The report discusses the problem of rating the various seaplane designs from the 1926 seaplane contest. The whole process of rating consists in measuring the climbing speed, flying weight and carrying capacity of a seaplane and then using these data as the basis of a construction problem.
This collection of data on airfoils has been made from published reports of a number of the leading aerodynamic laboratories of this country and Europe. The information which was originally expressed according to the different customs of the several laboratories is here presented in a uniform series of charts and tables suitable for the use of designing engineers and for purposes of general reference. The authority for the results here presented is given as the name of the laboratory at which the experiments were conducted, with the size of the model, wind velocity, and year of tests.
From Introduction: "The increasing use of airplane wings equipped with ailerons and the importance of knowing the aerodynamic characteristics of tail units (empennages) provided with movable parts (rudders and elevators) impart some interest to the so-called "empirical profiles." For this purpose we thought best to employ the method proposed by Munk for the approximate theoretical study of thin, slightly curved profiles, assimilable, from an aerodynamic view-point, to their mean camber line."
This report presents the first part of a two part study made under this title. In this part the symmetrical inviscid flow about an empirical strut of high service merit is found by both the Rankine and the Joukowsky methods. The results can be made to agree as closely as wished. Theoretical stream surfaces as well as surfaces of constant speed and pressure in the fluid about the strut are found. The surface pressure computed from the two theories agrees well with the measured pressure on the fore part of the model but not so well on the after part. From the theoretical flow speed the surface friction is computed by an empirical formula. The drag integrated from the friction and measured pressure closely equals the whole measured drag. As the pressure drag and the whole drag are accurately determined, the friction formula also appears trustworthy for such fair shapes. (author).
From Summary: "The purpose of this test was to compare six well-known airfoils, the R.A.F 15, U.S.A. 5, U.S.A. 27, U.S.A. 35-B, Clark Y, and Gottingen 387, fitted to the Sperry Messenger model, at full scale Reynolds number as obtained in the variable density wind tunnel of the National Advisory Committee for Aeronautics; and to determine the scale effect on the model equipped with all the details of the actual airplane. The results show a large decrease in minimum drag coefficient upon increasing the Reynolds number from about one-twentieth scale to full scale. A comparison is made between the results of these tests and those obtained from tests made in this tunnel on airfoils alone."
We are here giving a summary of the rules established by the Theoretical Section of the Central Aerodynamic Institute of Moscow for the different calculation cases of an airplane. It appears the engineers of the Aerodynamic Institute considered only thick or medium profiles. For these profiles they have attempted to increase the safety when the center of pressure moves appreciably toward the trailing edge.
Report includes the National Advisory Committee for Aeronautics letter of submittal to the President, Congressional report, summaries of the committee's activities and research accomplished, bibliographies, and financial report.
Described here is an automatic control that has been used in several forms in wind tunnels at the Washington Navy Yard. The form now in use with the 8-foot tunnel at the Navy Yard is considered here. Details of the design and operation of the automatic control system are given. Leads from a Pitot tube are joined to an inverted cup manometer located above a rheostat. When the sliding weight of this instrument is set to a given notch, say for 40 m.p.h, the beam tip vibrates between two electric contacts that feed the little motor. Thus, when the wind is too strong or too weak, the motor automatically throws the rheostat slide forward and backward. If it failed to function well, the operator would notice the effect on his meniscus, and would operate the hand control by merely pressing the switch.
Gasoline, the fuel now used, is an extremely volatile and inflammable liquid capable of forming explosive mixtures, the cause of many catastrophes in aviation. It is therefore of special interest to investigate the possibility of using fuels which, while being less volatile than gasoline, would nevertheless enable this engine to function satisfactorily.
Tested at the end of March, 1928, the C.A.M.S. 54 G.R. was built for the purpose of crossing the Atlantic from Europe by way of the azores. It has a biplane construction with wings mounted above the hull. It is powered by two new series 500 HP. geared Hispano Suiza V type engines.
For good profiles the profile-drag coefficient is almost constant in the whole range which comes into consideration for practical flight. This is manifest in the consideration of the Gottingen airfoil tests and is confirmed by the investigations of the writer (measurements of the profile drag during flight by the Betz method), concerning which a detailed report will soon be published. The following deductions proceed from this fact. The formulas developed on the assumptions of a constant profile-drag coefficient afford an extensive insight into the influences exerted on flight performances by the structure of the airplane.
This investigation was made for the purpose of determining the characteristics of five full-scale propellers in flight. The equipment consisted of five propellers in conjunction with a VE-7 airplane and a Wright E-2 engine. The propellers were of the same diameter and aspect ratio. Four of them differed uniformly in thickness and pitch and the fifth propeller was identical with one of the other four with exception of a change of the airfoil section. The propeller efficiencies measured in flight are found to be consistently lower than those obtained in model tests. It is probable that this is mainly a result of the higher tip speeds used in the full-scale tests. The results show also that because of differences in propeller deflections it is difficult to obtain accurate comparisons of propeller characteristics. From this it is concluded that for accurate comparisons it is necessary to know the propeller pitch angles under actual operating conditions. (author).
Tests were carried out in the variable density wind tunnel of the National Advisory Committee for Aeronautics on six airfoil sections used by the Bureau of Aeronautics as propeller sections. The sections were tested at pressures of 1 and 20 atmospheres corresponding to Reynolds numbers of about 170,000 and 3,500,000. The results obtained, besides providing data for the design of propellers, should be of special interest because of the opportunity afforded for the study of scale effect on a family of airfoil sections having different thickness ratios. (author).
The choice of the profile for the wings of an airplane is a problem which should be solved by a scientific method based on data obtained by systematic experimentation. The problem, in its present form, may be stated as follows: "To find a profile which has certain required aerodynamic characteristics and which encloses the spars, whose number, dimensions and separating distance are likewise determined by structural considerations." At present, the static test, corresponding to the case of accelerated flight at limited speed, requires the knowledge of the moment of the aerodynamic resultant at the angle of zero lift, and the possibility of controlling the magnitude of the corresponding absolute coefficient within more or less extensive limits.
This report gives a general method for drawing airplane profiles. This method is useful, but it leads to a somewhat laborious drawing which becomes quite complicated when we take a transformation function having terms of a high degree.
As part of a general program to study combustion in the engine cylinder and to correlate the phenomena of combustion with the observed performance of actual engines, this paper presents a sketchy outline of what may happen in the engine cylinder during the burning of a charge. It also suggests the type of information needed to supply the details of the picture and points out how combustion time and rate affect the performance of the engine. A theoretical concept of a flame front which is assumed to advance radially from the point of ignition is presented, and calculations based on the area and velocity of this flame and the density of the unburned gases are made to determine the mass rate of combustion. From this rate the mass which has been burned and the pressure at any instant during combustion are computed. This process is then reversed in an effort to determine actual rates of combustion and flame velocities from the pressures as recorded on indicator diagrams. The effects of different rates of combustion on engine performance are then discussed and the importance of proper spark advance is emphasized.
This report presents some results obtained during an investigation to determine the effect of high inlet air temperature on the performance of a Liberty 12 aviation engine. The purpose of this investigation was to ascertain, for normal service carburetor adjustments and a fixed ignition advance, the relation between power and temperature for the range of carburetor air temperatures that may be encountered when supercharging to sea level pressure at altitudes of over 20,000 feet and without intercooling when using plain aviation gasoline and mixtures of benzol and gasoline. The results show that for the conditions of test, both the brake and indicated power decrease with increase in air temperature at a faster rate than given by the theoretical assumption that power varies inversely as the square root of the absolute temperature. On a brake basis, the order of the difference in power for a temperature difference of 120 degrees F. Is 3 to 5 per cent. The observed relation between power and temperature when using the 30-70 blend was found to be linear. But, although these differences are noted, the above theoretical assumption may be considered as generally applicable except where greater precision over a wide range of temperatures is desired, in which case it appears necessary to test the particular engine under the given conditions. (author).
The tests described in this paper afford a direct comparison of the efficiency and smoothness of flow obtained with propeller fan and multiblade centrifugal fan drives in the same wind tunnel. The propeller fan was found to be superior to the centrifugal fan in that the efficiency was about twice as great, and the flow much smoother.
The propeller cannot be considered alone, but the mutual interference between propeller and airplane must be considered. These difficulties are so great when the joint action of propeller and airplane is considered, that the aerodynamic laboratory at Gottingen originally abandoned the idea of applying the efficiency conception of the test results. These difficulties and the methods by which they are overcome are outlined in this report.
This article resulted from the need of showing, in a simple way, how the aerodynamic properties of airfoils are affected by the shape of their profiles. No general solution of this problem could be found, since the profile shapes cannot ordinarily be expressed by simple mathematical formulas. This advantage is possessed only by the Joukowsky profiles and this discussion of the problem is therefore limited to them.
Since aircraft design is tending toward all-metal construction, the strong heat-treatable light aluminum alloy, duralumin (a generic name for a class of heat-treatable alloys containing Cu, Mg, Mn, and Si), is finding increasing application. Doubt has been expressed concerning the reliability and permanence of these materials. Information is given on the effect of corrosion on the tensile properties of 14-gauge sheet duralumin, heat treated by quenching in hot water after being heated for 15 minutes in a fused nitrate bath at 500 to 510 C. Intercrystalline corrosion and practical aspects of intercrystalline embrittlement are discussed with respect to duralumin.
The permanence, with respect to corrosion, of light aluminum alloy sheets of the duralumin type, that is, heat-treatable alloys containing Cu, Mg, Mn, and Si is discussed. Alloys of this type are subject to surface corrosion and corrosion of the interior by intercrystalline paths. Results are given of accelerated corrosion tests, tensile tests, the effect on corrosion of various alloying elements and heat treatments, electrical resistance measurements, and X-ray examinations.
As a result of testing, it was determined that control of the rate of quenching and the avoidance of accelerated aging by heating are the only means of modifying duralumin itself so as to minimize the intercrystalline form of corrosive attack. It is so simple a means that it should be adopted even though it may not completely prevent, but only reduce, this form of corrosive attack. By so doing, the need for protection of the surface is less urgent.
Although the corrosion resistance of sheet duralumin can be greatly improved by suitable heat treatment, protection of the surface is still necessary if long life under varied service conditions is to be insured. The coatings used for this purpose may be grouped into three classes: the varnish type of coating, the oxide type produced by a chemical treatment of the surface, and metallic coatings, of which aluminum appears to be the most promising. Since the necessary weather exposure tests are not complete, some of the conclusions regarding the value of various surface coatings are necessarily tentative.
Experiments with a two-stroke-cycle, crank case scavenging engine. Effect of systematic variation of the height of the scavenge and exhaust ports on the scavenging, as determined by gas analysis. The best results were obtained under conditions differing from the usual ones.
A peculiar phenomena in seaplane landing is observed and reported. The seaplane having executed a normal fast landing at low incidence, a forward movement of the control stick effected an unusual condition in that the seaplane left the water suddenly in an abnormal attitude. The observations describing this phenomena are offered as a warning against possible accident and as a conjectural cause of seaplane landing accidents of a certain kind.
Made for an Australian buyer, the Canberra is capable of carrying a payload of 1900 lbs. with a top speed of 126 M.P.H. At 105-110 M.P.H. it has a range of about 475 miles. It has a single Jupiter VI engine.
This note describes a simple and inexpensive method for determining the deflection of propeller blades under operating loads. Both the centrifugal force and air force loads are applied statically as a number of concentrated loads by means of weights and wires. Two methods of attaching the wires to the propeller blades have been tested, both giving approximately the same deflections. The method is considered useful for studying the deflections of propellers of different shapes under various operating conditions.
An investigation was conducted to determine the injection lag, duration of injection, and spray start and cut-off characteristics of a fuel injection system operated on an engine and injecting fuel into the atmosphere.
As a rule, the actual lift distribution at the wing tips shows deviations from the theoretical distribution, so that an approximate evaluation of the distribution may be regarded as satisfactory. After a few brief remarks on the fundamentals of the exact computation, the method will be so presented that the lift distribution for deflected ailerons may be determined for other values of the parameter p from the results already obtained. Coefficients will then be given in the form of diagrams and numerical tables, from which the desired forces and moments can be easily obtained by substitution in the given equations.
The thorough investigation of a Dorner four-cylinder, four-stroke-cycle Diesel engine with mechanical injection led me to investigate more thoroughly the operation of the Diesel as a vehicle engine. Aside from the obvious need of reliability of functioning, a high rotative speed, light weight and economy in heat consumption per horsepower are also indispensable requirements.
Measurements of the differential pressures on two navy air-speed nozzles, consisting of a Zahm type Pitot-Venturi tube and a SQ-16 two-pronged Pitot-static tube, in a tunnel air stream of fixed speed at various angles of pitch and yaw between 0 degrees and plus or minus 180 degrees. This shows for a range over -20 degrees to +20 degrees pitch and yaw, indicated air speeds varying very slightly over 2 per cent for the Zahm type and a maximum of about 5 per cent for the SQ-16 type from the calibrated speed at 0 degree. For both types of air-speed nozzle the indicated air speed increases slightly as the tubes are pitched or yawed several degrees from their normal 0 degrees altitude, attains a maximum around plus or minus 15 degrees to 25 degrees, declines rapidly therefrom as plus or minus 40 degrees is passed, to zero in the vicinity of plus or minus 70 degrees to 100 degrees, and thence fluctuates irregular from thereabouts to plus or minus 180 degrees. The complete variation in indicated air speed for the two tubes over 360 degree pitch and yaw is graphically portrayed in figures 9 and 10. For the same air speed and 0 degree pitch and yaw the differential pressure of the Zahm type Pitot-Venturi nozzle is about seven times that of the SQ-16 type two-prolonged Pitot-static nozzle.
An investigation on the cowling of radial air-cooled engines was conducted in the 20-foot Propeller Research Tunnel at Langley Field. Cooling and drag tests were made with each form of cowling. The propulsive efficiency was found to be practically the same with all forms of cowling.
This note describes tests of the drag due to a Wright "Whirlwind" (J-5) radial air-cooled engine mounted on a cabin type airplane. The tests were made in the 20-foot Propeller Research Tunnel of the National Advisory Committee for Aeronautics. The drag was obtained with three different types of exhaust stacks: Short individual stacks, a circular cross section collector ring, and a streamline cross section collector ring.
Measurements of drag were made on fittings taken from a typical fuselage to determine whether the difference between the observed full size fuselage drag and model fuselage drag could be attributed to the effects of fittings and surface irregularities found on the full size fuselage and not on the model. There are wide variations in the drag coefficients for the different fittings. In general those which protrude little from the surface or are well streamlined show very low and almost negligible drag. The measurements show, however, that a large part of the difference between model and full scale test results may be attributed to these fittings.
In this report a formula for calculating the induced drag of multiplanes with end plates is derived. The frictional drag of the end plates are used, is sufficiently large to increase the efficiency of the wing. Curves showing the reduction of drag for monoplanes and biplanes are constructed; the influence of gap-chord ratio, aspect ratio, and height of end plate are determined for typical cases. The method of obtaining the reduction of drag for a multiplane is described. Comparisons are made of calculated and experimental results obtained in wind tunnel tests with airfoils of various aspect ratios and end plates of various sizes. The agreement between calculated and experimental results is good. Analysis of the experimental results shows that the shape and section of the end plates are important.
This report contains the results obtained at the Langley Memorial Aeronautical Laboratory on an N. A. C. A. M-6 airfoil, fitted with a flap and ailerons, and tested in the variable density wind tunnel at a density of 20 atmospheres. Airfoil characteristics are given for the model up to 48 degree angle of attack with the flap set at various angles, and also with the ailerons set at similar angles. The approximate lift distribution and the center of pressure variation along the span are determined with the model at 18 degree angle of attack and with the ailerons displaced at 20 degrees. Approximate rolling moment and yawing moment coefficients are determined for the various aileron settings. A comparison of the calculated angles of zero lift and the calculated lift and moment coefficiencies with those observed is given in the appendix.
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