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The purpose of this paper is to analyze the active suppression of the nonlinear aeroelastic vibrations of ailerons caused by freeplay by robust H_∞ and linear quadratic Gauss (LQG) methods of control in case of incomplete measurements of the state of the system.

The flexible wing with nonlinear aileron with freeplay is treated as a plant-controller system with H_∞ and LQG controllers used to suppress the aeroelastic vibrations. The simulation approach was used for analyzing the impact of completeness of measurements on the efficiency and robustness of the controllers.

The analysis shows that the H_∞ method can be effectively used for suppression of nonlinear aeroelastic vibrations of aileron, although its efficiency depends essentially on completeness and types of measurements. The LQG method is less effective, but it is also able to prevent aileron vibrations by reducing their amplitudes to acceptable, safe level.

Only numerical analysis was carried out for the problem described; thus, the proposed solution is of theoretical value at this stage of analysis, and its application to the real suppression of aeroelastic vibrations requires further research.

The work presents a potentially useful solution to the problem of interest and results are a theoretical basis for further research.

This work may lead to a hot debate on the advantages and drawbacks of the active suppression of vibrations in the aeroelasticians community.

The work raises the important questions of practical stabilizability of the nonlinear aeroelastic systems, their dependence on completeness and types of measurements and robustness of the controllers.

The purpose of the paper is to analyze the active suppression of the aeroelastic vibrations of ailerons with strongly nonlinear characteristics by neural network/reinforcement learning (NN/RL) control method and comparing it with the classic robust methods of suppression.

The flexible wing and aileron with hysteresis nonlinearity is treated as a plant-controller system and NN/RL and robust controller are used to suppress the nonlinear aeroelastic vibrations of aileron. The simulation approach is used for analyzing the efficiency of both types of methods in suppressing of such vibrations.

The analysis shows that the NN/RL controller is able to suppress the nonlinear vibrations of aileron much better than linear robust method, although its efficiency depends essentially on the NN topology as well as on the RL strategy.

Only numerical analysis was carried out; thus, the proposed solution is of theoretical value, and its application to the real suppression of aeroelastic vibrations requires further research.

The work shows the NN/RL method has a great potential in improving suppression of highly nonlinear aeroelastic vibrations, opposed to the classical robust methods that probably reach their limits in this area.

The work raises the questions of controllability of the highly nonlinear aeroelastic systems by means of classical robust and NN/RL methods of control.

The separation of energy conversion and propulsor is a promising aspect of hybrid-electric propulsion systems, allowing for increased installation efficiencies and setting the basis for distributed propulsion concepts. University of Stuttgart’s Institute of Aircraft Design has a long experience with electrically powered aircraft, starting with Icaré 2, a solar-powered glider flying, since 1996. Icaré 2 recently has been converted to a three-engine motor glider with two battery-powered wing-tip propellers, in addition to the solar-powered main electric motor. This adds propulsion redundancy and will allow analyzing yaw control concepts with differential thrust and the propeller-vortex interaction at the wing-tip. To ensure airworthiness for this design modification, new ground vibration tests (GVTs) and flutter calculations are required. The purpose of this paper is to lay out the atypical approach to test execution due to peculiarities of the Icaré 2 design such as an asymmetrical aileron control system, the long wing span with low frequencies of the first mode and elevated wing tips bending under gravity and thus affecting the accuracy of the wing torsion frequency measurements.

A flutter analysis based on GVT results is performed for the aircraft in basic configuration and with wing tip propulsors in pusher or tractor configuration. Apart from the measured resonant modes, the aircraft rigid body modes and the control surface mechanism modes are taken into consideration. The flutter calculations are made by a high-speed, low-cost software named JG2 based on the strip theory in aerodynamics and the V-g method of flutter problem solution.

With the chosen atypical approach to GVT the impact of the suspension on the test results was shown to be minimal. Flutter analysis has proven that the critical flutter speed of Icaré 2 is sufficiently high in all configurations.

The atypical approach to GVT and subsequent flutter analysis have shown that the effects of wing-tip propulsors on aeroelasticity of the high aspect ratio configuration do not negatively affect flutter characteristics. This analysis can serve as a basis for an application for a permit to fly.

The presented methodology is valuable for the flutter assessment of aircraft configurations with atypical aeroelastic characteristics.

FUEL SYSTEM GENERALTHE standard version or the F.28 has a conventional two‐tank fuel system with an integral tank in each outer wing section contained by the wing torsion box with a total capacity of 2,170 Imp. gal. or 17,200 lb. of fuel. The centre wing torsion‐box pro‐vides space for additional bladder type tanks with a capacity varying from 312 to 700 Imp. gal. or 2,460 to 5,500 lb. as desired.

THE aerodynamic design of a transport aircraft is fixed by the functions it is intended to fulfil. When the Trident 1 design was begun the aim was to provide a performance that would make it the ultimate subsonic short range jet, able to remain in front‐line service for at least ten years. Maximum effort was therefore concentrated on achieving low drag at high Mach numbers with good handling qualities to match. Comet experience had shown the value of good low speed handling qualities, and so a continuous programme of wind tunnel and flight testing has been carried through to combine the requirements of high Mach number cruising speeds with those of a competitive CLmax. and an acceptable stall pattern, using, as far as possible, relatively simple and well tried high lift devices.

AS is to be expected, the various systems on the Trident 2E closely follow those evolved for the Tridents 1 and 1E, except for the changes in the fuel system necessitated by the introduction of the fin fuel tank, and the embodiment of a turbine‐compressor type of cold air unit in the air conditioning system.

THE various systems on the Trident 3B are, as is to be expected, logical developments of those evolved for the Tridents 1, 1E and 2E.

MUCH reference is made in the aeronautical field to the flutter problem and the subject is receiving the attention of many persons engaged in research, testing, and design. Many aeronautical engineers are well acquainted with some aspect of the problem, and although only a few are concerned with its several phases it is safe to say that all aeronautical men regard it with some degree of interest. It is fitting, therefore, that although it has been adequately treated by many authors from other points of view, a statement be here made summarizing the flutter problem as one of the aeroplane designer. In order that the exact nature of this problem be appreciated it is first necessary that a few of the fundamentals be reviewed.

A pair of wing‐tip control surfaces each consisting of a nose section 5 with hinged upper and lower rear sections 1,2 may be operated as ailerons by bodily rotation about nose hinges 6; as dive brakes by opening the sections 1,2 to an angle of 120 deg.; and as landing flaps by lowering them bodily through an angle of 30 deg. and then opening the sections 1,2 to an angle of 60 deg. so that the upper sections return to their neutral position. Full aileron control movements may be superimposed when the surfaces are operating as brakes or flaps. In the aileron control system shown in FIG. 1a, the valve 23 of the power cylinder 24 is controlled by a screwed rod 21 operated by the control column 11 through cables 10, quadrant 12, and link 16. The rod 21 may be rotated, to vary its length for independent operation of valve 23, by the rotation of a telescopic shaft 33 coupled to a second shaft 34 which may be connected to the flap operating mechanism, if normal landing flaps are fitted or, if not, to a separate power source. In the former case lowering of the flaps results in simultaneous lowering of the wing‐tip surfaces to give full‐span flap operation, while in the latter, flap effect is obtained by drooping the tip surfaces. The dive brake control mechanism shown in FIG. 1b, consists of a power cylinder 35 mounted inside the nose section 5 of each surface and controlled by a solenoid valve 53, to actuate linkages 40,41 … 47,48 connected to the hinged sections1,2. When the surface has been rotated through an angle of 30 degrees as a landing flap, the solenoid valve 53 is operated automatically to separate the sections 1,2 as previously referred to, When fitted to a tailless aircraft the surfaces may be operated as elevons and by differential dive brake operation be made to serve as drag rudders.

AT the present day the operations of civil transport aeroplanes are severely restricted under conditions of poor visibility and not infrequently flights have to be diverted or cancelled. The work of the Blind Landing Experimental Unit of the Ministry of Aviation in the development of a system of automatic landing for military aircraft has been described elsewhere.1 A flight control system is described in this paper, which given the necessary azimuth guidance signals from ground based installations, will extend the advantages of automatic landings into the civil field.