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747 goes supersonic* #5345371 02/09/20 03:44 PM
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DeepFriar Offline OP
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Well sort of. Would you believe an average of 801 mph between New York and London? I should live so long as to see a tailwind of 260! We'll miss her when she's gone, monumental achievement that she was.

https://jalopnik.com/with-help-from-a-storm-a-british-airways-747-just-brok-1841557907

Re: 747 goes supersonic* [Re: DeepFriar] #5345378 02/09/20 03:54 PM
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SubieRubyRoo Offline
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It's a darn shame that profreading(sic) is a lost art LOL


De omnibus dubitandum.
Re: 747 goes supersonic* [Re: DeepFriar] #5345411 02/09/20 04:33 PM
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I guess the meaning of supersonic has changed since I went to school.


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Re: 747 goes supersonic* [Re: PimTac] #5345464 02/09/20 05:56 PM
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tcp71 Offline
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801mph is over the supersonic speed of 768mph. That plane would beat sound from New York to London = “supersonic”. Works for me.
[Linked Image]

Last edited by tcp71; 02/09/20 05:57 PM.

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Re: 747 goes supersonic* [Re: DeepFriar] #5345493 02/09/20 06:41 PM
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JHZR2 Offline
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I was going to post on this too.

Are commercial jetliners “designed” (at least built with sufficient margin and safety factors) to go over 800mph?

I thought special considerations had to be made even for surface paint temperatures?

I’m not calling it supersonic because it’s awful high and awful cold up there, and those conditions change the speed of sound IIRC....

Re: 747 goes supersonic* [Re: DeepFriar] #5345497 02/09/20 06:44 PM
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spasm3 Offline
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Originally Posted by JHZR2
I’m not calling it supersonic because it’s awful high and awful cold up there, and those conditions change the speed of sound IIRC....

Also, is it really supersonic with a tailwind of 260? Relative to ground i guess its over 800. Relativity wise, is the air-frame really seeing 800mph?

Calling Astro!


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Re: 747 goes supersonic* [Re: DeepFriar] #5345498 02/09/20 06:45 PM
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CT8 Offline
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Jetstream 260 mph plus the plane speed is not actually the speed of sound ,


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Re: 747 goes supersonic* [Re: DeepFriar] #5345514 02/09/20 07:10 PM
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PimTac Offline
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The articles say subsonic.

This is Jalopnik. 🧂🧂🧂


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Re: 747 goes supersonic* [Re: PimTac] #5345526 02/09/20 07:22 PM
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Number_35 Offline
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Originally Posted by PimTac
I guess the meaning of supersonic has changed since I went to school.
Agreed, I think that supersonic speed is literally that at which the speed of sound is exceeded, and is thus relative to the surrounding air. The jet stream wind speed would have to be subtracted from the ground speed to give the actual air speed of the aircraft.

As well, the speed of sound (Mach 1) is c. 760 mph @ STP (standard temperature and pressure, 20 C @ sea level) but decreases with altitude, as atmospheric pressure drops. As atmospheric pressure drops, the air becomes less dense, and sound travels more slowly. This chart helps:

https://www.fighter-planes.com/jetmach1.htm

Per the chart, the speed of sound is about 660 mph at typical airliner altitudes. The aircraft under consideration is said to have hit a maximum ground speed of 825 mph, but if we subtract the 260 mph tailwinds, we're left with a maximum airspeed of 565 mph, well below supersonic (660 mph) at that altitude.

To put it another way, if you could somehow have projected a loud sound from the aircraft, its waves would have traveled in front of (that is, faster than) the aircraft, not behind the aircraft.

Re: 747 goes supersonic* [Re: DeepFriar] #5345530 02/09/20 07:27 PM
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Did anyone read the article ?

Originally Posted by article
...it wouldn’t have broken the sound barrier as the differential between the speed of the plane and the air moving around it was to low.

Re: 747 goes supersonic* [Re: SubieRubyRoo] #5345538 02/09/20 07:38 PM
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Originally Posted by SubieRubyRoo
It's a darn shame that profreading(sic) is a lost art LOL


You mean the Subsonic in the headline? Maybe it's correct as the jet didn't technically go supersonic but averaged 801 mph?



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Re: 747 goes supersonic* [Re: hallstevenson] #5345561 02/09/20 08:12 PM
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Originally Posted by hallstevenson
Did anyone read the article ?

Originally Posted by article
...it wouldn’t have broken the sound barrier as the differential between the speed of the plane and the air moving around it was to low.


I saw a different article. But that’s why I didn’t claim it to be supersonic.

Still, the ground speed, tailwind or not, seems to me to be impressive. Not that I know much about flying... but I know if I go much over 30 on a bicycle, down a hill and in a tailwind, it’s not the most comforting feeling... regardless of the reason the speed is achieved... thus my curiosity on what the design speed is.

Re: 747 goes supersonic* [Re: DeepFriar] #5345574 02/09/20 08:23 PM
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spasm3 Offline
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Try that on the next traffic stop!! " You were doing 20 over" ; " But i had a 12mph tail wind!"


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Re: 747 goes supersonic* [Re: DeepFriar] #5345640 02/09/20 09:39 PM
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Right time,right route,right conditions,even a four engine freighter/transport can do concorde like cross-Atlantic travel times.
The relative wind kept the loads to subsonic levels.

Re: 747 goes supersonic* [Re: DeepFriar] #5345653 02/09/20 09:47 PM
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DeepFriar Offline OP
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Gentlemen this item was firmly tongue in cheek hence the asterisk. Supersonic in this case is just numerical. The 747 was no more supersonic than when there is no tailwind. Sub five hour flight from New York to London is still remarkable even for the extreme swept wing wonder from Everett and is the real *story* here.

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