Comment on 'In-flight measurement of static pressures'

Abstract

R 1 includes some very interesting in-flight measurements of the steady and fluctuating trailing-edge pressures on an A310-200 aircraft at high speeds. However, Ref. 1 includes two remarks which could mislead some readers. When discussing the measured pressure spectra (Ref. 1, Fig. 11) it is noted that harmonics of torsion can be detected up to eighth order. Such indicates strong buffet motion. It is true that the peaks in the spectra indicate motion (better response or buffeting as defined in Ref. 2). The peaks cannot represent excitation (buffet) at those frequencies. The separations concerned are incipient and of very small scale. Hence, these are unlikely to be modifying the excitation. These motion-induced pressures should be related directly to the aerodynamic damping. It would be interesting to reanalyze the data to see if there are any changes in the phase of the trailing-edge pressures with respect to the wing motions as Q increases at constant Mach number. Later in the article there is a curious reference to buffet frequencies of 45-70 for aerofoils and Ref. 3 is cited. Such discrete (buffet) is determined by a frequency parameter based on the aerofoil chord (only 0.25 m in Ref. 3). With respect to a local chord of about 3.8 m at 71% semispan on the aircraft, the frequency parameter of Ref. 3 would imply frequencies of about 3-5 for flight at sea level. Therefore, the reference to /* = 25 Hz at M = 0.73 is unhelpful. Attribution of the lower frequencies observed to three-dimensional flow at flight conditions is wrong. It is well known that the on aerofoils and high-aspect-ratio swept wings is, in fact, similar in character (e.g., Ref. 4).