ALBERT

Description: An instrument for recording and indicating the frequency and intensity of aircraft icing conditions encountered in flight has been developed by the NACA Lewis Laboratory to obtain statistical icing data over world-wide air routes during routine airline operations. The operation of the instrument is based on the creation of a differential pressure between an ice-free total-pressure system and a total-pressure system in which small total-pressure holes vented to static pressure are allowed to plug with ice accretion. The simplicity of this operating principle permits automatic operation, and provides relative freedom from maintenance and operating problems. The complete unit weighing only 18 pounds records icing rate, airspeed, and altitude on photographic film and provides visual indications of icing intensity to the pilot.

Description: A camera designed for use in flight has been developed by the NACA Lewis laboratory t o photograph cloud droplets in their natural suspension in the atmosphere. A magnification of 32 times is employed to distinguish for measurement purposes all sizes of droplets greater than 5 microns in diameter. Photographs can be taken at flight speeds up to 150 miles per hour at 5-second intervals, A field area of 0.025 square inch is photographed on 7-inch-width roll film accommodating 40 exposures on an 18-foot length. Flight tests conducted in cumulus clouds have shown that approximate droplet-size distribution studies can be obtained and that a studies of the microstructure and physics of clouds can be made with the camera.

Description: A statistical survey and a preliminary analysis are made of icing data collected from scheduled flights over the United States and Canada from November 1951 to June 1952 by airline aircraft equipped with NACA pressure-type icing-rate meters. This interim report presents information obtained from a continuing program sponsored by the NACA with the cooperation of the airlines. An analysis of over 600 icing encounters logged by three airlines operating in the United States, one operating in Canada and one operating up the coast to Alaska, is presented. The icing conditions encountered provided relative frequencies of many icing-cloud variables, such as horizontal extent, vertical thickness, temperatures, icing rate, liquid-water content, and total ice accumulation. Liquid-water contents were higher than data from earlier research flights in layer-type clouds but slightly lower than previous data from cumulus clouds. Broken-cloud conditions, indicated by intermittent icing, accounted for nearly one-half of all the icing encounters. About 90 percent of the encounters did not exceed a distance of 120 miles, and continuous icing did not exceed 50 miles for 90 percent of the unbroken conditions. Icing cloud thicknesses measured during climbs and descents were less than 4500 feet for 90 percent of the vertical cloud traverses.

Description: Flight icing-rate data obtained in a dense and. abnormally deep supercooled stratiform cloud system indicated the existence of liquid-water contents generally exceeding values in amount and extent previously reported over the midwestern sections of the United States. Additional information obtained during descent through a part of the cloud system indicated liquid-water contents that significantly exceeded theoretical values, especially near the middle of the cloud layer.. The growth of cloud droplets to sizes that resulted in sedimentation from the upper portions of the cloud is considered to be a possible cause of the high water contents near the center of the cloud layer. Flight measurements of the vertical temperature distribution in the cloud layer indicated a rate of change of temperature with altitude exceeding that of the moist adiabatic lapse rate. This excessive rate of change is considered to have contributed to the severity of the condition.

Description: A lightweight instrument that utilizes resistance-wire electric strain gases to measure propeller-shaft thrust has been developed. A wind-tunnel investigation on a propeller installed, on a single-engine pursuit airplane showed that the instrument gave a reliable indication of propeller-shaft thrust to an accuracy of +/-2 percent within its calibrated range. No attempt was made to determine the relation of indicated shaft thrust to net propeller thrust.

Description: A statistical study is made of icing data reported from weather reconnaissance aircraft flown by Air Weather Service (USAF). The weather missions studied were flown at fixed flight levels of 500 millibars (18,000 ft) and 700 millibars (10,000 ft) over wide areas of the Pacific, Atlantic, and Arctic Oceans. This report is presented as part of a program conducted by the NACA to obtain extensive icing statistics relevant to aircraft design and operation. The thousands of in-flight observations recorded over a 2- to 4-year period provide reliable statistics on icing encounters for the specific areas, altitudes, and seasons included in the data. The relative frequencies of icing occurrence are presented, together with the estimated icing probabilities and the relation of these probabilities to the frequencies of flight in clouds and cloud temperatures. The results show that aircraft operators can expect icing probabilities to vary widely throughout the year from near zero in the cold Arctic areas in winter up to 7 percent in areas where greater cloudiness and warmer temperatures prevail. The data also reveal a general tendency of colder cloud temperatures to reduce the probability of icing in equally cloudy conditions.

Description: An investigation to determine the effectiveness of icing protection afforded by air-heating hollow steel unpartitioned propeller blades has been conducted In the NACA Cleveland icing research tunnel. The propeller used was a production model modified with blade shank and tip openings to permit internal passage of heated air. Blade-surface and heated-air temperatures were obtained and photographic observations of Ice formations were made with variations In icing intensity and heating rate to the blades. For the conditions of Icing to which the propeller was subjected, it was found that adequate ice protection was afforded with a heating rate of 40 1 000 Btu per hour per blade. With less than 40,000 Btu per hour per blade, ice protection failed because of significant ice accretions on the leading edge. The chordwise distribution of heat was unsatisfactory with most of the available heat dissipated well back of the leading edge on both the thrust and camber face's instead of at the leading edge where it was most needed. A low utilization of available heat for icing protection is indicated by a beat-exchanger effectiveness of approximately 47 percent.

Description: Data and analyses are presented on the relative frequencies of occurrence and severity of icing cloud layers encountered by jet aircraft in the climb and descent phases of flights to high altitudes. Fighter-interceptor aircraft operated by the Air Defense Command (USAF) at bases in the Duluth and Seattle areas collected the data with icing meters installed for a l-year period. The project was part of an extensive program conducted by the NACA to collect Icing cloud data for evaluating the icing problem relevant to routine operations. The average frequency of occurrence of icing was found to be about 5 percent of the number of climbs and descents during 1 year of operations The icing encounters were predominantly in the low and middle cloud layers, decreasing above 15,000 feet to practically none above 25,000 feet. The greatest thickness of ice that would accumulate on any aircraft component (as indicated by the accretion on a small object) was measured with the icing meters. The ice thicknesses on a small sensing probe averaged less than 1/32 inch and did not exceed 1/2 inch. Such accumulations are relatively small when compared with those that can form during horizontal flight in icing clouds. The light accretions resulted from relatively steep angles of flight through generally thin cloud layers. Because of the limited statistical reliability of the results, an analysis was made using previous statistics on icing clouds below an altitude of 20,000 feet to determine the general icing severity probabilities. The calculations were made using adiabatic lifting as a basis to establish the liquid-water content. Probabilities of over-all ice accretions on a small object as a function of airspeed and rate of climb were computed from the derived water contents. These results were then combined with the probability of occurrence of icing in order to give the icing severity that can be expected for routine aircraft operations.

Description: Icing data collected on routine operations by four DC-4-type aircraft equipped with NACA pressure-type icing-rate meters are presented as preliminary information obtained from a statistical icing data program sponsored by the NACA with the cooperation of many airline companies and the United States Air Force. The program is continuing on a much greater scale to provide large quantities of data from many air routes in the United States and overseas. Areas not covered by established air routes are also being included in the survey. The four aircraft which collected the data presented in this report were operated by United Air Lines over a transcontinental route from January through May, 1951. An analysis of the pressure-type icing-rate meter was satisfactory for collecting statistical data during routine operations. Data obtained on routine flight icing encounters from.these four instrumented aircraft, although insufficient for a conclusive statistical analysis, provide a greater quantity and considerably more realistic information than that obtained from random research flights. A summary of statistical data will be published when the information obtained daring the 1951-52 icing season and that to be obtained during the 1952-53 season can be analyzed and assembled. The 1951-52 data already analyzed indicate that the quantity, quality, and range of icing information being provided by this expanded program should afford a sound basis for ice-protection-system design by defining the important meteorological parameters of the icing cloud.