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kc135topboom
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Do B-757 Winglets Reduce Seperation?

Sun Feb 04, 2007 11:58 pm

The original B-757 had the aircraft following seperation requirements increased to 5nm because of the large vortex coming off the wingtips. This effected the stability of aircraft following a B-757 on approach into an airport. It was also blamed for a few aircraft accidents.

But, now airlines like CO and AA (and others) are equipping their B-757s with winglets. As we all know, winglets reduce drag of the wingtips by reducing the size of the wingtip vortexs.

So, will the FAA/ICAO now place the B-757s equipped with winglets back to the 3nm for aircraft following catagory? The winglet equipped B-757s could be filed on their flight plan as a different type (IIRC the B-757 is currently filed as "B757/R"), like "B757/W".
 
Tom12
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RE: Do B-757 Winglets Reduce Seperation?

Mon Feb 05, 2007 2:27 am

It makes sense to reduce the spacing between them, i'd say.

Tom
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2H4
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RE: Do B-757 Winglets Reduce Seperation?

Mon Feb 05, 2007 2:40 am



If I'm not mistaken, the 757's wake is produced by the trailing edges of the flaps more so than the wingtips.

EDIT: Here's some interesting information found at NASA's site:

It was found that numerous interacting vortices were shed by the typical transport in the landing configuration. For example, in addition to the vortices expected at the wingtips, strong vortices were also shed at the edges of wing trailing-edge flaps, and aft fuselage.

As a result of these types of interactive vortex effects, some wingtip vortex control concepts that were known to provide beneficial effects for cruise drag (such as winglets) had little or no effect on the wake vortex hazard when the aircraft was in the flaps-down, landing approach configuration.

Ower flyby tests of the Boeing 757 and 767 had been conducted at the NOAA vortex facility in Idaho Falls, Idaho, during 1990. The NOAA results proved to be controversial because they showed, for a peculiar set of weather conditions that lasted about 0.5 hour, the vortex velocity of the 757 was approximately 50 percent higher than that of the 767 at similar vortex ages (younger than 60 sec) measured in less favorable weather conditions.

However, the results also showed that overall the wake of the 757 decayed faster than that of the 767; in fact, the wake behaved as would be expected for an aircraft of the size and weight of the 757.

However, the single unusual measurement was widely quoted as showing that the 757 should be treated as a heavy category aircraft like the Boeing 747 and 767.

Another factor cited as relevant to the 757 accidents was the approach speed of the aircraft (125 knots) is relatively slow, in part because of its relatively low wing sweep and large wing area. As a result, business jets (such as those involved in the accidents) approach at higher speeds with inadvertently close separation.



2H4




[Edited 2007-02-04 18:48:20]
Intentionally Left Blank
 
IAHFLYR
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RE: Do B-757 Winglets Reduce Seperation?

Mon Feb 05, 2007 3:04 am

No separation changes in the U.S. for winglets or non-winglets.

Should there be a change with winglets, then the FAA would have to redesignate the aircraft type for the B752 so the controllers know which is and which isn't a winglet....other than CO not sure if any other carriers have the entire fleet of their B752's finished.

Quoting KC135TopBoom (Thread starter):
B757/W

Good idea however anything with a "/" after the type is applied to the equipment onboard the airplane for navigation purposes and RVSM capable or not. It could become the B75W, only issue then would be not knowing if it was a 200 or 300....that could be solved simply however as the B753 shows up as a "H" in the flight plan signifying "heavy" separation required.
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kc135topboom
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RE: Do B-757 Winglets Reduce Seperation?

Mon Feb 05, 2007 6:03 am

Quoting 2H4 (Reply 2):
If I'm not mistaken, the 757's wake is produced by the trailing edges of the flaps more so than the wingtips.

EDIT: Here's some interesting information found at NASA's site:

It was found that numerous interacting vortices were shed by the typical transport in the landing configuration. For example, in addition to the vortices expected at the wingtips, strong vortices were also shed at the edges of wing trailing-edge flaps, and aft fuselage.

As a result of these types of interactive vortex effects, some wingtip vortex control concepts that were known to provide beneficial effects for cruise drag (such as winglets) had little or no effect on the wake vortex hazard when the aircraft was in the flaps-down, landing approach configuration

So, what is different in the B-757 flap configuerations and settings than most other aircraft?
 
3201
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RE: Do B-757 Winglets Reduce Seperation?

Mon Feb 05, 2007 11:28 am

Quoting KC135TopBoom (Thread starter):
As we all know, winglets reduce drag of the wingtips by reducing the size of the wingtip vortexs.

Do we really all know that? Isn't the weight, and therefore the lift, the same?

The winglets move the vorticity further from the rest of the wing, reducing induced drag, but there's still just as much total vorticity in the wake. In fact, the total vorticity goes up a little tiny bit, since the winglets add weight, so more lift is needed.
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TheJoe
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RE: Do B-757 Winglets Reduce Seperation?

Mon Feb 05, 2007 3:22 pm

Quoting 3201 (Reply 5):
The winglets move the vorticity further from the rest of the wing, reducing induced drag, but there's still just as much total vorticity in the wake.

I thought that they reduced spanwise flow on the wing, thus reducing the size of the vorticy following the aeroplane.
 
Mir
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RE: Do B-757 Winglets Reduce Seperation?

Mon Feb 05, 2007 3:28 pm

Quoting IAHFLYR (Reply 3):
Good idea however anything with a "/" after the type is applied to the equipment onboard the airplane for navigation purposes and RVSM capable or not. It could become the B75W, only issue then would be not knowing if it was a 200 or 300....that could be solved simply however as the B753 shows up as a "H" in the flight plan signifying "heavy" separation required.

If I'm not mistaken, the flight plan system makes no distinction between a 777-300 and a 777-300ER - they're both H/B773/Q (or whatever nav equipment they may have). And since the 757-300 is heavy anyways because of weight, it could just be B75W (large separation), B752 (heavy separation) or H/B753 (heavy separation).

That said, I don't think the winglets would decrease wake turbulence by any significant amount.

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zeke
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RE: Do B-757 Winglets Reduce Seperation?

Mon Feb 05, 2007 8:48 pm

Quoting KC135TopBoom (Thread starter):
As we all know, winglets reduce drag of the wingtips by reducing the size of the wingtip vortexs.

It may or may not reduce the core circulation level and may or may not increase the overall size of the vortex, the energy loss (drag) still is transferred onto the surrounding flow by some means.

How this effects trailing aircraft is unknown, flight testing would need to be performed. The size and strength of a vortex leaving an aircraft is essentially irrelevant, what is relevant is by what mechanism that vortex breaks down, and the magnitude of induced rolling moments it will impart on a trailing aircraft 3-6 nm behind.

Quoting KC135TopBoom (Reply 4):
So, what is different in the B-757 flap configuerations and settings than most other aircraft?

757/777/747/321 all have flaps design which are conducive to stronger core circulation from the inner trailing edge flap. They have a similar inner trailing flap design and similar vortex break down mechanisms.
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IAHFLYR
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RE: Do B-757 Winglets Reduce Seperation?

Mon Feb 05, 2007 10:59 pm

Quoting Mir (Reply 7):
And since the 757-300 is heavy anyways because of weight, it could just be B75W (large separation), B752 (heavy separation) or H/B753 (heavy separation).

Why do you want to confuse me???  Smile

The 300's get heavy wake turbulance separation....the B752's that are large get the extra mile on final, making it 4 NM. The H/B75W/Q would work I believe, but if it makes sense at all, those who put out the standards could start working on that little change for winglets now and it won't make the public and become operational for years, that is lightning speed for the FAA.
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kc135topboom
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RE: Do B-757 Winglets Reduce Seperation?

Mon Feb 05, 2007 11:28 pm

Quoting Zeke (Reply 8):
How this effects trailing aircraft is unknown, flight testing would need to be performed. The size and strength of a vortex leaving an aircraft is essentially irrelevant, what is relevant is by what mechanism that vortex breaks down, and the magnitude of induced rolling moments it will impart on a trailing aircraft 3-6 nm behind.

Yes, I agree.

Quoting Zeke (Reply 8):
757/777/747/321 all have flaps design which are conducive to stronger core circulation from the inner trailing edge flap. They have a similar inner trailing flap design and similar vortex break down mechanisms.

Now that, I did not know. For the A-32X series, is it only the A-321, or is it all of the A-32X series?
 
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zeke
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RE: Do B-757 Winglets Reduce Seperation?

Mon Feb 05, 2007 11:47 pm

Quoting KC135TopBoom (Reply 10):
For the A-32X series, is it only the A-321, or is it all of the A-32X series?

Just the 321, it has a larger vortex than a 320 due to the different flap design, still nothing like the 757, DC8, 707, VC10 etc.
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