Nov. 20, 1891.Flight.Aerodrome.Results.1No. 30With 30 turns of the rubber, flew low through 10 metres.2No. 30Flew heavily through 12 metres.3No. 31Flew high and turned to left; distance not noted.4No. 31The right wing having been weighted (to depress it and correct the tendency to turn to the left), model flew high, but the rubber ran down when it had obtained a flight of 10 metres.5No. 31The wings were moved backward until theCPstood at 1493. The model still turned to the left; flight lasted three and a-half seconds; distance not noted.6No. 31Vertical tail was adjusted so as to further increase the tendency to go to the right. In spite of all this, the model turned sharply to the left, flying with a nearly horizontal motion; time of flight not noted; distance not noted.7No. 30Straight horizontal flight; time three and three-fifth seconds, when rubber ran down; distance 13 metres.8No. 30Straight flight as before; time two and four-fifth seconds; distance 13 metres.9No. 30With a curved wing in the same position as the flat wing had previously occupied, model flew up and struck the ceiling (nearly 30 feet high), turning to right, with a flight whose curtate length was 10 metres.10No. 30Wing having been carried back 5 centimetres, model still flew up, but not so high, and still turned to the right.11No. 30Wings carried back 5 centimetres more; model still flew high; time two and two-fifths seconds; distance 13 metres.12No. 30Wings carried back 4 centimetres more; model still flew high during a flight of 13 metres.The observations now ceased, owing to the breaking up of the model.
The observations now ceased, owing to the breaking up of the model.
The objects of these experiments, as of every other, were to find the practical conditions of equilibrium and of horizontal flight, and to compare the calculated with the observed positions of the center of pressure. They enable us to make a comparison of the performances given by earlier ones with a light rubber motor, with the relatively heavy motors used to-day, as well as a comparison of single flat, single curved, and superposed flat wings.
The average time of the running down of the rubber in flight was something like three seconds, while the average time of its running down when standing still was but one and a half seconds. It might have been expected from theory that it would take longer to run down when stationary, than in flight, and this was one of the many anomalies observed, whose explanation was found later in the inevitable defects of such apparatus.
The immediate inferences from the day’s work were:
1. That the calculated position of theCPat rest, as related to theCG, is trustworthy only in the case of the plane wing.
2. The formula altogether failed with the curved wing, for which theCPhad to be carried indefinitely further backward.
On comparing the previous flights of November 14, with these, it seems that with the old rubber motor of 35 grammes and 50 turns, the single wing, either plane or curved, is altogether inferior to the double wing; while with the increased motor power of this day, the single wing, whether plane or curved, seems to be as good as the double wing. It also seems that the curved wing was rather more efficient than the plane one.
The weight of the rubber in each tube was 72 grammes, or 0.16 pounds; mean speed of flight in horizontal distance412metres (about 15 feet) per second.16
From experiments already referred to, there were found available 300 foot-pounds of energy in a pound of rubber as employed, and in 0.16 of a pound, 48 foot-pounds of energy were used;4833,000or 0.00145 = the horse-power exerted in[p019]one minute, but as the power was in fact expended in 1/20 of that time we have 20 × 0.00145 = 0.029; that is, during the brief flight, about 0.03 of a horse-power was exerted, and this sustained a total weight of only about a pound.
In comparing this flight with the ideal conditions of horizontal flight in “Aerodynamics,” it will be remembered that this model’s flight was so irregular and so far from horizontal, that in one case it flew up and struck the lofty ceiling. The angle with the horizon is, of course, so variable as to be practically unknown, and therefore no direct comparison can be instituted with the data given on page 107 of “Experiments in Aerodynamics,” but we find from these that at the lowest speed there given of about 35 feet per second, 0.03 of a horse-power exerted for three seconds would carry nearly one pound through a distance of somewhat over 100 feet in horizontal flight.
The number of turns of the propellers multiplied by the pitch corresponds to a flight of about 16 metres, while the mean actual flight was about 12. It is probable, however, that there was really more slip than this part of the observation would indicate. It was also observed that there seemed to be very little additional compensatory gain in the steering of No. 30 for the weight of the long rudder-tail it carried. It may be remarked that in subsequent observations the superiority of the curved wing in lifting power was confirmed, though it was found more liable to accident than the flatter one, tending to turn the model over unless it was very carefully adjusted.
It may also be observed that these and subsequent observations show, as might have been anticipated, that as the motor power increased, the necessary wing surface diminished, but that it was in general an easier and more efficient employment of power to carry a surface of four feet sustaining area to the pound than one of three, while one of two feet to the pound was nearly the limit that could be used with the rubber motor.17
It may be remarked that the flights this day, reckoned in horizontal distance, were exceptionally short, but that the best flights at other times obtained with these models (30 and 31) did not exceed 25 metres. Such observations were continued in hundreds of trials, without any much more conclusive results.[p020]
The final results, then, of the observations with rubber-driven models (which were commenced as early as 1887, continued actively through the greater portion of the year 1891 and resumed, as will be seen later, even as late as 1895), were not such as to give information proportioned to their trouble and cost, and it was decided to commence experiments with a steam-driven aerodrome on a large scale.