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NASA’s X-59: The Quest for a Silent Sonic Boom

Written by Dave Page

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Ever since 1947, when NASAs X-1 aircraft became the first manned vehicle to break the speed of sound, teams of engineers across the globe have worked tirelessly to design and build faster and faster aircraft. Although great strides have been made in this field, with the current air speed record set at Mach 6.7 {or 5140.7 Miles per hour} there is one problem that continues to hold back the utilisation of such technology. We are of course talking about the sonic boom.

So, just exactly what is a sonic boom? According to NASA’s website: “A sonic boom is a thunder-like noise a person on the ground hears when an aircraft or other type of aerospace vehicle flies overhead faster than the speed of sound. Air reacts like fluid to supersonic objects. As those objects travel through the air, molecules are pushed aside with great force and this forms a shockwave, much like a boat creates a wake in water. The bigger and heavier the aircraft, the more air it displaces.”

Put simply, any vehicle travelling faster than the speed of sound will produce this shockwave which has the potential to cause structural damage to anything that it may pass over. This has led to supersonic flight being banned over land in most countries unless it is necessary for matters of security, such as the deployment of the United Kingdom’s quick reaction alert Eurofighter Typhoon Squadron covered in a previous post.

But what if this shockwave could be greatly reduced? This would allow for both passenger and military planes to routinely mix supersonic flights over heavily populated areas with no risk of damage to property or people. So, is such a reduction possible? Well, NASA certainly seems to believe that it is and in today’s episode we will take a look at just how they believe this might be accomplished. Please join us as we discover just exactly what is NASAs X-59 aircraft.

The result of a collaboration between NASA and Lockheed Martin, the X-59 has been specifically designed to achieve supersonic flight whilst greatly reducing the effects of the sonic boom that this creates. Currently, this project is still very much in the experimental phase. According to NASA’s website:

“The X-59 is an experimental aircraft only; it is not a prototype design for a commercial airliner and will never carry passengers. Its unique shape and set of technologies reduce the loudness of a sonic boom reaching the ground to that of a gentle thump.”

So, why is this important? As previously mentioned, it is not currently permitted to make supersonic flights over land unless it is necessary for matters of national security. This severely limits the effectiveness of any future plans for supersonic passenger travel and was actually one of the logistical factors that brought about the demise of Concorde in 2003. NASA hopes that, should the X-59 prove effective, it will pave the way for the removal of restrictions and greatly improve both the practicality and viability of supersonic travel.

But just how will the X-59 accomplish this? To begin with, the X-59 has been designed to be as slim and aerodynamic as possible. Although the aircraft is almost 100 feet {or about 30m} long, approximately 30 feet {or about 9.1m} of that length is taken up by the nose cone alone. This design helps to ensure the minimum of air disturbance which, in turn, helps to reduce the effects of the sonic boom. In addition to this, the aircraft is equipped with sweptback wings which also helps to reduce disturbance. But the team at Lockheed Martin did not stop there.

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Although the original designs included a standard style aeroplane canopy, it quickly became apparent that this would not be possible. According to Michael Buonanno, Air Vehicle Lead and Lead Engineer for the project at Lockheed Martin:

“In our initial design studies, we figured out that the disturbance that came from a large canopy was too large to be able to blend into the required area distribution for a low-boom shape,”

In order to circumnavigate this problem, a pilot’s canopy with large forward-facing windows has not been included. In fact, the X-59 has no front-facing windows at all. Instead, the single pilot must rely entirely on a video feed provided by two exterior cameras mounted on the top and bottom of the nose cone respectively. According to a NASA spokesperson:

“Part of the cockpit is something you might see in an office. The pilot will see the sky ahead through a 4K computer monitor, which will display complex computer-processed imagery”

According to one pilot who is involved with the program:” Essentially, it is very much like a Heads-Up Display {or HUD} that you would see in a traditional fighter aircraft. It actually gives us sometimes more capability than you would have with an actual window.”

Even the location of the engine will play a part in helping to reduce the sonic boom. The single General Electric F414 engine, the same engine used in the Super Hornet fighter plane, is mounted in the top of the tail section rather than beneath it and it is believed that this will also help to reduce the shockwave created by the craft. Although many of the components that make up the X-59 have been custom-made, such as the nose cone assembly, wings and tail section, there are a few features that have been borrowed from other aircraft such as the landing gear from the F-16 and the cockpit module from the T-38.

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This amalgamation of technologies both old and new just might have the potential to revolutionise air travel as we know it.

At this point, you may be wondering, why has it taken so long for these advancements to come about? The answer lies in advancement in computer technology. Previously, concept testing such as this was very difficult. Although some tests could be carried out with the use of wind tunnels and sensor arrays, this necessitated the building of physical, full-scale models. However, with the advancement of computer technology, it is possible to make digital models of concepts and then, through the use of various software, subject these models to different conditions in order to determine whether or not they are likely to be successful. As you can imagine, this simplifies the process a great deal.

So, what will happen next? Although the science behind the X-59 is theoretically sound, in reality it will not be until the aircraft takes to the skies for the first time that the design team will discover whether all the hard work has paid off. According to Craig Nickol, manager of NASA’s Low-Boom Flight Demonstrator project:

“When you get a real aircraft in a real atmosphere, there’s a lot of variables that are difficult to model, how that signature propagates through the atmosphere becomes difficult to predict.”

Although the initial test flight was scheduled to take place sometime during the autumn of 2021, various delays in testing prevented this from happening and there is, as yet, still no fixed date. However, progress is certainly being made. – during April of this year, the jet travelled from Fort Worth in Texas, where it was undergoing stress testing and fuel system calibration, to Lockheed Martin’s Skunk Works facility in Palmdale, where it will undergo final assembly in preparation for its first flight later this year.

If the results of this test flight do in fact result in a reduced sonic boom, NASA will begin further overground testing to gauge public response. According to Nils Larson, the test pilot who will be the 1st to fly the X59, “That could be coming to a town near you … Our researchers are going to work with the public and we are going to fly over various cities and towns and they are going to give us the feedback of that thump. Was that thump too loud? Did you even hear it at all?”

If all goes well, NASA plans to present the findings of these tests to the EFAA in an attempt to persuade them to lift the ban on commercial supersonic flight over land. If this ban is indeed lifted, it will pave the way for other manufacturers to capitalise on NASAs designs and produce viable commercial aircraft capable of supersonic travel.

In fact, Lockheed Martin recently unveiled plans to do exactly this. Although still in the conceptual stages, the QSTA-1 (The Quiet Supersonic Technology Airliner) was recently unveiled at an American Institute of Aeronautics and Astronautics conference in Dallas.

Borrowing heavily from the designs of the X-59, this sleek, two engine craft would be capable of transporting up to 40 passengers at speeds of Mach 1.8 (or approximately 1380 mph). In an interview with CNN Travel, Mike Buonanno said that:

“The technology is pretty much in place to go ahead once the concept is proved from NASA’s X-59 program… Right now, we’ve only done early conceptual design studies to establish that the design is feasible, do sizing for the concept, how big it should be, how much it should weigh… Those early sensitivity studies to make sure it all makes sense,”

However it is not just Lockheed Martin who have ambitious plans. The US start-up company Boom Supersonic recently received a $10 million investment from Japan Airlines and is alleged to have received many pre-orders, including one from American Airlines, for

its envisioned 55-seat jet which they claim will be capable of achieving a top speed of Mach 2.2 {or approximately 1687 mph}. Travelling at these speeds, the company claim that the flight from San Francisco to Tokyo could be achieved in six hours rather than the current time of 10 hours and flight from New York to London could be achieved in 3.5 hours rather than the current 6.5 hours. Although this particular aircraft will not utilise quiet boom technology, one employee told us that: “if NASA is successful in its research and the overground ban is lifted then it is highly likely that our future designs will utilise this technology.”

We really don’t believe that it is an exaggeration to say that the results of these tests have the potential to completely revolutionise the future of air travel. If there are no flight path restrictions, then not only will journeys flying over land be considerably quicker but it will also open up partially overland routes for international travel. This would mean that, in the not-too-distant future, it may once again be possible to fly from London to New York and back again in the same day or from New York to Sydney in a little over six hours.

Not only that, but this potential advancement also has the opportunity to change something else. The cancelling of the Concorde program represents one of the very few backward steps in any technological advancement and the X-59 program really does have the potential to turn this around.

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