An analysis of VGH data collected from one type of four-engine turbojet transport airplane

An analysis of VGH records collected on two identical four-engine turbojet trans port airplanes during routine commercial operations of a single airline has provided information on incremental normal accelerations and turbulence experienced and on a i r speed operating practices.The data cover operations on routes which extended over the eastern half of the United States, with a few additional flights being made to the west coast and to northern South America.No significant differences were seen in the results for the two individual airplanes operated by the same airline.Comparison of the present results with those for another type of four-engine turbojet transport also showed a high degree of similarity.At lower levels of acceleration, turbulence produced the most frequent loads whereas at the higher acceleration levels, check-flight maneuver accelerations were the most frequent source of loads.The airplanes w e r e operated at speeds close to the placard limit, particularly at the higher altitudes where the airplane w a s Mach limited.The observance of speed reduction for turbulence w a s apparent from the data when higher levels of turbulence were considered.The frequency of given levels of normal acceleration for landing impact and ground operations of the present results were of the same order of magnitude a s for other types of four-engine turbojet transports. IN TRODUC TIONIn a continuation of a project begun by the National Advisory Committee for Aeronautics in 1946, the National Aeronautics and Space Administration collects data on incremental normal acceleration, airspeed, and altitude during routine airline operations for most new airplane types.These measurements are being utilized to provide statis tical data on a number of operational aspects of the turbine-powered aircraft, such as accelerations due to gusts, maneuvers, and oscillations; operating practices; and landingimpact and other ground-induced accelerations.In the past, information obtained from the data-collection program has proved useful for comparison of the operational experi ences of airplanes with the concepts to which they were designed, for detection of new o r VNE never -exceed speed, knots indicated vNO normal-operating-limit airspeed, knots indicated W airplane weight, pounds force (newtons) airplane m a s s ratio, atmospheric density, slugs/foot3 (kilograms/meter3) P O atmospheric density at sea level, slugs/foot3 (kilograms/meter3) DATA Instrumentation and ScopeThe data were collected with NASA VGH recorders, which provide continuous timehistory r e c o r d s of indicated air speed, normal acceleration, and p r e s s u r e altitude.A detailed description of the VGH recorder is given in reference 9.The normal accelera tions were sensed by an accelerometer mounted in the lower fuselage at a location c o r r e sponding t o 24 percent of the mean aerodynamic chord.The recorder was connected to the autopilot static-pressure source and to the copilot's pitot tube.The two airplanes were operated on routes covering the eastern half of the United States, with a few additional flights being made t o the west coast of the United States and to northern South America.The scope of the data samples for the two airplanes is summarized in table I.As shown in the table, the s i z e s of the data samples were reasonably similar (2082 hours and 1904 hours) although airplane 1 spent a larger percent of time in check flights (6.38 per cent) than did airplane 2 (4.56 percent).The data-collection period covered almost 2 years, and except for one period of about 11 months for airplane 2, the recording peri 2 ods noted in table I were covered almost continuously.Histograms of flight duration and of p r e s s u r e altitude are shown in figure 1 to define the operation further.Characteristics of the airplane pertinent to the evaluation of the data are as follows: Span, ft (m) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .