novice
Topic Author
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### Boeing 737ng Flap Settings?

From what i know the Boeing 737ng has got 8 flap settings right? being; 1,2,5,10,15,25,30 and 40 does these numbers refer to degrees the angle its being reflected to the air at? if so why is there so little difference between 1,2 and 5 compared to the rest?

Thanks

BMI727
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### RE: Boeing 737ng Flap Settings?

 Quoting Novice (Thread starter): does these numbers refer to degrees the angle its being reflected to the air at?

Only in a very broad sense that it approximates the angle of the main flap. Once you're getting into the more complicated slotted flap setups of today, it gets muddled quickly.

Airbus, and most other manufacturers as well I believe, simply number the positions 1, 2, 3, etc. and completely dispense with angles. McDonnell Douglas, on the other hand, actually did have the designation correspond closely to the flap angle, which was actually important on their aircraft with the dial-a-flap feature.
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tdscanuck
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Joined: Wed Jan 11, 2006 7:25 am

### RE: Boeing 737ng Flap Settings?

 Quoting Novice (Thread starter):does these numbers refer to degrees the angle its being reflected to the air at?

No. Once upon a time, as BMI727 noted, they corresponded to the actual angle of physical things. That day is long past...now the numbers just stay what they are for commonality reasons.

 Quoting Novice (Thread starter):if so why is there so little difference between 1,2 and 5 compared to the rest?

1, 2, and 5 are takeoff settings. You don't want big deflections for takeoff because you don't want to drive drag up to high. For current Fowler flap designs, 1, 2, and 5 typically just push the slats out (improved stall AoA) and the slats back (not down), which increases area and hence lift.

Tom.

wilco737
Posts: 7275
Joined: Sun Jun 20, 2004 12:21 am

### RE: Boeing 737ng Flap Settings?

 Quoting tdscanuck (Reply 2):

The 737NG is certified for flaps 15 and 25 take offs. As you said, it induced a lot of drag, but adds more lift for field length limited take offs where the terrain is no problem. I did a flaps 25 take off once on the 737-800, was interesting.

wilco737

tdscanuck
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### RE: Boeing 737ng Flap Settings?

 Quoting tdscanuck (Reply 2):For current Fowler flap designs, 1, 2, and 5 typically just push the slats out (improved stall AoA) and the slats back (not down), which increases area and hence lift.

That should have said the *flaps* back...

wilco737's abosolutely right about the deep flap takeoffs...you get even more lift by deflecting the flaps but you pay a big drag penalty to do it. If you have the runway/terrain combination for it to work it can be useful.

Tom.

IAHFLYR
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### RE: Boeing 737ng Flap Settings?

Don't most 800/900 operators use Flaps 30 for landing when the runway allows to avoid high deck angles and tail strikes?
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wilco737
Posts: 7275
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### RE: Boeing 737ng Flap Settings?

 Quoting IAHFLYR (Reply 5):

Yes, we Used flaps 40 only when the runway was rather short. Most of the time we used flaps 30.

wilco737

chrisjw
Posts: 51
Joined: Sun Jan 11, 2009 7:42 am

### RE: Boeing 737ng Flap Settings?

 Quoting IAHFLYR (Reply 5):Don't most 800/900 operators use Flaps 30 for landing when the runway allows to avoid high deck angles and tail strikes?

I believe CO (now UA) forbid flaps 40 landings on their -900ER's due to the increased tailstrike risk. They also don't do derated takeoffs on the 900ER

BMI727
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Joined: Mon Feb 02, 2009 9:29 pm

### RE: Boeing 737ng Flap Settings?

 Quoting wilco737 (Reply 6):Yes, we Used flaps 40 only when the runway was rather short. Most of the time we used flaps 30.

I think many early 737s had flaps 40 deactivated due to noise concerns.
Why do Aerospace Engineering students have to turn things in on time?

barney captain
Posts: 1642
Joined: Tue Nov 06, 2001 5:47 pm

### RE: Boeing 737ng Flap Settings?

The option that WN took on our -800's delays full slat extension until Flaps 25, as opposed to the standard Flaps 10 position. This is apparently part of a short-field package offered by Boeing.
Southeast Of Disorder

Mir
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### RE: Boeing 737ng Flap Settings?

 Quoting BMI727 (Reply 8):I think many early 737s had flaps 40 deactivated due to noise concerns.

That doesn't make a lot of sense - why deactivate them if you could just put an item in the ops manual that says "Flaps 40 shall only be used if necessary for performance considerations"? That why you can still use them, but the crews won't do so unless they have to.

-Mir
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Jetlagged
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### RE: Boeing 737ng Flap Settings?

 Quoting Mir (Reply 10):That doesn't make a lot of sense - why deactivate them if you could just put an item in the ops manual that says "Flaps 40 shall only be used if necessary for performance considerations"? That why you can still use them, but the crews won't do so unless they have to.

That's exactly what they did though. That way crews can't accidentally select flap 40. But deactivating Flap 40 was simply a matter of blocking flap lever movement beyond the Flap 30 detent. Basically screwing a lump of metal into the pedestal.
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Fabo
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### RE: Boeing 737ng Flap Settings?

I am in no way to be held as knowledgeable, but it would not surprise me, if at some airports/countries, a "worst case" noise level was considered in some application. It would make sense then to disable Flaps 40. You would be essentially doing the same thing (for example) Ryanair is doing with lowering their MTOW on their 738s. Since many fees are made off of MTOW, they are saying "We know the airplane could do more, but we made it so it will not do more".
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CM
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### RE: Boeing 737ng Flap Settings?

737-700 & -800 flap handle detents correlate to flap deflection angles as follows:

Detent......Angle
1...........8 degrees
2...........11 degrees
5...........14 degrees
10.........19 degrees
15.........22 degrees
25.........26 degrees
30.........35 degrees
40.........46 degrees

The -900ER has the same detents, but I believe it has slightly different deflection angles than the -700 and -800.

YYZatcboy
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Joined: Fri Apr 22, 2005 2:15 am

### RE: Boeing 737ng Flap Settings?

The problem with flap 30 landings on the NG is it incorporates a 5-10kt increased speed bias in the VREF so you are flying your approach faster than you normally should to avoid tail strikes. Flaps 40 does not have this so you can fly your approach slower without that tailstrke risk.
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barney captain
Posts: 1642
Joined: Tue Nov 06, 2001 5:47 pm

### RE: Boeing 737ng Flap Settings?

 Quoting YYZatcboy (Reply 14):The problem with flap 30 landings on the NG is it incorporates a 5-10kt increased speed bias in the VREF

I'm fairly certain that's only true for the 8/900 - the 6/700 have no increased REF speed bias.
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YYZatcboy
Posts: 1032
Joined: Fri Apr 22, 2005 2:15 am

### RE: Boeing 737ng Flap Settings?

Yes I believe you are correct sir. My mistake. Will have to go back to my FOM and re read it...
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