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I am trying to work out the formula used for this graph, I don't really know where to start, does anyone have any suggestions? Its a bit unclear, its showing FAT, Mach No, CIT, FWD B/P Position.

Link to graph

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are you trying to justify a formula for that page that is given somewhere else? Or are you trying to come up with a formula out of the blue? Are you trying to fit a set of points on that page loosely (where you formula just has to get close to your points, using regression) or exactly (where the function goes exactly through each given point)? – Mitch Feb 10 '11 at 15:01
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First you need to figure out what are the inputs and what are the outputs. For the top graph, I would guess Mach No and FAT (is that some air temperature?) are the inputs and B/P positions and CIT are the outputs-you find a point in the center grid and read off horizontally and vertically. This looks like a reference for flight-you look up the flight conditions and it tells you how to set the aircraft controls. Collect a bunch of data by reading off points-for example at the intersections of the grid. Each point should be (Mach, FAT, B/P position, CIT). Then look at the curves and guess a functional form. You might even want to replot the data as two graphs with Mach and FAT on the axes and each of the other parameters as z and look at what it looks like. Finally feed your form to a multidimensional fitting routine to find the parameters and see how good the fit is. If you're not happy, try another form until you are.

If this sounds non-rigorous, that's because it is.

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You could try plotting each of the paths as a separate graph and work out the formulas for each one, then try working out a formula that links the separate graphs together.

Or read all the data off and break it down into a spreadsheet so the data can be analyzed more easily. Then you can re-plot the data in different ways and see how that works out.

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