Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/290

§ 185 Tables IV. and V., for $$\xi$$ taken as .03, .025, .02, .015, and .010 in the respective columns.

In the employment of this Table it must be remembered that we have to deal with British absolute units, so that $$P_2$$ will be poundals per square foot; thus, supposing- it were desired to design an aerofoil of aspect ratio $$n =$$ 10 to travel at a velocity of 40 feet per second, then the value of $$P_2$$ for least resistance will be = 1,600 $$\times$$ .0440 (taking $$\xi$$ = .03), or 70.4 poundals or 2.2 lbs. per square foot (approximately).

In Table X. the appropriate load per square foot is given for velocities from 10 to 80 feet per second for various values of “$$n ,$$” the value of $$\xi$$ has been taken as .03, .02, and .01.

§ 186. Aeroplane Loads for Least Resistance.—The pressure, or load, per unit area that an aeroplane will economically sustain is considerably less than that tabulated in the preceding section for aerofoils of pterygoid form.