Easy mental math question

[captdini 3]

Hi to all,

According to me, to be more precise, at the inital question was to be added "in ISA condition" because if you wasn't in isa (i.e. temperature 15 C at sea level your result could be different...)

anyway here it's another question if I'm travelling at Mach 0,78 and my TAS is 448 kts which is my outside air temperature?

Best Regards

 

Andrea Buono

 

Hi Andrea,

 

Since the ISA deviation is given, it is implied that the current OAT has deviated (+ or -) for the ISA temperature at that level. Therefore, there is no need to mention in ISA conditions, it is implied.

 

You have put a very interesting question. My ball park figure is around -57C ??

 

Reversing the same formula as you have asked above, calculate the Mach number from the photo above ?

 

Regards,

 

Dinshaw Parakh.

[killkenny1 22]

Underwater, FL-180

 

I wanted to say something above FL300, and then remember NGX tutorial 2 .

[Andrea1 6]

Hi Dinshaw, yes, you're right in my quiz SAT=-56 °C, you know sound speed is about 661,09 kts at msl isa (15°C=288 kelvin degrees) and decreasing according to the square root of temperature ratio so being -56°= 217 kelvin at that temp sound speed= 661,09*square root(217/288)=573,84 kts and Mach 0,78= 0,78*573,84= 447,6 kts, rounded at 448..Q.E.D., your question, from your pic SAT =-39 C =234 K, your TAS= 460 kts, sound speed= 661,09*sqrt (234/288)=595,90 kts, 460/595,9=(about) 0,77 Mach

 

Ciao

Andrea Buono

Como - I