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In my estimation, Friday the 24th of October, 2003 was indeed a very sad day for the entire world. This is the day that the 27 year long Concorde Program at Air France and British Airways came to an end. Even though we had crossed into a new Millennium, we took a major technological step backwards. From that day on, military personnel became the only people that are able to fly anything above Mach 1. As the Sunday Times columnist, Jeremy Clarkson put it as he was contemplating his seat on the very last scheduled flight of Concorde from John F. Kennedy, New York to Heathrow Airport, London, on that fateful October's day: "As I step off, the temptation will be strong to say ‘That was one small step for man. But one giant leap backwards for mankind.'"
Yes, Lockheed, Boeing, General Electric, Pratt & Whitney and the FAA had all worked on the development of an American, Mach 3, Super Sonic Transport (SST), starting in the mid 1950's, unfortunately however, this entire scheme was scrapped in 1965 because of the fear of the costs that would have been involved. Meanwhile across the ‘pond' in 1962, the British and French governments decided to commission the Mach 2.4, Concorde project. Additionally the Russians also built their Tupolov 144 which actually did work, but which ultimately failed due to its feeble 1,500 mile range. Also its crash at its debut at the Paris airshow didn't help either. Scheduled services for the Anglo/French Concorde began on Wednesday the 21st of January 1976. Amazingly, as Jeremy Clarkson points out: ‘For the first time, paying passengers could fly so fast they could watch the sun rise in the West (sic) and arrive in America before they left home.' For the next 27 years, the Concorde flew three-quarters full and made close to $40,000,000 a year for British Airways. With the demise of the Concorde, the Cessna Citation 750 became the world's fastest general aviation aircraft, ringing in at Mach 0.92, closely followed by the new, yet to deliver, Dassault Falcon 7X at Mach 0.90.
With the one and only SST type being grounded almost three years ago, why are there no other SST aircraft currently operating? Well before I attempt to answer this question, I will first try and provide a brief overview of the dynamics of Supersonic flight.
What is considered to be ‘Supersonic speed?'
Aircraft speeds have been defined as follows:
Subsonic Mach numbers < 0.75
Transonic Mach numbers > 0.75 to <1.20
Supersonic Mach numbers > 1.20 to <5.00
Hypersonic Mach numbers > 5.00
What is a Mach number?
Mach is the ratio of true airspeed to the speed of sound, i.e. V÷M= a
M = Mach Number
V = True Airspeed in Knots
a = Speed of Sound in Knots.
The Speed of Sound in air depends only on the Static Temperature of the air, decreasing with lower temperatures and increasing with higher temperatures. The speed of sound is 762 MPH (663 Knots) @ ISA (59°F/29.92" Hg) @ SL; 660 MPH (574 Knots) approx @ -50°F approx @ 100,000 Feet.
To actually break through the Sound Barrier and cruise at Supersonic speeds, an aircraft must have immensely powerful engines. This is why the four Rolls Royce Olympus engines on the Concorde had a system of jet exhaust nozzle ‘re-heat'; some people call them ‘after-burners.' Immense Power is needed to overcome the increase in Drag. The Drag rises with the Square of the Velocity, while the Power, which is Drag times Velocity, with the Cube of Velocity, i.e:
D = V² & P = D*(V³)
D is Drag V is Velocity
P is Power
Intense Heat is another by-product of Supersonic flight. It is actually Compression and Skin Friction which causes an extreme Temperature Rise of the Air surrounding the Aircraft. This can be illustrated by the following table:
Speed Temperature Rise
Mach 1 230°F
Mach 2 610°F
Mach 3 1,200°F
Concorde used to fly between Mach 2.2 to Mach 2.4 only, by design. This was to avoid the deleterious molecular altering effects of aerodynamic heating. This is because the temperature range at which aluminium alloys lose their strength is >250°F. This design specification thereby allowed the Angle French program to avoid the need to employ the use of expensive hybrid materials like titanium, nickel alloys, ceramics and ablative coatings, thus keeping the production costs much lower than they could have been if they had, like the Americans, attempted to operate at Mach 3.
The best known, and probably the most politically incorrect, negative side-effect of Supersonic flight are the Sonic Booms that are a result of the production of Shock Waves. Shock-Waves are technically a result of Compressibility Drag. To reduce this phenomena, the Wings generally have to have a thinner cross section, and also have a pronounced span-wise aft wing-sweep, with wing fences to delay and change the formation of Shock-Waves. Unfortunately wing sweep can accentuate tip-twist, wing tip stall and ‘Dutch Roll.' However with current aerodynamic design, now most supersonic aircraft (military) tend to generate two main shock-waves: One at the Nose (bow wave shock) and one at the Tail (tail shock.) Sonic Booms are basically caused by the folding, unfolding, refolding, and final unfolding of the air as a supersonic aircraft passes through it. The two shock-waves formed by a supersonic aircraft create this transitional folding effect, i.e. ‘compression' * ‘decompression' * ‘compression' and a final ‘decompression' resulting in two sonic booms that may be heard at ground level.
The negative effects of Shock waves also extend to the possible creation of Wing and Compressor Stall. What I mean by this is that the formation of shock-waves change the relative airflow around the aerofoil's of the wings/tail, etc. and unfortunately also the Compressor Blades in the inlet of an axial flow, jet-turbine engine. Shock-wave penetration or modification devices must be employed to change the airflow effect of a shock-wave. If you have ever looked at the complexity of the series of vanes and blocker doors that were designed into the air inlets on the Concorde, you will better understand the vital need to modify the pattern and flow of the sonic air before it enters the engine compressor. Additionally the amount of engine power output is also governed, to a certain extent, by the inlet temperature of the air entering the compressor, i.e. the colder the air is, the better the power output is. Frictional heating will have a drastic effect upon the total power output of the engine, if it is not controlled.
Finally another factor that must be considered in Supersonic operations is the quality and properties of the Jet Fuel used. Due to the extreme ambient conditions that a supersonic aircraft must operate within, the fuel must be refined and blended to an optimized performance level that provides a high BTU, a low volatility, a high flash point and a low freezing point.
So as you can see, Supersonic flight has a lot of technical obstacles that must be overcome to achieve success. However, all of these obstacles have been conquered in various ways by many multi-national aircraft manufacturers and therefore I believe that it is a valid question, when we ask again: ‘Why are we still not yet privately flying at Mach 3?'
Well hopefully we may be able to do so shortly after the end of this decade. This is because research and development in this area has not ceased. Although several companies have tried to develop their own Supersonic Business Jet designs, but have so far failed to bring an aircraft off the drawing board into the marketplace. Most notably these failures include a joint project between Sukhoi and Gulfstream with their S-21 and Dassault Aviation and Boeing separately in the early 1990's. Currently there are three companies that report that they are developing their own Supersonic Business Jet Aircraft. These companies are: Aerion Corporation; Tupolev and SAI.
Aerion Corporation is working on an F104 Starfighter inspired business jet that will carry eight to twelve passengers at 51,000 feet, just slightly below Mach 2.0. It is scheduled to deliver in 2011 and is targeted to cost $80,000,000.00 USD per copy.
Tupolev is reporting that they have developed a hybrid of the TU144, which is called the TU444 Charger. This aircraft is designed to carry six to ten passengers over 4,000 nautical miles at Mach 2.0. There is no reported delivery date or cost.
SAI (Supersonic Aerospace International, LLC) have employed the services of the Lockheed Martin ‘Skunk-works' design team that originally designed the SR-71. This group are spearheading the Quiet Supersonic Transport (QSST.) This aircraft is designed to carry 12 passengers over 4,000 nautical miles at speeds between Mach 1.6 to Mach 1.8. The surprising aspect of this design is the aerodynamically shaped sonic boom signature that is 1/100th of the booms generated by Concorde. This sonic boom suppression technology should, according to SAI, allow their aircraft to fly at Supersonic speeds over populated land areas, instead of being restricted to Supersonic flight only over the sea.
It is sad that it appears that no-one is shooting for the kind of speeds that the great Concorde used to achieve on a daily basis, but it is terrific to see that ability to privately fly above Mach 1.0 is still under development by several stalwart companies. I wonder though, if we will ultimately be prevented from achieving Supersonic speeds even if any of the aforementioned aircraft do actually make it to the prototype stage, because the draconian security people like the TSA, who appear to be imposing unreasonable and ungrounded legislation specifically against aviation, may decide ‘No' civilian Supersonic travel is too much of a security risk!?! I certainly hope not. Interestingly enough, the North American-Rockwell Space Shuttle actually re-enters the earth's atmosphere at an incomprehensible speed of Mach 25.0, so maybe we should be working on Shuttle type transports in place of the current designs in-play?
So, have you heard of any other civilian Supersonic aircraft designs that are currently in-work? Maybe you were fortunate enough to have flown on Concorde, and you have some reflections of this experience to impart to us here. Any input that you care to make will be of great interest to all of the readers here at Globalair.com. So please don't be bashful and go ahead and write your comments and suggestions here. Please don't forget that whatever you write here, can be seen publicly by everyone that visits this page, so please be funny, be inspired, but most importantly of all, please be nice. See you next month.