1. Mick West

    Mick West Administrator Staff Member

    [​IMG]

    In a rather odd reversal of known science, the latest chemtrail theory is that modern high-bypass engines do not create contrails. A comprehensive explanation of why this is incorrect can be found in the following video:


    As noted towards the end of the video, the idea can be debunked simply by a review of the scientific literature. The likelyhood that a particular engine will create a contrail is governed by the "contrail factor", and this is higher for high bypass engines - I encourage you to research this for yourself, and I give some links below.

    The classic demonstration of high bypass engines producing more contrails is the study:
    Ulrich Schumann and Reinhold Busen, 2000, Experimental Test of the Influence of Propulsion Efficiency on Contrail Formation
    http://elib.dlr.de/9247/1/aerscitech-2000.pdf
    [​IMG]
    As you can see, the newer high-bypass A340 produces contrails more frequently than the older, low-bypass B707

    Schrader, Mark L., 1997: Calculations of Aircraft Contrail Formation Critical Temperatures. J. Appl. Meteor., 36, 1725–1729.
    http://journals.ametsoc.org/doi/full/10.1175/1520-0450(1997)036<1725:COACFC>2.0.CO;2
    Fig 4 shows contrails forming at a wider range of temperatures than non or low-bypass engines. You don't have to follow exactly what the graphs mean, just note that for the high-bypass engine, the curves intersect the bottom axis at a higher temperature than the low-bypass or non-bypass engines.
    [​IMG]

    Walters, Michael K., Jeffrey D. Shull, Robert P. Asbury, 2000: A Comparison of Exhaust Condensation Trail Forecast Algorithms at Low Relative Humidity. J. Appl. Meteor., 39, 80–91.
    http://journals.ametsoc.org/doi/full/10.1175/1520-0450(2000)039<0080:ACOECT>2.0.CO;2

    Influence of propulsion efficiency on contrail formation Ulrich Schumann
    http://www.sciencedirect.com/science/article/pii/S1270963800010622
    Lynch, David K., et al, 2002: Cirrus, Oxford University Press
    http://books.google.com/books?id=58v1fg4xeo8C&lpg=PA233&ots=_-uNkL6yUM&dq=contrail factor high bypass&pg=PA233#v=onepage&q&f=false
    [​IMG]

    See also:
    https://www.metabunk.org/threads/engine-efficiency-high-bypass-and-contrail-frequency-how-much.226/

    So what did the theorists get wrong?

    This theory is particularly odd in the context of the chemtrail theory, as that normally claims that in previous decades (generally the 1980s and before) there were no persistent contrails, and that the contrails we see now are something new. But this new spin on the chemtrail theory seems to be arguing the opposite - that older planes would make contrails, and new planes will not.

    The thinking behind the "high-bypass = no contrails" seems to be the idea that the contrail is made from the air that an engine pushes backwards. This is incorrect - simply pushing air does not create an exhaust contrail. An exhaust contrail is created from, as the name implies, the exhaust of the the engine.

    [​IMG]

    The exhaust of the engine is the gasses that come out of the combustion chamber. It's the product of burning kerosene (hydrogen and carbon) with the oxygen in the air, and the result is carbon dioxide and dihydrogen monoxide (water). It's the water in the exhaust that makes the contrail. And the exhaust gasses are basically the same regardless of if it's a low-bypass, no-bypass, high-bypass or even an internal combustion engine.

    What creates a contrail is the mixing of the exhaust with cooler air. It does not matter if it's mixing with the air that passed through the bypass fan, or if it's mixing with the air that passed around the engine. It's still just exhaust gases mixing with the air. As the gasses mix, the temperature falls, and the water condenses out.

    The only difference with a high bypass engine is that the exhaust gasses in a high bypass engine are a little less hot (more of the energy has gone into producing thrust from the bypass fan). So they reach the condensation point quicker, and so are more likely to form contrails.

    In reality, any plane can make a contrail. High bypass, low bypass, no bypass, even prop planes will make contrails. And they always have.
     
    Last edited: Dec 30, 2015
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  2. MikeC

    MikeC Senior Member

    The following is the text of a posting I made about this on ATS a couple of months ago titled "How many times can a contrail believer be wrong?". As some with noted, the answer is blowing in the wind :D

    And so...:

    Global Skywatch has published something that I am sure they think is the definitive Truth about Contrails, but the truth about this is that it serves only as an illustration of how many "facts" can someone get wrong in a short bit of writing!
    there is no such thing as "high vacuum" - perhaps he means "low pressure"? And of course that is wrong- contrails will form at sea level if the humidity and temperature are suitable - hence "ice fog" in Alaska!
    Actually this is more-or-less correct - albeit in a pidgin-technical manner - denser air such as that compressed by a turbo fan will hold more moisture. As long as it remains denser of course....which isn't very long once it leaves the engine!
    lol - and that is why the contrails do not form at the output of the turbine, and why they form some distance behind - when the pressure is rapidly reducing - thus also rapidly reducing the temperature!
    There is no lack of fuel "in this ratio" - all jet engines seek a "perfect" mixture, which IIRC is about 14:1 air to fuel - some get closer than others, but there is always fuel!!
    Using less fuel does not render them "incapable" even by his own reasoning - it should render them less LIKELY by simplistic reasoning - however other considerations actually make it MORE likely- put simply the higher the efficiency of the engine, the higher the temperature at which contrails can form, and so the more likely they are to do so - the math is in the link if you want to examine it closely.
    simply said this guy is [wrong]
    WATER VAPOR IS INVISIBLE - YOU NEVER SEE IT!!
     
    Last edited by a moderator: Feb 26, 2014
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  3. Mick West

    Mick West Administrator Staff Member

    While that's all true, the reason I posted this new debunk (over TWCobra's) is that your rebuttals (while accurate) will be viewed as as simply opinions. I'm trying an approach of just giving references.
     
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  4. Hama Neggs

    Hama Neggs Senior Member

    Do we have a version of this vid here for debunking? Maybe it needs to be specifically addressed as well.



    Dane Wigington is touting this vid as being the 'slam-dunk' end to all arguments concerning contrails vs chemtrails.
     
    Last edited: Mar 9, 2014
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  5. Hama Neggs

    Hama Neggs Senior Member

    At about 49:00 in this show, Dane Wigington claims to have heard from "an engineer that works at Rolls Royce jet engines" who told him that the info in that vid is "spot on - it's correct". I can only guess that Dane is just flat lying about that.

    http://globalskywatch.com/assets/mp3/gwradio/2014-02-22.mp3
     
    Last edited: Mar 9, 2014
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  6. Mick West

    Mick West Administrator Staff Member

    What more debunking is needed other than what is in the first post?

    And if you want a point-by-point, the second.
     
  7. Hama Neggs

    Hama Neggs Senior Member

    If Dane is going to specifically point to the vid as proof of something significant, the debunk should prominently include the vid, I think.
     
  8. KC-10FE

    KC-10FE Active Member

    A pretty good video of a KC-10 with contrails

    Engines: General Electric CF6-50C2 High Bypass turbofans; Fan: 73%, Core: 27%

     
  9. Efftup

    Efftup Senior Member

    They have also missed , possibly on purpose, another point here with their descriptions.
    A higher PERCENTAGE of the air going into a High Bypass Turbofan does not go through the combustion chamber, BUT
    look at the SHAPE of the engines:
    [​IMG] [​IMG]
    I would say that just by looking at them, it would be fairly obvious that a similar amount of air is going into the combustion chamber in both engines, but the newer one sucks in LOADS of extra air to lower the overall output temperature and to increase fuel efficiency.
     
  10. Balance

    Balance Senior Member

    Yes. Fuel requires a certain amount of oxygen to burn. For efficiency, there is an optimum balance of oxygen/fuel known as stoichiometric combustion http://www.engineeringtoolbox.com/stoichiometric-combustion-d_399.html

    I'm pretty sure this means, regardless of how much air bypasses the combustion process, the engine still needs to consume the same amount of air per fuel into the combustion chamber to get the most efficient burn.
     
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  11. Hama Neggs

    Hama Neggs Senior Member

    They make such a big issue about the air passing through the fan. It's no different than if it was a propeller (or if it wasn't there at all) in terms of contrail production. Of course you can't present such points to the likes of Tanner or Wigington- they are protected from direct engagement on their claims.
     
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  12. TWCobra

    TWCobra Senior Member

    Agreed. The numerous photos available of propellor aircraft making contrails should be enough. Once again however one of their brethren, in this case Jack Baran, makes something up and confirmation bias does the rest.
     
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  13. Hama Neggs

    Hama Neggs Senior Member

    They say something "science-y" sounding about 80-90% of the air not being "combusted", whatever that is supposed to mean, as if the same thing isn't true about all the air which passes around the combustion chamber in any other jet engine ever built, whether it passes through a fan or not. :rolleyes:
     
    Last edited: Oct 15, 2014
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  14. WeedWhacker

    WeedWhacker Senior Member

    Yes, indeed.

    Combustion of a fossil-based fuel (in internal combustion engines, as they are termed) requires the fuel to be "atomized" (another unfortunate term, that is commonly used). It means that the liquid is shot through very fine nozzles, so that as it mixes with the air, it becomes "combustible".

    (A bit similar to your normal "rattle can" that sprays paint. The paint is a liquid, and is combined with a gas inside the can....so the paint itself is "atomized", mixed with the propellant [the gas] and thus sprays out...forced through a very small nozzle. No "combustion" in this scenario, because that is not the desired effect! Although, some pranksters have found a way.... ;) ).

    BUT, when you want a fuel-air mixture to ignite and 'combust', then you extract energy from that combination. (This is also happening in the pistons of your car's engine...unless you own a Tesla!).

    Now, having written all of that....a High-Bypass TurboFan engine STILL needs to extract energy from combustion. The significant thing about these types of jet engines is: They DO produce MORE pronounced contrails, and this is directly related to the amount of air that is "bypassed"...which acts as a sort of 'shroud' that contains the hotter air (that has undergone the combustion cycle, in the fuel/air mixture). The hotter air in the core, or center of a column (a horizontal column, in this case) encircled by the cooler 'bypass' air. Thus, increasing a mixing effect, and affecting the surrounding atmospheric effect on the hot exhaust.
     
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  15. MikeC

    MikeC Senior Member

    And while high bypass ratio fans are certainty more efficient, it is not by order of magnitude, so they still burn more fuel to produce more thrust.

    Eg the specific fuel consumption (SFC) of a Jt3D common in the days of 707's and DC-8's is ~0.78 lb/(lbf·h) (22 g/(kN·s)) @ 4000lbf thrust M 0.82,35000ft,ISA

    For a Rolls Royce Trent 500 HBR it is 0.54 lb/lbf-hr (at cruise) - so this is almost 50% more efficient assuming cruise is also at M0.82 and 35,000 ft ISA.
    (both figures from the respective wiki pages)

    assuming the cruise thrust is the same ratio as the max sea level thrust (which it probably isn't, but for illustration purposes), the Trent 500 will be making 56,000/17,000 * 4000lbs = ~13,176lbs. And to do so it will burn 7115 lbs/hr to do so.

    The JT3D will be burning 3120lbs/hr.

    So the newer high bypass ratio engine is burning 2.28 times as much fuel as the older engine.
     
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  16. WeedWhacker

    WeedWhacker Senior Member

    But of course, is producing more thrust (?)...yes? Which is the point. For ever, and ever larger and heavier airplanes. (Talking commercial passenger jets, here).

    EDIT: But of the specific science, and the "numbers" just make some people's eyes roll back into their heads. The MAIN point here is: "High-Bypass TurboFans DO produce contrails".
     
  17. MikeC

    MikeC Senior Member

    Yes - ~13,000 lb vs 4000 lb - 3.25 times as much thrust for 2.28 times as much fuel.
     
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  18. WeedWhacker

    WeedWhacker Senior Member

    YES!! SO, we see more efficiency, per "unit" of fuel consumption. Which IS THE POINT of inventing better jet engines.

    "Side-Effect"(??) More pronounced, often more persistent contrails.
     
  19. cloudspotter

    cloudspotter Senior Member

    More persistent? Isn't that a function of the RH once the contrail has formed?
     
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  20. Trailblazer

    Trailblazer Moderator Staff Member

    It is, but high-bypass engines produce persistent trails in conditions that older engines would not. (If you compare the charts for contrail formation in the opening post of this thread, you need lower RH for persistent trails at a given temperature with high-bypass engines than with low-bypass ones.)
     
  21. cloudspotter

    cloudspotter Senior Member

    Forming or persisting?
     
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  22. PCWilliams

    PCWilliams Active Member

    The color image above and the black & white image in the PDF file (http://tinyurl.com/oqdagjq) (Figure 7) are not the same images. Just an observation.

    aerscitech-2000 01.
     
  23. Mick West

    Mick West Administrator Staff Member

    Last edited: Jan 17, 2015
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  24. Efftup

    Efftup Senior Member

    the OTHER thing they neglect to mention when talking about how much of the air is NOT going into the combustion chamber is how much BIGGER the cross section of a modern Hi Bypass turbofan is compared to an old style engine.
    a JT3D has a 1.31m diameter. The Trent 500 has a 2.47mm diameter.

    So it has an 88% bigger cross section in the first place, as well as other fan shapes etc .

    I am not 100% certain of my maths on this one so please feel free (as always) to correct any mistakes.

    A JT3D has a bypass ratio of 1.42:1 and an air mass flow of 196kg/s. Therefore the actual amount of air going into the combustion chamber is 196/2.42 = 80.99kg/s.

    A Trent 556 has a bypass ratio of 7.6:1 and an air mass flow of 879kg/s so therefore the actual amount of air going into the combustion chamber is 879/8.6= 102.2kg/s.
     
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  25. Mick West

    Mick West Administrator Staff Member

  26. Mick West

    Mick West Administrator Staff Member

  27. Belfrey

    Belfrey Senior Member

    Russ Tanner made a post about the Schumann and Busen article yesterday on GlobalSkyWatch. The argument mostly consists of assertions that the article is incorrect, and an example of intentionally faked, false scientific evidence:
    Tanner then makes some familiar errors:
    The actual temperature figure is less than approx. -40 degrees (C or F, as they are the same at that point), and it's approx. >70% relative humidity that is pertinent, i.e. the amount of moisture relative to the saturation point at that temperature. These approximate values can be found in scientific papers published at least as far back as 1953. This paper by Knollenberg ("Measurements of the Growth of the Ice Budget in a Persisting Contrail," 1972), for example, examined the the development of a contrail and documented the conditions at which it formed:
    Knollenberg1972fig.

    Russ then repeats the claim that turbofan engines are less likely to make contrails for the following reason:
     
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  28. deirdre

    deirdre Moderator Staff Member

    this is pretty much off topic but reminded me of a question. you know how if i dont change the oil in my car regularly i butn more fuel? do airplanes use oil like a car? and if so do they have to change the oil everytime they land?
     
  29. WeedWhacker

    WeedWhacker Senior Member

    The oil in a turbine engine is used for the same purpose as in an automobile...lubrication.

    Oil in airliner engines is changed regularly (per prescribed maintenance protocols, as per the engine manufacturer and governing authorities' procedures), but not after every flight, no.

    Also, the notion that not changing one's car engine oil regularly results in higher fuel burns? Well...not that simple. IF one were to severely neglect the car engine (by letting it continue to operate with very dirty oil) then yes....there will be erosion of the mechanical surfaces and this could result in higher fuel consumption levels...but only a tiny and almost insignificant amount compared to the repeated need to keep adding oil!! (LOL)...since such 'abuse' to an engine would mean it would not only burn the gasoline, but also the oil that was not meant to get into the combustion cycle at all.

    If you see an old jalopy (like me!) with bluish smoke coming out the exhaust? That is oil being burned, in combustion.

    Eventually you will face a more expensive bill than higher gas prices....either a ring and/or valve job, or even an entire engine replacement (if it goes that far).
     
    Last edited: Mar 4, 2015
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  30. MikeC

    MikeC Senior Member

    Actually we would never change the oil in jet engines - just top it up!! :) Except at engine change of course, when it has to be emptied.

    However modern turbine engines use quite a bit of oil compared to cars - because they operate at much higher stresses they are "looser" when cold and "tighter" when hot. Oil consumption is recorded in the maintenance logs - how much is used to top up at each stop.
     
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  31. blargo

    blargo Member

    My memory of this is that they look for metal in the oil and based on the type they can make a good guess what part needs to be replaced.
     
  32. Jay Reynolds

    Jay Reynolds Senior Member

    Even though reciprocating piston engines and gas turbines are both internal combustion engines, the oil in a piston type engine is more directly exposed to the gases of combustion than oil in a continuous combustion gas turbine. Pistons and their piston rings have a direct contact with combustion gases and require lubrication while a turbine engine has no parts within the hot gas path which require lubrication. Because of this intimate contact with combustion gases, the oil in a piston engine becomes contaminated with acids and carbon from combustion and therfore eventually turns black and acidic and must be replaced. Oil breakdown in a properly running turbine is mainly a factor of temperature and time rather than contamination.
     
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  33. WeedWhacker

    WeedWhacker Senior Member

    This is a common factor in some turbo-prop engines. There are sensors in the oil system that will detect very small particles of metal....depending on the airplane, it is usually referred to as a "Chip" detector. Such a sensor will then illuminate a warning light, (often merely called a "Chip Light") appropriate to the engine where a "chip" was detected in the oil.

    Rest assured that the on-going maintenance, and also design of the large turbo-fan engines used on modern airliners have sufficient safeguards and procedures....including many levels of filtering during operation, and inspections during "ground-time" as part of routine inspection protocols.
     
  34. MikeC

    MikeC Senior Member

    SOAP sampling was (20 years ago - I forget what the acronym stands for - Standard Oil Analysis Procedure??) a routine analysis that was done on oil samples - it was different from analysis of chips on chip detectors or metal in filters.

    SOAP looked at things like chemical contaminants as well as metal particulates to give some indication of engine health every few hundred hours.

    Fragments on chip detectors are a sign of failure somewhere rather than condition monitoring.
     
  35. blargo

    blargo Member

    Well that dates me, I worked TF-39 and TF-33 from 1985-1990.
     
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  36. MikeC

    MikeC Senior Member

    I was working on JT8D's, ALF502's and PW120's at the same time. We did SOAP on all of them and also on the APU's - IIRC it was actually offered free by Mobil - covered by the cost of Jet Oil II!
     
  37. GavinMacQueen

    GavinMacQueen New Member

    Great thread! Does anyone know how exactly the myth about high bypass engines "NOT" producing contrails get started?
     
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  38. TWCobra

    TWCobra Senior Member

    A Canadian guy called Jack Baran made it up.
     
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  39. Hama Neggs

    Hama Neggs Senior Member

    Seems so, and then Russ Tanner and Dane Wigington promoted the heck out of it.
     
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  40. TEEJ

    TEEJ Senior Member

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