HYDRODYNAMIC DESIGN 



Weight. Lift, and Drag; Pitching Moments 



The DEFINITION SKETCH shows the depressor with biplane 

 wing and biplane horizontal stabilizer and defines, by illus- 

 tration, the principal linear dimensions relating the positions 

 of the wing, stabilizer, and towpointo The distances x^ and x 

 are the horizontal spacings of the mean quarter-chord points 

 of the wing and stabilizer forward and aft of the towpoint, 

 respectively. A longitudinal reference axis fixed on the body 

 and passing through the towpoint is chosen so as to lie in 

 the intended streamwise direction when the depressor is in 

 steady tow. The sketch also illustrates the pitch angle, 6, 

 defined by the inclination of the longitudinal reference axis 

 with respect to the direction of motion. The incidence angles 

 i^ and i are likewise defined as the inclinations of the chords 

 of the cambered wing and horizontal stabilizer, both with 

 respect to the longitudinal reference axis of the body. 



The sketch illustrates also the lift and drag forces, L^, 

 Lp^, D , and D , produced by the wing and horizontal stabilizer, 

 and the hydrodynamic moments iVL. and M^, all referred to points 

 at the quarter-chord and mid-gap poisitions of the biplanes. 

 These last points on the wing and tail are further related 

 to the reference axis by the vertical spacings h.. and h „ 



To attain the desired hydrodynamic downforce and the trim 

 condition, ^ = 0, and to provide static stability in pitch 



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