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Why Is 757 A "Heavy"?  
User currently offlineweb500sjc From United States of America, joined Sep 2009, 749 posts, RR: 0
Posted (4 years 9 months 2 weeks 5 days 2 hours ago) and read 6334 times:
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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?


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46 replies: All unread, showing first 25:
 
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 1, posted (4 years 9 months 2 weeks 5 days 1 hour ago) and read 6313 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.

Quoting web500sjc (Thread starter):
and do winglets soften the wake turbulence?

Yes.

Tom.


User currently offlineMir From United States of America, joined Jan 2004, 21803 posts, RR: 55
Reply 2, posted (4 years 9 months 2 weeks 5 days 1 hour ago) and read 6306 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



7 billion, one nation, imagination...it's a beautiful day
User currently offline747400sp From United States of America, joined Aug 2003, 3736 posts, RR: 2
Reply 3, posted (4 years 9 months 2 weeks 5 days 1 hour ago) and read 6298 times:

I think it mostly 757 200Es, and maybe 757 300s with the heavy call sign.

User currently offlineMir From United States of America, joined Jan 2004, 21803 posts, RR: 55
Reply 4, posted (4 years 9 months 2 weeks 4 days 18 hours ago) and read 6205 times:

Quoting 747400sp (Reply 3):
maybe 757 300s

All 757-300s are heavy. It's the 757-200 where some are and some aren't.

-Mir



7 billion, one nation, imagination...it's a beautiful day
User currently offlineweb500sjc From United States of America, joined Sep 2009, 749 posts, RR: 0
Reply 5, posted (4 years 9 months 2 weeks 4 days 15 hours ago) and read 6142 times:
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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?


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User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 6, posted (4 years 9 months 2 weeks 4 days 14 hours ago) and read 6129 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.

Tom.


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17118 posts, RR: 66
Reply 7, posted (4 years 9 months 2 weeks 4 days 8 hours ago) and read 5977 times:

Quoting web500sjc (Thread starter):
Why Is 757 A "Heavy"?

Have you ever tried to lift one?



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinekingFriday013 From United States of America, joined May 2007, 1304 posts, RR: 10
Reply 8, posted (4 years 9 months 2 weeks 4 days 1 hour ago) and read 5869 times:

Quoting Starlionblue (Reply 7):
Have you ever tried to lift one?

With that logic, a Dash 8 is heavy (at least for me!)  

-J.



Tho' I've belted you an' flayed you, By the livin' Gawd that made you, You're a better man than I am, Gunga Din!
User currently offlineFabo From Slovakia, joined Aug 2005, 1219 posts, RR: 1
Reply 9, posted (4 years 9 months 2 weeks 3 days 17 hours ago) and read 5798 times:

Quoting kingFriday013 (Reply 8):
With that logic, a Dash 8 is heavy (at least for me!)

Why stop at Dash 8, most single Cessnas are heavy  



The light at the end of tunnel turn out to be a lighted sing saying NO EXIT
User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 10, posted (4 years 9 months 2 weeks 3 days 16 hours ago) and read 5777 times:

Quoting Fabo (Reply 9):

Why stop at Dash 8, most single Cessnas are heavy

Hardly. A fully loaded C172 is barely heavier than a VW Beetle.


User currently offline2H4 From United States of America, joined Oct 2004, 8956 posts, RR: 60
Reply 11, posted (4 years 9 months 2 weeks 3 days 14 hours ago) and read 5698 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.


Intentionally Left Blank
User currently offlineSeaBosDca From United States of America, joined Sep 2007, 5768 posts, RR: 6
Reply 12, posted (4 years 9 months 2 weeks 3 days 13 hours ago) and read 5680 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.


User currently offlineCaryjack From United States of America, joined May 2007, 336 posts, RR: 0
Reply 13, posted (4 years 9 months 2 weeks 3 days 3 hours ago) and read 5540 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?

Thanks,  
Cary


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17118 posts, RR: 66
Reply 14, posted (4 years 9 months 2 weeks 3 days 2 hours ago) and read 5533 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.


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineKELPkid From United States of America, joined Nov 2005, 6428 posts, RR: 3
Reply 15, posted (4 years 9 months 2 weeks 3 days ago) and read 5499 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...).



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlinejgarrido From Guam, joined Mar 2007, 340 posts, RR: 0
Reply 16, posted (4 years 9 months 2 weeks 2 days 20 hours ago) and read 5467 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.


User currently offline2H4 From United States of America, joined Oct 2004, 8956 posts, RR: 60
Reply 17, posted (4 years 9 months 2 weeks 2 days 17 hours ago) and read 5417 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.  



Intentionally Left Blank
User currently offlineFabo From Slovakia, joined Aug 2005, 1219 posts, RR: 1
Reply 18, posted (4 years 9 months 2 weeks 2 days 6 hours ago) and read 5256 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  



The light at the end of tunnel turn out to be a lighted sing saying NO EXIT
User currently offlineIAHFLYR From United States of America, joined Jun 2005, 4790 posts, RR: 22
Reply 19, posted (4 years 9 months 2 weeks 1 day 20 hours ago) and read 5192 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.



Any views shared are strictly my own and do not a represent those of any former employer.
User currently offlineMir From United States of America, joined Jan 2004, 21803 posts, RR: 55
Reply 20, posted (4 years 9 months 2 weeks 1 day 18 hours ago) and read 5162 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
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17118 posts, RR: 66
Reply 21, posted (4 years 9 months 2 weeks 1 day 18 hours ago) and read 5159 times:

Quoting Mir (Reply 20):
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.

I stand corrected.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineSeaBosDca From United States of America, joined Sep 2007, 5768 posts, RR: 6
Reply 22, posted (4 years 9 months 2 weeks 1 day 15 hours ago) and read 5135 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.


User currently offlineIAHFLYR From United States of America, joined Jun 2005, 4790 posts, RR: 22
Reply 23, posted (4 years 9 months 2 weeks 1 day 8 hours ago) and read 5065 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.
User currently offlineXFSUgimpLB41X From United States of America, joined Aug 2000, 4224 posts, RR: 37
Reply 24, posted (4 years 9 months 2 weeks 11 hours ago) and read 4967 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.



Chicks dig winglets.
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 Post contains images 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 Post contains links 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 Post contains images 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 Post contains links and images HAWK21M : The Wake produced by a B757 can be quite serious. regds MEL.
43 Post contains links and images 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 Post contains images 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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