In the following year Dr. Woelfert, of Berlin, produced a cigar-shaped envelope, to which was attached rigidly a long bamboo framework containing the car. An 8 horse-power benzine Daimler motor drove a twin-bladed aluminium propeller, and another propeller for vertical movement was provided beneath the car. Four trial flights were attempted, but on each occasion the motor gave unsatisfactory results, and Woelfert sought to improve it with a benzine vaporizer of his own pattern. This improvement was not a success, as during the last flight an explosion took place and both Woelfert and an aeronaut named Knabe, who was accompanying him, were killed. In 1906, Major von Parseval experimented, in Berlin, with a non-rigid type of airship. His first ship had a volume of 65,200 cubic feet, but owing to his system of suspensions, the car hung 27 feet 6 inches below the envelope. A Daimler engine was used, driving a four-bladed propeller. Owing to the great overall height of this ship, experiments were made to determine a system of rigging, enabling the car to be slung closer to the envelope, and in later types the elliptical rigging girdle was adopted. His later ships were of large dimensions and proved very satisfactory. About the same time Major Gross also built airships for the German aeronautical battalion. It is, however, the rigid airship that has made Germany famous, and we must now glance at the evolution of these ships with which we became so familiar during the war. The first rigid airship bearing any resemblance to those of the present day was designed by David Schwartz, and was built in St. Petersburg in 1893. It was composed of aluminium plates riveted to an aluminium framework. On inflation, the frame-work collapsed and the ship was unusable.