Teruhiko Kida

Jet-Flapped Wings in Very Close Proximity to the Ground

The method of matched asymptotic expansions is applied to the problem of jet-flapped wings of finite span in very close proximity to the ground. For the linearization of this problem, the order of small parameters, the angle of attack and jet deflection, are assumed to be smaller than the ratio of the ground clearance to the root chord. This linearized problem is solved as a direct problem represented by a source distribution on the upper surface of the wing and jet sheet with concentrated sources around the leading and side edges plus a separate confined channel flow region under the wing and jet sheet. The two-dimensional, jet-flapped airfoil is examined in detail, and the calculated lift coefficients lie within 5% of corresponding results by Lissaman.1 In the three-dimensional case, a simple analytic solution is obtained for a flat plate semi-elliptic wing with a straight trailing edge, zero angle of attack and uniform momentum distribution of the jet. Spanwise lift distributions and lift coefficients are derived and the distributions of the jet momentum are discussed for minimum induced drag.

On a Calculation of the Lift of a Tunnel Type Ram Wing

In this paper, the lift coefficients of an idealized tunnel type ram wing of a truncated hemi-conical shell, which may expect to have no-induced drag, have been calculated by means of lifting surface theory. The assumptions used in this calculation are as follows: (1) The fluid is incompressible and inviscid. (2) Both wing tips are keeping in touch with the ground. (3) The total wing vortex system consists only of acontinuous ring vortex sheet of a truncated conical surface. The results obtained here are as follows: (1) The forward velocity which is induced by the total vortex system may attain to the half of the uniform flow at the maximum value. Therefore, it will be impossible to neglect this forward velocity. (2) Contrary to ordinary three-dimensional wings, when the aspect ratio of this ram wing decreases, the lift coefficient CL increases up to the value of 1. 2 (at α=5°).