Fifty years ago, the federal government banned all civilian supersonic flights from the ground. The rule prohibits non-military aircraft from flying faster than sound because the sonic booms startle the public below and alert them to potential property damage. The ban, which officially went into effect on April 27, 1973, was the result of opinion polls in cities where supersonic military jets flew overhead and many said they didn’t like what they heard or how they heard it. .

Although some research has suggested ways to mitigate the effects of sonic booms, aeronautical technology of the 1960s and early 1970s was not advanced enough to fully address the problem in time to avoid this rule. But today NASA is working on a solution.

“It’s a rule that many people don’t know today, but with the quiet X-59 supersonic aircraft, Quest is central to our mission,” said Peter Cohen, NASA’s Qusst mission integration manager.

NASA’s X-59 was designed to fly faster than sound, but with significantly reduced noise – the people below will hear audible “buzz” instead of roar if they hear anything. To test the public’s perception of this noise, part of the Quest plan includes flying the X-59 over several communities to study people’s reactions.

NASA will report the results to US and international regulators, who will evaluate new rules to lift the long-standing ban. The goal is a regulatory change to focus on the sound an aircraft makes rather than speed limits.

“We are absolutely poised to write a new chapter in the history of supersonic flight, making ground air travel twice as fast, yet safe, sustainable and much quieter than before,” said Cohen.

Boom Boom

The federal ban on supersonic flight has its origins in 1947, when the XS-1 rocket plane first broke the sound barrier and ushered in a heroic era in sound velocity research. At first it was about learning how to fly X-planes faster and higher. No one thought about sonic booms, mostly because very few people lived where the research was conducted.

Despite early interest in a mysterious phenomenon at the time when airplanes fly faster than the speed of sound and create atmospheric shock waves that we hear as sonic booms, there were few tools and only limited data to help figure out what was going on. But as the Air Force and Navy began deploying large numbers of supersonic jets to bases around the country, interest in sonic booms skyrocketed as more people were exposed to the often irritating noise.

From 1956 through the 1960s, the Air Force, Navy, NASA, and the Federal Aviation Administration (FAA) used resources to study how sound waves are generated under a variety of conditions, how they affect buildings, and how the public reacts in different situations. place

In those years, residents of Atlanta, Chicago, Dallas, Denver, Los Angeles, and Minneapolis, using many types of supersonic jet aircraft, were subjected, among others, to the sonic booms of military warplanes and bombers flying overhead.

One in 1961 in St. Louis, and the other in 1964 in Oklahoma City (named Bongo and Bongo II, respectively) left no doubt that the public did not fully support traditional sonic booms from above. The tests became national news and fueled negative sentiment about supersonic flight.

supersonic transport

As this work continues to better understand and predict the sound boom and generate the initial ideas for minimizing sonic boom by changing the shape of the aircraft, the US government began working with industry to develop a supersonic transport. , or SST. The announcement of the SST by President John F. Kennedy in June 1963 sparked interest in the study and attenuation of sonic booms from a technical standpoint and made research a top priority.

The SST project aimed to prototype a new commercial supersonic airliner that could carry 300 passengers anywhere in the world at three times the speed of sound.

(Note that the speed of sound varies with temperature and altitude. At sea level and 68 degrees Fahrenheit, it is 768 mph.)

The aviation community has rushed to improve understanding of supersonic shock waves to reduce the potential level of SST sonic shock. But these researchers couldn’t keep up with the pace at which environmental issues and political controversy emerged, threatening to ground the plane before it was even built.

Three events in the summer of 1968 demonstrated this:

• On May 31, during a ceremony at the US Air Force Academy in Colorado, an F-105 Thunderchief fighter jet broke the sound barrier by flying over the school grounds at an altitude of 50 feet. The sonic boom broke 200 windows on the side of the famous Air Force Chapel and injured a dozen people.

• A week later, on June 8, the New York Times published an editorial, using the Colorado incident, to highlight the dangers of sonic booms to the peace and well-being of the nation, claiming that many “were deathly afraid of it.”

• Then on July 21, Congress directed the FAA to develop standards for “Control and Reduction of Aviation Noise and Sound Blast.”

Within a few years, the FAA officially proposed a rule that would limit civilian aircraft from flying above Mach 1. Congress later canceled the SST program in May 1971, and the rule banning civilian supersonic flight over land took effect two years later. Later.

At the same time, Britain and France were developing and testing the Concorde, which provided commercial supersonic air travel from 1976 to 2003. There were many causes of his death, including a deadly disaster in 2000, but economic and environmental concerns top the list. Restrictions on flying from the ground at the speed of sound due to prohibition in the US and other countries greatly limited the possibilities for making a profit.

speed against sound

Going forward, the idea is for regulators to base the new rules on different standards than before, in order to lift the ban and provide a viable market for supersonic air travel above ground. The speed limit created in 1973 did not take into account the possibility that the aircraft could fly supersonic, but did not create sonic booms that could affect the following. This was a fair assessment as the technology needed for this was not yet available at the time.

“And now it is,” Cohen said. “So, we propose a rule based on sound rather than a rule based on speed alone. There is no reason why an aircraft shouldn’t fly supersonic unless the sound of supersonic flight is loud enough to disturb those below.”

For the past half century, NASA’s aerospace inventors have been systematically working on the problem of taming the explosion. Quest’s X-59 is well on its way to proving the technology, with public flights and critical public research to follow shortly. However, today’s public perception of overhead supersonic aircraft goes far beyond the sonic boom. Airport noise, emissions and climate impact are factors that still need to be addressed.

With partners in government, industry, and academia, NASA is working to meet these challenges. But all that won’t matter until the first step is taken – lifting the half-century-old ban on supersonic flying above the ground.

“We are very excited to take this big step, but we understand that more needs to be done,” said Cohen.