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The New Audi A6/A7 Family - Aerodynamic Development of Different Body Types on One Platform

The presentation describes the aerodynamic development and optimization process of the three different new models of the Audi A6/A7 family. The body types of these three models represent the three classic aerodynamic body types squareback, notchback and fastback. A short introduction of the flow structures of these different body types is given and their effect on the vehicle aerodynamic is described. In order to achieve good aerodynamic performance, the integration into the development process of the knowledge about these flow phenomena and the breakdown of the aerodynamic resistance into its components friction- and pressure drag as well as the induced drag is very important. The presentation illustrates how this is realized within the aerodynamic development process at Audi. It describes how the results of CFD simulations are combined with wind tunnel measurements and how the information about the different flow phenomena were used to achieve an aerodynamic improvement.

Aerodynamic Flow Visualization Techniques and Procedures

Flow visualization is an important factor in the aerodynamic development of passenger cars and ground vehicles. This report offers an overview of techniques used to examine complex flow fields, concentrating on techniques used in automotive wind tunnels. Includes numerous full-color photographs showing various flow fields. The following flow visualization techniques are discussed in this report: Surface Flow Description Using Yarn Tufts Surface Flow Description Using a Continuous Oil Film Flow Field Description Using Smoke Streamers Flow Field Description Using Helium Bubbles Streamer Flow Field Description Using a Continuous Motion Survey - Computer Generated Graphics And Many More
Technical Paper

Aircraft Propellers

NEARLY all the aircraft propellers used by both the Army and the Navy are of the detachable-blade type. The Navy has found it necessary to make its own designs and to furnish the propeller manufacturers with finished detail drawings. The author lists the sources from which data can be obtained and shows a chart from which can be found a diameter and setting of a pair of detachable blades that will give reasonably good performance for nearly any horsepower, revolutions per minute and airspeed commonly used with the direct-drive type of propeller. Discrepancies between model tests and wind-tunnel tests are cited, and the author then considers the subject theoretically. Substitute propellers are next considered, and also the strength of propellers.
Technical Paper

Streamlining Applied to Automobiles

STUDY of aerodynamics was first made in connection with airships and airplanes, asserts the author, and streamlined forms were developed as a result of wind-tunnel tests made by Paul Jaray in Austria and Germany before the World War and supported by mathematical studies. The findings were applied to improvement of the shape of Zeppelin airships, and later the streamline principles were incorporated in automobile designs. The author presents the results of wind-tunnel tests of streamlined automobile models in this Country which showed reduction by almost one-half in the wind resistance at speeds of 40 and 50 m.p.h., as compared with the conventional American sedan model. Results are also given of road tests of a standard Chrysler car and a Jaray-Chrysler car, using the same chassis model and each seating five passengers. The streamlined car is shown to coast farther, accelerate faster and consume much less fuel than the conventional sedan model.
Technical Paper

Efficiency Test for Radiator-Fan-Type Air-Cleaners

SINCE air-cleaners of the radiator-fan type cannot be tested satisfactorily by the older method, in which a known weight of dust is fed directly into the airstream entering the air-cleaner, a special method was found necessary in which the air-cleaner under test is mounted in its normal position behind a radiator fan that is located inside of an elliptical wind-tunnel within which the fan circulates air. A tractor engine running at constant speed and load drives the fan in the wind-tunnel and draws the air for its carbureter from the wind-tunnel through the air-cleaner under test and an absolute air-cleaner connected in series. A 100-gram charge of a standardized dust is introduced into the wind-tunnel. By averaging the results obtained from repeated tests, using three different collecting-type dry centrifugal air-cleaners, it is found that under normal conditions 15 per cent of the total dust-charge actually reaches the air-cleaner under test in the described apparatus.
Technical Paper

Tests of Pneumatic Means for Raising Airfoil Lift and Critical Angle

DISCOVERY of a satisfactory method of increasing the maximum lift of an airplane wing that should have structural simplicity, high wing-loading, low landing-speed and reasonably low drag, was the object of experiments and wind-tunnel tests made by the engineering division of the War Department Air Service at McCook Field. Previous study of the “burbling” characteristics, or discontinuity of air-flow, of airfoils at McCook Field indicated that the attainment of high lift depends upon an extension of the burble angle, that the angle at which burbling occurs can be controlled, within a range of about 5 deg., by changes in velocity or in turbulence of the wind, and that if burbling can be deferred artificially still further than the 5-deg. range the lift will increase in the same proportion. Studies abroad with rotating cylinders and the magnus effect confirmed the boundary-layer theory and principles enunciated by Dr.
Technical Paper

Possible Improvement of Present-Day Aircraft

WHAT can be done to increase safety, efficiency and comfort in flight of aircraft now in use? In answer, the author describes several devices designed to bring about this result and supplements this with the results of wind-tunnel research. Detailed descriptions of the particular devices mentioned are not included, the object of this paper being to show the great possibilities of their use and the resulting improvement in performance.
Technical Paper


A racing airplane seems to possess a special quality that sets it distinctly apart from the conventional type of airplane; but, unless a person has at least dabbled in its design, he cannot realize the enormous amount of time, effort and ingenuity that has been expended by the designers who have made these super-speed airplanes possible. Therefore, an outline is given of the procedure adopted in designing and producing a specific model of racing airplane, as well as an outline of the yearly progress made in development. The first procedure is to allocate the work to the various members of the engineering organization. Finally, a type of design is chosen after a series of engineering conferences, and the design section studies the detail design of the component parts. A wing section that is adapted to the design already chosen is developed, and an accurate weight estimate is made of each unit part of the complete airplane.
Technical Paper

Factors Pertaining to Installation of Inverted, In-Line AIRCOOLED AIRCRAFT ENGINES

CONSIDERATIONS of aircraft-engine installation singular to the inverted, in-line, aircooled type of engine are presented here in the light of current engineering development in this field. Items of this installation technique discussed are: cooling aspects, cowling arrangements, oil cooling systems, induction systems, engine mounts, and exhaust systems. Much of the information presented is based upon experience gained from wind tunnel and flight tests with Ranger engines. The application of design considerations discussed under the cooling aspects of the aircooled engine has been proved satisfactory in flight test operations. Latest methods of treatment of these factors are described. Substantial advancement has been made in handling the ever-present cooling problem common to all types of engines. This has been achieved by applying the design knowledge gained through considerable wind tunnel and flight research.
Technical Paper


STUPENDOUS efforts were made in the basic research of guided missiles by the Germans. In all it has been estimated that one-third of the aerodynamics research in Germany was devoted to problems of these weapons. Wind tunnels of undreamed-of speeds were under construction when the war was over. In fact a Mach number of 10 was not too great for the Germans to comprehend and strive for. The various types of developments grouped under the expression guided missiles (a loose term as some aren't guided and some aren't missiles) are discussed here by Col. Putt.
Technical Paper

The M.I.T.-Wright Brothers WIND TUNNEL and its Operating Equipment

WITH the M.I.T.-Wright Brothers wind tunnel and balance system, Prof. Markham explains, it is possible to obtain measurements very rapidly on a complete airplane model from which the coefficients for all six components can be plotted with a minimum of calculation. It is usually possible, he continues, to mount the model so that the point representing the center of gravity of the airplane is on the balance axis, a feature which increases the accuracy of the results and the simplicity of the calculations. This balance system was designed to fulfill the following general specifications: It had to be compact for the pressure-type tunnel in which it operates requires that the shell surrounding the test section be kept to a minimum diameter; it should be arranged so that measurements of all six components could be made remotely and that angular settings of the model in pitch and yaw could be made from a remote station.
Technical Paper


Gas-heated hollow propeller blades have been investigated both analytically and experimentally to determine heat requirements for the prevention of icing on the blade surfaces during flight. An analysis was made of a typical hollow propeller blade to determine the internal gas flow and temperature required to maintain the external surface temperature above 32 F. The basic wet-air equation is given and curves are presented to illustrate the blade heating and temperature distributions which were obtained for one set of conditions. Full-scale gas-heated propellers have also been investigated experimentally in an icing wind tunnel and typical results are presented. The rates of heating required to prevent icing are discussed and a modification of propeller blade interiors by using fins and partitions is shown by comparative experiments to permit large reductions in the required heat-source input.
Technical Paper

Effect Of Ice And Heated-Air Deicing On The Aerodynamic Performance Of Propellers

A review is made of several wind-tunnel investigations dealing with the effect of ice on the aerodynamic efficiency of a propeller, as compared to the efficiency loss associated with a heated-air anti-icing system. The propeller aerodynamic characteristics, thrust coefficient, and efficiency with and without the simulated ice are presented. A heated-air thermal anti-icing system for propellers is discussed and the results of an analysis of the losses inherent in such a system for an idealized case is presented. Two wind-tunnel investigations of propellers incorporating internal-flow systems are described: for one investigation the system was simplified almost to the ideal case, in the other investigation a propeller with a complete heated-air anti-icing system was used. The measured losses of efficiency are shown to be in good agreement with those predicted by theory.
Technical Paper

Development of Beech V-Tail

WHEN V-tails are applied to conventional airplanes, appreciable reductions in airplane drag, tail surface area, and weight are achieved, according to the author. He also states that improvements in flying qualities are possible. These conclusions are based on several years' wind tunnel testing, as well as flight tests on one twin-engine airplane and one single-engine airplane.
Technical Paper

GROUND Versus FLIGHT TESTS of Airplane Engine Installations

THE disadvantages of present methods of proving engine installations by flight tests are discussed in this paper. Some data are given to show the great expense of such methods. The conclusion is reached that adequate ground-test facilities should be provided for use in pre-flight development and service tests of new engine installations. A comparison of the results of ground tests on the Vega Ventura engine installation with flight-test results indicates some factors in ground-test technique which should be satisfied in order to insure reliable results. Similitude conditions to be met for cooling, vibration, and accelerated service tests are discussed to illustrate the method of approach for such problems. Various types of test equipment are described for attaining these conditions, the closed-return wind tunnel appearing to offer the greatest advantages for general testing.
Technical Paper

Farewell to the Horseless Carriage

THIS critical study of the possibilities of improving automobile performance and economy by aerodynamic refinement is begun by demonstrating the analogy between motor-car air-resistance and airplane parasite-drag. An example is then cited to illustrate the benefits of aerodynamic research in the latter field and to point out the potentialities of similar work in the former. Consideration of practical requirements and limitations in an analysis of motor-car air-resistance leads to the selection of a rear-engine arrangement as the most promising type and to the prediction that its air resistance will approach one-fourth that of conventional cars. This prediction is confirmed by the results of wind-tunnel model-tests. Full-scale replicas of the models tested would provide adequate passenger accommodations and engine space without exceeding accepted overall lengths.
Technical Paper

N.A.C.A. Study of Radial Air-Cooled Engine Cowling and Cooling

THE development of an N. A. C. A. cowling giving a low drag and satisfactory engine cooling for a particular airplane and engine installation requires the construction and flight testing of numerous experimental cowlings. An investigation has been undertaken by the National Advisory Committee for Aeronautics to determine a rational basis for the design of the N. A. C. A. cowling. The effect of front and of rear openings and of inner and outer lines of the cowling on the quantity of air flowing through the cowling, the pressure drop, and the drag have been determined from tests of models in a wind tunnel. The quantity of air and the pressure drop required for satisfactory cooling of a given design of air-cooled cylinder have been determined from tests of a single-cylinder engine. The results obtained from the tests of the models and the single-cylinder engine are being checked in a large wind-tunnel using a 550-hp. radial-engine fitted with a propeller.
Technical Paper

Further Progress in Controlled Cooling of Radial Aircraft Engines

DURING the last year studies by subsidiaries of United Aircraft Corp. on cowls for radial air-cooled engines have been continued in the wind tunnel and in flight. Model tests comparing the performance of fixed cowls under various conditions are reported, and further research on flapped cowls for controlled cooling is described. Tests were made over a wide range of flap angles to show the possibilities of this type of cooling regulation, and a new form of cowl with flaps located well behind the engine at the fuselage firewall was studied. Flight tests with such a cowl showed that the qualitative variations indicated in the wind tunnel adequately represent full-scale conditions. The results of these flight tests are described in some detail. An attempt is made to reduce the various wind-tunnel results to a form suitable for estimation of cowl characteristics for design purposes, and the results of this work are correlated with information obtained in flight.
Technical Paper

Radiator Development and Car Cooling

EVOLUTION of automobile radiators is recounted step by step from the primitive water-pipe types to those in use today. Pertinent heat-transfer principles are given to show cause for various changes. The effects of larger engines, higher speeds, quieter operation, are discussed fully. Poor water-jacket design is blamed for a multitude of cooling-system troubles, such as warped valves, valve seats, and cylinder bores, and it is believed that these troubles could be eliminated largely on the drawing board by the water-jacket designer. A special test apparatus, called a “dissipator” and built expressly for testing radiators, is described. Considerable space is devoted to test procedure and discussion of test results on hexagon-core, fin-and-tube core, double-center core, and a new vee-type radiator for different depths, air speeds, and frontal areas. In addition, tests made on a full-sized wind tunnel are discussed and interpreted.