344 ANNUAL EEPOBT SMITHSONIAN INSTITUTION, 1933 



make approximate determinations from a ship plying through quiet 

 seas abounding in these fishes. The estimates of observers have been 

 very indefinite : "A surprising distance " ; " 200 to 400 meters " ; 

 " distances of about a quarter mile are occasionally made." Ac- 

 curate estimates of the speed of flight must await determination of 

 the distance traversed. 



IV 



Studying the flying fishes from an aerodynamic standpoint justi- 

 fies the title here given them, " Nature's Own Seaplanes." After 

 describing the mode of flight in the biplane flying fishes in terms 

 similar to those here used, Breder (1930) has written: 



As soon as the tail leaves the water it immediately stops oscillating, and 

 the fish becomes a glider. Up to that time they may be considered as a 

 pusher type of plane. 



The lift, of course, as in the plane, is chiefly obtained by means of an an- 

 teriorly placed pair of wings. These are cambered very much as in the mod- 

 ern plane and the support is consequently chiefly from above. According to 

 Dowd,^ the flying fish wing is so constructed that the upper surface is smooth 

 and flush while the necessary thickness of the supporting rays is all below, 

 which causes the lower surface to be ribbed. This is good construction, the 

 sacrificing of the least efiicient surface in the interest of mechanical strength. 

 In the four-winged flyers considerable added lift is given by the ventral 

 fins. In these advanced types the section of the body is squarish, the lower 

 surface acting to increase the lift very much as in a plane built for large 

 lift in which the fuselage takes part. The Gypselurus type with four wings 

 and a flattened body seems to have gone in for large lift, whereas the Haloei/p- 

 selus type with but two wings and a more stream-lined body has apparently 

 gone in for speed. These may be directly compared with corresponding 

 fuselage types of modern planes (fig. 2, D). 



Resistance in the air is considerably less in the flying fish than in the plane. 

 The fish requires no landing gear whatsoever and there is a complete absence 

 of external braces and little to produce parasitic resistance. The vertical fins 

 are necessary as stabilizers. The skin friction must be slight on account of the 

 wet and mucous-covered surface. 



The inherent stability of fiying fishes varies with the type considered. Gen- 

 erally the most advanced fivers show indications of greater stability than the 

 more primitive ones. 



Considering longitudinal stability ; that is, in regard to a fore and aft pitch- 

 ing, without going into the details of the principles involved, the four-winged 

 types should be much more stable, the ventral fins acting as combination lower 

 planes and stabilizers (fig. 2, E). They may be considered as stabilizers placed 

 rather far forward and large in proportion to their decreased leverage incident 

 upon such a position or as the lower planes of a biplane type with an unusual 

 amount of stagger. They are set at such a position as to give the proper longi- 

 tudinal dihedral. Lateral stability is gained as in a plane by some sacrifice of 

 lift by means of a lateral dihedral ; that is, a slight tipping of the whags upward 

 (fig. 3, A). 



The horizontal stability is controlled by the lateral keelage, the total surface 

 viewed when examined from the side. Most of this is effective posterior to the 



iDowd, R. E., Aerial Age Weekly, pp. 464, 465. Jan. 10, 1921. 



