27th Aug 2010, 22:12
permalink Post: 145
Notfred
Love the lightning story, hadn't heard that one before.
That would have been production series test aircraft G-BBDG, A/C 202 before a purpose built hangar (more shed really) was built to house her, with fin and U/C removed. This aircraft has now been beautifully restored at Brooklands museum.
You are quite correct about the pushback, not having an APU (THAT story again
) meant that a one engine in each nacelle pair had to be started on the gate, and the other in each nacelle started after push. Having a symetrical pair started enabled all 3 hydraulic systems, and hence most of the critical systems to be checked puring pushback.
Brake temperatures always had to be monitored; they really could get very hot. If a wheel was still too warm after T/O, then the gear would be left down just a little longer to aid cooling. (Each brake also had an electric cooling fan).
Idle thrust was always a problem in that it was too high; there was a 'lo idle' setting, but depending on the temperature of the day the difference was not that big. You could not just reduce idle some more because of a malady known as rotating stall. This can plague any engine, but the Olympus 593 was particularly susceptible. At very low idle speeds, pockets of air 'rotate' around the first few compressor stages and can completely alter the airflows through the engine. It is important that the engine is always accelerated quickly through this zone on start-up, because serious damage can occur if the engine runs for any period of time in the rotating stall region. If the engine DOES operate in this zone, then the combustion process can even occur in the last few stages of the HP compressor, causing extreme damage. This damage, although malignant, can result in blade failure and the subsequent damage to the combustion chamber and turbine areas. This can occur within a few flights of the event, so just cranking down the idle was never an option.
Love the lightning story, hadn't heard that one before.
Quote:
| I was in the Air Training Corps in Bristol in the late 80s and flew in the Chipmunks based at Filton. Used to see the spare Concorde sitting there outside the hangar. |
Quote:
| And a question of my own - I've heard that the engines were pretty powerful even at ground idle, so powerful that if all 4 were running then a tug would not be able to push her back. Any truth to this? Were just 2 started, pushback and then start the remainder? Also heard that the pilots had to watch the brake temps whilst taxiing out to takeoff - was this also due to the power? |
) meant that a one engine in each nacelle pair had to be started on the gate, and the other in each nacelle started after push. Having a symetrical pair started enabled all 3 hydraulic systems, and hence most of the critical systems to be checked puring pushback.
Brake temperatures always had to be monitored; they really could get very hot. If a wheel was still too warm after T/O, then the gear would be left down just a little longer to aid cooling. (Each brake also had an electric cooling fan).
Idle thrust was always a problem in that it was too high; there was a 'lo idle' setting, but depending on the temperature of the day the difference was not that big. You could not just reduce idle some more because of a malady known as rotating stall. This can plague any engine, but the Olympus 593 was particularly susceptible. At very low idle speeds, pockets of air 'rotate' around the first few compressor stages and can completely alter the airflows through the engine. It is important that the engine is always accelerated quickly through this zone on start-up, because serious damage can occur if the engine runs for any period of time in the rotating stall region. If the engine DOES operate in this zone, then the combustion process can even occur in the last few stages of the HP compressor, causing extreme damage. This damage, although malignant, can result in blade failure and the subsequent damage to the combustion chamber and turbine areas. This can occur within a few flights of the event, so just cranking down the idle was never an option.
31st Aug 2010, 01:25
permalink Post: 166
Nick Thomas
...I just wondered how the engine was kept at a sub idle 30% N2?...
Just below each engine's individual start switch, there was a second switch, which would select the type of start required, either NORMAL or DEBOW.
When between ten minutes and five hours had elapsed since an engine was last run, a debow start was required. With a debow start selected, the engine was started normally, but the debow system automatically stabilised the engine at a sub-idle RPM, around 30% N2, whilst the interior engine temperatures became more uniform and the HP spool shaft re-aligned/straightened itself.
As to exactly how it did this, you're going to need a reply from an engineer not a pilot. As far as we were concerned, it was the PFM box in the engine start system!
After running for one minute stabilised in debow (or when the debow light came on) the F/E would return the debow switch to normal and check that the N2 returned to idle and the debow light went out. The F/E would monitor the N2 very carefully over these few seconds, as the engine came out of debow, to check that the engine cleared rotating stall.
If it didn't, two things would happen.
Firstly the F/E got fairly busy, trying to clear the engine out of rotating stall without causing it to surge, and secondly, as with any Concorde engine malfunction drill, I quietly give thanks that I was a pilot and not a F/E.
If a debow start was required, but somehow got missed, the engine could give a reasonable impression of an out-of-balance tumble drier, or so I'm told.
Best Regards
Bellerophon
...I just wondered how the engine was kept at a sub idle 30% N2?...
Just below each engine's individual start switch, there was a second switch, which would select the type of start required, either NORMAL or DEBOW.
When between ten minutes and five hours had elapsed since an engine was last run, a debow start was required. With a debow start selected, the engine was started normally, but the debow system automatically stabilised the engine at a sub-idle RPM, around 30% N2, whilst the interior engine temperatures became more uniform and the HP spool shaft re-aligned/straightened itself.
As to exactly how it did this, you're going to need a reply from an engineer not a pilot. As far as we were concerned, it was the PFM box in the engine start system!
After running for one minute stabilised in debow (or when the debow light came on) the F/E would return the debow switch to normal and check that the N2 returned to idle and the debow light went out. The F/E would monitor the N2 very carefully over these few seconds, as the engine came out of debow, to check that the engine cleared rotating stall.
If it didn't, two things would happen.
Firstly the F/E got fairly busy, trying to clear the engine out of rotating stall without causing it to surge, and secondly, as with any Concorde engine malfunction drill, I quietly give thanks that I was a pilot and not a F/E.
If a debow start was required, but somehow got missed, the engine could give a reasonable impression of an out-of-balance tumble drier, or so I'm told.
Best Regards
Bellerophon
7th Nov 2010, 00:09
permalink Post: 672
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
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
Last edited by M2dude; 7th Nov 2010 at 01:34 .
7th Nov 2010, 01:34
permalink Post: 674
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
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
7th Nov 2010, 07:34
permalink Post: 677
Cron
Sounds like the helicopter engineer's guess was right, they'd be the static wick mountings.
Feathers McGraw
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
).
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
Quote:
| I gazed long and hard at it (closest I ever got to the supreme lady) and noticed a series of mysterious \x91bolts\x92 sticking out of the rear edge of the rudder. One of the helicopter engineers present rubbed his beard thoughtfully and surmised they may be \x91static wicks\x92 \x96 but nobody present was really sure. |
Feathers McGraw
Quote:
| I assume that there must have been some sort of fuel control failure for a sub-idle N2 to establish with the engine lit. |
).
Quote:
| What steps were taken to prevent his happening again? Modification of the fuel control scheduling or something else? |
Dude
7th Nov 2010, 11:58
permalink Post: 679
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.
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.
7th Nov 2010, 21:59
permalink Post: 680
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
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
11th Dec 2010, 22:17
permalink Post: 856
Them darn intakes
Hi Guys, quite a few little points here, so here's my angle(s):
Pedalz
Ooo yes. The biggest problems we ever had associated with the ramps themselves were wear in the seals at the sides of the forward ramp. Even a few thou' over the maximum allowable side gap was enough to make the intake unstable and susceptible to surging. (It is quite interesting that the rear ramp side gaps were not in the least bit critical, and if Concorde intake development had continued, the rear ramps were going to be deleted altogether). Other failure factors were control unit malfuntions, rapid sensor drift; all of these causing either ramp/spill door drift or runaway. Primary nozzle misbehaviour could also result in intake surges. Having said all that, the monitoring of the intake system was truly superb, and surface runaways, themselves quite rare, would usually be picked up by the control system monitors causing either a lane switch or if that did not work, a total 'red light' failure with the surfaces frozen. No surge was treated as 'just one of those things', and much midnight oil was burned and hair pulled out (so that's what happened to mine
) to try and find the cause of the surge.
My friend EXWOK perfectly answered the intake hydraulics allocations.
EXWOK was right on the ball here as usual, in fact above Mach 1.6 an interactive surge was more or less guaranteed. The cause of interactive surge had nothing to do with the wing leading edge position, but to the radially generated distortion field coming out of the FRONT of the surging intake, severely distorting the adjascent intakes airflow. It mattered not if the originating surge was an inboard or an outboard intake, the other guy would always go also, above Mach 1.6.
You might want to take a look at 'When Intakes Go Wrong Part 1:
Concorde engine intake "Thrust"
and Parts 2 & 3:
Concorde engine intake "Thrust"
Not to mention Part 3:
dixi188
I can never recall this particular event happening with BA , certainly not as a result of a ramp failure. Although in the near 28 years of operation we had quite a few SNN diversions, none that I can ever recall were as the result of a ramp structural failure. The two major SNN diversions that I can recall were G-BOAF in the early 80s when an LP1 blade failed and resulted in a totally wrecked engine (although a completely contained failure) and G-BOAA in 1991, with another wrecked engine due to running in rotating stall. (Both of these events were covered previously in our thread). ChristiaanJ has mentioned quite rightly the event with A/C 001 spitting a ramp out, and Air France had a ramp failure going into JFK. (Covered previously in our thread, due to certain 'human foul ups'). I am not sure, but I think that
this
one in JFK DID require a double engine change in JFK. (Usually from SNN a BA aircraft would be 3 engine ferried back to LHR).
ChristiaanJ
Nope, you are quite right, no more French or British development aircraft ever suffered a ramp linkage failure again. The 001 ramp failure was a salutary lesson to the design team, and the intake assembly became tougher than old boots after that, nomatter WHAT you threw at it.
Due to the lateness of the hour (and me being up at 4
), that will have to do for now guys.
Best regards to all
Dude
Pedalz
Quote:
were the intake ramps in front of the engines ever known for problems? Especially during supersonic cruise where the airflow through the compressors and position of the ramps was determined by an exacting science which could turn into quite a situation if disturbed.
Which hydraulic system actuated these ramps?
|
) to try and find the cause of the surge.
My friend EXWOK perfectly answered the intake hydraulics allocations.
Quote:
| Due to the shape of the leading edge and positioning of the intakes themselves, could it be possible that disturbed airflow from a problem ramp or donk could also effect it's outboard neighbour (if I'm right in presuming that only the inboard engine surging etc. could effect the outboard and not vice versa)?[/ |
You might want to take a look at 'When Intakes Go Wrong Part 1:
Concorde engine intake "Thrust"
and Parts 2 & 3:
Concorde engine intake "Thrust"
Not to mention Part 3:
dixi188
Quote:
| A certain CFI (I think) at BA flying club, High Wycombe, who was also F/O on concorde, showed me some photographs of an engine that had eaten a piece of intake ramp. I think he said that the adjacent engine had surged and a piece of ramp went out the front and down the other engine. This resulted in a double engine failure mid atlantic. They landed in Shannon with very little fuel left. |
ChristiaanJ
Quote:
PS I have no record of any of the British development aircraft ever having lost a ramp, notwithstanding the number of deliberate engine surges they went hrough. But then maybe I wasn't told....
|
Due to the lateness of the hour (and me being up at 4
), that will have to do for now guys.
Best regards to all
Dude
Last edited by M2dude; 12th Dec 2010 at 04:51 . Reason: Adding a bit and correcting another