NACA Studies

Back to Index


I wanted to provides some links to various studies associated with air inlets for cooling of our planes.  External inlets, submerged inlets and wing type inlets.  An interesting note from one of the reports is:  


“The results of a preliminary investigation of submerged-duct entrances are presented. It is shown that an entrance of this type posses desirable critical speed and pressure recovery characteristics when used on a fuselage or nacelle in a region of low incremental velocity and thin boundary layer. The data obtained indicate that submerged entrances are most suitable for use with internal-flow system which diffuse the air only a small amount:  for example, those used with jet motors which have axial-flow compressors. When complete diffusion of the air is required, fuselage-nose or wing leading-edge inlets may prove to be superior. */The results of the investigation have been prepared in such a form as to permit their use by a designer and the application of these data to a specified design is discussed.”


It may be possible that the external type scoops may be more useful than NACA style scoops for applications such as oil cooling and engine cooling.   Engine air intakes may be more amenable to NACA style inlets.


My main interest in these studies is for efficient design of an oil cooling system.  I feel the down draft cooling works very well in our planes and I am very pleased with my current design.


Pressure available with cowling flaps:

Ducts for cooling within airplane wings:


Cooling systems for aircraft power plants:


Rear under slung fuselage ducts:


A method for the design of cooling systems for aircraft power-plant installations

(good for oil coolers)

The problem of cooling an air-cooled cylinder on an aircraft engine
 NACA Report 719, 15 pp. , 1941

An analysis of the cooling problem has been to show by what means the cooling of an air-cooled aircraft engine may be improved. Each means of improving cooling is analyzed on the basis of effectiveness in cooling with respect to power for cooling. The altitude problem is analyzed for both supercharged and unsupercharged engines. The case of ground cooling is also discussed. The heat-transfer process from the hot gases to the cylinder wall is discussed on the basis of the fundamentals of heat transfer and thermodynamics. Adiabatic air-temperature rise at a stagnation point in compressible flow is shown to depend only on the velocity of flow.


Pumping and thrust characteristics of several divergent cooling-air ejectors and comparison of performance with conical and cylindrical ejectors
NACA RM-E53J13, 44 pp. , 1954


Correlation of cooling data from an air-cooled cylinder and several multicylinder engines
 NACA Report 683, 25 pp. , 1940

The theory of engine-cylinder cooling developed in a previous report was further substantiated by data obtained on a cylinder from a Wright r-1820-g engine. Equations are presented for the average head and barrel temperatures of this cylinder as functions of the engine and the cooling conditions. These equations are utilized to calculate the variation in cylinder temperature with altitude for level flight and climb.

Performance characteristics of aircraft cooling ejectors having short cylindrical shrouds
 NACA RM E51E01, 41 pp. , 1951

The factors affecting the performance of ejector suitable for aircraft cooling are investigated theoretically and experimentally. The investigation covers a range of shroud- to-nozzle diameter ratios from 1.1 to 1.6,


Preliminary investigation of cooling-air ejector performance at pressure ratios from 1 to 10
Preliminary investigation was made of conical cooling air ejector at primary pressure ratios from 1 to 10.


Flight comparison of performance and cooling characteristics of exhaust-ejector installation with exhaust-collector-ring installation
 NACA RM-E6L13a, 37 pp. , 1947


Submerged Duct Studies (NACA style ducts):