274 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1962 



Posili'on of 

 . ^'flap"when 



\.Conhurof 

 fuselage or 

 nacelle 



1^ 



Secllon A-A 

 showing shape 

 of bames 



Figure 13. — Cooling-air flow in tractor installation of a cowled radial engine. Only the 

 upper half of the installation is shown. 



by Curtiss (pi. 21, fig. 1) and used soon afterward by Allison and 

 Rolls-Royce. This change, which allowed operation of the coolant at 

 250° F., reduced the radiator area required by about 50 percent. This 

 improvement, together with better radiator design and radiator cowl- 

 ing (pi. 21, fig. 2), brought the drag of liquid-cooled engines well be- 

 low that of air-cooled radials of equal power. Their installed weight, 

 which had been greater than that of air-cooled radials, also came down 

 to more comparable figures. Schlaifer gives the weight per horse- 

 power of the best liquid-cooled fighter installation as 30 percent more 

 at sea level and about the same at 25,000 ft." as a comparable air- 

 cooled installation. 



The fact tliat the "Battle of Britain" was won by liquid-cooled 

 engines (the Rolls-Royce "Merlin") gave a great impetus to the Army 

 prejudice in favor of water-cooled fighters.^*' Actually, both types 

 were used, and it was found that the air-cooled fighter was better at 

 low altitude both because of its lighter specific weight and its lesser 

 vulnerability to small-arms fire. 



'" Owing to the fact that radiator area can be designed large enough for any altitude, 

 while fin area on an air-cooled cylinder has a practical limit, and power of air-cooled 

 engines therefore is limited by cooling, above a certain altitude. 



18 One high officer answered the author's question, "Does the Army Tvant liquid-cooled 

 fighters even if better fighters can be built around air-cooled engines?" In the affirmative! 



