Wikipedia:Reference desk/Archives/Science/2010 April 17

= April 17 =

Jets in front of wings
All modern jetliners have jet engines that are placed well in front of the front edge of their wings. Why? —Preceding unsigned comment added by 71.70.143.134 (talk) 02:14, 17 April 2010 (UTC)


 * This is mostly speculation on my part, but I suspect weight distribution is at least part of the reason. Modern jetliners all use Tricycle gear arrangements, with the rear landing gear situated in the area of the wing.  The center of gravity must be in front of the rear landing gear or bad things might happen, so pushing the fairly heavy engines, also mounted to the wings, as far forward as possible is presumably helpful. Also due to the shape of an airplane wing there is more strength near the leading edge, so pushing the engine nacelle forward makes sense.  The engine nacelle itself should be attached at it's own center of gravity to keep it from torquing the wing, so if it is fairly long and attached near the front of the wing (where the wing is strongest) it's no surprise it might stick out.  It probably also makes it easier to do maintenance on the engines. Winston365 (talk) 06:44, 17 April 2010 (UTC)


 * False premise. McDonnell Douglas MD-80 is a modern aircraft with rear mounted engines.  Dragons flight (talk) 07:28, 17 April 2010 (UTC)


 * Sure, there are a bunch of airliners with rear mounted engines, although these days they are mostly for smaller aircraft (very common on business jets for example). These planes compensate by moving the wings farther towards the rear.  Larg airliners these days put the nacelles on the wings though, which was implicit in the question asked.  If you use engines mounted on the tail you can move the rear landing gear back as far as you need to to balance the aircraft, which also moves the wings towards the rear, but if you do decide to mount the engines on the wings that doesn't help as much, as moving the landing gear towards the rear of the aircraft would also move the engines back.  Winston365 (talk) 07:45, 17 April 2010 (UTC)


 * Aircraft, and particularly high speed aircraft, are vulnerable to a potentially-destructive phenomenon called flutter. Aircraft designers aim to ensure the minimum speed for onset of flutter is well above the maximum speed of the aircraft.  There are various modes of flutter and many of them can be avoided by ensuring the center of mass of the relevant part of the structure is ahead of the elastic axis of the part of the structure.  For example, hinged control surfaces (ailerons, elevators and rudder) usually have lumps of lead (or depleted uranium!) attached to their forward edges to move the center of mass of the surface forward of where it would otherwise be.  The more mass that is added means the higher is the flutter-onset speed.


 * Flutter of the wing can be avoided by ensuring the mass of the wing is well forward of the torsional axis of the wing. For this reason, aircraft designers place the engines well forward of the wing, on pylons.  The further forward that the engines are located the higher will be the flutter-onset speed.  This is just as true of turbo-props as jets.  Note the location of the engines on the Vickers Viscount and P3 Orion.  The further out along the wingspan that the engine is located, the more important it is to be located well ahead of the wing torsional axis.  Some British aircraft had their engines buried in the wing root and the engines could be located near the trailing edge of the wing eg de Havilland Comet and the V bombers.


 * Similarly, high speed aircraft with fuel tanks on the wing tips must have the tanks protruding significantly forward of the leading edge of the wing. See the image at Learjet 25.


 * Another option is to have very stiff wings of relatively short span. That way, it is not critical that the engines be located forward of the wing.  Concorde is an example of this third option.  Dolphin  ( t ) 08:30, 17 April 2010 (UTC)


 * The critical thing in any aircraft design is that the center of gravity be close to the center of pressure of the wing. (Generally, the 'center of pressure' is at the thickest part of the wing - a little way back from the front edge).  If you imagine the lift from the wing pulling the plane upwards at the center of pressure - and gravity pulling it down at the center of gravity - you an easily imagine why you'd want those two points to be at the same place if you want the plane to be stable and to fly straight.  So the entire issue of "balance" that everyone has been talking about relates to keeping those two points close together.  Concord has triangular wings - the center of pressure is much further back than on a typical subsonic airliner - hence the engines need to be further back to keep a reasonable balance. SteveBaker (talk) 15:05, 17 April 2010 (UTC)


 * SteveBaker's comment is a popular one, but not entirely correct. On an airfoil of symmetric cross-section the center of pressure stays in a fixed location, usually around 25% of the chord, but on a cambered airfoil the center of pressure moves as the angle of attack changes.  At high angles of attack (such as at low airspeed) the center of pressure is at its most forward position. But as the angle of attack reduces (such as when the airspeed increases) the center of pressure moves backwards, and may even lie behind the trailing edge of the wing!  See Movement of center of pressure.  It is impossible (and unnecessary) to always have the center of gravity close to the center of pressure because the center of pressure moves through significant distances during a flight.


 * To simplify the analysis of airfoils and aircraft stability, it is fortunate that there is a point that doesn't move and that helps determine the best position for the center of gravity. This point is called the aerodynamic center.  For positive stability, the center of gravity should always lie within the specified range relative to the aerodynamic center.


 * However, back to the original question. The location of engines and wing-tip fuel tanks on the wings of aircraft is related to the avoidance of flutter, not ensuring the center of gravity of the aircraft is within the specified range.  Dolphin  ( t ) 02:49, 18 April 2010 (UTC)

Space elevator
Why does the center of mass of the space elevator have to at the Earth's geosynchronous orbit? I realize that it's to minimize tension forces acting on the elevator, but my confusion is the following: I understand that a particle in that orbit will be rotating at the same rate as the earth, but for an extended body such as the space elevator, I didn't think that was true. I thought treating the gravitational force as acting at the center of mass was only true for spherical or elliptical bodies. If I don't make sense let me know. 173.179.59.66 (talk) 07:25, 17 April 2010 (UTC)


 * The motion of any rigid body can be considered as a combination of the linear or orbital motion of the centre of mass (considering all forces as acting through the centre of mass), and the rotational motion about the centre of mass (considering the moments of forces about the centre of mass). It doesn't just apply to symmetrical bodies.  At this scale. there might be a very small relativistic correction, and an adjustment because the centre of mass does not coincide with the centre of gravity, but the basic principle still applies and gives a reasonably accurate approximation.    D b f i r s   08:26, 17 April 2010 (UTC)


 * Not correct. The force, and thus acceleration, on a non-spherical body is not the same as the force on a point mass at the body's center of mass.  --99.237.234.104 (talk) 01:38, 19 April 2010 (UTC)


 * Centre of mass and centre of gravity mean exactly the same thing, don't they? --Tango (talk) 11:59, 17 April 2010 (UTC)


 * Normally, yes. But I think here the different (lower) gravity at the top of such a object means that the average centre of gravity is lower than the centre of mass. Our article, centre of mass, says "The center of mass is often called the center of gravity, but this is only true in a system where the gravitational forces are uniform.", I assume this is what it means. - Jarry1250 [Humorous? Discuss.] 12:19, 17 April 2010 (UTC)
 * Ah, yes. I suppose that makes sense. I'm not sure the concept of a centre of gravity is useful in that context, though. --Tango (talk) 14:01, 17 April 2010 (UTC)
 * Also note that there's another good reason to have a "station" at the geosynchronous height: so that space ships can dock there. At any other height any ships in orbit would zip past the station.  Depending on the relative size of this station, it might be a substantial portion of the overall mass of the elevator.  Also, at the geosynch height, it shouldn't exert any net force on the elevator shaft, which is a big plus. StuRat (talk) 13:40, 17 April 2010 (UTC)
 * The station (or something) needs to be above geosynchronous height in order to compensate for the cable below it. A large station would only have to be a tiny bit above, though. Once alternative suggestion is to have the cable continue a long way past geosynchronous height. A craft on a cable above that height would be accelerated upwards by centrifugal force (and yes, it does exist in the most natural frame of reference for this problem, which is one that co-rotates with the Earth). That gives you a very energy efficient way of reaching an Earth escape trajectory. --Tango (talk) 14:01, 17 April 2010 (UTC)

I understand the practical benefits of having the space elevator at a geosynchronous orbit, but my issues are more physics related. If external forces are applied on an object, then the object's center of mass will accelerate just as if all the mass were concentrated at that one point. Now, a small object (like a space shuttle) at a geosynchronous orbit will have the right combination of acceleration and orbital distance so that it's orbital period matches the rotational period of Earth. But if the space elevator's center of mass is at the same location, because its acceleration will be much bigger, then it seems to me that it won't be in a geosynchronous orbit. I would think that the center of mass ought to be higher than the geosynch orbit, but this doesn't seem to be the case, and I don't know why. 173.179.59.66 (talk) 18:12, 17 April 2010 (UTC)
 * Why would the acceleration be much bigger? The acceleration will be "g" (adjusted for height) whatever the mass, and whatever the size except for the correction for non-uniform gravity.  Can anyone find a reference for the integration of gravitational attraction over a typical mass distribution of a space elevator?  (I should be able to do this myself, but I'd probably get it wrong.)  I would estimate that the centre of gravity will still be not far from the centre of mass, but the difference might be significant.    D b f i r s   20:36, 17 April 2010 (UTC)
 * If you have a really heavy station at the top then the mass of the cable probably isn't very significant. --Tango (talk) 21:12, 17 April 2010 (UTC)
 * Yes, I agree that it will probably not be worth worrying about in that case.   D b f i r s   21:33, 17 April 2010 (UTC)
 * ... though I think that the torque produced by gravity (on a centre of gravity just below the centre of mass) should have the effect of keeping the elevator vertical, rather like a ship with the centre of gravity below the metacentre. (Do we have any experts on the dynamics of rolling ships who could check my theory?)   D b f i r s   20:47, 18 April 2010 (UTC)
 * Yes, that would be true in uniform or variable gravity - just consider a pendulum. I think the force on the cable due to it being attached to the Earth would also keep it vertical and would probably be a bigger factor. --Tango (talk) 21:51, 18 April 2010 (UTC)
 * No! A pendulum is suspended from a fixed pivot well above its centre of mass. A "pendulum" suspended at its centre of mass will rotate at random or remain at rest in any orientation.  Similarly, an object in any orbit is likely to turn at random unless it has some mechanism for keeping a fixed orientation.  Does a space elevator have the cable attached to the Earth?    D b f i r s   22:48, 18 April 2010 (UTC)
 * Ok, a pendulum is a bad example. It is still true, though. It is a result of tidal forces and is responsible for tidally locked moons often having their denser halves pointing towards the parent planet (an object with non-uniform density is roughly equivalent to a non-spherical one). Yes, the cable is attached to the Earth. I think the force is usually fairly small at that point, but it has been suggested that you could move the cable around to avoid space debris by having it attached to a moving platform, so the force can clearly by non-zero. --Tango (talk) 23:50, 18 April 2010 (UTC)
 * Yes, I think we are in agreement that gravitationally locked moons with a constant face to the centre of orbit are observable, but I suspect that the reason for the locking is non-uniform gravity, as well as non-uniform density, because they would tend to rotate about their centre of mass, not their centre of volume. (Tidal forces will have caused the slowing of rotation in the first place.) If the cable is attached to the Earth, then there is no problem anyway, except in designing incredibly strong tethers!  The engineering problems seem vast (though not necessarily insurmountable).   D b f i r s   08:26, 19 April 2010 (UTC)
 * Yes, it is due to non-uniform gravity. That is the cause of all tidal forces. --Tango (talk) 14:18, 19 April 2010 (UTC)

health/meth/sex/ed
(Removed question asking for medical advice) SteveBaker (talk) 14:55, 17 April 2010 (UTC)


 * Dude, I sympathize with your problems. Unfortunately we're not allowed to give medical advice like this on Wikipedia. I recommend you make an appointment to see your doctor. Axl  ¤  [Talk]  11:14, 17 April 2010 (UTC)


 * (Removed medical advice) SteveBaker (talk) 14:53, 17 April 2010 (UTC)

Communicating dates to future civilizations
I'm sure someone must have thought about this before. Say we want to create a carefully protected archive of information related to our civilization so that even if most of the artifacts of our civilization are destroyed, future civilizations can still learn about our civilization and its history. Future discoverers of the archive will have to learn the language in which the archived materials are written. Numbers and formulas for chemical elements are quite easy to explain. But what about dates in historical records? How can we communicate to future civilizations which trip around the sun is year 2010 in our calendar? I guess we can keep some samples of carbon together with precisely measured radioactivity values and the measurement date, but that's probably not accurate enough to allow someone in the future to determine that year 2010 was 610432 earth-years ago. What better methods are available? —Preceding unsigned comment added by 98.114.98.221 (talk) 17:01, 17 April 2010 (UTC)


 * You could record the exact position of each planet. I don't know how often all 8 planets (aw, what the heck, toss in Pluto, too) repeat the exact same position, but it can't be very often. StuRat (talk) 17:17, 17 April 2010 (UTC)


 * The locations of stars would also help. The proper motion of stars is very slow, so by comparing our star charts with their own, they could tell roughly how much time had passed. They could then use the planets or something to narrow it down. --Tango (talk) 18:24, 17 April 2010 (UTC)


 * We could place stones in certain positions so that, when looking towards a certain direction over one of the stones, certain star constelations appear over the other stones. Then engrave in the stones which constelations appear in which dates. --Enric Naval (talk) 19:27, 17 April 2010 (UTC)


 * Does the Moon's orbit decay? If so, just record exactly how far from the Earth it is. Or, give our best estimate of the state of the Sun. There's a predictable progression of stellar composition from Hydrogen to the heavier elements as it runs out of fuel. Vranak (talk) 22:14, 17 April 2010 (UTC)


 * The Moon's orbit does decay (outward), but the change per year is tiny compared with the values you get with different methods of measuring it. StuRat (talk) 22:20, 17 April 2010 (UTC)


 * I think the moon's orbit decays inwards, so it is getting nearer earth, and it can be accurately measured by using the lazer reflectors left there by various moon missions. 78.147.241.153 (talk) 22:44, 17 April 2010 (UTC)


 * No, it decays outward. It can be measured accurately now, using the laser system, but a thousand years from now the Moon reflector will be buried in dust and the Earth station will be gone.  An advanced civilization could set up a similar system, but the heights at both ends would be different from the current heights. StuRat (talk) 22:48, 17 April 2010 (UTC)

The Pioneer spacecraft carry information about the date and position from which they were sent as follows. There is a schematic drawing of the hydrogen atom and the 21 cm transition which defines a symbol for the unit of frequency that correpsonds to that 21 cm transiton. Then there is a drawing of pulsars with their frequencies showing where they are relative to Earth. If the Pioneer spacecraft are intercepted by some advanced civilization a million years later, they can not only tell from where it came from but also when it was launched using the spin down rates of the pulsars. Count Iblis (talk) 23:01, 17 April 2010 (UTC)

A fairly exact chronology of the Twelfth dynasty of Egypt was established based on clues left behind based on their references to astronomical events such as the heliacal rising of Sirius and to phases of the moon. See The Calendars of Ancient Egypt by Richard Anthony Parker. Gabbe (talk) 09:38, 18 April 2010 (UTC)

Head Hair
?Are there any disadvantages to not washing ones head hair for a long time (say 6 months)?--79.76.233.217 (talk) 17:17, 17 April 2010 (UTC)


 * Lice, ticks and fleas to name a few. --The High Fin Sperm Whale 17:24, 17 April 2010 (UTC)


 * You'll have to cite a source if you are claiming that these are prevented by head washing. I think they are prevented by avoiding such critters.  Lice, in particular, aren't eliminated by normal head washing, otherwise there'd be no need for lice shampoo and those superfine lice combs, and the alerts in the elementary schools when, horrors, one of the kids is found to have head lice.  Comet Tuttle (talk) 19:10, 17 April 2010 (UTC)


 * It tends to get greasy, smelly, and itchy. StuRat (talk) 17:29, 17 April 2010 (UTC)


 * Here's someone who conducted a similar experiment, though she also avoided showering and using deodorant. Google is failing me on my search for the person who I believe was a UK Member of Parliament who "outed" himself as not having washed his hair for the last decade, and claimed he had suffered no adverse effects, social or otherwise &mdash; anyone know who I'm referring to?  Comet Tuttle (talk) 19:09, 17 April 2010 (UTC)
 * Didn't fail me... Matthew Parris - . He does say he rinses it with water every day, but doesn't use shampoo.  Ghmyrtle (talk) 19:18, 17 April 2010 (UTC)
 * Thank you! Comet Tuttle (talk) 22:22, 20 April 2010 (UTC)


 * I think the main disadvantage is a reduced social life. Some might be able to get away without it, depending on their kind of hair. I'm not one of them. Dauto (talk) 20:11, 17 April 2010 (UTC)
 * Exactly, it depends on the person. I've heard quite a few accounts of this sort of behaviour and it seems to work out for the best, although some people eventually do go back to washing. For middle-ground, just trying washing without shampoo, or just a minimal amount, and see how it works out for you. Vranak (talk) 22:09, 17 April 2010 (UTC)
 * If you thoroughly rinse and comb your hair under hot-as-you-can-bear running water, you will need noticeably less shampoo to get it clean, so I suppose it is possible that if you did this daily and lived in a reasonable clean environment you might get away without the shampoo altogether. DuncanHill (talk) 23:30, 17 April 2010 (UTC)


 * We have an article on that: Polish plait. There are people who went their entire lives without ever washing their hair. Ariel. (talk) 02:05, 18 April 2010 (UTC)

I didn't wash my hair for ages out of laziness... No one noticed it, yet at the same time they were horrified to find I hadn't done so. Now that I've started using shampoo again I find my hair does need washing at least once a week. We'll have a massive range of hair flora (like skin flora) that will happily live in our hair and will eat away at all the gunk from our scalp. Washing with shampoo will obliterate them and disrupt the once pristine ecosystem, I'm guessing that it takes time for the balance to return and so soon after washing your hair will be greasy etc. Similarly, I've never washed my face with soap and yet never get spots, meanwhile people who use clearasil all the time seem to always have spots (making them use more clearasil!). Why were you asking? 131.111.30.21 (talk) 11:38, 18 April 2010 (UTC)


 * Yeah, I go for months at a time without using shampoo as well. I'm not exactly obsessed with my hygiene, but no one's ever complained about my hair smelling.  When I don't even rinse it for a week or two, though, it can start to smell.  Luckily, that's only when I'm camping, or something, so everyone else is in the same boat. Buddy431 (talk) 17:54, 18 April 2010 (UTC)


 * Personal Obsevation: acquaintances of mine in the past who stopped washing their hair in order to grow long dreadlocks all asserted that after an initial several-week period of smell, grease and dandruff the scalp's "natural self-cleaning properties" kicked in and thereafter their hair became and remained clean, non-greasy and non-smelly (which indeed it was). 87.81.230.195 (talk) 19:19, 18 April 2010 (UTC)


 * I was under the impression that the correct (i.e. traditional - I know that you can go to a salon and have dreads done with backcombing and glue) way to grow dreads was 'grow longish, then wash as normal - but never brush/comb it again'. Folks do seem to believe that you have to be black for this to work - but apparently this is not the case. Black peoples' hair tends to dread up quicker, is all. --Kurt Shaped Box (talk) 22:10, 18 April 2010 (UTC)


 * Maybe the reason they have to use Clearasil all the time is because they get lots of spots and not the other way around? Nil Einne (talk) 15:03, 19 April 2010 (UTC)

Article needs help
Hey guys and gals. If any of yall have some spare time, the article on Robbie Mannheim needs some serious help from rational science-minded perspectives. My templates were removed without significant improvement. Finals week is approaching so I don't have the time right now to deal with edit war or doing significant fact checking. It's important to quickly remedy the article because currently it could be damaging WP's credibility. Cheers. - Craig Pemberton 22:42, 17 April 2010 (UTC)
 * Lol! Yes indeed! I think it's probably best to just delete that whole article and start again.. Send User:Anupam who's responsible for pretty much the whole article to Reliable_sources. I don't think "Paranormal Experiences", "Strange Magazine", and "Good Spirits, Bad Spirits: How to Distinguish Between Them" count as reliable sources.. Unfortunately I think this requires someone a little more expert then me to tackle it. Vespine (talk) 23:11, 18 April 2010 (UTC)
 * I might at least put your templates back and start a thread on the talk page. Vespine (talk) 23:47, 18 April 2010 (UTC)

Dandelion-lettuce hybrid?
Earlier in the year I weeded something from my UK garden that had leaves like a dandelion, but was the shape of a lettuce as it had a large number of leaves. What could it have been? I may have scattered some salad-plant leaves there last year. 78.147.241.153 (talk) 22:48, 17 April 2010 (UTC)
 * It could not have been a dandelion-lettuce hybrid, because no exchange of genetic material occurred. However, lettuce and dandelions are both grouped in the tribe Cichorieae; it is possible there is a species sharing characteristics of both (for example, this). Intelligent  sium  23:57, 17 April 2010 (UTC)
 * Which, though the file is named 'Babcockia', is apparently a species of Sonchus, or "hare lettuce". --ColinFine (talk) 20:45, 18 April 2010 (UTC)

It was really like a hedgehog of dandelion leaves. The dandelions I've seen are quite flat, but this thing was like half a sphere in shape, and also had bigger than usual leaves. It might be due to some old salad plant seeds I scattered there, but I do not know what exactly. 89.240.44.159 (talk) 12:31, 19 April 2010 (UTC)

Is there any realistic danger to Europe from Icelandic Volcanos?
Ok, so at the moment we just have an ash cloud. No big deal. Anything else I should be concerned about, and if so, how concerned? Inquisitive Fellow (talk) 23:09, 17 April 2010 (UTC)
 * Besides the ash cloud, no. However, the ash cloud is a big deal if you want to travel to or over Europe, as it clogs up airplane engines. And in about a week or two when the ash has circled the Earth we may see much brighter sunsets. --The High Fin Sperm Whale 23:21, 17 April 2010 (UTC)
 * The article states, "As of April 15, the eruption was not large enough to have an effect on global temperatures like that of Mount Pinatubo and other major past volcanic eruptions. However, previous eruptions of the volcano have lasted as long as a year, and the potential remains for a temporary global cooling effect." 124.157.234.136 (talk) 23:45, 17 April 2010 (UTC)


 * Depends what you mean by "danger". If it continues it could cause airlines to go bust. It could have a knock on effect on the economies of other countries, because they won't be able to get their goods and services to Europe. Concerts and sporting events are already being cancelled because the players can't get to the venues. Businesses are cancelling meetings and conferences. If and when the ash cloud falls to earth, it could damage people's health. It just proves how interdependent we all are, and how dependent we are on the goodwill of Mother Earth. --TammyMoet (talk) 08:23, 18 April 2010 (UTC)


 * Without wishing to underestimate the personal inconvenience to people unable to travel this week, I think the overall economic impact will be minimal. UK airlines are estimated to be losing about £2m £200m per day, according to the BBC - but even if this continues for a whole year, it is far less than a tenth of 1% only 2.5% of the UK's GDP. And although airlines are losing money, ferry companies and rail operators are making money. Most goods travel by sea, road and rail, so the only products affected will be those that travel long distances with very short shelf-lives - and a shortage of Thai orchids in Tesco will hardly cause panic buying. As for business meetings, we have phones, video conferencing and net meetings - in my experience, most business travel is a non-essential luxury. Gandalf61 (talk) 09:16, 18 April 2010 (UTC)
 * On the surface Gandalf you're right. However, cancelling a conference where 600 delegates are attending from across the world costs the organisers money: they will still have to pay for the venue, catering... if you're stranded the other side of the world who's going to do your job? That could bring a business to its knees, especially the smaller ones. Take the F1 circus: 6 jumbo jets to get the freight stuff across the world, plus people, plus spectators... it's not just the commercial airlines here, it's the freight stuff. We could run out of fruit and veg within a week apparently! This article summarises this. The figure they give for airline losses is greater than Gandalf's by 100 times. As you can see from any supermarket shelf, many of the green veg are flown in from Africa or even South America. This will have an effect on their economies as well as our plates in the UK. --TammyMoet (talk) 10:07, 18 April 2010 (UTC)
 * Hmmm, typically the attendees of a conference will have paid for attending a few months in advance. If the organizers can see the problem happening a few days in advance, they could make last minute arrangements with the catering companies etc. and then be better off. They could then perhaps use the saved money to partially compensate the people who cannot attend. Count Iblis (talk) 13:50, 18 April 2010 (UTC)
 * Usually there are cancellation clauses in the contract which mean if you cancel less than a set period of time beforehand (could be 48 hours or 7 days) you still have to pay the full fee. Usually the hire fee has to be paid to the venue on booking, which is months if not years in advance, so in order to do what you suggest, you would first have to sue the venue to get even a partial refund. You can cancel the event, but the expenditure is still in place. And what if the flight ban gets lifted and people make the journey, only to find the event has been cancelled and they haven't informed you? (if you're travelling for over 24 hours this is a real possibility) I've organised events for many years, and cancelling is a real nightmare. --TammyMoet (talk) 14:06, 18 April 2010 (UTC)
 * I see, so you won't want to cancel a conference but perhaps scale it back as best as you can? I've only visted conferences and my experience is that the catering is often poor (under normal circumstances). There isn't enough food for the whole day; after a few days more and more people will eat extra meals in restaurants. So, it seems to me that conference organizers are not spending enough on catering. Count Iblis (talk) 14:26, 18 April 2010 (UTC)
 * It's poor but very expensive. You are not just paying for the bad food, you are paying for all the people who serve it, for them to put it all away, for them to rent the trucks they need to bring it in and out, assemble tables, etc. Even very minimal food is very expensive, as anyone who has planned a wedding reception knows, much less a full conference with hundreds of people. And since this is an "act of god" (that is, not anybody's fault), it screws up a lot of cancellation policies, insurance policies, etc. Anyway it's beside the point here—aircraft costs are just the tip of the iceberg, because they have an entire sector of the economy depending on their functioning. Shipping of all sorts is mangled by lack of flights; the ability of people to move around is a key aspect of global commerce even today; and there are huge opportunity costs and cancelled service costs which hurts everyone involved. --Mr.98 (talk) 14:38, 18 April 2010 (UTC)
 * Let's examine some of these exaggerated claims. Cancellation of conferences and sporting events - a headache for organisers, but no net economic impact very small net economic impact on a national or global scale, as refunds put money back into people's pockets, which they then spend elsewhere. "We could run out of fruit and veg within a week apparently!" - complete nonsense. The UK imports 90% of its fruit and 60% of its vegetables - but only very perishable luxury items are flown in. No-one is going to pay for potatoes or pasta to be air-lifted, are they ? I am sure we can survive without aspargus and fresh pineapple chunks if we have to. "The ability of people to move around is a key aspect of global commerce" - well, yes, but people can still travel by road, rail and sea. And most business travel is simply an excuse to be wined and dined at someone else's expense - I think many companies would actually be more profitable if their staff spent less time on corporate jollies. Gandalf61 (talk) 16:06, 18 April 2010 (UTC)
 * Why would you assume cancellations have no economic impact? Consider that the companies who you've booked in advance, even in an ideal situation where they've not put out expenses ahead of time that cannot be returned (like food purchases), are now stuck with a weekend worth of labor that they either have to pay for, or there are laborers who thought they'd be getting paid but are now not. In all cases, with insufficient cancellation time, somebody will be out some cost or opportunity cost. There are all sorts of NPR stories about people who ship to Europe from out of Europe being totally screwed, losing entire perishable shipments, etc. All of these things cost significant amounts of money. They are investments that have now gone bad and are probably not covered by insurance. A week's notice is not enough for things to be cancelled or redirected without some economic loss. --Mr.98 (talk) 17:02, 18 April 2010 (UTC)


 * I'm sure the people who are directly impacted by this are quite heavily inconvenienced (financially, or otherwise) but the impact on the economy of, say, the UK would be negligible. Most air travel is for business and most business air travel isn't necessary for business, in as far as business contributes to the overall economy. Zain Ebrahim (talk) 12:03, 19 April 2010 (UTC)
 * Small? Sure. Neglible, perhaps if this ends soon, but if it really goes on to some extent for months I doubt it. (As a point of reference, I wouldn't consider say 1% of a countries GDP neglible.) Also I'm unsure about your last claim. I tried a quick search but couldn't find any results but I strongly suspect most air travel is for pleasure (or similar) not business. Note that the money a business spends on the travel and associated costs (hotels etc) may make a neglible difference to the economy but it adds up. E.g. if all hotels and airlines shut down because no one uses them do you really think that will be no impact? This is clearly an impossible scenario but it does highlight the point that these things (i.e. tourism) are part of the economy and it's unlikely they won't be affected. As I said below, perhaps the business will be better off if they don't spend that money on the travel, but that means a positive impact, not no impact. Ultimately a scenario where there's no net impact is unlikely to me. Nil Einne (talk) 13:53, 19 April 2010 (UTC)


 * Well whatever anyone says, I'm still annoyed as I said in an earlier discussion that my packet from Germany has almost definitely been delayed because of the disruption. (Although I admit it's not going to make an economic impact although having paid a fair amount for the shipping because of Deustche Post/DHL's flatrate (i.e. not by weight) shipping costs I'm rather peeved.)
 * More to the point, plenty of people planning to go to Europe have likely cancelled their holidays. If they have travel insurance policies, they may or may not get most of their money back. But even if they do, it doesn't mean there's no impact because the insurance companies may still lose money and the people themselves may decide to travel elsewhere rather then travel to Europe, which means all the money they would have spent in Europe would go elsewhere, given the details I've mentioned (e.g. insurance), it's clear that 'no net impact' is not accurate but in addition, telling the European businesses and governments who've lost money because it went elsewhere, say Asia or the US, it's okay because there's no net impact is not going to go down well.
 * Back to my earlier point, there are plenty of European sellers of goods who will find people won't be buying stuff. Similar to the earlier case, these people may buy their goods from elsewhere, e.g. Asia or perhaps they'll buy them locally where the good costs more. This will be good for the other sellers of goods but arguing it makes no difference because there's no net impact seems odd, for example if they buy them locally this would probably mean they spent more (otherwise they would have always bought them locally).
 * In the converse example, sellers of goods elsewhere, like on eBay or DealExtreme are likely to find European buyers reduced; some may just delay their orders, others may turn to local dealers. Again if they're local there's a good chance these items will cost more which while good for the local dealers and perhaps local economy, clearly means 'no net impact' is rather inaccurate. Even if they simply delay their orders isn't going to mean no net impact. Money the sellers could have received and spent on other things is now not going to be received. It stays around in the buyers bank which again may be good for the European banks and therefore economy but as I've already said, there's clear not no net impact.
 * In terms of travel, yes there are other ways to travel, but the people who choose to travel by air much have had a reason, if that reason is speed then the loss of that option is not going to have no impact. Note that even if people travel less, and even if they good for the company, that ignores the impact their non-travel has on other people who would have benefited from their travel. More to the point, less travel doesn't mean positive impact if you have to pay more for the travel that does take place, e.g. because it costs more (flying is generally expensive but it's not always more expensive then other options) or because the person is away for longer.
 * P.S. It seems obvious to me that the Thai orchid growers will lose out if people don't buy their orchids. Or if people have already bought their orchids but they can't de delivered, there's a fair chance things will change for Tesco because they can't sell the orchids they purchased but which couldn't be delivered (and they've also wasted the money they spent on orchids, if they get it back from insurance or whatever, again someone loses out). Even if you presume the people still spend all the money they would have spend at Tesco at Tesco which is a big if, they'll be buying more other goods which may be beneficial for these sellers of other goods but is not a case of no impact.
 * To summarise, no net impact is overly simplistic or just wrong when there are plenty of lost opportunity costs (I think that's the economics term) and the money is going to substanially different places including different countries then it would have otherwise. Yes, some will gain, some will lose but for many countries the effect is likely to be negative and even from a global perspective it's not likely to be no net impact. Perhaps people will realise they're relying too much on air travel and may change as a result which may have a net positive effect but that's a big if.
 * As with others, I've wondered if this could be severe enough to push an airline over the edge, this hasn't happened yet but I've seen some suggestion it could last several weeks (although the latest news is flights may resume soon albeit things will remain relatively disrupted for weeks and of course people may still be concerned about what will happen so may change their plans). If all this does push an airline over the edge, I don't think anyone is going to go out and tell the people who lose their jobs if this happens not to worry because there was no net impact.
 * P.P.S. is an example of some of what I'm talking about. All very small scale, but no net impact is clearly overly simplistic and even then very likely wrong.
 * Incidentally I don't live in Europe as may be obvious, and the only inconvience I'me likely to suffer is very, very minor (my comment on the package was primarily intended to be facetious similarly to the last time I mentioned it). I don't know anyone that well who's much worse off then me (although as NZ is a agricultural exporter, it could have some impact here). So I have no personal reason to really care that much. However I do have a history of disliking statements that IMHO are overly simplistic, miss the point or are just plain wrong. Talking about things in the abstact is fine, and often beneficial but as I've emphasised it's worth remembering there are plenty of people who have far more reason to care, and you can bet many will be much more annoyed then me at any such statements.
 * P.P.P.S. Just for further clarification, I'm not saying this is going to destroy the economy of many countries or bring down the world, indeed as I said in another comment, as it stands, the impact may be small.
 * Nil Einne (talk) 23:48, 18 April 2010 (UTC)
 * Should have done this some time ago, but some references partially supporting Gandalf's point partially supporting my point supporting Gandalf's point about the small impact on food (although no one challenged that)  . I'm obviously biased, but these generally seem to support my POV. If this doesn't continue for much longer, the impact may be neglible, but potentially/probably not none for a many places nor for the global impact, however if it continues for long enough it definitely could have a small impact. Perhaps it's a matter of semantics, to me, saying there's no net impact means zero overall impact and is a quite different thing from saying there's neglible impact (which means there is potentially some impact but it's a as one of the sources says a blip on the radar), I obviously have no idea if that was what was intended. Nil Einne (talk) 14:51, 19 April 2010 (UTC)
 * As you seem to be very upset about the phrase "no net economic impact" - which I only used once - I have amended it to clarify what I meant. Gandalf61 (talk) 16:27, 19 April 2010 (UTC)
 * My last comment before I leave this discussion for good, in that case, although I do feel your comment only really considered one side and may missed some key points, I agree with the more generally point that some people are perhaps somewhat exaggerating the long terms effects of the disruption as things stand at the moment and the overall effect is likely to be small (however may still have some pretty big effects on some people and not just those trying to travel). As I mentioned, I do feel some statements can harm the discussion and have no qualms about pointing this out as I did in this case, even if the statement is only an aside (although it did seem to me to be the core of the argument, even if that wasn't your intention). As may be obvious, I also agree with a number of the other comments, e.g. Mr.98's. Edit: Er sorry was rereading the thread and realised I forgot one more point, I saw this in my earlier research and it's even in our article. AFAIK, the US$200 million/day figure is for all airlines. For the UK, I've seen £20m million/day for BA . This perhaps isn't surprising as I'm sure Gandalf and most would recognise, the UK airlines themselves aren't 2.5% of the UK's GDP. Nil Einne (talk) 16:49, 19 April 2010 (UTC)


 * If you cancel a conference you have to refund everyone that paid to attend it (whether they would actually be able to make it or not). --Tango (talk) 14:41, 18 April 2010 (UTC)
 * Incidentally, I am not sure why everyone thinks that conference funds are totally refundable. Many of them will already be spent and non-refundable (you cannot just cancel a huge booking at a hotel and get everything back). When I have been at conferences that were partially cancelled by weather (half of it was called off), I got nothing back. I was told that they might put on the conference again in a few months and then my previous conference ticket would be honored. That would have required twice the amount spent on travel and lodging, though (because my hotel wouldn't refund my costs, of course, because they don't care about the conference). Yes, if you cancel something weeks in advance you can sometimes (but not always) get the money refunded. But in many cases you cannot because you have signed contract of some sort that prohibit this. At least in the US. --Mr.98 (talk) 17:02, 18 April 2010 (UTC)
 * Back when I was involved in running conferences (or, strictly speaking, conventions) we usually took out insurance against events outside our control causing the event's cancellation. (For those I was involved in, accommodation and conference facilities were mostly provided by the same venue.) Whether or not a natural event like this would be included or excluded (as, say, an "Act of God") would depend on the terms of the particular insurance policy. 87.81.230.195 (talk) 19:12, 18 April 2010 (UTC)

I wouldn´t say the volcanic ash cloud clogs airplane engines. I got the impression that no one wanted to take chances. However, the Dutch airline KLM carried out a test flight Saturday night and detected no problems from the volcanic ash. As far as I know, they flew through the cloud.--Quest09 (talk) 17:18, 18 April 2010 (UTC)


 * There were two rather well-known incidents in the 1980s where Boeing 747s lost all four engines while flying through an ash cloud. Both times, the pilots were able to restart enough engines to land safely, but nobody wants to take the risk again. --Carnildo (talk) 01:34, 20 April 2010 (UTC)