Engine Power Settings Research Articles

Fixed-Range Optimum Trajectories for Short-Haul Aircraft

An algorithm, based on the energy-state method, is derived for calculating optimum trajectories with a range constraint. The basis of the algorithm is the assumption that optimum trajectories consist of, at most, three segments: an increasing energy segment (climb); a constant energy segment (cruise); and a decreasing energy segment (descent). This assumption allows energy to be used as the independent variable in the increasing and decreasing energy segments, thereby eliminating the integration of a separate adjoint differential equation and simplifying the calculus of variations problem to one requiring only pointwise extremization of algebraic functions. The algorithm is used to compute minimum fuel, minimum time, and minimum direct-operating-cost trajectories, with range as a parameter, for an in-service CTOL aircraft and for an advanced STOL aircraft. For the CTOL aircraft and the minimum-fuel performance function, the optimum controls, consisting of air-speed and engine power setting, are continuous functions of the energy in both climb and descent as well as near the maximum or cruise energy. This is also true for the STOL aircraft except in the descent where at one energy level a nearly constant energy dive segment occurs, yielding a discontinuity in the airspeed at that energy. The reason for this segment appears to be the relatively high fuel flow at idle power of the engines used by this STOL aircraft. Use of a simplified trajectory which eliminates the dive increases the fuel consumption of the total descent trajectory by about 10 percent and the time to fly the descent by about 19 percent compared to the optimum.

Acoustic loads on an externally blown flap system due to impingement of a TF-34 jet engine exhaust

One of the techniques being investigated in the studies of powered-lift augmentation of aircraft is the use of externally blown flaps. When the flaps deploy, the exhaust of the engine directly impinges on them and is directed downward, providing additional lift. Because of this direct impingement on the flap surface, severe dynamic loads may be induced on the flap elements. To obtain data on these surface loads, a section of a wing and triple-slotted flap system was mounted behind a TF-34 jet engine (nominal thrust of 7000 lb). Fluctuating pressure in the range from 20 to 10 000 Hz, temperature, and static pressure measurements were made at several locations over the span and chord of the second and third flap elements for a typical takeoff flap angle setting—0°, 20°, 40°—and a typical landing flap angle setting—15°, 35°, 55°. The effect of engine power setting was also investigated. The wing and flap sections were of boiler plate construction to minimize the effect of the structural response on the loads measurements. Data are presented showing the overall fluctuating pressure levels and power spectral densities as a function of engine performance. The maximum fluctuating pressures reached levels of 165 dB on the flaps. The spatial distributions of the loads are also presented and discussed. Some comparisons with previous results are discussed.

Exhaust noise field generated in the JT8D core engine—noise floor presented by the internal noise sources

An experimental study has been conducted to determine the strength of the acoustic radiation generated in the combustion and turbine stages of a JT8D core engine and transmitted out through the primary jet exhaust duct. The acoustic field within the tail pipe duct extension was measured by an array of microphones flush mounted on the extension wall. The interpretation of the cross-power spectral densities of the microphone signals by means of a theoretical model of the sound propagation within the duct permitted the acoustic energy transmission out of the nozzle exit to be determined. The results show that the internally generated noise is a dominant noise component from the core engine at larger angles from the jet axis for the case of low engine power settings. Although the internally generated core engine noise component lies well below the JT8D engine jet noise and fan noise components at the higher engine power settings, it represents an additional noise parameter that must be considered in the application of fan noise and jet noise suppression techniques.

超音速飛行における機外とう載品の抵抗

Drag of external stores installed on a supersonic aircraft deteriorates the performance like maximum speed, acceleration, endurance. Droptanks, pods, wing pylons belong to such stores. The drag coefficients of these stores are essential to estimate the performances, however, comparably difficult to acquire in supersonic region. When supersonic wind tunnel is not available, the coefficients can be derived through flight tests.The proposed method depends on a comparison of supersonic acceleration flights between the clean and the externally installed configurations. The test aircraft is flown successively in that different configurations.For each acceleration, flying altitude, starting speed of 0.9 Mach and initial aircraft weight are kept equal. Also the maximum engine power setting of after-burner is kept same all through the accelerations. Each acceleration range from 0.9 to 2.0 Mach is divided commonly into a number of small speed class. At each class, flight Mach number, time and fuel quantity representing aircraft weight or mass are recorded by the pilot.For each class, based on equation of motion of the aircraft, the drag of the stores is calculated from the difference of the products between the two configurations, the product being the aircraft mass multiplied by the acceleration rate. Then the drag coefficient is derived as usual and plotted for the supersonic range.As an example, drag coefficient for a wing pylon was derived from flight tests as 0.04 to 0.02 for the supersonic range regarding to its side area, and compared with the coefficient from wave and friction drag theory. Due to unfavorable flight conditions and lack of experience, the dispersions of the derived coefficients from the theory were not small.By improving measuring technique and choosing flight condition carefully, this method may bring more accurate drag data and may be suitable when the flight test is feasible with other missions.

Exhaust Noise Field Generated in the JT3D Core Engine—Noise Floor Presented by the Internal Noise Sources

An experimental study has been conducted to determine the strength of the acoustic radiation generated in the combustion and turbine stages of a JT8D core engine and transmitted out through the primary jet exhaust duct. The acoustic field within the tall pipe duct extension was measured by an array of microphones flush-mounted on the extension wall. The interpretation of the cross-power spectral densities of the microphone signals by means of a theoretical model of the sound propagation within the duct permitted the acoustic energy transmission out of the nozzle exit to be determined. The results show that the internally generated noise is a dominant noise component from the core engine at larger angles from the jet axis for the case of low engine power settings. In general, although the internally generated core engine noise component lies well below the JT8D engine jet-noise and fan-noise components at the higher engine power settings, it represents an additional noise parameter that must be considered in the application of fan-noise and jet-noise suppression techniques. [Work accomplised when the author was a member of the Aircraft Noise Staff of the Boeing Company, Seattle, Washington.]

Statistical Study of Aircraft Landing-Noise Levels

Recent work related to the aircraft noise problem has presented the opportunity to obtain a great deal of measured data of the landing noise produced by present day jet aircraft. The quantity of the measured data allows a statistical evaluation of the results. This paper presents the results of noise-level measurements made underneath the landing flight path at Los Angeles International Airport. The study study included measurements of noise spectra produced by 142 four-engine turbofan and 100 three-engine turbofan aircraft. Statistical analysis based on the measured data shows that the noise levels produced at a given ground station beneath the landing path are not part of a parent distribution that is Gaussian. The analysis also shows that the variation in noise levels is not correlated with aircraft altitude variations; i.e., the noisiest aircraft are not necessarily the lowest in altitude. The conclusion is reached that noise levels on the ground are greatly dependent on aircraft engine power setting during final approach to landing.