web500sjc From United States of America, joined Sep 2009, 588 posts, RR: 0 Posted (3 years 3 months 4 days 13 hours ago) and read 5046 times:
I realize the topic of whether a 757 is a heavy has been talked to death.
What i would like to know what causes the 757 wake turbulence to be so strong that it is classified as a heavy, and do winglets soften the wake turbulence?
tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 81 Reply 1, posted (3 years 3 months 4 days 11 hours ago) and read 5025 times:
Quoting web500sjc (Thread starter): What i would like to know what causes the 757 wake turbulence to be so strong that it is classified as a heavy
The vortex (wake turbulence) strength is, roughly, a function of weight and span. More weight increases vortex strength, more span decreases it. The 757 happens to live in a realm where its combination of weight and span results in enough turbulence to meet the "heavy" classification. It's at the low end of heavy, obviously.
Mir From United States of America, joined Jan 2004, 19687 posts, RR: 56 Reply 2, posted (3 years 3 months 4 days 11 hours ago) and read 5017 times:
Quoting web500sjc (Thread starter): What i would like to know what causes the 757 wake turbulence to be so strong that it is classified as a heavy
A relatively short span in comparison to the size of the aircraft. That will make the vortices bigger.
And, just to make it clear, not all 757s are "heavy" - those with MTOWs under 255,000lbs are "large", with separation befitting a "heavy" given to aircraft following them.
-Mir
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tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 81 Reply 6, posted (3 years 3 months 4 days ago) and read 4841 times:
Quoting web500sjc (Reply 5): So if it is the small size of the wing that is the root of the problem, why does the 757 have good hot and high performance?
It's specifically small *span* relative to weight. Vortex strength doesn't care about wing area (much), just span. The 757 still has lots of wing area and thrust, which is where the good hot/high performance comes from.
kingFriday013 From United States of America, joined exactly 6 years ago today! , 1277 posts, RR: 11 Reply 8, posted (3 years 3 months 3 days 11 hours ago) and read 4581 times:
2H4 From United States of America, joined Oct 2004, 8950 posts, RR: 62 Reply 11, posted (3 years 3 months 3 days ago) and read 4410 times:
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Past discussions have shown how the 757s strong wake turbulence can be attributed more to its wing flap geometry than the general size and shape of the wing. Wake imaging photos revealed very strong vorticies being shed from the edges of the flaps. These vorticies were noticeably stronger than those shed from the wingtips.
SeaBosDca From United States of America, joined Sep 2007, 4277 posts, RR: 4 Reply 12, posted (3 years 3 months 2 days 23 hours ago) and read 4392 times:
The "heavy" classification starts at 255,000 lbs MTOW. The heaviest of several possible MTOW options for the 757-200 is 255,500 lbs. (The 757-300 tops out at 272,500 lbs.)
That said, you will hear "heavy" used inconsistently by 752 pilots.
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Caryjack From United States of America, joined May 2007, 265 posts, RR: 0 Reply 13, posted (3 years 3 months 2 days 13 hours ago) and read 4252 times:
Quoting tdscanuck (Reply 1): The vortex (wake turbulence) strength is, roughly, a function of weight and span. More weight increases vortex strength, more span decreases it.
I understand that wing tip vortices cause drag and are a target for design engineers. Innovations such as air dams and winglets limit air flow off the wing ends which increases air flow over the wings, thereby increasing lift, and reducing vortices and drag. Raked tips diminish the wing until an insignificant amount of airflow travels off the tip thereby minimizing the vortices. At least that's how I see it.
Quoting Mir (Reply 2): And, just to make it clear, not all 757s are "heavy" - those with MTOWs under 255,000lbs are "large", with separation befitting a "heavy" given to aircraft following them.
Thanks for the effort. So if the 757 is under 255,000 lbs and classified as "large", it’s just best to give a separation as if the 757 were a "heavy", right?
And while you're at it, we’re dealing with three classifications, "large", "heavy" and "super" for commercial traffic, right? Are the big, twin turboprops considered "large"?
Quoting SeaBosDca (Reply 12): That said, you will hear "heavy" used inconsistently by 752 pilots.
Who calls it, the pilots or ATC? Once called, does this set seperations?
Quoting 2H4 (Reply 11): Past discussions have shown how the 757s strong wake turbulence can be attributed more to its wing flap geometry than the general size and shape of the wing.
This is my understanding. I would guess that flap tip vortices are tolerated because they only show up during takeoffs and landings so there are no efficiencies to be gained by eliminating them.
Quoting 2H4 (Reply 11): Wake imaging photos revealed very strong vortices being shed from the edges of the flaps. These vortices were noticeably stronger than those shed from the wingtips.
These noticeably stronger vortices are only an issue during takeoff and landings, right?
Starlionblue From Hong Kong, joined Feb 2004, 15867 posts, RR: 66 Reply 14, posted (3 years 3 months 2 days 12 hours ago) and read 4244 times:
As I understand it, ATC isn't this blunt anyway. They don't just lump heavies into one category and "diets" into the other. Different planes get different separation, even within "heavy" and such.
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KELPkid From United States of America, joined Nov 2005, 5929 posts, RR: 4 Reply 15, posted (3 years 3 months 2 days 10 hours ago) and read 4211 times:
Quoting Fabo (Reply 9): Why stop at Dash 8, most single Cessnas are heavy
You have an interesting definition of the word, then A 152 or 172 can be easily moved around the ramp by hand by a single human being (and I used to do that for a living). I wouldn't want to lift one, though, but you can easily manipulate their position on the ground using towbars, the prop, wing struts, and even pushing the tail down (word to the wise-don't try pushing the tail down unless you know what you are doing. You can damage the plane easily if you don't).
The 182 is a little harder to move around the ramp in this manner, the 206 even worse, and the 210 is pretty darned hard for one person to move (if you are going to move a 210 for a significant distance, I would recommend the use of a ramp vehicle with an appropriate towbar...).
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jgarrido From Guam, joined Mar 2007, 335 posts, RR: 0 Reply 16, posted (3 years 3 months 2 days 6 hours ago) and read 4179 times:
Quoting Caryjack (Reply 13): Thanks for the effort. So if the 757 is under 255,000 lbs and classified as "large", it’s just best to give a separation as if the 757 were a "heavy", right?
It's not just a good idea. There are specific separation requirements for those 757-200's MTOW is under 255k lbs.
Quoting Starlionblue (Reply 14): As I understand it, ATC isn't this blunt anyway. They don't just lump heavies into one category and "diets" into the other. Different planes get different separation, even within "heavy" and such.
Separation on final is based on weight class (small, large, heavy, super), the non-255k MTOW 752 is the only aircraft which has special separation rules.
2H4 From United States of America, joined Oct 2004, 8950 posts, RR: 62 Reply 17, posted (3 years 3 months 2 days 3 hours ago) and read 4129 times:
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Quoting Caryjack (Reply 13): These noticeably stronger vortices are only an issue during takeoff and landings, right?
My understanding is that they are an issue whenever the flaps are lowered.
Quoting KELPkid (Reply 15): The 182 is a little harder to move around the ramp in this manner, the 206 even worse, and the 210 is pretty darned hard for one person to move
This time of year, getting them stopped is the larger concern.
Fabo From Slovakia, joined Aug 2005, 1111 posts, RR: 1 Reply 18, posted (3 years 3 months 1 day 16 hours ago) and read 3968 times:
Quoting KELPkid (Reply 15): A 152 or 172 can be easily moved around the ramp by hand by a single human being (and I used to do that for a living). I wouldn't want to lift one, though
Yes I know it is a pretty easty plane to move around, but talk was about lifting
About sitting on the tail thing - been there, done that. It is amazing how many planes can people on Kladno airfield fit into their little hanger
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IAHFLYR From United States of America, joined Jun 2005, 4717 posts, RR: 26 Reply 19, posted (3 years 3 months 1 day 6 hours ago) and read 3904 times:
Quoting Mir (Reply 4): All 757-300s are heavy. It's the 757-200 where some are and some aren't.
Quoting Mir (Reply 2): those with MTOWs under 255,000lbs are "large", with separation befitting a "heavy" given to aircraft following them.
All the above is correct. Tis the MTOW that classifies the aircraft category, not the wake turbulence a particular aircraft may or may not leave behind. I've heard the B738's leave a pretty nasty wake and they are not even close to a MTOW in the 200,000 lbs area.
Quoting SeaBosDca (Reply 12): you will hear "heavy" used inconsistently by 752 pilots.
That is very interesting since I very rarely hear (and I hear quite a few) a crew of a B752 mistakenly use "Heavy" in their call sign.....even with operators that have both the 200 and 300 in their fleets.
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Mir From United States of America, joined Jan 2004, 19687 posts, RR: 56 Reply 20, posted (3 years 3 months 1 day 4 hours ago) and read 3874 times:
Quoting FLY2HMO (Reply 10): A fully loaded C172 is barely heavier than a VW Beetle.
Still, have you tried to lift one?
Quoting Starlionblue (Reply 14): Different planes get different separation, even within "heavy" and such.
Not as I learned it. There is no requirement to give a 747 any more separation than a 777.
Quoting Caryjack (Reply 13): So if the 757 is under 255,000 lbs and classified as "large", it’s just best to give a separation as if the 757 were a "heavy", right?
Not if it is the trailing aircraft. Remember that not only is wake turbulence about how bad the wake of an aircraft is, it's also about how easily that aircraft can be affected by the wake of other aircraft. If you've got a heavy following another heavy, the minimum separation is 4 miles. If it's a large following a heavy, the minimum separation is 5 miles, because it's assumed that a smaller airplane will have a worse reaction should it encounter the wake generated by the heavy. And since a 757 is technically a large, you need to give it 5 miles instead of 4. And before you ask, a 757 following another 757 needs 4 miles.
To explain it better:
- Heavy behind a heavy: 4 miles
- Small or large behind a heavy: 5 miles
- Large or heavy behind a 757: 4 miles
- Small behind a 757: 5 miles
EDIT: I should add that there are further separations given to small aircraft when following a non-small aircraft on final approach:
- Small behind large: 4 miles
- Small behind 757: 5 miles
- Small behind heavy: 6 miles
Note that the term "757" means a 757 that is not over 255k. If it were over 255k, it would be a "heavy", and treated as such.
Confused yet?
-Mir
[Edited 2010-02-17 06:20:41]
7 billion, one nation, imagination...it's a beautiful day
SeaBosDca From United States of America, joined Sep 2007, 4277 posts, RR: 4 Reply 22, posted (3 years 3 months 1 day 1 hour ago) and read 3847 times:
Quoting IAHFLYR (Reply 19): That is very interesting since I very rarely hear (and I hear quite a few) a crew of a B752 mistakenly use "Heavy" in their call sign.....even with operators that have both the 200 and 300 in their fleets
I'm more thinking of the other way around... crew of 255,500 lb. 752s, like all of the ones in the CO fleet and Delta's 75Es, failing to use "heavy" sometimes. Given the special procedures for non-heavy 757s I'd imagine this makes little difference.
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IAHFLYR From United States of America, joined Jun 2005, 4717 posts, RR: 26 Reply 23, posted (3 years 3 months 18 hours ago) and read 3777 times:
Quoting SeaBosDca (Reply 22): I'm more thinking of the other way around... crew of 255,500 lb. 752s, like all of the ones in the CO fleet and Delta's 75Es, failing to use "heavy" sometimes. Given the special procedures for non-heavy 757s I'd imagine this makes little difference.
Well I don't hear that mistake much at all either. Almost without fail the crew uses the correct "Heavy" or not for the aircraft they are flying.
Any views shared are strictly my own and do not a represent those of any former employer.
XFSUgimpLB41X From United States of America, joined Aug 2000, 3952 posts, RR: 36 Reply 24, posted (3 years 2 months 4 weeks 1 day 22 hours ago) and read 3679 times:
Quoting SeaBosDca (Reply 22): I'm more thinking of the other way around... crew of 255,500 lb. 752s, like all of the ones in the CO fleet and Delta's 75Es, failing to use "heavy" sometimes. Given the special procedures for non-heavy 757s I'd imagine this makes little difference.
No one at Delta in a 752 is failing to use heavy. No Delta "75E's" are certified for above 255,000 pounds, therefore they do not use "heavy." Same with the "75A."
The only Delta 757's that would use "heavy" are the 757-300s.
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25 web500sjc: at SNA as far as I know every time there is a 757 its always "XXX YYY heavy, cleared to land runway 19R". but then again that is the only thing close
26 XFSUgimpLB41X: That's not correct. Only if the aircraft is certified as a heavy will you hear it. It's not a term that is applied to something that is relatively he
27 IAHFLYR: I've never known any operator of a B753 to be used at SNA! So what are you actually hearing on the radio???
28 Max777geek: Mir can lift some. You guys make my forum, yuk very proud to be heavy. Are the wake turbolence so different from a 757 which weights 254.500 lbs and
29 XFSUgimpLB41X: "heavy" is not used off of actual weight. It is only based on certified max takeoff weight. Certified to 255,000 pounds or less? Not a heavy. Certifi
30 seabosdca: I've read in multiple places that the Delta 75Es are certified to 255,500. Is this incorrect?
31 XFSUgimpLB41X: That is incorrect. 256,000 max taxi weight. 255,000 max takeoff. Not a heavy!
32 Max777geek: tought that wasn't about weight but to inform followers of possible close turbolence ingenerated by the wings. So I was wondering why such a specific
33 tdscanuck: It is. The turbulence generated is related to the weight, and you need some way to distinguish the light variants from the heavy ones. You need to dr
34 web500sjc: People say xxx yyy heavy to land/ ready for take off and they are not fedex or ups, and considering those are the only widebodies at SNA I assume the
35 bond007: Well, perhaps you just tell us what they were! Then we won't be guessing and questioning, right? Jimbo
36 ednovak: This just in...as of April 8, the B757 is no longer considered a heavy by the FAA, regardless of weight or model. See FAA Notice JO 7110.520.
37 IAHFLYR: Yeah I learned of that about a month back, but till it came out in the press I was not sure if true or not. Can't wait to find the NOTICE and see how
38 jgarrido: The faa simplifying things? I don't believe it!!! http://www.faa.gov/regulations_polic...ment.information/documentID/215069
39 seabosdca: Kind of surprised they included the heavier 757-300 in the decision. To summarize, all 757 regardless of MTOW or model are now "large" when following
40 avioniker: History, kids: The 57 fleet got the heavy designation put on them after a number of incidents involving wake turbulence at extended distances relative
41 IAHFLYR: Please expand on your statements, I may require special handling on this. The decision you refer to call 757's heavy until a better fix was put in pl
42 HAWK21M: The Wake produced by a B757 can be quite serious. regds MEL.
43 Caryjack: Thanks. I had thought of trailing and following but I after going in a few circles I thought of something else. According to JO 7117.52 as posted by
44 jgarrido: To be clear notice 7110.520 does not go into effect until April. So in an official sense it has no merit yet. This is all semantics, but because of t
45 Caryjack: Just curious, where does "super" show up? I haven't notice that classification in the FAA documents plastered about. Fine, but what happens when it d
46 jgarrido: Super is another weight class, not an exception like the 757. It just so happens that there is only one type of A/C in that weight class. I don't kno
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So if the 757 is under 255,000 lbs and classified as "large", it’s just best to give a separation as if the 757 were a "heavy", right? 
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