Appendix

Summary

Note 1. (See p. 2.) It is now more usual to use the “quarter-chord point” as the point of reference for the measurement of moments. “The quarter-chord point” is the point on the chord line one quarter of the chord length from the leading edge.

Note 2. (See p. 39.) The contribution of the pressure and momentum integrals to the lift depends upon the shape of the large contour and the conclusion given on page 39 is not true for all shapes of contour; see Prandtl and Tietjens, Applied Hydro- and Aeromechanics, § 106.

Note 3. (See p. 95.) Since the publication of the first edition of this book a great deal of information on viscous flow and drag has been collected. This seems to show that vortex streets occupy a less significant place in the general picture than is indicated in Chap. VIII. For example, the wake of a circular cylinder takes the form of a vortex street in the range of Reynolds' numbers between 10² and 10⁵, but at higher Reynolds' numbers the flow in the wake is turbulent but not periodic. Similarly, for aerofoils below the stalling incidence, a vortex street is only present in the wake for Reynolds' numbers below 10⁵, which is outside the practical range. An account of modern work on this subject is given in Modern Developments in Fluid Dynamics (referred to elsewhere as FD).