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National Advisory Committe for Aeronautics, Research Memorandum - Performance of a 20'' Steady Flow Ram Jet at Mach Altitudes and Ram Pressure Ratios

The results of an investigation conducted in the Cleveland alti-
tude wind tunnel to determine the performance of a 20—inch ram Jet
are presented and discussed. The investigation was_conducted at alti—
tudes ranging from 7000 to 41,500 feet and at ram—pressure ratios
equivalent to free-stream Mach numbers as great as 1.84 using pre-
heated 62-octane fuel. Supplementary tests to determine any change
in performance caused by changing the fuel to preheated loo-octane
were also made. An extension of the methods of data reduction and of
the generalizing performance parameters applicable at supersonic Mach
numbers and over a wide range of operating conditions is presented.
The magnitudes of the total—pressure losses across the various phases
of the ram-Jet cycle are analyzed and discussed.

At an equivalent free-stream Mach number of 1.84 and a gas total-
temperature ratio across the engine of 5.7, the equivalent-sea-level
net thrust was 8135 pounds. For these conditions, the over-all effi-
ciency was-12.6 percent and the combustion efficiency was 70.5 percent.

The corresponding net—thrust coefficient was 0. 74. The investigation
also showed that no change in the performance er operating range of
the engine occurred when the fuel was changed from preheated 62- octane
to preheated 100— octane gasoline.

Experiments have been conducted at the NACA Cleveland laboratory
to determine the feasibility of operating a ram Jet at high altitudes
and at ram-pressure ratios equivalent to supersonic flight speeds.

Performance studies of a ram Jet at equivalent free-stream Mach numbers
to 1.26 and at altitudes to 50,000 feet were made at this laboratory
and are reported in references 1 and 2. Other ram- jet studies (ref—
erences 5 to 6) present subsonic ram-Jet performance.

In the present investigation made to extend the performance data,
dry refrigerated air was admitted to a 20—inch ram Jet mounted in the
altitude wind tunnel. The desired ram-pressure ratio across the engine
was obtained by throttling the inlet air to the ram Jet from approxi-
mately sea-level pressure and adjusting the static pressure in the
tunnel. The performance of the engine was studied at altitudes up to
41,500 feet and ram-pressure ratios equivalent to Mach numbers as great
as 1.84. The selection of the ram-Jet configuration used in this study
was based on the results of previous investigations (references 1 and 2).