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Could Concorde Fly Transatlantic Subsonic Flight?  
User currently offlineA380900 From France, joined Dec 2003, 1110 posts, RR: 1
Posted (10 years 3 weeks 2 days 1 hour ago) and read 6072 times:

Would flight mixing subsonic over land and supersonic over sea have been possible with concorde without reducing the range too much? Could it have gone supersonic twice during the same flight without burning too much fuel?

My question is in fact related to a possible new SST business jet. If it cannot fly supersonic overland, it will have to have good subsonic flight capabilities for flights mixing sea and ground flying. Is it a possible engineering achievement? How was the Concorde doing in this respect?

[Edited 2004-08-08 21:34:46]

30 replies: All unread, showing first 25:
 
User currently offlineDfwRevolution From United States of America, joined Jan 2010, 970 posts, RR: 51
Reply 1, posted (10 years 3 weeks 2 days 1 hour ago) and read 5997 times:

Possibly, but the Concorde would be even less fuel efficent if that is possible. Braniff tried to opperate the Concorde subsonically between DFW-IAD then onto LHR at one point, crusing at Mach .9 over land, but the economics were terrible. I think when BA/SQ tried LHR-SIN, they had to opperate a stage over India subsonically because the booms were spooking sheep heards.

Point is, the Concorde was not designed for subsonic flight. The wing profile is not very efficent at low speeds and the engines are very-low bypass which does not help fuel burn-

http://www.concordesst.com/history/events/sia.html
http://www.concordesst.com/history/events/braniff.html
http://www.concordesst.com/concordeb.html


User currently offlineLHR27C From United Kingdom, joined Aug 2004, 1279 posts, RR: 16
Reply 2, posted (10 years 3 weeks 1 day 23 hours ago) and read 5846 times:

Concorde's engines are as efficient as you can get on supersonic flight in terms of fuel used per mile. The Olympus/SNECMA 593s were designed very carefully to be very efficient turbojets at supersonic speeds.

However in subsonic flight the efficiency is very much lowered, due mainly to the drag experienced by the delta wing shape and the low lift/drag ratio. I think the fuel consumption per mile is (or was  Sad) almost 10 times on final approach what it is in supersonic cruise, so I doubt whether it would make it.

A newly designed SST might well be able to make it, one of the key features of the Concorde B project was the increase in fuel efficiency.



Once you have tasted flight, you will walk the earth with your eyes turned forever skyward
User currently offlineSpacecadet From United States of America, joined Sep 2001, 3624 posts, RR: 12
Reply 3, posted (10 years 3 weeks 1 day 22 hours ago) and read 5750 times:

There's work going on right now in "silent" supersonic travel - ie. supersonic without the sonic boom. That seems like a better answer than trying to create a plane that can travel at both sub and supersonic speeds efficiently.


I'm tired of being a wanna-be league bowler. I wanna be a league bowler!
User currently offlineBill142 From Australia, joined Aug 2004, 8445 posts, RR: 8
Reply 4, posted (10 years 3 weeks 1 day 20 hours ago) and read 5631 times:

How do you go supersonic without a boom?

User currently offlineGigneil From United States of America, joined Nov 2002, 16347 posts, RR: 85
Reply 5, posted (10 years 3 weeks 1 day 18 hours ago) and read 5521 times:

How do you go supersonic without a boom?

Modern math proves it to be impossible, however, the boom can be redirected away from the ground, and the one that does reach the ground will be minor.

N


User currently offlineB2707SST From United States of America, joined Apr 2003, 1369 posts, RR: 59
Reply 6, posted (10 years 3 weeks 1 day 17 hours ago) and read 5515 times:

How do you go supersonic without a boom?

It involves reshaping the aircraft, especially the nose, to weaken the shock wave. You can never completely eliminate the shocks, but they might be reduced enough to become tolerable -- quieter and more like distant rolling thunder than a single sharp bang. NASA has tested a design that reduces boom strength by 40% on fighter jets, but I have my doubts that large supersonic airliners will ever be able to break the sound barrier over populated areas: a 50,000 pound fighter is a far cry from a 750,000 pound SST.


RE the initial question, Concorde's subsonic range was about 3,300 miles, if memory serves. GDB would know for sure. Being pure turbojets designed for supersonic cruise, the Olympuses were not great performers in subsonic cruise and were quite inefficient (loud and gas-guzzlers) at takeoff and landing.

Could it have gone supersonic twice during the same flight without burning too much fuel?

Probably not. The acceleration and climb from 30,000 feet and Mach .9 to 50,000 feet and Mach 2 consumed an enormous amount of fuel: remember that the afterburners were lit until Mach 1.7. I doubt Concorde would ever have had enough fuel onboard to do it twice in a normal flight.

Is it a possible engineering achievement?

Possible, yes. Economical, not yet. Off the top of my head, there are two significant design elements that will boost subsonic efficiency:

- Variable-bypass engines act like high-bypass turbofans at takeoff, subsonic cruise, and landing, reducing noise and fuel consumption, and then "change gears" to act like pure turbojets or low-bypass fans at supersonic cruise to provide the necessary exhaust velocity.

- Variable-sweep wings adjust the aerodynamic profile to fit subsonic and supersonic requirements more closely. Delta wings are fine at supersonic speeds, but create enormous drag at slow speeds and aren't wonderful at subsonic speeds. Folding the wings back into a delta or arrow configuration at supersonic speeds achieves the best of both worlds.

Both elements are heavy, expensive, and very complex, but could bring an SST within striking distance of some subsonic airliners for cruise efficiency over land.

--B2707SST



Keynes is dead and we are living in his long run.
User currently offlineNWA757 From United States of America, joined Aug 2003, 172 posts, RR: 0
Reply 7, posted (10 years 3 weeks 1 day 17 hours ago) and read 5492 times:

How do you go supersonic without a boom? The answer to the question, yes Concorde could travel subsonicly over land but it would not be fuel efficient.



Fly High!
User currently offlineBellerophon From United Kingdom, joined May 2002, 583 posts, RR: 59
Reply 8, posted (10 years 3 weeks 1 day 8 hours ago) and read 5297 times:

A380900

…Would flight mixing subsonic over land and supersonic over sea have been possible with concorde…

Yes. This was done on charter flights such as LHR-CDG and LHR-FCO and on scheduled flights such as LHR-BAH and IAD-MIA.

…Would flight mixing subsonic over land and supersonic over sea have been possible with concorde ...without reducing the range too much?...

No. If Concorde stayed subsonic, her range would begin to reduce. In very general terms a completely subsonic flight would only achieve around 70% of the range of a supersonic flight.

…Could it have gone supersonic twice during the same flight…

Yes.

…Could it have gone supersonic twice during the same flight ...without burning too much fuel?...

No. Every transonic acceleration, from M0.95 to M1.7 using re-heat, would burn an extra 6 to 10 tonnes of fuel, depending on ambient conditions.

There were quite restrictive time limits on the total use of re-heat during any one flight, and these were always a factor to be considered before deciding whether one could do a second acceleration to supersonic flight.

Regards

Bellerophon



User currently offlineConcordeBoy From , joined Dec 1969, posts, RR:
Reply 9, posted (10 years 3 weeks 1 day 2 hours ago) and read 5182 times:

IAD-MIA

IINM, IAD-MIA did go supersonic off the coast.

I think GDB wrote about it as well, when expressing his feeling that it should've been nonstop to LHR instead.


User currently offlineBellerophon From United Kingdom, joined May 2002, 583 posts, RR: 59
Reply 10, posted (10 years 3 weeks 1 day ago) and read 5134 times:

ConcordeBoy

...IINM, IAD-MIA did go supersonic off the coast...

No, you're not mistaken, that is what I've just said.

However, what she couldn't do was to mix subsonic and supersonic flight without incurring a fuel penalty and consequent loss of range.

Regards

Bellerophon


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17030 posts, RR: 67
Reply 11, posted (10 years 3 weeks 1 day ago) and read 5126 times:

Flying with a decreased boom signature will probably involve:

- Reshaped fuselage, probably with a bulbous nose
- Increased dihedral on the wing in order to make the noise travel from the plane more sideways instead of downwards
- Smaller wing=smaller boom

[Edited 2004-08-09 23:01:34]


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineCancidas From Poland, joined Jul 2003, 4112 posts, RR: 11
Reply 12, posted (10 years 3 weeks 19 hours ago) and read 5048 times:

why not just buy some B-1Bs from the USAF, cut holes in the fuselage for windows and paint them in some livery? maybe that would work?


"...cannot the kingdom of salvation take me home."
User currently offlineNudelhirsch From Germany, joined Oct 2003, 1438 posts, RR: 19
Reply 13, posted (10 years 3 weeks 16 hours ago) and read 4997 times:

Concrode actually mixed subsonic and supersonic. She went subsonic over land and did not accelerate before being away from the coastline, due to the super sonic boom. Then reduced speed early enough.
So actually, she did mix.



Putana da Seatbeltz!
User currently offlineXXXX10 From United Kingdom, joined Jan 2000, 777 posts, RR: 0
Reply 14, posted (10 years 2 weeks 5 days 3 hours ago) and read 4646 times:

Wasn't there once a time when the maximum time on the reheats was elapsed before M 1.7 was reached. Not sure what happened

User currently offlineStarlionblue From Greenland, joined Feb 2004, 17030 posts, RR: 67
Reply 15, posted (10 years 2 weeks 5 days 2 hours ago) and read 4639 times:

why not just buy some B-1Bs from the USAF, cut holes in the fuselage for windows and paint them in some livery? maybe that would work?

I'd love to fly in one but they're not exactly quiet. Also, military jets often have maintenance regimes which would be prohibitively expensive for a civilian operator. Maybe this is the reason the BC-17X never "took off".




"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineAireuropeUK733 From United Kingdom, joined Apr 2004, 978 posts, RR: 11
Reply 16, posted (10 years 1 week 6 days 9 hours ago) and read 4233 times:

With regard to reducing the supersonic boom couldn't the techy guys try to produce an inverse boom to cancel out the original - just like the anti-noise and vibration technology used in the new Dash 8?

Please note that I am not an engineer and don't know a huge amount about it. Just an uneducated thought!

Mike



It's nice to fly with friends
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17030 posts, RR: 67
Reply 17, posted (10 years 1 week 6 days 8 hours ago) and read 4221 times:

I'm not an engineer either but putting out more noise to cancel the original noise creates it's own problem. The energy has to go somewhere. Heat?


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineKlaus From Germany, joined Jul 2001, 21442 posts, RR: 53
Reply 18, posted (10 years 1 week 6 days 8 hours ago) and read 4219 times:

There is a second, inverted boom, already! ("bow" and "tail" shockwaves)

The trouble is that nobody has found a practicable way to have them cancel each other out so far...

You´d basically have to "persuade" the air to compress only locally when the nose parts the still air and to quietly decompress locally again at the tail. The problem is that the shockwaves separate from the moving system, so the energy is lost and can´t be recovered.

As far as I understand, a large portion of the engine´s power goes into the shock waves - so eliminating the shockwaves (and the boom) might also help increasing the overall cruise efficiency of a supersonic transport. Now we only have to find a way...  Wink/being sarcastic


User currently offlineB2707SST From United States of America, joined Apr 2003, 1369 posts, RR: 59
Reply 19, posted (10 years 1 week 5 days 21 hours ago) and read 4148 times:

With regard to reducing the supersonic boom couldn't the techy guys try to produce an inverse boom to cancel out the original - just like the anti-noise and vibration technology used in the new Dash 8?

I'm not an engineer either but putting out more noise to cancel the original noise creates it's own problem. The energy has to go somewhere. Heat?


As Klaus indicated, the problem is more complex than sound waves, which can be cancelled by an opposing signal. As an aircraft moves forward, air is displaced around the fuselage and wings. At subsonic speeds, the air ahead of a plane can "feel" its approach and begins to move ahead of the actual aircraft. You can see this personally when light objects like snow or leaves are deflected by the airflow around a car without actually touching it. The displaced air then flows back together as the plane passes, like water flowing around a ship into its wake.

At supersonic speeds, the plane is moving faster than the speed at which pressure disturbances are transmitted through air. The first "warning" of the approaching aircraft is the nose itself shoving air molecules out of its path. The pressure wave occurs as a shock around the nose and other protruding parts of the aircraft (wings, engines, antennae, etc.). A second set of shocks form at the trailing edge of the wings and fuselage as the air returns to normal pressure.

Shocks forming around a supersonic T-38:



The two sets of shock waves usually coalesce into an overpressure shock at the nose and an underpressure shock at the tail. These create the double-boom heard when an aircraft flies supersonically. The pressure distribution over time looks like an N, hence the term "N wave" for sonic boom shocks:



As far as I know, there is no conceivable way to eliminate sonic booms entirely. An aircraft will always displace some amount of air, and as long as it travels supersonically, shocks will form. The current avenue of research is to break apart the shocks and prevent them from forming two sharp booms (in other words, "depeak" the N-wave). In the image above, a modified NASA fighter achieved some reduction in boom intensity with a modified overpressure shock. This might be audible as a rumble or series of muted thuds instead of a single boom.

I have my doubts that boom intensity can be reduced enough to allow supersonic flights over populated areas. A 750,000-pound aircraft moving at Mach 2 or 2.4 moves an awful lot of air, and studies have shown that a socially acceptable boom would have to be many times quieter than we can achieve now. A 10-seat business jet might be able to pull it off, but a 300 passenger SST -- probably not, at least in the near future.

--B2707SST



Keynes is dead and we are living in his long run.
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17030 posts, RR: 67
Reply 20, posted (10 years 1 week 5 days 21 hours ago) and read 4148 times:

So we're left with the suborbital model instead, which would solve the boom issue by going around it.


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineSimProgrammer From France, joined Aug 2004, 193 posts, RR: 0
Reply 21, posted (10 years 1 week 5 days 20 hours ago) and read 4131 times:

Suborbital SST is technically quite feasible but the problems are political.

Quite a few theories have been privately punted around for some years now and its the engine thats also a stumbling block. The most recent one is a quad delta wing with an inverse dihedral design where engines 1 and 4 are subsonic for gaining the altitude to above FL460 (approx) and engines 2 and 3 produce the supersonic thrust into sub orbit. The a/c is affectively and accurately 'catapaulted' and its momentum carries it until it drops below FL450 and becomes subsonic prior to approach.

There are lots of other theories knocking about, but this one caught my attention the most.



Drive a bus, an Airbus, easier than a London bus!
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17030 posts, RR: 67
Reply 22, posted (10 years 1 week 5 days 20 hours ago) and read 4131 times:

Does sound like something I put forward in another thread. Dual propulsion seems easier than designing engines optimized for two so disparate flight regimes..


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineBellerophon From United Kingdom, joined May 2002, 583 posts, RR: 59
Reply 23, posted (10 years 1 week 5 days 19 hours ago) and read 4117 times:

XXXX10

...Wasn't there once a time when the maximum time on the reheats was elapsed before M 1.7 was reached...

This happened several times over the years, caused by unusually warm outside air temperatures, in the order of ISA +20ºC, between FL280 - FL430.

There was a time limit of 15 minutes on the use of re-heats for the transonic acceleration, and under these conditions this limit could be reached before M1.70 was achieved.

...Not sure what happened...

The re-heats were turned off, and the main engines then took her the rest of the way to M2.00, albeit more slowly than normal.

Regards

Bellerophon


User currently offlineBENNETT123 From United Kingdom, joined Aug 2004, 7566 posts, RR: 3
Reply 24, posted (10 years 1 week 4 days 12 hours ago) and read 3910 times:


Silly question

Why would you WANT to fly the Atlantic subsonically.

There are plenty of aircraft that could do that.


25 Fritzi : Bennet, This thread is talking about flying supersonic over water and subsonic over land, in order to eliminate the sonic boom which is very noticable
26 Starlionblue : Suborbital would neatly bypass all the problems. Let's do that instead. Pretty please with sugar on top. As Ian douglas pointed out in "Semper Mars",
27 GDB : A B-1B would be no good for pax, wrong shape fuselage, too much equipment there, besides, it or the B-1A, could not even approach Concorde's performan
28 MD-90 : This thread is talking about flying supersonic over water and subsonic over land, in order to eliminate the sonic boom which is very noticable from th
29 Post contains images KingGeo3 : A B-1B would be no good for pax, wrong shape fuselage, too much equipment there, besides, it or the B-1A, could not even approach Concorde's performa
30 Ba97 : Supersonic over land. I flew on the last BOAG flight to Toronto and we rocketed to a point about 300 miles from Toronto. I have a nice picture of me s
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