The induced drag is considered for a hemicircular front view wing with both tips in close proximity to the ground surface, using the lifting line theory. The integral equation is exactly treated and, assuming that the lift distribution is optimum, the exact expression of the span efficiency factor is obtained. Also, the lift distribution is discussed analytically and numerically.
The minimum induced drag is discussed for the hemi-elliptic front view wing. Two limiting cases, when the gap angle from the ground is nearly 0 and π/2, are treated by the method of the series expansion. The effect of the height ratio in the front view on the span efficiency factor is expressed as the difference from that of the hemi-circular wing. It is shown that the span efficiency factor of the wing with height ratio λ is equivalent to that of the wing with 1/λ.
An analysis is presented for the Frahm-type blade-vibration-absorber (BVA) when the second flapwise bending natural circular frequency (ω2) coincides with the three per revolution (3Ω). The rate of change in ω2 with increasing the mass of BVA is drastic for the smaller mass ratio, but becomes mild for the larger one. For the purpose of comparison, the effect of a simply fixed weight is also investigated. The effect of BVA is much larger than that of the fixed weight for a same mass ratio in the both devices, if the mass ratio is reasonably small and if the station does not coincides with modal shape nodes.
Trajectories of the solar sailers which fall inward to the sun, starting from the earth orbit, are studied. Using the lightness number λ, approximate trajectories for constant sail angle β are obtained and they show satisfactory agreement with the exact motions for reasonable values of λ. Finally, Euler-Lagrange equations are solved to find optimum β-time relationships. And conparison is made between the optimum constant sail angle solution and the variational solution.