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Aviation History
1979
1979 - 0020.PDF
internal fuel capacity, while some are even shy of pub lishing engine thrus.t. This article will concentrate on thrust/weight ratio and wing loading. In every case the Flight sliderule has been used to calculate a typical com bat weight. This assumes 50 per cent internal fuel and a 5001b allowance for each crew member, his oxygen supply and any other expendables such as gua ammunition. Two or four external missiles have been assumed as combat armament, depending on the size of the aircraft. Where official figures are not available, Flight estimates have been substituted. Wing loading continued to rise throughout the 1950s and 1960s. This trend has now been reversed*; as can be seen in our diagram, although none of the aircraft quite match the modest wing loading of the F-86, shown here for com parison (see graph on page 24). T/W ratio is important, but enough fuel must be avail able to feed the ever-hungry afterburners. There is little point in a superb T/W ratio if the clockwork runs out of gas after a few minutes of afterburning flight. On a typical first-generation Mach 2 fighter—the F-4E or MiG-21, for example—the engine(s) can swallow be tween 2-5-3 per cent of the internal fufj every minute when maximum dry thrust is demanded, ifhis figure rises to around 9 or 10 per cent if maximum afterburning thrust is required. On the Mirage F.1C maximum afterburning thrust accounts for only around 7 per cent of internal fuel per minute, though this is reflected in a lower T/W ratio. The pilot, most nervous of using his afterburner is prob ably the F-15 driver. His twin F100 engines swallow around 15 per cent of the internal fuel each m&HTte, compared with only just over three per cent at maximum dry thrust. This is not as alarming as it seems, since an F-15 at maxi mum dry thrust has the same T/W ratio as a Mirage F.1C at full afterburner. If an Eagle were to indulge in a maxi mum dry thrust race against a Phantom, the pilot of the latter would be left wondering how soon he could trade in his badly outclassed F-4. We have adopted fuel fraction as a measure of fuel cap acity. It is defined as "weight of internal fuel divided by empty weight + internal fuel weight". In most cases the value is around 0 • 3. Wing loading and thrust/weight ratio W'aye both been calculated on the basis of our estimated eombat weights so that the different aircraft can be realistically compared. The values obtained are also more realistic than take-off figures for combat conditions. Details such as dimensions, performance and powerplant data have been omitted to make room for information on the radar, electronic countermeasures and other avionic systems. The normal run-of-the-mill data may be obtained from Flight's annual Military Aircraft Survey or any other standard reference work. Though any fighter can carry pod-mounted jammers, this ties up valuable pylon space which could be used for weaponry; All countermeasures equipment listed in our table is internally mounted and creates no drag penalty. Items marked with an asterisk are optional. Bargain-basement fighters IF CASH is in short supply and all potential opponents operate relatively unsophisticated subsonic types such as the MiG-17 or Hunter, the Hindustan Aeronautics Ajeet wet-wing version of the Gnat could be a useful and in expensive air-superiority fighter. A low-cost supersonic alternative would be the Shenyang F-6. This MiG-19 copy seems to be well built and adequate in performance. Some Pakistani Air Force pilots prefer it to the Mirage III or F-104. The only problem, apart from the possibility that spares will arrive on the legendary slow boat from China, is that the type is not over-burdened with internal fuel. Supersonic performance is achieved largely by the brute force of a high T/W ratio. Unless funds are short, the Northrop F-5E or Mikoyan MiG-21 Fishbed would be a better bet. The MiG-2l may be faster, but the F-5E suggests that capitalists make better aircraft. The US type has more internal fuel and the gauge unwinds less rapidly than in the Soviet machine. FLIGHT Internationa/, 6 January 1979 Aerodynamic devices can improve the performance of older designs. Top Leading-edge slats on the F-4E. Above Canards on the Kfir-CZ Even the avowedly neutral Swiss were won over by the qualities of Northrop's widely exported Tiger II Early MiG-21s looked as if they had been built by black smiths rather tfifan aerospace engineers, though the quality of Soviet aircraft has greatly improved over the last decade. If Mach 2 performance is a must, there can be little to choose between the Qassault-Breguet Mirage 50 and the Israel Aircraft Industries Kfir. This is hardly surprising, considering the origin of the Kfir, which is available in two versions (with or without canards) and has a useful T/W edge over the Mirage IIIC. The Mirage 50 is however a leaner animal with a more powerful Atar 9K50 power- plant in place of the earlier 9C.
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