768 HENNE 3500 目Over Water 3000 Over Land 2500 2000 1500 1000 500 Average range:1290 n.m. Percent of miles flown over water:25% Fig.5 Random sample of small civil aircraft operation compatible.6 In this context,environmentally compatible means effectively addressing the following:1)sonic boom,2)engine ex- Initial Cruise Sonic Boom Strength haust emissions,and 3)airport noise.A feasible design must reduce 3.0 the configuration's sonic boom signature such that supersonic flight HSCT over land is acceptable to the public.As discussed earlier,the market 2.5 research studies have repeatedly confirmed that supersonic overland Concorde flight is of critical importance to the value of the vehicle..3.5 The 2.0 design must also minimize adverse atmospheric effects due to en- gine exhaust emissions throughout all operations.Emissions must SBJ be minimized during both low-speed,low-altitude airport operations 1.5 as well as high-altitude supersonic cruise operations.Furthermore, a successful QSJ must be a quiet,good neighbor to the airport en- 1.0 vironment.It should make no more noise than today's quiet small QSJ Shaped DARPA QSP Goal subsonic civil jets. QSJ Internal Concepts Sonic Boom The effort to suppress sonic boom successfully has several ma- 200000 400000 600000 800000 jor aspects.First,the vehicle aerodynamic design is used to shape Initial Cruise Weight-lb the sonic boom signature.Shaped signatures are defined by the prevention of coalescence of the signature into an annoying N- Fig.6 Sonic boom initial overpressure strongly affected by vehicle shaped pressure wave.Second,psychoacoustic testing is being used weight. to establish signature levels and desired signature shapes that are considered environmentally acceptable.Third,a flight demonstra- Gulfstream has defined several unique airplane configuration tion will be required to prove boom suppression acceptability.A details that reduce the initial overpressure and enhance the vehi- flight demonstration will provide a foundation of scientific data cle designer's ability to control the shape of the ground signature necessary for regulation of supersonic overland flight,as well as produced.Results for several of these configurations are in- risk reduction for the business decision to launch a production dicated in Figs.6 and 7.Several of these design concepts have program. been validated in recent wind-tunnel testing conducted at NASA When the physics of sonic boom are considered,it is very clear Langley's 4 Foot Unitary Wind Tunnel.As indicated in Fig.8 that a small aircraft has a profound advantage over large aircraft.The the data for the advanced boom suppression concepts show very size and weight of a vehicle has a first-order effect on the strength of promising signature characteristics.Based on these computational the sonic boom signature.As the vehicle weight decreases,the sonic fluid dynamics(CFD)and wind-tunnel test results,initial overpres- boom disturbance is decreased.Careful attention to the physical sures of less than 0.2 psf and peak overpressures of 0.5-0.6 psf shape of the vehicle can result in a shaped ground signature rather seem quite achievable.Clearly,additional model and flight test- than a coalesced N wave.Shaped ground signatures avoid the large ing are needed to develop,validate,and fully exploit sonic boom abrupt pressure increases associated with beginning and end of a suppression technology.This aerodynamic technology need is a typical sonic boom N wave.Shaped signatures have lower initial long-standing aeronautical barrier that has not yet been adequately and final pressure increases and are perceived as substantially quieter addressed. due to their more-sinusoidal,very-low-frequency character.Shaped Sonic boom strength for configurations with signatures such as signatures can be thought of as precoalesced signatures designed to those in Figs.7 and 8 have been analyzed in terms of perceived a special wave shape. level of noise in decibels (PLdB)and A-weighted noise in decibels Figures 6 and 7 show the impact of vehicle size and shaping [dB(A)].The results shown in Fig.9 show a remarkable improve- on the sonic boom ground signature.These charts show data for a ment in the cruise signature acoustic strength.Results for configu- 300-passenger high-speed civil transport(HSCT),the Concorde,a rations shown in Fig.9 indicate that the noise levels can be reduced generic supersonic business jet(SBJ),and two QS]configurations. more than 35 dB below that of the Concorde sonic boom.These The effect of weight alone is shown in Fig.6 by the line connecting levels are at or below conversation-level acoustics.Such signatures three N-wave vehicles:HSCT,Concorde,and SBJ. are better characterized as sonic puffs rather than as sonic booms.768 HENNE Fig. 5 Random sample of small civil aircraft operation. compatible.1,6 In this context, environmentally compatible means effectively addressing the following: 1) sonic boom, 2) engine ex￾haust emissions, and 3) airport noise. A feasible design must reduce the configuration’s sonic boom signature such that supersonic flight over land is acceptable to the public. As discussed earlier, the market research studies have repeatedly confirmed that supersonic overland flight is of critical importance to the value of the vehicle.1,3,5 The design must also minimize adverse atmospheric effects due to en￾gine exhaust emissions throughout all operations. Emissions must be minimized during both low-speed, low-altitude airport operations as well as high-altitude supersonic cruise operations. Furthermore, a successful QSJ must be a quiet, good neighbor to the airport en￾vironment. It should make no more noise than today’s quiet small subsonic civil jets. Sonic Boom The effort to suppress sonic boom successfully has several ma￾jor aspects. First, the vehicle aerodynamic design is used to shape the sonic boom signature. Shaped signatures are defined by the prevention of coalescence of the signature into an annoying N￾shaped pressure wave. Second, psychoacoustic testing is being used to establish signature levels and desired signature shapes that are considered environmentally acceptable. Third, a flight demonstra￾tion will be required to prove boom suppression acceptability. A flight demonstration will provide a foundation of scientific data necessary for regulation of supersonic overland flight, as well as risk reduction for the business decision to launch a production program. When the physics of sonic boom are considered,9 it is very clear that a small aircraft has a profound advantage over large aircraft. The size and weight of a vehicle has a first-order effect on the strength of the sonic boom signature. As the vehicle weight decreases, the sonic boom disturbance is decreased. Careful attention to the physical shape of the vehicle can result in a shaped ground signature rather than a coalesced N wave. Shaped ground signatures avoid the large abrupt pressure increases associated with beginning and end of a typical sonic boom N wave. Shaped signatures have lower initial and final pressure increases and are perceived as substantially quieter due to their more-sinusoidal, very-low-frequency character. Shaped signatures can be thought of as precoalesced signatures designed to a special wave shape. Figures 6 and 7 show the impact of vehicle size and shaping on the sonic boom ground signature. These charts show data for a 300-passenger high-speed civil transport (HSCT), the Concorde, a generic supersonic business jet (SBJ), and two QSJ configurations. The effect of weight alone is shown in Fig. 6 by the line connecting three N-wave vehicles: HSCT, Concorde, and SBJ. Fig. 6 Sonic boom initial overpressure strongly affected by vehicle weight. Gulfstream has defined several unique airplane configuration details that reduce the initial overpressure and enhance the vehi￾cle designer’s ability to control the shape of the ground signature produced.10,11 Results for several of these configurations are in￾dicated in Figs. 6 and 7. Several of these design concepts have been validated in recent wind-tunnel testing conducted at NASA Langley’s 4 Foot Unitary Wind Tunnel. As indicated in Fig. 8, the data for the advanced boom suppression concepts show very promising signature characteristics. Based on these computational fluid dynamics (CFD) and wind-tunnel test results, initial overpres￾sures of less than 0.2 psf and peak overpressures of 0.5–0.6 psf seem quite achievable. Clearly, additional model and flight test￾ing are needed to develop, validate, and fully exploit sonic boom suppression technology. This aerodynamic technology need is a long-standing aeronautical barrier that has not yet been adequately addressed. Sonic boom strength for configurations with signatures such as those in Figs. 7 and 8 have been analyzed in terms of perceived level of noise in decibels (PLdB) and A-weighted noise in decibels [dB(A)]. The results shown in Fig. 9 show a remarkable improve￾ment in the cruise signature acoustic strength. Results for configu￾rations shown in Fig. 9 indicate that the noise levels can be reduced more than 35 dB below that of the Concorde sonic boom. These levels are at or below conversation-level acoustics. Such signatures are better characterized as sonic puffs rather than as sonic booms