Zuluaviator994
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Krueger Flaps

Thu Apr 17, 2008 10:49 pm

Sorry, but i don't get the entire idea of Krueger flaps.
I know what they are...sorta.
But what is the real advantage to these and how are they different to normal slats?
Pictures would be appreciated
rgrds
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oly720man
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RE: Krueger Flaps

Thu Apr 17, 2008 11:35 pm

Pictures here.

http://www.desktopaero.com/appliedaero/airfoils2/highlift.html

http://www.hq.nasa.gov/pao/History/SP-468/ch10-5.htm

The main advantage is that they are simpler and lighter, but not as good aerodynamically. What they do is to change the shape of the leading edge of the wing (giving it a bigger radius) to reduce the adverse pressure gradient and high suction peak.
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Jetlagged
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RE: Krueger Flaps

Fri Apr 18, 2008 1:13 am

The main difference is no slot, which adds a lot to the effectiveness of a slat, allowing airflow to remain attached at greater angles of attack (slats work mainly by increasing the stall AOA, so more lift can be generated).

Krueger flaps work like a hinged leading edge flap rather than like a slat. An airflow separation bubble is formed behind the Kreuger flap by the angled section which unfolds as the flap extends, so although it looks as though it didn't ought to work the air flowing behind it behaves very much as if there is a complete lower surface there, reattaching further aft. Crude looking but effective. Basically a Krueger flap increases wing camber and, like a slat, increases the AOA at which the wing will stall.

Boeing combined the slat with the Krueger flap and came up with the variable camber flap, as used outboard on the 747 leading edge.


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jetmech
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RE: Krueger Flaps

Fri Apr 18, 2008 2:23 am



Quoting Jetlagged (Reply 2):
An airflow separation bubble is formed behind the Kreuger flap by the angled section which unfolds as the flap extends

Interesting  scratchchin . So the Krueger flap develops a laminar recirculation bubble over its flat surface which in turn "mimics" a generously rounded leading edge radius similar to that of the variable camber leading edge devices?

Regards, JetMech
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qslinger
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RE: Krueger Flaps

Fri Apr 18, 2008 4:18 am



Quoting JetMech (Reply 3):
Interesting . So the Krueger flap develops a laminar recirculation bubble over its flat surface which in turn "mimics" a generously rounded leading edge radius similar to that of the variable camber leading edge devices?

Regards, JetMech

Ouch....my head hurts!!
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113312
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RE: Krueger Flaps

Fri Apr 18, 2008 4:58 am

The more typical Krueger flap is seen inboard of the engines on B737-200/300 as well as on Boeing 707s and the inboard devices on the B727. The ones shown, for the B747, are a bit different as they are flexible and go from flat when stowed to curved when extended.
 
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jetmech
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RE: Krueger Flaps

Fri Apr 18, 2008 5:37 am



Quoting Qslinger (Reply 4):

Was it my grammar or the content which hurts  Smile ?

Quoting 113312 (Reply 5):

True, but the leading edge lift enhancement devices between the wing root and inboard engines of the 747 are also flat-panel kruegers.

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
SFOMB67
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RE: Krueger Flaps

Fri Apr 18, 2008 6:15 am

I only remember Boeing refering to the l/e devices, inbd of the pylons as krueger flaps, and the others as variable camber l/e flaps, on 747's.
Not as easy as originally perceived
 
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HAWK21M
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RE: Krueger Flaps

Fri Apr 18, 2008 9:57 am

On the B737s,The Kruger flaps are located Inboard of the Powerplants,with the Slats outboard.
The swinging outward mvmt & extending round nose are typical of this type.

regds
MEL
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OldAeroGuy
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RE: Krueger Flaps

Fri Apr 18, 2008 5:13 pm

Quoting Sfomb67 (Reply 7):
I only remember Boeing refering to the l/e devices, inbd of the pylons as krueger flaps, and the others as variable camber l/e flaps, on 747's.
At Boeing, the 747 outboard leading edge devices as refered to as VCK's for Variable Camber Kreugers.

In the deployed position, there is a slot between the Kreuger trailing edge and the wing leading edge.

[Edited 2008-04-18 10:15:00]
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twal1011727
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RE: Krueger Flaps

Tue Apr 22, 2008 7:08 pm

Another big reason Kruegers were on inboard sections of the wings is if by chance you were to stall,
the outboard sections (where the flight controls were located) would still have aileron control authority
Kruegers tended to have a much sharper and cleaner stall than the slats.

KD
 
soon7x7
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RE: Krueger Flaps

Tue Apr 22, 2008 8:52 pm

Just happened to have 747 Vaiable Camber Flap which by the way is composite in skin structure rienforced with aluminum extruded longerons and machined hinging assembly....Who ever designed this should be president!

The other is an example of all aluminum construction leading edge slat , typical to 727, 737, 757, 767 and 777.
This unit slides forward and down on a series of curved steel rails while the former(747) type is stowed under the leading edge of the wing and drops down and forward, while assuming it's cambered shape. The photo of it laying flat actually is in reverse position. If it were attached to the wing it would be inverted with all the (crap ) up inside the wing.
Big version: Width: 3912 Height: 2610 File size: 1463kb
Big version: Width: 3884 Height: 2591 File size: 1170kb
inverted, but stowed configuration...
Big version: Width: 3924 Height: 2618 File size: 1370kb
typical SLAT cross section...
 
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jetmech
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RE: Krueger Flaps

Wed Apr 23, 2008 1:10 am



Quoting Soon7x7 (Reply 11):

Nice! How did you happen to come into possession of that VC Krueger panel and mechanism  Smile ? Besides the cleverness of the linkage, which manages to camber the panel and flip the bull-nose, what used to amaze me about those panels was how stiff they were. Using both arms, my feet and the ground, I could only ever bend them a fraction of the distance they bend in service  weightlifter   faint  !

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
soon7x7
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RE: Krueger Flaps

Wed Apr 23, 2008 4:14 am



Quoting JetMech (Reply 12):

I love to collect Space Junk...yeh, your correct, it takes some sweat to configure that VC flap by hand...Boeing engineers were amazing when you consider no computers were used to figure this stuff out...You'd be amazed where you can find goodies like these...The VC component I purchased in AZ from Lee King. Boneyard2u...The slat I bought from a gent in California...Aviation Warehouse...But places all over the US exist and will sell as collectibles...gerard
 
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zeke
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RE: Krueger Flaps

Wed Apr 23, 2008 7:48 am



Quoting Jetlagged (Reply 2):
An airflow separation bubble is formed behind the Kreuger flap by the angled section which unfolds as the flap extends, so although it looks as though it didn't ought to work the air flowing behind it behaves very much as if there is a complete lower surface there, reattaching further aft. Crude looking but effective. Basically a Krueger flap increases wing camber and, like a slat, increases the AOA at which the wing will stall.

That is true of the simple Krueger like found on the inboard wing of the Boeing 707, the bull-nose Krueger (727) flow on the upper surface of the Krueger is attached over a wider angle-of-attack range, and normally they have more than one setting, takeoff and landing. The variable camber Krueger flap (747) improved the the airfoil shape of the Krueger dramatically and also improves the aerodynamic performance, however that came at a cost of complexity (complex 4-bar linkage, and lower bending stiffness of the fiberglass panel and only two stiffeners basically doubling the number of two span wise hinges). Variable camber Krueger flap were optimized in two positions for landing, they are not as effective for takeoff, they tried to add another optimum position for takeoff, it was considered too complex.
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OldAeroGuy
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RE: Krueger Flaps

Wed Apr 23, 2008 9:43 pm



Quoting Zeke (Reply 14):
Variable camber Krueger flap were optimized in two positions for landing, they are not as effective for takeoff, they tried to add another optimum position for takeoff, it was considered too complex.

And that's the reason they appear on the 747 but not the Boeing twins.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
OldAeroGuy
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RE: Krueger Flaps

Thu Apr 24, 2008 4:19 pm



Quoting Zeke (Reply 14):
Variable camber Krueger flap were optimized in two positions for landing

There is only one extended position for the 747 VCK's. It is the same for landing and takeoff.

While the VCK's are sometimes referred to as two position devices, the two positions are extended and retracted.

There maybe some confusion as the Flaps 1 detent does not extend all the 747 leading edge devices.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis

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