WITH engine outputs continually going up it is worthy to note that the in-line air-cooled engine possesses certain inherent characteristics which make it particularly suitable as an aircraft engine of high output.
Satisfactory cooling of this type of engine has been obtained at higher rated specific outputs than have yet been achieved in any other kind of air-cooled engine.
A type of valve gear can be used which, in addition to being suitable for high-speed operation, permits long periods of operation without the necessity for checking valve clearances.
The lubrication of this type of engine appears to be less of a problem than that of the slower speed radials.
Smoothness of operation and relative quietness at high speed not only afford comfort to pilots and passengers, but also affect favorably the life of both engine and airplane.
The cowling of the in-line engine is relatively simple and permits excellent visibility, combined with the possibility of reduced drag.
Specific weights of in-line engines compare favorably with other engines of equal horsepower. As specific outputs are increased, the in-line engine should gain a weight advantage over other types.