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The instability of a thin sheet of liquid moving in the same direction as an air stream is studied theoretically. It is found that instability occurs if the Weber number is less than a critical value related to the ratio of the air and liquid stream velocities. Also, the wavelength for maximum instability is found to be inversely proportional to this critical value.

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T HE effect of trailing vortices from a large leading wing on a trailing aircraft is studied experimentally. The aerodynamic response of the trailing aircraft is examined through measurements of lift, drag, and pitching moment for various angles of attack of the two models and different separation distances between them. The results show that trailing vortices cause a remarkable loss of lift on the trailing aircraft. This phenomenon becomes more significant as the angle of attack of the leading object is increased. Results demonstrate that in order to maintain the same lift, drag would increase as the leading wing angle of attack is increased. Nomenclature C= chord length of the trailing aircraft C D = drag coefficient of the trailing aircraft C L = lift coefficient of the trailing aircraft CM = pitching moment coefficient of the trailing aircraft X = separating distance between the two models in the horizontal plane Y = separating distance between the two models in the vertical plane a.= trailing aircraft angle of attack (} = leading wing angle of attack