Concorde question

[EXWOK]

Fuel: Conc vs 737

For those who wanted to know what the difference in fuel burn between a 737 and Concorde LHR-MAN........I don't know! (Never had the pleasure of flying the 737).

My best guess - at least 200% more. Probably higher.

A comparison:

Typical Concorde taxying fuel burn: 6500kgs/hr

Typical 777-200 cruising fuel burn: 6500kgs/hr

Of course, as we've already discussed earlier, the magic thing about Concorde was that once you'd got to Mach2 its efficiency was outrageously good - better miles per gallon than a 747. An option not available, however, between LHR and MAN.

Edited to add: a slow taxy out at LHR would almost definitely consume more fuel than the 737 would burn for the sector.

[Jo90]

Fuel comparison

No experience on 737, nor, sadly, on Concorde but do recall an occasion when travelling from Compass Centre on northside of LHR to T4 on the south side in the BA001 crew's van when we got to comparing fuel figures.

Turned out that they would burn slightly more fuel getting their 100 pax from T4 to 1000' agl than we would use to get our 180 pax on the 757 all the way to Amsterdam!

Typical burn on a 757 LHR - MAN was 2200 kgs or 2000 kgs on an a/c with the much more efficient E4 engines.

[M2dude]

I have to admit that some of the subsonic fuel burn figures for Concorde were truly eye watering, and without massive engine and airframe modifications there was precious little in service that could be done to improve things. Paradoxically improvements to the supersonic efficiency of the powerplant were easier to implement, and several modifications were implemented, tried or proposed to improve fuel burn:
Way back in the late 1970's we did a major modification to the intakes that increased capture area by 2.5% and gave us typically a 1.6% improvement in trans-Atlantic fuel burn, and although this was our biggest performance improvement modification, there were more:
The famous elevon and rudder trailing edge extension modifications (that due to poor design, produced in later life the water ingress induced honeycomb failures) together with the re-profiled fin leading edge modification, I never saw the performance gains quantified (anyone have any ideas?).
Can anyone here remember the riblet trial? In the mid 1990's Airbus supplied 'stick on' plastic riblets, applied to various areas on the under-side of the wing on G-BOAG. These riblets had very fine undulations moulded into the surface; the idea being that as the air flowed through and around the riblet patches, boundary layer turbulence, and hence induced drag would be reduced. Now, the performance gains (if any) were never quantified, mainly because the riblet patches either peeled off or the surface deteriorated with the continuous thermal cycle. (I was over in JFK when the aircraft first arrived after having the riblets fitted, and as the crew were trying to proudly show me these amazing aerodynamic devices, they were sadly embarassed, as several had dissapeared in the course of a single flight).
There was one modification, proposed by Rolls Royce in the late 1990's that did have quite a lot of potential; this was to increase the engine N1 by around 1.5%. This would have had the effect of increasing engine mass flow and therefore reducing the drag inducing spill of supersonic air over the lower lip of the intake. Depending on the temperature, the performance gains were in the order of a 1.5% improvement in fuel burn at ISA Plus upper atmosphere temperatures ('normal' LHR-JFK) to none at all at significant ISA Minus temperatures (LHR -BGI). The modifacation had been trialed on G-BBDG before her retirement in the early eighties, and was proven in terms of performance enhancement and engine stability. In order to keep TET at the pre-modification level, there was a small increase in N2 commanded also. (The higher N1 required an increase in primary nozzle area, reducing TET). The main reason for the modification not being implemented was one of cost; The Ultra Electronics Engine Control Units were analog units, and the modification was a simple replacement of two resistors per unit. However because ultimate mass flow limitation was also controll by the digital AICU (built by British Aerospace Guided Weapons Division) the cost of getting a software update for this exremely 'mature' unit was found to be prohibitive.
A certain 'brainy' SEO and myself were working on a modification to improve fuel burn on ISA minus sectors. The idea was to force the autopilot, in Max Cruise at low temperatures only, to fly the aircraft close to Mmo, rather than at Max Cruise speed of Mach 2 - 2.02; this would have given us gains of up to 1%, depending on the temperature. The basic electronics involved for the modification were relatively straightforward, but it was never pursued due to the complexity of dealing with temperature shears and the cost of certification.

Dude

[stilton]

Sincerely, this thread just gets more interesting.




Was any consideration given to the fitting of a Head up display ?




With such a manually flown Aircraft it would seem to be a natural for such an aid.




I realise the technology was in it's infancy at the gestation of the Concorde project but was there ever a proposal or even testing of such a device ?

[ChristiaanJ]

Originally Posted by stilton

Sincerely, this thread just gets more interesting.

Flattery will get you nowhere....
But I agree, post after post has either an interesting question or an interesting answer!

Was any consideration given to the fitting of a Head up display ?
With such a manually flown aircraft it would seem to be a natural for such an aid.

I don't think it was ever considered... which may be a tribute to the 'fit' of the SFENA 'clock-work' primary flight instruments of the time.... which was carried over to the next generation such as the A300 and A310.
AFAIK, even today, only very few commercial aircraft types have HUDs installed.

I realise the technology was in it's infancy at the gestation of the Concorde project...

Not really true, basic HUDs alreay existed well before Concorde flew.

....but was there ever a proposal or even testing of such a device ?

On Concorde? Not that I know.
SFENA (the firm I worked for) did work on a very limited HUD, basically just for runway alignment during take-off and roll-out, and IIRC some were installed on early A300s and A310s, but the idea never really seems to have caught on.

CJ

[stilton]

Thanks Christiaan.




Yes I think the Mercure had a HUD if i'm not mistaken.

[Brian Abraham]

Yes I think the Mercure had a HUD if i'm not mistaken

Was the first HUD installation on a commercial airframe (Thomson/Sextant). Certified to CATIIIb.

[twochai]

One of your earlier posts makes reference to the three engine ferry case, so I assume it was an authorised procedure?

Can one of your number remember the technique, the limitations and any comments on the rotation/acceleration/climb. I'm curious about the handling implications.

[ChristiaanJ]

stilton, Brian Abraham,

Just Googled this to confirm a less-than-certain memory.....
Today, only the 737 (later variants) has a HUD fitted.
Not sure if it's a standard fit, or a customer option.

CJ

PS : off-topic, but the Mercure was a nice aircraft, even rarer than Concorde (incl. the prototypes only 12 built).
One is at the LBG museum, looking immaculate, and being kept "alive" by volunteers, but of course out of hours.

[NW1]

Concorde had a very advanced HUD fitted. It was a spring-loaded wire frame (a bue transparent plastic thing on 'OAG) which you could flip up in front of you to help judge the landing attitude. With final attitude about 11 degrees and secondary nozzles scraping the runway at (from memory) about 12.5 degrees attitude control was key.

Three-engined ferrys were approved. Went through it on the sim, and this is only from memory but you set full re-heated power on the symmetric pair, and the assymmetric engine at 75kts. "Power Set" was called slightly later than normal (130kts). Any re-heat failure before V1 = RTO.

There were loads of complex additional issues to go through at planning (the 3-engine ferry manual wasn't the thickest on the fleet - but it was thick enough!) and I don't think I'd have been too keen on doing one (I was never asked, and I don't know of any Concorde having done it - more "seasoned" fleet members may know better!): I think it was a slighly more critical proposition even than doing it on a blunty, and most guys I know have reservations about it on their fleets too...

[ChristiaanJ]

Originally Posted by NW1

Concorde had a very advanced HUD fitted.

LOL...
Wasn't that the same thingmabob that was used to set your 'throne' to the exact eyeheight?

I knew it existed, but somehow never saw it. How and where was it stowed when not in use?

CJ

[M2dude]

NW1 and ChristiaanJ
Ahh yes, the super hi-tech 'HUD'. It was right up there with the 'eye level datum' indicator and not to forget, the reheat capabiliy indicator in terms of sophistication. (Extremely reliable though ).
As far as 3 engined ferries went; well NW1, not sure if you'd call me seasoned or just just clapped out and wrinkly, but it did happen a very few times in days of yore, mostly from SNN back to LHR. There were at least two; OAF in 1980 when she had the infamous LP1 blade fail (and Monty Burton's immortal words during the 'event' "what *** ing drill?). The second one that I can remember was OAA in 1991 when there was another far less serious compressor blade failure. In each case for the ferry flight, the broken engine was 'swaged' to prevent it windmilling and the aircraft would be flown back to the LHR garage by a management crew. There was however another required ferry measure as well as the engine swaging, this measure was to prevent the good engines going into contingency, due to the very slightly flamed out dead 'donk'. This procedure required the Engine Speed Unit to be removed from the electronics rack and a special jumper plug fitted in it's place (without the jumper fitted the start switch would never latch in. In this case also the E/O would also need to manually disengage the start switch at 25% N2). I have to admit that I never in my life ever saw this jumper plug, and in the cases that I can remember the aircraft departed SNN with the three engines at contingency. I remember that the case of OAA back in '91 most certainly was; I was flown out to SNN equiped with a pile of circuit diagrams and test boxes to investigate what we all thought was just a surge related engine shutdown. only to find a slightly more hairy state of afairs, with a very broken engine indeed. As a matter of interest, this particular failure was the only one ever in the history of Concorde in BA attributed to the engine having run for a protracted time in rotating stall. (This had happened on the previous day). A lot was learned by both BA and Rolls Royce after this event, and this failure never occured again.

Dude

[Feathers McGraw]

You can't just leave it there Dude!

Would you be so good as to explain what happened and why? It certainly doesn't sound healthy....

[M2dude]

Oh darn it Feathers, if you insist (LOL).
First of all, what is rotating stall? All gas turbine engines are prone to this to some degree or another, the Olympus was particularly prone (so we discovered to our cost). What happens is that extremely LOW figures of N2, small cells of stalled air rotate around the anulus of the early stages of the HP compressor (at approximately half the rotational rpm), resulting in parts of the airflow becoming choked and highly distorted. This often results in the combustion process being disturbed to the extent that combustion instead of occuring in the combustion chamber, occurs in the turbine itself. This of course results in massive overheating of the turbine blades and stators (and is what is suspected occured in the #2 engine on G-BOAA in 1991.
To prevent running in rotating stall, the Olympus automatic fuel start schedule would accelerate the engine quickly to around 67% N2 before dropping back to the normal idle figure of around 65% N2. (The stall clearance N2 figure was ambient temperature dependant, the higher the temperature the higher the N2 that was required and hence scheduled by the automatics).
What had happened on G-BOAA was an engine starting/accelerating problem, where the N2 ran at a sub-idle of around 40% N2 for several minutes. This was enough for the malignant effects of rotating stall to take hold, and the resulting turbine blade failure over the Atlantic the following day. In all fairness to everyone involved, none of us, including Rolls Royce realised just how potentially serious this phenonomen was, and salutary lessons were learned by one and all. (The following year Air France had a similar failure; their first and last also).
I flew out to Shannon on a BAC 1-11, that was sent to fly the Concorde passengers back to London. As I and my colleague were coming down the ventral door steps of the 1-11, a chirpy Aer Lingus engineer asks 'have you guys come to fix the broken engine?, there are bits of it lying in the jet pipe'. Now up to now, from the information we'd been given in London, we thought that we were going to be looking at either an intake or engine induced surge, a few systems checks and boroscope inspections and we'd all be on our way, so we naturally thought the Aer Lingus guy was joking. He was most certainly was not; as you looked into the jetpipe (through the secondary nozzle buckets) you could see a large quantity of metal debris, accompanied by a strong smell of burnt oil. I remember this day well, it was the day that the first Gulf war ended; how ironic.
The aircraft departed on three engines, flown by a management crew late the following day, my colleague and I returned to London by Aer Lingus one day later. (No passengers whatsoever are permitted on ferry flights, even expendable ones like me).

Dude

[Cron]

Odd question this which requires a bit of background to give authenticity.

When I could afford to fly R22s from an airfield neat Stratford on Avon the Heli company’s owner’s son attended some kind of auction of Concorde parts and came back with part (or all) of a Concorde rudder which was duly mounted on the hangar wall.

I gazed long and hard at it (closest I ever got to the supreme lady) and noticed a series of mysterious ‘bolts’ sticking out of the rear edge of the rudder. One of the helicopter engineers present rubbed his beard thoughtfully and surmised they may be ‘static wicks’ – but nobody present was really sure.

All this of course went straight over my head but whilst they were all on tea break I managed to chip of a couple of flecks of deep blue paint from the rudder and stash them in a match box. (Back in Birmingham later that evening I sat with friends in the garden of the 'Rose and Crown' and we all touched reverentially those paint chips that had been places we could only dream of – but I digress).

What were those bolt like things on the trailing edge of the rudder?

[Feathers McGraw]

OK Dude, thanks very much for that. Extremely interesting, I assume that there must have been some sort of fuel control failure for a sub-idle N2 to establish with the engine lit.

I've never heard of this phenomenon before, although I know that some fairly odd things can happen in helicopter rotors where the air below the rotor can be pulled around by the passing blades which sounds vaguely similar.

What steps were taken to prevent his happening again? Modification of the fuel control scheduling or something else?

[M2dude]

Cron

I gazed long and hard at it (closest I ever got to the supreme lady) and noticed a series of mysterious ‘bolts’ sticking out of the rear edge of the rudder. One of the helicopter engineers present rubbed his beard thoughtfully and surmised they may be ‘static wicks’ – but nobody present was really sure.

Sounds like the helicopter engineer's guess was right, they'd be the static wick mountings.
Feathers McGraw

I assume that there must have been some sort of fuel control failure for a sub-idle N2 to establish with the engine lit.

Yes there was, that was the problem alright Feathers. I'd only heard an engine stuck in rotating stall during startup once; even on the flight deck it sounded like a tom cat with his gonads trapped in a vice, and we shut the thing down straight away. (The engine, not the tom cat ).

What steps were taken to prevent his happening again? Modification of the fuel control scheduling or something else?

It was mainly a case of increased vigilance during engine start; it was always noticable to see rotating stall clearance on startup as the N2 went past normal idle and then rolled back. As far as modifications go, I'd designed a modification to detect and alert the crew if rotating stall had not been cleared on startup, but it was felt to be too costly and complex, when increased vigilance by all could prevent the nasty event happening in the first place. (I suppose only one BA occurence in 27 years is not so bad, and if the automatics did their job you had no problem anyway). But now at least EVERYBODY was aware of the malignant consequences of not clearing rotating stall on startup; it was no longer just a phrase that we all learned in training, but scary reality.

Dude

[Vinni3]

Does anyone know what happened to the pilots that featured on the ITVV Concorde video?
There's a preview here (I think it only lasts for this Sunday though)
ITVV British Airways Concorde Preview :: ITVV

[Landroger]

Rotating stall.

Sorry Dude, I'm behind on this again. I must be in the hard of thinking class on this. Would you just confirm - or jump all over - what I am visualising here please?

Due to some quite esoteric disturbance in the area where fuel first hits compressed air, the flame front either detaches from the nozzles or establishes some way downstream? As far, indeed, as the turbines with a very hot (too lean?) mixture that damages the blades? Is that anywhere on the right track?

The closest analogy I can think off is with a plumbers blow torch, where the fuel pressure/temperature is disturbed while lighting it. The flame detaches from the burner and exists - usually briefly - up to an inch from where it ought to be, often with a very harsh, high pitched roar. I've seen it happen with my oxy/acetylene torch on light up as well, but only briefly and it usually goes out.

Roger.

[M2dude]

Landroger
Good to see you here again Roger, I'll try my best to give you my take on rotating stall. (I worked very closely with Rolls Royce in the Concorde days, and everything I know about the process is thanks to them). Turbine engine combustion is a precise and delicate affair, particularly during start, and too much or too little fuel can cause severe problems. With rotating stall, the rotating cells of stalled air. if they manage to take 'hold' can cyclically choke the flow into the latter compressor stages (it's the cyclic nature of the cells that is the real problem, hence the 'rotating' stall term). The cells as they 'hit' the compressor blades (the cells are rotating at half shaft speed in the opposite direction of shaft rotation) can cause blade vibration and can also cause minor surges within the engine. The combustion fire literally can burn in the turbine section, but any distortion to the combustion process will result in local overheating, due to poor air/fuel mixing etc. In some engine types, damage can be also be caused to the HP compressor blades (due to vibration) but with the Olympus the main danger was to the turbine blades and stators. It's difficult to relate to any common analogy for this lot I'm afraid Roger.
Rotating stall was avoided in the Olympus by starting the engine with the primary nozzle driven wide open, and controlling two parameters; those being the opening rate of the fuel valve and the rate of rise of exhaust gas temperature. (During the start sequence, once ignition had occured the EGT rise was held to 6 degrees per second, right up until rotating stall clearance at 65% temperature corrected N2 ). So the engine accelerates without let or hinderance right through the danger zone, but was prevented from dipping below 65% temperature corrected N2, where the danger zone starts again. (Absolute minimal idle for the Olympus 593 was set at 61% N2).
I sincerely hope this blurb helps Roger, if not then feel free to ask again or PM me.
Regards

Dude