AERONAUTICS IN RELATION TO NAVAL ARCHITECTURE. 47 
towed free to trim, the model pivoting about a point corresponding to the relative 
position of the propeller thrust. 
Curve G shows the water-planing power for this condition. 
The performance indicated is typical. At first the water resistance rises 
rapidly, then as the influence of the wing lift becomes appreciable and the model 
begins to plane, the resistance reaches a maximum at about 6 knots for the fixed con- 
dition, and 6 knots for the free to trim condition. The resistance then falls away 
steadily for both conditions, but, in the case of the free to trim condition, holds up 
longer and usually has a secondary hump. As at high speeds the aeroplane is 
usually controllable, the fixed trim condition is attainable and, therefore, represen- 
tative. At low speeds, however, the squatting effect may predominate, or may be 
even purposely produced to advantage, as the maximum resistance for the free to 
trim condition is practically always less than that for the fixed trim condition. 
From a comparison of similar models of 2,000-pound and 6,000-pound floats, 
Froude’s law of comparison appears to apply satisfactorily, and it also appears that 
dimensions proportioned to the displacement have planing power in proportion to 
the displacement, assuming the same get-away speeds in both cases and that the 
loads correspond to speeds. 
Many forms and dispositions of floats have been proposed and tried, and for 
inland waters several successful forms now exist, but for work in the open sea no 
form is yet known to have all the required qualities. 
The first success was attained by Curtiss with floats of an exaggerated blade 
form, but these were not as satisfactory as the normal rectangular section float hav- 
ing a skidform profile. This is a simple and successful form for inland work, and it 
seems to matter little from a resistance point of view what form of bow curve is 
used. An examination of the curves of Plate 33 will show the close agreement in 
performance of bows having widely different forms of curvature. Various other 
forms of bows were tried—convex, concave, flat sloping bows, corrugated bows— 
and all show essentially the same characteristics. 
The influence of steps has been tried—one, two, and up to six. From a resist- 
ance point of view it appears unnecessary to provide more than two steps for aero- 
plane conditions. The first break is usually placed nearly under the center of grav- 
ity, and the second forms the stern of the float. If both steps are inclined in the 
same sense a biplane float is formed, but if the after step rises relative to the for- 
ward one, it more nearly approaches the monoplane or single-step form, which has 
desirable qualities. This is the form which has proved so successful in the flying 
boat and is the form used in model No. 1844, whose resistance curves have already 
been referred to. Ventilation of the steps facilitates quick planing and is useful, 
but is not essential if there is ample reserve of power. 
Interference between twin floats at the separation usual in practice appears in- 
appreciable, except at very low speeds. 
Flat-bottom floats pound heavily and the flat-bottom-step type porpoises 
strongly, unless it is handled very nicely, even in smooth water. 
The introduction of a moderate V-bottom greatly reduces the shock of landing 
