**Abstract**

Lately, the interest for passenger space planes, supersonic passenger aircraft, and supersonic business jets has greatly increased. In order to mitigate the sonic boom effects at ground level, some aerospace companies proposed airplanes that have a very small transversal fuselage section or that have a curved ("shaped") fuselage. Obviously, shaping the fuselage leads to the increase of dynamic drag and manufacturing cost. Reducing the fuselage transverse section leads to reducing the useful volume inside fuselage and increases the landing distance of aircraft. The solution presented in this chapter shows that it is theoretically and technologically possible as the shock wave to be dispersed through mechanical or electrical means. The shock wave is in fact a stationary effect generated by the move of aircraft with constant speed relatively to surrounding air. If this feature is in a way or another canceled, the shock wave is dispersing. Due to dispersion of the shock wave the 'N' wave at the ground is tens of times larger and the sonic boom is correspondingly lower. The shock wave dispersion system of the future could be mechanical or electrical is activated only when the supersonic aircraft/space plane is flying horizontally over community.

**Keywords:** sonic boom mitigation, shock wave dispersion, supersonic aircraft, supersonic business jet, space plane

#### **1. Introduction**

The first manned airplane, which exceeded the speed of sound in horizontal flight was the American airplane X-1 manufactured by Bell Aircraft Corporation [1]. On the 14th of October 1947, the X-1 aircraft was air-launched at the altitude of 7000 m from the bomb bay of a Boeing B-29 and then climbed to the test altitude of 13,000 m. Piloted by Chuck Yeager, the aircraft reached a speed of 1127 km/h (Mach = 1.06) in horizontal flight. Since the maiden flight, the aircraft accumulated a number of 78 flights and on the 26th of March, 1948 it attained a speed of 1540 km/h (Mach = 1.45) at the altitude of 21,900 m.

Because at that time no jet engine was powerful enough, the aircraft Bell X-1 was powered by a four-chamber XLR-11 rocket engine that produced a static thrust of 26.5 kN. This was the first time when the sonic boom was revealed as a natural phenomenon generated by the aircraft breaking the sound barrier. In essence, the sonic boom is the manifestation of the shock waves generated by a supersonic aircraft perceived at ground level.

After this important event, a multitude of supersonic aircraft having exclusive military applications was developed and manufactured in series by the most technologically advanced countries. Simultaneously, the phenomenon of sonic boom was intensively researched from a theoretical and experimental point of view [2–6]. Dassault, and Aerion Corporation proposed airplanes having thin or curved (shaped) fuselages, and other designers proposed biplane type aircraft.

current technology is necessary.

*Sonic Boom Mitigation through Shock Wave Dispersion DOI: http://dx.doi.org/10.5772/intechopen.85088*

of aircraft.

**Figure 1.**

**Figure 2.**

**113**

*An advanced Lockheed Martin concept [19].*

*An advanced Northrop Grumman concept [19].*

Some design solutions are presented in **Figures 1** and **2** [19]. The long aircraft having a small cross section (**Figure 1**) needs a too long landing distance, and the space for passengers inside fuselage is small. Nevertheless, it seems that this solution began to be preferred at present by aircraft manufacturers. This preference is explained by the manufacturing costs that are low because no major change in the

Obviously, the curved (shaped) fuselage (**Figure 2**) strongly perturbs the airstream flowing around the aircraft. As a result, more power is required for flight. At the same time, the curved fuselage considerably increases the manufacturing costs

At the beginning, due to the fact that the interest for the supersonic flights was exclusively for military applications, the ecological impact of sonic boom was not taken into account.

However, on the 2nd of March 1969, the first flight of Concorde supersonic passenger aircraft took place. This aircraft was produced by the French company Aerospatiale and British Aircraft Corporation (BAC). Concorde was a large enough aircraft (much larger than a usual military supersonic aircraft) to reveal the extremely high negative environmental impact of the sonic boom [7]:

Length: 62.19 m Wingspan: 25.6 m Height: 12.19 m Empty weight: 79,260 kg Capacity: max. 144 passengers Maximum speed: Mach 2.04 (≈2179 km/h) at cruise altitude Cruise speed: Mach 2.02 (≈2158 km/h) at cruise altitude Range: 7222.8 km Service ceiling: 18,290 m

On the 24th of October 2003, Concorde operated its last flight, leaving the aircraft market and airspace. An important reason was the impact of the sonic boom produced on the environment/community.

This fact raised the interest for sonic boom mitigation. Thus, important papers [8–11] were written on this subject, and a number of solutions for sonic boom mitigation were filled in patent [12–18].

Lately, an important change on the aircraft market took place: the start of a high demand for supersonic business jet and a continuous rise of interest for very highspeed passenger transportation, supersonic and hypersonic airliners.

An important problem generated by supersonic aircraft is the effect of sonic boom at the ground level. The sonic boom is an "N"-shaped pressure distribution, which spans the ground when an aircraft is flying at supersonic speed. The lower the flying height, the higher the material damages and annoyance produced in community.

This problem blocked the development of supersonic civil aircraft for a long period of time.

The state of the art regarding the solutions for mitigation of sonic boom effects at ground level is presented in Chapter 2 together with the drawbacks of these solutions.

In the next points of this chapter, the authors underline some important characteristics of shock wave, which support a new possible solution to mitigate the sonic boom impact at ground level: dispersion of shock wave mainly through vibration of aircraft nose surface and wing leading to edge surface. The explanation is simple: the shock wave is a steady-state effect, which is generated through moving of aircraft with a constant speed. If this steady-state characteristic of flight is canceled through vibration of the specified surfaces, the shock wave is dispersed, and its effect at ground level (known as "sonic boom") is greatly reduced.

#### **2. The state of the art**

For reducing sonic boom effects at ground level, companies as Supersonic Aerospace International, Lockheed, in collaboration with NASA, Boeing, Airbus,

*Sonic Boom Mitigation through Shock Wave Dispersion DOI: http://dx.doi.org/10.5772/intechopen.85088*

After this important event, a multitude of supersonic aircraft having exclusive military applications was developed and manufactured in series by the most technologically advanced countries. Simultaneously, the phenomenon of sonic boom was intensively researched from a theoretical and experimental point of view [2–6]. At the beginning, due to the fact that the interest for the supersonic flights was exclusively for military applications, the ecological impact of sonic boom was not

*Environmental Impact of Aviation and Sustainable Solutions*

However, on the 2nd of March 1969, the first flight of Concorde supersonic passenger aircraft took place. This aircraft was produced by the French company Aerospatiale and British Aircraft Corporation (BAC). Concorde was a large enough aircraft (much larger than a usual military supersonic aircraft) to reveal the extremely high negative environmental impact of the sonic boom [7]:

On the 24th of October 2003, Concorde operated its last flight, leaving the aircraft market and airspace. An important reason was the impact of the sonic boom

This fact raised the interest for sonic boom mitigation. Thus, important papers [8–11] were written on this subject, and a number of solutions for sonic boom

Lately, an important change on the aircraft market took place: the start of a high demand for supersonic business jet and a continuous rise of interest for very high-

An important problem generated by supersonic aircraft is the effect of sonic boom at the ground level. The sonic boom is an "N"-shaped pressure distribution, which spans the ground when an aircraft is flying at supersonic speed. The lower the flying height, the higher the material damages and annoyance produced in community. This problem blocked the development of supersonic civil aircraft for a long

The state of the art regarding the solutions for mitigation of sonic boom effects at ground level is presented in Chapter 2 together with the drawbacks of these

In the next points of this chapter, the authors underline some important characteristics of shock wave, which support a new possible solution to mitigate the sonic boom impact at ground level: dispersion of shock wave mainly through vibration of aircraft nose surface and wing leading to edge surface. The explanation is simple: the shock wave is a steady-state effect, which is generated through moving of aircraft with a constant speed. If this steady-state characteristic of flight is canceled through vibration of the specified surfaces, the shock wave is dispersed, and its

For reducing sonic boom effects at ground level, companies as Supersonic Aero-

space International, Lockheed, in collaboration with NASA, Boeing, Airbus,

Maximum speed: Mach 2.04 (≈2179 km/h) at cruise altitude Cruise speed: Mach 2.02 (≈2158 km/h) at cruise altitude

speed passenger transportation, supersonic and hypersonic airliners.

effect at ground level (known as "sonic boom") is greatly reduced.

taken into account.

Length: 62.19 m Wingspan: 25.6 m Height: 12.19 m

Range: 7222.8 km Service ceiling: 18,290 m

period of time.

**2. The state of the art**

solutions.

**112**

Empty weight: 79,260 kg Capacity: max. 144 passengers

produced on the environment/community.

mitigation were filled in patent [12–18].

Dassault, and Aerion Corporation proposed airplanes having thin or curved (shaped) fuselages, and other designers proposed biplane type aircraft.

Some design solutions are presented in **Figures 1** and **2** [19]. The long aircraft having a small cross section (**Figure 1**) needs a too long landing distance, and the space for passengers inside fuselage is small. Nevertheless, it seems that this solution began to be preferred at present by aircraft manufacturers. This preference is explained by the manufacturing costs that are low because no major change in the current technology is necessary.

Obviously, the curved (shaped) fuselage (**Figure 2**) strongly perturbs the airstream flowing around the aircraft. As a result, more power is required for flight. At the same time, the curved fuselage considerably increases the manufacturing costs of aircraft.

**Figure 1.** *An advanced Lockheed Martin concept [19].*

**Figure 2.** *An advanced Northrop Grumman concept [19].*

For a very long period of time, the "shaping" solution was the preferred one. According to this solution, shaping the fuselage leads to the changing of the "N" wave shape at ground level and mitigation of its impact.

The theory of sonic boom mitigation through shaping was established during the 1960s–1970s with the papers written by Seebass, Carlson, and Darden [8, 20, 21]. This theory was not proven until 2002.

In 2002, the Defense Advanced Research Projects Agency (DARPA) selected several companies for the Phase II of the Quiet Supersonic Platform (QSP) program [22]. The allocated research funds were of about 9 million USD. The selected companies were the following:


These system integrators updated their aircraft and engine designs and technologies; performed validation of their designs, utility, and cost analysis; and developed technology maturation roadmaps.

Additional funds were received by Northrop Grumman Corporation to conduct flight demonstration of direct sonic boom mitigation using a modified F-5E aircraft.

A special nose glove was designed for modification of aircraft to produce a shaped sonic boom profile with a lower impact at the ground level. Before the flight demonstration, tests done in wind tunnel validated the computed sonic boom signature predictions for the modified F-5E aircraft. A series of flight tests validated the predicted persistence of shaped sonic booms.

This program was very important because it demonstrated for the first time that an appropriately shaped aircraft can mitigate of sonic boom.

The experimental F-5E aircraft modified by Northrop Grumman Corporation (named F-5 Shaped Sonic Boom Demonstrator (SSBD)) is presented in **Figure 3** [23].

The theory was proven to work under practical design, fabrication, flight, and atmospheric conditions. Results of tests confirmed that shaping was successful in altering the sonic boom signature at the ground. Ground measurements matched predictions (flattop modified waveform relative to N-wave unmodified vehicle, **Figure 4**) [23]. In **Figure 4**, one can see that the "N" wave is no longer sharp in the case of shaped nose of F-5 SSBD (blue line) in comparison with the case of unmodified aircraft F-5E (red line). During this experiment, sonic boom reduction technology worked by achieving a shaped sonic boom, validating that shocks could be kept from coalescence all the way to the ground.

The image of modified aircraft from **Figure 3** shows at a glance the important drawbacks of this solution, affecting aerodynamic characteristics, frame's strength, weight, useful volume, and manufacturing cost of aircraft. An acceptable compromise is difficult to be found especially in the case of large passenger aircraft.

Boomless cruise: 1.1–1.2 Mach Long range cruise: 0.95 Mach Max. range, Mach 1.4: 7780 km Max. range, Mach 0.95: 10,000 km

*The F-5E aircraft modified by Northrop Grumman [23].*

*Sonic Boom Mitigation through Shock Wave Dispersion DOI: http://dx.doi.org/10.5772/intechopen.85088*

*First measurement of F-5E-shaped sonic boom aircraft modified by Northrop Grumman [23].*

Wing area: 140 sq.m Interior dimensions: Height: 1.9 m Width: 2.2 m Cabin length: 9.1 m Exterior dimensions: Length: 51.8 m

**Figure 4.**

**115**

**Figure 3.**

These drawbacks of shaping solution oriented the aircraft manufacturers to solution of supersonic aircraft with very thin fuselages. The first supersonic business jet is expected as to be Aerion AS2 which will be launched on market in 2023 (**Figure 5**) [24].

Main characteristics of this aircraft are [24]: Supercruise: 1.4 Mach

*Sonic Boom Mitigation through Shock Wave Dispersion DOI: http://dx.doi.org/10.5772/intechopen.85088*

For a very long period of time, the "shaping" solution was the preferred one. According to this solution, shaping the fuselage leads to the changing of the "N"

The theory of sonic boom mitigation through shaping was established during the 1960s–1970s with the papers written by Seebass, Carlson, and Darden [8, 20, 21].

In 2002, the Defense Advanced Research Projects Agency (DARPA) selected several companies for the Phase II of the Quiet Supersonic Platform (QSP) program [22]. The allocated research funds were of about 9 million USD. The selected

• Lockheed Martin, Advanced Development Company, Palmdale, California

These system integrators updated their aircraft and engine designs and technologies; performed validation of their designs, utility, and cost analysis; and devel-

Additional funds were received by Northrop Grumman Corporation to conduct flight demonstration of direct sonic boom mitigation using a modified F-5E aircraft. A special nose glove was designed for modification of aircraft to produce a shaped sonic boom profile with a lower impact at the ground level. Before the flight demonstration, tests done in wind tunnel validated the computed sonic boom signature predictions for the modified F-5E aircraft. A series of flight tests validated

This program was very important because it demonstrated for the first time that

The experimental F-5E aircraft modified by Northrop Grumman Corporation

The theory was proven to work under practical design, fabrication, flight, and atmospheric conditions. Results of tests confirmed that shaping was successful in altering the sonic boom signature at the ground. Ground measurements matched predictions (flattop modified waveform relative to N-wave unmodified vehicle, **Figure 4**) [23]. In **Figure 4**, one can see that the "N" wave is no longer sharp in the

unmodified aircraft F-5E (red line). During this experiment, sonic boom reduction technology worked by achieving a shaped sonic boom, validating that shocks could

The image of modified aircraft from **Figure 3** shows at a glance the important drawbacks of this solution, affecting aerodynamic characteristics, frame's strength, weight, useful volume, and manufacturing cost of aircraft. An acceptable compromise is difficult to be found especially in the case of large passenger aircraft. These drawbacks of shaping solution oriented the aircraft manufacturers to solution of supersonic aircraft with very thin fuselages. The first supersonic business jet is expected as to be Aerion AS2 which will be launched on market in 2023

• Northrop Grumman Corporation, El Segundo, California

• Arizona State University, Tempe, Arizona

the predicted persistence of shaped sonic booms.

be kept from coalescence all the way to the ground.

Main characteristics of this aircraft are [24]:

an appropriately shaped aircraft can mitigate of sonic boom.

(named F-5 Shaped Sonic Boom Demonstrator (SSBD)) is presented in

case of shaped nose of F-5 SSBD (blue line) in comparison with the case of

• General Electric, Cincinnati, Ohio

oped technology maturation roadmaps.

**Figure 3** [23].

(**Figure 5**) [24].

**114**

Supercruise: 1.4 Mach

wave shape at ground level and mitigation of its impact.

*Environmental Impact of Aviation and Sustainable Solutions*

This theory was not proven until 2002.

companies were the following:

**Figure 3.** *The F-5E aircraft modified by Northrop Grumman [23].*

#### **Figure 4.**

*First measurement of F-5E-shaped sonic boom aircraft modified by Northrop Grumman [23].*

Boomless cruise: 1.1–1.2 Mach Long range cruise: 0.95 Mach Max. range, Mach 1.4: 7780 km Max. range, Mach 0.95: 10,000 km Wing area: 140 sq.m Interior dimensions: Height: 1.9 m Width: 2.2 m Cabin length: 9.1 m Exterior dimensions: Length: 51.8 m

through liquids, which fill metallic ducts. These ducts act as "wave guides" (see **Figure 6**). Piston, 1, oscillates in a sinusoidal manner and creates longitudinal waves of pressure, a. These waves propagate through liquid, b, which fills duct, 2, and actuates driven piston 3. Pistons 1 and 3 are going to oscillate with the same

frequency. Crank drives, 4, assure the continuous motion of pistons. This method of power transmission relies on liquid compressibility. The phase difference between pistons 1 and 3 depends on the ratio of duct length and wavelength. If this ratio is an odd number, pistons 3 and 1 oscillate in opposition (i.e., the phase difference is equal to π). The amount of power that can be transmitted is proportional to the pressure of liquid within duct. Finally, George Constantinescu demonstrated that sonic waves act like alternative current and built many wave generators and sonic engines with power of tens of kW. Frequencies of sonic waves used for power

This new solution was proposed for the first time in a previous paper of authors [26]. It consists in dispersion of shock wave during its generation by an aircraft in supersonic flight having as a consequence extension of "N" wave (sonic boom) on a much larger area at ground level. In this way, the impact of sonic boom on com-

This solution offers to aircraft designers the possibility to create supersonic aircraft with a larger space in fuselage and transportation of a higher number of passengers.

The new proposed solution for sonic boom mitigation is based on the following

2. For low values of Mach no. (M = 1, … 1.8), a low variation of the semi-angle α of a wedge, which is placed in a supersonic stream produces a larger variation

The thickness of shock wave is extremely small. This thickness depends by Mach number as presented in **Figure 7** [27]. For this reason, when the shock wave hits the

According to Observation 1, in normal circumstances, the shock wave cannot be

<sup>2</sup> *<sup>M</sup>*<sup>2</sup> sin <sup>2</sup>*<sup>β</sup>* � <sup>1</sup> � � � <sup>1</sup> " #

(1)

eliminated because it is a physical effect governed by natural laws. However, if circumstances are changed, for example, the steady-state is substituted with a transient state; the effect of sonic boom on ground surface will be much reduced. Taking as example the oblique shock wave created by a wedge having the semiangle α (**Figure 8**), the semi-angle β of the shock wave is given by Eq. (1) [28]. Looking to Eq. (1), one can see that β is depending on the semi-angle α and the

cot *<sup>α</sup>* <sup>¼</sup> tan *<sup>β</sup>* ð Þ *<sup>k</sup>* <sup>þ</sup> <sup>1</sup> *<sup>M</sup>*<sup>2</sup>

1. The shock wave is a steady-state effect, which appears when the speed of

aircraft is higher than the speed of sound in air.

ground, a sudden increase of local air pressure is produced.

speed of aircraft given by the Mach number, M:

transmitting can be from several tens to tens of thousands of Hz.

**4. New solution for sonic boom mitigation**

*Sonic Boom Mitigation through Shock Wave Dispersion DOI: http://dx.doi.org/10.5772/intechopen.85088*

munity is much reduced.

observations:

**117**

**4.1 The bases of the new solution**

of shock wave angle, β.

**Figure 5.** *Aerion supersonic business jet [24].*

Wingspan: 23.5 m Height: 6.7 m Fuel quantity: 26,800 kg

Looking to the lengths of cabin (9.1 m) and aircraft (51.8 m), one can see at a glance one of the most important drawbacks of this solution: The space for passengers is extremely low due to the need of the aircraft fuselage to be very thin and long.
