Effect of Increased Cooling Surface on Performance of Aircraft-Engine Cylinders as Shown by Tests of the NACA Cylinder.

摘要

A method of constructing fins of nearly optimum proportions has been developed by the NACA to the point where a cylinder has been manufactured and tested. Data were obtained on cylinder temperature for a wide range of inlet-manifold pressures, engine speeds, and cooling-pressure differences. The results indicate that an improvement of 40 percent in the outside-wall heat-transfer coefficient could be realized on the present NACA cylinder by providing a thermal bond equivalent to that of an integral fin-cylinder wall combination between the preformed fins and the cast cylinder wall. Estimates over a range of wall thicknesses from 0.75 inch to 1.5 inches show that the pressure drop required for cooling could be decreased as much as 80 percent for a range of powers from present cruising to take-off power if the head fins on a present-day cylinder were replaced by fins of NACA cylinder proportions and if the thermal bond between the wall and the fins were equivalent to that of an integral arrangement. Calculations based on an inside-wall head temperature of 5000 F indicate that the pressure drop required for cooling hypothetical cylinders of varying head-wall thickness could be decreased 50 percent by increasing the thickness from 0.7 inch to 1.5 inches. An estimate based on an inside-wall head temperature qJ 500 deg F and an integral fin bond indicates that the improved cooling obtained through the use of fins of NACA cylinder fin proportions will permit an increase of 35 percent in power output. This estimate of power increase is made solely for cooling criteria and does not include other factors limiting power output.