The world has been spinning at 1670 km/hr thousands of years and humans just came into existence recently. In a span of 100 years aviation has grown drastically and so has our “need for speed”. Never would have the Wright brothers thought of crossing the Atlantic in a period of 1.5 hours. It is true that yesterday’s fiction can become today’s reality and we now have aircrafts that can easily break the sound barrier. One of the depressing facts is, the technology that helped “develop” human civilisation has not been very friendly to mother Earth.
When we say Super Sonic Transport (SST), most of us will get the Concorde in our mind. The Concorde and Tupolev Tu-144, particularly the former has been actively used in the commercial sector for transportation in the supersonic regime. Concorde was up in the sky till the 26th of November, 2003. One of the turning points of the Concorde’s legacy is the crash of Air France 4590 back in 2000. The primary reason why she was grounded was high maintenance and development costs the airline had to bear in order to have her in their fleet. The noise that is produced when the aircraft breaks the sound barrier is also another reason why people didn’t want the Concorde up in the sky. The other challenges that one will face with a SST aircraft are, designing the aircraft so that they are aerodynamically efficient, building powerful enough engines, making sure the aircraft is structurally safe and rigid, the high cost that can blow a hole in your pocket, the noise it generates while taking off, the sonic boom when the sound barrier is broken, the temperature the skin has to withstand, the various speed regimes the aircraft has to fly in, the poor range of the craft and the most important factor would be the desirability of the airline. (click for more information)
Airline desirability is the return on investment the airline gets because of the aircraft. Now the major constraint an SST aircraft will face is to fly below the sonic speed over land. This makes the SST only slightly faster than a normal aircraft. If they can travel full-time above the sonic speed then, they can make more number of trips per day. Meanwhile the oil market always changes and because of this the ticket price changes and ultimately, the passengers have to face the charges. Even with so many challenges the need for supersonic business jets have not decreased and there has been so many models already being designed and fabricated considerably in the 2010s. (Check article 1 for citation)
You might have come across news articles about Airbus or Boeing building SST aircrafts. As cool as it sounds are we in a world that needs to travel faster? We are about to produce monsters that will rule the skies. I agree that the world is growing at a rapid pace and the general statement is that humans must grow and move at the same pace. Keeping this in mind, let us have a brief look at what could be the next look of airports!
Aerion AS2
Spike S-512
Lockheed Martin N+2
Concorde 2
These are some of the things SST aircraft designers have to keep in mind while designing the aircraft
[1] Attain supersonic flight over land by sonic boom reduction (half the sonic boom strength of the Concorde)
[2] Meet noise level standards applied to current subsonic passenger aircraft during takeoff and landing (In compliance with ICAO Chap. 4)
[3] Reduce air resistance to reduce fuel consumption and to lengthen the cruising distance (cruising lift–drag ratio: higher than 8.0)
[4] Reduce structural weight to reduce fuel consumption and to lengthen the cruising distance (15% of the structural weight of the Concorde) (Check the article 1 for citation)
Such active research studies are being carried out in the aircrafts of the future. Out of all the reasons the sonic boom is what scientists are trying to avoid. There has been studies confirming the effect of noise reduction by placing the engines above the aircraft. Now how do we travel faster than the speed of sound, yet be silent when doing so? We can first have a look at what really is the sonic boom all about and then see what is being done to reduce it.
Whenever an aircraft breaks the sound barrier the high-speed impact waves are integrated over the body of the aircraft and they propagate towards the ground. When they touch ground they are in the form of a N type pressure wave. There is a sudden double-change in pressure and the human ears recognise this as a loud cracking “boom” sound.
Stretching the distance between the nose and tail helps reducing the power of the sonic boom. Concorde’s boom was a window-rattling 105 PLdB. Researchers believe 75 PLdB would be an acceptable level for unrestricted supersonic flight over land, but NASA is aiming more ambitiously for 70 PLdB or lower. (For more info, click here)
Scientists are primarily working towards reduction in the sonic boom. In wind-tunnel tests, designs from both Boeing and Lockheed Martin – funded by NASA – which would carry between 30 and 80 passengers, achieved boom levels as low as 79 PLdB, beating the target.(For more info, click here)
The D-SEND project is one methodology that helps scientists understand how sonic booms are generated at high speeds on the designed aircraft and can look at ways of reducing them. D-SEND project is nothing but attaching a scaled remotely operated model to a helium balloon and dropping them from the edge of the atmosphere. As the model free falls it picks up speed, crossing the sound barrier and producing shock waves along the way. To picture it easily imagine Superman dropping down to save his girl! There are a series of sensors at various altitudes that picks up data from the free-falling model. Once the limited height is reached the model is controlled to glide and land safely wherever suitable. This helps the scientist to gather data needed for enhancing the performance.
There are also Sonic Boom Simulators that artificially generate sound equivalent to sonic booms with the help of 8 large speakers. These simulators help investigate the human’s tolerance of sonic booms.
Pretty soon we will get aircrafts that can travel faster and at the same time be more silent while in operation. The National Aeronautics and Space Administration (NASA) is working on making this fiction come true. They partnered along with Lockheed Martin for the preliminary design of Quiet Super Sonic Transport (QueSST). The work will be conducted under a task order against the Basic and Applied Aerospace Research and Technology (BAART) contract at NASA’s Langley Research Centre in Hampton, Virginia. Keeping in mind to maintain the sound levels, the aircraft will give a mild thump rather than a loud bang.
“The prime purpose of noise certification is to ensure that the latest available noise reduction technology is incorporated into aircraft design demonstrated by procedures which are relevant to day to day operations, to ensure that noise reduction offered by technology is reflected in reductions around airports.”
The seventh meeting of the Committee on Aviation Environment Protection (CAEP/7), 2007
NASA says that there will be a community response while they demonstrate the Low Boom Flight Demonstration (LBFD) so, I would suggest you to have your ears open! The aircraft is half the size of Concorde and the aerodynamics is fine tuned to make it more silent. The canard (the tiny forward wing) is has a higher swept angle thus offering superior lift.
Now that we know that the tech is proven and we are to get aircrafts that can travel fast and be well below the sound limits, do we need them? I do not understand why there should be further enhancement. I feel that needs are not met instead, needs are created and humans are finding solutions. This is not only in the field of air transportation but also in other sectors as well. When in a journey everyone needs a pit stop, a pause not to relax but to reflect on what we have done to get where we are. The pause has to come. So is travelling faster really the solution?
As Charlie Chaplin words from The Great Dictator still electrifies in our hearts “We have developed speed, but we have shelled in”
Sixty360 
April 14, 2016 at 3:42 am
Good read! Food for thought
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April 14, 2016 at 6:36 am
Thank you !
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