Abstract: A helicopter (1) has a horizontal rotor (2) driven for rotation about a vertical rotor axis (4), and a tail (9) extending backwards from the rotor axis (4) at a fixed angle (10) between about 20° and about 60° to a vertical longitudinal middle plane (7) of the helicopter (1) on a retreating blade side of the horizontal rotor (2). The tail (9) comprises a profiled body (16) including aerodynamic effective surfaces (19, 20) for selectively generating lift on the retreating blade side of the horizontal rotor (2) in forward flight of the helicopter (1). For hovering flight of the helicopter (1), the profiled body (16) can be swiveled about a swivel axis running parallelly to the main axis (21) of the tail for reducing a cross-sectional area of the profiled body facing the horizontal rotor (2).

Abstract: A digital particle image velovimetry (DPIV) method for contactless measurement of three dimensional flow velocities comprising the steps of seeding a flow with tracer particles; repeatedly illuminating a plane-like interrogation volume of the seeded flow; projecting the repeatedly illuminated interrogation volume onto at least a photo sensor in a projection direction for recording pictures of the illuminated interrogation volume; and determining the three dimensional flow velocities from the pictures of the repeatedly illuminated interrogation volume recorded by the photo sensor. The plane-like interrogation volume of the invention comprises at least two partial volumes positioned parallelly parallel to each other with regard to the projection direction. The step of repeatedly illuminating the interrogation volume comprises the step of illuminating the partial volumes in such a way that the pictures of different partial volumes are distinguishable from each other.

Abstract: An apparatus for the three-dimensional determination of flows has a light source for briefly illuminating a light section (3) and a stereoscopic recording device (10). The stereoscopic recording device (10) comprises two equivalent objectives (11, 12) aligned parallel to each other as well as perpendicular to the plane (22) of the light section (3), and behind the objectives (11, 12) two optical sensor fields (15, 16) aligned parallel to the plane (22). A forward displacement device for the synchronized forward displacement of the projections of the light source (3) onto the two sensor fields (15, 16) has two revolving mirrors (13, 14) aligned parallel and rotating in synchronization about a common axis of rotation (23) as well as in synchronization with the light source, whereby the axis of rotation (23) runs parallel to an imaginary line joining the two objectives (11, 12).