44 AERONAUTICS IN RELATION TO NAVAL ARCHITECTURE. 
The most prominent effect of the special conditions of operation of aeroplane 
floats is that of the greatly reduced resistance at high speeds. Plate 31 indicates 
decided differences existing under ordinary displacement conditions and the con- 
ditions governing the use of aeroplane floats. On this plate curve A represents the 
resistance of a simple hull of constant displacement. Curve B represents the re- 
sistance of the same hull run at displacements corresponding to speeds. Curve C 
is the same hull as that for curve B, but is fitted with submerged blades; while curve 
D shows a typical resistance of a twin step float run at displacements corresponding 
to speed. The great advantage, so far as resistance is concerned, due to the lift of 
the wings, is clearly apparent from an inspection of these curves, and the addition 
of submerged blades clearly increases this advantage so far as resistance is con- 
cerned. But the performance of such blades is decidedly tricky, and although they 
have been used in a few instances they are considered tricky and unsatisfactory 
and unsuited to use in rough water. 
A matter of considerable interest is that two different states of flow may be en- 
countered at the same speed, depending on the manner in which the speed is ap- 
proached. Thus, an aeroplane getting under way will require full power to attain 
the planing condition at about 25 miles per hour. However, once planing speed has 
been attained, it is possible to ease off the power very decidedly and still maintain 
planing at a lower speed. 
When using water blades to assist in planing, a critical condition appears, and, 
if the blades are heavily loaded, this causes a sudden failure of lift as the blades 
approach the surface. When this happens the flow suddenly breaks from the back 
of the blade, causing a sheet of spray to rise at about 60 degrees to the surface of 
the water, and this appears to be independent of the sharpness of the edge of the 
blade itself. Following this failure in lift, the float then settles quickly until the 
original flow is re-established, when the blade again lifts as before and proceeds to 
follow the cycle of performance just described. 
The suction effect referred to was discovered in an attempt to reduce frictional 
resistance of the float to a minimum by the use of a parallel middle body having semi- 
circular midship sections with ogival ends. This form behaved admirably at mod- 
erate speeds, but, when the get-away condition was approached, the model, instead 
of planing, indicated a strong suction effect and proceeded to lift sheets of spray 
well clear of the surface. Finally, at the get-away condition, with the model coun- 
terweighted to a zero displacement and just in contact with the surface, the suc- 
tion influence of the curved bow and buttock lines was sufficient to drag the float 
down into the water until the deck was flush with the original surface, and a com- 
plete glassy sheet of spray was lifted several feet clear of the surface of the basin. 
The resistance was abnormally high. This effect in modified form has been found in 
several types of floats and in several instances has produced failure of designs, or 
seriously affected their performance. The effect may be readily understood by sus- 
pending a spoon, holding the end of the handle lightly between the fingers, and then 
letting the bottom of the bowl of the spoon touch a stream from a hydrant. 
