vikkyvik
Topic Author
Posts: 12111
Joined: Thu Jul 31, 2003 1:58 pm

Flap Extension Question

Hello everyone...did a search, but didn't turn anything up.

Anyway, I believe the max flap extension on the 777 is 30 degrees. Now, after looking at numerous pictures, the inboard flaps appear to be extended downwards to at least 60-70 degrees from the wing incidence angle. So I was wondering how Boeing (and McDonnell Douglas, I believe) measures the flap degree (Airbus doesn't use degrees as far as I know).

 View Large View MediumPhoto © Garry Lewis - AirTeamImages View Large View MediumPhoto © Jet City Aviation Photography

Also, it is surprising that the flow around the wing and flaps can follow that extreme a curvature. The flow would be within 20 degrees of going straight downwards at full flap extension.

Thanks for all replies.

~Vik
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".

citationjet
Posts: 2312
Joined: Sun Mar 09, 2003 2:26 am

RE: Flap Extension Question

It is possible that the 30 degree flap deflection is max flight deflection. The higher (60-70 degree) may be ground flaps only.
Some airplanes like the Cessna Citation 525 series of jets have 35 or 40 flap deflections for flight, and 60 degrees for ground operation only.
Boeing Flown: 701,702,703;717;720;721,722;731,732,733,734,735,737,738,739;741,742,743,744,747SP;752,753;762,763;772,773.

SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Flap Extension Question

We'll have to wait to hear from a tripleSev person on the nominal flap settings but I agree that depicts more than thirty degrees.

The airflow always astonishes me too. I look at leading edge Krueger flaps as used to be found on Boeing wings and they looked like they started at 90o to the airflow. They looked more like an airdam.

On the TE flaps, remember that the air flowing over the upper surface of the trailing-most segment was on the underside of the wing until the last slot. The slots in slotted flaps are sort of a low-tech boundary layer control and serve to help in keeping airflow attached.

It is also helpful to remember that flaps are mostly lift through the takeoff range settings, and mostly drag beyond that.

CitationJet it is hard for me to picture touching down - then having more flaps extend. It seems like that would unweight the wheels and make the brakes less effective just when you need them most. Can you amplify on that?
Happiness is not seeing another trite Ste. Maarten photo all week long.

goboeing
Posts: 2477
Joined: Mon Jun 05, 2000 5:31 am

RE: Flap Extension Question

The nominal flap settings on the B-777 are UP, 1, 5, 15, 20, 25, 30.

Nick

vikkyvik
Topic Author
Posts: 12111
Joined: Thu Jul 31, 2003 1:58 pm

RE: Flap Extension Question

CitationJet,
I am quite sure that this flap extension is used on approach. As Slamclick stated, it doesn't seem logical to extend flaps more once on the ground.

View Large View Medium

Slamclick,
I understand the function of slotted flaps, and the fact that they produce much more drag when fully extended than lift. Still, I guess it's hard to imagine the airflow going almost straight downwards at the trailing edge of the wing. It just looks quite a bit more extreme than most other aircraft.

The 737 flaps (at least some models) go up to 40 degrees, but I've never seen them at such an angle.

Goboeing,
Thanks for the info.

~Vik
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".

citationjet
Posts: 2312
Joined: Sun Mar 09, 2003 2:26 am

RE: Flap Extension Question

Slamclick,
The ground flap operation does not unweight the wheels for two reasons:
1. Ground flap deployment on Citation CJ1, CJ2 and CJ3s automatically deploys the speedbrakes. (I failed to include this in my earlier post)
2. Going from 35 degree flaps (landing) to ground flaps (60 degrees) adds very little lift, it is almost all drag.

Even on wet runways, pilots still use the ground flaps.

Vikkyvik,
Believe me, I am 100% certain that the CJ1, and CJ2 are certified for ground flap operations of 60 degrees. You can check the Type Certificate Data Sheet that shows this. http://www1.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/CFBB75CA23335ED986256A9A00541A1C?OpenDocument
The CJ3 is being certified for the same operation.
I discussed my above answer with the Director of Engineering Flight Test Operations, Cessna Aircraft before making the above reply.

[Edited 2004-06-03 20:03:18]
Boeing Flown: 701,702,703;717;720;721,722;731,732,733,734,735,737,738,739;741,742,743,744,747SP;752,753;762,763;772,773.

RduBE90Pilot
Posts: 62
Joined: Wed Jun 02, 2004 9:18 am

RE: Flap Extension Question

As a former pilot on a CE-525 I agree with CitationJet.

Per the Flight Safety Citation Jet 525 Training Manual:

Ground Flaps are prohibited in flight.

The ground flap position is not locked out in flight. Selection of ground flaps will significantly increase drag and sink rate. We normally didn't use them as we operated out of fairly long runways, however, there were times that we did. Like the thrust attenuators on the CJ's, the ground flaps do work but you don't feel much affect as Vref speeds aren't that high normally.

Also the British Aerospace/Raytheon Hawker series has the same "lift-dump" style of ground flaps.

Eric

citationjet
Posts: 2312
Joined: Sun Mar 09, 2003 2:26 am

RE: Flap Extension Question

RduBE90,
As a 525 pilot, you will be interested to know that the new 525B (CJ3) currently in development will not have Thrust Attenuators. It was discovered that with FADEC engine controlling the idle thrust, the T/As are not required. It saved weight and cost also when removing them. The CJ1 (525) and CJ2 (525A) still have T/As, because they are not FADEC controlled.

You are correct, there is no lockout of the ground flaps in flight. There is an emergency airspeed placard of 140 kts with the ground flaps deployed in flight (emergency condition).

--Kim
Boeing Flown: 701,702,703;717;720;721,722;731,732,733,734,735,737,738,739;741,742,743,744,747SP;752,753;762,763;772,773.

vikkyvik
Topic Author
Posts: 12111
Joined: Thu Jul 31, 2003 1:58 pm

RE: Flap Extension Question

CitationJet and RduBE90Pilot,
Interesting that there is a ground flap setting that is different from flight flaps on the Citation. I didn't mean to say that you were wrong; just that based on photos and from what I know of the 777, flaps 30 is the max and is used on approach and on the ground.

Are the ground flaps an automatic function once the plane has touched down, like spoilers? Meaning, can they be armed and automatically deploy when the wheels are on the ground?

Anyway, if anyone knows the answer to my original question, I'd appreciate it!

~Vik
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".

citationjet
Posts: 2312
Joined: Sun Mar 09, 2003 2:26 am

RE: Flap Extension Question

Vikkyvik,
You say you believe that the 777 max flap deflection is 30 deg. What is that based on?
I suspect that Boeing measures their flap deflections the same as every other aircraft manufacturer. Based on the photos in your original post, I would say that either the 30 degrees you stated is a max flight deflection, or the 30 degree max deflection limit is not correct.

As for auto-deploy of ground flaps, I don't believe the Citations are automatic. The pilot has to manually choose ground spoilers upon landing (which automatically also deploys speedbrakes) or manually choose speedbrakes only.
Boeing Flown: 701,702,703;717;720;721,722;731,732,733,734,735,737,738,739;741,742,743,744,747SP;752,753;762,763;772,773.

vikkyvik
Topic Author
Posts: 12111
Joined: Thu Jul 31, 2003 1:58 pm

RE: Flap Extension Question

Alright, I am not claiming to be an expert on the 777, and if I am wrong, someone please correct me. However, based on 3 things (Reply #3 by Goboeing, the following picture, and FS2002), it seems that the max flap deflection is indeed 30 degrees. Note that I am in no way citing FS2002 as an accurate portrayal of a flight deck or aircraft.

Open the image as large, as it's a bit hard to see in medium.

View Large View Medium

I don't really know what else to say. I just hope someone can answer my question.

Also, CitationJet, how does every other manufacturer measure their flap deflection? Especially in the case of slotted flaps, different parts could be at different angles. This is why I originally asked the question.

Thanks again.

~Vik
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".

RduBE90Pilot
Posts: 62
Joined: Wed Jun 02, 2004 9:18 am

RE: Flap Extension Question

Correct, On the CitationJet the crew must select ground flaps. Just one notch below the selection for landing flaps. Just a simple pull up on the handle and bring it down to the ground position.

Eric

QantasA332
Posts: 1473
Joined: Sat Dec 13, 2003 5:47 pm

RE: Flap Extension Question

The question of how exactly flap deflection is measured got me curious. I did a google search and found a page from NASA declaring that:

The Flap Deflection (df) = number of degrees (o) of flap rotation from fully retracted position to fully extended position.

I'm thinking that "rotation" is the key word, and that the deflection has to be considered as the flap rotating in a sense... Very interesting question!

Cheers,
QantasA332

N243NW
Posts: 1597
Joined: Thu Jul 24, 2003 4:29 am

RE: Flap Extension Question

Hi all-

I will wager a guess with this one. It appears that even though the trailing edge of the flap appears to be down 70-80 degrees, the first "panel" of the flap barely extends down at all, moving mostly aft instead. I can't remember whether the 777's have double- or triple-slotted flaps (I think it is the former), but perhaps the degree angle of the flap deployment is based on the whole flap (like an average angle) rather than the aftmost panel. Here's a diagram of various flap types, courtesy of HowStuffWorks.com:

I have made it easier to state my theory, as shown in the next photo:

As you can see, the flap as a whole isn't deployed to 80 degrees like the last panel. The angle formed by the red lines (professionally drawn by moi with MS Paint ) looks to be about 30 degrees. It's just a theory; anyone agree/disagree?

Cheers!
-N243NW
B-52s don't take off. They scare the ground away.

QantasA332
Posts: 1473
Joined: Sat Dec 13, 2003 5:47 pm

RE: Flap Extension Question

That theory ran through my mind as well, N243NW, in addition to measuring the angle-change between the effective AoAs of a plain and flapped wing...there must be some sort of definitive guide to this somewhere!

Cheers,
QantasA332

lehpron
Posts: 6846
Joined: Tue Jul 10, 2001 3:42 am

RE: Flap Extension Question

>> "As Slamclick stated, it doesn't seem logical to extend flaps more once on the ground." <<

Wouldn't doing so in addition to the speed brakes on top of the wing, act as a split-wing (as opposed to the space shuttle's split-rudder) to create lots of drag just after touchdown, to slow the plane in addition to wheel brakes?

Thereby extending flaps on the ground, just to slow down.
The meaning of life is curiosity; we were put on this planet to explore opportunities.

liamksa
Posts: 301
Joined: Mon Oct 29, 2001 1:13 pm

RE: Flap Extension Question

I think the answer here is that Boeing flap settings are not actually measured in degrees at all - it is just a reference to a flap position.

AAR90
Posts: 3140
Joined: Fri Jan 21, 2000 11:51 am

RE: Flap Extension Question

The 737 flaps (at least some models) go up to 40 degrees, but I've never seen them at such an angle.

Probably because the flap handle positions do not correspond to degrees of flaps extended. Quite simply, they are names (labels) for the flap handle positions only. The MD OpMans I recall seeing the flap handle positions corresponding to actual flap positions, but the Boeing OpMans all state the detents as Flap Handle Positions. i.e. B738 OpMan says:

"Moving the Flap Lever aft allows selection of flap detent positions 1, 2, 5, 10, 15, 25, 30, or 40."

"Flap positions 30 and 40 are normal landing flap positions. Flaps 15 is used for high density altitude landings."

Nowhere will you find Boeing stating the flap handle position corresponds to any specific degree of flap extention. During my B767/757 initial training (many many moons ago) this distinction (flap handle position did not necessary correspond to actual flap position) was emphasized early and often since AA was relatively new to B757s and Flaps-1 caused trailing edge flap extention on one bird, but not the other (I don't recall which was which anymore; 757 vs 767). Same for landing flap handle positions... they were simply "normal landing flap settings" and anything else would be a non-normal landing.

Hope that's not confusing the issue.
*NO CARRIER* -- A Naval Aviator's worst nightmare!

vikkyvik
Topic Author
Posts: 12111
Joined: Thu Jul 31, 2003 1:58 pm

RE: Flap Extension Question

CitationJet and Lehpron,
I didn't really think completely through the ground flap configuration before replying. I am somewhat surprised that this is necessary, but i suppose anything to get the airplane stopped.

AAR90 and Liamksa,
Thanks for the info; I believe that this clears up my original question. It is still interesting that Boeing chooses numbers which, to a certain extent, make sense when measured in degrees, whereas they actually do not represent degrees at all. Have you any idea why these numbers were chosen (i.e. are they proportional in some way to flap deployment)?

Thanks for all the replies!

~Vik
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".

QantasA332
Posts: 1473
Joined: Sat Dec 13, 2003 5:47 pm

RE: Flap Extension Question

Okay, so Boeing doesn't use a degree scale on flap deflection selectors. Flap deflection is still often given in degrees, however, and I'm still curious about how exactly that deflection angle is measured. Besides, some aircraft's flight-deck flap deflection selectors do use a degree scale...

Cheers,
QantasA332

oly720man
Posts: 5808
Joined: Fri May 21, 2004 7:13 am

RE: Flap Extension Question

The flap controls in cockpits are to make life easy for the pilot. They don't especially care what the deflection is, they just need to know that a flap in positions A and B are used for take off and positions C, D and E for approach and position F for touchdown/landing roll, or whatever.

The design of flaps is a very complicated business, aerodynamically and structurally. In some research it is felt that a slat/wing/flap configuration should be considered as 3 wings flying close together rather than just as a wing with bits hanging off the front and back. This is because moving the flap will affect what happens over the main wing and even the slat. All the elements can affect each other.

It is in the design stage of the aircraft that the various flap settings are decided upon so that it will be known in advance what angle is going to give what lift and drag and what speed will give what pitch angle.

http://ntrs.nasa.gov/index.cgi?method=display&redirect=http://techreports.larc.nasa.gov/ltrs/PDF/tm4583.pdf&oaiID=oai:ltrs.larc.nasa.gov:rdp4583.tex

As an example, the above NASA report details the investigations that are done on a generic high lift system for what looks vaguely like a C17/C141 with leading and trailing edge devices. Sorry folks it's more than 15Mb and 445 pages (!).... lots of graphs.

If you go here

http://ntrs.nasa.gov/

you can search for abstracts and in some cases there are PDFs you can download. Search for Flap, for example.

Similarly here

http://naca.larc.nasa.gov/

for reports up to the end of NACA and beginning of NASA for earlier work.

Andy
wheat and dairy can screw up your brain

citationjet
Posts: 2312
Joined: Sun Mar 09, 2003 2:26 am

RE: Flap Extension Question

I agree with Oly720man, flap and slat design are a design challenge. Getting the aerodynamics correct on slat design is particularly tough.
Also, flaps are one piece of structure that basically sees limit load each time they are used. Flaps are usually deflected near their max flap extension speeds in normal operation.
There is no other structure I can think of that routinely operates near its limit load. I know many people may think that the landing gear does, but very few landings are near the 10 ft/sec limit sink rate. I have seen data of measured commercial aircraft landing sink rates, and most are less than half the 10 ft/sec.
Boeing Flown: 701,702,703;717;720;721,722;731,732,733,734,735,737,738,739;741,742,743,744,747SP;752,753;762,763;772,773.

Rick767
Posts: 2613
Joined: Sun Jan 30, 2000 8:11 pm

RE: Flap Extension Question

Liamksa and AAR90 have it here, the readings on the flap gauge on Boeing aircraft do not represent the true flap angle, they are used purely to achieve commonality.

Take the 767, "Flap 1" only extends the leading edge slats - no actual flap. "Flap 30" is at a true angle of greater than 30 degrees.

Roll on Airbus and the straightforward flap "config" settings - far more sensible. Pilots don't actually need to know what the true flap angle is, nor do they care.
I used to love the smell of Jet-A in the morning...

SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Flap Extension Question

N243NW I think that is a good explanation of the flap angle thing.

The nominal flap settings used by Boeing may just be for pilot convenience. They are sort of intuitive. The settings just sound right for the desired configuration.

CitationJet thanks for the explanation on the landing flaps. I was operating with "conventional wisdom" dating back to the earliest days of my career which held that air would get bottled up" under the wings and form a ground cushion. I'd even heard of low-wing airplanes where pilots would retract the flaps immediately on landing to kill the lift and get weight on the wheels for braking. (A questionable personal techniqe for sure.)

I must say though, that in airline flight ops no one ever extends flaps at their maximum speed during an arrival. We wait until well down into the speed range. Flight training departments stress that flaps are fragile and and that they are not to be considered drag, but lift. As most of our planes can use flight spoilers with at least some flap, that is the usual mode.

Happiness is not seeing another trite Ste. Maarten photo all week long.

citationjet
Posts: 2312
Joined: Sun Mar 09, 2003 2:26 am

RE: Flap Extension Question

SLamclick,
From my experience, the large Caravan 208 operator (who shall remain nameless) apparently uses their flaps at relatively high speeds. Part of the reason for this may be because the Caravan does not have spoilers nor retractable gear.
Boeing Flown: 701,702,703;717;720;721,722;731,732,733,734,735,737,738,739;741,742,743,744,747SP;752,753;762,763;772,773.

vikkyvik
Topic Author
Posts: 12111
Joined: Thu Jul 31, 2003 1:58 pm

RE: Flap Extension Question

Hey all...alright, the matter seems to have been cleared up. Still seems weird to me that Boeing wouldn't just use flaps 1, 2, 3, 4, 5, etc. instead of flaps 1, 2, 5, 15, 25, etc., and I guess this is what led me to believe they were degree measures.

Thanks!

~Vik
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".

AAR90
Posts: 3140
Joined: Fri Jan 21, 2000 11:51 am

RE: Flap Extension Question

Have you any idea why these numbers were chosen

I believe they are relatively close to the flap settings used in earlier Boeing aircraft where the flap handle position was the actual flap degree position. A matter of simply rounding the position to nearest 5 degree point (for normal landing settings). MD80/90 I flew used "28 degree" and "40 degree" for normal landings, but also had "dial-a-flap" for takeoffs in addition to normal "11 degree" setting. The MD80/90 also has "UP/RET" [for Up & Retract] and "UP/EXT" [for Up & Extend] positions, so much more direct correlation to what's going on outside.
*NO CARRIER* -- A Naval Aviator's worst nightmare!

DeltaGuy
Posts: 3965
Joined: Wed Sep 12, 2001 5:25 am

RE: Flap Extension Question

I always wondered why MD did that, with the 1, 5,11, 15, 28, 40 flap settings...I've seen flaps out at 40, looks way more than even 45 degrees. There isn't anything but single slotted flaps on that aircraft, so it begs the question, where do they measure it from?

I always understood it as angle between the top edge of the flap compared to the trailing edge of the wing...as the angle of the bottom skin of the flap would be even more skewed....was never really sure though, it's probably completely wrong though

DeltaGuy
"The cockpit, what is it?" "It's the little room in the front of the plane where the pilot sits, but that's not importan

QantasA332
Posts: 1473
Joined: Sat Dec 13, 2003 5:47 pm

RE: Flap Extension Question

Thanks for the references and comments, Oly720man. I know all the stuff having to do with the aerodynamics and considerations/details regarding the fitting of flaps, but it was just the angle measurement that had me puzzled. I'm pretty sure now that it is indeed done as N243NW described...

Cheers,
QantasA332

air2gxs
Posts: 1443
Joined: Mon Jun 18, 2001 1:29 pm

RE: Flap Extension Question

Just looked in the B757 & B767 AMMs. There is no reference to degrees. The flap handle and indicator are graduated in units. Thus 30 units does not necessarily mean 30 degrees.

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