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Why Do I Never See Turbprops Making Contrails?  
User currently offlineBa757gla From United Kingdom, joined Mar 2006, 760 posts, RR: 2
Posted (8 years 3 months 1 week 1 day 21 hours ago) and read 6392 times:

i live under flight path to INV and some to ABZ. I have seen flybe dash8s high up but i have never seen them pull contrails despite people on a neyt saying that they pull contrails! so why dont they ? is it you have to be over FL30 TO PULL contrails?

41 replies: All unread, showing first 25:
 
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17041 posts, RR: 66
Reply 1, posted (8 years 3 months 1 week 1 day 21 hours ago) and read 6378 times:

Quoting Ba757gla (Thread starter):
is it you have to be over FL30 TO PULL contrails?

You do not. Contrails depend on temperature. When it's very cold (say, at the South Pole), contrails are quite possible on the runway.

I'm pretty sure I've seen pics of Tu-95s with contrails.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineKeta From Germany, joined Mar 2005, 448 posts, RR: 0
Reply 2, posted (8 years 3 months 1 week 1 day 20 hours ago) and read 6368 times:

Quoting Ba757gla (Thread starter):
Why Do I Never See Turbprops Making Contrails?

Because they don't bother puting chemicals on turboprops, it's enough having chemtrails on jets  Wink

Seriously, though...

Quoting Starlionblue (Reply 1):
I'm pretty sure I've seen pics of Tu-95s with contrails

Googled a little bit, here you go:




Where there's a will, there's a way
User currently offlinePilotaydin From Turkey, joined Sep 2004, 2539 posts, RR: 51
Reply 3, posted (8 years 3 months 1 week 1 day 17 hours ago) and read 6301 times:

there may be contrails but you might not see them, i guess it also has to do with how much thrust comes from the fan and how much from the core of the engine....i think the more thrust from the core, makes it a more favorable environment for contrail formation


The only time there is too much fuel onboard, is when you're on fire!
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17041 posts, RR: 66
Reply 4, posted (8 years 3 months 1 week 1 day 17 hours ago) and read 6281 times:

Quoting Pilotaydin (Reply 3):
there may be contrails but you might not see them, i guess it also has to do with how much thrust comes from the fan and how much from the core of the engine....i think the more thrust from the core, makes it a more favorable environment for contrail formation

Sounds right. Since contrails are formed by hot air from the core being cooled to a point where water droplets form, a turbofan with cool air that envelops the core air more completely will have more contact area than a turboprop.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 5, posted (8 years 3 months 1 week 1 day 17 hours ago) and read 6279 times:

Quoting Pilotaydin (Reply 3):
i guess it also has to do with how much thrust comes from the fan and how much from the core of the engine..

Not exactly...

View Large View Medium
Click here for bigger photo!

Photo © Bailey - AirTeamImages



I believe that the drop in air pressure over the top of the wings can produce the temperature drop necessary. (The Bernoulli Coulli)



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineMiamiair From , joined Dec 1969, posts, RR:
Reply 6, posted (8 years 3 months 1 week 1 day 16 hours ago) and read 6269 times:

What about those pictures of B-17's during WW2? It looked like a road map of New Jersey. Piston powered engines will cause contrails as well.

User currently offlineKdtwflyer From United States of America, joined Jun 2004, 830 posts, RR: 1
Reply 7, posted (8 years 3 months 1 week 1 day 15 hours ago) and read 6231 times:

B-17 contrails..

http://www.af.mil/shared/media/photodb/photos/020903-F-9999b-006.jpg



NW B744 B742 B753 B752 A333 A332 A320 A319 DC10 DC9 ARJ CRJ S340
User currently offlineDavid L From United Kingdom, joined May 1999, 9524 posts, RR: 41
Reply 8, posted (8 years 3 months 1 week 1 day 15 hours ago) and read 6219 times:

Quoting Kdtwflyer (Reply 7):

From the propeller tips, too. Cool!


User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 9, posted (8 years 3 months 1 week 1 day 14 hours ago) and read 6200 times:

Those who are old enough to remember the many overflights of B-36 bombers during the 1950's will surely recall the contrails they left behind...a LOT.

Also, you could hear these aircraft before you could see 'em, way up high above 30,000 feet.

No, not engine noise...propellor noise.
MUCH lower frequency.


User currently offline777WT From United States of America, joined Jan 2005, 877 posts, RR: 1
Reply 10, posted (8 years 3 months 1 week 1 day 14 hours ago) and read 6186 times:

Quoting Kdtwflyer (Reply 7):
B-17 contrails..

All the contrails shows all the props are turning in the same direction. Not the opposite on the other wing.
I thought they'd have opposite rotating props on the opposite wing?


User currently offlineDavid L From United Kingdom, joined May 1999, 9524 posts, RR: 41
Reply 11, posted (8 years 3 months 1 week 1 day 13 hours ago) and read 6175 times:

Quoting 777WT (Reply 10):
I thought they'd have opposite rotating props on the opposite wing

I think that's pretty rare. Why complicate things by not keeping all the engines and prop gear the same?


User currently offlineDavid L From United Kingdom, joined May 1999, 9524 posts, RR: 41
Reply 12, posted (8 years 3 months 1 week 1 day 13 hours ago) and read 6169 times:

Aha! I thought there was something about this recently...

Do Turboprop Multis Counter Rotate? (by KELPkid May 18 2006 in Tech Ops)


User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 13, posted (8 years 3 months 1 week 1 day 12 hours ago) and read 6145 times:

Above a certain altitude, contrails will form. Below it, it will not.

Turboprops fly at lower altitudes than jets.

Hence, it is rare to see contrails behind turboprops. Above the contrail altitude, they will generate contrails. As will recips, for that matter.

Pressure drops, such as those found in vortices coming off wings, propeller tips, flaps, and in the low pressure region above the wing, generate a drop in temperature (recall the formula for an ideal gas, pV = nRT). If the dewpoint is close to the ambient temperature, this temperature drop will put the temperature below the dewpoint and mist will form. It will typically dissipate fast though, normally forming just a small region of mist in the affected region.

Cheers,
Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 59
Reply 14, posted (8 years 3 months 1 week 1 day 12 hours ago) and read 6124 times:
AIRLINERS.NET CREW
DATABASE EDITOR



There was an interesting thread about contrails awhile back:

http://www.airliners.net/discussions/tech_ops/read.main/149810




2H4





Intentionally Left Blank
User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 15, posted (8 years 3 months 1 week 1 day 11 hours ago) and read 6092 times:

Quoting 411A (Reply 9):
old enough to remember the many overflights of B-36 bombers during the 1950's

Remember them well.

Thirty six of them in six cells of six, came over our house at maybe two thousand feet once. Staggering! But at altitude they, and the B-50s and other big recips would draw a con from one horizon to the other.

Quoting 411A (Reply 9):
you could hear these aircraft before you could see 'em, way up high above 30,000 feet.

No, not engine noise...propellor noise.

That was a wonderful sound. You get just a taste of it in Strategic Air Command with Jimmy Stewart.

Last time I saw a B-36 in flight must have been about 1958 or so at Hamilton AFB, California (KSRF) A pair of them did a low flyby during open house. Announcer said they were at 1500' and they blotted out the sun.



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 16, posted (8 years 3 months 1 week 1 day 10 hours ago) and read 6085 times:

Quoting 777WT (Reply 10):
All the contrails shows all the props are turning in the same direction. Not the opposite on the other wing.
I thought they'd have opposite rotating props on the opposite wing?

If I'm not mistaken they'd have been the first airplane ever to have such an innovation if they'd had. They predate the P-38 by quite a bit.

It is just not so much a problem with four engines. If you lose two on one side you've in for a bad day, but just losing one - well, you've still got three. You can even pull the symmetric engine back a little and still have half your thrust.

Any gains in lower VMC would have been offset by lack of commonality in parts. And consider that when that plane was in its heyday it was flying out of England at the far end of a very long supply train that reached all the way back to Seattle. Spare parts were rarely put on airplanes for the trip because they mainly needed to carry gasoline to cross the Atlantic. Most spares got put on ships and the German U-boats were in the business of preventing their delivery. So the engine and prop on a B-17 would also hang on a number of other airplanes. Commonality was your friend.



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineNewark777 From United States of America, joined Dec 2004, 9348 posts, RR: 29
Reply 17, posted (8 years 3 months 1 week 1 day 10 hours ago) and read 6075 times:

Quoting SlamClick (Reply 5):
I believe that the drop in air pressure over the top of the wings can produce the temperature drop necessary

Happens right on the ground:


View Large View Medium
Click here for bigger photo!

Photo © Stefan Sjögren - Stockholm Arlanda Photography



Although that is a different phenomenon than the contrails forming behind engines from freezing moisture being expelled by the engines.

I have a question about the aerodynamic contrails in the picture before. On the ground what is happening is that the air rushing over the wing looses pressure, therefore cooling, and dropping below the dew point, causing the condensation. Is this simply the same thing happening at a higher altitude, or is there something more complicated going on?

Harry



Why grab a Heine when you can grab a Busch?
User currently offlineBobster2 From , joined Dec 1969, posts, RR:
Reply 18, posted (8 years 3 months 1 week 1 day 10 hours ago) and read 6057 times:

Quoting Newark777 (Reply 17):
Is this simply the same thing happening at a higher altitude, or is there something more complicated going on?

At higher altitude you're seeing moisture from the burning fuel being added to the cold, moisture saturated air, resulting in ice formation. That's why you get contrails from any airplane that burns fuel that has water as a product of burning when the atmosphere is saturated with water. It doesn't have to be a jet, it depends on the temperature and water content of the air.

On the ground you're seeing moisture saturated air cooled until mist precipitates out. So the ground contrails are water, high altitude contrails are ice particles.

[Edited 2006-06-17 01:58:21]

User currently offlineNewark777 From United States of America, joined Dec 2004, 9348 posts, RR: 29
Reply 19, posted (8 years 3 months 1 week 1 day 10 hours ago) and read 6047 times:

Quoting Bobster2 (Reply 18):

At higher altitude you're seeing moisture from the burning fuel being added to the cold, moisture saturated air, resulting in ice formation. That's why you get contrails from any airplane that burns fuel that has water as a product of burning when the atmosphere is saturated with water. It doesn't have to be a jet, it depends on the temperature and water content of the air.

Yes, but this doesn't explain the "contrails" coming off the wings, not the engines, linked above, which I was referring to.

Harry



Why grab a Heine when you can grab a Busch?
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 59
Reply 20, posted (8 years 3 months 1 week 1 day 9 hours ago) and read 6042 times:
AIRLINERS.NET CREW
DATABASE EDITOR




Quoting Newark777 (Reply 19):
Yes, but this doesn't explain the "contrails" coming off the wings

Most contrails at altitude are produced by the engines, but then affected by the wake vorticies from the wingtips:


View Large View Medium
Click here for bigger photo!

Photo © Josef P. Willems






Quoting Bobster2 (Reply 18):
So the ground contrails are water, high altitude contrails are ice particles.

Contrails don't care about their proximity to the ground. They only care about the ambient atmospheric conditions. If the proper atmospheric conditions exist on the ground, you'll get contrails:

http://polar4.home.att.net/feb-04-pics/contrails-take-off-Baker-cr.jpg




2H4





Intentionally Left Blank
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17041 posts, RR: 66
Reply 21, posted (8 years 3 months 1 week 1 day 9 hours ago) and read 6025 times:

Quoting Bobster2 (Reply 18):
At higher altitude you're seeing moisture from the burning fuel being added to the cold, moisture saturated air, resulting in ice formation. That's why you get contrails from any airplane that burns fuel that has water as a product of burning when the atmosphere is saturated with water. It doesn't have to be a jet, it depends on the temperature and water content of the air.

On the ground you're seeing moisture saturated air cooled until mist precipitates out. So the ground contrails are water, high altitude contrails are ice particles.

Good point. In cold weather, cars produce contrails.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineNewark777 From United States of America, joined Dec 2004, 9348 posts, RR: 29
Reply 22, posted (8 years 3 months 1 week 1 day 9 hours ago) and read 6025 times:

Quoting 2H4 (Reply 20):

Most contrails at altitude are produced by the engines, but then affected by the wake vorticies from the wingtips:

Yes, but I was specifically referring to the photo linked already by SlamClick:


View Large View Medium
Click here for bigger photo!

Photo © Bailey - AirTeamImages



It is clear much of that is NOT coming from the engines.

Harry



Why grab a Heine when you can grab a Busch?
User currently offlineBobster2 From , joined Dec 1969, posts, RR:
Reply 23, posted (8 years 3 months 1 week 1 day 9 hours ago) and read 6021 times:

Quoting Newark777 (Reply 19):
but this doesn't explain the "contrails" coming off the wings, not the engines

I tried to explain in my second paragraph, but I omitted some details. The air flow over the wings causes the temperature to drop above the wings, because a drop in pressure results in a lower temperature. If the air is already saturated with water, the temperature drop will force some of the water to precipitate out as mist. So in this type of contrail, you're just dealing with water that was already there, it is not necessary to add water; the steam coming from the engine is hot and the air isn't cold enough to freeze it.

Quoting 2H4 (Reply 20):
Contrails don't care about their proximity to the ground.

Well, I oversimplified.  Smile The air temperature on the ground is usually much warmer than the air temperature at the South Pole. In most parts of the world, you have to get to a high altitude in order for the air to be cold enough to turn heated steam into ice in a few seconds. This type of contrail requires water to be added to the air, the water comes from the burning fuel.


User currently offlineBobster2 From , joined Dec 1969, posts, RR:
Reply 24, posted (8 years 3 months 1 week 1 day 9 hours ago) and read 6018 times:

Quoting Newark777 (Reply 22):
It is clear much of that is NOT coming from the engines.

In that case, the caption on the photo answers your question. The aerodynamics (in other words, the pressure drop and temperature drop above the wings) causes the part of the contrail that isn't coming from the engines.


25 Ba757gla : thanks for the feed back
26 Post contains links and images B2707SST : I can think of (at least) three possible ways to create contrails: 1. Water vapor in engine exhaust condenses and freezes into a contrail. These are
27 Post contains links and images Newark777 : Right, I understand the whole concept of condensation forming close to the ground. I'm just trying to figure out what is going on in the picture, whi
28 Bobster2 : Yes, but only when the engine is cold. The cold engine has excess water that gets blown out the exhaust for a few minutes. A hot car doesn't usually
29 Post contains images Bobster2 : OK. You're correct. Thanks to B2707SST in Reply 26 for clearing up the issue that was confusing both of us.
30 Ba757gla : CONTRAILS very interesting!1
31 Newark777 : Thanks a lot, that is exactly what I was looking for. Thanks to Bobster also. Harry
32 Bobster2 : It's possible for the wings to be much colder than the surrounding air after the fuel gets cold soaked at high altitude and the plane descends to warm
33 2H4 : Good point. It could be the condensation of water on the surface of the wing. 2H4
34 CosmicCruiser : Absolutely, I had the pleasure of seeing the Memphis Belle during it's renovation and not only did it have 8 engines during it's tour but they found
35 XFSUgimpLB41X : Rumor mill: I heard they both went outboard for increased instability and better combat manueverability.
36 Post contains links SuperDan : In this thread about counter rotation RE: Do Turboprop Multis Counter Rotate? (by 2H4 Jun 2 2006 in Tech Ops)#ID155788 , they mentioned that the ones
37 L-188 : Exactly. All fuel has a % of water. Through filteration we trying and keep that amount as small as possible, but all engines are capable of putting o
38 Post contains links FredT : The water isn't in the fuel. It is created through combustion. http://en.wikipedia.org/wiki/Combustion
39 L-188 : Wikpedia is only half right. Water is a byproduct, but there is also water suspended in all fuels, that water doesn't burn.
40 FredT : ...but is a very marginal contribution to the forming of contrails.
41 Bongo : That only happens on the Flight Simulator...always at FL30 or higher....only.
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