Western727
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727 LE Flap Design - Why So Unique?

Mon Nov 26, 2012 9:44 pm

Forgive me but I couldn't find this in a search on A.net. Got 3 questions about the unique 727 LE flaps:

1. Why were LE Kreuger flaps installed inboard and conventional LE slats outboard (same can be said for the 737)?
2. What's the purpose of the "fence" on the inboard-most LE slats?
3. Why did only two (on each wing) LE slats extend at the lowest flap setting, followed by all the rest on the next setting, versus all coming down at once like most other jetliners? The 32x, MD-80 and DC-10, for example, have LE slats that extend together, and at higher flap settings they extend even further, but still together.

Thanks in advance for any insight. As many of us know, the 727 was groundbreaking in its time, with its triple-slotted TE flaps designed to allow the 727 to operate from shorter runways...so surely the LE flap design, as diverse as it was, was designed with the same purpose in mind.
Jack @ AUS
 
boeingfixer
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RE: 727 LE Flap Design - Why So Unique?

Mon Nov 26, 2012 11:11 pm

Quoting Western727 (Thread starter):
1. Why were LE Kreuger flaps installed inboard and conventional LE slats outboard (same can be said for the 737)?

At the point where the slats and Kruger flaps meet the wing gets thicker and the leading edge actually has a higher sweep angle to the wing root. The Kruger flaps kept the weight down in this thicker area as compared to slats which would have been quite large in this area. It was also easier to deal with the interference of the Kruger flaps and slats due to the sweep angle change.

Quoting Western727 (Thread starter):
2. What's the purpose of the "fence" on the inboard-most LE slats?

You'll notice that the slat fence is located directly forward of the inboard aileron. I was told this is to help straighten the span wise flow to improve inboard aileron performance.

Quoting Western727 (Thread starter):
3. Why did only two (on each wing) LE slats extend at the lowest flap setting, followed by all the rest on the next setting, versus all coming down at once like most other jetliners? The 32x, MD-80 and DC-10, for example, have LE slats that extend together, and at higher flap settings they extend even further, but still together.

My take on this was due to simplicity of design. Each Kruger flap and slat actuator have only 2 positions... extended and retracted. Only slats 2,3,6 and 7 were extended at flaps 2 during approach to keep the trim changes acceptable while decelerating. The rest came out at flaps 5. The main difference between this method and what was designed for the B737 was the use of a 3 position slat actuator(retracted/extend/full extend) on that type. The 3 position slat actuator allowed all of the slats to extend and retract together but was heavier due to the actuator design and the extra hydraulic line for the extend position. I also found the setup on the B737 to be less reliable than the B727 system.

Cheers,

John
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Western727
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RE: 727 LE Flap Design - Why So Unique?

Tue Nov 27, 2012 2:21 am

Your detailed, sensible descriptions are much appreciated, John. Now I can sleep better!

At the same time, I must interject that the 727's wing was fun to watch from a pax's perspective, both LE for the "diverse" actions discussed above as well as the TE, due mostly to the fairly-visible TE flap jackscrews and the inboard ailerons you mentioned.
Jack @ AUS
 
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n901wa
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RE: 727 LE Flap Design - Why So Unique?

Tue Nov 27, 2012 3:56 am

I argree the 727 flap / slat was fun to watch as a Mech too. I remember doing walkarounds on the 727. What a Great Airplane. The only thing that use to scare me, was if you were changing the landing light in the kruger flap, I lowered the flaps, but I use to know guys that did that with hyd off, with the kruger flap drooped down and changed the light. If some one turned on the Hyd, that flap would close up quick.
 
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tb727
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RE: 727 LE Flap Design - Why So Unique?

Tue Nov 27, 2012 5:08 am

Quoting n901wa (Reply 3):
The only thing that use to scare me, was if you were changing the landing light in the kruger flap, I lowered the flaps, but I use to know guys that did that with hyd off, with the kruger flap drooped down and changed the light. If some one turned on the Hyd, that flap would close up quick.

That's the best way to do it other than powering down the airplane. I've b*tched out a couple FE's for slamming the Hydraulic Ground Interconnect switch for their preflight walk-around without clearing the airplane, i.e. banging on the nose for me to throw the switch as they watched to make sure the plane was all clear. Unbelievable what guys will do when they get lazy.


I have also heard that the split design in the leading edge devices were so that the root of the wing would stall first with them out due to the "rougher" design of the Kruger flaps instead of out near the outboard ailerons which would be bad.

I still think it's the coolest wing ever designed....and all on paper!

[Edited 2012-11-26 21:10:23]
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stratosphere
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RE: 727 LE Flap Design - Why So Unique?

Tue Nov 27, 2012 6:06 am

Quoting tb727 (Reply 4):
That's the best way to do it other than powering down the airplane. I've b*tched out a couple FE's for slamming the Hydraulic Ground Interconnect switch for their preflight walk-around without clearing the airplane, i.e. banging on the nose for me to throw the switch as they watched to make sure the plane was all clear. Unbelievable what guys will do when they get lazy.

Yep I saw an AA mechanic get caught in a Kruger after an FE hit the B pumps. He lived but just as much his fault as the FE's in my opinion. Safety is everyones responsibility.

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