Shock-cell noise—aircraft measurements

A description is given of flight test measurements designed to determine the cause of severe acoustic loading on the tail planes of early V.C. 10 and B.A.C. 11̄1 aircraft. This loading was found to be due to in-flight shock-cell noise. A convergent-divergent nozzle design, together with minor structural modifications, was found to give the greatest overall alleviation of the problem for these two particular aircraft.