12 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 62 



§5. LONGITUDINAL BALANCE 



The complete model, using wings of the section described above 

 and fitted with the tail shown in figure i, was mounted in the wind 

 tunnel on the balance with the wings vertical. A vertical spindle 

 from the balance was driven into the side of the body at the point 

 shown on figure i. By swinging the model about the vertical axis 

 passing through the spindle, the angle of the wind to the wing chord 

 was varied from +20° to —8°. At each attitude the force across 

 the wind or lift L, force down wind or drift D, and the pitching 

 moment about the spindle were measured. The wind velocity was 

 30 miles per hour for all tests. The signs were taken so that an 

 actual lift, actual drift, and a stalling moment are positive. Density 

 of air is at 15° C, 776 mm. Hg., dry. 



Test No. I was made with the horizontal tail surface making an 

 angle of — 2°75 with the wing chord. That is to say, the rear edge 

 of the tail was tilted up. Test No. II was a repetition but with the 

 tail at —7°. Test No. Ill had the tail surface at —5°. 



The lift and drift in pounds on the model at 30 miles per hour are 

 given below, and on figure 4. 



The lift and drift at first sight appear to differ for the three cases, 

 but it will be observed that the maximum lift is 1.65, 1.64, and 1.64, 

 and the minimum drift is .099, .101, and .101 for the three cases 



