## 3 Description of SST and Its Departure Noise Modeling  
The study considers a next-generation SST configuration (Figure 3) with a maximum takeoff mass of 72 tons, powered by three engines with a bypass ratio of 2.5 at takeoff. It has a seating capacity of 20 passengers and is designed for a cruise speed of \(M=1.8\), a flight range of 7400 km, and a balanced field length of 3200 m. Its takeoff thrust-to-weight ratio is 0.52, takeoff wing load is 450 kgf/m\({}^{2}\), and the maximum lift-to-drag ratio of the aircraft at takeoff is \(L/D=6.5\)[30]. As has been noted in the Introduction, in this study, the modeling of aircraft noise involves decoupling of engine noise data determination from flight trajectory calculations. This is commonly performed for subsonic aircraft when the static acoustic test data are available for aircraft engines. At the moment, it seems that such data are absent for engines of next-generation SST, which makes the researchers, and the industry rely on the simulation results based on semi-empirical models of powerplant noise sources. The SST configuration used in this study has been developed with a view to an existing subsonic donor engine (Figure 1b), which has the same bypass ratio of 2.5 and can produce the same thrust at takeoff that is required for the SST departure procedure. Indeed, it is likely that engines of future SST will be different from their subsonic analogs with the same thrust and bypass ratio. However, SST engines are still under development, and how their acoustic characteristics differ from the engines for subsonic aircraft is one of the uncertainties of the SST research. Since the objective of the study consists of the assessment of VNRS efficiency for noise reduction, and not in determining the compliance of the SST with Chapter 14 norms, it was deemed possible to use the experimental acoustic data of the subsonic engine for noise calculations of the SST at takeoff [27]. Such an approach ensures that all the noise sources of the engine are accounted for and allows the uncertainties associated with engine cycle modeling to be excluded from the analysis of VNRS efficiency. In general, noise modeling of the next-generation SST in this study is performed in such a manner as to minimize the uncertainties of noise calculation methods. For instance, although one engine of the next-generation SST is located above the fuselage, so that its noise can be shielded by the airframe, no correction for the shielding has been implemented. The under-the-wing engines of the next-generation SST have long inlets that can result in significant noise reduction, especially after acoustic liners are installed inside the inlet ducts. However, sound propagation in such long and curved ducts with impedance walls  
Figure 3: The notional next-generation SST: (**a**) side view, (**b**) top view (adopted from [30; 31]). is not sufficiently understood at the moment, so no additional correction for this effect has been used as well. Such assumptions are intended to allow for isolating (decoupling) the effect of VNRS by engine thrust control from the effects of installed engine noise modeling. Airframe noise is considered an important noise source of subsonic aircraft at approach [32]. During takeoff, the contribution of airframe noise is small even for subsonic aircraft; the available estimates show that airframe noise of SST at takeoff is small as well [14; 17; 21]. In [21], it was obtained that the airframe noise of the SST is smaller than engine noise by 27.9 EPNdB at the lateral certification point K\({}_{2}\), and by 23.7 EPNdB at the flyover certification point K\({}_{1}\). Similarly, in [17] it was shown that the airframe noise is less than engine noise by 15 EPNdB and 25 EPNdB at the flyover and lateral certification points, respectively. Although the authors of [14] did not provide quantitative estimates of airframe noise, their calculations led to the conclusion that this noise source was insignificant compared to engine noise.