aaflt1871
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Wake Turbulence

Sat Dec 25, 2004 1:59 pm

Many someone on here can help with a question. Of the planes listed below, I was wondering which one would cause the most wake turbulence to aircraft departing or arriving after it? Basically which one is given the widest birth when taking off or landing.

747 (all series)
777 (all series)
A-380 (Yes I know it has not flown yet)
Concorde
SR-71 Blackbird
AN-225
C-5 (fondly nicknamed F.R.E.D)
B-52 Stratofortress
C-17

[Edited 2004-12-25 06:31:29]
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Starlionblue
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RE: Wake Turbulence

Sat Dec 25, 2004 11:31 pm

"Widest birth"  Big grin Sorry but that's funny. It's widest berth. I'm pretty sure the 225 and the 747 generate the most of those you list.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
MEA-707
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RE: Wake Turbulence

Sat Dec 25, 2004 11:40 pm

Not that it generates the most wake turbulence of all but the 757s amount of wake turbulence used to be underestimated. I believe about 3 lighter aircraft have gotten in problems including 1 or 2 fatally behind a 757. That urged the 757 to be labelled heavy and have according waiting time for aircraft behind.
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rh703
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RE: Wake Turbulence

Sun Dec 26, 2004 12:20 am

Speaking not as an FAA employee, but as a member of the National Air Traffic Controllers Association that works at Potomac TRACON in Warrenton VA, I can tell you the following:

Wake turbulence is USUALLY understood to correspond with aircraft weight, the heavier the aircraft....the greater the wake. Aircraft with maximum takeoff weights in excess of 300,000 lbs are considered 'heavies' and given extra separation. The FAA had to rethink this after a series of events involving aircraft following B757's. The max take off weight of the 757 is usually around the 255,000 range, but apparently the highly efficient wing design (try getting one to descend quickly) has something to do with the vortice generation. We now have a separate wake turbulence category in between heavies and regular aircraft that is just for the 757.

There are so many variables to wake turbulence that it is hard to answer your question with just one answer.

I think 'clean and slow' (pilots help me out) puts out the most wake behind any aircraft. Vortices have a life span of 1-2 minutes and a sink rate of approximately 500 fpm (?)......if I were a pilot, I would much rather follow 2 miles behind a 747 with a 30kt cross wind then 4 miles behind a 757 in still air. (I am sure other factors like humidity and temperature play a role in this too, but I am not sure if anyone understands them fully yet.) Of course you always want to be above the other aircrafts flight path because those vortices fall before they die.

To try and answer your question, in very general terms, depending on what you are flying, you are probably going to get either 3 or 5 miles and 1000 feet separation between the aircraft listed.

If you are flying a C172 and conducting an instrument approach, you will receive the following separation behind:

B737 - 4 miles
B757 - 5 miles
B747 & I think the rest of the aircraft you listed - 6 miles

If you are flying a 737 you should get 3 or 2.5 miles behind a 737/md80, and 5 behind a 757 or heavy.

If you are flying a 757, you should get 3 miles behind a 737 or MD80, 4 miles behind a 757, and 5 miles behind a 747 or any other aircraft you listed.
 
aaflt1871
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RE: Wake Turbulence

Sun Dec 26, 2004 7:48 am

I always thought the B-52 would cause the most Turbulence for aircraft following behind.

Thank you Rh703 for the detailed response

And Starion Blue Birth >>>>> Berth, you get the idea  Big grin
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ILSApproach
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RE: Wake Turbulence

Mon Dec 27, 2004 7:57 am

Here at MSP, NWA's 753's are "heavies" their 752's are not, per ATC here. As above mentioned take-off weight is the factor

Mike @ MSP
 
goboeing
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RE: Wake Turbulence

Mon Dec 27, 2004 8:56 am

Rh703

"Aircraft with maximum takeoff weights in excess of 300,000 lbs are considered 'heavies' and given extra separation."

A heavy has a maximum gross takeoff weight of more than 255,000 pounds. From the pilot/controller glossary:

AIRCRAFT CLASSES- For the purposes of Wake Turbulence Separation Minima, ATC classifies aircraft as Heavy, Large, and Small as follows:

a. Heavy- Aircraft capable of takeoff weights of more than 255,000 pounds whether or not they are operating at this weight during a particular phase of flight.

I think it used to be 300,000?

Nick
 
QantasA332
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RE: Wake Turbulence

Mon Dec 27, 2004 10:26 am

Firstly, just to clear things up a bit, variations in wake turbulence strength between different aircraft can depend on a number of different factors - not just weight. For given speeds and atmospheric conditions, the foremost factor is wing loading (aircraft weight divided by wing area, or total lift divided by wing area for level, unaccelerated flight), followed by aircraft weight in general (which, of course, mostly plays into wing loading but can be a good indicator in its own right) and specific wing geometry. There are other defining components but, as I said before, the above is what you mainly look for in comparing different aircraft's wakes. So, out of the original poster's list of aircraft, you could get a rough idea of comparative wake turbulence strengths by looking at the respective aircraft's wing loading first and foremost. You can find such figures for some of those aircraft here. Now...

I think 'clean and slow' (pilots help me out) puts out the most wake behind any aircraft.

That is correct. It can seem counter-intuitive (especially the 'clean' part), but the very simple reason behind it can be found in the basic equation for induced drag and by considering the effects of slow flight on an aircraft's wing's coefficient of lift CL.

Vortices have a life span of 1-2 minutes and a sink rate of approximately 500 fpm (?)

I have a feeling that vortex life span is a bit longer, but the sink rate is indeed about 300-500 fpm. The sink stabilizes around 500-900 feet below the generating aircraft.

The max take off weight of the 757 is usually around the 255,000 range, but apparently the highly efficient wing design (try getting one to descend quickly) has something to do with the vortice generation.

The 757's wing design isn't really considerably more efficient than others currently in the air and it doesn't play a major part in the 757's 'heavy' classification. Rather, the main culprit for the 757's relatively nasty wake is its relatively slow landing speed (for an aircraft its size). As I explained above, the slow speeds involved lead to a stronger wake during approach and landing (wake-critical periods of flight).

Hopefully this mess makes at least a little sense...  Laugh out loud

Cheers,
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2H4
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RE: Wake Turbulence

Mon Dec 27, 2004 12:50 pm

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DeltaGuy
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RE: Wake Turbulence

Mon Dec 27, 2004 1:08 pm

Was on a DL MD-88 on approach to ATL when this happened, we were following a 757, jet was in a dirty config....the Mad Dog suddenly rolled over about 35-45 degrees or so, everything in the cabin shook. Company traffic at it's best  Smile/happy/getting dizzy

Hell, you'll even get a bit of turbulence from a CRJ if you aren't high enough behind their glide path...happened to us on our way into MGM a little while back (visual approach, VMC)....right about the time we were gettin a little bounce from it, tower goes "caution, wake turbulence from heavy CRJ"....just about died laughing on approach while trying to keep her steady lol.

DeltaGuy
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2H4
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RE: Wake Turbulence

Mon Dec 27, 2004 1:32 pm

If you sit beneath the approach path of an Avro RJ, near the runway threshold, you can sometimes hear the wake turbulence.

It sounds like a single electrical crackle, traveling up and down the final approach path, alternating direction at a very high rate of speed.


2H4
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Newark777
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RE: Wake Turbulence

Mon Dec 27, 2004 1:47 pm

I thought those crackling noises were the vortices formed on the wingtips and other locations? I could be wrong, it's getting late.  Nuts

Harry
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2H4
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RE: Wake Turbulence

Mon Dec 27, 2004 1:53 pm

I thought those crackling noises were the vortices formed on the wingtips


Yep. That's wake turbulence.  Smile


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FinnWings
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RE: Wake Turbulence

Tue Dec 28, 2004 1:55 am

Usually the vortices have a sink rate of about 300-500ft/min indeed, but there might be some conditions when vortices are going upwards. In that case there is usually a windshear which might stop the normal movement of the vortices and the change of direction might occur or then it will stay at constant altitude. This could be extremely hazardous as the vortices might stay exactly in the glide path.

The risk of wake turbulence is also extremely high when you have a crosswind component of 5kts. This is the same speed which vortices are usually moving apart, but if there is a 5kts crosswind then the wind will cause the other vortice staying exactly where it formed causing trouble for following aircrafts.

Best Regards,
FinnWings
 
SlamClick
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RE: Wake Turbulence

Tue Dec 28, 2004 2:05 am

One fun place to watch wake turbulence was on final into SFO, to land on 28 left or right. Sailboards launch from some place near Coyote Point and you will see them scooting straight north or straight south across the prevailing west winds. You can also see the wingtip vortices of a preceding plane settling onto the water. Sometimes they will come together and I've seen a sail ripped right off the board by wake turbulence.

When I lived in Seattle I liked to walk Des Moines Creek Park just south of SEA. When they are landing north, about twenty seconds after a plane passes over, the vortices settle into the tree tops. It makes that unforgettable whistling, crackling noise and the trees will shake violently. I've seen it break off a fair size Douglas fir branch.

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Santhosh
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RE: Wake Turbulence

Tue Dec 28, 2004 2:35 am

Category
. LIGHT = less than 7 tons (15,500 lb)
. MEDIUM = between 7 and 136 tons
. HEAVY = higher than 136 tons (300,000 lb)

ARRIVALS :
. ALL CASES = 3 NM (no time limit) except for the following :
. HEAVY behind HEAVY = 4 NM (no time limit)
. MEDIUM behind HEAVY = 5 NM or 2 mins
. LIGHT behind MEDIUM = 5 NM or 3 mins
. LIGHT behind HEAVY = 6 NM or 3 mins

DEPARTURES :
. LIGHT or MEDIUM behind HEAVY = 2 mins (3 mins if L or M performing an intermediate departure)
. LIGHT behind MEDIUM = 2 mins (3 mins if L performing an intermediate departure)

For Departures and Arrivals does the ATC follow the spacing between aircraft just on the basis of time or on basis of distance of aircrafts from each other? Is there any regulation for ATC that,either they have to follow the time scale or the distance between aircrafts for adequate spacing. Or can they follow both?

Regards
George
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saab2000
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RE: Wake Turbulence

Tue Dec 28, 2004 4:07 am

Slamclick is right on, once again.

The other day I was on approach into KLGA following a Westjet Boeing 737-700 and I was flying. The captain suddenly exclaimed, "Hey, cool, look at the wake vortices on the water!". Sure enough, there were a number of little "tornadoes" on the surface of the water. It was really cool to watch.

We were on the LDA-A (more or less visual) to RWY 22 at La Guardia.

FWIW, I fly a CRJ-200 and I have seen pretty cool little vortices formed by the flaps on approaching CRJs in damp conditions.
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SATL382G
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RE: Wake Turbulence

Tue Dec 28, 2004 5:37 am

When I lived in Seattle I liked to walk Des Moines Creek Park just south of SEA. When they are landing north, about twenty seconds after a plane passes over, the vortices settle into the tree tops. It makes that unforgettable whistling, crackling noise and the trees will shake violently. I've seen it break off a fair size Douglas fir branch

Another good place to see, and especially hear wake turb. is at Gravelly Point just north of Reagan National when they are landing on 18. haven't been there post 9/11, is the Point still open to spotters?
"There’s nothing quite as exhilarating as being shot at and missed" --Winston Churchill
 
SlamClick
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RE: Wake Turbulence

Tue Dec 28, 2004 5:44 am

There was a recent post in the Photography forum directing someone to Gravelly Point, so I assume it is still open.

In San Diego there is one lone palm tree in the median of Interstate-5 more or less on the centerline of Runway 27. I've seen that tree shaking violently once, then drove my VW bus into the same wake turbulence that was shaking the tree - almost got rolled. It was a National DC-10 IIRC.

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DeltaGuy
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RE: Wake Turbulence

Tue Dec 28, 2004 9:57 am

VW bus huh? Have some flower power painted on the side?  Big grin lol, kidding Slamclick  Smile/happy/getting dizzy

I wonder if the palm tree is still there...I love that approach, just the sight of people looking out their cubicles at us is pretty cool Big grin

DeltaGuy
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2H4
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RE: Wake Turbulence

Tue Dec 28, 2004 10:32 am

A friend of mine once said driving his VW bus in a crosswind was like driving a garage door down the freeway. Guess he wasn't exaggerating after all...

 Smile


2H4
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SlamClick
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RE: Wake Turbulence

Tue Dec 28, 2004 10:34 am

Hey DeltaGuy that's not the half of it! My bus had wooden bumpers and a cactus growing on the dash. With this low-profile machine I smuggled drugs out of Mexico.

Okay, it was Laetrille for family being treated for cancer, but it was smuggling nonetheless.

Good background for a crusty old conservative.

I love that approach too - we modified our ground prox to say "Garage! Garage" on short final.
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SPREE34
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RE: Wake Turbulence

Tue Dec 28, 2004 12:39 pm

Rh703...."Speaking not as an FAA employee, but as a member of the National Air Traffic Controllers Association that works at Potomac TRACON"
and then
"Aircraft with maximum takeoff weights in excess of 300,000 lbs are considered 'heavies'"

Randolph. If you HAD spoken as an FAA employee,(Support Specialist) I wouldn't expect correct information. Sir, you spoke as a member of The National Air Traffic Controllers Association. (NATCA) If you are going to speak in a public forum as a representative of the organization, know your facts.

FAAH 7110.65 Appendix A Page A-1 AIRCRAFT WEIGHT CLASSES sub part A " Heavy. Aircraft capable of takeoff weights of more than 255,000 pounds whether or not they are operating at this weight during a particular phase of flight."

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I don't understand everything I don't know about this.

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