THE COMPONENT PRESSURE RECORDER 65 



pressure for a zero angle of inclination. This, of course, must be the case for a 

 plane of no thickness, and cannot be true for any planes of finite thickness with 

 square edges, though it may be and is sensibly so with those whose edges are 

 rounded to a so-called "fair" form. Now, the actual planes of the experiments 

 presented a squarely-cut end-surface one-eighth of an inch (3 mm .2) thick, and 

 for low angles of inclination this end-surface is practically normal to the wind. 

 Both the computed pressures for such an area and the actually measured 

 pressures, when the plane is set at 0, indicate conclusively that a large por- 

 tion of the pressures measured at the soaring speeds of 2°, 3°, and 5° is end 

 pressure, and if this be deducted, the remaining pressure agrees well with the 

 position of the curve. The observed pressures, therefore, when these features 

 are understood, become quite consistent. The curve represents the result obtained 

 from these observations for the horizontal pressure on a plane with "fair "shaped 

 edges at soaring speeds. 



A comparison of this experimental result can now be made with the formula, 

 which appears to be nothing else than an expression for a simple resolution of 

 forces. I say " appears," since error is so subtle in its intrusion in these cases 

 that I have preferred to give the matter, even here, experimental confirmation. 



From the analysis above given we have the equation B = W tan a, W being 

 the vertical component of pressure which, at the instant of soaring, is the weight 

 of the plane. For the purpose of comparing the points given by this equation 

 with the curve deduced from the observed pressures, the former are shown by 

 crosses on the diagram with the curve. The agreement between the two is 

 remarkably close, and, according to the standpoint from which the subject is 

 viewed, we may say that the formula is actually identifiable, as it appears to be, 

 with a simple case of the resolution of forces, or that the accuracy of the har- 

 monized experiments is established by their accordance with an unquestioned 

 law of mechanics. 



WORK NECESSARY TO BE EXPENDED IN FLIGHT. 



Having now obtained final values for the horizontal pressure, or the resist- 

 ance to the horizontal advance of inclined planes, and having determined their 

 soaring speeds at different angles of inclination, the work necessary to be expended 

 per minute in propelling such planes through the air is given in kilogrammeters 

 by the expression GOBY, B being the horizontal pressure in grammes, and V 

 the soaring speed expressed in meters per second. 



The following table, XIII, contains a computation, for the case of the 30 x 4.8 

 inch plane weighing 500 grammes, of the work necessary to be expended per 

 minute, the values of B being taken from the curve of figure 11 : 



9 



