skywatch
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What Makes An Aircraft "Heavy"?

Tue Mar 08, 2005 11:42 am

I have heard some educated guesses, but have never had a sure answer about what makes an aircraft a Heavy? Is it weight, fluid displacement, ect....
If it is weight, is it based on empty weight or total payload weight? If it is based on payload weight, can an aircraft take off of the runway as a heavy
and land without the heavy status because of burned fuel?

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KYIPpilot
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RE: What Makes An Aircraft "Heavy"?

Tue Mar 08, 2005 11:55 am

It is considered heavy if its max gross weight is 255,000 thousand lbs or greater.

It can still be called heavy even if it isn't at that weight for the actual flight. It goes by max certified weight, not weight per flight.

757's fall under "heavies", as well as all widebodies.

[Edited 2005-03-08 03:56:16]
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skywatch
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RE: What Makes An Aircraft "Heavy"?

Tue Mar 08, 2005 12:12 pm

I have not heard 757's refered to as heavies. Are you sure? Also, is a DC-8 a heavy?
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2H4
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RE: What Makes An Aircraft "Heavy"?

Tue Mar 08, 2005 12:17 pm

Quoting Skywatch (reply 2):
I have not heard 757's refered to as heavies. Are you sure? Also, is a DC-8 a heavy?


The 757-300 exceeds 255,000 lbs max gross weight, as do DC-8's.


2H4


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Klaus
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RE: What Makes An Aircraft "Heavy"?

Tue Mar 08, 2005 12:20 pm

Skywatch: I have not heard 757's refered to as heavies. Are you sure? Also, is a DC-8 a heavy?


It was discovered that the 757 produces much stronger wake turbulence than other narrowbody aircraft, so it enforces separation distances comparable to "heavy" widebodies. It´s a special exemption primarily due to aerodynamic effects, not actual weight.
 
2H4
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RE: What Makes An Aircraft "Heavy"?

Tue Mar 08, 2005 12:28 pm

Klaus,

Think the upcoming winglets on 757's will alleviate that wake turbulence, or is it mainly a result of the trailing edge flap configuration?


2H4


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Klaus
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RE: What Makes An Aircraft "Heavy"?

Tue Mar 08, 2005 12:34 pm

2H4: Think the upcoming winglets on 757's will alleviate that wake turbulence, or is it mainly a result of the trailing edge flap configuration?

I can´t say for sure, but I seem to remember reading that it was due to the general wing/flap design.
 
N766UA
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RE: What Makes An Aircraft "Heavy"?

Tue Mar 08, 2005 1:00 pm

We need to have a FAQ section for this particular question... Big grin

Anything over 255,000 lbs MGTOW. ATA flies the only heavy 752s.
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QantasA332
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RE: What Makes An Aircraft "Heavy"?

Tue Mar 08, 2005 2:51 pm

Quoting 2H4 (reply 5):
Think the upcoming winglets on 757's will alleviate that wake turbulence, or is it mainly a result of the trailing edge flap configuration?


Keep in mind that a large portion of winglet operation is the production of thrust through a forward vectoring of the resultant freestream-vortex flow at the wingtips, an effect which doesn't relate directly to wake turbulence strength at all. The reduction of vortex strength is the other (sometimes smaller) part of winglet operation, which does affect wake strength, but it is probably not major enough to significantly reduce the 757's wake turbulence strength. Having said that, the main source of the 757's disproportionately strong wake is indeed its general wing-flap geometry (as Klaus correctly stated), anyway, so with that in mind winglets would have an even smaller overall effect on the wake strength.

Whether the 757's wake really is so grossly out of proportion to its size and weight is another much-debated question...

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RE: What Makes An Aircraft "Heavy"?

Tue Mar 08, 2005 4:18 pm

I have heard in this forum that UA also has or had some 752's that qualify as heavies over 255,000 lbs, in addition to ATA. I agree with Qantas332 that winglets won't reduce the 752's wake that much. I have read winglets help reduce it, but by minimal amounts.

Quoting QantasA332 (reply 8):
Whether the 757's wake really is so grossly out of proportion to its size and weight is another much-debated question...


In 1993 a 757 caused a private jet to crash with the founder of In N Out on board during final to SNA, killing all on board. Separation was a key factor, but so was the 752's wake.
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Starlionblue
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RE: What Makes An Aircraft "Heavy"?

Tue Mar 08, 2005 5:25 pm

What Makes An Aircraft "Heavy"?

Gravity Big grin
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skywatch
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RE: What Makes An Aircraft "Heavy"?

Tue Mar 08, 2005 10:00 pm

Does the aircraft's payload weight increase wake turbulence, or is that solely caused by the size of the aircraft and the shape of it?
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HAWK21M
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RE: What Makes An Aircraft "Heavy"?

Tue Mar 08, 2005 10:10 pm

What are the Heavy's around presently.
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Starlionblue
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RE: What Makes An Aircraft "Heavy"?

Tue Mar 08, 2005 11:10 pm

Does the aircraft's payload weight increase wake turbulence, or is that solely caused by the size of the aircraft and the shape of it?

One follows the other. While the shape, size and speed are the only direct effects on the strength of the wake, a heavier plane will have larger surfaces=more wake.

What are the Heavy's around presently.

Limiting myself to A and B currently in common use:
747
757-300
767
777
330
340
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dw747400
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RE: What Makes An Aircraft "Heavy"?

Tue Mar 08, 2005 11:18 pm

To add to Starlion's list,

Frequently spotted heavies (around here) can include:
A300
A310
DC-8 (normally only F's these days)
DC-10
MD-11

There are also several Russian airliners that are heavies which visit the US East Coast.
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Starlionblue
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RE: What Makes An Aircraft "Heavy"?

Tue Mar 08, 2005 11:27 pm

Oops, forgot the 300/310.

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geedo
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RE: What Makes An Aircraft "Heavy"?

Wed Mar 09, 2005 9:19 am

I often hear Paul Allen's ride flying out of PDX. The radio operator always calls themselves "7 alpha fox heavy". Its a 757.

Don't forget about the 707/KC-135

[Edited 2005-03-09 01:23:53]

[Edited 2005-03-09 01:28:36]
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Newark777
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RE: What Makes An Aircraft "Heavy"?

Wed Mar 09, 2005 9:34 am

Quoting Skywatch (Reply 11):
Does the aircraft's payload weight increase wake turbulence, or is that solely caused by the size of the aircraft and the shape of it?


EDIT: Mis-read question, sorry.  Embarrassment

Harry

[Edited 2005-03-09 01:35:01]
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Thenoflyzone
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RE: What Makes An Aircraft "Heavy"?

Thu Mar 10, 2005 6:16 am

The B752 is considered a heavy when IN FRONT of another airliner, and a medium plane when BEHIND another airliner.

Therefore, you need 5 nautical miles separation when a 752 is following a heavy, but you need 4 nautical miles separation when the heavy is following the 752!

AK
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skywatch
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RE: What Makes An Aircraft "Heavy"?

Thu Mar 10, 2005 1:25 pm

I will ask yet again: Does the payload weight increase wake turbulence? Likewise, can, for example, 747A be full of pax, and 747B empty, and they still generate the same amount of wake turbulence?
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2H4
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RE: What Makes An Aircraft "Heavy"?

Thu Mar 10, 2005 1:41 pm



Quoting Skywatch (Reply 19):
I will ask yet again: Does the payload weight increase wake turbulence? Likewise, can, for example, 747A be full of pax, and 747B empty, and they still generate the same amount of wake turbulence?

No. The heavier an aircraft is, the more lift it has to produce to remain airborne. The more lift it produces, the stronger the wingtip vorticies become. Stronger wingtip vorticies create stronger wake turbulence.

The only part I'm not totally clear on is how the trailing-edge flap design contributes to the wake turbulence. Perhaps someone more knowledgeable than myself can explain things further.


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sprout5199
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RE: What Makes An Aircraft "Heavy"?

Thu Mar 10, 2005 2:19 pm



Quoting Starlionblue (Reply 10):
What Makes An Aircraft "Heavy"?

Gravity

I thought it was us fat Americians  stirthepot 

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skywatch
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RE: What Makes An Aircraft "Heavy"?

Fri Mar 11, 2005 1:31 am

2H4: Flaps generate wake turbulence by a process called the Bernoulli Principle. This can be defined as "the sideward pressure exerted by a moving fluid decreases as the fluid's velocity increases." This is the reason for the airfoil design on wings. The reason this produces lift is because the air traveling over the top of the wing has to travel faster than the air on the bottom of the wing to meet up with the air from the bottom side of the wing. If you add flaps to this, you can imagine how this would upset this process. Lots of miniature vortices resembling whirlpools are formed, causing the extra wake. And, the faster it is going, with the given degrees of flaps, the more wake turbulence there will be.
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skywatch
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RE: What Makes An Aircraft "Heavy"?

Fri Mar 11, 2005 1:12 pm

Wait a minute everyone! I looked up some stats on the 757 and 767, and their gross empty weights are below 255,000 lbs by a long shot! So what is the real weight criteria for a heavy? It can't be 255,000lbs! Or does that MGTOW mean something that I don't know about?

[Edited 2005-03-11 05:13:41]
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Newark777
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RE: What Makes An Aircraft "Heavy"?

Fri Mar 11, 2005 1:26 pm

Quoting Skywatch (Reply 23):
Wait a minute everyone! I looked up some stats on the 757 and 767, and their gross empty weights are below 255,000 lbs by a long shot! So what is the real weight criteria for a heavy? It can't be 255,000lbs! Or does that MGTOW mean something that I don't know about?

I'm pretty sure MGTOW stands for Maximum Gross Take Off Weight, which is quite different than empty weight.

Harry
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OPNLguy
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RE: What Makes An Aircraft "Heavy"?

Fri Mar 11, 2005 1:45 pm

In the begining, a "heavy" was defined as any aircraft that was capable of a max gross takeoff weight MGTOW) of 300,000 lbs. or more, irrespective of whether the aircraft was actually loaded up to that weight. It was based upon what MGTOW the aircraft was -capable- of.

Later, the threshold was changed from 300,000 lbs. to 255,000 lbs.

In a nutshell,

-There are some 757-200s that have MGTOWs -below- 255,000 and are NOT considered "heavy" (officially).

-There are some 757-200s that have MGTOWs -above- 255,000 and ARE considered heavies.

-There is no way to tell (by looking) which 757-200 is <255,000 and which is >255,000. Some airlines may have some of each in their fleets.

-The 757-300 is definitely >255,000 and IS considered a heavy.

-For wake turbulence separation purposes, ATC treats ALL models of the 757 as heavies, whether they technically are or not. In FAA training manuals, they refer to "heavy aircraft/757" and the "757" in that statement refers to the <255,000 757-200s which are not tecnically heavies, but must still be treated as one.

-Occasionally, it's possible that a controller or crew might slip and inadvertently refer to a <255,000 757-200 as a "heavy" even though it technically isn't one. Anyone hearing this on a scanner (or UAL's channel 9) might then get the erroneous idea that a particular aircraft is a heavy when it might not be.
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bri2k1
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RE: What Makes An Aircraft "Heavy"?

Fri Mar 11, 2005 1:54 pm

Please do a thorough search of this forum before posting anything like "the air has to travel faster to meet up with the air on the bottom." Air is not afraid of being lonely, and does nothing to meet other air in public places.
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skywatch
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RE: What Makes An Aircraft "Heavy"?

Fri Mar 11, 2005 2:08 pm

Would some 752's have greater takeoff capacities than other 752's because of different engine manufacturers?
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OPNLguy
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RE: What Makes An Aircraft "Heavy"?

Fri Mar 11, 2005 3:07 pm

>>>Would some 752's have greater takeoff capacities than other 752's because of different engine manufacturers?

Can't say, as I'm not familar with those, but I guess it's possible.

Airlines can order different weight ratings/limits on the same aircraft type. For example, the old 737-200 ADV was available with MTOGWs of 115,000, 117,500, 119,500, and 124,500, and I think the corresponding engines were the JT8D-9, the -15, the -17, and the -17R. Some 737-300s are maxed at 130,000, and some are maxed at 135,000. It's all what one is willing to pay Boeing for...  Wink
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Starlionblue
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RE: What Makes An Aircraft "Heavy"?

Fri Mar 11, 2005 4:54 pm

Quoting Skywatch (Reply 23):
The reason this produces lift is because the air traveling over the top of the wing has to travel faster than the air on the bottom of the wing to meet up with the air from the bottom side of the wing

As Bri2k1 says, this explanation for lift is flawed. Try this instead (keep reading a few pages on): http://travel.howstuffworks.com/airplane3.htm
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CRJ200Mechanic
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RE: What Makes An Aircraft "Heavy"?

Fri Mar 11, 2005 6:03 pm

Okay that article just threw everything I learned in school out the window.
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skywatch
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RE: What Makes An Aircraft "Heavy"?

Fri Mar 11, 2005 11:38 pm

What the article said is basically what I had in mind, but I did not want to type that much! Wink Thanks for keeping me in check.
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sprout5199
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RE: What Makes An Aircraft "Heavy"?

Sat Mar 12, 2005 8:09 am

Quoting CRJ200Mechanic (Reply 30):
Okay that article just threw everything I learned in school out the window.

Same here. I guess its just PFM. (pure F$%king magic)

Dan in Jupiter
 
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Starlionblue
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RE: What Makes An Aircraft "Heavy"?

Sun Mar 13, 2005 12:08 am

Quoting Skywatch (Reply 27):
Would some 752's have greater takeoff capacities than other 752's because of different engine manufacturers?

Yes, for example AAs RB211 powered 752s have higher MTOW than the Pratt powered ones.

Quoting CRJ200Mechanic (Reply 30):
Okay that article just threw everything I learned in school out the window.

Isn't life fun Big grin
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bri2k1
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RE: What Makes An Aircraft "Heavy"?

Sun Mar 13, 2005 12:29 am

It IS fun.

Flying requires faith, because you certainly can't "see" lift - just it's effects.

Humans don't necessarily understand every single thing about the world in which we live. It's sufficient to know there is lift, and essentially how to produce it.

Sir Isaac Newton, and Daniel Bernoulli (working from a theory of Leonhard Euler), have found ways to explain most of what we're seeing using math and science. But as you have seen, the conventional application of either of them fails to offer a 100% complete explanation for everything related to aerodynamic lift. We can change their application as our understanding improves, but what does that say about our understanding?

In fact, it was just a few years ago that scientists finally discovered how bees and birds are able to fly. The power-to-weight ratio required seemed to be far too great for the amount of energy a small bird or insect could store, but yet we see them flying all the time. Just like airplanes.

If you want to blow your mind even more, read up on the Coanda effect. One good link is here: http://jef.raskincenter.org/published/coanda_effect.html
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