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737 Take Off Question  
User currently offlineShamrocka330 From Ireland, joined Sep 2005, 287 posts, RR: 0
Posted (7 years 9 months 1 week 21 hours ago) and read 8265 times:

On a 737 - 800 flight recently I was closely watching the wing as we rotated and just started to climb... My question is why did the spoilers activate (come up) on the top of the wings as we rotated? I was under the impression that the spoilers were there to disturb (spoil) the airflow over the wing. Why would you want to disturb this airflow at this critical moment when you want every ounce of lift from your wing?


aka thebigjd (member since Sept 2001)
52 replies: All unread, showing first 25:
 
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 1, posted (7 years 9 months 1 week 21 hours ago) and read 8263 times:
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What you saw was almost certainly the roll control spoilers. After the ailerons reach a certain angle of upward deflection, those spoilers are mixed in to assist.




2H4





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User currently offlineMighluss From Spain, joined Oct 2001, 936 posts, RR: 8
Reply 2, posted (7 years 9 months 1 week 20 hours ago) and read 8259 times:

the spoilers are used to aid roll control in the 737. If you have crosswind at take off, you will need ailerons to compensate wind at lift off, and if you need too much ailerons, spoilers will deploy also.


Miquel.
User currently offlineShamrocka330 From Ireland, joined Sep 2005, 287 posts, RR: 0
Reply 3, posted (7 years 9 months 1 week 20 hours ago) and read 8252 times:

Quoting 2H4 (Reply 1):
What you saw was almost certainly the roll control spoilers. After the ailerons reach a certain angle of upward deflection, those spoilers are mixed in to assist.

Is this done to gain a steeper angle of attack after the rotation? Something that the ailerons can't achieve on their own so the spoilers come in and help out?



aka thebigjd (member since Sept 2001)
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 4, posted (7 years 9 months 1 week 20 hours ago) and read 8244 times:
AIRLINERS.NET CREW
HEAD DATABASE EDITOR




Quoting Shamrocka330 (Reply 3):
Is this done to gain a steeper angle of attack after the rotation? Something that the ailerons can't achieve on their own so the spoilers come in and help out?

The 737 drivers will be able to answer much more accurately, but the spoilers simply increase roll authority and response. Without them, roll control would be very sluggish and difficult. The 737 isn't the only aircraft that uses such a system.




2H4





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User currently offlineShamrocka330 From Ireland, joined Sep 2005, 287 posts, RR: 0
Reply 5, posted (7 years 9 months 1 week 20 hours ago) and read 8235 times:

Thanks for the replies guys!


aka thebigjd (member since Sept 2001)
User currently offlineMighluss From Spain, joined Oct 2001, 936 posts, RR: 8
Reply 6, posted (7 years 9 months 1 week 20 hours ago) and read 8215 times:

Quoting 2H4 (Reply 4):

hehe! you are answering at the same time than me... :p

just to add that ailerons (and eventually spoilers) have nothing to do with AoA (angle of attack), they are just for roll control. Elevators makes the plane go nose up.



Miquel.
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 7, posted (7 years 9 months 1 week 20 hours ago) and read 8211 times:
AIRLINERS.NET CREW
HEAD DATABASE EDITOR




Quoting Mighluss (Reply 6):
just to add that ailerons (and eventually spoilers) have nothing to do with AoA (angle of attack)

While I agree that AOA isn't the focus in this particular question/discussion, ailerons certainly do effect the AOA. During a stall, for example, commanding left roll input will result in a roll to the right.

Why? Because the aileron on the right is deflected downward, increasing the angle of attack to a point beyond the critical AOA, and causing that wing to stall first.




2H4





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User currently offlineBri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 8, posted (7 years 9 months 1 week 19 hours ago) and read 8203 times:

Nothing like overcomplicating things. Ailerons also increase drag disproportionately.

But that 737 wasn't in a stall at takeoff, hopefully...



Position and hold
User currently offlineAirWillie6475 From United States of America, joined Jan 2005, 2448 posts, RR: 1
Reply 9, posted (7 years 9 months 1 week 18 hours ago) and read 8172 times:

Yes it has something to do with angle of attack but for the wing not the airplane. For example to turn left, the ailerons on the left wing must be up and the ailerons on the right wing must be down. When the aileron is down on the right wing(use your arms) this will increase the angle of attack and create lift. BUT this lift also causes drag on the right wing. This means that even though the plane is established in a left turn the aircraft will still have a tendency to turn to the right or not turn as efficiently to the left because of this induced drag on the right wing. That is where the spoilers come in. The spoilers don't turn the aircraft they just disturb the airflow over the wing on the inside of the turn just enough so the ailerons can better bank the aircraft. They use spoilers because using the rudder as is the case in small aircraft to help bank the plane is not an option for large aircraft such as the 737. Hope you understand.

User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 10, posted (7 years 9 months 1 week 18 hours ago) and read 8167 times:
AIRLINERS.NET CREW
HEAD DATABASE EDITOR




Quoting AirWillie6475 (Reply 9):
Yes it has something to do with angle of attack but for the wing not the airplane.

The airplane doesn't have it's own AOA. AOA, by definition, applies only to things with camber and chord lines (ie: airfoils). AOA in reference to only the fuselage is meaningless in terms of lift production.




2H4





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User currently offlineVikkyvik From United States of America, joined Jul 2003, 9400 posts, RR: 27
Reply 11, posted (7 years 9 months 1 week 17 hours ago) and read 8155 times:
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Quoting AirWillie6475 (Reply 9):
They use spoilers because using the rudder as is the case in small aircraft to help bank the plane is not an option for large aircraft such as the 737.

Not to get TOO far off-topic, but I thought the rudder was indeed used, just via the Yaw Damper, instead of footpedal inputs (landing phase excepted).

The spoilers are certainly not used on all rolls. They also are typically only extended while the airplane is actively rolling (to decrease lift on the inside wing). I don't think this is really comparable to what the rudder does in a coordinated turn, but maybe I'm wrong.

~Vik



"Two and a Half Men" was filmed in front of a live ostrich.
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 12, posted (7 years 9 months 1 week 17 hours ago) and read 8143 times:
AIRLINERS.NET CREW
HEAD DATABASE EDITOR




Quoting AirWillie6475 (Reply 9):
They use spoilers because using the rudder as is the case in small aircraft to help bank the plane is not an option for large aircraft such as the 737.

No, I'm with you, Vik....this is a rather confusing statement. If it were accurate, then only large aircraft would utilize roll control spoilers....which doesn't explain their presence on smaller aircraft like the MU-2 and Cessna Caravan.




2H4





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User currently offlineAirWillie6475 From United States of America, joined Jan 2005, 2448 posts, RR: 1
Reply 13, posted (7 years 9 months 1 week 17 hours ago) and read 8141 times:

Quoting 2H4 (Reply 10):
The airplane doesn't have it's own AOA. AOA, by definition, applies only to things with camber and chord lines (ie: airfoils). AOA in reference to only the fuselage is meaningless in terms of lift production.

I know that, I was telling the thread starter that because he said tha angle of attack of the aircraft.


User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 14, posted (7 years 9 months 1 week 17 hours ago) and read 8132 times:
AIRLINERS.NET CREW
HEAD DATABASE EDITOR




Quoting AirWillie6475 (Reply 13):
I know that, I was telling the thread starter that because he said tha angle of attack of the aircraft.

Ah, sorry about that, Willie. I misread what you said.




2H4





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User currently offlineBri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 15, posted (7 years 9 months 1 week 17 hours ago) and read 8123 times:

Quoting Vikkyvik (Reply 11):
Not to get TOO far off-topic, but I thought the rudder was indeed used, just via the Yaw Damper, instead of footpedal inputs (landing phase excepted).

The spoilers are certainly not used on all rolls. They also are typically only extended while the airplane is actively rolling (to decrease lift on the inside wing). I don't think this is really comparable to what the rudder does in a coordinated turn, but maybe I'm wrong.

It's not what the rudder does in a coordinated turn, no, but there's more. The high-speed, swept-wing design of big planes like the 737 mean that rudder inputs do more than just yaw the plane -- they actually bank it, too.

The yaw damper deflects the rudder a very small amount to maintain turn coordination and control yaw during flight -- much smaller corrections than could be made by the pilot's booted feet. Look at the size of the rudder! Only a tiny deflection is a huge control input with the amount of air flowing over that huge control surface.



Position and hold
User currently offlineAirWillie6475 From United States of America, joined Jan 2005, 2448 posts, RR: 1
Reply 16, posted (7 years 9 months 1 week 16 hours ago) and read 8101 times:

Quoting Bri2k1 (Reply 15):
It's not what the rudder does in a coordinated turn, no, but there's more. The high-speed, swept-wing design of big planes like the 737 mean that rudder inputs do more than just yaw the plane -- they actually bank it, too.

Rudder input on any plane will eventually cause the plane to bank.


User currently offlineHighFlyer9790 From United States of America, joined Jul 2005, 1241 posts, RR: 0
Reply 17, posted (7 years 9 months 1 week 16 hours ago) and read 8099 times:

heres a video showing the roll control on a 737 during takeoff...

http://www.flightlevel350.com/Aircra..._Airlines_Aviation_Video-2582.html


highflyer  spin 



121
User currently offlineShamrocka330 From Ireland, joined Sep 2005, 287 posts, RR: 0
Reply 18, posted (7 years 9 months 1 week 6 hours ago) and read 8020 times:

Quoting HighFlyer9790 (Reply 17):
heres a video showing the roll control on a 737 during takeoff...

cool video HighFlyer9790, that's exactly what I saw the spoilers do on the aircraft I was on!

Sorry to drag this on guys but the term roll control has been used many times in the previous replies but the take off I started this thread talking about had no turns or sideways movement at all during rotation and the beginning of climb. There was no wind either. I'm thinking that roll control manages the aircraft during turns but I'm thinking this maybe isn't the case?  Confused



aka thebigjd (member since Sept 2001)
User currently offlineHAWK21M From India, joined Jan 2001, 31573 posts, RR: 57
Reply 19, posted (7 years 9 months 1 week 5 hours ago) and read 7980 times:

Was it on the Side of the Wing going Down.Those are Flight Spoilers.
Operated with Roll control.
regds
MEL



Think of the brighter side!
User currently offlineBri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 20, posted (7 years 9 months 1 week 5 hours ago) and read 7972 times:

Quoting Shamrocka330 (Reply 18):
There was no wind either.

That's a bold assertion. How do you know? There's always wind. Always. And it's never, ever straight down the runway...it's at least a few degrees off the nose. Many times, on longer runways, airliners will take off with a slight tailwind component to get a more favorable initial heading or to avoid noise-sensitive areas whenever possible.

Even if there wasn't any wind, the plane still has to be controlled after takeoff. The wind could also shift right after takeoff, especially if buildings or terrain played a part in wind dynamics at the surface. That can play a part in a tower reporting "wind calm" when there's actually some wind, at least light and variable winds, at another part of the field, or just a few feet above the ground.



Position and hold
User currently offlineShamrocka330 From Ireland, joined Sep 2005, 287 posts, RR: 0
Reply 21, posted (7 years 9 months 1 week 4 hours ago) and read 7961 times:

Quoting Bri2k1 (Reply 20):
That's a bold assertion. How do you know?

I could see the wind sock at the end of the runway, it was fairly lifeless! I'm sure there was some element of wind but not enough to cause a large amount of roll control (which was mentioned in a number of replies above where I assumed they were talking about strong winds).



aka thebigjd (member since Sept 2001)
User currently offlineCptSpeaking From United States of America, joined Apr 2006, 639 posts, RR: 1
Reply 22, posted (7 years 9 months 1 week 4 hours ago) and read 7954 times:

Quoting Bri2k1 (Reply 20):
There's always wind. Always. And it's never, ever straight down the runway...it's at least a few degrees off the nose. Many times, on longer runways, airliners will take off with a slight tailwind component to get a more favorable initial heading or to avoid noise-sensitive areas whenever possible.

With all due respect, this is false. Up at altitude there is always wind, but on a lot of nights, the surface winds are completely calm. And as for direction, mother nature doesn't know or care which magnetic heading the runway is aligned with, so you can't say that the wind is always a few degrees off. Most times it may be, but when planning an airport, designers look at the prevailing winds to determine which way(s) to face the runway(s).

As for taking off with a tailwind, the only reason I'm aware of for airliners doing this is runway slope. Small airplanes may do this to save time, but not airliners. Especially on longer runways, which are usually at bigger airports with lots of traffic. ATC has an active runway for a reason, and won't take special requests for direction just to get on a better initial heading. This would totally screw up their spacing and such unless its VERY late at night. In LYH, sometimes the Dash-8s will take off on 22 instead of 4 because of the runway gradient and required takeoff distance. It's not a huge difference in elevation from end to end, but enough to make the pilots want gravity on their side.

Your CptSpeaking



...and don't call me Shirley!!
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 23, posted (7 years 9 months 1 week 4 hours ago) and read 7944 times:
AIRLINERS.NET CREW
HEAD DATABASE EDITOR




Quoting Shamrocka330 (Reply 21):
I could see the wind sock at the end of the runway, it was fairly lifeless!

That only tells you what the wind was doing at the end of the runway....




2H4





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User currently offlineVikkyvik From United States of America, joined Jul 2003, 9400 posts, RR: 27
Reply 24, posted (7 years 9 months 1 week 3 hours ago) and read 7937 times:
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Quoting Shamrocka330 (Reply 21):
I'm sure there was some element of wind but not enough to cause a large amount of roll control (which was mentioned in a number of replies above where I assumed they were talking about strong winds).

I think it's less about how much roll you need as opposed to how fast the roll was commanded. I believe the spoilers will help with roll control when faster rates of roll are commanded (where the ailerons may not be able to meet the commanded roll rate on their own).

Also, there could have been a gust of wind at that time.

Keep in mind, also, that there was probably a good mile or more between the windsock and where you rotated. Airports are big places; as 2H4 stated, the wind may not necessarily be the same all across the field.

Quoting Shamrocka330 (Reply 18):
Sorry to drag this on guys but the term roll control has been used many times in the previous replies but the take off I started this thread talking about had no turns or sideways movement at all during rotation and the beginning of climb.

The roll for crosswind correction would probably be pretty small in the grand scheme of things - small enough that you may not have really noticed it. I'm sure in my life I've been in plenty of crosswind takeoffs and landings. It's only been noticeable once or twice.

~Vik



"Two and a Half Men" was filmed in front of a live ostrich.
25 Bri2k1 : I have to disagree with all of that. Surface winds result from uneven heating of the Earth. Clearly, the runway surface absorbs a different amount of
26 Starlionblue : My old remote control motor glider didn't even have ailerons. Rudder and elevator. The turns weren't perfectly coordinated and I couldn't do a snap r
27 DH106 : Yep - but your rc glider would have more dihedral than otherwise with ailerons to help the rudder bank the aircraft. On a simple plane with no dihedr
28 Post contains links and images Starlionblue : Quite right. Lots of dihedral. This is a smaller version of my old model. Same planform except mine had a conventional tail. http://www.kyosho.co.jp/
29 AirWillie6475 : Every time the pilot moves the yoke past a certain degree the ailreons will deploy much like that video that was posted on this thread. That plane wa
30 Post contains images DH106 : " target=_blank>http://www.kyosho.co.jp/web/products....html Great looking model Starlionblue! I fly gas power stuff myself, but am getting more and m
31 Post contains images Starlionblue : Haven't flown anything in years The advantage of electric is silence. I used to fly in a large city park in Stockholm (no car at the time). Endurance
32 Post contains images CptSpeaking : I agree with you there, there is the basis for wind due to uneven surface heating, but this isn't always enough to cause measurable surface winds. I'
33 AirWillie6475 : I really doubt it. Most pilots have a monkey-see, monkey-do mentality. They just follow what other pilots do. Plus I don't think anybody cares if the
34 Bri2k1 : Ahh, I'm sorry that confused you. My use of "many times" here could have implied large airports since they see more operations. Even if it's not a la
35 2H4 : While I don't fly for an airline, I'm with you, Bri2k1. That particular statement doesn't contain a shred of accuracy. 2H4
36 Post contains links and images Meister808 : Nope... you have that backwards. With no dihedral or sweep, the roll moment is actually stronger in that case. As the aircraft yaws, the outside wing
37 CptSpeaking : wow...in the future, keep the discussion on the topic. Age has nothing to do with what we're talking about, but even so, this 20 year old has much mo
38 ThrottleHold : When I flew the BAe146, we often had full into wind aileron at the start of the take-off roll to counter-act wing lift. There was a greatly reduced ri
39 AirWillie6475 : Ok I guess I should back-up what I said. I agree Meister808, it's not exactly monkey see monkey do but you know what I mean. I tend to have this too,
40 DH106 : I agree with your statement about the roll moment caused by wing speed differential (I was actually considering a steady, damped yaw with no wing spe
41 TWAL1011727 : AOA is the relation between the wing chord line and the relative wind. The wing chord line changes with extension/retraction of flaps/slats or with a
42 Meister808 : Fair enough Gotcha, I see what you're getting at now and, yes, it happens all the time. Hm.. I think you've got me on the sweepback. I swear I recall
43 Post contains links and images HighFlyer9790 : Whenever a gust of wind requires a correction input from the yoke, you are essentially doing the same motion on the yoke that you would do to enter a
44 Bri2k1 : Not chronologically possible. But since you brought it up (and I did not -- read more below) I'm a pilot, too. I'm reminded of the joke...How do you
45 DH106 : Why isn't is chronologically possible ? Are ALL the forum posters commercial pilots with many years service? No. Bri2k1 holds a CPL which makes him c
46 ChrisMUC : The activation of flight spoilers on a B737 depends on control wheel displacement, if it's larger than appr. 10� the flight spoilers will be mixe
47 Post contains images CptSpeaking : Are you serious? Even if I had just one flight hour in my logbook, that would give me more experience than some in here. Thats cool that they're here
48 Eddie757 : An important fact concerning the aid of spoilers in the act of roll at low speeds is that in the case of an engine failure after t/o it is extremelly
49 Bri2k1 : I disagree. You would have more logged flight time than many here. But this is the kind of thing that no one can tell you, you just have to experienc
50 Post contains images DH106 : But that's just it - by having any flying time he HAS experienced it. So he has more experience than someone with no flying time. Gracious of you to
51 ChrisMUC : on a b737 initial engine failure recovery is done with the aileron, than the control wheel is centered by the rudder (without delay). reason is that
52 Post contains links and images LTU932 : You mean similar to what those US pilots did here: View Large View MediumPhoto © Ruben HofsNotice the aileron deflection on the leftwing, as the
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