What should be the ratio of the fuselage and wings in a maximum dimension limited condition supersonic delta wing aircraft? Also can anybody explain clearly the "supersonic area rule" or "Whitcomb area rule"? Is there anything else I need to take care of while designing a fuselage for supersonic conditions? Thanks.
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asked Jun 16, 2014 at 9:41
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5$\begingroup$ you could start by taking some lessons in aerodynamics and fluid dynamics. $\endgroup$– jwentingCommented Jun 16, 2014 at 12:27
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$\begingroup$ Way above my pay grade, but a short answer is that if you plot the length of the aircraft on the x-axis and its cross sectional area on the y-axis, you want that curve to be as smooth as possible. If it isn't, you're going to have a large drag rise during transonic flight. So, if, say, as was true with the first F-102, you got a sudden increase in cross sectional area at the point of the fuselage and wing juncture, you could fix it (and they did) by narrowing the fuselage at the point to produce the now familiar "coke bottle" shape, which avoided that large drag rise. $\endgroup$– TerryCommented Jun 16, 2014 at 13:39
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1$\begingroup$ Gaurang, you seriously cannot expect to rock up to some internet forum and find out everything you need to know to design supersonic planes. Very probably, nobody here has that kind of knowledge. Even if they did, it's the sort of thing you'd need to write a whole book to explain, if not a series of books. Nobody is going to invest that kind of time. $\endgroup$– David RicherbyCommented Jun 16, 2014 at 15:39
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$\begingroup$ @DavidRicherby Also, this is not a forum. $\endgroup$– FedericoCommented Jun 16, 2014 at 15:40
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$\begingroup$ A continuation of my previous comment: As I remember it, the area rule was necessary in an era of engines with insufficient power to overcome the transonic drag rise without it and then push aircraft through the transonic range. It's not necessary and not used today with our much more powerful engines. $\endgroup$– TerryCommented Jun 16, 2014 at 16:12
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1 Answer
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There is no ideal ratio. Make the wing as big as it needs to be for your take-off run, your cruising altitude or your approach speed, whatever demands the biggest wing, and make the fuselage just big enough to hold the pilot(s) and all equipment, payload, fuel and whatever you choose to carry around. Asking for a specific ratio without any details on the mission or the design parameters is silly.
The comments tell me I should say something about area ruling, though. Terry correctly mentions the x-wise gradient of the aircraft's cross section, but this is only helpful at Mach 1. At higher speeds, you need to look at the area which is covered by Mach cones which run along the longitudinal axis. Sum up the area of the intersection between those Mach cones and your aircraft's structure, and make the lengthwise distribution follow a Sears-Haack-body. Please note that the inclination of those Mach cones varies with angle of attack, so there is not a single optimum shape, but only a best compromise for all expected flight conditions.
Area ruling is only helpful around Mach 1, but there (or slightly above) is the transsonic drag maximum, and area ruling helps to get across this quickly, even with the high thrust of modern engines. If your task is to get to this strange radar blip at 16 km altitude in a hurry, every second counts. Also, modern airliners need to employ area ruling techniques to make cruise Mach numbers above Mach 0.8 economical.
And this is just scratching the surface ...
answered Jun 16, 2014 at 22:19
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2$\begingroup$ Am sorry for the question.Should have broken it into multiple specific questions.Thanks for the answers though. $\endgroup$ Commented Jun 17, 2014 at 8:17