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I've noticed most aircraft are as long as they are wide from nose to tail and from wing tip to wingtip, particularly private jets despite recent swept wing technology. You can almost draw a perfect circle with a compass if you could find the centre. Is it for aesthetic purposes, principles of flight aerodynamics or any other reason. Please explain

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    $\begingroup$ Perhaps you are just looking at a too-limited set of aircraft? E.g. sailplanes and cargo planes like the C-130 have a much longer wingspan than length; many jet fighters (the F-104 being the classic example) have wingspan shorter than length. $\endgroup$ – jamesqf Nov 21 '17 at 19:15
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    $\begingroup$ Swept wing technology is recent? Maybe in the late 1930s it was, being publicly unveiled at the 1935 Volta congress in Rome, but certainly not since maybe the last 60 years. $\endgroup$ – Peter Kämpf Nov 21 '17 at 22:39
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By curious coincidence it is simply what the optimal aspect ratio for speeds around 250–280 knots indicated results in. Aircraft designed for different cruise speeds have different ratios.

The wing span is governed by desired cruise speed. There are two main forms of drag—induced and parasite. Induced drag decreases with wing span and with speed, while parasite drag increases with them. So at lower speed, you need long wings to keep the induced drag at bay, while parasite drag is low simply because of the low speed. And at higher speed, you need shorter wings to avoid too much parasite drag.

Jet aircraft are most efficient at transsonic speeds (Mach number 0.75–0.85) and altitudes around 10-12 km (33,000–40,000 ft) and it so happens that the wing span and cabin length to contain corresponding payload are similar. Turboprop aircraft are most efficient at somewhat lower speeds and altitudes and consequently their wings are a bit longer. And yet slower piston-powered aircraft have even longer wings relatively to fuselage.

(update, as suggested in comments): The extremes are on one side gliders that achieve low drag by having very long slender wings and flying slow and on the other side supersonic aircraft that have short wings with long chord to keep the frontal cross-section low, the very extreme being the very fastest aircraft like X-15 or SR-71.

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    $\begingroup$ You could add a glider and the F-104 as examples for the extremes. Airliners are in between. $\endgroup$ – Peter Kämpf Nov 21 '17 at 22:38
  • $\begingroup$ @PeterKämpf, it's strange why F-104 in particular has such short wings when it's not all that fast, just ~M2.0. Other M2 jets have still quite a bit bigger wings. $\endgroup$ – Jan Hudec Nov 22 '17 at 7:55
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    $\begingroup$ @JanHudec The F-104 was, for a time, the fastest plane in the world, so part of the explanation may be "first attempt to build something that fast." Even today, the F-15 is the only USAF plane that's faster (in terms of air speed, rather than mach number). Also, as an interceptor, its primary mission was presumably to fly at maximum speed, whereas the F-15 is also required to do other things. $\endgroup$ – David Richerby Nov 22 '17 at 10:57
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    $\begingroup$ One extreme in sailplane extremity could be SB-13 flying wing, span 15m length 3m $\endgroup$ – qq jkztd Nov 22 '17 at 13:20
  • $\begingroup$ @qqjkztd: Hey, the fuselage alone is 3.05 m long. And then the winglets reach a little further back. See here for proof. $\endgroup$ – Peter Kämpf Nov 22 '17 at 17:38

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