that flight, the Waverider suddenly lost acceleration, and the vehicle was “terminated” (destroyed – as planned, the Air Force said) while moving at Mach 5. The loss of acceleration was attributed to a design flaw, which led to hot exhaust gas leaking from the engine into electronics bays.

[/caption]

The scramjet is an air-breathing engine, where intake air blows through its combustion chamber at supersonic speeds. This has been compared to lighting a match in a hurricane, and the concept has had limited success. The engine has no moving parts, and the oxygen needed by the engine to combust is taken from the atmosphere passing through the vehicle, instead of from a tank onboard, making the craft smaller, lighter and faster. Designers say it could reach speeds of anywhere from Mach 12 to Mach 24. Mach 24 is more than 29,000 km/hour (18,000 miles per hour.) This could cut an 18-hour trip to Tokyo from New York City to less than 2 hours.

Sources: NASA, The Register, Spaceports

## What is a Flying Wing?

The field of aviation has produced some interesting designs over the course of its century-long history. In addition to monoplanes, jet-aircraft, rocket-propelled planes, and high-altitude interceptors and spy craft, there is also the variety of airplanes that do away with such things as tails, sections and fuselages. These are what is known as Flying Wings, a type of fixed-wing aircraft that consists of a single wing.

While this concept has been investigated for almost as long as flying machines have existed, it is only within the past few decades that its true potential has been realized. And when it comes to the future of aerospace, it is one concept that is expected to see a great deal more in the way of research and development.

## Description:

By definition, a flying wing is an aircraft which has no definite fuselage, with most of the crew, payload and equipment being housed inside the main wing structure. From the top, a flying wing looks like a chevron, with the wings constituting its outer edges and the front middle serving as the cockpit or pilot’s seat. They come in many varieties, ranging from the jet fighter/bomber to hand gliders and sailplanes.

A clean flying wing is theoretically the most aerodynamically efficient (lowest drag) design configuration for a fixed wing aircraft. It also offers high structural efficiency for a given wing depth, leading to light weight and high fuel efficiency.

## History of Development:

Tailless craft have been around since the time of the Wright Brothers. But it was not until after World War I, thanks to extensive wartime developments with monoplanes, that a craft with no true fuselage became feasible. An early enthusiast was Hugo Junkers who patented the idea for a wing-only air transport in 1910.

Unfortunately, restrictions imposed by the Treaty of Versailles on German aviation meant that his vision wasn’t realized until 1931 with the Junker’s G38. This design, though revolutionary, still required a short fuselage and a tail section in order to be aerodynamically possible.

Flying wing designs were experimented with extensively in the 30’s and 40’s, especially in the US and Germany. In France, Britain and the US, many designs were produced, though most were gliders. However, there were exceptions, like the Northrop N1M, a prototype all-wing plane and the far more impressive Horten Ho 229, the first jet-powered flying wing that served as a fighter/bomber for the German air force in WWII.

This aircraft was part of a long series of experimental aircraft produced by Nazi Germany, and was also the first craft to incorporate technology that made it harder to detect on radar – aka. Stealth technology. However, whether this was intentional or an unintended consequence of its design remains the subject of speculation.

After WWII, this plane inspired several generations of experimental aircraft. The most notable of these are the YB-49 long-range bomber, the A-12 Avenger II, the B-2 Stealth Bomber (otherwise known as the Spirit), and a host of delta-winged aircraft, such as Canada’s own Avro-105, also known as the Avro Arrow.

## Recent Developments:

More recent examples of aircraft that incorporate the flying wing design include the X-47B, a demonstration unmanned combat air vehicle (UCAV) currently in development by Northrop Grumman. Designed for carrier-based operations, the X-47B is a result of collaboration between the Defense Advanced Research Projects Agency (DARPA) and the US Navy’s Unmanned Combat Air System Demonstration (UCAS-D) program.

The X-47B first flew in 2011, and as of 2015, its two active demonstrators successfully performed a series of airstrip and carrier-based landings. Eventually, Northrop Grumman hopes to develop the prototype X-47B into a battlefield-ready aircraft known the Unmanned Carrier-Launched Airborne Surveillance and Strike (UCLASS) system, which is expected to enter service in the 2020s.

Another take on the concept comes in the form of the bidirectional flying wing. This type of design consists of a long-span, low speed wing and a short-span, high speed wing joined in a single airframe in the shape of an uneven cross. The proposed craft would take off and land with the low-speed wing across the airflow, then rotate a quarter-turn so that the high-speed wing faces the airflow for supersonic travel.

The design is claimed to feature low wave drag, high subsonic efficiency and little or no sonic boom. The low-speed wings have likely a thick, rounded airfoil able to contain the payload and a wide span for high efficiency, while the high-speed wing would have a thin, sharp-edged airfoil and a shorter span for low drag at supersonic speed.

In 2012, NASA announced that it was in the process of funding the development of such a concept, known as the Supersonic Bi-Directional Flying Wing (SBiDir-FW). This came in the form of the Office of the Chief Technologist awarding a grant of \$100,000 to a research group at the University of Miami (led by Professor Gecheng Zha) who were already working on such a plane.

Since the Wright Brothers first took to the air in a plane made of canvas and wood over a century ago, aeronautical engineers have thought long and hard about how we can improve upon the science of flight. Every once in awhile, there are those who will attempt to “reinvent the wheel”, throwing out the old paradigm and producing something truly revolutionary.

We have written many articles about the Flying Wing for Universe Today. Here’s an article about the testing of the prototype blended wing aircraft, and here are some jet pictures.

If you’d like more information on NASA’s aircraft programs, check out NASA’s Dryden photo collection, and here’s a link to various NASA research aircraft.

We’ve also recorded many related episodes of Astronomy Cast. Listen here, Episode 100: Rockets.

Sources:

## NASA Unveils Personal Aircraft

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Forget about jetpacks or flying cars. How about your own personal stealth aircraft? NASA has unveiled the Puffin, an experimental electrically propelled, super-quiet, tilt-rotor, hover-capable one-man aircraft. According to Scientific American, the 3.7-meter-long, 4.1-meter-wingspan craft is designed with lightweight carbon-fiber composites to weigh in at 135 kilograms (not including 45 kilograms of rechargeable lithium phosphate batteries.) The Puffin can cruise at 240 kilometers per hour, but for those high speed chases, can zoom at more than 480 kph. See video below.

Since it doesn’t have an air-breathing engine, the Puffin is not limited by thin air. So, basically, it doesn’t have a flight ceiling. The designers say it could go up to about 9,150 meters before its energy runs low enough to drive it to descend. With current state-of-the-art batteries, it has a range of just 80 kilometers if cruising, “but many researchers are proposing a tripling of current battery energy densities in the next five to seven years, so we could see a range of 240 to 320 kilometers by 2017,” says researcher Mark Moore, an aerospace engineer at NASA’s Langley Research Center in Hampton, Va. He and his colleagues unveiled the Puffin design on January 20, 2010 at an American Helicopter Society meeting in San Francisco.

For takeoff and landing, the Puffin stands upright. But during flight the whole aircraft pitches forward, putting the the pilot in the prone position, like in a hang glider.

Of course, the original idea for this personal aircraft is for covert military operations. But if they can design them safe enough and cheap enough, everyone will want one. It could change our ideas about electric propulsion and personal aircraft.

By March, the researchers plan on finishing a one third–size, hover-capable Puffin demonstrator, and in the three months following that they will begin investigating how well it transitions from cruise to hover flight.

Hat tip to my sister Alice!