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In Detail —— the CF18 Hornet fighter ——

by Allan Ng M.Eng., P.Eng.

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Canadian Defence Procurement  –  November 2003 The CF18 Hornet fighter aircraft  –  In Detail    (Part 5) Allan Ng examines the development and modernization of the CF's fighter Some Words from the Professor  –  Thrust, Weight, and Why They Matter When engaged in classic air-to-air combat, fighter pilots must able to manoeuvre into an advantageous firing position. Victory in the dogfight is decided by being able to gain this position while avoiding giving opponents the same opportunity. This means that fighter aircraft must have both a good turning-performance and power margin to be victorious. High maximum speed generally does not come into play in air-to-air combat unless it can be reached quickly and sustained.[1]  Most air-to-air combat occurs at subsonic speeds. In fact there have been few recorded air-to-air combats above Mach 1, with none at all recorded above Mach 1.6. Turn-performance is the ability to manoeuvre quickly from one flight direction to another. While a fighter's turn-performance is dependent on a number of factors, for most comparative analysis it suffices to say that turn-performance is inversely proportional to the wing loading ratio (wing loading being the total aircraft weight divided by the wing area). The lower the weight per unit of wing area, the better a turn-performance a fighter will have. Naturally, this value changes throughout the flight as the fuel burns away and the aircraft carries less weight. Power margin through engine thrust gives the aircraft the energy to complete its manoeuvres, to climb, and accelerate. A high power margin also helps to quickly replace energy lost during aggressive manoeuvering.  A fighter's power margin can be assessed as being proportional to the thrust-to-weight ratio – ie: the total weight of the aircraft divided by the thrust of its engines. (Now, aren't we glad we stuck with pounds instead of Newtons and kilograms?) The higher the thrust-to- weight ratio, the better the power margin. When an aircraft is in a flight condition where its thrust-to-weight ratio is greater than 1, the aircraft can overcome gravity – literally standing on its tail and climbing like a rocket. Obviously, any thrust-to- weight ratios above parity denote very high power margins indeed! In the case of the CF18, with its take-off weight of 35,800 lbs and wing area of 400 square feet, we get a wing loading of 90 lbs per square foot.  The CF18's military thrust of 21,600 lbs (2 x 10,800 lbs) and afterburning thrust of 32,000 lbs (2 x 16,000 lbs) gives thrust-to-weight ratios of 0.60 and 0.89 respectively. As a rule, a margin of about 10% in wing loading and/or thrust-to-weight ratio is required before any fighter pilot can exploit the inferior characteristics of an opponent's aircraft. Compare CF18 wing loadings and thrust-to-weight ratios with those of selected fighter aircraft in the table below.  As can be seen, the CF18 and F-16C are very evenly matched and both of these aircraft significantly outclass fighters that are still in service from the 1960s. Not until the Soviet Union introduced the MiG-29 in 1977 did the eastern block began to catch up in fighter capability once again. Aircraft Type   Take-Off Weight lbs Wing Loading lbs/ft sq Thrust-to -Weight Military Thrust-to -Weight Afterburn First Flight Year CF105 68,602 56 0.56 0.76 1958 CF18A 35,800 90 0.60 0.89 1978 F-16C 26,536 88 0.57 0.94 1974 Mirage F1 25,530 94 0.44 0.63 1966 MiG-23 38,000 117 0.46 0.67 1967 MiG-29 35,000 88 0.64 1.05 1977