1078 km/h possible with Boeing 747-400?
Hello everyone.
I flew in a Lufthansa Boeing 747-400 today. The cabin monitor showed a speed of 1000 km/h when I happened to look at it. I watched it for a while. The 747 reached a maximum speed of 1078 km/h. Somehow that seems strange to me, that should be almost the speed of sound.
According to the rule of thumb, the speed of sound would be 343 m/s at 20°C = 1235 km/h. We were in the middle of the Atlantic at full altitude and with a tailwind. Since it was certainly > -40°C at this altitude, the speed of sound would have to occur much earlier than 1235 km/h, wouldn't it?
Hence my question, is it theoretically possible to reach Mach 1 with a 747-400? or did the instruments go crazy?
Best regards, Philadou
(2 votes)
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To answer your question first: Of course, it is possible to reach with a 747 Mach 1. This goes faster than you think, let’s get out of the machine and the engines stay on Cruise speed. Then a 747 can easily get into the supersonic range.
What you’ve been watching is a normal thing. Large airliners like the 747 often fly very close to the sound limit. It’s logical, of course you want to fly as fast as you can or can. In this case it is not possible to determine exactly how the speed of sound is reached at any moment on the basis of the km/h. The km/h display only serves to allow the passenger to imagine how fast the machine flies. Under km/h you can easily imagine more than under knots.
You have already recognized correctly, the speed of sound drops with increasing height. The pilot, however, depends on the Mach meter during the trip and not on km/h or node. On the Mach meter, the pilot can see at a glance how close it is to the speed of sound. In the case of the 747, the Mach meter must never reach Mach 1. It always moves in the 0,xx range. The Mach meter indicates the ratio of the flight speed to the sound speed of the surrounding air. Thus, it can be quite possible that the machine flies at over 1000 km/h as long as it is in the area under Mach 1, this is completely okay.
In addition, the pilot must observe the “critical number” of the machine. Unfortunately, I can’t tell you exactly how big this is now at a 747, I’m just a plane mechanic, not a pilot. In any case, the critical Mach number of the point at which the aircraft itself is still flying with subsonics is individual parts (e.g. the area above the supporting surfaces) of the machine, but already go into the supersonic area.
Thanks for the great and detailed answer!
That’s exactly what I wanted to know, and of course I’m sad,
that I didn’t fly the speed of sound:-(
Better be glad to have sound speed in a 747 you would probably have survived… : You can say that you were faster than 1000 km/h.
You can forget. I used to call a pilot. The plane starts to vibrate, everyone goes into fear and it goes automatically slower. That’s one of the instincts. So if no stewardess has come to you, and even has been kind of afraid, there was no fear in the cabin – there were no indications that you would have to pay the plane now, then it was subsonic.
I’m the fastest here. I’m sorry, I didn’t want to get oversonic, but on a step flight, (the pilot was lazy and talented) because I wanted to be like in the world. I knew at that time that it was exactly the same as on the rollercoaster (never only heard) and even in air holes, certain accelerations etc. See Mark Shuttleworth, who wanted his money back. And unfortunately also see this private weightlessness try, which also worked out. Because the pilot came back and said it was the same thing, why would I risk my life for it? But have already invested millions. Therefore they came with ‘Sabotage’ etc.. NASA has repeatedly pointed out that they should leave it. They thought NASA was afraid of the competition and liked the advertising.
So I was in the supersonic area and in space. Must be said was so in my twenties and friend Weg and Stewardess..
They flew safely from West to East…USA-FRA or FRA- Asia.
This is where you flee with the jetstream so you have backwind of about 150-200km/h
The Jumbo itself flies around the 800km/h so it can add up to over 1000km/h GROUND SPEED.
At the OST-WEST flight you have the reverse effect and the ground speed is less
Your flight time was also certainly short when it was flying
Choppch
The sound velocity relative to the surrounding ludt must never reach it due to the construction, the speed over the ground should have been indicated.
Here are the relationships
very well explained:
http://walter.bislins.ch/blog/index.asp?page=A+air rate%2C+different+advertisements
Thanks for the great link! Even though I don’t understand everything, and some of it is definitely Spanish for me, I can get some of it!
Then ask for the details …
LG
This is because the speed is displayed on the ground. By 0.88 you can fly with a 747-400, but usually it is 0.85.
So we take -50°C, which is quite realistic, then the speed of sound is about 1080km/h. When you flew Mach 0.85, that was 918km/h compared to the air and 160km/h wind from behind. It can be with a strong jetstream.
Best regards
Bastian
Well, then this should be almost true with Mach 1. As far as I remember it was something between -46 and -52 °C and on the display was 1078 km/h.
Morje!
This is already possible, as already described by pre-posters, but you have to take care of what this display means.
There is the air speed (airspeed) measured via a so-called dam on the nose of the aircraft. Here, the flow air builds up pressure on a membrane in a forward-directed tube and thus the computer calculates the speed.
The real speed (Ground Speed) is calculated by the GPS and shows the speed that the aircraft has relative to the Earth.
This will seem to be the display that can be found on the monitors at LH.
Due to lower air pressure at large altitudes, the airspeed is only 360kn (e.g. 666km/h), but can already be close to Mach 1 on the ground, and vice versa, MAch 1 is, as you had described, only 700km/h on the floor and 1400 km/h at normal pressure, but in 39000ft it can be only 700km/h.
If you understand, do something about it until then
Preparatory action
We fly you-where you want to go.
Hey :
This is so for many long-haul flights that they fly just below the speed of sound. Vlt if you can still remember what the speed was on the flight, you will notice that this is only going with a tailwind. She was probably less on her way.
The pilot uses less kerosene and flies faster.
Some flights couldn’t find a city without a tailwind.. Singapore Airlines flies directly from Singapore to New York with an A345. In pure business class seating with 100 passengers and no cargo. This 18h flight is possible due to the light weight and strong backwind that always prevails above the North Pole. They’re flying even less below the sound limit. It’s quite normal.
But no airline tries to reach Mach 1 because the plane is not built for it. This can often be seen in plane crashes. -> a plane drops steeply and gets a too high speed and wing etc break off.. The same would happen if a 747 Mach1 would reach on your flight.
(aja a 747 can theoretically reach Mach1 but ONLY when it drops with full power when it flies horizontally it was the MAximal speed)
Thanks for the great and detailed answer!
As my pre-posters have already written, it is not possible to achieve “normal” jets such as a 747 (over-)sound speed due to the construction.
However, if the machine has tailwind, the flight speed also increases with respect to the ground. The “Jet-Stream” – a west-east stream with over 300 kmh, also accelerates the travel flight.
Because of the jet stream, the route from FRA to the USA is also rather north (we fly over Sweden, Iceland, Greenland, while on the return flight about at the level of Central England you are the first time over Europe.
The oversonic speed is weak-sense…the maximum Machnumber of a Boeing 747 is 0.85 there is still a small piece…The speed indicator has indicated with 100% safety the ground speed, the speed above the ground. If the maximum flight speed is exceeded, the flyer starts to vibrate and eventually flies apart under the high load and that would happen before the speed of sound…
This is possible because the sound wall is not broken at 1000KM/H but only at 1112, or so!
At sea level… but not on FL 350
Depends on whether it was the speed relative to the ground or relative to the surrounding air.
Hmmm, okay… and how do I get this out?
as a rule, miles are displayed on the plane!
? I don’t understand your answer.
First, 1078 mph would be much more km/h
and secondly, km/h are also specified in a German airline.
Can anyone who knows about this please give a meaningful answer?
Thank you:-)
be not evil, he is a newcomer!
If, then air nodes (so nodes) are displayed as speed, but not miles. And if km/h is behind it, it certainly does not stand for miles per hour. The km/h display in the passenger compartment serves only to illustrate the passengers. Because not every passenger can imagine how fast the plane flies when you would blind the nodes. But it knows how fast everyone is 1000 km/h.
http://de.wikipedia.org/wiki/Boeing_747
That doesn’t answer my question either. The indication of 913 km/h is only the specified travel speed without taking into account wind conditions.
MIt Backwind is clear that it flies faster than its normal travel speed.