Engineering topics
Publications and source records attributed to Johnson, J. L., Jr..
Airflow favorably altered if propeller placed above and behind wing. Relocating propeller induces flow over wing airfoil leading edge, which produces leading-edge suction forces not usually attainable by wing in free-stream flow. Concept reduced drag significantly on aircraft model in 12-foot (3.7-meter) wind tunnel. Relocation also helps to reduce cabin noise.
Recent NASA wind-tunnel investigations of advanced unconventional configurations are surveyed, with an emphasis on those applicable to general-aviation aircraft. Photographs of typical models and graphs of aerodynamic parameters are provided. The designs discussed include aft installation of tractor or pusher-propellor engines; forward-swept wings; canards; combinations of canard, wing, and horizontal tail; and propeller-over-the-wing configurations. Consideration is given to canard-wing flow-field interactions, natural laminar flow, the choice of canard airfoil, directional stability and control, and propulsion-system location.
A recent low-speed wind-tunnel investigation of a three-surface regional transport configuration has shown large favorable power effects on longitudinal and lateral stability and marginal engine-out trim characteristics for some aft engine and empennage configurations. The present paper discusses these results in terms of static force test information obtained for power-off and power-on conditions. Also discussed in this paper are wind-tunnel results which indicate that mounting propellers over the wing can introduce large favorable slipstream interference effects which significantly reduce the wing drag at climb power conditions.
Wing-leading-edge modifications included leading-edge droop and slat configurations having full-span, partial-span, or segmented arrangements. Other devices included wing-chord extensions, fences, and leading-edge stall strips. Good correlation was apparent between the results of wind-tunnel data and the results of flight tests, on the basis of autorotational stability criterion, for a wide range of wing-leading-edge modifications.
The application and analysis of dynamic stability parameters were examined. The effects of wing leading edge modifications on the stalling and spinning characteristics of a single engine general aviation research airplane are evaluated. It is illustrated how dynamic stability parameters measured in wind tunnel tests are used to predict the spin resistance of this class of aircraft, and that autorotation criteria are derived from the relationships which exist between static and dynamic aerodynamic characteristics.
The paper presents highlights of a recent study which illustrates the application and analysis of dynamic stability parameters. More specifically, the investigation consisted of an evaluation of the effects of wing leading-edge modifications on the stalling and spinning characteristics of a single-engine general aviation research airplane. The results of the investigation illustrate how dynamic stability parameters measured in wind-tunnel tests are used to predict the spin resistance of this class of aircraft; and that autorotation criteria can be derived from the relationships which exist between static and dynamic aerodynamic characteristics.
The paper presents the results of a recent investigation to determine the effects of wing leading-edge modifications on the high angle-of-attack aerodynamic characteristics of a low-wing general aviation airplane in the Langley Full-Scale Wind Tunnel. The investigation was conducted to provide aerodynamic information for correlation and analysis of flight-test results obtained for the configuration. The wind-tunnel investigation consisted of force and moment measurements, wing pressure measurements, flow surveys, and flow visualization studies utilizing a tuft grid, smoke and nonintrusive mini-tufts which were illuminated by ultra-violet light. In addition to the tunnel scale system which measured overall forces and moments, the model was equipped with an auxiliary strain-gage balance within the left wing panel to measure lift and drag forces on the outer wing panel independent of the tunnel scale system. The leading-edge modifications studied included partial- and full-span leading-edge droop arrangements as well as leading-edge slats.
A recent low-speed wind-tunnel investigation of highly-swept wings has shown that vortex breakdown at high angles of attack can cause large destabilizing effects on static lateral-directional stability characteristics, and that the destabilizing effects of vortex breakdown can be greatly aggravated by model support strut interference effects. The present paper discusses these effects based on the results of static force tests of several highly-swept wing configurations for different wind-tunnel strut setup arrangements. Also included in the paper are photographs obtained during tuft-, smoke-, and helium-bubble flow visualization studies to indicate wing flow behavior patterns
A wide variety of model and airplane tests were conducted to explore the effects of wing leading-edge modifications on the stalling and spinning characteristics of a low-wing general aviation research airplane configuration. The results presented herein discuss the effects of leading-edge airfoil modifications applied to the full wing span and to partial-span locations. The results obtained in the study indicate that the wing modifications can produce large effects (both favorable or unfavorable) on spin resistance, developed spin characteristics, and spin recovery.
This paper summarizes the significant results of recent full-scale wind tunnel tests at the NASA-Langley Research Center of the Ayres S2R-800 Thrush Agricultural Aircraft. The purpose of the tests was to provide fundamental aerodynamic, performance, and stability and control information of the airplane and dispersal equipment; and to study near-field wake interaction characteristics behind the aircraft. The aerodynamic tests included the use of a propeller thrust-torque balance to measure the efficiency of the propeller in the presence of the engine and to provide data for determining slipstream interference effects and slip-stream drag.
The results of recent wind tunnel investigations to provide fundamental information on the upper surface blown (USB) jet flap concept demonstrated that the USB concept provides good high-lift performance. It is shown that the low speed performance is dependent upon the jet turning angle and turning efficiency and on the use of proper leading and trailing edge treatment to prevent premature flow separation. The best means of achieving good turning performance in any particular USB application must be determined from overall operational considerations in which high speed performance, structures and noise, as well as low speed performance, are evaluated. The large diving moments generated at high lift coefficients can be trimmed satisfactorily with a large, conventional horizontal tail; a high tail position is best from longitudinal stability considerations. Large rolling and yawing moments are introduced with the loss of an engine, but these moments can be trimmed satisfactorily through the use of asymmetrical boundary layer control and through the use of spoiler and rudder deflection as needed.
Review of the results of recent wind-tunnel investigations conducted to provide fundamental aerodynamic information on the upper-surface blown jet-flap concept incorporating high-bypass-ratio turbofan engines. The results of the investigations have shown the concept to have aerodynamic performance generally comparable to that of other externally blown high-lift systems. Some of the more critical problem areas associated with this concept are covered, and solutions which have been found for these problems are discussed.
Low speed wind tunnel force and flight tests of control systems for paragliders
Low-subsonic flight characteristics of model supersonic aircraft configuration with parawing as a landing aid
Wind tunnel stability and control tests of flexible wing manned aircraft - parawing
Application of the tension structure concept for flexible wings to be used in spacecraft recovery and landing, emphasizing para-wing aerodynamics
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