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A SIGNIFICANT NUMBER of the helicopters presently in the US Army inventory are inherently unstable and use pressurised hydraulic fluid in the hydromechanical flight control system. The development of a hydrofluidic stability‐augmentation system which can be integrated into the helicopter primary control system, offering promise of improved reliability, maintainability, and reduced cost over conventional electromechanical stability augmentation systems, has been accomplished.

The following classified, annotated list of titles is intended to provide reference librarians with a current checklist of new reference books, and is designed to supplement the RSR review column, “Recent Reference Books,” by Frances Neel Cheney. “Reference Books in Print” includes all additional books received prior to the inclusion deadline established for this issue. Appearance in this column does not preclude a later review in RSR. Publishers are urged to send a copy of all new reference books directly to RSR as soon as published, for immediate listing in “Reference Books in Print.” Reference books with imprints older than two years will not be included (with the exception of current reprints or older books newly acquired for distribution by another publisher). The column shall also occasionally include library science or other library related publications of other than a reference character.

This paper describes the typical maneuvering courses of helicopters with mathematics systematically and presents the formulas and approaches for calculating the dynamics characteristics. A set of generalized equations which govern the kinematics and dynamics of helicopters in maneuvering flight is given. Three aerobatic maneuvers for loop, roll and turn are specially analyzed in detail and the sample calculations are presented. The method established in this paper is of practical significance for aerobatic employment and design of helicopters.

DURING the past 40‐odd years or so, a number of experimental aeroplane types have been invented, visualized, designed, constructed and even flown which, in a quite unorthodox manner, had neither behind the wing nor in front of it any sort of stabilizing and/or controlling surfaces.

Monday, February 23, 1981. A British cargo flight crashed near Billerica, Massachusetts, after the aircraft took off with an accumulation of ice and snow on the airframe and then encountered moderate to severe icing conditions in flight.

Parallel hybrid electric (HE) propulsion retrofit is a promising alternative to reduce fuel burn of aircraft operating on short regional flights. However, if the batteries are depleted at the end of the mission, the hybrid powertrain designs with downsized gas turbines (GTs) and additional electric motors might not meet the one-engine inoperative (OEI) missed approach climb performance required by the certification. Alternatively, hybrid designs using the original full-size GT can perform one engine climb without electric assistance. This paper aims to evaluate the impact of overshoot climb requirements on powertrain design and performance comparing the two design approaches.

An aircraft-level parametric mission analysis model is used to evaluate aircraft performance combined with an optimization framework including multiple constraints. An indirect approach using metamodels is used to optimize powertrain sizing and operation strategy.

Considering OEI climb requirements, no benefits were found using a design with downsized GTs. Equivalent fuel burns were found for hybrid designs that keep the original size GTs, but do not require electric energy for the OEI overshoot at the end of the mission. Then, it is recommended to size the GT to maintain the emergency climb capabilities with no electric assistance to ensure power availability regardless of remaining battery energy.

This work introduces a new perspective on parallel HE sizing with consideration for the dependency of power capability at aircraft level on the electric energy availability in case of critical mission scenarios such as overshoot climb at the end of the mission.

THE study of the flight of birds has provided and will still provide much valuable information for tiie progress of human flight. Many suggestions for the improvements of wings by the use of special wing tips owe their existence to the observation of nature. In spite of such suggestions, free‐flight experimentation—as far as published work goes—is still rather rare and restricted in scope. This reluctance may be due to practical design considerations (handling) as well as to the necessity of making the conventional aileron as efficient as possible; it may also be caused by the impression that experiment in this direction is not worth the effort.

FROM the standpoint of the structural design of transport or “non‐acrobatic” aeroplanes, which never need be subjected to manoeuvres more severe than the very mild turns, etc., required to achieve a given destination, the “bumps” experienced in flying through “rough” air are of considerable importance, since they give rise to the structural loads for which the wings should be designed. In the past, practically no quantitative information on the structure of the atmosphere in its relations to applied loads on the aeroplane has existed. To supply this deficiency, the National Advisory Committee for Aeronautics is conducting an investigation of the accelerations obtained in flight through rough air on a number of transport aeroplanes flying regular scheduled trips. Only a small amount of information has been obtained to date. Enough has been accumulated, however, to throw considerable light on the subject of applied load factors in rough air. With the object of presenting this information this note has been prepared.

THE complexity of the problems which are associated with the lateral stability and directional control of tailless aeroplanes was not realized until rather late.