1720. Operating Costs of Transport Airplanes, Influence of the Wing Aspect Ratio and Flight Conditions

Paper

Abstract

This paper can be regarded as an obvious consequence of two others presented by the same authors to the 43rd and 44th International S.A.W.E. Conferences. Those papers defined the wing aspect ratio values, for optimizing the payload and the fuel consumption, for transport propeller and jet airplanes. It is evident that both parameters (payload and fuel consumption) influence directly the dire6t operating costs (D.O.C.). In fact the more useful and significant way to define this kind of costs is to refer the different items to the payload-unit and to the distance traveled. We followed this way too, and so the payload appears in the denominator term of each cost, while the fuel consumption is only one of the items of the direct operating costs. Therefore the optimum wing aspect ratio will have – in the case of minimum D.O.C. – an intermediate value among those defining, for a certain kind of airplane utilized on a certain range, the maximum payload or the minimum fuel consumption values. It is clear the advantage of defining – already in the conceptual design phase – the geometrical configuration of the airplane and, particularly, an essential component like the wing aspect ratio, without the use of a complex calculation program. But this work intends to define a suitable criterion also for the utilizer, that must choose, among many airplanes available, the more qualified to fulfill the following service requirements: carried payload and traveled distance. A great part of the paper preparation consisted of getting ready a computer program: the geometrical data peculiar of the airplane class (maximum weight, wing area and available thrust) were the inputs; it furnishes the direct operating costs as a function of the wing aspect ratio. In fact this one influences the airplane weight and the induced drag of the wing and therefore alters not only the fuel consumptions, but the percentage of the total weight due to the payload too, as well as all the items forming the direct operating costs. Examples of the results obtained are presented in diagrams, in parametric form – as in the two past papers – in order to make evident: 1) the mutual influence of the quantities involved in the problem, 2) their way of varying, 3) the easy singling out of the optimum values. In the paper presented it has been considered the case of jet airplanes. This is the most general case, because the variable height appears. However it is evident that – with small changes in the computer program – the method can be applied also to the propeller airplanes.