FIFTY YEARS OF FLYING PROGRESS — LOENING 213 



POWER-PLANT FORMS 



Engines have gone through many stages of development, with many 

 changes in form, until we have finally come to the jet engine — a totally 

 different type. Propellers, which may be considered part of the power 

 plant, have also undergone many alterations. The Wrights' original 

 design was little less than inspired. Even with our present knowledge 

 of propellers — our materials of construction, technical skills, and 

 methods of manufacture — the Wrights' solution of the problem of 

 turning B. t. u.'s of gasoline into effective driving thrust for flying 

 cannot be improved upon. Their approach from the correct stand- 

 point of considering their blades rotating airfoils, and their calcula- 

 tions and method of design are an outstanding tribute to their scien- 

 tific knowledge and engineering ability. In this field of design they 

 really had very little to go on, except some marine screw-propeller 

 theory, much of which they quickly discarded. While they of course 

 had a power loss between the engine and the propellers, owing to the 

 chain drives and sprockets and extra shaft-bearing frictions, this was 

 all more than made up for by the fact that their two large propellers 

 were given a very high order of efficiency at their flight speed of 30 to 

 40 miles an hour. This they could never have obtained if there had 

 been only one small direct-drive propeller on their little 12-horsepower 

 engine. Also, the Wrights had the good sense to eliminate torque as 

 an added complication to their stability and control problems by hav- 

 ing their propellers turn in opposite directions. As the years passed, 

 however, and the power of engines became ever greater — and the 

 power of controls also increased — torque was not too great a problem 

 other than on takeoff. But from the efficiency standpoint, the value of 

 geared-down, large-diameter propellers is becoming increasingly im- 

 pressed upon us even today by such advanced planes as the Helioplane 

 of Koppen and Bollinger. 



It was years before the efficiency of variable pitch was recognized 

 and adopted in the design of propellers because of the strange unwill- 

 ingness of aircraft engineers to see the direction progress was taking, 

 even though the signposts were so clear. The propeller construction 

 of the Wrights was of wood with fabric covering to protect the wood 

 from splitting too easily when hit with stones from a field. These 

 wooden propellers were soon found to suffer from humidity and other 

 variables so they were gradually succeeded by metal, first a steel hub 

 with aluminum blades, and then steel blades; and lately there have 

 been some new plastic developments of great interest. The Wrights 

 started out with an engine in a flat pattern. Then they put their four 

 cylinders into an upright model with the crankshaft low. In Europe 

 a start was being made on the first radial air-cooled engine. Next 

 came the tremendously successful Gnome rotary engine, and then, 



