a hybrid arrangement to process large volumes of experimental data which are otherwise impractical to analyze. The new method was especially effective in extracting information from complex random and transient signals characteristic of aerodynamic noise generated in the boundary layer of supersonic aircraft, pilot control real time studies, helicopter bladeslap noise investigations, and studies of anomalies in the human heart beat. Improvement factors of 50 to 1 or more, were achieved in processing certain types of complex data.

Goddard Space Flight Center established the feasibility of applying laser and coherent optics technology to the processing of large volumes of spacecraft telemetry data. The key element is a reuseable recording medium of photochromic material, which provides real time conversion of electrical telemetry signals to optical form for analysis by an optical computer. When completely developed, the new method will replace conventional photographic film conversion methods and is expected to reduce the cost and processing time by at least one-tenth. Electronic Techniques and Components

Continued research and development work on metal oxide silicon field effect transistors (MOSFET) made it possible to fabricate devices with low power consumption and high packing densities. Both of these features are extremely desirable for space flight applications. Goddard Space Flight Center applied integrated circuits employing MOSFETs to the electronic circuitry in the Interplanetary Monitoring Platform Explorers 33, 34, and 35. The MOSFETs, which averaged about ten active devices per integrated circuit, achieved approximately 200,000 hours of successful operation in the space environment, demonstrating their feasibility as well as the possibility of using larger-scale integrated circuits. Units having 500 or more active devices per circuit are being developed for use on advanced spacecraft.

Aircraft Aerodynamics

Aeronautical Research

A study was made to determine whether the large high-bypass fanjet engines for the next generation of subsonic transports will create severe adverse wing-nacelle interference. The problem was investigated in a transonic wind-tunnel with a large model of a representative transport airplane. A model jet engine in an underslung pylon-nacelle was located at various positions relative to the wing. The results indicated that both nacelle position and addition of engine power strongly influenced the interference drag (the difference between the drag for the complete airplane and the sum of the drag of its components). An increase in transonic Mach number above the sign cruise value had an adverse influence on the interference drag.

Aircraft Loads and Structures

The maneuverability and performance of aircraft at high subsonic and transonic speeds is limited by the flow separation on the wing which manifests itself in a buffeting of the airframe and large increases in drag.

To assess the various ways of solving the buffeting problem, an extensive research program was undertaken in which the effects of systematic variations in wing design parameters on buffeting tendencies were studied. The program included an investigation in the Langley high speed 7-by-10 foot tunnel to determine the buffet and static aerodynamic characteristics of a systematic wing series at Mach numbers from 0.28 to 0.94. The results indicated that, for a given Mach number, wings which display superior aerodynamic efficiency characteristics generally display the highest buffet-free lift coefficient. The findings also showed that correlations can be made between the onset of buffet and selected divergences in the static aerodynamic characteristics. Of the static elements, axial force was found to be the most sensitive to the onset of buffeting.

Studies of the susceptibility of titanium-alloys to hot-salt-stress corrosion began in 1962; interest in the problem arose from the fact that these alloys might be used as skin materials for a supersonic transport airplane operating at speeds up to Mach 3. Preliminary results confirmed the susceptibility of several titanium alloys to this type of corrosion. Consequently, an extensive investigation was undertaken with exposures up to 20,000 hours at temperatures from 400° to 600° F. It was found

• that for certain titanium alloys hot-salt-stress corrosion crack initiation can be analytically predicted over a broad range of stresses, times, and temperatures;

⚫ that the threshold stresses decrease with an increase in exposure temperatures and time;

⚫ that there was no stress-corrosion cracking at 400° F. for exposures up to 20,000 hours, but it developed after 17 hours at 600° F. for 50 k.s.i. stress;

• that the presence of stress corrosion cracks causes a large drop in elongation and moderate drop in tensile strength; and

• that the residual tensile properties depend only on the depth of crack, regardless of the temperature or time at which the cracks were developed.

Aircraft Noise

As a part of a board program to reduce noise emanating from turbine powered engines, contracts were made with two engine manu

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facturers to integrate existing knowledge and new technology into an experimental turbofan engine to demonstrate potential noise reductions at the source. The initial objective of the Quiet Engine program is to demonstrate a minimum noise reduction below present turbofan engines of at least 15 PNdb (preceived noise level in decibels) during takeoff and 20 PNdb during landing approach conditions. Preliminary results of studies conducted to date indicated that fan noise reductions of about 25 PNdb on takeoff and 20 PNdb during approach appear feasible through proper design of engine components and through the use of nacelle sound absorption treatment.

Two airframe contractors were given contracts to investigate the feasibility of suppressing fan/compressor noise through the application of sound absorbent material in the engine nacelle inlet and fan exhaust duct. Nacelle acoustic treatment, which is quite flexible in application appears to be easily adopted to a wide variety of fan engine designs, reduced fan noise about 12 PNdb during ground tests with full-scale engines and nacelles.

Operating Environment

Runway Grooving. In research on controlling and stopping air craft on wet runways, laboratory tests at the Langley Landing Loads Track showed that transverse grooves in the runway surface greatly increase the tire traction and improve aircraft directional control and braking. Full-scale airplane tests at Wallops Station to assess the effectiveness of the grooves under dry, wet, flooded, and slush covered conditions used transverse grooves 1/4" wide by 1/4" deep, spaced 1" apart, which provided near optimum traction in laboratory tests. The results of tests with a Navy fighter aircraft and jet transport aircraft indicated that the grooves effectively improve tire-runway traction and aircraft braking and control on wet surfaces. (Figs. 44 and 4–5.)

Related tests were being conducted at Wallops to evaluate and correlate various devices to measure runway friction levels. Friction level is an important measure of aircraft braking performance, and a universally acceptable way of determining the friction level would enable pilots to determine the braking available regardless of the airfield location or runway surface condition. (Fig. 4-6.)

General Aviation Technology.-Wind tunnel and flight tests of a typical light twin-engine executive jet aircraft were being conducted to evaluate handling characteristics and pilot display requirements for this class of aircraft. (Fig. 4-7.)

V/STOL Aircraft

Wind-tunnel and flight tests were continued on a number of V/STOL concepts, including the tilt-wing deflected slipstream type.

(Fig. 4-8.) Earlier wind-tunnel tests of tilt-wing models, conducted out of ground effect, indicated that wing airflow separation would limit descent performance and cause buffeting in the low speed transitional flight regime. More recent tests, conducted in the Ames 40- by 80-foot tunnel to determine the effects of ground proximity on the aerodynamic characteristics of a large-scale, propeller-driven, tiltwing transport aircraft, showed that ground proximity significantly reduced lift and drag and increased the nose-down pitching moment. They also revealed that aileron effectiveness for yaw control in hover diminished with decreasing ground height.

Another study conducted in the 40- by 80-foot tunnel was of a largescale deflected-slipstream STOL aircraft typical of a conventional propeller-driven transport airplane capable of operating in and out of 1000 to 2000 foot runways. In these tests, lift coefficient increased and drag coefficient decreased as the wing tips were extended outboard. Maximum lift coefficient appeared to be limited by flow separation between the nacelles on all configurations, even though the wing tip of the high aspect ratio configuration was not protected by the propeller slipstream. Leading-edge slats controlled the progression of flow separation and extended the angle of attack for maximum lift

approximately 10°. For each wing span tested, descent capability could be improved by spanwise variation of propeller thrust. However, the spanwise variation of propeller thrust was most effective on the short span wing.

Progress was made in research on a reliable method of determining analytically the combinations of helicopter height and velocity at which autorotation could be carried out safely. Based on recently obtained FAA flight data, NASA developed a semiempirical procedure which