NO. 3 EUROPEAN AERONAUTICAL LABORATORIES — ZAHM Q 



change of model. Such new types I have had in contemplation since 

 first devising the bell-crank aerodynamic balance, in 1902. 



The small wind-tunnel house, a wing of the engineering building, 

 is of structural iron and covers rather more space than the room 

 just described. Its chief apparatus is a four-foot wind channel for 

 testing small models. (Jther apparatus in this room are an engine 

 testing plant, now dismantled ; a horizontal water channel, described 

 in the Advisory Committee's report for 1912-13 ; and a small vertical 

 tube down which tobacco smoke, formed at its top, can be sucked 

 by an up-draft in a parallel pipe beside it having a burning gas jet 

 in the bottom to maintain a heated column, the purpose of the 

 descending air mingled \vith the smoke being to delineate the flow 

 about models immersed therein and visible through the glass sides 

 of the tube. 



The small wind-tunnel is the working prototype of the seven-foot 

 tunnel already described. Made of one inch lumber, it measures 

 some 40 feet in length and is supported more than 6 feet above tiie 

 floor by heavy angle iron trestle work which also forms the fram- 

 ing for the wooden tunnel wall. The first half of the tunnel measures 

 4 feet square; the second half, joined to it by an expanding metal 

 cone, measures 6 feet square, is thickly perforated with inch square 

 holes in its sides, and has its farther end abutting against the brick 

 wall of the room. In the expanding cone at mid-tunnel is a low-pitch 

 four-blade wooden screw driven by a steel shaft proceeding from a 

 ten horse-power electric motor on a wall bracket at the large closed 

 end of the tunnel, and capable of maintaining an air current of 40 

 feet per second in the four-foot tunnel. The character of the air 

 flow and the instruments used are practically the same for the small 

 as for the large tunnel. Some $20,000 was expended in developing 

 and constructing this small tunnel and its appurtenances. 



The small water channel, some 4 inches square in cross-section, 

 has been used to exhibit the stream-line flow about models of ships' 

 hulls, aeroplane posts, inclined wing forms, etc. By photographing 

 the stream, duly dotted with tiny particles of foreign matter, clear 

 pictures of the stream-lines and eddies have been obtained. These 

 serve to show what forms are likely to encounter least resistance 

 in moving through a fluid. But it can hardly be supposed that the 

 phenomena of flow about a model slightly submerged in a shallov/ 

 stream of water are identical with those for deep submergence in 

 the atmosphere, unless for very slow speeds. 



