8 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27 



whose blades are usually made of two feathers, or of stiff paper, and whose motive 

 power is a twisted strand of rubber. This power maintains it in 1 he air for a 



few seconds and with an ordinary capacity for flight of 50 feet or so, but it em- 

 bodies a device for automatically securing horizontal flight, which its inventor 

 was the first to enunciate. 4 



Although Penaud recognized that, theoretically, two screws are necessary in 

 an aerial propeller, as the use of a single one tends to make the apparatus re- 

 volve on itself, he adopted the single screw on account of the greater simplicity 

 of construction that it permitted. One of these little machines is shown as No. 

 11, Plates 1 and 2. 



AB is a stem about 2.5 mm. in diameter and 50 cm. long. It is bent down at 

 each end. with an offset which supports the rubber and the shaft of the screw 

 to which it is hooked. The screw HIV is 21 cm. in diameter, and has two blades 

 made of stiff paper; two are preferable, among other reasons, because they can 

 be made so that the machine will lie flat when it strikes in its descent. About 

 the middle of AB there is a " wing " surface DC, 45 cm. Ion-- and 11 cm. broad, 

 the ends C and D being raised and a little curved. In front of the screw is the 

 horizontal rudder GK having a shape like that of the first surface, with its ends 

 also turned up, and inclined at a small negative angle with this wing surface. 

 Along its center is a small fin-like vertical rudder that steers the device later- 

 ally, like the rudder of a ship. 



The approximately, hut not exactly, horizontal rudder serves to hold the 

 device in horizontal flight, and its operation can best be understood from the 

 side elevation. Let CD be the wing plane set nearly in the line of the stem, which 

 stem it is desired to maintain, in flying, at a small positive angle, a, with the 

 horizon, a being so chosen that the tendency upward given by it will just coun- 

 teract the action of gravity. The weight of the aeroplane, combined with the 

 resistance due to the reaction of the air caused by its advance would, under 

 these conditions, just keep it moving onward in a horizontal line, if there were 

 mi disturbance of the conditions. There is, however, in the wing no power of 

 self restoration to the horizontal if these conditions are disturbed. But such 

 a power resides in the rudder GK, which is not set parallel to the wing, but at 



a negative angle (a') with it equal to the positive angle of the wing with the hori- 

 zon. It is obvious that, in horizontal flight, the rudder, being set at this angle, 

 presents its ed^e to the wind of advance and consequently offers a minimum 

 resistance as long as the flight is horizontal. If, however, for any reason the 

 head drops down, the rear edge of the rudder is raised, and it is at once subjected 

 to the action of the air 11)1011 its upper surface, which has a tendency to lower the 

 rear of the machine and to restore horizontality. Should the head rise, the lower 



'His device for obtaining automatic equilibrium is found in connection with the description of 

 his "Aeroplane Auto Moteur," in " I.'Aeronaute " for January, 1S72. 



