Posts about: "Sonic Boom" [Posts: 24 Page: 1 of 2]¶

Biggles78
Sorry Biggles78, I'd forgotten to answer your CofG query, so here we go: CofG was a really critical parameter on Concorde, being a delta, with no tailplane made it more so at take off speeds, and as we've previously said, was how we trimmed the aircraft for supersonic flight. CG was expressed as a percentage of the aerodynamic chord line. To get indication of CG you needed to know the mass of fuel in each tank; easy, from the FQI system. You needed to know the moment arm of each tank, (fixed of course). You then needed the zero fuel weight (ZFW) and zero fuel CG (ZFCG); these were manually input into the CG computers by the F/E, from load control data. The final parameter you needed was total fuel weight, again easy from the FQI system.
The 'normal' T/O CG was 53.5%, but in order to increase fuel weight (and hence range) an extra 'bump' was enabled to allow a max T/O CG of 54%. (CG was indicated on a linear gauge, with forward and aft limit 'bugs' either side of the needle. These bugs would move as a function of Mach and at the lower end of the speed range, A/C weight also). As the A/C accelerated, the limit bugs would move rearwards (with of course the rearward shifting centre of pressure) and so the fuel would be moved from the two front trim tanks 9 & 10 to the rear tank. 11. Once tank 11 reached it's preset limit (around 10 tonnes), the remainder of the 'front' fuel would automatically over-spill into tanks 5 & 7. (Once the fuel panel was set up, the whole process was controlled with a single switch). At Mach 2, the CG would be around 59%, the whole rearwards shift being in the order of 6'. As we said before, the 'final' CG could be tweaked to give us a 1/2 degree down elevon, for minimum drag.
I really hope this helps Biggles78.

Guys, back to the Airbus thing; My friend ChristiaanJ gave some really accurate insights, (he always does) but there is another legacy that carries on the this day; some of the audio warning tones were COPIED from Concorde into Airbus. (For example, the A/P disconnect audio is identical). I think this is great, and gives 'our' aircraft a lasting everyday legacy.

As far as the fly by wire goes, Concorde had a relatively simple analog system, with little or no envelope protection (Except at extreme angles if attack). As has been previously poted before, production series test aircraft 201, F-WTSB, pioneered the use of a sidestick within a new digital fly by wire Controlled Conviguration Vehicle sytem, with envelope protection and attitude rate feedback. (This evolved into the superb system known and loved by the Airbus community). It is a really bizaar twist of fate that the Concorde FBW system has more mechanical similarities to the system used in the B777 than Airbus. (Mechanically similar at the front end, with an electric backdrive system moving the column in A/P mode; Concorde being backdriven by a hydraulic relay jack).
As a final piece of irony; the Primary Flight Control Computers on the B777 are designed and built by GEC Marconi Avionics in Rochester Kent, now BAe Systems. This is the same plant where Elliot (becoming Marconi and finally GEC Marconi Avionics) developed and built the UK half of the AFCS computers. Isn't this aviation world strange?
Galaxy Flyer
Your inputs here are great, and I'm sure appreciated by all. (I assume from your name that you were a C5A pilot. While I was in the RAF on C-130's, our Lockheed rep' used to supply us all with company magazines, that were full of stuff on this new (it was then) giant of the sky. I fell in love with it there and then).
Anyway, back to Conc': The decel' positions were carefully worked out and adhered to; the aim was to be subsonic to within (I think) 50 nm of the east coast. I'll wait for one of my Concorde pilot friends to confirm that here, but i think I'm correct. I do have a fond memory of one flight out of JFK; we were temporarily 'held' by Boston ATC to Mach 1.6 (and at around FL440) because of an Air France Concorde heading for JFK. We saw this guy above us, at around FL580 on a near reciprical , doing Mach 2, screaming straight over the top of us. We were excited by this amazing spectacle, and so were the AF crew over the VHF ('you never boomed us, did we boom you?'). But the most excited person of all was this guy in Boston ATC. ('I've never seen anything like it guys, your two blips whistled over each other on my my screen like crazy').
Stliton
As far as the F/D noise levels were concerned, once the nose and visor were raised, it was as if someone had switched off the noise . The main source of noise up there was just the equipment cooling, and that was not bad either. It was, in my view, little noisier up than most subsonics. (But not the 744, where you are so far away from all the racket ).
Ozgrade3
You're making us blush here; thanks for your comments, I think we are just trying to share some of our experiences (and 'bit's we've picked up over the years).
From my perspective, I did write some stuff used by our pilots, AF even got a copy or two I think.

First, I must apologise to Stilton for hi-jacking his thread. I had inadvertantly asked a question in the wrong thread and have only just realised it, so sorry Stilton. The good part of this is all this delicious Concorde info that were are privileged to be receiving from M2dude and ChristiaanJ is all in the one thread. Unless anyone has any objections maybe the Forum Moderator could merged the other 2 threads into this one.

Thank you for the CoG answer. 6 feet sounds like an awful lot but then I am only able to compare it to the littlies that I fly. The ability to use the trim tanks to only have to use a \xbd\xb0 of elevon must have made a substantial impact on performance and the resulting reduced fuel consumption. To think it was all computer controlled at the time when the PC didn't even exist.

M2, you have said that the fuel system was a work of elegance and the above desciption give me a small insight into this. I know that I am just going to have to find books written about this lady to find out more. I have been lazy when asking about item that I could Google but there was a method behind my laziness. When you and Christiaan share your knowledge there is always a personal anecdote or insight that will never be found in any books that I may be able to find. Gentlemen, for this THANKS seem so insufficient.

The TOC=TOD had me thinking and I believe insomnia may have assisted with some understanding (otherwise the stupid sign for me comes out again ). Gee I hope I have this even partly right. I assume that when accelerating to Mach 2, that it was done while climbing. I was initially stuck with the compression factor of Mach 1 and without thinking the same would happen at Mach 2 (A C Kermode was the hardest book I have read that I didn't understand ). Therefore with that in mind I was stuck trying to figure TOC=TOD. Am I right or even slightly so in thinking that cruise climb and cruise descent was the flight and there was minimal actual level cruise in the "pond" crossing?

I had also forgotten to take into account the speed factor, DUH!! Subsonic climbs, what 35 - 45 mins to FL4xx and then it is in level cruise for the next 6 hours before TOD. The lady took what, about 3.5 hours, and the extra 20,000 feet it had to climb and descend ate up or into any level cruise it had (or didn't have). Am I on the right track or am I making an ass out of me and me.

I was in the jump seat of a B767 on a trans Tasman crossing, CAVOK, when about 2,000 feet lower a dot followed by a straight white cloud approached and passed by. I found that impressive so the 2 supersonics passing at the speed of an SR71 must have been spectacular. Shame radar track isn't available on You Tube. Oh yes, did they boom you?

As you have said, fuel flow was reduced the higher you got. I think it was 5T per powerplant at FL500 down to 4.1T at FL600. Was there any figures for higher the Levels? I am curious to see how much less fuel would have been used at the higher FLs considering it was reduced by 900Kg/hr for just 10K feet. Very interesting what you said about when the temps were ISA+. I would never have thought such a small temperature change could have effected such a signifigant performance result. It also sounds odd, as you said, the faster you go the less fuel you use.

Last greedy question for this post. How much of the descent was carried out while supersonic and how did this affect the fuel flow?

Thank you for allowing me, a non-techy, to participate in your lovely thread!

Just a short story about the adorable, charming and all-round fantastic bloke, Capt. John Cook.

During an exceptionally busy flight (MPs, press with cameras and sound booms on board - cc trying to negotiate the aisle with mayhem abounding) - John came out of the F/D and was standing in the forward galley looking bewildered.

"What can I do for you, skip?" I asked as I rushed in to replenish a drinks tray.

"Oh Landlady, thank goodness.... I'd love a coffee but I can't work the boiler............"

This from a training captain par excellence, with a twinkle in his eye who knew every inch of that machine - (and in the days before bev makers), who just wanted to save me a job!

I hope the angels are making your coffee now, John.

But that's what everyone was like....we certainly were a team which, I'm sorry to say, isn't always the case these days.

Now boys, I will leave you to get back to your sprockets and widgets.

Galaxy flyer

Absolutely correct the T-heads often went up past us at 60000ft, which is quite scarey when you think of the energy required to do that. Makes you as part of mankind seem somewhat insignificant.

Avoiding them as another problemas the Malacca Straits is quite narrow, well it is for Concorde trying hard not to boom the land on either side, but as I remember it there were two good points

The T-storms seemed to be normally over the land either side, but more important we would start to slow down shortly after entering the Malacca Straits and once subsonic we were in the same ball park as other aircraft , avoid them at all cost, and we could then fly over land without upsetting people

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bio161

No the crews flew just the one trans Atlantic sector and then got off for a rest. Well you could not have us boys working too hard now .

In fact it was just possible for the crews to do a return trip and indeed when there were crew problems this was indeed done.

Morning flight
The Concorde report time was 1.5 before departure and a turn around at JFK would have been about 1.5 hours so when all added up it could have just been done. However any delay to either service could result in the home bound flight being late or indeed cancelled due to flight time limitations. This the company deemed to be unacceptable risk on an aircraft which was sold as saving time.
In fact as the morning flight was on approach to JFK,the morning flight back to LHR was already taking off. For the crew to now wait for the late departure back to London would put them way over FTLimitations

That did not mean the crews only did one sector a day

LHR-IAD-MIA was a days work as was the return.
On some of the charter flights it was often a multi sector day such as

Sydney--Brisbane --Guam --Beijing

I was only doing the PR on that trip so I have not got the times but it did seem a long day's work

At some point during the development of Concorde, there were a number of flights performed in the UK where RAF Lightnings flew at supersonic speed over various places to assess the effects, including how many complaints were received.

I don't remember exactly when this happened, but I would guess about 1970. What I do remember was being in my bedroom in North London when there was a double boom and just managing to see for an instant the aircraft that made it heading south towards Central London before disappearing behind the trees and houses at the bottom of our garden. I can't recall how high it was flying but it did look very small from my perspective.

Of course by this time Concorde was already flying so it was clear that it would have to stick with its general configuration and deal with overflight problems by changes in routing, but I did enjoy the experience. I think it was the first sonic boom I had ever heard, but I was already interested enough in aircraft to know what it was.

Feathers McGraw ,
Nice one.
Concorde itself also did some of the early test flying in "boom alley", a route along the west coast of Scotland and over the Irish Sea.
The result was the usual batch of bogus claims for glass damage, minks eating their young, etc., even on days when Concorde didn't fly....

I would say that 99% of the stories about Concorde (and other supersonic aircraft) actually causing damage are fiction.
However, a sonic bang IS loud, and totally unexpected, hence startling, and NOT what you want when you are doing a precision job, for instance.
IMO a few dozen bangs a day, every day, would never have been acceptable.

(Where I live, we get about one a month, when a Mirage returning from the Mediterranean misjudges his deceleration, so I'm still regularly reminded of what they sound like.)

Christian

Dare I ask for the more complicated version?

Sidebar: in a supersonic wind tunnel test, do you get a sonic boom?

Not sure I know how to answer this! I will need to think on it.

I had thought I might have some pretty pictures but I haven't got anything for low AoA. I find it difficult to respond to such a general quetion though. Could you be a little more specific as to the bits that interest you?

Good question!

I THINK the answer is no. You will get the bow shock of course and this will be reflected off the tunnel walls so you must have a big tunnel or a small model to avoid these reflected waves interfering with the flow over the tail of the model, but the pressure rise on the tunnel floor is 'static' and the tunnel walls are massive steel construction. I may be wrong here, but I associate sonic booms with a rapid rise in pressure and a 'movement' of that pressure rise past the observer. In a tunnel you don't get this 'dynamic' effect (unless of course you can arrange to walk past the working section at 660 mph


CliveL

Edited after some thinking

I really like this question..... and I admit to still being baffled....

A Mirage 2000, a Rafale or a Mirage F1 is only about 15m (50ft) long.
Yet the booms we get locally (see above re returns from exercises over the Med), are still the same double boom - "whah-boom" (N-wave).

Of course, when it comes to judging the exact duration of a sonic boom, things get very subjective.... I wouldn't trust my own judgment, since it's as much based on the rattling of the window/door as the actual sound.

CliveL, are there any documented records of the trials in "Boom Alley" we could use to settle some of the issue?

CJ

Quote:
CliveL, are there any documented records of the trials in "Boom Alley" we could use to settle some of the issue? Unquote:

Christiaan, there isn't anything particular to "Boom Alley", but there is enough data around to quantify the issue.

SSD, you were quite right when you said that the shock waves diverge as they get farther from the aircraft; that could be as much as 25% of the aircraft length at the ground. Near the aircraft the rise time would be proportional to length/speed of sound.

To cut a long story short, plotting all the available data leads to a pretty good expression for the rise time:

T = 0.011*LOA + 0.0001*FL

To give you a feel for the numbers, the measured value for an F18 at FL600 is 0.18 secs, for Concorde at FL520 about 0.25 secs or for an F104 at FL190 0.08 secs.

After that it would depend on your own perceptions I think, but I could easily envisage either a single or double bang for a fighter size aircraft depending on altitude.

Green bean
Remember the Heros well, one of the pleasures of JFK especially having grown up on spam.....

Sonic booms
Experienced the trials in the sixties over East Anglia, one rogue one over Berkshire in the 70s, three or four from the French concorde whilst sailing across the channel and latterly annual ones from the French airforce.
The Concorde ones seemed much louder and frightening - first time I thought we had hit a mine (wouldn't be the first time although fortunately it didn't explode).
And contrary to a previous opinion they did do damage - odd window and a vase.

Just for theories sake, if there were no noise, speed or boom considerations what would be the optimum profile for Concorde to fly after departure ?



In normal service I understand it had to comply with normal noise abatement departures, speed limits and remain subsonic until far enough from land to prevent the boom being a consideration.


But what if it could accelerate immediately, with no restrictions of any kind ?


I imagine you would stay in afterburner, accelerate to VMO and on to M2 in the climb ? or would airframe heating at lower altitudes prevent this ?



Lastly, was this ever done in testing, or for example leaving Barbados ?

My only reminiscence is trying to persuade my parents that they could not hear Concorde go supersonic when living in Bournemouth,


Dowot.
Well the following may be of interest to you.


When working with the guys at Alderney the boom from Concorde rattled the windows. On enquiring I was told that the AF Concorde usually ignored the noise restrictions and opened the throttles early so it was a regular event and to hell with the complaints.


I was at Heathrow and a guy I worked with said he heard the boom in the Bracknel area. This was confirmed as the AF Concorde and the boom was bouncing off the clouds hence him hearing it at Bracknell.

I just have a problem with studies that try to analyze human activities with reductionist statistics and math. Most of human achievement comes not from the masses (which perhaps can be studied that way) but from the outliers, the screwballs, the few who, through enhanced human cussedness and stubbornness, decide NOT to stay with the obvious, efficient or safe thing.

Concorde was a political animal, heavily subsidized because someone want it to happen, regardless of efficiency.

But then, ALL advances in transportation have been - and often still are - political animals, subsidized because someone with money and power wants it to happen, regardless of efficiency.

Columbus and Magellan were subsidized, to head straight out to sea when everyone else was sticking close to the coastlines. Look up the land grants to U.S. trans-continental railroads. Or the Air Mail contracts that supported the fledgling American air transport industry (and if you think "that was then, and this is now," - consider the budget of the FAA and NTSB and TSA, and the military contracts to Boeing and its suppliers.)

Cars? Consider how much tax money goes to build and maintain highway systems.

And consider the man who stood up in the U.S. Capitol and declared, "I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the moon and returning him safely to the earth."

Concorde failed because it lost political support** - just like Apollo and the Space Shuttle. But most of the other aircraft on those charts would also be, or have been, far rarer in the skies (or never appeared) if they lost (or never had) their own political backing and subsidies, direct and indirect.

**If the French government had felt it was in France's interest for Concorde to continue, I'm sure money for, and political pressure on, Airbus would have been found to keep her flying.

And Concorde also faced substantial political opposition - its market viability would have been much higher if U.S. authorities had been as lenient with its "furrin" sonic booms as they had been with our own home-grown booms ("The Sound of Freedom!", it was called.)

Now - Concorde's technology was pushing 40, and no doubt that particular airframe would have faded away, just like the 727 and the other designs from the 1960's. To be replaced with something newer. But the future of supersonic transport in general was cut short not because of some statistical failing, but simply because it no longer shared the same political support as subsonic aviation.

It's not that simple. Political support didn't diminish for no good reason. When you talk about Concorde, or any supersonic vehicle, you cannot ignore what used to be called "the sound barrier".

In a sense, it really is a barrier; not so much physical, but financial. If the drag curve between Mach 0.8 and Mach 1.8 was just a similar extension of the drag curve between Mach 0.5 and Mach 0.8 (i.e. a simple V squared relationship), then the political support along with the economic viability of supersonic airliners would mean rich folks could still buy a fast ride across the Atlantic. And, if there were no sonic boom either, then these fast airliners would be flying everywhere and be even more viable.

But that huge spike in the real-world drag curve as you pass through transonic air-speeds and the steep power-required curve beyond that forms what amounts to a really big spike in the money required to operate at high Mach numbers both from an initial hardware point of view but, more importantly, in the money required to both fuel and maintain such exotic airplanes. Pile the sonic boom issues on top of those costs, and it's no suprise very few people have ever gone supersonic.

Political support for the Concorde didn't simply go out of fashion. It faded for very good reasons, mostly related to good old Mother Nature and the odd shape of the real-world drag curve.

@mozella

I guess my point would be that the same problems of supersonic flight existed in 1963-1976 as did in 2003. It was a technological challenge, and it was expensive.

The physics of the sound barrier did not change over that time. Nor did the constituent gases in Concorde's exhaust plume*, nor did the volume of the sonic booms.

However, in 1976, going supersonic was considered worth the costs, and in 2003 it was not, and that was a political (or if you prefer, cultural) calculation.

*Actually, I think the engines were tweaked to be less "smoky", but that may have been before commercial ops began.

@tomahawk, pattern is full

You really need an input from a BA pilot, but my memory is that the approach to LHR was up the Bristol Channel not the English Channel.
Original decel point was moved back about 100 n.ml to avoid secondary boom effects over West Couhtry. This put it somewhere south of the southern tip of Ireland

Interesting to see references to the secondary boom here. I lived in Crowborough, East Sussex, close to MAY VOR location, in 70s and 80s, at about 600ft elevation facing southwest. Often at about 2100hr on a quiet evening we would hear a faint boom from the AF Concorde coming up the Channel and turning towards Paris. Local dogs would sometimes bark just before we heard the sound!

Ah yes, living in Minehead throughout the entire Concorde operational era, I fondly remember those evening "babooms", usually preceded by the clattering calls of startled pheasants (no, not peasants or dogs) in the woods behind us who seemed to get a second or so advance warning, presumably at a frequency range above mine.

There was also a definite difference in the intensity of those secondary booms between summer and winter, with the latter being slightly louder and more reliable than the summer ones.

What a beautiful sight it was too in a clear blue sky, with that gleaming white shape spearheading the contrails that would gradually knot up and disperse as it headed up the Bristol Channel and disappeared towards Bristol. Twice a day in the evenings and another in the afternoon when the Washington flights were operated.

Happy days, much missed!!

FraserConcordeFan

... How exactly would you get the INS into memory mode so you could input the two digit code to activate the route section...

Concorde did have a facility to input a flight plan route segment into the INS and this facility was used on most flights. To explain this very briefly , let\x92s take a typical LHR-JFK flight as an example:

\x95 Press the amber REMOTE button on each INS CDU
\x95 Load the first waypoint (#1), usually Woodley, manually into an INS
\x95 Key WAYPOINT CHANGE and enter and insert \x930 to 1\x94 on each CDU.
\x95 Select DSTRK/STS and HOLD
\x95 Key WAYPOINT CHANGE
\x95 Key the DME catalogue number (from the flight log, usually 90 on a LHR-JFK sector) and insert
\x95 Key WAYPOINT CHANGE
\x95 Key the Route Segment number (from the flight log, usually 10 on a LHR-JFK sector) and insert
\x95 Cancel HOLD

Then the usual checking routine of:

\x95 Checking the lats and longs of the loaded waypoint lats with those given on the flight log
\x95 Checking the INS distances between waypoints with those given on the flight log
\x95 Checking the lats, longs and frequencies of the DMEs against the database guide

Return the displays back to WAYPOINT, cancel REMOTE, select AUTO and check the INS alignment.

Remember, with only nine waypoints available in the INS, this procedure would have to be repeated in flight, sometimes more than once. Takes much longer to write about than it did to do!


tomahawk pa38

... I'm just curious about what eastbound routings were into Heathrow...

The usual Eastbound routing on a JFK-LHR flight would be via track SN to 15\xb0W then on SL3 to BARIX to MATIM to PITEM to NIGIT and then OCK.


... and where the decel point was....

Let me just check we are talking about the same thing! The Decel Point was the point at the end of the cruise/climb, where we first throttled back and started to decelerate from M2.00 and then descend from, say, around FL 560.

The decel point was calculated in order that we would be just under M1.00 at the designated Speed Control Point , and so the Decel Point was obviously further back than the Speed Control Point.

The usual route was up the Bristol Channel, a bit to the South of our outbound route, crossing the Devon coast just to the North of Barnstaple, routing to a waypoint called MATIM, which is around 51\xb0N 004\xb0W.

In winter, on a JFK-LHR flight via SL3, the Speed Control Point was 110nm before MATIM , and we were required to be subsonic at this point. Typically, we would be just under M1.00, and around FL410, when we crossed the speed control point, having started down from FL 560 around 105nm earlier.

The decel point was of no real relevance to those living on and around the coast of Devon and Somerset, but the Speed Control Point was. The position and time at which we decelerated through M1.00 and became subsonic were always recorded on the flight log, along with the altitude and spot wind, in case of any future claims of boom damage due to a misjudged decel.

Best Regards to all

Bellerophon

Dedicated to the memory of Andr\xe9 \xc9douard Turcat (1921 -2016)