274 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1930 



settled the type of construction suitable for gliders. It was a canti- 

 lever low-wing monoplane, in which great care was given to keep 

 down drag with its adverse effect on performance. 



In the following year the same principle of keeping down body 

 drag was more fully applied by G. Madelung to his glider Vampyr^ 

 the design of which has had a lasting influence. The Vampyr type 

 prevails at the present time, and this is a measure of Madelung's 

 contribution to glider design. 



Since gliding flight depends on the use of slowly rising currents 

 in the air, a practicable glider is chiefly characterized by a small 

 vertical component of velocity, or sinking speed. A small rate of 

 descent may be obtained either by reducing the sum of the resistances 

 or by reducing the wing loading. These two methods have been 

 applied, and lead to two special types of glider, both of which 

 find application for special purposes. A large span and good aspect 

 ratio are favorable to a small (induced) drag, and further reduc- 

 tion of drag is gained by a closed body, cantilever contruction (no 

 external bracing) and by dropping the starting carriage. 



From the Vampyr^ the prototype of German high-performance 

 gliders, onwards, all these methods of reducing drag have been 

 carefully studied and carried out, so that further fundamental im- 

 provements are scarcely to be expected. The following photographs 

 show the best-known German high-performance gliders from the 

 Vampyr of 1921 to the Wien of 1929 : 



Vampijr^ Academical Flying Club of Hanover, 1*921 (pi. 1, fig. 2) ; 

 Consul, Academical Flying Club of Darmstadt, 1923 (pi. 2, fig. 2) ; 

 Miinchen, Academical Flying Club of Munich, 1928 (pi. 3, fig, 1) ; 

 Wien, R. Kronfeld. Built by A. Lippisch, 1929 (pi. 3, fig. 2.). 



On the Wien, Kronfeld carried out his great duration flights, 

 covering distances up to 150 km. 



In designing for low head drag the structural weight is in- 

 creased to a restricted degree, and the structural methods, illustrated 

 above, produce medium heavy gliders with a margin of strength for 

 high performance and for flying in gusty weather. The additional 

 weight gives the greater air speed required for progress against 

 strong winds and for passing rapidly through unfavorable belts of 

 down wind. The glider of low drag and considerable structural 

 weight is the best all round for long cross-country glides by virtue of 

 its slow descent and high air speed. 



Another method of reducing the sinking speed, by reducing the 

 wing loading, is widely applied to glider design but quite unsuit- 

 able for high performance. It produces a very special type with 

 low air speed, poor gliding angle, light structural weight, and simple 

 form. 



