Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/414

§ 247 .03, rarely being less than the former or greater than the latter.

It is, perhaps, of some interest to record the fact that for air in motion in a pipe the accepted resistance coefficient gives, on the present basis of computation (i.e., for a double surface in terms of the pressure on a normal plane of equal area), a value of $$\xi =$$ .016, which is in substantial agreement with the present conclusions, in spite of the totally different conditions that obtain.

The author considers that the method of the ballasted aeroplane has not at present had a fair chance of showing its capabilities. The method is one that demands considerable nicety of manipulation. In the absence of any mechanical launching device, it is quite easy to obtain faulty data if any but straight uniform glides are recorded, and if such data are utilised it is as likely as not the values of the constants deduced will be wide of the mark, even negative values being sometimes obtained. The method is one of which the advantages have only very recently impressed themselves on the author, and time and opportunity have been at present lacking to carry out more than a few rough preliminary experiments. The present publication, in this respect, must therefore be regarded more in the light of an exposition of method than a serious experimental demonstration.