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Aviation History
1927
1927 - 0119.PDF
FEBRUARY 24, 1927 19 THE AIRCRAFT ENGINEER SUPPLEMENT TO PLIGHT PROPELLER DESIGN : A SIMPLE SYSTEM BASED ON MODEL PROPELLER TEST DATA—III.—No. 237. By FEED E. WEICK, Langley Memorial Aeronautical Laboratory. This report, the third of a series of four, describes a simple .atem for designing propellers of a standard form. In this 7pp.>rt the system is based on tests of a family of model propellers of standard Navy form, the data from which have iicon extended by means of calculations to cover the complete range likely to be found in practice. However, it can be worked out for any family having propellers of one general form. This system can also be applied as given to propellers of different forms by means of form factors. Modifications arc made for full-scale flight conditions, i.e., the particular tip speed of the propeller, and body or fuselage interference. SIMPLE METHOD FOR STRENGTH OP PRO- PROPELLER DESIGN : A DETERMINING THE PELLERS—IV.—No. 238. By FEED E. WEICK, Langley Memorial Aeronautical Laboratory. The object of this report, the last of a series of four on propeller design, is to describe a simple method for determin- ing whether the strength of a propeller of a standard form is sufficient for safe operation. An approximate method of stress analysis is also given. STEAM POWER PLANTS IN AIRCRAFT.—No. 239. By E. E. WILSON, Bureau of Aeronautics, Navy Department. The employment of steam power plants in aircraft has been frequently proposed. This paper makes a brief analysis of the proposal from the broad general viewpoint of aircraft power plants, and the conclusion is reached that on the basis of the weight of the power plant alone, steam power plants for aircraft are precluded. On the basis of economy alone they are again precluded. On the basis of the resist- ance of the cooling surface required alone they are pre- cluded. On the basis of the sum of these three considerations they are absolutely impossible. THE N.A.C.A. CYH AIRFOIL SECTION.—No. 240. By GEORGE .1. HIGGINS, Langley Memorial Aeronautical Laboratory. The N.A.C.A. CYH airfoil section is described and its aerodynamic characteristics are given as tested in the N.A.C.A. variable density wind tunnel at 20 atmospheres pressure. This section has a low drag, a high maximum lift, and a small travel of centre of pressure. TESTS OF SEVERAL BEARING MATERIALS LUBRICATED BY GASOLINE.—No. 241. By W. F. JOACHIM and HAROLD W. CASE, Langley Memorial Aeronautical Laboratory. This investigation on the relative wear of several bearing materials lubricated by gasoline was conducted at the Langley Memorial Aeronautical Laboratory, Langley Field. Virginia, as part of a general research on fuel injection engines for aircraft. The specific purpose of the work was to find a durable bearing material for gear pumps to be used for the delivery of gasoline and Diesel engine fuel oil at moderate pressures to the high-pressure pumps of fuel injection •'ngines. The bearing surfaces were prepared for test by scraping, 'ud by wearing them in under load with the shafts. The •tarings were then baked and weighed to within 0-003 grain n analytical balances. The bearings were held in rockers ttached to the bottom of a gasoline tank and to a lever, and •e loads imposed by weighing the lever. The tests were ade with 0-5-in. diameter shafts turning at approximately -00 r.p.m., the shafts and bearings being immersed in -oline. The wear was determined by baking and weighing ' e bearings after test. Eighteen bearing materials were tested. These tests in- *ded determinations of the wear of two bearing materials "arious loads with both machine steel and hardened tool steel shafts ; seizing load tests of 16 bearing materials ; and wear tests of 8 bearing materials, selected from the seizing load tests, at a load of 250 lb. per square inch, with hardened tool steel shafts. When a machine steel shaft was used, the seizing load for a commercial hard bronze was about 65 lb. per square inch, and for another commercial, but softer, more porous bronze, it was about 80 lb. per square inch. With a hardened tool steel shaft, the seizing load for the hard bronze was about 115 lb. per square inch, and for the soft bronze it was about 210 lb. per square inch. Special bearing bronzeB, containing lead up to approximately 35 per cent, or graphite up to approximately 50 per cent., carried loads up to 500 lb per square inch, without seizing, though in all cases con- siderable wear occurred above a load of about 300 lb. per square inch. The wear obtained in the tests on the eight selected bearing materials ranged from 0 -53 to 21 -55 grains per million turns per square inch of bearing contact surface. The least wear was obtained with a hard alloy of graphite and powdered bronze pressed and sintered at high tem- perature. It was found that, with a machine steel shaft, a hard bear- ing material had less wear below the seizing load than a soft bearing material, These results were reversed with a hardened tool steel shaft. Soft bearing materials and bearing alloys containing special anti-friction metal or graphite have higher seizing loads than hard bearing materials for either kind of shaft. These tests indicate that a porous bearing material, sufficiently hard to support the loads imposed and containing anti-friction materials and relatively hard crystals to minimize wear, will give durable service with a hardened tool steel shaft. LECTURES AND PAPERS. THE SUPERCHARGING OF AIRCRAFT AND MOTOR VEHICLE ENGINES. The official secrecy surrounding much of the work that has been carried out on the problems of supercharging aero engines was responsible for certain shortcomings in the paper read by Mr. Roy Fedden on February 1 before a joint meet- ing of the Royal Aeronautical Society and the Institution of Automobile Engineers. These omissions can in no way be laid at the door of the lecturer, but are a result of circum- stances as they obtain at the present time, and Mr. Fedden, who, as probably the great majority of our readers are aware, is the designer of the famous "Bristol" aero engines, remarked in the course of his lecture : " The author cannot refrain from expressing his regret on this matter, as he feels that, providing really confidential information is withheld, an open interchange of ideas must be of benefit to all con- cerned." Mr. Fedden expressed his belief that within the next few years practically all classes of military aircraft engines would be supercharged as a matter of course. He suggested that by the standardization of supercharged engines on military aircraft: " (1) It will be possible to obtain a better performance on scouts with a ground-boosted gear-driven blower engine of considerably smaller capacity than the naturally-aspirated engine used at present, with a consequent gain in the all- round efficiency of the machine. " (2) That for the larger general-purpose machine super- charged engines throttled on the ground and opened out to full power at some predetermined altitude will provide greatly increased performance over any type of existing or oversize engine. " (3) That for long-distance bombing machines operating at high altitudes, and when fuel consumption over long distances is of the utmost importance, there is an important field for the exhaust-driven turbo-compressor." The lecturer also thought that as the art of supercharging advanced the mechanism would be applied as standard to commercial aircraft, with a consequent all-round increase in efficiency and reduction in fuel consumption. Most probably the supercharger would not be used continuously, but would be employed for mild ground-boosting to obtain maximum lOOg
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