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Technical Paper

Wingtip Vortex Turbine Investigation for Vortex Energy Recovery

A flight test investigation has been conducted to determine the performance of wingtip vortex turbines and their effect on aircraft performance. The turbines were designed to recover part of the large energy loss (induced drag) caused by the wingtip vortex. The turbine, driven by the vortex flow, reduces the strength of the vortex, resulting in an associated induced drag reduction. A four-blade turbine was mounted on each wingtip of a single-engine, T-tail, general aviation airplane. Two sets of turbine blades were tested, one with a 15° twist (washin) and one with no twist. The power recovered by the turbine and the installed drag increment were measured. A trade-off between turbine power and induced drag reduction was found to be a function of turbine blade incidence angle. This test has demonstrated that the wingtip vortex turbine is an attractive alternate, as well as an emergency, power source.
Technical Paper

Wings-a Coordinated System of Basic Design

TAKING as basic requirements such fundamental characteristics as can be largely separated from the problem of wing design or assumed as attributes of the complete airplane, the author discusses the independent variables consisting mainly of the geometrical characteristics that can be varied to obtain maximum performance without changing the basic requirements. He develops a weight and a drag equation, each founded on the chosen basic requirements and including in the simplest possible form the combined effect of the independent variables. The terms in these equations are defined and the equations are applied to a low-wing monoplane in power and gliding fight and to a rectangular-wing biplane in gliding flight. The results are tabulated in some instances but are principally shown on charts. The accuracy of the results obtained is stated to depend largely upon the proper choice of approximations with an appreciation of their limitations.
Technical Paper

Wing-Diffuser Interaction on a Sports Car

Amongst the aerodynamic devices often found on race cars, the diffuser is one of the most important items. The diffuser can work both to reduce drag and also to increase downforce. It has been shown in previously published studies, that the efficiency of the diffuser is a function of the diffuser angle, ground clearance and most importantly, the base pressure. The base pressure of a car is defined by the shape of the car and in particular the shape at the rear end, including the rear wheels. Furthermore, on most race cars, a wing is mounted at the rear end. Since the rear wheels and wing will influence the base pressure it is believed that, for a modern race car, there could be a strong interaction between these items and the diffuser. This work aims to systematically study the interaction between the rear wheels and wing; and the diffuser of a contemporary, sports car type, race vehicle.
Technical Paper

Wing Modification for Increased Spin Resistance

A simple wing leading-edge modification has been developed that delays outer wing panel stall, thus maintaining roll damping to higher angles of attack and delaying the onset of autorotation. The stall angle of attack of the outer wing panel has been shown to be a function of the spanwise length of the leading-edge modification. The margin of spin resistance provided by the modification is being explored through flight tests. Preliminary results have been used to evaluate spin resistance in terms of the difference in angle of attack between outer wing panel stall and the maxiumum attainable angle of attack.
Technical Paper

Wing Airfoil Simplified Design and Analysis

The thickness ordinates of most wing airfoil sections once normalized to their maximum thickness ordinates become quite similar between each other, and can be represented by some few functions as those presented in the tables and graphics of section 2, and Appendix I formulas. It is shown that by combining these functions with different thickness with the uniform loading NACA a=1 mean line [1], airfoils for quite different applications, ranging from gliders [2], to high speed airplanes can be designed as exemplified by the six new airfoils presented with their main aerodynamic characteristics in Appendix II The criteria for the selection of the airfoil design parameters are discussed, as well as the simplified numerical airfoil analysis method used to verify the aerodynamic properties of the new airfoils, are presented.
Technical Paper

Windshield Injury Potential as a Function of Windshield Installation Method

A series of carefully controlled simulated barrier crashes at speeds from 20 to 30 mph are used to compare the relative safety of rubber gasket, butyl tape and polysulfide adhesive methods of installing windshields. Only subtle differences were found in the severity index and the laceration index. There is an indication that the rubber gasket installation has a higher resistance to interlayer tears and the lacerations from impacts to polysulfide installations are slightly more severe. Head attitude at impact was found to have a significant effect on interlayer tears and resultant lacerations.
Technical Paper

Windshield Impact Response: An Empirical Study of the Standard Three-Ply Construction

An experimental program to characterize the impact response of a standard 3-ply high penetration resistance (HPR) windshield was conducted using a specially designed linear impactor test facility (1). * Parameters varied included the location and angle of impact, impactor mass and velocity, windshield bonding system, and windshield integrity (whether it was pre-cracked). Specific findings included the following: The magnitude of the initial spike in the force-time history is a function of the inertia of the windshield mass localized around the impact site. The windshield bond has no effect on this initial force spike and thus cannot be used to alter or control it. Minor pre-cracking of the windshield has no effect on the impact event. The impact severity decreases as the rake angle (mounting angle with respect to the vertical) increases. The location of the initial impact site has only a minor effect on the impact severity.
Technical Paper

Windows Opening Influence on the Drag Coefficient of a Hatchback Vehicle

Aerodynamics plays a key role in nowadays vehicle development, aiming efficiency on fuel consumption, which leads to a green technology. Several initiatives around the world are regulating emissions and efficiency of vehicles such as EURO for European Marketing and the INOVAR Auto Project to be implemented in Brazil on 2017. In order to meet requirements in terms of performance, especially on aerodynamics, automakers are focusing on aero-efficient exterior designs and also adding deflectors, covers, active spoilers and several other features to meet the drag coefficient. Usually, the aerodynamics properties of a vehicle are measured in both CFD simulations and wind tunnels, which provide controlled conditions for the test that could be easily reproduced. During the real operations conditions, external factors can affect the flow over the vehicle such as cross wind in open highways.
Technical Paper

Wind-Tunnel and On-Road Wind Noise: Comparison and Replication

A KIA Soul was instrumented to measure the relative velocity (magnitude and yaw angle) at the front of the vehicle and in-cabin sound at a location close to the side glass near the A-pillar vortex impingement. Tests were conducted at a proving ground under a range of conditions from low wind conditions (~3 m/s) to moderate (7-8 m/s) wind speeds. For any given set of atmospheric conditions the velocity and sound data at any given position on the proving ground were noted to be very repeatable, indicating that the local wakes dominated the "turbulent" velocity field. Testing was also conducted in an aeroacoustic wind tunnel in smooth flow and with a number of novel turbulence generating methods. The resulting sounds were analyzed to study the modulation at frequencies likely to result in fluctuation strength type noise.
Technical Paper

Wind-Tunnel Tests of Vehicle Cooling System Performance at High Blockage

Wind tunnels provide a convenient, repeatable method of assessing vehicle engine cooling, yet important draw-backs are the lack of a moving ground and rotating wheels, blockage constraints and, in some tunnels, the inability to simulate ambient temperatures. A series of on-road and wind-tunnel experiments has been conducted to validate a process for evaluating vehicle cooling system performance in a high blockage aerodynamic wind tunnel with a fixed ground simulation. Airflow through the vehicle front air intake was measured via a series of pressure taps and the wind-tunnel velocity was adjusted to match the corresponding pressures found during the road tests. In order to cope with the inability to simulate ambient temperatures, the technique of Specific Dissipation (SD) was used (which has previously been shown to overcome this problem).
Technical Paper

Wind-Tunnel Modelling off Commercial Vehicle Drag-Reducing Devices: Three Case Studies

Road and wind-tunnel tests are presented which examine the drag coefficient reductions from aerodynamic devices fitted to three trucks. A modified SAE Type II procedure utilising an instrumented chase car, evaluated on-road, constant-speed drag reductions as a function of yaw angle. At 100 km/h, turbulence intensities of 1% - 4% were measured. The wind-tunnel results generally overestimated drag savings, particularly at high yaw angles. This was greater for cabin deflectors than for solid fairings. Simulating higher turbulence intensities gave improved agreement and it is argued that turbulence is a dominant modelling parameter.
Technical Paper

Wind-Tunnel Measurements of Wing-Canard Interference and a Comparison with Various Theories

CANARD-CONFIGURED AIRCRAFT DESIGNS have played a historic role in aeronautical research. However, only in the past decade or two has a canard been incorporated into a significant number of aircraft designs. Powered flight began with the Wright Flyer, which was a canard-configured aircraft. Unfortunately, however, that aircraft was longitudinally unstable and the misconception arose that all canard aircraft would be unstable in pitch, irrespective of the placement of the center of gravity. In the early years of aircraft development, the canard concept was dropped in favor of conventional tailaft designs. It was not until the 1960s that canards were again seriously considered for several high-speed, designs. For example, in the United States’ supersonic transport program, a canard was initially considered; because of several problems with aerodynamic interference, however, the idea was abandoned.
Technical Paper

Wind-Tunnel Investigation of the Low-Speed Aerodynamics of Slender Accelerator-Type Configurations

An investigation was conducted in the Langley 14- by 22-Foot Subsonic Tunnel to determine the low-speed aerodynamic characteristics of a generic, hypersonic accelerator-type configuration. The model consisted of a delta wing configuration incorporating a conical forebody, a simulated wrap-around engine package, and a truncated conical aftbody. Six-component force and moment data were obtained over a range of angle of attack from -4° to 30° and for a sideslip range of ±20°. In addition to tests of the basic configuration, component build-up tests were conducted; and the effects of power, forebody nose geometry, a canard surface, fuselage strakes, and lower surface engines alone were also determined. Control power was investigated via the testing of wing flap deflections as well as the deflections of an aftbody flap in the exhaust flow. Surface pressure data were obtained at several longitudinal locations along the conical forebody.
Technical Paper

Wind-Tunnel Investigation of the Forebody Aerodynamics of a Vortex-Lift Fighter Configuration at High Angles of Attack

Results of a recent low-speed wind-tunnel investigation conducted to define the forebody flow on a 16% scale model of the NASA High Angle-of-Attack Research Vehicle (HARV), an F-18 configuration, are presented with analysis. Measurements include force and moment data, oil-flow visualizations, and surface pressure data taken at angles of attack near and above maximum lift (36° to 52°) at a Reynolds number of one million based on mean aerodynamic chord. The results presented identify the key flow-field features on the forebody including the wing-body strake.
Technical Paper

Wind-Averaged Drag Determination for Heavy-Duty Vehicles Using On-Road Constant-Speed Torque Tests

To investigate the feasibility of various test procedures to determine aerodynamic performance for the Phase 2 Greenhouse Gas (GHG) Regulations for Heavy-Duty Vehicles in the United States, the US Environmental Protection Agency commissioned, through Southwest Research Institute, constant-speed torque tests of several heavy-duty tractors matched to a conventional 53-foot dry-van trailer. Torque was measured at the transmission output shaft and, for most tests, also on each of the drive wheels. Air speed was measured onboard the vehicle, and wind conditions were measured using a weather station placed along the road side. Tests were performed on a rural road in Texas. Measuring wind-averaged drag from on-road tests has historically been a challenge. By collecting data in various wind conditions at multiple speeds over multiple days, a regression-based method was developed to estimate wind-averaged drag with a low precision error for multiple tractor-trailer combinations.
Technical Paper

Wind Tunnel-to-Road Aerodynamic Drag Correlation

A comprehensive test program was conducted to correlate aerodynamic drag measurements from the General Motors Aerodynamics Laboratory with coastdown results. An improved method of coastdown testing was used to minimize the sources of error in determining aerodynamic drag. Several vehicles were tested, covering a large range of aerodynamic drag values, representative of current and future production vehicles. Wind tunnel and coastdown results were determined to be in good agreement, with an average drag coefficient difference of only. 008 (2%).
Technical Paper

Wind Tunnel for Aerodynamic Research

The following presents in detail one full-scale automobile wind tunnel and two thermodynamic wind tunnels, their development and integration for an economic solution. Information is given on machinery equipment, air speed and temperature ranges and measurement-possibilities. Two thermodynamic test stands, smaller wind tunnels, are described. The first one is designed for measurements on heat exposed parts of the car, in particular engine cooling. The second one is able to simulate all climatic conditions and was designed for solving problems concerning heating and air conditioning systems. The presentation concludes with reports on initial experiences with these test facilities.
Journal Article

Wind Tunnel and Track Tests of Class 8 Tractors Pulling Single and Tandem Trailers Fitted with Side Skirts and Boat-tails

A 1:10-scale wind tunnel development program was undertaken by the National Research Council of Canada and Airshield Inc. in 1994 to develop trailer side skirts that would reduce the aerodynamic drag of single and tandem trailers. Additionally, a second wind tunnel program was performed by the NRC to evaluate the fuel-saving performance of boat-tail panels when used in conjunction with the skirt-equipped single and tandem trailers. Side skirts on tandem, 8.2-m-long trailers (all model dimensions converted to full scale) were found to reduce the wind-averaged drag coefficient at 105 km/h (65 mi/h) by 0.0758. The front pair of skirts alone produced 75% of the total drag reduction from both sets of skirts and the rear pair alone produced 40% of that from both pairs. The sum of the drag reductions from front and rear skirts separately was 115% of that when both sets were fitted, suggesting an interaction between both.
Technical Paper

Wind Tunnel Testing of Micro Air Vehicles at Low Reynolds Numbers

This paper documents the development of the capability to test MAVs (Micro Air Vehicles) in the University of Florida’s wind tunnel facility. The main goal of this work was to obtain, with a reliable procedure, good quality experimental data from wind tunnel tests of air vehicles at low Reynolds numbers, in the order of 100,000. An overview of the instrumentation and data analysis techniques will be presented, followed by some samples of results from tests on specific aircraft. A standard aerodynamic characterization test was developed to perform a “quick” System Identification (SID) characterization of an air vehicle. The requirements for those tests were established by the modeling and control portion of the project. The test procedure was aimed to find the main aerodynamic derivatives that will be used to model the aircraft and design the flight control system. Three distinctly different vehicles ranging in size from 60 cm to 15 cm wingspan are discussed.
Technical Paper

Wind Tunnel Test of Cab Extender Incidence on Heavy Truck Aerodynamics

A wind tunnel experiment has been conducted to determine the changes in drag and side force due to the presence and position of cab extenders on a model of a commercial tractor-trailer truck. The geometric variables investigated are the cab extenders angle of incidence, the tractor-trailer spacing and the yaw angle of the vehicle. Three cab extender angles were tested-0°, 15° (out) and -15° (in) with respect to the side of the tractor. The cab and trailer models have the same width and height. The minimum drag coefficient was found for the tractor and trailer combination when the cab extenders were set to 0° angle of incidence with respect to the headwind. This result holds for all yaw angles with moderate gap spacing between the tractor and trailer. This study suggests that commercial tractor-trailer trucks can benefit from adjustable cab extender settings; 0° when using a trailer and -15° when no trailer is used.