NO. 5 STABILITY OF AEROPLANES HUNSAKER AND OTHERS 7 



Maximum speed 8/ miles per hour. 



Minimum speed 35 '"i^es per hour. 



Initial rate of climb 900 ^^- P^r min. 



Best glide i in 9 



Endurance, full power 1 5-6 hours. 



Endurance, reduced power, 14 hours at. . 47 miles per hour. 



§3. MODEL 



A model, ^^ scale, was made by Edward Tighe, model maker, 

 26 



giving a span of 1.58 feet. The size of the model was limited by the 



size of the wind tunnel which is 16 square feet in section. The model 



is shown in figure i (see pp. 8 and 9). Note that wires are omitted 



and struts are made round instead of " stream line " in section. It is 



believed that the effects of these changes on total resistance largely 



counterbalance each other. This model was carefully shellacked and 



polished to minimize skin friction. The model is, of course, much 



more smooth than the full-size aeroplane, as it should be, in order that 



the surfaces may remain geometrically similar. Model work was to 



the nearest hundredth of an inch. No propeller was fitted, but in the 



design account was taken of the propeller race in augmenting 



resistance. 



For simplicity, the model was made with trailing ailerons or wing 



flaps integral with the wings. This somewhat increases the effective 



supporting area. The stabilizer and elevator were made in one, 



corresponding to the elevator flaps in neutral position. These points 



are made clear on figure i. 



§4. WING COEFFICIENTS 



In the course of the design, a wing section was devised by Clark 

 which showed a low resistance at high speed and small angle of 

 attack and at the same time was thick enough to permit the use of 

 robust wing spars. A model of this wing was made, of 18 inches 

 span by 3 inches chord, and tested in the wind tunnel. For various 

 angles of wing chord to wind, the lift L, drift D in pounds, and 

 pitching moment M in pounds-inches were observed for a wind of 

 30 miles per hour; air of density .07608 pound per cubic foot. 



The wind tunnel and balance are duplicates of the 4-foot installa- 

 tion at the National Physical Laboratory, England, and reference 

 may be made to the technical report of the Advisory Committee for 

 Aeronautics, year 1912-13, for a description of the apparatus and 

 method of operation. 



