Disappearing Contrails

[HairyYellowButt]

A few days ago I watched two aircraft flying large race-track type patterns at about 20 000feet. Both were contrailing and one was leading the other by 2 to 3 miles. The lead aircraft generated a larger contrail for a mile or so and then there was no contrail at all. Both aircraft continued to fly race-track patterns, however, the leader wasn't trailing whilst the second aircraft was. They both appeared to be at the same altitude.

Is it possible to make a contrail disappear? Would making a contrail disappear be that beneficial to you military guys?

I expect what I saw was simply an atmospheric effect. However, it did get me thinking, especially as it was the lead aircraft which wasn't trailing - almost as if the second was the observer.

[FJJP]

The aircraft were at different heights. One was above the 'Mintra' level [where trails start] and the other below. It is also quite common to see an aircraft intermittently trailing, as it flies through air of different relative humidities.

The only way to stop contrailing is to change altitude until the trailing stops.

[BEagle]

Sure that it wasn't just the chemtrail dispenser running out of subjugation agent......??

[The Helpful Stacker]

Sure that it wasn't just the chemtrail dispenser running out of subjugation agent......??
We have you hat in stock Beagle.
http://www.ericisgreat.com/tinfoilhats/chaplinside.jpg
;)

[Pontius Navigator]

Personally I think you are all wrong. It was a practice flight by the new RAF aerobatic team. As we can no longer afford the number of aircraft and pilots for the Red Arrows or the fuel for low level work and there have been numerous complaints about red dye, it was decided to use just two aircraft and inject specially pure distilled water into the slip stream.

The Two Swans, as they will be known, were practising a sequence from the Nut Cracker.

[Confucius]

We have you hat in stock Beagle.
http://www.ericisgreat.com/tinfoilhats/chaplinside.jpg
;)

That's what they issue to E-3 Mission Crew.

[HairyYellowButt]

I also meant to say: they were a pair of Typhoons from Warton flying over the Irish Sea.

[GlosMikeP]

That's what they issue to E-3 Mission Crew.
I thought that was an E-3 mission crewman!:eek:

[stickmonkeytamer]

Dumping fuel, perchance? Oh no, we can't afford to do that...

SMT

[Pontius Navigator]

I also meant to say: they were a pair of Typhoons from Warton flying over the Irish Sea.

You must admit your opening gambit was too good to miss. You were very lucky to get the right answer straight off.



FJJP

Spoil sport.

[wg13_dummy]

Oh FFS not the Chemtrailers again!


I'll bet the older members here on Pprune remember the Chemtrail website chenanigans from about five years ago? Heady, carefree days........

[LowObservable]

Chloro-fluorosulphonic acid, d00d











Dang, now I have to shoot all of you.

[FJJP]

Pontius, no, dammit, I was trying to protect national secrets. I was hoping that the thread would die at that point to avoid just what happened - Beags spilled the beans [again], letting the cat out of the bag about Bliar's subjugation chem weapon.

Never mind - I suppose it would all have come out in the wash when some squealer leaked details to the media...

[Pontius Navigator]

Pontius, no, dammit, I was trying to protect national secrets. ...

Blown it again. Beagle's bit was the plausible cover story now they really will start digging.

Last thing we want is for the press to discover it was the Irish Air Force long range navigation flight.


Then they will be able to calculate the length of the string.

[Melchett01]

Is it possible to make a contrail disappear? Would making a contrail disappear be that beneficial to you military guys?

Here's a scenario for you. You decide you want a new all singing all dancing toy with all the bells and whistles on it. So you spend a few hundred billion developing a brand new fighter that is invisible to everything. Feeling very chuffed with yourself, you strap in and take off, tearing up the sky and M2+ safe in the knowledge that no one can see you.

Until you look in the mirror and see a bloody huge contrail behind you giving away your presenceto every man and his dog without need for a radar! So you light up your cigar (it's your toy with all the bells and whistles and that includes a cigar lighter !) and enjoy your Hamlet moment as the target acquisition radar locks you up and every peasant with a rifle has a pot shot :E

From what I remember from the very dim and distant past of my met modules at uni, contrails are a combined function of engine inefficiencies and meteorological conditions. So until you get a 100% efficient engine, you will always get some contrails if you're above the mintra level due to the water vapour and condensation nucleii in the exhaust gases. Or something like that!

[Brian Abraham]

From Wiki
An aircraft engine's exhaust increases the amount of moisture in the air, which can push the water content of the air past saturation point. This causes condensation to occur, and the contrail to form.

Aviation fuel such as petrol/gasoline (piston engines) or paraffin/kerosene (jet engines) consists primarily of hydrocarbons. When the fuel is burned, the carbon combines with oxygen to form carbon dioxide; the hydrogen also combines with oxygen to form water, which emerges as steam in the exhaust. For every gallon of fuel burned, approximately one gallon of water is produced, in addition to the water already present as humidity in the air used to burn the fuel. At high altitudes this water vapour emerges into a cold environment, (as altitude increases, the atmospheric temperature drops) and the local increase in water vapour density condenses into tiny water droplets and/or desublimates into ice. These millions of tiny water droplets and/or ice crystals form the contrails. The energy drop (and therefore, time and distance) the vapour needs to condense accounts for the contrail forming some way behind the aircraft's engines. The majority of the cloud content comes from water trapped in the surrounding air. At high altitudes, supercooled water vapour requires a trigger to encourage desublimation. The exhaust particles in the aircraft's exhaust act as this trigger, causing the trapped vapor to rapidly turn to ice crystals. Contrails will only occur when the outside air temperature around the aircraft is at or below -57 degrees Celsius.
Also see http://www.epa.gov/OMS/regs/nonroad/aviation/contrails.pdf

[ORAC]

The secret is to sit about 15K above the top of the contrail layer. As well as using your radar you can keep a nice 360 visual scan to see if anyone trying to sneak up on you into Mx range.....

[Pontius Navigator]

The secret is to sit about 15K above the top of the contrail layer. As well as using your radar you can keep a nice 360 visual scan to see if anyone trying to sneak up on you into Mx range.....

I was going to mention something like that but could not find any proof. About 1968 I believe a Vulcan raid at Darwin, flying at about 65k amsl, sneaked in and evaded visual detection because the GCI had no height info (jamming of the height finders) and the RAAF Mirage at 35k, in behind, were looking in the wrong place - the Vulcans were behind the AI cone when the fighters were at the correct firing range.

I looked at the high level temperature profiles for Singapore and, from memory, although there was a temperature inversion above FL540 the temperature was still -70C and contrails should have been persistent.

I am not sure, therefore, why there is an upper limit to the trail height.

[Solid Rust Twotter]

...When the fuel is burned, the carbon combines with oxygen to form carbon dioxide; the hydrogen also combines with oxygen to form water

Carbon Monoxide, surely?:confused: [Pedantic git mode now disabled]

[Pontius Navigator]

The main by-product of combustion of hydro-carbon fuel is indeed water. As stated it is produced at the same quantity of hydro-carbon fuel combusted. In combustion of the fossil fuel the hydrogen component combines with oxygen to produce water, H2O. The carbon content of the fuel combines separately with oxygen molecules (O2) to produce CO2 as well.

Carbon Monoxide is also a by-product of petrol but not of diesel or, AFAIK, of kerosene. The different by-products are a result of the actual composition of each fuel. Petrol, and I guess some of the others, also combine with nitrogen to produce NxOs.

[Solid Rust Twotter]

Many thanks. Learn something every day...:ok:

[teeteringhead]

Without wishing to be a scaremonger, what about the dangers of the Dihydrogen Monoxide (http://www.dhmo.org/) present in the contrails .......;)

[Melchett01]

Without wishing to be a scaremonger, what about the dangers of the Dihydrogen Monoxide present in the contrails

Quite right too Teeteringhead. A little understood killer, responsible for literally milllions of deaths - it should be banned forthwith! It is also one of the most pernicious agents of climate change and global warming - we should all be ashamed of the amounts of DHMO produced.

I think we should start a petition and get Tony Bliar to do one good thing during his reign and lobby the UN to get this evil compound banned.












:p

[Brian Abraham]

Melchett01 and teeteringhead - will you tell them or shall I? We dont want to increase the number of converts as theres not enough seats to go around these days it seems. ;)

[Beeayeate]

It is also one of the most pernicious agents of climate change and global warming - we should all be ashamed of the amounts of DHMO produced.
Quite right. Totally agree. There's enough produced by contrails such that we'll soon be drowning in the stuff. It can be a deadly killer - especially to any good single malt. :ok:


.

[Windbag]

"Never mind - I suppose it would all have come out in the wash when some squealer leaked details to the media..."

FJJP,
so is that what the Tornado was doing???:ugh:

[GlosMikeP]

The main by-product of combustion of hydro-carbon fuel is indeed water. As stated it is produced at the same quantity of hydro-carbon fuel combusted. In combustion of the fossil fuel the hydrogen component combines with oxygen to produce water, H2O. The carbon content of the fuel combines separately with oxygen molecules (O2) to produce CO2 as well.

Carbon Monoxide is also a by-product of petrol but not of diesel or, AFAIK, of kerosene. The different by-products are a result of the actual composition of each fuel. Petrol, and I guess some of the others, also combine with nitrogen to produce NxOs.
What a load of old stoichiometrics!

[Kitbag]

Excellent link to DHMO, will be subscribing to their organisation for the latest e-mail updates from now on, I for one am converted. :ok:

[movadinkampa747]

What a load of old stoichiometrics!

Interesting........did you know that in Stoichiometric coefficients of reactions that each reaction is written in way that all components are in the left side of equal sign i.e.

aA + bB + cC + dD + ... = 0:{

[Pierre Argh]

All this science has me baffled... I do remember a dit about contrails though?

Many years ago I was showing a bunch of elderly visitors around the Air Traffic Control Tower where I worked. I was explaining the local airspace, and pointed out the airways that surrounded us and explained what they were, when an old lady from the back chipped in with, "Oh yes, I see them marking them out with white smoke every morning"

[GlosMikeP]

Interesting........did you know that in Stoichiometric coefficients of reactions that each reaction is written in way that all components are in the left side of equal sign i.e.

aA + bB + cC + dD + ... = 0:{
I was pleased to leave the old 15:1 well behind and carry on depleting the ozone layer. Flame speeds were always interesting though!

[BEagle]

Years ago when the RAF had more aircraft able to reach contrailing level, 'contrail willies' were occasionally created. Errm, 'meat and 2 veg' floating across the sky - which could be seen for miles.....

Reportedly, someone from Leuchars did this - and the offending item floated serenely over Edinburgh one RAFVR weekend in the pre-Duncan Sandys days. Much to the consternation of the chief god-botherer of that fair city who phoned the station and complained.

"No problem",came the reply "we'll sort it out!".

So, a few minutes later, a whole gang of Meteors, Vampires or whatever clambered up to Flight Level nosebleed in line abreast, then charged through the offending item. A few complicated battle formation turns later, they came back through it again at 90 deg to their original track.....

So, if the general public hadn't noticed the willy before, an obviously scrawled out one certainly got their attention.

Harry-the-Staish did not quite see the funny side, I am led to believe!

[GlosMikeP]

Priceless. No sense of humour some people.

[Tartan Giant]

I was interested to see Brian A's statement
Contrails will only occur when the outside air temperature around the aircraft is at or below -57 degrees Celsius.
Does not equate with this website info.
http://asd-www.larc.nasa.gov/GLOBE/resources/activities/appleman_teacher.html
Nice little chart/s.
Cheers
TG

[Pontius Navigator]

I was interested to see Brian A's statement
Does not equate with this website info.
http://asd-www.larc.nasa.gov/GLOBE/resources/activities/appleman_teacher.html
Nice little chart/s.
Cheers
TG

IIRC the Mintra level was based on the height at which a Spitfire would begin trailing. As it was a piston engine with higher water content in the exhaust it trailed at a lower altitude than a jet.

I will dig the AP out Monday.

[mystic_meg]

Wasn't over Liverpool, perchance?
Those b*ggers will nick anything if it's not nailed down:E

[Melchett01]

IIRC the Mintra level was based on the height at which a Spitfire would begin trailing

PN - spot on. At the risk of now having nightmares about hours spent pouring over tephigrams at uni, wondering what the hell was going on .......

The MINTRA line that you get on the tephigrams was (is) indeed based on a Spit and was based on condensation with respect to ice. Although it uses a Spit it is still useful today because it represents the limiting temp above which contails are unlikely to be formed by anything. In practice that means you are unlikely to get contrails until the ambient temp is a few degrees lower than the MINTRA value given on the tephigrams.

Using a tephigram, if you draw 2 lines on it that are 11 and 14 deg C colder than the MINTRA critical temp (Tc) at any level and then plot a representative point at any level, then the chances of contrails are as follows:

T > (Tc-11) = contrails unlikely
(Tc-11)>T>(Tc-14) = short non-persistent contrails
T<(Tc-14) = long persistent contrails

Persistent trails are more likely with hight humidity and you are more likely to get them if you fly at/ around the same level as layers of cirriform clouds.

The link given above goes to the Appleman chart which is a graphical way of predicting contrails including the effects of relative humidity (RH). Four lines are the 4 lines show the Tc for jet ac at different values of RH. As long as the tem lies to the left of the O% RH, you will get contrails, but if it lies to the right of the 100% RH line, all things being equal you won't get anything.

And on that note, my head hurts, I'm having horrible horrible flashbacks and am off to lie down in a darkened room with a good stiff drink.

Class dismissed!

[Pontius Navigator]

Melchett, did you do all that off the top of your head?

If so, have an A-cat, or you're a met man in which case is it going to be fine at 1100 on Sunday?

[Melchett01]

PN

I am neither an A-Cat (fat chance!) nor a met man, although I do have some not inconsiderable experience of the meteorological variety from my time at uni.

It's amazing what rubbish you can dig out from the back of your mind from years before; now a days I struggle to remember what happened at the start of a film 90 minutes later, but I was sure I we had covered this sort of thing as part of the course. A bit of rummaging through my old notes later ... and hey presto.

Sorry if I have just ruined any impression of being an aeronautical genius that you may have had! As for Sunday, it should be ok if you're in the midlands - east of the country, bit cloudy up the west side of England, Wales and east Scotland and a bit rainy up over the west of Scotland (shock horror). Although I must put a Michael Fish sized caveat on that ...... it's dark and I can't see anything out of the window which is my preferred method of forecasting !

[movadinkampa747]

Do tephigrams still have the mintra line on them? From what I understand this
is a hangover from the wartime when aircraft did not wish to make themselves too visible for obvious reasons.

[Melchett01]

Do tephigrams still have the mintra line on them? From what I understand this is a hangover from the wartime when aircraft did not wish to make themselves too visible for obvious reasons

It's been a long time since I've dabbled into the murky and head scratching world of the tephigram, so things may well have changed. But from what I understood, it was a bit of a UK thing for precisely that reason and if you looked at tephigrams from other countries they may not have the MINTRA line on them.

That said, it's probably all a bit irrelavant in practice these days .... some tefal-head in the Met Office probably punches a few keys on his super computer and the result pops up on the screen!

[movadinkampa747]

You could be right. I don't suppose the airlines are concerned with the Mintra line

[Brian Abraham]

Tartan Giant - re -57C. That'll learn me to cut and paste from Wiki. Since the standard atmos only gets to -56.5 would mean you never get a trail. Right? :=

[Pontius Navigator]

That'll learn me to cut and paste from Wiki. Since the standard atmos only gets to -56.5

And that is another can of worms. I needed the definition of the standard atmosphere. I did a Google and found several all subtly different. So standard, yes, but which standard and I am not including ICAN.

Dare to be different:

http://www.pdas.com/atmos.htm

[GlosMikeP]

And that is another can of worms. I needed the definition of the standard atmosphere. I did a Google and found several all subtly different. So standard, yes, but which standard and I am not including ICAN.
For aeronautical engineering when I were a lad it was 1013.25mb at 15 Celcius at sea level (per barometric ISA for altimeters), lapse rate .0065C per m (1.9812 C per 1000ft).

I'd write the equation but it's not easily transposed into text to put here. However.....

In essence the equation of state is dependent upon starting pressure that is multiplied by a temperature variable that is raised to the power determined by combination of ((gravity/Universal Gas Constant xLapse Rate) -1).

You see why I didn't write the whole equation!:eek:

[Pontius Navigator]

1013.25mb at 15 Celcius

'twere centigrade in my day.

[Brian Abraham]

There are a great many different definitions of the standard atmosphere reference conditions currently being used.The International Organization for Standardization (ISO), the U.S. Environmental Protection Agency (EPA) and National Institute of Standards and Technology (NIST) each have more than one definition of standard reference conditions in their various standards and regulations.

The following organisations have their own standards and of course aviation uses the ICAO model.
International Union of Pure and Applied Chemistry
National Institute of Standards and Technology
ICAO's International Standard Atmosphere
International Organization for Standardization
European Environment Agency
Electricity and Gas Inspection Act (of Canada)
U.S. Environmental Protection Agency
Standard Ambient Pressure and Temperature
Compressed Air and Gas Institute
Society of Petroleum Engineers
U.S. Occupational Safety and Health Administration
California's South Coast Air Quality Control District
Organization of Petroleum Exporting Countries
U.S. Energy Information Administration
U.S. Army's Standard Metro (used in ballistics)

1976 ICAO International Standard Atmosphere.

At sea-level on a standard day:

the temperature, T_0 = 59°F = 15°C = 288.15°K (°C=Celsius °K=Kelvin,
T°K=T°C+273.15)
the pressure, P_0 = 29.92126 "Hg = 1013.250 mB = 2116.2166 lbs/ft^2
= 760.0 mmHg = 101325.0 Pa = 14.69595 psi = 1.0 atm
the air density, rho_0 = 1.2250 kg/m^3 = 0.002376892 slugs/ft^3
The standard lapse rate is T_r= 0.0065°C/m = .0019812°C/ft below the tropopause h_Tr= 11.0km= 36089.24ft

Above the tropopause, standard temperature is T_Tr= -56.5°C= 216.65°K (up to an altitude of 20km) Standard temperature at altitude h is thus given by:

T_s= T_0- T_r*h (h < h_Tr)
= T_Tr (h > h_Tr)
= 15-.0019812*h(ft) °C (h < 36089.24ft)

[Pontius Navigator]

Brian, thank you for that useful summary. I shall print it for future reference.

On an OU course the figures they used on a supposedly academic course bore no resemblance to any of the above.

They also, helpfully, quoted metic and imperial measurements. Unfortunately the only thing consistent was their inaccuracy.

[GlosMikeP]

'twere centigrade in my day.
Me too but K for calculations.

[Brian Abraham]

Pontius - http://williams.best.vwh.net/avform.htm may be of interest to you. Have a print out on the bookshelf and gets use. (Aviation Formulary)

[Pontius Navigator]

Brian,

Thank you for that. Keep the cogs from going rusty.

[Pierre Argh]

Ref. earlier post regarding Spitifre's not trailing to avoid detection. It's been a while since I sat in on a FW Pre-sortie brief, but Sea Harrier Squadrons onboard Invincible would brief the levels of Persistent Contrails for exactly this reason... stealth.

[Pontius Navigator]

Pierre,

Standard on most types actually. On exceptional days you could trail quite low down so even a Nimrod at the top if its patrol area could trail, albeit usually non-persistent. Last thing you needed was delicate tracery in the sky telling your target "Here I am".

[BEagle]

"Standard on most types actually."

Except, presumably, the dear old Shacklebomber?

[Pontius Navigator]

"Standard on most types actually."
Except, presumably, the dear old Shacklebomber?

Oddly no.

We especially briefed on the Shacklebomber so that we did not send our own interceptors into the trailing area.

Also, when we were playing as a Bear (joke at 150kts) but at FL210 it was useful as well.

[BEagle]

But weren't the Shacklebomber's trails mainly of burnt oil and the odd bit of red hot ironmongery ejected from ailing Griffons?

[Pontius Navigator]

But weren't the Shacklebomber's trails mainly of burnt oil and the odd bit of red hot ironmongery ejected from ailing Griffons?

:ouch:

At the risk of serious thread drift, one day Mrs PN received a phone call to say I would not be back that night. "I know" she said. "????, how did you know?" "PN took his civvies in with him today." "How did he know?" :}

One week we had 3 (maybe 4 I was on leave) into Waddo for the week, each rescue aircraft went sick.

By Friday they were all home.

On the following Monday we landed at Waddo. By Friday all 3 Shacks were serviceable once again.

[Shackman]

Originally Posted by BEagle
"Standard on most types actually."
Except, presumably, the dear old Shacklebomber?
I can remember 2 or 3 occasions on both MR and AEW when we went high enough to get 'proper' trails - very impressive to watch from the astrodome. However it was just a b*****ation factor for half the crew who had to stop smoking once we went above 10000ft and on to oxygen!

[GlosMikeP]

OK, so who has the prize for the highest Shacklebomber?

I bid FL270

[Pontius Navigator]

GMP,

Our attempt stalled when a Spam hit the oxygen tube instead of the elsan.

For the unitiated, the oxygen tube was stowed securely in a clip and is about 3/4 in diameter. It was next to the chemical toilet 'flush' with racasan fluid sloshing around with its characteristic square wave pattern.

How could he miss . . .

6 hours rations for 15 men for about 8 of us to get through in 2 hours. T-bone steak for tea chaps? Come to think of it we could have used girlies on the Shack down in the galley . . .

[GlosMikeP]

That was a stroke of bad luck.

One of our other attempts at the World of Shacks Altitude Record ended when sparks were seen coming from between the props on one of the engines....shutdown followed in short order. About 1/2 bolt left between us and an overspeed!

[Wader2]

And the Shack World High Speed record?

I remember a Shack doing 300 kts. Very impressive. They scraped it when they got it back to UK; at least I hope they did.

It was doing the explosive drogue deployed back pack trial. Eventually commonsense prevailed. How could you have peole warning around an aircraft with a parachute pack on and likely to fire a bolt through the roof, or worse.

[GlosMikeP]

And the Shack World High Speed record?

I remember a Shack doing 300 kts. Very impressive. They scraped it when they got it back to UK; at least I hope they did...

Can't remember for certain and wouldn't swear to it but I think we once got about 300-310kts TAS above 20,000ft. Full chat, everyone leaning out blowing backwards. No trails.

[GPMG]

If I remember rightly 'Bomber' by Len Deighton has a very good bit about avoiding contrails at the start of the book. It is regarding a Photo Recon Spit keeping below the Mintra to avoid alerting the 'target for tonight'.