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FROM Karavodine's inefficient tube in 1908 through American developments after the recovery of German V-1 bombs, Mr. Edelman sketches the history of pulsating jet engines. Work in the United States has centered on instrumentation, tube geometry, fuel injectors, air inlet valves, fuel properties, and performance estimation. Realized performance is still low in comparison with predictions of best possible performance; but the author suggests use of the pulsating jet for helicopters having jets at the blade tips, for gliders, for starting turbines of aircraft gas turbine powerplants, and for auxiliary power with conventional aircraft.

TROLLEY coaches have a lower cost of operation per seat per mile in the range of 800 to 3500 passengers per hour than do either motor buses or trolley cars, the author's curves show. Outside this range, motor buses are most economical for lighter traffic and trolley cars for heavier traffic. Many passengers prefer trolley coaches to buses and streetcars, according to a Columbus, Ohio, poll. Other users of the street appreciate curb loading, which permits traffic to pass coaches at stops. Because of the relatively small amount of wear, the life of the vehicle is limited by obsolescence rather than by mechanical failures.

THE great increase during the last 20 years in the knowledge of fuel behavior in piston engines the author attributes largely to the use of full-scale engines for fuels testing and engine development work, the use of pure compounds as reference standards, and the standardizing of laboratory knock-test methods. He sees preignition, fuel-air mixture distribution, and stability of stored fuels as engine-fuel problems which may have to be tackled in the next few years if development of the piston aircraft engine continues. Mr. Heron presented this lecture after receiving the Horning Memorial Award for 1945.

A SERIES of charts for predicting the performance of the continuous-flow jet engine and its individual components is presented here. Efficiencies of components as well as the momentum pressure loss in the combustion chamber (assuming constant cross-sectional area) are taken into consideration. Performance of a typical jet engine under various operating conditions is calculated by means of the charts and graphed to show the effect of each operating condition on performance when all other conditions are held constant. A set of large, usable charts similar to the figures in this paper may be obtained upon request to the Cleveland Laboratories, National Advisory Committee for Aeronautics.

INCREASED utility of personal planes which can operate on readily available motor fuel warrants redesign of their engines to use premium or house-brand grades of motor gasoline, Mr. Kerley believes. He presents data to show that light aircraft engines can be modified to operate on fuels having a lead concentration equal to that of Grade-80 all-purpose fuel. Other problems connected with the use of motor fuels-high vapor pressure and volatility-are not insurmountable, he says. Cost is no longer a fair argument in favor of motor fuel, he claims, for the price differential between unleaded aviation fuel and motor fuel is too slight.

HIGH combustor-inlet temperatures and pressures and low inlet velocities promote combustion, study of an early Westinghouse 19B combustor shows. Altering any one of the three inlet conditions in an undesirable direction affects combustion the same as an increase in altitude. Unfavorable conditions are said to account for operational limits at altitude. As altitude increases, combustion efficiency drops and resonance develops; the maximum temperature rise obtainable and the fuel-air ratio at which it occurs decrease. The more adverse the inlet conditions, the greater their detrimental effect on combustion. In accelerating at a given altitude, there may be a range of engine speeds where operation is impossible because increased inlet velocities more than counterbalance beneficial effects of increased inlet temperatures and pressures.

MUCH useful information about cold starting has been compiled from tests made by the AAF in Alaska. The present minimum starting temperature with AN-F-28 fuel and the standard priming system was found to be between 0 and -10 F for radial engines with pressure-type carburetors, and between -10 and -15 F for radial engines with direct cylinder-injection carburetion and for inline engines. The authors estimate that more effective priming systems could lower the limits to -30 or -35 F without the use of special fuels or equipment. Present limits result partly from poor starting technique and from low cranking speeds caused by improper oil dilution. Oil dilution, however, receives strong approval from the authors, who believe that, properly used, it lengthens engine life under Arctic conditions. Turbojets will probably be superior in cold-starting ability. Supplying enough power to crank the engine to firing and sustaining speeds is the main problem.

BOTH cranking torque characteristics and starting characteristics of three types of Wright Cyclone engines were studied by the author. Torque can be minimized, he found, by keeping both oil viscosity and the speed at which the engine is cranked as low as safety will permit. Throttle quadrants may be marked with a “start” position, he says, because there exists an optimum setting good throughout the temperature range. Investigations of cranking speeds and priming systems are reported.