Month in the Patent Office

A ram jet comprising in the duct wall upstream of the heat receiving zone slot like passages inclined at an acute angle to the duct wall for bleeding off a layer of air next the inner surface of the ram jet considerably thicker than the boundary layer and discharging this air in the direction of the external air flow and means for varying the effective cross section of the passages, has the passages defined by one or a cascade of aerofoil like vanes arranged so that under prescribed conditions of operation, i.e., subsonic or supersonic, as the case may be, the pressure acting on the extrados of the vanes downstream of the passage throats nowhere exceeds the static pressure at the entry of the duct. A ramjet a, FIG. 1, has between its inlet and the burner b a number of openings in which are mounted a number of vanes c. The size and spacing of the vanes are chosen so that the layer of air d which is discharged through the vanes is thicker than the boundary layer. The bleeding off of this layer of air reduces the effective inlet area of the duct from Wo to W1.o. When the flow is subsonic the vanes may be of aerofoil section and form convergent passages. When the flow is supersonic, the vanes may be as shown in FIG. 2 in which the backs of the vanes are relieved to cause an abrupt increase of the passage area downstream of the throats 5b, 6b so that the pressure p on the backs of the vanes is never more than the static pressure at the inlet end of the duct. In a modification, the vanes are shaped to form convergent‐divergent passages. The quantity of air bled off may be varied by pivoting the vanes and connecting the vanes to an operating rod actuated manually or by a servomotor controlled by a pressure in the duct or by the pilot's throttle lever. In a further modification, FIG. 3. the outlet of the vanes 31 is covered by a slideable plate 91. The plate 91 is curved at its outer edges to form races for ball or roller bearings 10. The complementary races are formed by members 11 fixed to the outer face of the duct.