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Facility Components

PSL No. 1 and 2 included two altitude chambers, a modern control room, a combustion air supply system, an exhauster system, and cooling water system.


The Propulsion Systems Laboratory (PSL) No. 1 and 2 relied on complex systems and components to be the state-of-the-art facility that it was. The combustion air line provided highly pressurized dry conditioned air to the test chambers. The air could be heated or cooled depending on the nature of the test. The engine being tested was installed in one of the two altitude chambers and operated from the control room. The combustion air flowed through the chambers and engine. Powerful exhausters reducing the density of the air in the test chambers to simulate the selected altitude for a test. Water-fed coolers were used to reduce the temperature of these exhausted air flows.

NACA engineers built upon their experience with previous, less powerful altitude test facilities to create the nation’s most state-of-the-art facility for studying full-scale engine systems in simulated flight conditions. The Propulsion Systems Laboratory (PSL) No. 1 and 2 included two altitude chambers, a modern control room, a combustion air supply system, an exhauster system, and cooling water system.

Compressed Air System

Although not a wind tunnel, PSL could create high-speed airflow through the interior of the engine. The combustion air system provided highly pressurized dry conditioned air to the test chambers. The air could be heated or cooled depending on the nature of the test. Large compressors pushed the air through the system, heating and refrigeration equipment adjusted it to the desired temperature, and air dryers removed moisture from the air. The air flow system was linked to the lab’s central air system, which allowed it to augment the compressors in other test facilities.


Large Elliott Company air compressors in the Equipment Building generated the air flow to simulate the speeds of flight. The compressors forced the air rapidly through the pipes towards the test section. After passing through temperature adjusting equipment, the air flowed through a pipe to the Shop and Access Building. The pipe split and wrapped around both sides of the building before entering from the front on the second floor level. The air then flowed into the north end of one of the two test chambers. It passed through the chamber’s air-straightening vanes, a bellmouth cowl in the bulkhead, and finally through the test section and the engine.

Over the years, the center continually upgraded and modified the air compression system. In 1956 there were three 16,500 horsepower centrifugal compressors capable of delivering 112 pounds of air per second at 45 psig for a total 336 pounds of air. Each of these possessed three wheels in each of their three casings: two casings in the first stage and one in the second stage. A separate booster compressor could provide 183 pounds of air per second at 150 psig. Pressure-regulating valves in the test chambers kept the air supply at the desired range.

Air Temperature Control

Depending on the type of test being run, the air flow into the engine had to be either heated or refrigerated. Engines operated at supersonic speeds had to be tested in high temperatures that simulated the heat generated by their velocity. Jet engines traveling at subsonic speeds required cold conditions that simulated the lower temperatures found at high-altitudes.

Three combustion air heaters located on the exterior of the Equipment Building created the high temperatures. The heaters ingested ambient air and passed through vertical tubes that had been heated by a natural gas flame. Each heater unit produced 125 pounds of air per second from 40 °F. Later, a pebble bed heater was added to a test chamber to create extremely high temperatures found at hypersonic speeds.

The refrigeration system for the high-altitude testing was added shortly after the original PSL construction was completed. Temperatures found at 50,000 feet and speeds of Mach 0.6 to 1.5 could be recreated without the refrigeration equipment, but slower speeds required colder conditions. Expansion turbines located in the Equipment Building could cool up to 112 pounds of air per second by 100 °F.

The air at high altitudes was very dry, so the air flow had to be dehydrated before entering the test section. The two dehydrator units could reduce the moisture of 125 pounds of air per second or 100,000 cubic feet of air per hour. The air flowed up through a vertical tank and cascade trays containing the liquid cooling medium. The dryer contained 190,000 pounds of activated alumina that could dry the air to 1 grain of moisture per pound.

Test Equipment

The PSL’s Shop and Access Building contained two test chambers, a control room, and balance chamber. Mechanics installed the engine being tested inside the test section of one of the chambers and fitted it with extensive instrumentation. Once the chamber was sealed, the altitude conditions were introduced, and the engine was ignited. Operators in the control room could run the engine at the various speeds and adjust the altitude conditions to the desired levels.

Altitude Chambers

The two 100-foot-long altitude chambers ran parallel to one another inside the Access Building with a control room in between. The chambers were pressurized and water-cooled. Each chamber contained three sections: the test section, inlet section, and exhaust section. A set of vanes that stretched across the conical inlet section straightened the airflow. Bulkheads at each end separated the test section from the rest of the chamber. An engine platform inside the test section held the engine in place and measured its thrust loads and drag. An overhead crane lowered the engine onto the stand. A large clamshell hatch sealed the test section before testing began. The engine’s exhaust flowed into the tubular exhaust section, which expanded until connecting to the primary cooler.

PSL could be configured in either a direct-connect or free-jet mode. The direct-connect was the simplest way of studying the internal performance of the engine. The engine was mounted on the thrust stand inside a test section with the air flow connected directly to the engine inlet. A free-jet method was required, however, to test the air inlet system. A nozzle created a supersonic jet of air that enveloped the engine inlet. The stream was powerful but narrow, so it did not permit the study of air flow over the complete engine. The free-jet setup was more beneficial than the direct-connect since the entire engine system, including the inlet duct, could be studied.


Control Room

The control room for PSL No. 1 and 2 was located between the two chambers on the second floor of the Shop and Access Building. The control room had separate stations for each chamber. From this area, the operators ran the engine and worked with technicians in the Equipment Building to create the proper altitude conditions inside the test chamber. During the 1950s, large manometer boards in the rear of the room indicated pressure measurements from the test. The operator could monitor them from a console in the center of the room, cameras on fixed stands recorded the pressure measurements.

The control room was frequently updated and modified. By the 1960s, the center replaced the manometers with electronic equipment. Television consoles were installed to provide the test engineers with a view of the engine during the test. Temporary data recording equipment was occasionally installed for certain tests and later removed, and the control panels were rearranged periodically.


To obtain useful data from the tests, instrumentation had to be installed in both the engine and the test chamber. The setup varied depending on the requirements for the specific test. It could take weeks or even months for technicians and electricians to set up the multitude of thermocouples, rakes, and other required instruments. Sometimes, it was necessary to get data from each of the engine’s compressor stages. This process often began in the shop area before the engine was installed in the chamber. Once the test article was in the chamber, the staff could access it through the main hatch or a smaller access door in the inlet section. The engine itself was atop a thrust stand that measured the thrust and drag. A periscope camera was first set up inside one of the chambers in the 1950s, and additional cameras were set up in the 1960s.

Exhauster System

Large exhauster equipment in the Equipment Building reduced the density of the air inside the test chambers to simulate high altitudes and removed the hot gases produced by the engines. Coolers lowered the temperature of these gases before they reached the exhauster equipment. The coolers required a large quantity of water and a cooling tower.

Exhaust Equipment

A series of Roots-Connersville exhausters in the Equipment Building pumped the air and engine exhaust out of the PSL system. The original configuration could remove 3500 °F gases at a rate of 100 pounds per second when the simulated altitude was 50,000 feet. Each of the thirteen 5100-horsepower exhauster units contained two J33 compressor wheels that could be adapted to work in tandem or as parallel units. The number of units could be varied to control the power load.

In 1955 the center added a fourth line of exhausters. The three centrifugal exhausters were capable of supplying 166 pounds of air per second at the test chamber altitude of 50,000 feet or 384 pounds per second at 32,000 feet. These exhausters had two first-stage castings driven by a 10,000-horsepower motor and thee additional stage castings driven by a 16,500-horsepower motor. The system’s total inlet volume was 1,650,000 cubic feet of gas per minute.


It was necessary to cool the extremely hot temperature of the engine’s exhaust so that it did not damage the exhauster equipment. The air flow exited through the 12-foot-diameter and 37-foot-long exhaust section of the test chamber and entered into the giant primary cooler. A series of narrow, water-filled vanes stretched across the cooler. The heat from the air transferred to the water as the air flow passed through the vanes. The cooling water was continually cycled out of the system, carrying with it much of the exhaust heat. Each test chamber had its own primary cooler but shared a secondary cooler.

The air then flowed through a secondary cooler that further reduced the temperature. This secondary cooler, or spray cooler, also scrubbed the contaminants from the exhaust gases to reduce explosion hazards. The air was then pumped through the exhausters in the Equipment Building and expelled out into the atmosphere.

The water circulated through a closed-loop system with make-up water added. The system supplied the primary and secondary coolers and protected the exhaust ducts and valves from the hot engine exhaust. A cooling tower dissipated the remainder of the heat from the circulating water before recycling it back to the facility. The cooling tower had several large pumps, three water softening units, and a settling basin. The water softeners prevented scale and corrosion in the pipes.

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