Debunked: High Bypass TurboFans not making contrails, and other misconceptions


Senior Member.
Tanner has published another article that is almost entirely wrong about the properties of water vapor and Jet engines

For a detailed look at the science behind this, with references, see:

If you go to an airport and watch jets take off, you will see that they emit a faint trail of black soot, which is typical of burnt jet fuel (kerosene), but you will not see water vapor. [...] In other words, if an engine was to produce visible water vapor, it would be most likely witnessed during takeoff. However, these engines are incapable of producing trails even during their most inefficient operating condition: Takeoff.
Content from External Source
Water vapour is not visible at any time. It is a fundamental property of water vapour. Even when causing contrails it is not visible as evidenced by the gap behind the engines where the water vapour cools and condenses into a visible state, that being of ice.

Some more of Tanners "facts" debunked.

Fact: Modern high-bypass turbofans - which are used on virtually all large commercial and military aircraft - burn much less fuel per unit of ejected air; often 25% less fuel. Therefore, they produce much less water vapor than older engines.
Content from External Source
This is irrelevant. The water vapour produced is simply a function of the total fuel burnt. While the turbofans allow large engines to be built, the amount of water vapour created has also increased due to the large fuel flows of those engines.

Fact: Air traffic increases less than 1% per year. This amounts to a total increase of about 9% in the past 10 years.
Content from External Source
Air traffic has been increasing at 5% a year since 1970. It increased 53% in the 10 years of 2001-2011. See:

Fact: The handful of photos from the 50s showing military jets and prop planes used water injection or internal combustion piston engines, not high-bypass turbofans. High-bypass turbofans - the type of engines that we are on the jets producing the massive plumes today - are incapable of generating condensation trails and are not used on old military jets.
Content from External Source
Water injection, such as in the Rolls Royce Spey engines, is designed for use as a thrust augmentation system on takeoff. It is only used on takeoff, ironically for Tanner, due to the weight of the water required.

His claim that water injection is not used on high bypass turbofans is also false. Early versions of the Pratt and Whitney JT9D, the original engine fitted to the Boeing 747 used water injection. I have personally flown 747-200 series aircraft with this feature fitted.

Water injection is not used at any other stage of flight other than the first 90 seconds of takeoff. The water methanol tank size on the 747 was only 3000 lbs or 1360 kgs, giving a usage rate of almost 1000kgs a minute.

High bypass turbofans have been around since the late 60s and were fitted to military jets like the C5A.

Fact: The vast majority of witnessed trail formation has been witnessed by low-flying jets rendering this claim irrelevant.

Fact: The altitude in which aircraft fly has remained unchanged for over 30 years. This widely-known fact renders this claim irrelevant. The favored altitude for commercial air traffic ranges between 25K to 35K feet, well within the Earth's Troposphere.

The vast majority of early trails (between 1995 and 2005) were witnessed at altitudes so low, the public was easily able to identify the jet type and count the engines.

Between 2005 and 2010, numerous skywatchers witnessed sudden changes. First, they witnessed a majority of the jets changing from low altitudes to high altitudes. Second, they witnessed a majority of the jets changing their trail size from long-persistent trails to short, non-persistent trails. Both of these changes typically took place on the same day in any given location.
Content from External Source
Tanner manages to contradict two of his "facts" in consecutive sentences. "Skywatchers" did not possess the technology to accurate gauge the altitude of aircraft until the recent availability of ADSB feeds to the public. The claim of low flying jets spraying is unsupported, and bogus.

The claim that between 2005 and 2010 of jets going from low altitude to high altitude is also unsupported by any facts or observations by pilots.

[Admin: Edited for formatting and posting guidelines]
Last edited by a moderator:


Closed Account
Good god - how many "facts" can someone get wrong in a short bit of writing:

Every Condition is Wrong for Contrail Formation

The formation of condensation trails requires high vacuum,
Content from External Source
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!

cold temperatures, and high humidity, however, the output side of a jet engine contains mostly outside air that has been pushed through the engine by the large ducted fan (The ducted fan is the set of spinning blades that you see when you look at the front of the engine). This high-pressure at the output of the engine is contrary for the formation of condensation trails because pressurized air has the ability to hold much more water in suspension, without condensation.
Content from External Source
Actually this is more-or-less correct - albeit in a pidgin-technical manner - denser air such as that compressed by a turbo fan wil hold more moisture. As long as it remains denser of course....which isn't very long once it leaves the engine!

A fraction of the air that enters the engine is taken in by the turbine engine. This air is mixed with jet fuel (essentially kerosene), combusted, and then exits the engine under very high pressure and high temperature. Condensation formation requires a decrease in ambient air pressure to form, but the output of the turbine is under very high pressure which prohibits the formation of condensation trails.

Physics also tells us that condensation forms when air is cooled, but since the exhaust of the turbine engine within a jet is very hot, condensation formation is - once again - prohibited.
Content from External Source
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!

Furthermore, the ratio of air-to-fuel used in turbofan engines is as high as possible (lots of air but relatively little fuel) so as to keep engines efficient and cost-effective, and this lack of fuel in this ratio results in a lack of water vapor; yet another reason jet turbofans cannot produce condensation trails.
Content from External Source
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!!

In short, the more efficient the engine, the less fuel it uses per unit of air moved, and this renders turbofans incapable of producing condensation trails, unless they use water injection (see section below).
Content from External Source
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.

If you go to an airport and watch jets take off, you will see that they emit a faint trail of black soot, which is typical of burnt jet fuel (kerosene), but you will not see water vapor.
Content from External Source
And as you started with highlighting this bit of gross nonsense it is a good place to sign off :)
Last edited by a moderator:

David Fraser

Senior Member.
I got booted from a site for suggesting a simple test to the water vapour claim. Simply hold an upturned jar over a paraffin burner, or even a candle, and watch what accumulates.

I find it fascinating that people blindly accept this guff. I have to be honest I have difficulties understanding engine mechanics but you can't just make up the principles of chemistry.

Jay Reynolds

Senior Member.
I think Russ Tanner has actually talked himself into believing this. Let me explain. In the big scope of things, he didn't have to do this at all. Less than 10% of his flock understand or even care to try understanding most of what he said. Most of them would have been perfectly fine not knowing anything about the mechanics of contrail formation at all. They haven't for fifteen years, why try to tell them now?

I think that Russ dug himself into a hole with his claim that very few people have ever seen a contrail in their lives. He has either had a crisis of conscience, been confronted about it, or someone in the movement has questioned him about it. In Russ's World, that required some sort of response.
He had to both rationalize the contradiction between his claim and reality, somehow. I believe this may have happened during a call-in when he felt inadequate.

In doing this, he had to contort the facts and use his grandiose imagination to suit the hypothesis, and in his closed mind he has done so, despite the major errors that you have pointed out above. This might actually stick, given that most in his circle of influence are ignorant, uncaring or too intimidated to challenge him.

In Russ's world this might seem to be the end of it. I'm absolutely sure that he has wrapped this up and owns it deeply enough that he probably cannot be said to be deliberately lying. By now, he has personally gone through it dozens of times and by now has talked himself into it. He truly believes it.

In the real world, however, he has just dug himself deeper into the hole and likely has dragged some along with him. There, it is another additional liability, a weakness, an error which easily shows he is bereft of knowledge, short on facts, and unwilling to admit error. Eventually, it will come back to haunt him and anyone who drinks his flavor of kool-aid.

Hama Neggs

Senior Member.
I have repeatedly challenged one of Tanner's steadfast believers as to why they accept what he says about jet engines not producing contrails, but I could get no substantive response. They simply defer to Russ because they believe he is extremely knowledgeable and won't question any pronouncement he has made.

Any challenges made directly to Russ about such things have been ignored or deleted.