Following hard upon the heels of the Viennese engineer Wilhelm Kress, whose aeroplane has been illustrated and described in the Scientific American comes a Berlin inventor, Regierungsrath J. Hofman, who has constructed what is claimed to be a working model of a flying-machine. Kress, for lack of funds, was severely hampered in building his device. Unable to purchase a motor an obstacle which, we are glad to note, has been overcome with the assistance of the Emperor of Austria Kress could test his contrivance only on water. Hofman, on the other hand, did not immediately proceed with the building of a full-sized machine, but has first constructed a model on a scale of 1 to 10.
To start and to land are the most difficult feats in operating a flying-machine. For this reason ingenious inventors, among them Prof. Langley, have erected special frames from which they start their machines in order to secure sufficient living force, the machines themselves being merely of sufficient strength to meet the requirements of the speed to be attained. Hofman's machine differs materially from the contrivances of these inventors, in so far as he uses no particular launching frame or other construction. He employs legs which are provided with wheels at their lower ends, and which are normally in the position shown in Fig. 2, but which are suddenly drawn from the ground close to the body when the propellers are set in motion. Robbed of its support, the machine falls, driven forward by its propellers. But the machine drops barely a second; beneath the wings, projecting far out from each side, sufficient air has collected to sustain the entire apparatus. New masses of air continually collect beneath the wings, so that, it is claimed, the buoyant force of the air becomes so great that the machine is not only supported in its flight, but is even driven further upward, there to be maintained at the desired height by the action of its propellers. The little steam-engine used to drive the propellers is supplied with steam at a pressure of 165 pounds by a boiler composed of 72 water-tubes The engine itself is made of steel. For a full-sized flying machine, Hofman intends to use coal as fuel although the firing of the boiler with petroleum has also been contemplated.
The wing or sail surfaces have an area of over 21 feet, and project laterally to a distance of 4.66 feet. The entire weight of the little model is 7.7 pounds.
Originally appeared in Scientific American, 84,, May 4, 1901, p. 281.