294 SMITHSONIAN CONTBIBTJTIONS TO KNOWLEDGE VOL. 27 



SECRETARY LANGLEY'S INSTRUCTIONS TO ASSISTANTS 



Smithsonian- Institution, Washington, D. C, November 30, 1895. 



Deai: Sib: 



The following instinct ions are to replace those of May 13, 1895: 



1. The minimum fraction of its own " flying weight " (that is, weight com- 

 plete with initial water and fuel), which the aerodrome shall lift on the pendu- 

 lum, is 50 per cent, 1 under such engine power as can certainly be gotten up in the 

 field and maintained during forty seconds from the time the aerodrome is let go. 



The blast, the pumps, and all other essential parts must, in other words, be 

 in such a condition that steam enough for this lifting over 50 per cent of weight 

 can be gotten up readily and surely in the field and in a time which will still 

 leave at least forty seconds' supply. 



2. The mini in inn relation of supporting area to weight in any aerodrome 

 const meted hereafter, is to be two feet to the pound, 1 and the minimum of power 

 at the rate of one steadily-maintained horse power 1 at the brake under ordinary 

 conditions, to not over twenty-two pounds (ten kilos) of flying weight. In 

 absence of a brake determination horse power may be taken — 



„ „ r evs, per min. at rest X pitch x - diame ter (in ft.) X thrust (in lbs.) 



These rules do not apply to No. 5, but they do to No. 6, which is to be built over, 

 if necessary, to meet them. 



3. In balancing an aerodrome, unless otherwise instructed, set wings at a 

 root angle of either 10°, 7°, or 5°, after being certain from previous inversion and 

 sanding, that the tip angle in motion will not differ from this root angle as much 

 as 5°. 



The object in balancing any aerodrome with a single pair of wings is to be 

 able to bring the c g-. under their c p, without any reference to the tail, which 

 supports nothing, unless specially ordered. But as this condition cannot now be 

 obtained in Nos. 5 and 6, those at any rate, and perhaps future aerodromes, are 

 to carry a second pair of wings. When this second pair of wings is of nearly 

 equal size with the first, it is to be assumed, in preliminary adjustments for 

 weighl and center of pressure, that the second pair has two-thirds the lifting 

 efficiency per unit area of the first. 



Calling the whole distance from the mean center of pressure of the wings 

 to the center of gravity .1/. .1/ is to have a definite relation to the breadth of 



1 All those minimum permissible conditions are connected by the tacit assumption that the sup- 

 porting area is not greatly over 2 ft. to the pound of weight. If for instance the weight were in- 

 creased by larger wings or more wings, furnishing a much greater supporting area per pound, these 

 conditions would not necessarily apply. 



