Which speed should be used in calculating the mach number?
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Mach, KEAS, Altitude Relationship
The selection of values for any two of the Mach, KEAS, or altitude variables automatically defines the value of the third, regardless of ambient temperature. For instance, if cruise is scheduled for Mach 3 and the desired initial cruise altitude is 72,000 feet, the KEAS must be 396 knots.
Both crew members of the SR-71 carried a chart of the relationships in order to check their displays.
Both crew members of the SR-71 carried a chart of the relationships in order to check their displays.
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The selection of values for any two of the Mach, KEAS, or altitude variables automatically defines the value of the third, regardless of ambient temperature. For instance, if cruise is scheduled for Mach 3 and the desired initial cruise altitude is 72,000 feet, the KEAS must be 396 knots.
Both crew members of the SR-71 carried a chart of the relationships in order to check their displays.
Both crew members of the SR-71 carried a chart of the relationships in order to check their displays.
Does the temp increase slightly here? . . yes it does(I just checked again)
It is not -129 degrees C though is it . . ? Or the TAS would be 5,607 kts.
I noticed that the . . . Blackbird,? has an Indicated airspeed of some 129 knots - very low, at a height which gave a nice view of the curvature of the Earth - say - 70/80,000feet.
So - if your 72,000 equals about 21 kilometres high then the temp at that altitude would be -56.6 deg C, with a slight increase starting up towards the top of the stratosphere, so we can safely calculate -56.6 as a constant
This then would give you 572kts LSS which should be about 1718 kts at mach 3. TAS.
So bearing in mind what someone posted about a few posts ago - then the spread (between TAS and EAS) could = what you put, but I would need a whizz wheel and I did not bring it so I am the most boring person in the world.
but, but, the True AirSpeed is however 1718 knots - howzthat, ok?
This sounds feasible as 4,000 kts has been done in a blackbird, or am I wrong and that was MPH with a tailwind groundspeed?
You know what? If there are any blackbird pilots out there _ would very much like to come up and do a reading or three.
Last edited by Natstrackalpha; 1st Jul 2013 at 17:30.
