Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/325

Rh be taken to give the correct pressure value for all points along the blade, the pressure scale being determined by assigning a value to some convenient point from the Table.

§ 208. “Load Grading.”—Reference has already been made to the term thrust grading as representing the distribution of the sternward reaction along the length of the blade. We have now to discuss the considerations governing the form of the thrust grading curve, and also the curve of distribution of the normal reaction from point to point, which we may term the load grading.

Dividing the propeller disc into a number of concentric areas, we have, on the principle discussed in § 198, to distribute the momentum as nearly as may be possible in proportion to the mass of fluid passing through each annular element: that is, the force exerted by each small linear element of the blade should be proportional to the area it sweeps; that is to say, it will be proportional to $$r .$$

Our thrust grading curve on this basis would be that shown in Fig. 129 (α)—simply an inclined line. But we must complete A.F.