On Physical Aeroacoustics with Some Implications for Low-Noise Aircraft Design and Airport Operations

Abstract

Air traffic is growing at a steady rate of 3% to 5% per year in most regions of the world, implying a doubling every 15-25 years. This requires major advances in aircraft noise reduction at airports, just not to increase the noise exposure due to the larger number of aircraft movements. In fact it can be expected, as a consequence of increased opposition to noise by near airport residents, that the overall noise exposure will have to be reduced, by bans, curfews, fines, and other means and limitations, unless significantly quieter aircraft operations are achieved. The ultimate solution is aircraft operations inaudible outside the airport perimeter, or noise levels below road traffic and other existing local noise sources. These substantial noise reductions cannot come at the expense of a degradation of cruise efficiency, that would affect not just economics and travel time, but would increase fuel consumption and emission of pollutants on a global scale. The paper reviews the: (i) current knowledge of the aircraft noise sources; (ii) the sound propagation in the atmosphere and ground effects that determine the noise annoyance of near-airport residents; (iii) the noise mitigation measures that can be applied to current and future aircraft; (iv) the prospects of evolutionary and novel aircraft designs towards quieter aircraft in the near term and eventually to operations inaudible outside the airport perimeter. The 20 figures and 1 diagram with their legends provide a visual summary of the review.

On the Extrapolation of Stability Derivatives to Combined Changes in Airspeed and Angles of Attack and Sideslip

“…The dimensionless stability derivatives (19,20) involve division by the square of the velocity, leading to (28):…”

“…(iv)-(vi) the ratio of airspeeds (23d) and ratios of cosines of AoA (23b) and AoS (23c) between each flight condition 2-11 (13)(14)(15)(16)(17)(18)(19)(20)(21)(22) and baseline flight condition 1 ( 12); (vii)-(viii) the five extrapolation factors (40/30/38/43b) for the stability derivatives (42/41/24/38/42), respectively. Tables 7 and 8 gives the stability matrix for the reference landing (takeoff) flight condition 1 (12) in Table 4, for which the airspeed, AoA, and AoS are repeated at the bottom of Tables 5 and 6.…”

“…The extrapolation of stability derivatives is illustrated for a V-tailed single-aisle jetliner design but can be applied not only to V-tailed aircraft [11][12][13][14][15] but to other configurations [16][17][18][19], such as blended-wing bodies [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] and joined wings [40,41], that can have large number of control surfaces changing their geometry. The effort of determination of each stability derivative for a given airspeed could be reduced from one full table (combinations of the AoA and AoS) to (a) a list (dependence on one extrapolated to the other) or (b) a single value (extrapolation from given AoA and AoS).…”

On the Handling Qualities of Two Flying Wing Aircraft Configurations

“…If the flying wing has overwing engines for noise shielding, there is a strong pitch-down moment to be compensated more easily with a long moment arm by smaller deflection of pitch control surfaces with less area. The overwing engine location, while ideal for noise shielding [54][55][56][57][58][59], places the engine nacelles in an accelerated flow leading to significant wave drag at lower cruising speeds. The short-and-wide BWB2 would subject outboard passengers to larger roll motions than the long-and-narrow BWB 1.…”

On the maximisation of control power in low-speed flight

“…Thus the present paper is also a contribution to the expanding literature on various aspects of the BWB aircraft. (23)(24)(25)(26) The theory concerns the maximisation of control power in low-speed flight for a FW aircraft configuration and is considered as concerns several components of control forces and moments. First a method of finding the minimum and maximum forces and/or moments is presented (section 1); it finds the extrema (section 3) of forces and moments (section 2), taking into account the range of possible control surface deflections (section 4).…”