Free Spinning Tunnel

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Facility 646
Free Spinning Tunnel

Center: Langley Research Center
Location: Hampton, Virginia
Year Built: 1935
Historic Eligibility: National Register Eligible
Important Tests: Jet Shoes, Scout Project, Space Suits, Viking

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[top] History

Now known as the East Area Compressor building, Building 646 in the NASA East Area was the site of five historically significant activities since its construction in 1934. Originally named the 15-Foot Free Spinning Tunnel, it was designated building 193A. It was also known as the Free Spinning Tunnel, the Dynamics Tunnel Building, and the Engineering Technology Laboratory.

The tunnel was decommissioned in 1946. In 1962, initial work was begun to convert the building to Advanced Life Support Systems with a ILSS Tank installed and operational in 1966. The tank was later moved when the new life support facility was constructed in building 1250.

The following discussion provides information on research activities for some of the most important aeronautical research programs conducted in Building 646.

[top] 15-Ft Spin Tunnel (Free-Spinning Tunnel)

When the Langley Memorial Aeronautical Laboratory initiated operations in 1917, one of the most challenging problems facing heavier-than-air flight operations was the dreaded tailspin. The international aeronautical engineering community knew very little about the primary factors that influenced the spin or the relative effectiveness of piloting methods to recover from spins. In the 1920s Langley’s staff conceived a testing technique that used catapult and/or hand-launched aircraft models dropped from the interior ceiling of an Army airship hangar at Langley which was about 105 feet high. After using the method to study spins, the Langley staff concluded that the catapult technique was excessively time consuming and resulted in frequent damage to the fragile models.

Langley then constructed a 5-ft diameter vertical wind tunnel in Building 580 (previously the site of the first NACA wind tunnel) to provide for measurements of the aerodynamic loads on aircraft models during simulated spinning motions. The models were not in free-flight during the tests, but were mounted to a balance that was driven in simulated spinning motions by an electric motor. Airflow in this early tunnel was vertically downward, and tests were directed at the aerodynamics encountered in the spin. Using the aerodynamic data in equations of motion, the staff attempted to predict spin behavior.

Meanwhile, the British researchers at the Royal Aeronautical Establishment (RAE) in England had observed the disappointing NACA efforts with catapult-launched models and subsequently conceived the idea of a vertical wind tunnel to permit free-spinning tests of aircraft models. Such a technique was much more productive than either catapult launches or wind-tunnel aerodynamic measurements. Following initial trials with a small model of the free-spinning tunnel, the RAE constructed a 15-ft full-scale version of the tunnel and proceeded to conduct fundamental research on spinning and spin recovery.

In turn, researchers and management at NACA-Langley had followed the developments in England and proceeded to design and construct a similar 15-ft free-spinning tunnel in 1934 under the direction of Charles H. Zimmerman. The construction site for the new tunnel was next to the Langley Full Scale Tunnel. Initially the building was designated Building 193 and known as the 15-Ft Free-Spinning Tunnel. Research operations began in 1935. The airflow in the 15-ft tunnel was vertically upward to simulate the downward descent velocity of an aircraft during spins. At the beginning of a typical test, the model was mounted with pro-spin controls on a launching spindle at the end of a long wooden rod held by a tunnel technician. A tunnel operator increased the vertical air speed until the air forces on the model equaled its weight. At this point, the model automatically disengaged from the spindle and continued to rotate in a spin as the airspeed was continuously adjusted to maintain the model’s position at eye level in the test section. The model’s control surfaces were moved from pro-spin settings to pre-determined anti-spin settings by a clockwork mechanism, and the rapidity of recovery from the spin was noted. After the test was completed, the tunnel airspeed was decreased and the model was allowed to settle into a large net at the bottom of the test section. The model was then recovered with a long- handled clamp and prepared for the next test.

As aircraft designs evolved in the 1930s, the increasing weight of full-scale aircraft required heavier models which in turn required higher tunnel air speed capability. The free-spinning tunnel had been designed with a maximum speed of only about 40 mph. Although the 15-ft tunnel remained operational until the mid-1940s, it was replaced by a more capable 20-Foot Spin Tunnel in 1941. During World War II, the two tunnels combined to test over 300 different military aircraft designs, resulting in modifications to over half the configurations to improve their spin recovery characteristics. The 15-ft Spin Tunnel was demolished after World War II.

[top] 5-Ft Free-Flight Tunnel

In the late 1930s after successfully advocating for, designing, and initiating operations of the 15-foot vertical spin tunnel, Charles H. Zimmerman conceived and successfully developed another unique wind-tunnel apparatus in Building 646 to study the dynamic stability and control characteristics of an aircraft model during conventional flight in a free-flying condition. The innovative new facility began operations in 1937.

A 5-foot-diameter “proof-of-concept” wind tunnel was constructed and suspended from a yoke in Building 646 that permitted it to be rotated about a horizontal axis and tilted from the horizontal position to a nose-down orientation up to angle of 25º. A tunnel operator stood at the side of the test section and controlled the tilt angle of the tunnel as well as the airspeed produced by a fan located at the right rear of the test section. His main function was to adjust the airspeed and tunnel angles so that the model remained stationary in the center of the tunnel during a test. The evaluation pilot was positioned at the rear of the tunnel where he could easily see the lateral motions of the model and provide inputs to the model’s controls via fine wires that were kept slack during the flight.

In a typical free-flight test, the model was placed at the center of a takeoff platform and the elevator or model pitch control was manually adjusted to a desired setting. The tunnel angle was adjusted to the expected glide path of the unpowered model and the airspeed was slowly increased until the model rose from the platform and assumed a flying attitude. The tunnel operator and evaluation pilot coordinated their tasks to permit an assessment of the relative stability and responses of the model to control inputs.

Initial testing in the 5-ft free-flight tunnel started in 1937 with very encouraging results, including the development of an automatic light-beam-control device to reduce crashes during the learning process. After a very limited number of evaluation experiments, the free-flight concept was quickly matured into a larger 12 Foot Free-Flight Tunnel in Building 644. The 5-ft tunnel in Building 646 was demolished after the Langley 12 Foot Free-Flight Tunnel became operational. The successful pioneering studies of the free-flight technique in the smaller tunnel paved the way for applications to some of the nation’s most critical civil and military aircraft in subsequent years.

[top] Catapult Model Apparatus

Free-spinning model tests provide significant information regarding the types of spins that aircraft may exhibit and the probability of success of attempts to recover from the spins. However, spin-tunnel tests do not provide information about how easily an aircraft may enter a spin from conventional controlled flight. Experiences showed that some aircraft are reluctant to enter dangerous spins predicted by spin-tunnel tests because of aerodynamic or mass characteristics. On the other hand, some aircraft can enter potentially deadly spins with little effort. In order to provide information in this critical area, Langley researchers revisited the catapult-launch testing technique that had been discarded in the 1920s.

In the 1950s, a catapult apparatus consisting of a bungee cord and launch ramp were installed near the ceiling of Building 646 to permit observations of models launched into a stall and incipient spin condition during their descent. By 1950 the 15-ft Spin Tunnel and the 5-ft Free-Flight Tunnel had been demolished, resulting in a large empty area within the building. For catapult testing, a huge net was placed across the open area near the floor to provide an area of impact and retrieval following the model tests. Motion pictures of the catapult testing conducted in Building 646 are included in the video section.

Unfortunately, experience with the catapult technique once again highlighted the shortcomings of the testing technique and inspired researchers to seek other techniques to provide information on the transition from conventional flight to fully developed spins. As a result of several studies and searches for suitable test sites, Langley evolved a drop-model technique which consisted of launching unpowered models from a helicopter and controlling the models from ground-based control stations. The drop-model technique was initially implemented with testing at the West Point, Virginia airport and later at the Plum Tree test site near Poquoson, Virginia.

[top] Free Flight Tests of VTOL Models

In the mid-1950s the U.S. military’s interest in vertical takeoff and landing (VTOL) aircraft intensified as concerns over the vulnerability of fixed runways in Europe began to increase. Following close collaboration and communication with the Air Force and Navy, researchers from Langley’s 12 Foot Free-Flight Tunnel developed a testing technique to evaluate the dynamic stability and control characteristics of VTOL airplane concepts during hovering flight. A large number of different concepts were evaluated including vertical attitude tail sitters, tilt-wing designs, tilt-jet configurations, and “stand-on” flying jeeps. The large enclosed test area of Building 646 proved to be an ideal test site to evaluate these radical aircraft concepts. Powered by electric motors and remotely controlled by research pilots, the VTOL models demonstrated the feasibility of unconventional vertical flight and defined the level of control required for satisfactory flying characteristics. Motion-picture records of the flight testing conducted in Building 646 are included in the videos of this site.

In the late 1950s the successful hovering demonstrations had captured the interest of the aeronautical community, and relocation of the free-flight tunnel staff from Building 644 to the Langley Full Scale Tunnel (Building 643) provided the capability to evaluate the flying characteristics of VTOL models during the transition from hovering flight at zero airspeed to conventional flight. Hovering flight testing was then conducted within the return passage ways of the Full Scale Tunnel and flying was no longer conducted in Building 646.

[top] East Area Compressor

After the dynamic model testing techniques were moved to the Full Scale Tunnel and outdoor drop-model sites, Building 646 served as a shop and office area until the 1970s when the decision was made to locate a large 300-psi air compressor in its open bay. The compressor and associated pressure lines were designed to serve several East Area facilities, including the Langley Full Scale Tunnel and the Langley Low Turbulence Pressure Tunnel complex.

Today, the building is essentially vacant and closed for research operations. It is scheduled for demolition.

[top] Photo Gallery

[top] Construction

19341934 Foundation19341934

Construction of Passenger Elevator From September 1948 through May 1949, a passenger elevator was added

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[top] Exterior

1966 Front and Side Exterior View1966 Side View1974 Langley Spin Tunnel1978 Exterior view of Free Spinning Tunnel, 12-Foot Low Speed Tunnel, and 20-Foot Spin Tunnel BldgExterior views of Free Spinning and 12-Foot Low Speed Tunnel Bldg Entrance19952003 Exterior

[top] Interior

1934193519351936 Tom Hulcher<1950 Tom Hulcher

5-Foot Free Flight Tunnel

NACA 13177.jpgL-17256.jpg

15-Foot Free-Spinning Tunnel

1934 view of tunnel inside building 646


[top] Models and Tests

Model on catapultNACA12428.jpgLAL 93651.jpgLAL 82722.jpgMore Model Photos

[top] Floor Plans

2013 Relative location of Smaller Tunnels646.jpg646first.jpg646second.jpg646third.jpg

[top] Films

1930s: Spin Tests in RAE Vertical Wind Tunnel

~1945 Dynamic Tunnel Work

1950: Hovering Flight Tests of a Model of a Vertical Take-Off Airplane with Tilting Wing and Propellers

1950: Stability and Control Records

1954 Dynamic Stability and Control Characteristics of a Ducted Fan Model in hovering Flight and Associate Report

1960: Spin Entry Tests of a 1/60-Scale Model of the North American B-70 Airplane

Dynamic Stability and Control Characteristics of a Cascade-Wing

Preliminary Tests of an 0.034-Scale Model of the Chance-Vought F7U-3 Airplane in the Spin Tunnel Catapult Facility

Stability and Control Tests of Straight Wing Airplane

Film Supplement to Paper Entitled "Some Stability Problems with Vertically Rising Aircraft"

Incipient Spin Tests of a 1/35-Scale Model Convair F-102A Airplane

Spin Tests of Various Models in the 15-ft. Spin Tunnel

Flying Platform Experiment

Hovering Flight Investogation and Paper.

[top] Documents

Project No. 2: Brewster XF2A-1

1937 Description with 1940 Updates

1941 Spin Tunnel Project Index

1942 Property Details

Three-View Drawings of Airplanes

1956 Progress of X-15

1959 Technical Memorandum X-168

1959 Technical Memorandum X-179

1961 Post-stall Gyrations

1965 Real Property Record

1967 Real Property Voucher

1967 (?) History

1971 Space Utilization report

1974 Stall Spin Research

1977 Spin Tunnel Investigation

1978 Beech 33

1978 Low-wing Research

1979 Beech 76 Tests

1979 Beech T-34C Tests

1979 Similitude Requirements

1980 Evaluation of Spin Tunnel

1980 Aerodynamic Data

1980 Mechanics of Spin Model Testing Technique

1981 Approcimate Force Balance During a Spin

1981 Rotary Balance Prediction of Aircraft Spin Modes

1981 Theory of Ballasting Model

1985 Factors that Affect Spin Recovery

1986 AIAA

1986 Wind Tunnel Plans

1988 AIAA

Model and Airplane Spinning Characteristics

Model and Airplane Spinning Characteristics

Comparison of results from spin tunnel and radio control model spin tests

Scale Model of P-39D

1993 Spin Tunnel Utilization

1996 Closing Facility

1999 Spin Tunnel Models

Spin Tunnel Reports

2005 Reopen Facility

2013 Historic American Building Survey

2015 Master Data Sheet with Vouchers

[top] Technical Reports

Compilation of Test Data in 111 Free-Spinning Airplane Models Tested in the 15-Foot and 20-Foot Free-Spinning Tunnels. Frank S. Malvestuto, Jr., Lawrence J. Gale, and John H. Wood. 1947. RM-L7E15.

Formulas for additional mass corrections to the moments of inertia of airplanes. Frank S. Malvestuto, Jr. and Lawrence J. Gale. 1947. TN-1187.

Pilot's Loss of Orientation in Inverted Spins. Stanley H. Scher. 1955. TH-3531.

Hovering Flight Investigation of Two Methods of Controlling a Man-Carrying Ducted-Fan Vehicle of the Flying-Platform Type. Lyslie P. Parlett. 1961.

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