202 



SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE 



VOL. 27 



46 cm. and was weighted at different percentages of its length to such an extent that it was de- 

 flected 11 per cent of its length, or 5 cm. The weight of the 4G 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. 



Point of 



application 



of weight 



in terms of 



length. 



0.39 



0.445 



0.56 



0.75 



0.95 



1.00 



Absolute 



weight 



in 



grammes. 



7680 

 5980 

 36S0 

 2300 

 1100 

 930 



Weight in 

 terms of 

 greatest 

 weight. 



1.0 



0.78 



0.48 



0.30 



0.143 



0.121 



Deflection 

 in terms 



of 

 length. 



0.11 

 0.11 

 0.11 

 0.11 

 0.11 

 0.11 



A lighter rib than the above, which was constructed at the same time, was 

 also tested with the results shown in the following table. This rib was also 

 80 cm. long, but was only one-half the linear dimensions in section of the rib 

 previously tested. The rear portion of it projected 46 cm. from the clamp. The 

 total weight of the rib was 11 grammes, or 5.5 grammes for the 46 cm. on which 

 the measurements were made. 



A still lighter rib of the same length, weighing 9 grammes, suitable for use 

 in the wings of the quarter-size model, was constructed and a set of tests was 

 made on it witli the following results. As in the above test, 46 em. of the rear 

 portion of it projected from the clamp which held it. 



Among quite a number of different forms of cross-ribs which were con- 

 st ructed of a size suitable I'm- use in the model aerodrome, but made primarily 

 for use in tests to determine the best form to employ, may be mentioned the 

 following, in which both ribs were seven-sixteenths of an inch outside diam- 

 eter and five-sixteenths of an inch inside diameter. One was filled witli elder 

 pith, formed up into a round rod that just fit the interior of the hollow rib, and 

 was glued into it when the rib was glued up. The other rib was left hollow. 

 Tpon testimr these by suspending weights at different points, the rib without 



