338 



SCIENCE 



[N. S. Vol. XXXVI. No. 924 



purposes), will be given to this work when it 

 reaches a stage which warrants publication. 



(Signed) S. P. Lanqlet 



Like many men of his kind Langley seems 

 to have had that passionate sense of privacy 

 which resents alike the curiosity of the pub- 

 lic and the sensationalism of the newspapers. 

 The antagonistic attitude of the press gave a 

 character of finality to experiments which to 

 Langley himself were but members of a long 

 series bringing him each year nearer the goal. 

 Had his health and strength remained to com- 

 bat the hostility of press and public, he would 

 in all probability have gone on to success, un- 

 deterred by criticism and misunderstanding. 

 To such patient and unremitting labor as his 

 is owed the accomplished fact of mechanical 

 fl-ight. He began his investigations at a time 

 when even progressive men of science thought 

 flying a wild dream, and a large part of that 

 exact investigation which transformed vague 

 ideas into scientific knowledge is due directly 

 to him. His work is measured not solely by 

 his contributions, but much more by the 

 unswerving advance in a field of scientific in- 

 quiry in which no road was marked. 



The spirit of the man is made evident by 

 his steadfast refusal to entertain propositions 

 made him to assist in the development of the 

 aerodrome provided arrangements were made 

 for later commercialization. He had given 

 his time and energy without hope of remu- 

 neration, and even when no assistance could 

 be obtained from any other source and suc- 

 cess seemed but a step away, he could not 

 bring himseK to capitalize his scientific work, 

 although his age was such that any delay in 

 achieving success increased the probability of 

 his not living to see it. He died February 27, 

 1906, about two years before the Wright 

 brothers astonished the world by their feats 

 in sustained flying in 1908. 



FUTURE OF THE AEROPLANE 



The Prohlem of Velocity. — The mechanical 

 theory of the behavior of the aeroplane is 

 built on the principle that in steady horizontal 

 flight the normal thrust on the sustaining 



surface is proportional to the area, to the 

 square of the relative velocity, and to the sine 

 of the angle of attack, or: 



(1) 



F = TcSV^ sin i, 



where, for small values of i, Tc is a. constant 

 for a given surface under constant atmos- 

 pheric conditions, 8 is the area of the sustain- 

 ing surface, V its velocity relative to the air 

 stream, and i the angle of attack. For uni- 

 form horizontal flight i equals the fixed in- 

 clination of the sustaining surface to the 

 horizontal axis of the aeroplane, and is a con- 

 stant of the machine. 



The vertical component of this normal 

 thrust — the lift — ^must equal the weight of 

 the whole machine, and denoting the lift 

 by L and the weight by W, there follows : 



(2) L=:W=lcSV^ sin t cos i=JcSVH (nearly). 



The sustaining resistance B is given by the 

 horizontal component of the normal thrust, 

 whence : 



(3) B = fcSF» sinM = A;SFH^ (nearly). 



The power P required to overcome the sus- 

 taining resistance B is : 



(4) P = Er = TcSVH'. 

 From (2) and (4) we have: 



V'=W/lcSi, 



These two relations lead to the very im- 

 portant result that the velocity of sustention 

 V increases as the angle of attack decreases, 

 and the power required to drive the sustaining 

 plane against its own resistance decreases as 

 the velocity increases. The advantage of 

 flying at high velocity and " close to the wind " 

 is at once evident. 



Li these relations, however, the resistance 

 offered by the motor and its accessory parts 

 including the framework— i/ie passive resist- 

 ance — has been neglected. The power required 

 to overcome this is proportional to the cube 

 of the velocity and the " equivalent surface " 

 presented to the air stream, and is enormously 

 increased at high velocities. It is at once evi- 

 dent that for a given machine there is a maxi- 

 mum velocity beyond which the motor can 



