192 



SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE 



VOL. 27 



by sprinkling sand uniformly over it to such a thickness as to cause it to have 

 a load of 0.75 pounds per square foot. As it showed no serious deflection or 

 change of form under the sanding test, it was decided that it was strong enough 

 for use in tests of the model aerodromes in actual flight. 



Upon the completion of these whirling-table tests, the cloth covering of this 

 wing was painted with collodion varnish, which increased the weight of the 

 wing only 50 grammes. In order to make the results of its tests more easily 

 comparable with those obtained before varnishing, the cross guy-wires on the 

 wing were changed to a slightly smaller size in order to make the weight of 

 the wing the same as before. It was tested on March 3, and the following re- 

 sults were obtained: 



Weight of wing = 1025 grammes; weight of guy posts, etc.. = 320 grammes; equivalent weight of 

 guy-posts, etc., = 150 grammes applied at CP of the wing: equivalent load on wing = 1175 grammes 

 = 2.585 pounds; area of wing = 21.85 square feet; equivalent load on wing = .1183 pounds per 

 square foot. 



Anglo of 

 chord. 



5.0° 



5.0° 



10.0° 



10.0° 



Revolutions 

 of turn- 

 table. 



10.5 



10.5 



8.5 



8.5 



Velocity of 

 center <u 

 wing [ft 



per min.). 



1000 



1060 



859 



859 



Velocity 

 (ft. per 

 second). 



17.7 

 17.7 

 14.3 

 14.3 



Drift 

 (grammes). 



250 

 250 

 250 

 250 



Drift 

 (pounds). 



0.55 

 0.55 

 0.55 

 0.55 



Foot- 

 pounds 

 per sec. 

 B V. 



9.75 

 9.75 



7.88 

 7.88 



Calculated 

 soaring 

 speed, 



carrying 0.6 



pounds per 



b<[. ft. 



(ft.persec). 



36.37 

 36.37 

 29.4 

 29.4 



Although the varnishing of the wing seemed to have no effect on the " drift," 

 the soaring speed was slightly decreased. 



As a result of these tests it was decided to construct three more wings like 

 this second type, the four forming a complete set for use on the steam-driven 

 models Nos. 5 and 6. Although the tests on the whirling-table indicated a su- 

 perior efficiency for the " single-tier " wings, and it was not expected that in 

 actual use on the aerodrome the result would be different, yet it was felt that 

 as the conditions of actual use are so very different from those of a whirling- 

 table experiment it would not be safe to decide too definitely against the su- 

 perposed wings without first' giving them a test under actual conditions. Aside 

 from the decreased lifting effect shown by the superposed wing when com- 

 pared with the " single-tier " one, it was also thought that under the actual con- 

 ditions of use on the machine the superposed wing would show up slill worse. 

 The defied ion of the aii - by the front wings diminishes the lift of the rear ones 

 even for the " single-tier " type, and this, it seemed certain, would be greatly 

 aggravated in the case of the superposed type. 



Tn order to emphasize more fully the results of these tests the following 

 table is added, which gives the data for the " single-tier " wing and this sec- 

 ond type of superposed one, when each was tested at ten degrees angle of 

 elevation : 



