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- Thread starter aquajet
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aquajet said:
I want to say the world record for the heavies glider was set by a 777. If not I know it was a large airplane over Hawanian islands and for like 15-20mins (dont rememeber the exact number or plane). What happen was a voloncic equration cause the enginees to get clog and shut down. Well the plane was the world heavies glider during that time while the crew got the enginees restarted which happen to take 15-20mins. Then the plane landed safely no really damage was done no big story.
But in theory a 777 could glide/fly for 180 mins with both enginees out. It come down to what the alitude was at the time. What the the air speed was at the time and then the weather and aircondition down to the ground. Because it could be they where in a jet stream at the time and they stay in it as long as possible after the enginees go out so they have a higher ground speed. So when the air speed drops to low and they have to leave the jetstream their air speed will spike back up allowing for even more air time. (so they have about a 90+knot tail wind while in the jet stream. Leave the jet stream and the tail wind goes to 0. Guess what they just gain 90+knots of air speed which means even more flying time). Plus keep moving the plane right they can keep the air speed pretty high by ajusting for more and more of a head wind to keep the air speed up.
Nobody knows how long a 777 could stay aloft with both engines out because they don't test the aircraft for this situation. Also, winds have no effect on airspeed, only ground speed, so wind has no influence on the time an airplane can remain airborne without thrust, only the distance over the ground that can be covered.
Timepass said:
The assumption here is that there is a solid line which separates the jet stream. This is not the case. There are wind gradients which lead to the jet stream.
As IJ mentioned, winds only affect ground speed (I know this sounds backwards at first, but you have to think from the airplane's perspective, not the ground's). Provided you are on a steady glideslope without engines, generally your airspeed will remain constant, but your groundspeed will decrease as altitude decreases. Your airspeed indicator doesn't spike as you exit the jetstream. This would imply you're getting something for nothing, which doesn't happen. The only thing that can give you extra airspeed in an engine out situation is gravity.
IJ Reilly said:
Not directly. The only way windspeed could change how long an airplane could remain airbone with out thurst is if it changes (droppign out of a jet stream for example you airspeed will change) but when it changes it effects the Airspeed.
For remaining in the air the only thing that matters is airspeed not ground speed like you are saying. And you are right only thing that truelly matters is airspeed. Wind effect on airspeed is only if it changes and the effect it changes is how much your airspeed change.
An example to explain that is and airplane is flying at 100mph airspeed with a tail wind of 30mph. Well all of a sudden the wind changes from a 30mph tail wind to a 30mph head wind. Now the airspeed is 160 mph.
Some people are right that airplanes will fly into jetstreams and tail winds to save fuel. They save fuel because they need less airspeed to keep the same ground speed so that means less thrust which translate into less fuel. But the Airspeed still has to remain about a certain leval. It also a good way to make up time in the air with out increasing cost.
But to follow this argument you have to understand the diffence bettween airspeed and ground speed and rememeber that groundspeed does not matter in any way shape or form on if an airplane can fly. The only thing that matters is airspeed.
Timepass said:
Again, prevailing winds do not affect airspeed. The reason why airplanes save fuel by flying with a tailwind is because your ground speed is higher, which means you get to where you're going in a shorter amount of time.
You're still thinking from the ground's perspective. The airplane doesn't care about the ground. It needs airspeed to fly.
aquajet said:
Oh I know that. But for illstating the point the solid line is a better way of explaining it. It same same as in physic how a lot problems on done on a frictionless surface. Impossible in the real word but a much easier way to illstrated and explain things. Less confusition in it.
Yeah it changes in a a a slower pace but all that translate into is how many ft/s the airplane must go down to maintain the same airspeed.
the basic of it is I understand it completely and see it all but most people in this world can not understand thing on the engineering and science lv that IJ and I are seeing it.
Understanding airspeed and ground speed is a lot like understand theroy of relitivity. Confusing as hell to get and it hurts the mind to think about it but when you understand it things like airspeed and ground speed are a lot easier to understand (and yes I do understand Theory of relitivty. Hurts the mind to think about it at times but I understand it.) Just though I make all that clear.
aquajet said:
I think you need to reread my post and what I stated. I said they like tail winds because with a tail wind you need less Airspeed to maintain the same ground speed..
I know Ground speed=Air speed+Wind speed. So for an Airplane wants ground speed XXX. To figure out the required Airspeed it is XXX-Windspeed=req Air speed. All wind speed effect is what is the required Air speed to get a desired ground speed.
I think you just miss read what I stated. We both unstand that Windspeed has no effect on Air speed and it only effects ground speed. I was just taking it a step farther and showing how Wind speed effects the required airspeed to get a desired ground speed.
Airlines flight times are based on ground speed. To get a desired flight time you require a figure out what the required airspeed will be with is depending on windspeed.
Sum it up Ground speed = Air speed + wind speed. If you want a 600 mph ground speed and there is a 20mph head wind the require airspeed would be 620 mph. I think that explain where I am coming from the best. And yes airplane will reduce there thurst to a lower ammount but still be high enough to maintain a safe airspeed.
Timepass said:
Okay, I think I know what you're on about now...
However, this isn't the way things work in the real world. All airplanes have specified operational parameters, including proper cruising airspeed. Reducing airspeed would require a higher angle of attack in order to maintain altitude due to decreased lift. A higher angle of attack creates additional aerodynamic drag, which isn't good for efficiency. Worst case scenario, reduced airspeed will result in a stall. The most efficient way to fly is at the proper airspeed with a good tailwind.
When did this turn into a testosterone-laden "I know more about planes than you do" versus "personal electronics on planes" thread?
aquajet said:
Entering/exiting wind shear boundaries can cause funny things to happen to airspeed indicators, but basically you are correct. Typically, when you cross such a boundary other things will be going on, such as moving from a stable to a descending air mass. If this happens, you may find that you need to add power and raise the nose just to hold your altitude. All of this is independent of horizontal winds, though.
BTW, an unscientific observation that I think most pilots will share: Headwinds are far more common than tailwinds. I've flown places with a headwind, turned right around and come back -- into another headwind. I can't remember ever having it work the other way round.
IJ Reilly said:BTW, an unscientific observation that I think most pilots will share: Headwinds are far more common than tailwinds. I've flown places with a headwind, turned right around and come back -- into another headwind. I can't remember ever having it work the other way round.
You have a lot more practical experience than I do, so I'll take your word for it.
IJ Reilly said:Hey buddy, you got a problem with that? Huh, do you?
Not really.
It's kind of like the inevitable road that processor-talk threads go in.
This is true, but partly because head winds are sought out by ATC and pilots for many flying conditions. It requires more engine power, but it's easier to maintain control of the aircraft and easier to generate predictable lift in a mild head wind as opposed to a tail wind, which of course is why aircraft almost always take off and land into the wind wherever possible.IJ Reilly said:BTW, an unscientific observation that I think most pilots will share: Headwinds are far more common than tailwinds. I've flown places with a headwind, turned right around and come back -- into another headwind. I can't remember ever having it work the other way round.
matticus008 said:
No, not really. First, ATC doesn't concern itself with winds aloft, only pilots do, and second, no pilot in his right mind would deliberately choose a headwind for cross-country flying. There is simply no advantage, and the disadvantage of lower ground speed, more flight time, more fuel burned. The reason airplanes take off and land into the wind whenever possible is lower ground speed. If an airplane rotates at 70 knots, a ten knot headwind means this number is achieved at 60 knots of ground speed; with a ten knot tailwind, this speed occurs at 80 knots of ground speed. As the old aviation expression goes, "There's nothing so useless as the air above you and the runway behind you."
Or fuel left on the ground!IJ Reilly said:
The airspeed vice groundspeed discussions have been interesting for sure. Always fun to be IMC doing holding with high winds aloft in either a small airplane or helicopter. Inbound time 2-3 minutes, outbound time 20-30 seconds.
One thing that separates military vice civilian aviation maneuvering is that with civilian aviation you generally will always go with favorable wind conditions for landing and taking off.
On the military side of the house this may not be possible due to the tactical situation. Tailwinds can sux!
No one said ATC was concerned with high altitude winds (except that they are in terms of impacts on stacking at airports and remaining fuel supplies of backed up aircraft, not to mention the fact that they need the information to pass on to other pilots and to make adjustments in flight plans for aircraft on the ground), and no one said that headwinds would be selected for cross-country flying conditions. I said there are many conditions under which a head wind is preferable--including takeoff and landing. In choppy weather, you're also going to prefer a head wind for more stability in the controls, and in a number of other flying situations too complex to write briefly. Turbofan engines do not respond well at all to variable loads, unlike piston or even turboprop models, and a moderate head wind can actually result in a lower fuel burn than an inconsistent tail wind--the more acceleration and deceleration in the engine rotational speed, the worse the fuel economy (this is also true to a lesser extent for piston engines in cars and small planes, but turbines suffer far worse effects). So no, for commercial aviation, there is not "no reason" to choose a head wind. For personal craft, there are fewer reasons to do so, but they still exist.IJ Reilly said:
OT post, sort of IMO
I agree with the idea of turning off electronic devices. since there is some scant evidence as voiced here that they can interfere with the aircrafts electronics.
I also agree with the idea of showing up to the gate 30 minutes before the flight. It allows the flights to depart the gate on time. It is about respect.
But it is also about respect of the passengers that airlines and airports TRY to prevent the growing practice of sending flights from the gates on time, from what I am told to maintain on time departure, only to taxi around the airport or sit on the tarmac. In the very least advise the passengers waiting that that there may be a delay in actual take-off time.
As I have mentioned I was on the tarmac for over two hours for a ground stop at LGA. Came to find out that the previous flight had a delay of an hour on the tarmac before we even boarded.
Maybe I am a different air traveler, but that notice would have given me an opportunity to get some food and drink for whatever delay (the airline had told me that everything was on time), and would not have "gone off" over the delay.
But it is about setting expectations. When I checked in on the DCA-LGA shuttle, I expected in about 1 1/2 hours to be able to grab a quick lunch at LGA (my check-in was at 11:30AM, departure at 12N, and arrival by 1PM) for the limo ride to the hotel. As it happened wheels-up was at about 2:30PM, with a VERY quick trip to LGA - arriving at the gate by 3:15PM. Because of the late arrival, I did not get a chance to stop for a meal to go at LGA, since they were already holding the limo for a previous arrival (a senior exec of my host company) for 15 minutes waiting for my flight.
I guess I have had my expectations set now. Treated to lack of information, treated to mis-information, and to plan for two to three hours sitting on the tarmac.
Chundles said:
I agree with the idea of turning off electronic devices. since there is some scant evidence as voiced here that they can interfere with the aircrafts electronics.
I also agree with the idea of showing up to the gate 30 minutes before the flight. It allows the flights to depart the gate on time. It is about respect.
But it is also about respect of the passengers that airlines and airports TRY to prevent the growing practice of sending flights from the gates on time, from what I am told to maintain on time departure, only to taxi around the airport or sit on the tarmac. In the very least advise the passengers waiting that that there may be a delay in actual take-off time.
As I have mentioned I was on the tarmac for over two hours for a ground stop at LGA. Came to find out that the previous flight had a delay of an hour on the tarmac before we even boarded.
Maybe I am a different air traveler, but that notice would have given me an opportunity to get some food and drink for whatever delay (the airline had told me that everything was on time), and would not have "gone off" over the delay.
But it is about setting expectations. When I checked in on the DCA-LGA shuttle, I expected in about 1 1/2 hours to be able to grab a quick lunch at LGA (my check-in was at 11:30AM, departure at 12N, and arrival by 1PM) for the limo ride to the hotel. As it happened wheels-up was at about 2:30PM, with a VERY quick trip to LGA - arriving at the gate by 3:15PM. Because of the late arrival, I did not get a chance to stop for a meal to go at LGA, since they were already holding the limo for a previous arrival (a senior exec of my host company) for 15 minutes waiting for my flight.
I guess I have had my expectations set now. Treated to lack of information, treated to mis-information, and to plan for two to three hours sitting on the tarmac.
iGary said:
And here I am poised to talk about my exploits with a B-727 on the MS Flight Sim program. 60+ minutes, all three engines out....
A valid gripe, but one to which no good solution exists. If there is going to be a delay after boarding, the normal practice is to inform you after the safety video during pushback. The plane has to leave the gate on time, even if there's nowhere for it to go, because the gate is needed by another incoming flight--gate services are essential for just-landed aircraft, so departing aircraft are sometimes pushed straight back to a holding area while another plane takes the gate. If they told passengers before boarding, there would be boarding delays as passengers scatter in the terminal to get food, etc.--while they can leave one or two passengers behind, dozens of missing passengers will hold up the flight.Chip NoVaMac said:
Gate servicing also creates far bigger delays than runway backups--planes can take off at a rate of one per minute or so if there is a clear exit vector, but gate servicing takes a solid 25-30 minutes even at perfect efficiency. There's also fewer gates than empty tarmac for planes, which has a funnel effect meaning that gates are the most precious resource on the ground and no plane that doesn't need to be at the gate is allowed to stay. If arriving planes don't have gates, flight crews can't switch planes and there's a snowball effect on the delay.
Airports are overcrowded, but many of them are land-locked or victims of local municipal rules (no flights after 11pm, no more than 6 back-to-back takeoffs on the same runway, restrictions on thrust reverser use, etc.) that prevent airports from serving travellers to their best abilities. Sitting on the ground for an hour or two is certainly annoying, especially on a plane with limited food supplies, but sometimes it's the only option.
hmm you are right. when ever I been at an airport waiting to board a flight I noticed that a gates dont tend to be empty very long. Maybe 5 mins or so before the next plane pulls up. Yeah some times there may be more lag time if an incoming flight is late but they like to push off as fast as possible so incoming flights can get to the gate to get off there passagers. And depending on weather condition plans can be coming in earily. Heck when I fly out of Lubbock on the way home we quite offen land in dallas earily. Best time I seen is making up a good 15-20 mins in the air on the 300 mile flight (made up the rest of the dealy on the flight to houston) or to quite the pilot "Well forks looks we had one heck of a tail wind going in to dallas. Thanks to the 90knot tail wind we made up a lot of time."
Quite offen the flights from lubbock will pick up some good tail winds so they will land in dallas a few mins earily.
But yeah next time you are in the air ports watch the gates and see how fast the time is bettween planes coming and going from them. you noticed that the lag time bettween Planes is pretty small. and watch after a plane leave you will see them gearing up for the next plane right off the bat.
Like the guy said you want to prevent the gates from becoming a bottle neck and only way to do that is to keep them clear. Also if they started delaying them a few mins at a gate for late passagers those few mins add up. On top of that if people learn they can be a few mins late more and more people will start being late and then complain when they miss it. yeah it sucks to miss a flight by just 1 or 2 mins. I been there done that but they run a tight ship. You either get there on time or you miss your flight. People know this and they stick to it. there is a reason you get to the air port earily.
1 hour is the general rule. Depending on the air port you might be able to cut into that time some but 30 mins is really the lastest you should be.
Quite offen the flights from lubbock will pick up some good tail winds so they will land in dallas a few mins earily.
But yeah next time you are in the air ports watch the gates and see how fast the time is bettween planes coming and going from them. you noticed that the lag time bettween Planes is pretty small. and watch after a plane leave you will see them gearing up for the next plane right off the bat.
Like the guy said you want to prevent the gates from becoming a bottle neck and only way to do that is to keep them clear. Also if they started delaying them a few mins at a gate for late passagers those few mins add up. On top of that if people learn they can be a few mins late more and more people will start being late and then complain when they miss it. yeah it sucks to miss a flight by just 1 or 2 mins. I been there done that but they run a tight ship. You either get there on time or you miss your flight. People know this and they stick to it. there is a reason you get to the air port earily.
1 hour is the general rule. Depending on the air port you might be able to cut into that time some but 30 mins is really the lastest you should be.
Yes, why on earth would anyone DESPERATELY NEED to listen to your ipod or watch your dvd or turn on your phone whilst taking off/landing?!???!?! Just take the opportunity to relax and for once, do absolutely nothing, ZEN....
matticus008 said:
You still don't seem to be getting the difference between ground speed and airspeed. Airspeed is not affected by wind direction and speed. Not, as in, not. The flight controls are not affected either. Not, as in, not.
matticus008 said:
Sorry, but a bad argument perhaps. My example was extreme IMO - since it was a shuttle flight between DCA and LGA - so my last minute (30 minutes before departure) was not the norm IMO. But I was left waiting at least 15 minutes at the gate, so I had time to grab some water and snacks at the news stand if I had been told of the TRUTH for that days departures!
[qoute]Gate servicing also creates far bigger delays than runway backups--planes can take off at a rate of one per minute or so if there is a clear exit vector, but gate servicing takes a solid 25-30 minutes even at perfect efficiency. There's also fewer gates than empty tarmac for planes, which has a funnel effect meaning that gates are the most precious resource on the ground and no plane that doesn't need to be at the gate is allowed to stay. If arriving planes don't have gates, flight crews can't switch planes and there's a snowball effect on the delay.[/quote]
Good point that I learned. But why do not the airlines "advise" us that due to airport traffic that there might be significant delays before take-off? They warn us of delays at TSA checkpoints. Why not advise us to pack food and drinks for ATC and other post-gate delays? (I have learned my lesson on this point).
This is a "chicken vs. the egg" argument. I remember not so long ago that flights were held at the gates. But that was at the time that airports did not see the benefit of the "mini-mall" at the gates.
My trip last month on the shuttle from DCA to LGA is a worst case scenario for the airline. Given the hourly departures, and the number of associates departing from 11AM to 3PM, scheduled flight times, we were able to catch the airline, the airport, and the Federal ATC system in a whole pack of lies.
Air travel is meant to be convenient. In my case my DC to Long Island, NY trip would have been shorter if I drove (door to door was 10:30AM to 4:30PM; vs. what should had been a 10:30AM to 2PM). Lucky for me, it meant not being able to visit a museum (in my free time). But I heard from more than one passenger on my flight about a "missed meeting" because of the delay.
Your comments remind me of a recent news story of a SWA flight that had to turn back to the originating airport - only because there was "nobody in the tower". IIRC, even DCA allows "delayed" flights due to ATC and other "delays" - as long as the aircraft meets "noise reduction standards".
IMO we have a broken system. One that allows "credit" to airlines that have on-time departures, without regard to the impact to the passengers.
The other is that we make it impossible to add to (with additional airports) or expand the needs of the airports we already have. The airports and the Federal ATC allow for the airlines to meet the volume of air travel - not recognizing that the system can't handle the load.
Add to this the popular "Republican/conservative" supply vs. demand economic model. Less availability, boosts the costs.
You don't seem to be getting that I'm not talking about speed at all--I fully understand the difference, and I'm telling you it doesn't matter. I'm talking about engine-internal performance and airworthiness. Are you really trying to say that wind has nothing to do with the handling characteristics of an aircraft?IJ Reilly said:
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