Operating Efficiency of Military Jet Transports

Currently there is great emphasis on achieving efficient and optimised flight and operations. The planned budgets and future constraints may reflect this. The need for overall energy savings is being felt in all spheres of defence and commercial aviation. The military scene includes many types of aircraft fulfilling diverse roles during training and in action. An appreciation of Efficiency parameters leads to the consideration of speed (V), lift-drag ratio (L/D) and engine efficiency (SFC) with Range (R). A range parameter X = V L/D/SFC follows. Operational aspects e.g. Air to Air Refuelling (AAR) and Close Formation Flying (CFF) also contribute. Interplaying all these leads to new designs or morphing technologies for flight optimisation. We can think in terms of sub-systems or in a more global sense, incorporating several technologies optimally. We consider here the efficiency aspects of heavy-lift, military jet transports. Currently, there are only a few types in service and limited consistent data is on weight fractions available. Consistent data-sets on Russian aircraft are rare. We use the various weight fractions and payload range for the dimensional / non-dimensional parameters. Efficiency trends, established for civil passenger aircraft and later expanded to include civil freighter aircraft, have been described. These provide the background, a foundation and nature of comparative aspects for building a quantitative assessment of the military jet transports (even with data limitations). The non-dimensional parameters introduced (e.g. PRE/X and Z = R/X) allow use of data from current and older types and implied technology levels, with relative ease. This is an important feature of the work. Several similarities are noted in the weight ratios for the military transports and freighters. However, a surprising notable trend was that military transports use less Thrust to Weight ratio for “normal” 2.5 g flights.