Help Needed With Maths

[lenny100]

For you math people what speed in mph and the mach number  would be needed to travel from tokyo to london in 35 mins,

This flight would be done in low earth orbit

[AeroplaneDriver]

Well London-Tokyo is roughly 6,000 statute miles (about 5,200nm), so speed would need to be about 12,000mph/10,400kts to do it in a half hour.  

Mach number isnt so clear cut, since Mach changes with altitude.  As the air becomes less dense with altitude sound travels slower.  Mach 1 at sea level is much faster than M1 at 50,000 feet (something like 750mph vs 600 IIRC).  As your spaceplace leaves the atmosphere into low orbit MAch number becomes academic since there is no speed of sound outside the atmosphere.  Having said that I've heard Mach 17 thrown around as the speed of the shuttle orbiter as it begins reentry.  

All of the above figures are off the top of my head and may be wildly inaccurate, so take it with a pinch of salt.

[B777LR]

Hmm, why?  Please tell us why

 

[jcf]

Go here for the distance between the two cities.
World Air Distance locator

Take the distance number(9536) and divide it by your time factor(35) that will give you your speed in miles per minute(272.46) multiply the result by 60(minutes in an hour) the result is about 16,437.428 mph.

Mach number varies with altitude.
Mach Number by Altitude

Picking a low end value of 125 miles for your low earth orbit we get Mach 1 = 702.1mph.

Therefore 16,437.428mph divided by 702.1mph gives a velocity of Mach 23.28.

Cheers, Jon

[lenny100]

Hmm, why?   Please tell us why

got something on they way which will make a few people happy

( A vulcan with spats and a rocket engine, and hypersonic aircraft parasite)

[AeroplaneDriver]

Duhh...obviously I screwed up on the distance.  I was looking at a list showing distance from London for several world cities and read vancouver instead of Tokyo (alphabetical list).

Anyway...sound does not travel at 700mph+ 125 miles up.

[jcf]

( A vulcan with spats and a rocket engine, and hyposonic aircraft parasite)

Hi Lenny,
it is definitely a parasite if its hyposonic ...hypersonic is the term you want.
Hypo means low, under, beneath, down or below...the opposite of hyper.

Cheers, Jon  

[jcf]

Anyway...sound does not travel at 700mph+ 125 miles up.

Suggest you check the charts I linked...the speed of sound does weird things as the altitude changes as air density  is not the only factor, temperature plays a major role.

Cheers, Jon

[kitnut617]

I've always read that low flying aircraft that can do Mach 1 at sea level have a speed of about 780+ mph whereas an aircraft at 40,000 ft the speed is up around 1000+ mph for Mach 1.

[Archibald]

Hell, I missed this thread 2 months ago    

Speed of sound (my favourite coldplay song   If someone ever understand the lyrics, please PM me )

sorry for the metric system...

1224 kph at sea level

1061 kph at 40 000 ft, after what it doesn't move anymore.

Your model seems very thunderbird-ish (wasn't one of the Thunderbirds vehicle flying at mach 7 or so ? )

[GTX]

sorry for the metric system...

Why appologise?!

Regards,

Greg

[Jennings]

The speed of sound definitely goes down at higher altitudes.  That's why you get into "Mach corner" wherein you're simultaneously close to the airplane's critical Mach number and its stall speed.  The early U-2s operated so close to this corner (of the flight envelope) that they often had only about 5kts between the two speeds.  Go too fast and you break apart, go to slow and you stall, spin, and die.  Not fun.

We could get into a while thread on indicated vs. true airspeed, but that's way too complicated for mere mortals to understand (you have to be a pilot), and isn't really relevant here.  Suffice it to say, the higher you go, the slower you're actually going for a given indicated airspeed.

J

[Archibald]

sorry for the metric system...

Why appologise?!

Regards,

Greg

In the sense that statute miles, nautic miles, and knots had been used in revious posts    Using meters add another complication to the whole discussion    

[Brian da Basher]

Did someone mention spats?

I love spats!

Brian da Basher