Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/277

given plotted for different values of aspect ratio in Figs. 105 and 106, and, tabulated, are as follows:—

Table II.

Aspect Ratio "$n.$"	Constant "$C.$"
3 4 5 6 7 8 — 10 — 12	2.16 (?) 2.27 (?) 2.38 (?) 2.48 (?) 2.55 (?) 2.62 (?) — 2.73 (?) — 2.80 (?)

§ 178. On the Constants $\kappa$ and $\epsilon$.—Of the constant $\kappa$ we know but little with certainty. Langley's experiments with two pairs of planes four inches by fifteen inches superposed (Fig. 102) suggest that for planes whose aspect ratio is about 4 or 5 $\kappa$ has a value of somewhat less than 1. For reasons given in § 161 the actual value is probably somewhat greater than that ascertained experimentally for pairs of superposed planes.

On the value of $\epsilon$ we are entirely without information so far as direct experiment is concerned. If the value of $\kappa$ were known for an aerofoil of given aspect ratio, the value of $\epsilon$ can be obtained from the equation given in the preceding article, i.e., $\epsilon ={\frac {c\ C}{\kappa }}-1.$

We may provisionally assume that $\kappa$ is a function of $n$ and constant in respect of other variables. It is true that we have taken no account of the influence of plan-form, but we may legalise our position in this respect by specifying some standard form such as a rectangle, and leave the onus of drawing up tables of equivalent proportions in any other form to future experimenters.

At present the quantitative data are in so unsatisfactory a