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Guest Wags94

Cruise speed and TAS!

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Is there a specific equation to get your TAS? This whole cruise speeds and TAS is kicking my a$$, I don't know how to get my correct cruise speed.In the FSX glossary, it says that airspeed increases 2% for about every 1000 feet. The example given is: an aircraft is flying at 100 kts, at 10,000 feet, so its TAS is 120 kts. So, lets say I'm cruising at FL350, what should my indicated airspeed be to fly at the correct true airspeed?

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True, but these formulars probably won't help you much for you won't usually know all the variables involved. Furthermore, your 2%-rule-of-thumb only works well for lower altitudes AFAIK. To go from IAS to TAS you'd have to follow these steps: IAS + position/instrument error = CAS + compressibility = EAS + density = TAS. You could also use a mechanical calculator like Aristo Aviat or some electronic version, e. g. from Jeppesen. Or one of the online tools, see link above. :(

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True, but these formulars probably won't help you much for you won't usually know all the variables involved. Furthermore, your 2%-rule-of-thumb only works well for lower altitudes AFAIK. To go from IAS to TAS you'd have to follow these steps: IAS + position/instrument error = CAS + compressibility = EAS + density = TAS. You could also use a mechanical calculator like Aristo Aviat or some electronic version, e. g. from Jeppesen. Or one of the online tools, see link above. :(
How do I get the position/instrument error, the compressibility, and the density (density of the air, correct?)?

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How do I get the position/instrument error, the compressibility, and the density (density of the air, correct?)?
It does not have to be that complicated. You can get a reasonably close answer considering corrections for only pressure altitude and temperature, so long as you are not flying high speeds at high altitudes. The link you were given at NewByte works for those two corrections, and if you can't work online, you can use an E6B computer, one side of which is a circular slide rule with scales specific to aviation calculations. When I was flying Flight Sim 2, I got the celluloid version of for about $5; if only I could remember the "safe place" where I put it, during my flight sim hiatus. In some aircraft, there is a TAS scale on the air speed indicator (same as E6B. you match temperature to pressure altitude, then IAS and TAS line up).There is a computer version of the E6B that operates as a gauge within FS9. I found it in a package for Amelia Earhart's L10E model, but I think it is more generally available to be installed in any aircraft model.

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It does not have to be that complicated.
Of course not, as stated before there are very good approximations available. :(

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Rule of squares.5000 = 3^210000 = 4^215000 = 5^2...40000 = 10^2So TAS at 15000 for an IAS/CAS of 250kts would be about 310ktsTAS at 35000 for an CAS of 250kts would be around 450ktsJust work it backwards so 450/1.81 would be around 250kts :)

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So, lets say I'm cruising at FL350, what should my indicated airspeed be to fly at the correct true airspeed?
Above FL260, airspeed is generally referred to in Mach numbers. That is, a percentage of Mach (0.60, 0.80, 1.20, etc.). The 2% rule works in lower altitudes and speeds because of many factors like compressability of the air.IAS (indicated air speed) is the speed your instruments say your are flying. True Air Speed is higher beacause at altitude there are less molecules of air entering your pitot tube and therefore the ASI will read lower than you are actually flying. As you approach Mach 1, the air is compressed by the relative motion of your aircraft so that lends even more error to the mix.JoeM

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