Angels and Demons

[kmox]

Near the start of the book our hero is flying at Mach 15 at 60,000 ft, can someone please tell me what the speed over the ground would be.

[Runaround Valve]

Mach 15 is equal to.......

11121.82 miles per hour

17898.84 kilometres per hour

9664.6 knots.

[kmox]

Thanks Runaround Valve
They are an argumentative lot, possible to tell me how you calculated the answer?

[Runaround Valve]

I found a converter program on the internet. It is Freeware. Go to the Google website and put in Joshua F Madison Convert and you will then find and download the program. It has 17 different items, Force, Light, Mass, Speed, Power are some of what is there.
A very nifty program that I recommend you to try.
I hope that this is not advertising that upsets the Moderator. !!!

[kmox]

Your answer is very close to one already suggested, is Mach 15 at 60,000 ft a different ground speed than Mach 15 at sea level?

[rubik101]

Same Mach Number, cold air, slower G/S, warm air, faster G/S. So it follows that at sea level you will have more bangs for your bucks!

[kmox]

Rubik101
Question is, in ISA conditions at 60,000 ft at Mach 15 what would be your ground speed in knots ?

[727gm]

Mach 15 is equal to.......

11121.82 miles per hour

17898.84 kilometres per hour

9664.6 knots.


What the speed over the ground would be:

9964.6 knots gs + or - the wind @60000ft

[mutt]

mach 15 at 60000 feet - Wolfram|Alpha (http://www58.wolframalpha.com/input/?i=mach+15+at+60000+feet)

Gives the answer as 8614 kts

and 9990 kts at Sea Level...

Mutt

[Fark'n'ell]

Formula for speed of sound is

39 x square root of temp in degrees kelvin.

[Will Fraser]

Doesn't his rate over the ground decrease as his distance from it (altitude) increases
at a given velocity?

[Basil]

My Computer Dead Reckoning MK. 4A. by The London Name Plate Mfg. Co. Ltd.
using a cor. OAT of -56.5 and M15 gives 8560kn.
First time it's been used >M1.0 - poor thing looks quite worn out.
Correcting for radial change at 60000' gives 8535kn over the ground in still air.

Anyhoo, at M15 with a DT of about 9650C, speed would be the least of his problems.

[Torque2]

Plus or minus the rotational speed of the earth at the given latitude.

I think a ballpark figure is required here, too many variables to supply. :hmm:

[Genghis the Engineer]

Indicated, calibrated and equivalent airspeed are irrelevant here, we can convert directly from mach number to true airspeed.

The standard formula for the speed of sound is SQRT (Gamma x R x T)

Gamma for a diatomic gas such as air pretty much is, is 1.4

R, specific (something or other) for air, is normally quoted at 287 J/kg.K [sorry, I'm doing this from memory, I can remember the values but not the full name of the constant.]

T is in this instance fairly easy, it's the air temperature. Whilst layers vary a bit with conditions, you can reasonably assume that the aircraft(!) is in the lower stratosphere, which ISA quotes as a constant temperature layer at -54deg.C - 219.15K.


So SQRT (1.4 x 287 x 219) = 297 m/s

At Mach 15 then, this gives you 297 x 15 = 4,450 m/s

To convert m/s to knots: 1 m/s = 1.94kn.

So, Mach 15 in the lower stratosphere is 8,632 knots TAS (True Air Speed).


Well into the lower statosphere, you're well above most winds, which tend to exist primarily in the troposphere, and even the jetstream which sits around the tropopause (typically 30-50,000ft) so by and large TAS = G/S.


So, M=15 @ FL600 gives you about 8,632 kn (or 9,944 mph).

G

(Currently writing a chapter of a book on high altitude aerodynamics for a European Comission study group on high altitude UAVs).


N.B. I made the mistake of buying the audiobook of Angels and Demons for a long drive. Utter and total drivel I thought - is the film any better or worse?