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# How many miles per hour is Mach .80?

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The Mach Number is defined as the speed of an object relative to a fluid medium - for instance air - divided by the speed of sound in that medium. It is a measure of relative speed and is named after the Austrian physicist Ernest Mach

It is often associated with the speed of sound and if an airplane is traveling at Mach 1 it is traveling at the speed of sound relative to the air.

The Mach number is not constant and changes depending on the temperature.

The formula used to calculate the Mach number depends on whether the object is traveling subsonic (M<1) or supersonic (M>1).

In fact at M = 0.8 we are talking about the transonic region. For transonic, compressibility effects and air density varies because of local shock waves and other effects. This is mainly because in this region some of the airflow across the aerodynamic surfaces can be supersonic (M>1).

In fact the equations are complex. To answer the question, I have used a on-line calculator supplied by NASA - see link below.

So to answer the question we can just take an example. An aircraft traveling at Mach 0.8 at 36,000ft is traveling at 529 mph, and at sea level it would be traveling at 610 mph.

So to give a complete answer to your question you need to supply more information - more specifically the height - as you can see from the answers at differing heights it can vary a lot.

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• Mach Miles Per Hour

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• Mach 1 is the speed of sound which is 760 mph

.80 mach would be 760 x .8 = 608 mph

The trick is to know or know how to find the speed of sound and know that the speed of sound equals mach 1.

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• The answer to your question is more complicated than you probably suspect (see link below). The speed depends on several variables, including the medium involved, the ambient temperature, etc.

Although, if you meant to ask, "What subsonic speed is an aircraft flying at Mach 0.8?"

In that case, simply solve the following equation for 's':

M = s / (speed of sound)

0.8 = s / 760 MPH

s = 608 MPH

(See second link below for specifics of this calculation.)

Hope this helps!

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