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IN connexion with the development of the modern transport aeroplane it is of growing importance to pay proper attention to the take‐off characteristics of these aeroplanes and to consider the means suitable to improve them. For the realization of economically justified air transport two trends have been indicated; both having an unfavourable effect on take‐off performance. These trends are:

THE increase in aeroplane speed, brought about by improved aerodynamic design and higher engine powers, together with the design restriction on airscrew tip speed resulting from efficiency considerations, has reacted on the airscrew performance during take‐off, and has made the take‐off more difficult.

THE problem of designing an aircraft so that the pilot is able easily to regain and maintain control following the sudden failure of an engine has been for some years a serious one. It is thought that an elementary description of the aerodynamics of the problem and of the flight tests which are made to assess a particular aircraft may be of interest. The equally important problem of ensuring adequate performance after an engine failure is not discussed here.

When comparing and contrasting different types of fixed-wing military aircraft on the basis of an energetic efficiency figure-of-merit, unmanned aerial vehicles (UAVs) dedicated to tactical medium-altitude long-endurance (MALE) operations appear to have significant potential when hybrid-electric propulsion and power systems (HEPPS) are implemented. Beginning with a baseline Eulair drone, this paper aims to examine the feasibility of retro-fitting with an Autarkic-Parallel-HEPPS architecture to enhance performance of the original single diesel engine.

In view of the low gravimetric specific energy performance attributes of batteries in the foreseeable future, the best approach was found to be one in which the Parallel-HEPPS architecture has the thermal engine augmented by an organic rankine cycle (ORC). For this study, with the outer mould lines fixed, the goal was to increase endurance without increasing the Eulair drone maximum take-off weight beyond an upper limit of +10%. The intent was to also retain take-off distance and climb performance or, where possible, improve upon these aspects. Therefore, as the focus of the work was on power scheduling, two primary control variables were identified as degree-of-hybridisation for useful power and cut-off altitude during the en route climb phase. Quasi-static methods were used for technical sub-space modelling, and these modules were linked into a constrained optimisation algorithm.

Results showed that an Autarkic-Parallel-HEPPS architecture comprising an ORC thermal energy recovery apparatus and high-end year-2020 battery, the endurance of the considered aircraft could be increased by 11%, i.e. a total of around 28 h, including de-icing system, in-flight recharge and emergency aircraft recovery capabilities. The same aircraft with the de-icing functionality removed resulted in a 20% increase in maximum endurance to 30 h.

Although the adoption of Series/Parallel-HEPPS only solutions do tend to generate questionable improvements in UAV operational performance, combinations of HEPPS with energy recovery machines that use, for example, an ORC, were found to have merit. Furthermore, such architectural solutions could also offer opportunity to facilitate additional functions like de-icing and emergency aircraft recovery during engine failure, which is either not available for UAVs today or prove to be prohibitive in terms of operational performance attributes when implemented using a conventional PPS approach.

This technical paper highlights a new degree of freedom in terms of power scheduling during climbing transversal flight operations. A control parameter of cut-off altitude for all types of HEPPS-based aircraft should be introduced into the technical decision-making/optimisation/analysis scheme and is seen to be a fundamental aspect when conducting trade-studies with respect to degree-of-hybridisation for useful power.

Rolls‐Royce Ltd. designs, develops and manufactures gas turbine engines for aircraft and marine industrial purposes and in 1971 the gas turbine business was reconstructed to continue independently of the motor car and other piston engine manufacture. The British Government is the sole shareholder, but the Company determines its own commercial policy.

The problem of supplying additional power to a helicopter rotor for take‐off or hovering under overload, hot‐day or altitude conditions is discussed briefly, and the boost system requirements are defined qualitatively. The Mirquardt Aircraft Co. is in process of developing a novel ram‐jet engine to meet these requirements under the sponsorship of the United States Air Force. The progress to date is reviewed, and the eventual application of this engine is discussed.

TO facilitate airscrew performance calculations an entirely new series of charts have been developed embodying wider use than hitherto of the term solidity ratio. These charts are applicable to airscrews with any number of blades. Whilst the number of blades is incorporated in the solidity ratio no further inclusion has been made of their tip speed effect on the interference velocity through the actuator disc. This effect has been investigated by Lock in conjunction with tip speed losses, but it was felt that its inclusion did not justify the added complication to the charts. In fact it makes their simple presentation impossible. The effect, however, can be incorporated with a correction factor to the power input to the airscrew. This factor is not dealt with in detail in this article and would form the subject‐matter of a separate work.

IN the mathematical treatment of the take‐off problem it was formerly difficult to define any general relationships for the airscrew thrust. This difficulty was avoided usually by assuming certain mean values, such as, for example, 1 • 1 to 12 kg/h.p. for the static thrust and by using this value in the calculation. This procedure is incorrect in that the airscrew thrust is assumed to be constant for a given output and so ceases to be suitable as a governing factor. As we have shown in a previous article, it is now possible to estimate the static thrust more accurately and by appropriate engine design the static thrust can be made to satisfy the necessary demands within wide limits [11]‡ This makes it possible to adopt new viewpoints in the treatment of the take‐off problem, which it is proposed to examine.

THE performance of civil aircraft having pure jet engines as opposed to turbine‐propeller engines will be considered since it is thought that for the latter the methods usually adopted for piston‐engined aircraft are on the whole applicable. It will be assumed that the performance of the jet engine (i.e. its thrust and fuel consumption at various r.p.m., forward speeds and altitudes) is given and that the aerodynamic properties of the aircraft in its various configurations are known.

SINCE 1945 discussion of international standards for the fundamentals of civil aviation has been going on in the divisions and council of I.C.A.O. A highly controversial part of the airworthiness and operational legislation has been the relatively small section dealing with performance requirements. A considerable amount of time and money has been spent in the study and development of these requirements, and it is opportune at this moment to review the way in which the work has progressed and its importance to civil operations for the future.