280 ANNUAL, EEPOUT SMITHSONIAN INSTITUTION, 19 3 , 



flew with considerable loss of height to the Himmeldankberg as pre- 

 arranged, and there soared for some time in the iip-currents. On the 

 approach of another cumulus cloud Kronfeld used it to gain consid- 

 erable height, and then flying always from cloud to cloud he reached 

 the Wasserkuppe at his maximum height of 540 m. above the start- 

 ing point. 



These details illustrate the difference between hill and cloud fly- 

 ing, between flying from hill to hill over a course, which must be 

 adjusted to the contours of the ground, and flying from cloud to 

 cloud over hill and plain, when the ground is ignored and the 

 pilot scans the cloud formations and adjusts his course to their 

 motion. 



Plate 13, Figure 2, shows a barogram of Groenhoff's flight with 

 a passenger on the 2-seater Rhoenadler^ Jiily 30, 1929. 



The next flight shows the extended performance obtained by fly- 

 ing into the cloud instead of soaring below it. Groenhoff started 

 from the west slope of the Wasserloippe and soared over it for a 

 short time, then flew under a cumulus cloud and rose through it 

 almost to its summit, reaching a maximum height of 1,250 m. above 

 the starting point, and covering a course of 33.3 km., both figures 

 being records for soaring fligiit with a passenger. 



The sinking speed of the glider in still air was 1.1 m./sec, from 

 which the vigor of the upwinds may be inferred. 



Severe vertical gusts were met with in the cloud. At 1,800 m. 

 the glider was driven down 140 m. in a few seconds and immediately 

 after it was carried up 170 m. Two more such gusts followed after. 

 The reduction gives a down-current of 9 m./sec, and an up-current 

 of 10 m./sec. 



On the same day and under the same weather conditions Kronfeld 

 made his great cross-country flight of 150 kilometers. Plate 13, 

 Figure 1, shows Kronfeld's soaring flight from the Wasserkuppe 

 to Bayreuth (150 km.) 



Immediately after the start Kronfeld flew under a cumulus cloud 

 and was carried up continuously to a height 2,150 m. above the 

 starting point. The up-current given by the measurements was 

 5 m./sec. After leaving the cloud, height was slowly lost in passing 

 over flat country. In two hours the Threungerwald was reached, 

 and the flight was continued for 4 hours in the rising currents from 

 the ridges. Finally a landing was made at the Fichtelgebirge 150 

 kilometers from the Wasserkuppe. 



This masterly fliglit is a fine example of the art of soaring, and 

 illustrates the manner of utilizing the various means available. In 

 particular a record height in this manner wag gained in the up- 

 current of a cumulus cloud formation sufficient to cross flat and 



