Supersonic in a 777
Feb 7, 2007 | 8:12 am
#16
Join Date: Dec 2006
Posts: 1,452
;
My understanding is that a normal jet aircraft will have a real hard time approaching and breaking the speed of sound at whatever density, temperature it's at. This is because at the speed of sound, the cone shaped shock wave would intersect the relatively wide wings causing drag and mechanical shock.
My understanding is that a normal jet aircraft will have a real hard time approaching and breaking the speed of sound at whatever density, temperature it's at. This is because at the speed of sound, the cone shaped shock wave would intersect the relatively wide wings causing drag and mechanical shock.
At Mach 1,0, the shock cone has apex angle of 180 degrees - it is a flat plane supported at the nose, and will not touch nose.
However, a big issue with sound barrier is backwards shift of the centre of lift. Concorde had to pump fuel backwards during acceleration to transonic. A subsonic airliner does not have such pumps. If it were to accelerate near the speed of sound, it would suffer a Mach tuck - as the centre of lift moves backwards, the plane drops nose and enters into dive, the elevator authority is not enough to raise nose, so the plane accelerates in a supersonic dive till it meets ground or is broken mid-air by excessive aerodynamic forces.
Feb 7, 2007 | 8:17 am
#17
FlyerTalk Evangelist
Join Date: May 1998
Location: Massachusetts, USA; AA 2.996MM & Plat Pro, DL 1MM, GM & Flying Colonel
Posts: 25,037
Basically, the drag (drag coefficient, C sub D, for the aerodynamic geeks among us) approximately triples as you go throught the speed of sound. Nobody will give an aircraft three times the power it needs otherwise unless going through the "sonic barrier" is a requirement. Once past it, it drops off again to about 50 percent higher than its subsonic value, so cruising at supersonic speeds is practical (though expensive, for a bunch of other reasons besides drag as well).
Feb 7, 2007 | 8:37 am
#18
Join Date: Nov 1999
Location: if it's Thursday, this must be Belgium
Programs: UA 1K MM
Posts: 6,579
But interesting about the shifting center of lift!
Feb 7, 2007 | 8:44 am
#19
Original Poster
Join Date: Sep 2006
Location: SAN
Programs: CO plat, BR gold, SPG gold
Posts: 320
Real supersonic (airspeed, not ground speed) has been done before in a 747. Coincidentally, also on the TPE-LAX route.
http://www.airliners.net/open.file?id=0067630&size=M
Glad I wasn't on that flight.
http://www.airliners.net/open.file?id=0067630&size=M
Glad I wasn't on that flight.
Feb 7, 2007 | 8:49 am
#20
Join Date: Dec 2006
Posts: 1,452
Real supersonic (airspeed, not ground speed) has been done before in a 747. Coincidentally, also on the TPE-LAX route.
http://www.airliners.net/open.file?id=0067630&size=M
Glad I wasn't on that flight.
http://www.airliners.net/open.file?id=0067630&size=M
Glad I wasn't on that flight.
It is not known how many g-s the plane and passengers suffered, because the acceleration broke the acceleration sensors for the black box, but it was more than 5 g.
Out of over 270 passengers and crew, only two were injured - one crew and one passengers. Everyone else was completely unscathed.
Feb 7, 2007 | 9:35 am
#21
Original Poster
Join Date: Sep 2006
Location: SAN
Programs: CO plat, BR gold, SPG gold
Posts: 320
Scary, but funnily with very little harm done!
It is not known how many g-s the plane and passengers suffered, because the acceleration broke the acceleration sensors for the black box, but it was more than 5 g.
Out of over 270 passengers and crew, only two were injured - one crew and one passengers. Everyone else was completely unscathed.
It is not known how many g-s the plane and passengers suffered, because the acceleration broke the acceleration sensors for the black box, but it was more than 5 g.
Out of over 270 passengers and crew, only two were injured - one crew and one passengers. Everyone else was completely unscathed.
Maybe there were few serious injuries to passengers but I bet their underpants were not so lucky.
Feb 7, 2007 | 10:50 am
#22
Join Date: Apr 1999
Location: Homosassa, FL & Ringwood, NJ -UA-G(Lifetime); SPG-Plat (Lifetime)
Posts: 6,122
I was one of the lucky ones at CO's Houston DO II that got to 'fly' the 777 flight sim. While in many ways it was no more difficult than driving a car, one of the things on my list that we never got to because everyone needed 2 shots a landing to succeed was to take it supersonic 
My plan, if I could not pull out of a dive in a reasonable period of time was to do a mid-air engine reverse. It would have been interesting to see the result.
Maybe next time
My plan, if I could not pull out of a dive in a reasonable period of time was to do a mid-air engine reverse. It would have been interesting to see the result.
Maybe next time
Feb 7, 2007 | 3:29 pm
#25
Join Date: Jan 2006
Location: ABE/PHL
Programs: CO Pt Infinite (1k life)/ 1MM - NW/DL Silver life/1 MM
Posts: 1,309
Feb 8, 2007 | 11:05 am
#27
Join Date: Jul 2004
Programs: CO Gold; SPG Gold***; AvisFirst;
Posts: 3,970
Feb 8, 2007 | 11:31 am
#28
Join Date: Feb 2002
Location: BNA
Programs: HH Silver. (Former UA PP, DL PM, PC Plat)
Posts: 9,560
Feb 8, 2007 | 4:03 pm
#29
Join Date: Jan 2006
Location: ABE/PHL
Programs: CO Pt Infinite (1k life)/ 1MM - NW/DL Silver life/1 MM
Posts: 1,309
I'm sure you are aware that a FL altitude is just a pressure level above some standard reference level of 29.92 inches. While the absolute altitude will vary w/ pressure changes, the relative part doesn't and todays instruments are very very precise. Witness the Gol and Embraer collision over Brazil.
Feb 8, 2007 | 5:16 pm
#30
Join Date: Nov 2002
Location: London
Programs: I've got three passports, A couple of visas, Don't even know my real name.
Posts: 909