What does the " heavy "...

[gonzal59]

I been asking myself long ago..what was the "heavy" designation in some of the aeroplanes callsign..Can you guys tell me whats does it mean..Thanks..

Gon

[admin]

from http://www.faa.gov/ATpubs/AIM/Chap7/aim0703.html

For operations conducted behind heavy aircraft, ATC will specify the word "heavy" when this information is known. Pilots of heavy aircraft should always use the word "heavy" in radio communications.

[n250jg]

It's used for aircraft heavier than 255,000 lbs. Why? Aircraft following a "heavy" may fly through it's wake and have an interesting flight.

Wake turbulence is the spinning air mass that comes off the wing tip of an airplane, all airplanes and not just the heavies, but it is most pronounced with heavy, clean (flaps and gear retracted), and slow flying aircraft generating a lot of lift. Think of it as the air below the wing (high pressure) trying to replace the air above the wing (low pressure) and as it travels out the wing and comes to the end it goes up and starts the air spinning... clock-wise off the left wing and counter clock-wise off the right wing if your following it.

Here's a few pictures for you to get a better visual...

[gonzal59]

Another question Jeff..So basically the engines of the right wing are spinning (i mean the fans) counter clock wise and the ones on the left wing clockwise?

...Thanks Steve and Jeff..

I CAN PROOVE THAT YOU LEARN SOMETHING NEW EVERY DAY, Gonzalo.

[n250jg]

Actually all of the engines (or compressors and turbines) "turn" the same direction and the thrust they produce is directed straight back behind the plane. If the plane in the first picture was not generating any lift with the wings somehow and was still moving through the air, the smoke trails from the engines would be straight back.

Try to picture the wing tip vortices as cylindrical cones that start with the point at the wing tip and the open end straight back behind the plane. As that low pressure upward moving air travels out the wind and reaches the tip, it now moves up and back in a direction that follows the cone. Here's a couple more pictures that can explain it better.

[gonzal59]

Oh..that is interesting..So the smoke that comes out from the wings is generated ..part from the condensation of the warm air from the turbines and part from the wing tips right? The 4 smoke lines come from the 4 engines the 'swirl' from the displacement of the air right?


Thanks so much Jeff...OI really appreciate this..Gonzalo.

[n250jg]

Originally Posted by gonzal59

The 4 smoke lines come from the 4 engines the 'swirl' from the displacement of the air right?

You've got it.

You also mentioned the warm air creating the trails. With low enough temperatures and high relative humidity, the vapor warm exhaust air condenses and forms visible moisture in condensation trails, or contrails. However I would guess that the airliner in the picture is producing it's own smoke in the engines, which is done by injecting oil (we used concrete form release oil) into the hot exhaust so it burns. Usually you can see from the ground the distance between the aircraft and the contrail because of the time it takes the vapor to condense, but smoke is visible immediately.

[gonzal59]

Thanks a lot Jeff..Gonzalo

[onepersonsopinion]

Originally Posted by n250jg

.... the smoke trails from the engines would be straight back.

Why are today's high [air] bypass turbines (outfitted on almost all modern commercial aircraft) creating such dense [smoke] trails, dispersing widely and sometimes lasting for hours? These are not the typical con-trails that I'm used to seeing, that remain in tight cones and disperse relatively rapidly.

[GT_ATCfan]

As a clarification, it is not "smoke" coming out of the engines what you are seeing in some of these pictures. It is in fact water vapor that condenses and/or crystallizes becoming visible. The formations that result are generally referred to as contrails. The engines exhaust gases and particulate matter (PM, or soot) that result from the combustion of air and fuel. These combustion products are visible, for example, in older aircraft that are equipped with gas-guzzling turbojet engines. The smoke is clearly black.

Water vapor naturally found in the air is also ingested into the engines and exhausted with the combustion products. Under the right conditions of temperature and pressure, such as those sometimes found in the exhaust trail of jet engines, this water vapor will condense and becomes visible, thus creating contrails. You must realize though that weather conditions have a strong impact in the occurrence of this phenomenon. That is why you can see contrails on some days, but not in others. How long contrails last in the atmosphere is also dependent on weather conditions. In fact contrails can disappear quickly, remain suspended (and undisturbed) for a long time, or even disperse and grow over time. The International Council on Civil Aviation (ICAO) considers contrails as man-made emissions and as a pollutant precisely because it may result in the formation of clouds that would otherwise not occur.

Newer engines have a higher bypass ratio (BPR) which means that they generate thrust with a greater mass of air that has NOT gone through combustion. They also have cleaner, more environmentally friendly combustion technology. Thus you are less likely to see “smoke” in the traditional sense. None the less they will still generate contrails when the right meteorological conditions are present.