mach number

[Pat Mussotte 92]

@Scott:

    Indicated Mach is indeed corrected in that it relates to TAS rather than IAS, but is still subject to instrument and measurement errors.  In particular, the placement of the pitot/static probes with relation to the airflow over the fuselage and the formation of shockwaves can have a significant effect on  pressure measurements.  Indeed, the same is true for IAS and TAS, which are both "indicated" values in the sense that "they are what the indicator says they are".  The "true" values are called "calibrated" values, and are used in the design phase and carefully measured during flight test, but are not used in normal operations.

Exactly!

[albar965 1,043]

Thanks, guys. Very valuable information here.

 

I played a bit around and added the mach calculation similar to the online calculator. See below for test output.

The resulting mach number is the same as the one from FS. Also the other values match the results from the Aviation Calculator, give or take a knot.

 

So it seems that ISA deviation is considered.

 

Now where is this .572 mach number coming from?

Looks like Mustang does *not* apply a temperature correction while FS does.

 

Or did I miss anything?

 

Alex

 

Altitude

Indicated:

31.999 ft

Actual:

31.598 ft

Above Ground:

30.963 ft

Ground Elevation:

635 ft

Speed

Indicated:

211 kts <<<<< Aviation calculator: 209.816 kts CAS

Ground:

312 kts

True Airspeed:

336 kts

Mach:

0,586 <<<<< Simulator value (Aviation calculator: 0.58594)

Mach (corrected):

0,586 <<<<< Calculated value based on SAT, ISA deviation and TAS

Vertical:

0 fpm

Environment

Wind Direction and Speed:

283°M, 25 kts

 

25 kts▼

Total Air Temperature:

-41°C, -42°F

Static Air Temperature:

-56°C, -69°F

ISA Deviation:

-9°C,

Sea Level Pressure:

1.000 hPa, 29,52 inHg

Conditions:

None

Visibility:

> 20 nm

[lzamm 143]

 

 

Also I was using no weather just clear skies

 

That puts paid to my theory that the ISA deviation is the cause

 

Alex, now that I'm home I've also run some trials in FSX and confirm that the TAS-Mach relation is spot on, at various temperatures.  There are some differences in the IAS, which may be responsible for the conflicting results, but I can't see it at the moment.

 

ISA

ISA-8

[awash2002 12]

Cool

[albar965 1,043]

Did some tests too yesterday in the Milviz 737-200 which even has an accurate analog mach display. I can confirm what you see. Mach matches (own calculation and sim value) and IAS/CAS are a few knots off. Nothing spectacular.

 

I assume that CAS is equal to IAS for the flight simulator.

 

I also didn't notice the comment with the default weather. :smile:

 

awash2002:

You can add a separate gauge showing the mach number in the Mustang and compare the values, if you're interested. Or you can ask in the Flight1 forum what they are doing there.

Maybe they are tweaking their mach number to get closer to the real values. In that case I'd rather call that a service instead of a bug. :smile:

 

Alex

[awash2002 12]

Cool I have had it as fast as .60 mach which believe it or not where I like to cruise at right up near the barber poll