MANUFACTURERS of radial air-cooled engines have centered their attention upon low specific weight for their product. This is accomplished by compact design, using the best of materials and the highest grade of workmanship and finish, with the production of the maximum possible horsepower per cubic inch of engine displacement. High output can be accomplished by a combination of high rotative speed and high brake mean effective pressure with low friction losses. Many considerations of design and operation must be correctly proportioned to approach the ultimate in horsepower.
Important advances have been made in improving engine output by cooling air-cooled cylinders with well designed fins supplied with air from directing baffles, thus increasing the brake mean effective pressure which can be produced on a given fuel without detonation. The complete elimination of all hot spots and a general reduction of temperature in the combustion-chamber at the end of the compression stroke will permit this gain in performance to be carried to even further limits. Other advances in this line are expected through the use of better fuel, mechanical fuel-distribution, compensated valve-gear, higher supercharger-pressure, higher compression-ratio and more efficient superchargers. The standardization and distribution of fuels with a high antiknock rating will make possible substantial increases in output.
Great as are the advances in low specific engine weight, it has recently been found that at least as great an advance in performance of the combined airplane and engine can be accomplished by attention to the aerodynamic characteristics of engines and propellers. The engine manufacturer must apologize for the radial engine in this respect until it is covered with a ring or N. A. C. A. cowl, after which it becomes surprisingly acceptable in drag coefficient.
As engine speeds are increased for the purpose of additional power, reduction gears will become necessary to maintain or improve propeller efficiency.
Discussion of the paper* had to do largely with engine noise which, it was agreed, will need to be reduced.
It was stated that availability of improved fuels would make possible an increase of 50 per cent in the output of present aeronautic engines.