Happy-flier
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Jets Without Leading-edge Devices

Sat Apr 21, 2012 8:18 pm

You'd think that any machine with fewer parts to maintain should also be cheaper to own. However, medium to large passenger jets without leading-edge flaps (of any design) are exceedingly rare.

Smaller jets, like the Fokker 100 or BAE-146 seem to manage just fine without leading-edge devices, though their degree of wing sweep appears to be less than that of, say, a 767.

Any chance that the deletion of leading-edge devices and their replacement with a longer or less-swept-back wing might be reintroduced into modern jet design as a means of reducing overall maintenance costs ... or are the maintenance / parts-replacement costs associated with the devices not so high as to warrant their deletion?
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Pihero
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RE: Jets Without Leading-edge Devices

Sat Apr 21, 2012 8:47 pm

Quoting happy-flier (Thread starter):
medium to large passenger jets without leading-edge flaps (of any design) are exceedingly rare.

Until the sixties, quite a few airliners weren't equipped with leading edge devices The DC-8, the TU 134, the Caravelle.
Some modern jets seem not to need them, like the Canadair CRJs 100 and 200, but not the 700 series, a much longer and heavier aircraft... And that's the main reason for leading-edge devices : increase the lift coefficient of a given wing, hence reducing approach and takeoff speeds.
For reasons of cruise drag, we are forced to keep a certain amount of wing sweep ( note that it's been drastically reduced since the first generation of jetliners ) and we need to optimize the low speed qualities of that wing : hence the slats.
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Mir
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RE: Jets Without Leading-edge Devices

Sat Apr 21, 2012 10:25 pm

Quoting Pihero (Reply 1):
Some modern jets seem not to need them, like the Canadair CRJs 100 and 200

The CRJs don't necessarily need them, but they really should have had them. Bombardier figured that out when they built the 700, which has better field performance despite being large and heavier, in large part due to having leading edge devices.

-Mir
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Viscount724
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RE: Jets Without Leading-edge Devices

Sun Apr 22, 2012 12:27 am

Quoting Pihero (Reply 1):
Quoting happy-flier (Thread starter):
medium to large passenger jets without leading-edge flaps (of any design) are exceedingly rare.

Until the sixties, quite a few airliners weren't equipped with leading edge devices The DC-8, the TU 134, the Caravelle.
Some modern jets seem not to need them, like the Canadair CRJs 100 and 200, but not the 700 series, a much longer and heavier aircraft.

Don't the DC-8's wing slots (not slats) count as leading edge devices? There are quite a few threads on the DC-8 slots. They weren't on the original DC-8-11 but were added to the -12 and all subsequent DC-8 models and were retrofitted to the early production -11s. Discussed in this thread with links to a couple of photos of the upper wing surface showng the slots in the closed position. I recall many DC-8 flights and seeing them open and close.
"Slots" On The DC-8 (by MASB747 May 17 2003 in Tech Ops)

Photo here showing the slot intakes in the open position on the bottom of the wing, just inboard of both engines.


View Large View Medium
Click here for bigger photo!

Photo © Marlo Plate - Iberian Spotters

 
kcrwflyer
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RE: Jets Without Leading-edge Devices

Sun Apr 22, 2012 12:35 am

Quoting Pihero (Reply 1):
Some modern jets seem not to need them, like the Canadair CRJs 100 and 200
Quoting Mir (Reply 2):
The CRJs don't necessarily need them, but they really should have had them. Bombardier figured that out when they built the 700, which has better field performance despite being large and heavier, in large part due to having leading edge devices.

The CR1/2 don't have them...but I think it's universally agreed that they do need them lol. I imagine they'd even make it a more fuel efficient jet.
 
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RE: Jets Without Leading-edge Devices

Sun Apr 22, 2012 1:31 am

Quoting kcrwflyer (Reply 4):
I imagine they'd even make it a more fuel efficient jet.

I don't think they would make the airplane any more efficient unless the addition of leading edge devices also changed the shape of the airfoil when not deployed. But I'd imagine Bombardier designed the CRJ100/200 wing to be nearly as efficient as possible, particularly in the cruise phase of flight.
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Mir
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RE: Jets Without Leading-edge Devices

Sun Apr 22, 2012 2:31 am

Quoting amccann (Reply 5):
But I'd imagine Bombardier designed the CRJ100/200 wing to be nearly as efficient as possible, particularly in the cruise phase of flight.

They designed that wing for the Challenger 600. It does fine for a plane of that size, but for the larger CRJ, it's not very good at generating lift as low speed, thus the relatively poor takeoff and landing performance.

-Mir
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Happy-flier
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RE: Jets Without Leading-edge Devices

Sun Apr 22, 2012 4:47 am

Also, aren't many of the CRJ100/200s operating without reverse thrust capability? I find that a bit odd, considering, as many have pointed out, that they don't have the leading-edge devices - which would suggest that their landing speeds are relatively higher.

Another jet I forgot to mention which is ancient but still relevant: the Comet. It had no leaing edge devices at all, though it did have pretty large trailing edge flaps. But its wing sweep was rather slight - so maybe it somehow managed to have okay field performance, all things considered. Just guessing...

[Edited 2012-04-21 21:47:41]
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kcrwflyer
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RE: Jets Without Leading-edge Devices

Sun Apr 22, 2012 6:37 am

Quoting happy-flier (Reply 7):
Also, aren't many of the CRJ100/200s operating without reverse thrust capability? I find that a bit odd, considering, as many have pointed out, that they don't have the leading-edge devices - which would suggest that their landing speeds are relatively higher.

never heard of that one. That's true of some ERJ 135/145.

Quoting amccann (Reply 5):
I don't think they would make the airplane any more efficient unless the addition of leading edge devices also changed the shape of the airfoil when not deployed. But I'd imagine Bombardier designed the CRJ100/200 wing to be nearly as efficient as possible, particularly in the cruise phase of flight.

I'm thinking from a takeoff perspective. Using my airport as an example. They've got 6800ft. to gun it to make 145 or so. With a leading edge they're probably looking at VR speeds in the 130's, meaning they could further derate thrust and still get airborne.

You're probably right about cruise.
 
Max Q
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RE: Jets Without Leading-edge Devices

Sun Apr 22, 2012 11:21 am

Another aspect of not having slats is, historically jets not equipped with them have been shown to be more prone to crashes because of icing contamination.


Those slats produce a huge amount of lift, making for, perhaps a more forgiving airfoil.
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Goldenshield
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RE: Jets Without Leading-edge Devices

Sun Apr 22, 2012 4:06 pm

Quoting happy-flier (Reply 7):
Also, aren't many of the CRJ100/200s operating without reverse thrust capability? I find that a bit odd, considering, as many have pointed out, that they don't have the leading-edge devices - which would suggest that their landing speeds are relatively higher.

None have TR's locked permanantly that I know of. As for landing speeds, the CRJ-900 is the same landing category, and it has slats (In essence, it's a CRJ-700 wing, with a bigger fuselage, thus more weight.)
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Jetlagged
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RE: Jets Without Leading-edge Devices

Sun Apr 22, 2012 4:50 pm

Quoting happy-flier (Reply 7):
Another jet I forgot to mention which is ancient but still relevant: the Comet. It had no leaing edge devices at all, though it did have pretty large trailing edge flaps. But its wing sweep was rather slight - so maybe it somehow managed to have okay field performance, all things considered. Just guessing...

The early Comet had a near symmetrical aerofoil and so was prone to over-rotation on takeoff. Adding LE devices would have helped that by increasing the stall AOA, but de Haviland reprofiled the wing leading edge instead to reduce the problem.

Unlike TE flaps, LE slats don't increase lift at a given AOA, they allow increased AOA before a stall occurs, and therefore increased maximum lift. If an aircraft can't rotate on the ground to an AOA where stall might occur adding slats will mainly increase drag.
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jetstar
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RE: Jets Without Leading-edge Devices

Sun Apr 22, 2012 11:33 pm

Some smaller bizjets like the Falcon 20 and the North American Saberliner had leading edge flaps.

Interestingly on the Sabreliner, there was no pilot’s control over deployment because there was no way to deploy them mechanically, they were only attached by rollers to the LE flap brackets and it was the airload on the wings that determined when they extended and retracted.

While I never flew the Sabreliner, I worked on them and I remember it was fairly easy to push them up the LE flap to the stowed position on the ground and then they would just roll back down when you let go of the LE flap.

These non controllable LE flaps was also used on the F-100 Super Sabre Jet, it has been said that the Sabreliner used the wing design of a F-100 Super Sabre Jet, and the tail section of an F-86 Sabre Jet, with a pressurized cabin and rear mounted engines.

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vikkyvik
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RE: Jets Without Leading-edge Devices

Mon Apr 23, 2012 3:16 am

Quoting Max Q (Reply 9):
Those slats produce a huge amount of lift, making for, perhaps a more forgiving airfoil.

Not to be picky, but slats don't exactly produce huge amounts of lift by themselves, like flaps do. They instead allow the wing to operate to higher angles-of-attack without stalling, which will give you more lift.
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Alias1024
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RE: Jets Without Leading-edge Devices

Mon Apr 23, 2012 3:36 am

Quoting kcrwflyer (Reply 8):

I'm thinking from a takeoff perspective. Using my airport as an example. They've got 6800ft. to gun it to make 145 or so. With a leading edge they're probably looking at VR speeds in the 130's, meaning they could further derate thrust and still get airborne.

Flaps 20 VR on the CRJ-200 is around the mid 130kt range at heavier weights. 145 kt would really only be seen as VR using flaps 8 takeoff performance, which is used most often at high density altitude airports with longer runways like DEN, ABQ, COS, SLC etc...

Even without leading edge devices the CRJ-200 does just fine the vast majority of the time from an obstacle clearance standpoint. Our limiting weight is almost always Maximum Landing Weight.
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Pihero
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RE: Jets Without Leading-edge Devices

Mon Apr 23, 2012 8:37 am

Quoting jetstar (Reply 12):
they were only attached by rollers to the LE flap brackets and it was the airload on the wings that determined when they extended and retracted.

That technology wasn't really new : the Fieseler Storch had it.
The most interesting installation of the automatic slats was on the MS Rallye, in all probability the safest light aircraft ever :
its high-lift devices comprise a Fowler flap (!!!) and these slats; In it, I started my aerobatics lessons and I still remember the fantastic sense of safety I felt.
Here are some spectacular pics of that little plane :
the MS Rallye
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Max Q
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RE: Jets Without Leading-edge Devices

Mon Apr 23, 2012 10:39 am

Lovely Aircraft Pihero,


Looks like a lot of fun.
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DashTrash
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RE: Jets Without Leading-edge Devices

Mon Apr 23, 2012 1:19 pm

Quoting jetstar (Reply 12):
While I never flew the Sabreliner, I worked on them and I remember it was fairly easy to push them up the LE flap to the stowed position on the ground and then they would just roll back down when you let go of the LE flap.

I flew a 40 and 60. Those slats took some serious abuse at low speeds. They extended below 170kts, but in the 160-180 range they could slam back and forth between extended / retracted wildly.

Part of the exterior walk around is pushing them into the retracted position and making sure they fall back into extended.

The Citation X has some small LE slats. They don't look like much but judging by the emergency checklist, they're worth 10 kts of Vref.
 
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Jetlagged
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RE: Jets Without Leading-edge Devices

Tue Apr 24, 2012 12:00 am

Quoting Pihero (Reply 15):
That technology wasn't really new : the Fieseler Storch had it.

It goes back even further than that. Handley-Page patented the automatic LE slat in 1919.
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Pihero
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RE: Jets Without Leading-edge Devices

Tue Apr 24, 2012 12:24 am

Quoting Jetlagged (Reply 18):
Handley-Page patented the automatic LE slat in 1919.

Didn't know that. More info and pics, please !

I only knew that ther most famous aircraft equipped with auto-slats was the Me 109, in many ways the most advanced fighter of its time.
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Jetlagged
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RE: Jets Without Leading-edge Devices

Wed Apr 25, 2012 4:47 pm

Quoting Pihero (Reply 19):
Didn't know that. More info and pics, please !

Here you go:

http://www.centennialofflight.gov/es...nology/High_Lift_Devices/Tech6.htm

Quoting Pihero (Reply 19):
I only knew that ther most famous aircraft equipped with auto-slats was the Me 109, in many ways the most advanced fighter of its time.

I think the Bf109 was probably the most significant user of the technology at the time, both in terms of numbers built and tactical advantage. A 109 pilot always had clear warning he was at or near stall so could pull g with confidence. It turned the otherwise heavily loaded 109 into a great dogfighter. I suspect Messershmitt had to pay H-P a licence fee to use the technology.
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Pihero
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RE: Jets Without Leading-edge Devices

Wed Apr 25, 2012 6:56 pm

Thanks !

Although the Spitfire was the sexiest fighter of WWII, in many ways I think the 109 was the most advanced and it's difficult to believe that these tiny wings would keep the plane aloft, let alone make it a good dogfighter, so good tha I read somewhere that in 1943 the relative score vs the Spit was some 5 to 1.

Back to our subject, on the 320, no slat means landing config 3 and add 25 kts to the Vref. (just think of the increased landing distance !)

[Edited 2012-04-25 12:32:33]
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OldAeroGuy
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RE: Jets Without Leading-edge Devices

Thu Apr 26, 2012 7:43 pm

You can add the DC-9-10 to the list of jet airliners with no leading edge device. (Big fences don't count)
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