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Take Off: Where Is The Danger With Tailwinds?  
User currently offlineDairy From Germany, joined Nov 2003, 241 posts, RR: 0
Posted (4 years 11 months 2 weeks 2 days 7 hours ago) and read 8799 times:

Today I wanted to spot in Frankfurt (EDDF), by its runway 18. But every departure took place on 7L, arrivals on 7R. RWY18 was closed the time I was there - and I was alone there - it was closed due to strong tailwinds: That's what I am supposing seeing the direction and strength of the wind by the wind cone.

Well, I know that aircrafts have to take off against the wind in optimal circumstances. But several times I have seen some aircrafts departing in the two directions (i.e. at ZRH) nearly at the same time, close after each other (but there surely was no strong winds).
It now brought me to the question where the concrete danger is, when aircrafts take off with (strong?) tailwind behind them?


A318/A319/A320/A321 AB3/A306/A310/A333/A343/A346 732/733/735/736/744/752/763/764/772/773 DH3 F70 F100 CR2 CR1 CR7 ATR42
35 replies: All unread, showing first 25:
 
User currently offlineBlrsea From India, joined May 2005, 1426 posts, RR: 3
Reply 1, posted (4 years 11 months 2 weeks 2 days 7 hours ago) and read 8799 times:

wouldn't take off with strong tail wind mean lesser power to use? And if they take-off into head winds, wouldn't they face more resistance and hence more power/fuel consumed?

What is the logic of taking off with head wind?

While landing, do they prefer head wind or tail winds? I am assuming head-winds  Smile


User currently offlineNWADC9 From United States of America, joined May 2004, 4898 posts, RR: 9
Reply 2, posted (4 years 11 months 2 weeks 2 days 7 hours ago) and read 8787 times:

The danger is with the increased roll length. With a strong headwind, more air is blowing towards the airfoil, allowing a shorter takeoff roll while still providing sufficient amount of lift. With a tailwind, however, the wind just pushes the plane down the runway without going through the airfoil [in the right direction] and creating lift, and if it's strong enough, the takeoff roll can exceed the length of the runway, which no one wants (except funeral directors  duck  ). With a strong headwind, all it does is shorten the takeoff roll, and theoretically can make the roll zero.


Flying an aeroplane with only a single propeller to keep you in the air. Can you imagine that? -Capt. Picard
User currently offlineDualQual From United States of America, joined Mar 2006, 786 posts, RR: 1
Reply 3, posted (4 years 11 months 2 weeks 2 days 7 hours ago) and read 8761 times:

The question is a bit multi-faceted in terms of answers. Airplanes can and sometimes do take off with a tail wind. However there are many things that go into the performance equation to determine if this can happen. First, the tailwind cannot exceed the published limit for the airplane. All aircraft have wind limits for tailwind, crosswind, any direction, and are further broken down into runway condition (icy, wet, dry, etc). Second, for takeoff the airplane must be able to take off in the runway required AND meet climb performance parameters as dictated by established minimums or higher if terrain is involved. Basically, if the tailwind component is within limits, allows the aircraft to meet it's performance requirements in the available runway, and clear the terrain you can go.

User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 4, posted (4 years 11 months 2 weeks 2 days 7 hours ago) and read 8763 times:



Quoting Dairy (Thread starter):

It now brought me to the question where the concrete danger is, when aircrafts take off with (strong?) tailwind behind them?

You increase the takeoff distance. In some cases even a seemingly small 10 knot tailwind could mean using up to 1000ft of extra runway. Not good if you're heavy and in hot weather and a short runway.

Quoting Dairy (Thread starter):
RWY18 was closed the time I was there - and I was alone there - it was closed due to strong tailwinds:

Runways aren't closed. They are unused. If it was closed there would be a big lighted X over it.  Wink

If the wind is calm, (less than 3kts) then it doesn't play much of a factor and you can land either way safely.


User currently onlineXT6Wagon From United States of America, joined Feb 2007, 3423 posts, RR: 4
Reply 5, posted (4 years 11 months 2 weeks 2 days 7 hours ago) and read 8748 times:

Lift, Its all about lift. When you take off into a headwind you get "free lift" since your airspeed is higher than your ground speed.

The reverse is true in a tail wind. You need a higher groundspeed to get your minimum airspeed to take off.

So yes a headwind makes the plane accelerate slower to a given groundspeed, but the difference is that if it takes you an extra couple seconds to hit 130mph... you don't NEED to hit 150mph, but only 130mph its going to that 130mph alot quicker.

Tailwinds are very nasty since they push planes into and past thier limits very quickly. Needing an extra 10 to 20mph groundspeed means alot more runway used, alot more runway needed for an aborted takeoff (stopping distance), and wheel speed restrictions.


User currently offlineMax777geek From Italy, joined Mar 2007, 538 posts, RR: 0
Reply 6, posted (4 years 11 months 2 weeks 2 days 7 hours ago) and read 8705 times:



Quoting Dairy (Thread starter):
It now brought me to the question where the concrete danger is, when aircrafts take off with (strong?) tailwind behind them?

That you go long.

Long means longer distance to reach the minimum speed to give your airplane enough lift to fly,
which is the difference in beetween airplane speed and steady air. If you add wind from the back of the plane, you'll remove that speed from the airplane speed, more or less. So you will need more. More speed needs more rwy to reach, hopefully there's enough. Don't know what you chaps calls on here, but here in Italy we call it "to sail" to express actually "to glide", to mean what the back wind brings you. Can't say about other types, on md80 is up to 10knots backwind, there's no problem.

To come back to your question, no problem until you have enough rwy and you don't have buildings etc before you lift off.


User currently offlineTimz From United States of America, joined Sep 1999, 6895 posts, RR: 7
Reply 7, posted (4 years 11 months 2 weeks 2 days 7 hours ago) and read 8661 times:



Quoting FLY2HMO (Reply 4):
Runways aren't closed.

Runways are often so described in the ATIS; think they have hauled the X-machine out there, every time they say that? Is ATC allowed to say the runway is closed, even though they haven't positioned the X-machine yet?


User currently offlineCatiii From United States of America, joined Mar 2008, 3058 posts, RR: 4
Reply 8, posted (4 years 11 months 2 weeks 2 days 7 hours ago) and read 8624 times:



Quoting Timz (Reply 7):
Runways are often so described in the ATIS

And to amplify on that, airports are often closed, which by extension means their runways are also closed.


User currently offlineAirbuske From United States of America, joined Jun 2007, 466 posts, RR: 0
Reply 9, posted (4 years 11 months 2 weeks 2 days 7 hours ago) and read 8566 times:



Quoting XT6Wagon (Reply 5):
Lift, Its all about lift. When you take off into a headwind you get "free lift" since your airspeed is higher than your ground speed.

Maybe I am misunderstanding you but are you saying that wind affects the amount of lift your require to lift off the ground? If so, I must respectfully disagree. The amount of lift required remains the same - wind or no wind. The difference lies in how long you must accelerate until you have enough airspeed to lift off, which in turn relates to how far you travel down the runaway.

Let me try say what others have said in different words. Say you have a 20 knot headwind and you need to calculate the distance required to an airspeed of 150 knots (for lift off) with all engines running. When the airplane is positioned, unmoving, at the end of the runaway ready to begin it's takeoff roll, it already has a 20 knot airspeed. (Recall that lift is a function of airspeed, not ground speed) So instead of having to increase over a total speed increase of 150 knots as you would do with no wind, you only need to accelerate over a speed increase of 130 knots hence a shorter takeoff roll.

The converse is true with a tailwind. Say you have a 20 knot tailwind and you need to calculate the distance required to an airspeed of 150 knots (for lift off) with all engines running. When the airplane is positioned, unmoving, at the end of the runaway ready to begin it's takeoff roll, it has a -20 knot airspeed. So instead of having to increase over a total speed increase of 150 knots as you would do with no wind, you now need to accelerate over a speed increase of 170 knots hence a longer takeoff roll.


User currently offlineDragon6172 From United States of America, joined Jul 2007, 1203 posts, RR: 0
Reply 10, posted (4 years 11 months 2 weeks 2 days 6 hours ago) and read 8478 times:



Quoting Airbuske (Reply 9):
Maybe I am misunderstanding you but are you saying that wind affects the amount of lift your require to lift off the ground? If so, I must respectfully disagree. The amount of lift required remains the same - wind or no wind. The difference lies in how long you must accelerate until you have enough airspeed to lift off, which in turn relates to how far you travel down the runaway.

I think it is a misunderstanding. For the purpose of this thread, there are two ways to get lift. Point the wing into the wind, or propel the aircraft forward. When you propel the aircraft, the lift you get is "costing" you fuel....but when you point the aircraft into the wind the lift you get is "free". Not sure if that helped, but that is how I understood his use of "free lift". I do not believe he meant that less lift would be required.



Phrogs Phorever
User currently offlineAirbuske From United States of America, joined Jun 2007, 466 posts, RR: 0
Reply 11, posted (4 years 11 months 2 weeks 2 days 6 hours ago) and read 8415 times:



Quoting Dragon6172 (Reply 10):
When you propel the aircraft, the lift you get is "costing" you fuel....but when you point the aircraft into the wind the lift you get is "free". Not sure if that helped, but that is how I understood his use of "free lift". I do not believe he meant that less lift would be required.

Aaah I see. Now I see what he means and it makes perfect sense. Thanks so much for your clarification.  Smile


User currently offlineKELPkid From United States of America, joined Nov 2005, 6428 posts, RR: 3
Reply 12, posted (4 years 11 months 2 weeks 2 days 5 hours ago) and read 8409 times:

Also not mentioned in this thread (and they are, in the case of many jets, one of the reasons for tailwind limitations, in addition to the factors mentioned above): ground speed limits for tires and wheels. Tires can and will blow out if you exceed the maximum certified ground speed of the tire...


Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineAT From United States of America, joined Jul 2000, 1050 posts, RR: 0
Reply 13, posted (4 years 11 months 2 weeks 2 days 3 hours ago) and read 8355 times:

This has been one of the most informative posts (and it stuck to the original topic too!)
I always just assumed that you would want to take off into a tail wind in order to maximize speed, but now I understand!

Just to make it more complex, how does a crosswind affect the takeoff parameters?

And, from a definition point of view, how deviated from a head or tail wind does the wind have to be to qualify as a crosswind? For example, if the wind is just five degrees off the axis of the aircraft, would it still qualify as a headwind or a X-wind?


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17108 posts, RR: 66
Reply 14, posted (4 years 11 months 2 weeks 2 days 3 hours ago) and read 8350 times:

To add another tidbit, this is the reason aircraft carriers typically steam into the wind when conducting air ops. Also the forward speed of the carrier counts as headwind. I don't think you'll find an aircraft carrier conducting air ops when sitting still.


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineShmax525 From United States of America, joined Apr 2009, 13 posts, RR: 0
Reply 15, posted (4 years 11 months 2 weeks 2 days 3 hours ago) and read 8330 times:



Quoting AT (Reply 13):
And, from a definition point of view, how deviated from a head or tail wind does the wind have to be to qualify as a crosswind?

Pilots use a crosswind component chart to figure out the crosswind "component" of particular wind speed and heading. Basically to use the chart all you do is figure the angle between the runway and wind heading. (for example taking off on runway 09 with a wind out of 050 would give you a difference of roughly 40 degrees) From here using the velocity of the wind you can come up with the headwind and crosswind components acting on the airplane.

As for the rest of the thread, for the sake of simplicity it could be described as this: the wings/airfoil care about the speed of the air going over the wing (airspeed), rather then the speed over the ground (ground speed).

Perhaps best visual to describe the difference between air and ground speed is this; I was flying a Cessna a few months ago and entered slow flight into a direct 40 kt headwind at 6,000ft. I held the airspeed around 40 kts and had ground speed of around 1-2kts most of the time. The reason this applies to takeoffs/landings into the wind is because the converse is also true. A plane flying an indicated 120kt approach with a 10kt tailwind would actually be flying 130kts, but the wings would only be using 120kts of the wind.



Airspeed, altitude or brains: Two are always needed to successfully complete the flight
User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 16, posted (4 years 11 months 2 weeks 1 day 22 hours ago) and read 8263 times:



Quoting Timz (Reply 7):

Runways are often so described in the ATIS; think they have hauled the X-machine out there, every time they say that? Is ATC allowed to say the runway is closed, even though they haven't positioned the X-machine yet?



Quoting Catiii (Reply 8):

And to amplify on that, airports are often closed, which by extension means their runways are also closed.

Slow down guys. I know how runway closures work. I was being nitpicky.  cheeky 

What I was getting at is that if runway 36 is in use, 18 isn't "closed". And for a runway to be actually closed, you'd have to close both sides of course. In which case you'll see in the ATIS and NOTAMS as RWY 36/18 closed.


User currently offlineCosmicCruiser From United States of America, joined Feb 2005, 2255 posts, RR: 15
Reply 17, posted (4 years 11 months 2 weeks 1 day 22 hours ago) and read 8259 times:

Don't forget that accel/stop dist is also affected by a head/tailwind. With a tailwind V1 might very well be much lower.

Quoting FLY2HMO (Reply 16):
What I was getting at is that if runway 36 is in use, 18 isn't "closed"

No because if ATC so wished they could "let" you land/t/o on the opposite runway. It happens alot it's just traffic at most busy arpts won't allow it. I've landed and took off "against the grain" many times.


User currently offlineJarheadK5 From United States of America, joined Nov 2005, 216 posts, RR: 1
Reply 18, posted (4 years 11 months 2 weeks 1 day 22 hours ago) and read 8255 times:



Quoting Starlionblue (Reply 14):
To add another tidbit, this is the reason aircraft carriers typically steam into the wind when conducting air ops. Also the forward speed of the carrier counts as headwind. I don't think you'll find an aircraft carrier conducting air ops when sitting still.

It's also the reason carriers (at least USN carriers) are the fastest ships in the battle group - the more wind they can create over the deck, the larger the delta between the aircraft's stall speed and the airspeed off the cat.

About the only flight ops a CV/CVN will conduct while on the hook or at steerage, is helicopter ops.



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User currently offline2H4 From United States of America, joined Oct 2004, 8956 posts, RR: 60
Reply 19, posted (4 years 11 months 2 weeks 1 day 21 hours ago) and read 8250 times:
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Of course, most tailwinds can be effectively countered with a large enough conveyor belt.  duck 

2H4



Intentionally Left Blank
User currently offlineThirtyEcho From United States of America, joined Dec 2001, 1656 posts, RR: 1
Reply 20, posted (4 years 11 months 2 weeks 1 day 20 hours ago) and read 8225 times:

After reading the first two posts on this thread, it is hard to believe that airplanes have been flying for over a century yet this level of misunderstanding still exists.

Indeed, if my stick shift car ever had a dead battery, I would release the brake and let it roll uphill to get a start.


User currently offlineRwessel From United States of America, joined Jan 2007, 2391 posts, RR: 2
Reply 21, posted (4 years 11 months 2 weeks 1 day 20 hours ago) and read 8225 times:
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Quoting JarheadK5 (Reply 18):
It's also the reason carriers (at least USN carriers) are the fastest ships in the battle group - the more wind they can create over the deck, the larger the delta between the aircraft's stall speed and the airspeed off the cat.

While wind over the deck is crucial to (CATOBAR) carrier ops, and carriers are, in fact, usually the fastest (or one of the fastest) ships in the battlegroup, at least by a small margin, they do not use that extra speed under normal circumstances. If they did, they would lose their escorts whenever they were conducting flight operations. The need for wind over the deck does mean that all the escorts in a CBG will be fast, so they can keep up.


User currently offlineTF39 From United States of America, joined Jul 2006, 110 posts, RR: 0
Reply 22, posted (4 years 11 months 2 weeks 1 day 19 hours ago) and read 8220 times:



Quoting 2H4 (Reply 19):
Of course, most tailwinds can be effectively countered with a large enough conveyor belt.

here we go . . .  Cool


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17108 posts, RR: 66
Reply 23, posted (4 years 11 months 2 weeks 1 day 16 hours ago) and read 8180 times:



Quoting ThirtyEcho (Reply 20):
After reading the first two posts on this thread, it is hard to believe that airplanes have been flying for over a century yet this level of misunderstanding still exists.

Not among pilots, surely.  Wink But wait, recall that Mythbusters episodes about (dare I even bring it up) a plane taking off on a conveyor belt. The pilot did not thing it would work!!! Gah...



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineRwessel From United States of America, joined Jan 2007, 2391 posts, RR: 2
Reply 24, posted (4 years 11 months 2 weeks 1 day 16 hours ago) and read 8177 times:
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Quoting Starlionblue (Reply 23):
Not among pilots, surely.

Next time you're hanging around the hanger, bring up downwind turns... It's really kinda sad...


25 CosmicCruiser : Everyone one knows you can't make a downwind turn close to the ground, why you'll stall!!
26 Post contains images FLY2HMO : What did you expect from a bored 60 year old "pilot" that built his plane (a kite with an engine) in his garage?      No no no, your plane will sp
27 Swiftski : Or a whiz wheel - one of the best inventions ever.
28 Moose135 : To add to the thorough explanation of how to determine headwind and crosswind components by Shmax525, let me add that as was mentioned above, aircraf
29 Starlionblue : I agree. It's just sad. I mean all it takes is a little logical thinking...
30 B777LRF : It's actually quite simple. Aircraft don't, aerodynamically speaking, care about speed over the ground - the only thing that keeps the things flying i
31 AAR90 : I don't know about the E-2D, but all previous versions of the Hawkeye could be "shot" while "on-the-hook" (from most CV's). Same for S-3A [it could t
32 Bri2k1 : I'd like to clarify this a little. The POH for my airplane does not have any limitations on operations based on surface winds -- unless you consider
33 KELPkid : A Bob Hoover (of airshow fame) or is this Navy terminology for something that sounds like a vacuum cleaner?
34 AAR90 : "Hummer" = unofficial nickname of E-2 Hawkeye. "Hoover" = unofficial nickname of S-3 Viking. The reasoning is pretty obvious if you've ever been near
35 Starlionblue : AFAIK it is only called a Hoover in the UK and some former British territories.
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