wardialer
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Swiss A340 Cruising At Mach ONE?

Fri Oct 16, 2009 8:06 pm

Check this out from Flightaware....And scroll down until you see that the speed hits MACH 1.04...Just scroll down until you see Gander Center...And you will see it...

Is this true or what???

http://flightaware.com/live/flight/S.../20091016/0234Z/KLAX/LSZH/tracklog
 
Lemmy
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RE: Swiss A340 Cruising At Mach ONE?

Fri Oct 16, 2009 8:11 pm

That's probably the equivalent speed in still air. They must have had a nice tailwind, which would mean that their indicated speed was much lower.
I am a patient boy ...
 
wardialer
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RE: Swiss A340 Cruising At Mach ONE?

Fri Oct 16, 2009 8:15 pm

Yes, I had flown Swiss many time from KLAX to Zurich, and the Eastbound flights do have a nice tailwind always in that area...

So, would this be the True Mach speed, or please explain.....

I though aircrafts over land cannot do Mach 1 at all because it may cause a SONIC BOOM...
So please explain why this log indicates Mach 1.

Also, this is interesting....How can I find an online calculator that will convert the Alt, Ground Speed, IAS, to the Mach number like that log??? So I need to find out how the log calculated a speed of Mach 1 at FL350 that would be equivalent to still air.....

Because flying at actual MACH 1 speed would of had caused a Sonic Boom.....


How can this be done using a calculator or something....????

[Edited 2009-10-16 13:34:41 by wardialer]

[Edited 2009-10-16 13:36:19 by wardialer]
 
Fly2HMO
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RE: Swiss A340 Cruising At Mach ONE?

Fri Oct 16, 2009 8:36 pm

Quoting Lemmy (Reply 1):
That's probably the equivalent speed in still air.

Groundspeed is the correct term.

Quoting Wardialer (Reply 2):
So, would this be the True Mach speed, or please explain.....

Mach speed is Mach speed, there are no other variations of it.

Quoting Wardialer (Reply 2):
So please explain why this log indicates Mach 1.

It is not doing mach 1 per se. And there is no sonic boom. Mach speed is in relation to the air, altitude, pressure and temperature. This high groundspeed is a product of a strong tailwind. Online tracking services can only show groundspeed as it is radar based information.

[Edited 2009-10-16 13:38:20]
 
wardialer
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RE: Swiss A340 Cruising At Mach ONE?

Fri Oct 16, 2009 8:48 pm

Ok, i understand....But not quite.

All I wish to have or do, is calculate this the same way as in the log above.

So for example, how did they get Mach 1.04 at a Ground Speed of 690 knots at FL350?
Now, of course, we cannot tell at which IAS Airspeed or even the temp. at that altitude from this tracking service....But lets all assume that it was like something at a temp -48 C and an IAS of 280 knots...

I just need to know how they came up with the Mach 1 number relative to that Ground Speed at FL350???
 
Fly2HMO
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RE: Swiss A340 Cruising At Mach ONE?

Fri Oct 16, 2009 8:50 pm



Quoting Wardialer (Reply 4):
I just need to know how they came up with the Mach 1 number relative to that Ground Speed at FL350???

They are probably interpolating standard temps for the given altitudes and doing a conversion like you would from say, kmh to mph
 
71Zulu
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RE: Swiss A340 Cruising At Mach ONE?

Fri Oct 16, 2009 8:56 pm

Yep, Flightaware only tracks groundspeed. The mach figures are the equivalent ground speed in knots taking the tailwind into consideration.

Check some speed records here,

http://www.groundspeedrecords.com/database%20commercial.htm

Current record of those submitted for the A343 is 721 knots.
Clickable links only please!
 
A342
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RE: Swiss A340 Cruising At Mach ONE?

Fri Oct 16, 2009 9:16 pm



Quoting Wardialer (Reply 4):
So for example, how did they get Mach 1.04 at a Ground Speed of 690 knots at FL350?

For example if the aircraft flies at an airspeed of M0.82 (normal A340 cruise speed) and the tailwind adds the equivalent of M0.22.

A342
Exceptions confirm the rule.
 
rwessel
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RE: Swiss A340 Cruising At Mach ONE?

Fri Oct 16, 2009 9:30 pm



Quoting Wardialer (Reply 2):
Also, this is interesting....How can I find an online calculator that will convert the Alt, Ground Speed, IAS, to the Mach number like that log??? So I need to find out how the log calculated a speed of Mach 1 at FL350 that would be equivalent to still air.....

This one is my favorite:

http://www.aerospaceweb.org/design/scripts/atmosphere/
 
tdscanuck
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RE: Swiss A340 Cruising At Mach ONE?

Fri Oct 16, 2009 10:51 pm



Quoting Wardialer (Reply 2):
Because flying at actual MACH 1 speed would of had caused a Sonic Boom.....

Not necessarily...Mach 1 groundspeed may not be Mach 1 at the aircraft...you need to be supersonic at the aircraft to generate a shock wave.

In addition, speed of sound drops with altitude (at commercial jet heights), so even if the aircraft is generating a shock wave it may not propagate to the ground. Some of the supersonic BBJ concepts use this effect to go supersonic without causing an audible boom on the ground.

Tom.
 
soon7x7
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RE: Swiss A340 Cruising At Mach ONE?

Sat Oct 17, 2009 12:30 am

Last April we had a "Noreaster in New York"...dumped 10" of snow...("Noreasters are famous for intense winds, both surface and aloft")...the next day I departed JFK to Geneva...wheels up to wheels down=6 hours....we caught the lower side of the low off on St. Johns Bay and it sling shot us eastward. At 35K the outside temp was-86F...we had to descend to 27,000ft. Had just enough time for two meals and to listen to five cd's!...j
 
wardialer
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RE: Swiss A340 Cruising At Mach ONE?

Sat Oct 17, 2009 6:50 am

Ok, thanks for the great links.
So, just to conclude this....The Mach 1 speed thats in that track log is NOT the same as going actually at Mach 1 (the speed of sound)???

So in that log, the Mach 1 speed is actually the MACH Ground Speed and not the same as the Mach number which indicated on the Airspeed dials???

I did not know that there are two versions of Mach numbers...

So theres Mach ground speed and the Mach speed that is on the IAS Airspeed dials??
 
rwessel
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RE: Swiss A340 Cruising At Mach ONE?

Sat Oct 17, 2009 7:19 am



Quoting Wardialer (Reply 11):
So, just to conclude this....The Mach 1 speed thats in that track log is NOT the same as going actually at Mach 1 (the speed of sound)???

Correct.

Quoting Wardialer (Reply 11):
So in that log, the Mach 1 speed is actually the MACH Ground Speed and not the same as the Mach number which indicated on the Airspeed dials???

I did not know that there are two versions of Mach numbers...

So theres Mach ground speed and the Mach speed that is on the IAS Airspeed dials??

There isn't really. "Mach ground speed" is basically a useless bit of information. FlightAware presumably only knows the actual speed of the aircraft relative to earth (IOW, the groundspeed). They're presumably computing the other numbers from that, *without* knowing the exact conditions aloft (specifically wind speed, temperature and pressure), and just assuming that standard conditions apply.
 
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TripleDelta
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RE: Swiss A340 Cruising At Mach ONE?

Sat Oct 17, 2009 10:40 am

Quoting Wardialer (Reply 11):
So, just to conclude this....The Mach 1 speed thats in that track log is NOT the same as going actually at Mach 1 (the speed of sound)???

One could also use the old "walking in a train" concept to explain why the ground speed is in the supersonic range and the aircraft's speed is still subsonic.

Imagine that you have a train doing 100 mph. And you have a person in the train walking/running at say 5 mph in the direction in which the train is traveling. His speed in relation to the ground would be 100+5 mph, because the train is moving relative to the ground and the person is moving relative to the train. If the person would be walking in the opposite direction, his "groundspeed" would be 100-5 mph and so on...

In flight, the aircraft is the passenger and the moving airmass - or wind - is the train. The indicated airspeed you read of the ASI and the Mach number are measured relative to the air mass, not the ground. So if an aircraft has a cruise speed of M0.8, that means that it's flying at that Mach relative to the air. And if the air itself is moving in the same direction at say M0.3, the speed of the aircraft relative to the ground is M0.8 + M0.3 -> M1.1 - that is, it's groundspeed is such as if the aircraft were doing M1.1 in still air.

EDIT: for clarification  

[Edited 2009-10-17 03:45:06]

[Edited 2009-10-17 03:50:00]
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CosmicCruiser
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RE: Swiss A340 Cruising At Mach ONE?

Sat Oct 17, 2009 2:43 pm



Quoting FLY2HMO (Reply 3):
Groundspeed is the correct term.

Right on. The confusion here is the fact that this flight tracker or whatever gave the GS in Mach. That's a little bit of a stretch and I've never thought of GS in Mach. He was probably doing .82 and had 175 kts + on the tail, not uncommon in the winter.
 
Fly2HMO
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RE: Swiss A340 Cruising At Mach ONE?

Sat Oct 17, 2009 5:57 pm



Quoting Wardialer (Reply 11):
I did not know that there are two versions of Mach numbers...

There aren't two. Like I said in my first post, there's only one type of Mach speed. It's impossible for flightaware to know the plane's actual Mach speed short of them having the pilots radio them the information. Flightaware is just guesstimating it using the ground speed in knots as a reference.

Quoting TripleDelta (Reply 13):

In flight, the aircraft is the passenger and the moving airmass - or wind - is the train. The indicated airspeed you read of the ASI and the Mach number are measured relative to the air mass, not the ground. So if an aircraft has a cruise speed of M0.8, that means that it's flying at that Mach relative to the air. And if the air itself is moving in the same direction at say M0.3, the speed of the aircraft relative to the ground is M0.8 + M0.3 -> M1.1 - that is, it's groundspeed is such as if the aircraft were doing M1.1 in still air.

Excellent explanation.  yes 

Quoting CosmicCruiser (Reply 14):
He was probably doing .82

Sounds about right.
 
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DocLightning
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RE: Swiss A340 Cruising At Mach ONE?

Sat Oct 17, 2009 11:04 pm



Quoting FLY2HMO (Reply 3):

Groundspeed is the correct term.

On a trip in early February from EWR to LHR on a BA 777, our groundspeed was, at points, in excess of 770 MPH. We made the trip in under 5 hours. That's not a heck of a lot worse than Concorde.

The trip back was almost 8 hours.  crowded 
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liffy1a
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RE: Swiss A340 Cruising At Mach ONE?

Sat Oct 17, 2009 11:17 pm



Quoting FLY2HMO (Reply 3):
Mach speed is in relation to the air, altitude, pressure and temperature.

Correct me if I'm wrong, but is the mach no. not affected by the temperature of the air and that only.
 
tdscanuck
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RE: Swiss A340 Cruising At Mach ONE?

Sat Oct 17, 2009 11:31 pm



Quoting LIFFY1A (Reply 17):
Correct me if I'm wrong, but is the mach no. not affected by the temperature of the air and that only.

Speed of sound in most gases is a function of the temperature (and the gas) only. Assuming we're talking standard air at normal pressures all the time, then it's just a function of temperature.

Mach number is a function of airspeed and local speed of sound or, equivalently, airspeed and local temperature.

Tom.
 
liffy1a
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RE: Swiss A340 Cruising At Mach ONE?

Sat Oct 17, 2009 11:47 pm



Quoting Tdscanuck (Reply 18):
Mach number is a function of airspeed and local speed of sound or, equivalently, airspeed and local temperature.

Would I be correct in saying, for example, if you have a TAS of 400kts, and a Mach No. of .82, then if the TAS remains constant and the temperature changes, then the Mach No. will change regardless of changes in pressure?
 
wardialer
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RE: Swiss A340 Cruising At Mach ONE?

Sun Oct 18, 2009 4:35 am

I actually needed a calculator that would allow me to convert TAS, Ground Speed, and the equivelant Mach number relative to "still air"

So for example....

If I was flying at a TAS of 480 kts with a tailwind of 100 kts that would of course be a GS of 580 kts. What I want to know from this point, is the Mach number that would be equivelant to still air, like in that flight tracking log.....

The online calculator below will not give me the Ground Speed Mach number, it only gives or converts it to the aircraft's Mach number relative to the air mass, and not relative to the ground.

In other words, by using the online calculator below, is there any way of knowing the "ground-relative" Mach Number (also refered to as Ground Speed Mach) rather than the Mach measured relative to the air mass?

I understand the difference between TAS and Ground Speed, but I want to convert the Mach number used in Airspeed Indicators to the Mach number relative to the groundspeed just the way that flight log does.

http://www.aerospaceweb.org/design/scripts/atmosphere/
 
Fly2HMO
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RE: Swiss A340 Cruising At Mach ONE?

Sun Oct 18, 2009 4:46 am



Quoting Wardialer (Reply 20):
I actually needed a calculator

Google to the rescue...

http://www.globalaircraft.org/converter.htm
 
tdscanuck
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RE: Swiss A340 Cruising At Mach ONE?

Sun Oct 18, 2009 4:35 pm



Quoting LIFFY1A (Reply 19):

Would I be correct in saying, for example, if you have a TAS of 400kts, and a Mach No. of .82, then if the TAS remains constant and the temperature changes, then the Mach No. will change regardless of changes in pressure?

Yes. It will change proportional to the square root of the temperature.

Tom.
 
HaveBlue
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RE: Swiss A340 Cruising At Mach ONE?

Sun Oct 18, 2009 5:03 pm

Mach is the speed an aircraft is traveling.... in relation to the air around it. Another words at sea level on a standard day the aircraft would have to be going 760 mph faster than the air it is in. So if its doing 700mph, and a tail wind is pushing it 60 mph faster, the aircraft is still subsonic. It is doing 700 mph on its airspeed indicator in the cockpit, it is going 700 mph faster than the air it is traveling in, but its groundspeed is 760mph which is equivalent to Mach 1.

The sonic boom comes from the overpressure of air not being able to get out of the way of the aircraft as it goes supersonic. This happens (for our example) when the plane is going 760 mph faster than the air it is traveling thru. So it is irrelevant if the plane is going 740mph indicated and has a 200 mph tailwind, it is still subsonic... though it would have a hell of a groundspeed of 940mph. Groundspeed simply being the amount of ground that is covered in a given timeframe and is completely irrelevant to the aircraft itself.

Think of it this way. Your in a boat this only capable of doing 10mph, period. Well if you have the throttle wide open but the river your running in is doing 5mph the same direction, then your boat will be covering ground at 15mph. Consequently if that same boat is going against that same tide it would be only covering ground at 5mph. The boat is still doing 10mph thru the water either way, but its progress overall will be dependent how fast the stream its moving in is going.

You see the wing on the airplane doesn't care about groundspeed. It will go supersonic or stall depending on the aircrafts speed thru the air its moving in. Regardless of how fast that air is moving. This is how we hovered Cessna's in flight school. The Cessna 152 stalls at 40 knots without the flaps down. So put your nose into a 40 knot headwind and you are hovering over the same spot on the ground. Now we know the Cessna cannot hover, it is moving thru the air at 40 knots but the air is moving it backwards at 40 knots, which means we aren't progressing over the ground. Now turn the plane around at that same 40 knots and now we're covering ground at 80 knots groundspeed without changing anything but direction.

Hope that helps. The groundspeeds you see on flightaware and in the plane on the map track having nothing at all to do with supersonic or shockwaves. Supersonic is how fast YOU are traveling THRU the air, regardless of how fast the air may be moving you along.

[Edited 2009-10-18 10:07:29]
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Fly2HMO
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RE: Swiss A340 Cruising At Mach ONE?

Sun Oct 18, 2009 6:11 pm

So what happens if you grab a runway and make it into a giant conveyor belt?  duck   duck   duck 
 
HaveBlue
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RE: Swiss A340 Cruising At Mach ONE?

Sun Oct 18, 2009 7:39 pm



Quoting FLY2HMO (Reply 24):
So what happens if you grab a runway and make it into a giant conveyor belt?

Then you've just flogged a very dead horse to death again. lol.  Smile
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DocLightning
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RE: Swiss A340 Cruising At Mach ONE?

Tue Oct 20, 2009 5:27 pm



Quoting FLY2HMO (Reply 24):
So what happens if you grab a runway and make it into a giant conveyor belt? duck duck duck

We take you out back and beat the crap out of you?  Wink
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flybaurlax
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RE: Swiss A340 Cruising At Mach ONE?

Wed Oct 21, 2009 4:21 am



Quoting Tdscanuck (Reply 18):
Speed of sound in most gases is a function of the temperature (and the gas) only. Assuming we're talking standard air at normal pressures all the time, then it's just a function of temperature.

 checkmark 

Quoting Wardialer (Reply 2):
How can this be done using a calculator or something....????

Mach is just a unitless number that is a ratio of relative speed to the speed of sound (at that altitude). As stated before, it's a function of temperature, and temperatures change with altitude.
The equation for Mach number is
M= u/a,
where u is the velocity of the aircraft,
a is the speed of sound. a = (ɣRT)^(1/2) (square root of (ɣRT)).
ɣ = 1.4 (for air)
R = 287.058 J/KgK (for air, and metric) or R = 1716.6 ft*lbf/(slug*R) (for English)
T = temperature, either in K, or R depending on if you're using metric or English


Here is a standard atmospheric table.
http://www.pdas.com/e2.htm
It's the only one I could find in table form, but the temperature is in Rankine, so you need to keep that in R if you're using English, or convert it to K if you want to use Metric. So you can now calculate Mach numbers for any altitude if you'd like, but you need to have the flight velocity. Just choose one, or look up typical cruising speed.

You can always rearrange the equation and calculate the velocity of the a/c if you know the Mach number, and what altitude it's flying at. Anyways, I know this is way more in depth than you were looking for, but I hope this helps. It's really not that hard. If this doesn't make sens I'll try to clarify tomorrow.
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113312
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RE: Swiss A340 Cruising At Mach ONE?

Wed Oct 21, 2009 5:03 pm

Flightaware is not doing anyone a service by displaying incorrect and erroneous data. Mach number is the aircraft's true airspeed relative to the speed of sound. The speed of sound, in turn, is related to temperature. The data captured through down-linking does not get the temperature data from the flight. Thus, any "mach" shown in the data is really fake! It appears that they are inferring the number from ground speed. Ground speed has nothing to do with Mach number. Most aircraft flying above FL270 operate at a constant Mach number and that should be your first clue that what flightaware is showing is false.

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