60 



L. HAKGBAVE. 



The question arises as to what is the use of trying to make a 

 large soaring machine, if under ordinary circumstances one may 

 wait weeks for a few hours' trial with small models. Irrespective 

 of the pleasure to be derived from attempting to unravel nature's 

 secrets, there is the prospect that an apparatus fitted with soaring 

 curves may be raised by thrust in calm weather with greater 

 facility than the ordinary screw-driven aeroplane; and that 

 although the air is calm near the earth's surface, a few hundred 

 feet elevation would bring the machine into disturbed air where 

 the soaring curves would develop their full power and the machine 

 could then proceed without steam. 



The late gales (May 5) enabled me to find out that the pounds 

 per square foot suitable for a fourteen miles per hour wind did 

 not give as good results in thirty-five miles ; and served to show 

 that there are three cases in which soaring is possible : 



Case 1. When all the surfaces are shaped for soaring. This 

 form of apparatus will be extremely difficult to steer. 



Case 2. When the cellular kite part of the machine is inclined 

 at a slight positive angle. This form is for use in the lightest 

 winds in which soaring can be done. 



Case 3. When the cellular kite as well as the propeller is at a 

 negative angle. This is for very strong winds. 



There is no reason why the propeller should not act if the axis 

 of the vortex is not horizontal. Possibly concentric ring propellers 

 may be found to give steady and uniform results with little 

 weight. The kite shown in the Fig. 1 has been greatly improved 

 by increasing the rigidity of the tubular rod; it is now -55 inches 

 external diameter, and all the ballast is put inside the ends. 

 There is 12-75 inches of -5 inch round lead in the forward end 

 and 6-75 inches inside the tail. This brings the weight up to l*9Ibs. 

 per square foot. When loaded to 1*87 lbs. per square foot with a 

 wind of sixteen or seventeen miles per hour, the propeller set at a 

 negative angle of 6*3°, and centre of gravity 3 inches abaft the 

 leading edge of the propeller, it has frequently soared to the 

 end of its tether. 



