# v speeds for Rob

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Rob,I know there is a rule of thumb how to calculate V1, Vr and V2, but forgotten and Google didn't give much help.You use these factors in your vspeed gauge: - L:VSPEED_V1: 114 + 36/35273 * ("total weight in pound" - 61729) knots IAS.That is for the Fokker.I have the V speeds of the 767-300 and total / empty weight.What does mean the factors:1. 36/352732. .....weight - 61729Are they universal?I couldn't find these numbers in the fokker weight/balance section of the aircraft.cfg.Jan"Beatus Ille Procul Negotiis"

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Hi Jan,No, there are no rules of thumb; it's completely aircraft dependant.If you look at an aircraft manual (like the Fokker100, or the 767) you will find tables that specify the Vspeeds depending on weight and flaps setting. Now if you look closely to those tables, there is a more or less linear relation between weight and a Vspeed. And that is what the formula is.Eg. from a 767-300 performance manual (Pw4060 engines)At Flaps-5:- Max.specified T.O.weight in table: 400000 lbs, V1=161 knots|||- Min specified T.O. weight in table: 240000 lbs, V1=114 knotsSo lineair interpolation of these two table extremes gives the formula:V1 = 114 + (161 - 114)/(400000-240000) * (actual weight-2400000)Now if you check the table-value for V1 for each specified weight, against the result of the formula, you'll see it's fairly accurate (within one or two knots).In other words: the formula is just a lineair approximation of the long Flaps-Weight-Vspeed table.Hence you need a formula for each allowed takeoff flapssetting.Same for Temp and Alt. corrections; usually the specified graphs can be approximated by simple, lineair formula's - Like: add 0.2 knots to V1 for each degree above 30 degrees C.- Or: add 0.1 knots to V1 for each 1000 ft above 2000ft PressureAltitude.See :-) ??Cheers, Rob

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Rob,Thanks!I was testing the gauge, but never heard anything, probably caused by the already named variables.I have all performance charts, so now, with more understanding, i can make the formula and use it also to set the speed bugs automatically.Jan"Beatus Ille Procul Negotiis"

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