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Early Right, what you say has been mentioned a number of times iin different places. (Not sure if it on this thread though).
In fact, it is not correct to say that desert dust is from the same origin as volcanic ash. They are created through completely different processes and have very different qualities. Firstly, dust is generally rounded and smooth and also significanlty larger. This means much less or possibly no erosion and abrasion on surfaces. Also, it is generally accepted that the melting point of dust is much higher than temperatures typically found inside a jet engine, so the threat of melting and deposits forming on turbine sections does not exists. Volcanic ash is quite unique in that sense. A comparison with dust storms or similar events is not accurate. |
Once again, the smaller the particle (dust vs sand) the hotter it gets as it passes through the combustor.
The larger the particle (sand and young eruption volcanic stones that haven't fallen to the ground yet) the more likely it is to be centrifuged out the fan duct. Volcanic ash particles often are made up of stuff that melts at temperatures lower than most earth surface dust-sand storms. It's a statistical thing and you manage your way around it finding air clean enough to fly in. |
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In case you missed it, Bang Goes the Theory, episode 5, BBC1 iPlayer did a interview with the D-CALM engineers during the event and an explanation/demonstration of the ash coating of turbine blades.
BBC iPlayer - Bang Goes the Theory: Can You Train Your Brain? |
To amplify another posting re. different engines and different air intake volumes....
A massive high bypass engine needs much more air than a small low bypass one. There's also the question of what percentage of ash particles will get 'centrifuged' into the fan duct and therefore not cause any problems in the core of the engine. Clearly, the smaller the particle, the less energy it will gain as it goes through the fan and therefore the lower the probability it will make it into the duct (assuming it started its journey near the centre of the fan). Particles already towards the circumference will definitely go straight into the duct. .. this is all stuff for the engine builders to measure and calculate when deciding how much ash of what average particle size a particular engine will tolerate. Presumably a somewhat new experience for them now that 'zero ash' has been declared an unachievable aspiration in European airspace. :) And potentially at least, REALLY fine ash will pass through the cooling plenum, through the blade passages and out the cooling holes without causing a blockage??? Tricky stuff! The average ash particle size is also determined by the age of the plume and, crucially, by how much water / ice is left in the caldera of the volcano. If a lot of water gets in amongst the outflowing lava and flashes to steam, this produces a semi-explosive eruption (the special name was mentioned earlier but I can't relocate it) and much finer ash. Now the eruption has been going for a while, presumably the ash particles are bigger on average and therefore will fall out of the plume faster?.... Someone who knows about volcanoes, please put me right on this..... |
On HIGNFY Andy Hamilton suggests we need a jet engine which can cough.
We already have, it's called a pulse-jet. Sod fitting a RAT, have a drop down pulse-jet instead! :} |
I made it back to LHR as rebooked on BA on Friday 23rd, on the daylight flight from Boston. My fears of unbridled applause on touchdown at Heathrow were a great exaggeration. There was none.
Many large official notices at passport control in Heathrow that "there are long delays here today due to Volcanic Ash". This just seemed a ridiclous excuse. There were indeed large queues, but as we all know Heathrow is normally at full runway capacity, and there is therefore little scope for additional flights. Load factors seem little different, and there are stories of some flights very lightly loaded. There also seemed proportionately less overseas visitors than normal compared to UK residents (very few Americans in the flight from Boston), so they will be easier to process. No, the main reason for the long queue at T5 seemed that a large number of immigration desks on the right hand side were unstaffed. So it seems that many UK residents have been stuck overseas, some in desperate circumstances, but the Home Office staff can in no way organise overtime or similar arrangements to speed their flow. After all, it's not as if they have been rushed off their feet in the last week, is it ? Let us move on from the world of the bureaucrats to real engineering. As we cruised along I was looking at the various dirt marks back across the wing. Now if there is any impact of ash in the atmosphere this must surely show up in additional external dirt accumulation, and the need for additional demineralised cleaning of airframe exteriors. Has anyone noticed the need for this ? |
brooksjg, sorry but that's just not the case. A high bypass engine will of course have alot of air going through the fan and ash here is unlikely to do anything other than abrade the leading edges of each fan blade. But my point is that even a large 777 engine needs vast amounts of air going thourgh the engine core, in order to produce power, in order to drive the fan!!! It doesn't get it's power from anywhere else! Power comes from the core, but the majority of the thrust comes from the fan. You're confusing the two. This core airflow will unquestionably exceed the air requirement of a small low bypass miltary engine.
There is no "centrifuging" of air in a turbine engine. Unless you consider free turbine engines which generally use a centrifugal compressor, but then these have no bypass! Centrifuging in a bypass jet engine just does not occur! I can't comment on very fine ash and it's likelihood of blocking cooling passages, but ash also contaminates oil systems and breaches bearing seals, etc, etc. This risk must surely increase with finer ash.... |
captainpaddy
There is no "centrifuging" of air in a turbine engine. Unless you consider free turbine engines which generally use a centrifugal compressor, but then these have no bypass! Centrifuging in a bypass jet engine just does not occur! |
Virgin's Branson attacks volcano cloud shutdown...
From the AFP wire....
LONDON: Richard Branson, the boss of airline Virgin Atlantic, Saturday hit out at the decision to ground flights due to volcanic ash from Iceland, saying there had been "no danger at all to flying". Branson also called on Britain's government to pay compensation to airlines, who have been left at least 1.7 billion dollars (1.3 billion euros) out of pocket, according to the airline industry umbrella body International Air Transport Association (IATA). "This was very much a government decision to ground the planes and we would suggest that the government should compensate the industry," Branson said in London. "Behind the scenes, our engineers and all the experts were telling us that there was no danger at all to flying and that the danger would have been if we had flown close to Iceland through the volcano." He added there were "plenty of corridors" which airlines could have flown through and said: "I think the government has accepted that there was overreaction. "A blanket ban of the whole of Europe was not the right decision." Clouds of ash from an Icelandic volcano caused a week of massive disruption and left hundreds of thousands of travellers stranded as many European countries closed their airspace, only reopening earlier this week. Virgin Atlantic says its flying programme has returned to schedule but that a small number of flights could still be delayed because of the knock-on effects of the shutdown. - AFP/jy |
What Branson is saying is just... funny.
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Says it all Really:
:ugh: Volcanic ash too hot for politicians • Rob Lyons • From: The Australian • April 24, 2010 12:00AM IS that it? After six days of a near shutdown of the skies over northern Europe, the British government announced British airspace would reopen at 10pm on Tuesday, local time. Now that things are getting back to something like normal, it is time to learn some lessons from the whole mad affair. What does it say about contemporary society that it is grounded by a relatively small, distant volcano? The answer lies in a mixture of precaution, organisational cowardice and a negative attitude towards flying. When flights were brought to a halt on April 15, it appeared that the ash would be a temporary inconvenience with flights quickly resuming. However, over the subsequent 24 hours it became clear that the cloud could hang around for days, if not weeks. We were the victims, we were told, of a peculiar combination of volcanic activity and weather patterns. Flying, we were assured, was simply too risky. The proof was to be found in the startling experiences of a British Airways flight over Indonesia in 1982 and a KLM flight over Alaska in 1989. On both occasions, aeroplanes flew through clouds of volcanic ash; all four engines on each aeroplane stopped working and the pilots were forced to descend thousands of feet before being able to restart the engines. For those involved, the experiences must have been terrifying. But there seems to have been too little effort to understand how the situation over the past few days may have been very different from those earlier incidents. For example, the KLM flight was a mere 240km from the volcano in question, Mount Redoubt, while London's Heathrow airport is 1900km from the volcano in Iceland's Eyjafjallajokull glacier. While neither the British Airways nor the KLM crew knew immediately what was going on, the cabin filled with the smell of sulphur and what appeared to be cigarette smoke. When the British Airways plane landed, the windscreen of the aircraft was so sandblasted that the pilots could not see out well enough to taxi the plane and it had to be towed off the runway. KLM, Lufthansa, Air France and British Airways reported nothing like that during test flights last weekend. This would suggest that the concentrations of ash particles in those earlier incidents were far higher than have been found over Europe in recent days. Yet even in those two most notable examples, the engines of the planes all restarted at lower altitudes and the planes landed safely, even if it was touch and go for a while. So, in 2010, hundreds of millions of dollars have been lost to the travel industry, hundreds of thousands of people have been stranded and imports of perishable goods have been badly affected - all to avoid a scenario that has never cost a single life. As one writer noted, if we took a similar approach to driving, our motorways would be full of cars pootling along at 50km/h. Yet many commentators have ridiculed airlines for questioning the restrictions. Gathering the available evidence is certainly sensible, but the expert worship in this instance is misplaced. Someone whose expertise is meteorology or vulcanology may well be able to measure particle concentrations in the atmosphere and make some educated guesses about how those concentrations might change. But it is highly unlikely that the same expert can tell us anything definitive about whether those concentrations will damage a jet engine. Is it really mad to suggest that the airlines, whose reputations after all would be on the line if they got it wrong, might have some useful insights into whether flying is safe or not? Other commentators have offered what they seem to think is an inspired argument: if critics of this safety-first approach are so certain, they should take part in a test flight. The fact that airline bosses like BA's Willie Walsh and KLM's Peter Hartman did that last weekend seems to have passed such insightful wits by. We also need to be aware that experts don't necessarily have a brilliant track record on estimating risk in the face of uncertainty. For example, in the 1990s there were claims that hundreds of thousands of people could die from the human form of mad cow disease (BSE). In truth, there have been 168 deaths from variant Creuzfeldt-Jakob disease (vCJD), but 1139 deaths from the long-standing form of the disease in the same period (such a tiny rate of incidence that some have called the BSE-CJD link into question). As Frank Furedi notes, from the Millennium Bug to influenza, experts have provided apocalyptic scenarios of what might happen and governments have been very willing to act upon them. This is symptomatic of a contemporary problem with political leadership. In recent years, responsibility for making decisions has been increasingly farmed out to independent experts. These decisions are designed to make sure politicians can't be held responsible if things go wrong. "It wasn't us, guv, it was the experts wot did it. We were just following advice." Which does rather raise the question of why we elect leaders in the first place. Such reliance on experts is not helpful. Just as the vulcanologist cannot tell us much, if anything, about jet engines, so it is not the place of experts, no matter how eminent, to make policy. Scientists, engineers and aviation officials can all bring their knowledge to the table but it is elected officials who must decide how to balance the risks and the benefits of a situation like flying through an ash cloud. The promotion of experts allows our supposed leaders off the hook. So British Transport Secretary Andrew Adonis could say yesterday: "It's fair to say that we have been too cautious." "We" being the international safety regulators. The only thing that might drown out the noise of jet engines in the next few days is the sound of the buck being passed. Unfortunately for all those affected, the politicians have gone missing. Oliticians fail to take decisions on an important matter, and blame others for not giving them the right information. It is over-caution combined with cowardice dressed up as outsourcing. For six days there was political paralysis in the face of this natural event. The notion of "no safe threshold" for atmospheric ash particles was clung to even when test flights conducted by the airlines suggested it was not true. And there appeared to be positive rejoicing at the absence of planes from our skies. Far from there being desperation to get transport working normally, to release people stuck in departure lounges or stuck thousands of kilometres from home, flying was treated as an optional extra, something that society could happily do without. It was not a volcano that brought sections of society to a standstill: it was political disorientation, the application of the precautionary principle, and a cavalier attitude among the elite towards the value of flying in the first place. Spiked |
responsibility for making decisions has been increasingly farmed out to independent experts. Ironic that experts are the airlines themselves who set the safe level they so objected to. CEO's who complain AFTER a well know, serious, threat to their business occurs are incompetent. I do not want politicians making important technical descisons, especially about safety, because they are unqualified, incapable and biased towards making the unsafe choice. If it was a political decision the airspace would have re-opened within hours against all advice. |
A north-easterly with snow at KEF to break the gloom, but forecast back to 'volcano wind' later. I see Astraeus, like Icelandair, are operating from AEY.
All seems quiet on the eruption front - is it lack of interest by the media or is it less active? Anyone up norf to comment? The latest I can find from the Met Office is Friday "Eruptions from Eyjafjallajökull are continuing periodically with debris being emitted into the atmosphere. Weather patterns over the next few days mean that any new areas of ash will be mainly blown away from the UK." |
Originally Posted by peter we
(Post 5657129)
Ironic that experts are the airlines themselves who set the safe level they so objected to.
CEO's who complain AFTER a well know, serious, threat to their business occurs are incompetent. I do not want politicians making important technical descisons, especially about safety, because they are unqualified, incapable and biased towards making the unsafe choice. If it was a political decision the airspace would have re-opened within hours against all advice. BD |
All seems quiet on the eruption front - is it lack of interest by the media or is it less active? Anyone up norf to comment? The latest I can find from the Met Office is Friday Met Office: Volcanic Ash Advisory Centres |
Ta Bamra - 2.5km I see. Anyone any current pics?
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The Met Office started from the premise that any VA is dangerous to jet engines, therefore the presence of any VA must mandate a total ban on aviation.
In any cubic metre of air anywhere on the face of the Earth, there will be a small amout of VA, therefore no aviation must take place anywhere. QED I'm afraid this is the kind of expertise we have in the UK today. That other countries still hold the UK in high scientific regard is surely on the momentum of a former glory? Many scientific degrees from some provincial universities are 'cheap' acadmically, and deliberately avoid some of the challenging, yet absolutely critical concepts. Such is the political apetite for 'inclusive' and 'accessible' education that public sector organisations are encouraged to promote and engage such minor graduates. It comes therefore as no surprise that absurd deductions such as these are published with no peer review and little consultation amongst the real experts of the piece, those who live and work in the atmosphere everyday, and craft their trade around it. Still worse, the aviation community in general, and pilots in particular are dogmatically sidelined as natural class enemies and polluters of the planet, wholly anathema to the Islington wine bar clique of champagne socialism. Thank heavens for the CEO of Big and his uncompromising and confrontational style, which every other day would be directed at us, but in this instance pricked the bubble of stasis, and dragged the Alice in Wonderland world of sofa to armchair cabinet government, its unelected peers, and its cosy mates in Brighton Poly, unceremoniously into the real world. http://www.reallyfabcards.com/media/...G_195780_S.jpg |
And now the Media Turn
The ash cloud that never was: How volcanic plume over UK was only a twentieth of safe-flying limit and blunders led to lock-down | Mail Online
What a strange world we live in. The Media who panicked everyone with selective publishing have now made a U turn the other way :ugh: I think many of us are loosing confidence in the science when literally every forecast world disaster has turned to nothing. The media called for governements to destroy millions of birds over bird flu. 65000 deaths predicted over the mexican flu (345 actual) And now this I hope the airlines do sue Pace |
I would not consider anything printed in the Mail to have much relation to the truth
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