contrails

[wayoutwest]

hi everybody.not sure if this is the right place for this thread but the moderaters do a great job.as bowling all afternoon with jets flying from eastern oz to the west and all with long contrails have been out side with dog in dark with jets flying overhead but no contrails am sure sombody will be able to explain. many thanks mike.:ok:

[John Farley]

The formation of contrails (or not) is associated with something called the Mintra Level.

Google is your friend

[K.Whyjelly]

Ahh, MINTRA...............Minimum Trail Altitude. Many a happy hour spent poring over tephigrams!!! Very useful to military crews who don't want to be aquired visually.

To aid the forecasting of condensation trails emitted (or not) from high-flying aircraft, a line marking the critical temperatures (altitude dependent), above which trails are not possible, is marked on a tephigram. The values are approximately -24degC at 1000 hPa (i.e. roughly sea-level), -39degC at 250 hPa (34000ft / 10.4 km) and about -45degC at 130 hPa (50000feet/15km). Using the MINTRA line (as it has come to be called - based on experiments by JK Bannon during World War II with the piston-engined Spitfire), a forecaster will mark two further lines on a tephigram: MINTRA minus 11degC (A) and MINTRA minus 14degC (B). If the ambient temperature (from the tephigram air temperature plot) lies between (A) and (B), then short, non-persistent trails are possible. If colder than (B), then long, persistent trails should be expected. However, some note should be paid to the relative humidity - high values will tip the balance to trailing (or longer/persistent trails.), even with air temperatures warmer than (A); ultra-low rh% will reduce the risk of condensation trails - the design of engines will have an effect as well. In broad terms, warm Tropical Maritime airmasses with a high but cold tropopause will result in a good deal of trailing, whilst cold, polar air-masses with a low, relatively warm tropopause will seldom give rise to significant aircraft trails.

[Reverserbucket]

have been out side with dog in dark with jets flying overhead but no contrails

Perhaps becuase it was dark? :}

[pasir]

I can still recollect viewing my first 'con' trails - dozens of them and dogfights in the clear blue cavok skies above Croydon Airport 1940 - and the resulting tiny white parachutes seeming to take ages on descent probably to alight somewhere over Kenley.

[chevvron]

Then there was a Farnborough display in the late '50s (I think); from my home in Bucks, about 50 contrails appeared to the south as a mass V -bomber 'raid' was demonstrated.

[Yellow Sun]

In June 1972 I participated in Exercise Capricorn. Although we were not to know it at the time, this was the last occasion on which almost all of the "front line" RAF in the UK was exercised together. Our crew was dispersed from Waddington to Wyton and after about 30 hours at readiness 15 (RS15) we were brought up to RS05 at 0100 in the morning. We held RS05 for about 90 minutes before all the Bomb Lists were simultaneously scrambled. Note that at this time we were not aware of the scale of the exercise. We were that last of the 4 Vulcans at Wyton and shortly after we became airborne Wyton Tower instructed all 4 aircraft to call Eastern Radar. We checked in in turn with Eastern and then the controller asked whether all 4 aircraft were VMC? . When we confirmed this (It was a beautiful clear morning) he responded:

"I assume that your tracks have been deconflicted, continue as briefed"

This was our first clue that we were taking part in something unusual.

There was a contrail layer that morning starting in the upper 20s and extending to the mid 30s. As we climbed, trails started appearing all over the sky and the size of the force getting airborne became apparent, all the strike aircraft, tankers, air defenders, both RAF and USAF seemed to be out that morning and all heading East!

I reckon that as the trails appeared there must have been 250 to 300 visible and those were only the ones I could see. I recall thinking as we headed for the GO/NO GO line that I hoped that someone had given the other side a bit of warning that this was only an exercise and we were only practicing for Armageddon, it wasn't the real thing!

YS

[Warmtoast]

1957 Farnborough Air Show featured 90 Valiants and Canberras of Bomber Command contrailing at 35,000 ft as here:

http://i145.photobucket.com/albums/r231/thawes/Contrails.jpg

Original photo appeared in 13th September 1957 Flight Magazine and can be seen here:

bomber command | pdf archive | aviation traders | 1957 | 1341 | Flight Archive (http://www.flightglobal.com/pdfarchive/view/1957/1957%20-%201341.html)

As quoted in the article:


....After civil transports, it was the turn of the R.A.F., and today there was something splendidly new as a background to the formations. Approaching high from the east were the contrails of the first dozen or more of over 90 Valiants and Canberras of Bomber Command which, flying at 35,000ft, were using Farnborough as a “target for operational exercises.” While the C.F.S. Provosts manoeuvred with precision; while the Javelins’ noise was felt in our stomachs; and while the glistening black fish, roundel-eyed, that were the incomparable Hunters of 111, swam in rock steady shoal around the lower sky, the high trails formed a fantastic backdrop. To the east, a tangle of thin white threads; above and to the west, a strong sunlit pattern of bold, white brush strokes on a glaring blue canvas.
This was display spectacle unsurpassed for many years. It is much to the credit of the remaining pilots and aircraft that no sense of anti-climax followed....


I was abroad in the Far East in 1957 so missed the 1957 show, however I'm fairly sure I DID see a similar contrailing Bomber Command demo at Farnborough, but cannot recall the date.