**1. Introduction**

The crucial issue of development of a new generation of supersonic civil aeroplanes (SCA) is to meet environmental requirements like sonic boom level, community noise level during landing and take-off cycle (LTO) and engine/CO2 emission levels. According to the requirements of Chapter 12 of the current ICAO noise standard, maximal SCA noise levels at certification reference points (RP) should be satisfied the noise limitations for subsonic jet aeroplane at the same maximum certificated take-off mass (MTOM), i.e. to the current requirements of Chapter 14, Annex 16, Volume I [1].

The SCA design features leads to the generation more intense noise during the LTO cycle vs. the noise of the subsonic jet aeroplane with the same MTOM. The estimations of the noise levels applied to advance SCA shown that it is still

impossible to meet the requirements at the current level of aviation technologies. The CAEP (Committee on Aviation Environmental Protection) has not yet developed the new standard for SCA noise at RP.

The lack of an international standard for SCA noise and the expectation of the implementation of several USA SCA projects in the current decade motivated the USA Federal Aviation Administration (FAA) to develop national standards. In March 2020, FAA published a preliminary version of the national noise standards for a distinct SCA class. The limit line of USA noise standards locates exactly in the middle between the Chapter 4 and Chapter 14 of the ICAO standard for subsonic jet aeroplanes [2]. The SCA class is limited by the MTOM value of 68 000 kg and by the cruise speed corresponding to the Mach number of 1.8.

NASA and other research centers assessments showed that meeting the FAA's published limits on the SCA noise level, and even more so meeting the requirements of Chapter 14, Annex 16, Volume I, may not be satisfied on the current technology level [3, 4].

The FAA rules also suggest the some changes to the existing noise certification reference procedures applied to the subsonic jet aeroplanes. It is specifically stipulated that the SCA noise certification will use of technical equipment (like Variable Noise Reduction System) that will implement new approaches to the SCA community noise reduction. The capability for SCA noise management during LTO cycle using the engine thrust variation providing engine automatic (programmed) thrust/power throttling was considered in the number of publications [3–8]. The aim of the studies was to assess the maximal SCA community noise reduction using the thrust management at LTO cycle.

## **2. Problem statement**

The take-off thrust (power) throttling has a contradictory effect on the noise levels in each take-off RP, i.e. on the lateral and flyover (cutback) noise levels. On the one hand, the lateral noise level is reduced due to a decrease of the engine exhaust jet velocity as well as fan circumferential velocity. On the other hand, the flyover noise level is increased due to the lower thrust settings are associated with the lower climb path, and therefore the distance from the community noise source to the take-off RP is decreased. Thus, a compromise solution on the engine thrust management (TM) during the take-off is required to reduce the take-off (lateral plus flyover) noise level.

In accordance with the noise certification procedure, the approach noise level is measured at approach using the constant flight speed along the path and the fixed glide slope angle θ which is equal to -3o [1].

To provide the flight along such path with the constant flight speed and glide slope angle, it is necessary to maintain a certain level of the engine thrust (power setting). The level of the thrust will be uniquely determined by the values of the specified flight speed and glide slope angle. In other words, if an aeroplane is flying along glide slope at a constant speed, there is a direct relationship between the levels of the required engine thrust and the glide slope angle.

The approach RP is determined by the point on the ground, on the extended center line of the runway at the distance Lapp = 2000 m from the threshold. Therefore, the approach noise level at varying the glide slope angle θ will mainly depend on the 2 factors: the flight altitude above the approach RP and the change of the engine parameters associated with a change in the required engine thrust (i.e. approach power setting).

*Estimation of Cumulative Noise Reduction at Certification Points for Supersonic Civil… DOI: http://dx.doi.org/10.5772/intechopen.97465*

Therefore, the variation of the approach power setting leading to a change of the glide angle is considered in the paper as a measure of the reduction of the approach noise level.

The paper presents the results of a computational study of the acoustic efficiency of using the programmed reduced cumulative (sum of the lateral, flyover and approach noise levels) noise thrust management with so-called Programmed Lapse Rate (PLR) during the take-off as well as the approach. The approach provides the reduction of the cumulative community noise taking into account the fan and exhaust jet noise.

It is well known that the current ICAO standard, Chapter 14, imposes more stringent requirements for the subsonic jet aeroplane than the previous Chapters 3 and 4 [1]. The intention of the SCA designers to follow the global trend of reducing the impact of aviation on the environment pushes them to consider the propulsion systems based on the turbofan with higher bypass ratio (BPR).

At the same time, there is a cardinal redistribution of the contributions between engine noise sources as increasing BPR. The dominance of the jet noise for the turbofan with lower BPR (~ 0.5…1.5) is replaced with an approximate equality of the fan and jet contributions for the turbofan with mediate BPR (~ 2.5…3.5) and then with predominant fan noise for the turbofan with higher BPR (~ 4.0…5.0).

The comparison of the effective perceived noise levels in case of use of the reference and the proposed programmed reduced cumulative noise thrust management using PLR (from here on programmed TM) is carried out as applied to a notional twin-engine supersonic business jet (SBJ). The SBJ has the range L = 7400 km, seating capacity n = 8 pax and balanced field length BFL = 2000 m.

The considered SBJ propulsion system is based on the turbofan with BPR = 2.5 … 5.0. The values of the range L, the seating capacity n and the balanced field length BFL are kept constant under the BPR variation. The take-off thrust loading is defined under provision of the specified balanced field length value.

The turbofan with BPR up to 5.0 is considered to maximize the SBJ noise reduction. At the same time, it is obvious that it is necessary to find a compromise solution, accounting the contradictory factors like nacelle size/drag, which is increased with increasing BPR.
