The Laws of Air Screws II.—The Screw with Axial Motion

Extract

This paper gives the results of experiments with air-screws having axial motion, the same propellers being tested that were described in the first article (appearing in the AERONAUTICAL JOURNAL for October, 1910): namely, sector-shaped, flat-bladed, true screws having diameters of 1.5, 2, 2.5, 3, and 3.5 feet; also several of 2.5 feet diameter having pitch-coefficients varied from 0.4 to 2.0.

In the light of Laugley's experiments with a whirling-table, I firmly believe that accurate results can only be obtained with .straight line experiments in still air; so, for the purpose of these experiments. I had a track constructed of 30 inch gauge and over 300 feet long, arranged as shown in the profile sketch (Fig. 1). The part A B, 68 feet long, is curved to obtain the initial speed rapidly and without undue length of track ; the remainder, from B to F, was 275 feet long, accurately level and straight. From C to D is 50 ft., and from D to F is 50 ft.; between the points C and E all readings are taken, the portion E to F being simply used to bring the truck gradually to rest. The track from A to E is of iron carefully bonded at the joints to convey electric current from a storage battery; from E to F it is of wood.