PL. 66. DETAILS OF RIBS AND FITTINGS FOR WINGS [◊] [lgr]

PL. 67. CROSS SECTION OF RIBS [◊] [lgr]

The quill on which the measurements were made was 19.5 inches long and had a gradual curve, the highest point of the curve being about the center of the length of the quill, and the depth of curvature being about 2 inches. When the butt of this quill was placed in the clamp the tip stood 17 cm. above the horizontal. The hollow spruce rib, when clamped at a point 5 feet from the tip (the point from which it tapers in both directions) had its tip 2.2 cm. above the horizontal, there being very little curve in that portion of the rib. The quill weighed 4 grammes when stripped and 18 inches of it projected from the [p201] clamp which held it during the tests. The rear portion of the spruce rib projected 5 feet from the clamp, being thus 3.3 times as long as the quill, and it weighed 120 grammes, the weight for the larger size having, therefore, increased slightly less than the cube of the length.

The results of the tests of both the quill and the rib are given in the following table. The approximate cross-section of the quill at the point of clamping, the middle and the tip are shown in diagrams A, B and C, respectively, of Plate [67]. The cross-sections of the rib at the corresponding points are shown in diagrams D, E and F. The cross-sections of the quill, enlarged five times, are shown in diagrams A′, B′, and C′.

QUILLFROMTHEREMIGESOFHARPYEAGLE.
Weight, 4 grammes; length, 45 cm.; tip, 17 cm. above butt when the latter is horizontal.
Point of application of weight in terms of length.Absolute weight in grammes.Weight in terms of greatest weight.Deflection in terms of length.
0.39 10501.0  .38
0.445 6050.58 .38
0.56  4050.39 .38
0.75  2100.20 .38
0.95   770.075.38
HOLLOWSPRUCERIB.
Weight, 120 grammes; length 153 cm.; section, rectangular; tip, 17 cm. above butt.
Point of application of weight in terms of length.Absolute weight in grammes.Weight in terms of greatest weight.Deflection in terms of length.
0.39 15,0001.0  .11
0.44511,4000.76 .11
0.56  7,9000.53 .11
0.75  4,0000.27 .11
0.95  2,0000.135.11

In each case the unit of length was the portion extending beyond the clamp; the unit of weight, the greatest weight employed to produce the deflection. It should be noted, however, that the relative deflection was quite different in the two comparisons. In the case of the quill the deflection was 17 cm. in 45 cm., or 38 per cent; in the case of the rib it was 17 cm. in 153 cm., or 11 per cent. In the case of the rib at the point 0.39 the absolute weight was 15,000 grammes, the relative weight unity and the deflection in terms of length 0.11. While no rigorous comparison can be instituted, since the rib was not deflected nearly as much proportionately as the quill, yet the general inference is that while the rib was not intended to be, and was not as elastic proportionately as the quill, it was probably at least as strong in proportion to its weight. Briefly summarizing these results it will be noted that the spruce rib was about 3.3 times the length and 30 times as heavy, while it was 15 times as stiff near the butt and 26 times as stiff at the tip, as the quill.

As this test on the rib for the large wings had apparently shown that the plan of constructing the ribs in the form of a hollow square secured maximum strength for minimum weight, it was decided to construct a few sample ribs after the same plan for the wings of the new quarter-size model of the large aerodrome, and to test, these ribs in a similar manner. The following table shows the results of the test on one of these ribs:

Total length of rib = 80 cm. Curve = 1 in 18. Highest point of curvature = 0.25 from front. Section of rib = 10 mm × 14 mm. at the point of attachment to mid-rib, tapering to 8 mm. × 12 mm. at the front point and to 7 mm. × 2 mm. at the tip. The rib was clamped with the tip projecting [p202] 46 cm. and was weighted at different percentages of its length to such an extent that it was deflected 11 per cent of its length, or 5 cm. The weight of the 46 cm. length of rib which projected from the clamp was 11 grammes, the whole rib weighing 22 grammes and balancing on a knife edge placed at the point where it was clamped.