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AWT Facility Description

Illustration of the AWT complex. — An early drawing of the AWT with the Shop and Office Building (center), Exhauster Building (left), and Refrigeration Building (right).

The AWT employed sophisticated design features to overcome the difficulties associated with operating engines in simulated altitude conditions. These included a unique steel shell, an air scoop, a make-up air system, and unique banks of cooling coils.

Overview

The Altitude Wind Tunnel (AWT) was among the most complex wind tunnels ever designed when it began operations in early 1944. Its state-of-the-art systems created the wind speeds, air pressure, and sub-zero atmospheric conditions experienced at high altitudes. National Advisory Committee for Aeronautics (NACA) engineers devised a number of ingenious features to overcome the difficulties associated with operating engines in simulated altitude conditions, including a robust steel shell, an air scoop, and a make-up air system. Carrier Corporation to develop an unprecedented refrigeration system to cool the massive air flow. The tunnel’s 20-foot diameter test section was large enough to operate full-size aircraft engines. The tests were conducted from a soundproof control room and complex instrumentation was employed to record test data. The tunnel test section was enclosed within the facility’s Shop and Office Building.

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Aerial view of the Altitude Wind Tunnel. — The T-shaped building housed the AWT’s test section, control room, high-bay, shop area, and offices. The Exhauster Building (left), and the Refrigeration Building (right).

Altitude Wind Tunnel Schematic Diagram — This schematic drawing depicts the AWT’s components and support buildings (2007).

Blueprint with AWT elevations and general plan. — NACA drawings showing the overall view of the AWT and a frontal elevation (1944).

Aerial view of AWT in 2005. — The AWT/SPC complex as it appeared in October 2005.

Tunnel Shell

The tunnel itself was a massive rectangular structure, which for years provided one of the highest vantage points at the center. The tunnel was 263 feet long on the north and south legs and 121 feet long on the east and west sides. The larger west end of the tunnel was 51 feet in diameter throughout. The east side of the tunnel was 31 feet in diameter at the southeast corner and 27 feet in diameter at the northeast. The throat section, which connected the northwest corner to the test section, narrowed sharply from 51 to 20 feet in diameter.

The overall shape of the AWT was similar to several other contemporary NACA wind tunnels. The AWT’s low internal pressure and temperature levels, however, required the use of new engineering concepts to design the tunnel’s steel shell.The tunnel shell consisted of two steel layers with a blanket of insulation between. The 1-inch-thick inner steel layer could withstand the external atmospheric pressure when the interior was evacuated to low pressure levels. The designers employed a T-1 steel alloy with three times the strength of normal carbon steel so that the shell could endure the low temperatures within without becoming brittle. A 4-inch layer of glass wool and steel mesh was applied over the inner tunnel shell to retain the tunnel’s low temperatures. The outer 1/8-inch-thick steel shell was then constructed over the insulation to protect the structure from the environment.

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View from southeast of Altitude Wind Tunnel. — The AWT was was 263 feet long on the north and south legs and 121 feet long on the east and west sides (1955).

Men on top of AWT applying insulation. — Application of insulation to the AWT shell. A second shell was then placed over the insulation (1943).

AWT with inner and out shells visible. — This photograph shows both the 1-thick inner shell to the right and the thin outer shell to the left during the conversion of the AWT to the SPC in 1961.

Two men atop wide end of AWT tunnel shell. — Two men inspect the top of the west end of the AWT’s shell, which was 51 feet in diameter (6/6/1945).

The tunnel was braced by a large elliptical support ring in each corner, the test chamber in the middle, and a series of 120 support rings which lined the tunnel at 6-foot intervals. Each of the rings were anchored to concrete and steel piers which elevated the tunnel. Unique steel rollers bore the weight of the tunnel in a way that allowed the shell to contract and expand during the tunnel’s dramatic temperature and pressure fluctuations. The rollers were placed between the concrete piers and the support ring buttresses.

Construction of supports for AWT. — The Sam W. Emerson Company commenced the excavations for the AWT’s foundations in the spring of 1942 and completed the task by late-December.

AWT foundations from inside tunnel loop. — The AWT was elevated by concrete stands on steel pylons. Steel rollers located at the top of the concrete stands allowed the shell to contract and expand (6/6/1945).

Northeast Corner of the Altitude Wind Tunnel. — The rollers, which allowed the shell to expand and contract, are visible between the concrete foundation and the steel corner ring at the northeast corner of the AWT (2005).

H-shaped support under AWT. — This H-shaped concrete and steel support held up the northeastern leg of the AWT (2007).

A series of steel stairs, ladders, and platforms provided access to the top of the tunnel from the second floor of the test chamber. A stairway rose from the narrow throat section to the top of 51-foot-diameter west end of the tunnel. From there, a walkway on top followed the entire tunnel circuit.

Men on top of AWT. — Two men work on top of the 51-foot diameter west end of the AWT. The walkway provided access to the tunnel roof (6/6/1945).

AWT roof with walkway and refrigeration pipes. — The top of the AWT contained a walkway running along the top of the tunnel (1955).

Aerial of AWT complex from the northeast. — The ladders and walkways atop the AWT in April 1955.

Aerial View of Repainted Altitude Wind Tunnel. — The AWT was repainted in 1984 as the center was exploring the feasibility of restoring the tunnel.

Air Flow System

The AWT could produce wind speeds up to 500 miles per hour through its large 20-foot-diameter test section at the standard operating altitude of 30,000 feet. The average speed at lower altitudes was 345 miles per hour. A 12-bladed, 31-foot-diameter spruce wood fan near the southeast corner generated the airflow. An 18,000-horsepower General Electric (GE) induction motor located in the rear corner of the adjacent Exhauster Building rotated the fan at 410 revolutions per minute.

Flexible couplings protected the extended drive shaft, which connected the two structures, from the movement of the tunnel shell. A bronze screen secured to one of the turning vanes protected the wooden fan from flying debris and failed engine parts. Nonetheless, the blades became worn or cracked over time and required replacement. The lab installed an entire new fan assembly in 1951.

Elliptical panels of turning vanes in each corner guided and evened the airstream around the tunnel’s square corners. The tunnel contracted from a diameter of 51 feet to just 20 feet as it approached the test section. This contraction accelerated the air velocity as it passed the engine studied.

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AWT Drive Fan drawing (1944)

Two men in front of Altitude Wind Tunnel drive fan. — The 31-foot diameter spruce fan inside the southeast corner of the AWT was driven by an 18,000 horsepower motor in the Exhauster Building (2/29/1944).

Turning vanes in the AWT. — One of four sets of turning vanes in the AWT that helped to evenly move massive volumes of air through tunnel (2/29/1944).

Man examines damaged wooden fan blade . — A researcher examines a worn wooden fan blade in the AWT. The blades were damaged and worn over time despite protective screens upstream (12/7/1949).

Blades for new AWT drive fan. — New fan blades in the shop area prior to their installation during a modernization of the tunnel in 1951.

The operation of engines in the tunnel, necessitated constant purging and replenishing of the airflow to maintain the altitude conditions. A unique air scoop on a vertical support immediately downstream from the test section collected combustion byproducts exhausted by the engines. Compressors in the nearby Exhauster Building drew the vented air out of the tunnel and discharged it into the atmosphere.

Compressor in Exhauster Building Addition. — New exhauster equipment in the adjacent Exhauster Building helped remove contaminated air from the tunnel through the air scoop (4/2/1955).

Lockheed YP-80A in Altitude Wind Tunnel with Air Scoop behind. — Lockheed’s YP-80A in the AWT with the tunnel’s air scoop behind it. The air scoop removed contaminated exhaust from the air stream (3/16/1945).

J57 in AWT with air scoop behind. — The air scoop, which removes combustion byproducts from the air stream, is visible directly behind the J57 engine (1/29/1957).

Air scoop underneath AWT. — This pipe underneath the AWT removed air from within the tunnel to reduce the atmosphere and expel engine exhaust contaminants (5/29/1951).

A make-up air system replenished the exhausted air with cool, dry air. A large dryer located outside the tunnel’s southwest corner removed condensation from the air to prevent shocks to the tunnel’s airflow. There, atmospheric air passed over a set of cooling coils, then over beds of activated alumina in a large dryer, and finally over another set of cooling coils to reduce the temperature to the desired level.

The system introduced the processed air into the AWT through two portals in the western tunnel wall. One of the nozzles extended well into the tunnel and piped the new air directly into the test section. Later this pipe was extended and attached to the engine inlets to increase the tunnel’s capacity. The system could exchange 6,000 pounds of air per minute, which reduced airstream contamination to roughly 5 percent.

Aerial view of Air Dryer Building. — The Air Dryer Building is visible diagonally below the tunnel’s southwest corner. This three section building cooled and dried atmospheric air before it was added to the tunnel’s air stream (9/10/1945).

Make-up Air Line inside AWT. — Cool, dry uncontaminated air was pumped from the refrigeration system through a 36-inch diameter nozzle. This nozzle, seen in this 2005 photograph, originally extended well into the tunnel and through the corner turning vanes.

Ramjet in test section with air directed to inlet. — The AWT’s make-up air line enters the test section from the right and is connected directly to the engine inlet for this 1946 test.

Altitude Simulation

The most complex aspect of the AWT’s operation was the simulation of altitude conditions. The massive exhauster system thinned the air and an unrivaled refrigeration system produced the low temperatures necessary for this simulation. The NACA originally designed the tunnel for temperature altitude simulation of up to 30,000 feet and pressure altitude simulation of 45,000 feet. This capacity was increased to 100,000 feet by the mid-1950s.

Engineers from the Carrier Corporation developed a unique refrigeration system that lowered the AWT’s interior temperature to –47°F, and, if applied to commercial purposes, could generate 10,000 tons of ice per day. Fourteen Carrier compressors in the Refrigeration Building powered the cooling system. The compressors converted the Freon 12 refrigerant into a liquid, which was then pumped into the eight identical banks of cooling coils arranged in an innovative zigzag design. This collection of 260 copper-plated coils covered the entire 51 foot width of the return leg. The Freon absorbed heat as the air flow passed through the coils and transferred it to cooling water. The cooling water flowed to an external cooling tower which the heat dissipated into the atmosphere. The system required 20,000 gallons of cooling water every minute.

Cooling Coils inside the Altitude Wind Tunnel. — Cooling coils inside the return leg of the AWT were constructed in a unique accordion-like structure that increased their surface area (3/16/1950).

Cooling equipment inside the Refrigeration Building. — Carrier Corporation cooling equipment inside the AWT’s Refrigeration Building (9/21/1944).

Aerial view of Refrigeration Bldg. and cooling lines into AWT. — The Refrigeration building, immediately to the right, contained the 14 Carrier compressors and a flash cooler for the AWT’s refrigeration system (9/10/1945).

Exterior of Altitude Wind Tunnel Cooling Tower. — Cooling Tower No.1 supplied water for the AWT refrigeration system. Water which carried heat away from the tunnel was piped to the cooling tower where the heat was disipated (6/14/1944).

In addition to removing contaminated air through the air scoop, the exhaust system reduced the tunnel’s air pressure to create the thin atmosphere found at high altitudes. The Exhauster Building, directly to the east of the tunnel, housed four 1,750-horsepower exhausters which pumped 2/3 of the air out of the tunnel and expelled it into the atmosphere. Roots-Connersville centrifugal compressors in the Engine Research Building’s basement removed the remaining air. The original configuration could simulate altitudes up to 45,000 feet. The Exhauster Building was expanded in 1951 to house more powerful compressors, and the system was soon linked to exhaust systems at other test facilities.

Worthington exhausters inside the Exhauster Building. — One of four 1750-horsepower Worthington reciprocating exhausters in the Exhauster Building that removed air and contaminants from the AWT to simulate high-altitudes (10/24/1962).

Technician with Compressor in Exhauster Building Addition. — One of three new Ingersoll-Rand compressors added to the AWT’s Exhauster Building in 1951.

Altitude Wind Tunnel Exhaust Pipe outside AWT. — This 36-inch diameter exhaust pipe connected the AWT and the Exhauster Building (10/12/2005).

Central Control Room in Engine Research Bldg. — This control room in the Engine Research Building coordinated the air flow systems around the laboratory, including the AWT (7/21/1948).

Test Chamber

The size of the AWT’s 20-foot-diameter and 40-foot-long test section was driven by the desire to test full-scale engines up to 3000-horsepower. This was larger than the piston engines in use in the early-1940s. A large overhead crane lifted the engines through the high-bay and the second-story test chamber before being lowering them into the test section. Technicians then spent days or weeks hooking up the supply lines and instrumentation. The engines were generally mounted on wing spans that stretched across the test section. The wing tips attached to the balance frame’s trunnions which could adjust the angle of attack. The balance frame included six measurement devices that recorded data and controlled the engine.

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AWT Test Section Drawings (1942)

A rail crane lowers an inlet duct into the 20-foot diameter AWT test section. The test section lid can be seen to the left (10/3/1951).

Technicians examine Pratt & Whitney J57 engine installed in the Altitude Wind Tunnel test section. — A Pratt & Whitney J57 engine is installed in the 20-foot diameter AWT test section in January 1957.

A mechanic examines the Allison T-38 inside the AWT's test section. — A mechanic examines the Allison T-38 inside the AWT’s test section. The test section lid is closed in this photograph (7/21/1953).

Test filmed through window in AWT test section . — A cameraman films a test inside the AWT through one of the observation windows in the test section’s clamshell lid in October 1951.

Staff operated the tunnel and the experimental engine from a soundproof control room next to the test section. The test operators worked with assistants in the Exhauster Building and Refrigeration Building to manage the large systems. Although the configuration of the control panels changed frequently, the room’s principal wall contained the make-up air, drive fan, and engine controls. It also included two sets of pneumatic levers that operated different facets of the engine. The panels on the opposite wall managed the combustion, refrigerated and cooling air, and the exhauster systems.

AWT Control Panel for Engines. — This panel in the AWT’s soundproof control room controlled the engine being tested in the tunnel. A camera on a stand to the right recorded the gauge readings (4/13/1945).

Researcher sits at Altitude Wind Tunnel Control Panel. — A researcher moniters the impact, lift, thrust, yaw, pitch, control, and roll of the test article from the AWT’s control room adjacent to the test section (4/13/1945).

Operator operates refrigeration controls in Altitude Wind Tunnel Control Room. — A researcher demonstrates the refrigeration controls along the back wall of the AWT control room (8/20/1952).

A crane lowers inlet into AWT test section. — During tests of the Allison J-71 turbojet in the summer of 1952, a number of instruments were blown out in the control panels.

The AWT’s test section, control room, and balance chamber were located in a three-story test chamber in the rear of the Shop and Office Building. The control room, fan room, and manometer boards were located on the mezzanine level next to the test section. The upper level was a large open space, approximately 50 feet high, with the test section sunken up to its midpoint in the floor. This main level contained a large, wooden viewing platform with stairs built so that people could get from one side of the test section to the other. A mechanical pulley system raised and lowered the tunnel’s large clamshell lid into place. Hand-turned locks accessible from the viewing platform sealed the lid. Viewing windows in the lid permitted the filming and visual inspection of the tests.