I know that one knot is 1.15mph(that could be wrong). Dose anyone know how to covert mach in to knots or what ever.

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Quoting Lastordu (Thread starter):Dose anyone know how to covert mach in to knots or what ever. |

Mach refers to the speed of sound, the speed of sound depends on air density and so varies with altitude. I'm sure someone can put this down a lot better though

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First you need to calculate the speed of sound, a. This is proportional to ambient temperature (OAT):

a = SQRT( OAT * 287 * 1.4) m/s (where OAT is in deg K)

Convert this speed into whatever units your true airspeed is in (mph, knots, etc.). Note this must be true airspeed, not indicated.

Mach number = TAS/a

BTW 1.15 is close enough for practical purposes to convert mph to knots.

a = SQRT( OAT * 287 * 1.4) m/s (where OAT is in deg K)

Convert this speed into whatever units your true airspeed is in (mph, knots, etc.). Note this must be true airspeed, not indicated.

Mach number = TAS/a

BTW 1.15 is close enough for practical purposes to convert mph to knots.

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There is a much simpler way, valid for subsonic aircraft, that I still use to check my instruments, as it is easily done mentally.

To get a true airspeed (in knots) from a mach number, take as basis a temperature of -35 degrees celsius.At that temperature, the airspeed is*exactly* equal to the Mach number x 600. Then add or substract 1 kt per degree, rerspectively above or below your -35° basis.

As our mach reading are presented with three digits after the decimal, I just multiply that figure by .6.

Example :Mach .845 and OAT -45° c.

.845 x.6 = 507 kts, from which I substract 10 kts, as -45° c is ten degrees colder than my -35° c basis.

Result : TAS = 497 kts.

It's surprisingly accurate.

To get a true airspeed (in knots) from a mach number, take as basis a temperature of -35 degrees celsius.At that temperature, the airspeed is

As our mach reading are presented with three digits after the decimal, I just multiply that figure by .6.

Example :Mach .845 and OAT -45° c.

.845 x.6 = 507 kts, from which I substract 10 kts, as -45° c is ten degrees colder than my -35° c basis.

Result : TAS = 497 kts.

It's surprisingly accurate.

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