[22] See Introduction, note to § 1.
[23] The voltage, etc., is not stated.
[24] Note.—Since the above was written some really remarkable flights have been obtained with a 1 oz. model having two screws, one in front and the other behind. Equally good flights have also been obtained with the two propellers behind, one revolving in the immediate rear of the other. Flying, of course, with the wind, weight is of paramount importance in these little models, and in both these cases the "single stick" can be made use of. See also ch. iv., § 28.
[25] See also ch. viii., § 5.
[26] Save in case of some models with fabric-covered propellers. Some dirigibles are now being fitted with four-bladed wooden screws.
[27] Vide Appendix.
[28] Vide Equivalent Inclinations—Table of.
[29] One in 3 or 0·333 is the sine of the angle; similarly if the angle were 30° the sine would be 0·5 or ½, and the theoretical distance travelled one-half.
[30] Flat-Faced Blades.—If the blade be not hollow-faced—and we consider the screw as an inclined plane and apply the Duchemin formula to it—the velocity remaining the same, the angle of maximum thrust is 35¼°. Experiments made with such screws confirm this.
[31] Cavitation is when the high speed of the screw causes it to carry round a certain amount of the medium with it, so that the blades strike no undisturbed, or "solid," air at all, with a proportionate decrease in thrust.