494 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1940 



An attractive development in flying boats is the provision in the 

 Dornier D0.26 of retractable wing-tip floats which fold inward into 

 spaces in the wing. This is a 20-ton machine with two tractor and 

 two pusher airscrews. It is a promising move in a very much de- 

 sired direction. The remaining structural feature to be made aero- 

 dynamically clean is the "step" at the hull provided for ease in taking 

 off. It is no doubt difficult so to design a hull as to be equally effi- 

 cient whether on the water or in the air, but designers will not be 

 happy until they have satisfied both requirements. 



It is naturally impossible in the course of this address to discuss 

 all the many problems in the science of aeronautics which are being 

 investigated at the present time. They are far too numerous and the 

 time too short. But to some of them I must refer. One of gi-eat 

 importance and quite fascinating interest is the investigation of the 

 change in the air flow over a wing surface from the laminar to the 

 turbulent state. It is known that if the flow could be kept laminar 

 the drag would be vastly reduced, but it has yet to be discovered 

 how to do this. A step in the right direction may lately have been 

 made at the Langley Field Laboratories, for during Dr. Lewis' recent 

 Wilbur Wright lecture before the Royal Aeronautical Society mention 

 was made of some wind-tunnel tests in which a special form of airfoil 

 gave a drag coefficient figure of only about one-third of that usual. 

 Further particulars will be awaited with interest. Many laboratories 

 and experimental stations are studying this same problem, and, as 

 not infrequently happens in such cases, success once met with, itself 

 creates a batch of new problems. For one thing it is clear that the 

 presence of laminar flow can but be hindered by the use of the tractor 

 type of airscrew now almost universal. It may be necessary to change 

 to pusher designs, and as this will involve a marked rearward move- 

 ment of the center of gravity of the whole aircraft, all the stability 

 factors will be gravely affected, to say nothing of the many engine 

 problems also raised. 



Other special problems rfelate to the possibility of having wing areas 

 adjustable in flight by telescopic or other means, to the study of the 

 very considerable increase in the control forces required of the pilot 

 in large machines of high speed capacity, of the special problems 

 raised by variable-pitch airscrews, particularly in relation to the 

 landing run, of the advantage at high air speeds of two-speed gear 

 boxes, and of the special problems involved in pressure cabins. 



The problem of the rotating wing is in a class by itself. Aircraft 

 so fitted are quite unable to compete in speed with those with normal 

 wings, but they easily beat the latter in take-off and landing. Many 

 types are now in the field, the Cierva, the Hafner, the Kay, and the 

 Focke, to mention no others. The scientific problems are largely 

 solved, as are the great mass of the mechanical ones. What is 



