NO. 3 l.Wol.F.Y MEM0IB ON MECHANICAL PLIGHT 1!' 



one minute, but as the power was in fan expended in 1, 20 of thai time we have 

 20x0.00145 = 0.01'!); thai is, during the brief flight, about 0.03 of a horse power 

 was exerted, and this sustained a total weighl of only about a pound. 



In comparing this flighl with the ideal conditions of horizontal flighl in "Ae 



rodynamics," it will be remembered thai this model's flighl was so irregular and 

 so far from horizontal, thai in one ease it flew up and struck the lofty ceiling. 

 The angle with the horizon is, of course, so variable as to be practically un- 

 known, 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 lfi metres, while the mean actual flight was about 12. It is 

 probable, however, that there was really more slip than this part of the obser- 

 vation 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. 1 " 



It may be remarked that the flights this day, reckoned in horizontal dis- 

 tance, 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. 



10 Observers following de Lucy have long since called attention to the fact that as the scale of 

 Nature's flying things increases, the size of the sustaining surfaces diminishes relatively to the weight 



sustained. M. Harting (Aeronautical Society, 1870) has shown that the relation rea . is sur- 



*\ \\ eight 

 prisingly constant when bats varying in weight as much as 250 times are the subject of experiment, 

 and later observations by Marey have not materially affected the statement. As to the muscular power 

 which Nature has imparted with the greater or lesser weight, this varies, decreasing very rapidly as 

 the weight increases. The same remark may be made, apparently with at least approximate truth. 

 with regard to the soaring bird, and the important inference is that if there be any analogy between 

 the bird and the aerodrome, as the scale of the construction of the latter increases, it may be reason- 

 ably anticipated that the size of the sustaining surfaces will relatively diminish rather than increase. 

 We may conveniently use M. Harting's formula in the form a = n s iej = '", where a — area in so. 



cm., «■ the weight in grammes, I the length of the wing in cm., n and m constants derived from 

 observation. 



