WRIGHT BROTHERS — BAKER 215 



inch-diameter propeller fan mounted on the shaft of their shop bench 

 grinder driven at 3,000 revolutions per minute provided a wind veloc- 

 ity of about 27 miles per hour. The precautions taken to insure a 

 straight flow included the quadrant shield, a grid frame, and small 

 areas of wire mesh at strategic points on the grid. 



The files indicate that the Wrights had a method of altering this 

 instrument to measure drag, but as it was not too satisfactory they 

 soon developed a separate instrument for that purpose. Plate 4, 

 figure 1, shows that the drag instrument was just as ingenious as the 

 other, but with the difference that here they measured D/L rather 

 than drag alone. Note that the lift acts in the direction of the shackle 

 arms, and, therefore, the tangent of the angle indicated by the dial 

 pointer is really the prevailing D/L ratio. The angle of attack 

 could be adjusted readily by turning the whole assembly about its 

 mounting screw. The product of the lift coefficient and the D/L 

 ratio for any model and setting gave the drag coefficient. 



Each of these instruments is surprisingly sensitive when acted upon 

 by even a very light breeze. By closing all doors and windows of 

 their shop and allowing no one to move about in the room, they ob- 

 tained data which requires very little fairing to plot as smooth curves. 



Plate 4, figure 2, is a photograph of their remaining test models, 

 and text figures 1 and 2 are reproductions of two pages from their 

 *4ittle black notebook" giving some of their typical data. 



At the beginning of this test work, the Wrights believed that lift 

 was proportional to the angle of attack, and we can well imagine 

 their surprise at suddenly observing one day that the lift for one 

 particular surface was the same at 30° as it was at 50°. Here again, 

 we note their ingenuity in mounting two of this type surface on vane 

 arms at 80° spread, checking to see if the surfaces balanced in the 

 tunnel at 30° and 50°. This device is shown in plate 5, figure 1. 



At the completion of their test progi'am, the Wright brothers not 

 only had an imposing collection of measured data but were also able 

 to draw the following conclusions : 



1. Increasing aspect ratio does not increase maximum lift but does 

 lower the attack angle at which maximum lift occurs. 



2. Curvature gives greater lift to a surface and a steadier rate of 

 increase. 



3. The camber ratio of a curved surface has a more marked effect 

 on drag. 



4. By having the maximum-camber point forward, lift is increased 

 at the smaller angles. 



They observed the inefficiency of biplane effect. Also they observed 

 the effects of the taper and cut-outs in the wing plan form. They noted 

 the stall point, although they didn't define it as such. 



92275&— 51 15 .' / 



