NO. 3 LANCiLEV MEMOIR OX MECHANICAL FLIGHT ]'.', 



The aerodromes made at this time were too heavy, as well as too large, to 

 be easily launched by hand, and it was not until L89] thai the firs! one was con 

 structed light enough to actually fly. This first flighl was obtained from the 

 north window of the dome of t he Allegheny Observatory, on March 28, L891, and 

 imperfect as it was, served to show that the proper balancing of the aerodrome 

 which would bring the center of gravity under the center of pressure, so as to 

 give a horizontal flight, had yet to be obtained. 



From this time on until 1893, experiments continued to be made with rub- 

 ber-driven models, of which, as has been stated, nearly 40 were constructed, 

 some with two propellers, some with one; some with one propeller in front and 

 one behind; some with plane, some with curved, wings; some with single, some 

 with superposed, wings; some with two pairs of wings, one preceding and one 

 following; some with the Penaud tail ; and some with other forms. A few of these 

 early forms are indicated on the accompanying Plates 1 to 4, but it does not 

 seem necessary to go into the details of their construction. 



No. 11 with which an early flight was made, closely resembles the Penaud 

 model. 



No. 13 has two propellers, one in front and one behind, with a single wing. 



No. 14 has two propellers, nearly side by side, but oue slightly in advance, 

 with a single wing and a flat horizontal tail. 



No. 15 has one leading propeller and two broad wings, placed one behind 

 the other. 



No. 30 has the propeller shafts at an angle, and one pair of wings. 



No. 31 has the propeller shafts at an angle, and two pairs of wings super- 

 posed. 



The wings in general were flat, but in some cases curved. The rubber was 

 usually wound to about 100 turns, and trouble continually arose from its " kink- 

 ing " and unequal unwinding, which often caused most erratic flights. 



It is sufficient to say of these that, rude as they were, much was learned from 

 them about the condition of the machines in free air, which could never be learned 

 from the whirling-table or other constrained flight. 



The advantages and also the dangers of curved wings as compared with 

 plane ones, were shown, and the general disposition which would secure an even 

 balance, was ascertained; but all this was done with extreme difficulty, since 

 the brief flights were full of anomalies, arising from the imperfect conditions of 

 observation. For instance, the motor power was apparently exhausted more 

 rapidly when the propellers were allowed to turn with the model at rest, than 

 when it was in motion, though in theory, in the latter case more power would 

 seem to be expended and a greater speed of revolution obtained in a given time. 

 The longest flights obtainable did not excoo) 6 or 8 seconds in time, nor 80 to 100 

 feet in distance, and were not only so brief, but, owing to the spasmodic action 

 of the rubber and other causes, so irregular, that it was extremely difficult to 

 obtain even the imperfect results which were actually deduced from them. 



