So I’m watching a jet taking off at a distance where all I can tell is that its a shiny dot, and its ascending at about 30 deg. I don’t know the crow-fly distance to JFK or La Guardia airports, but can get them.
All of this is to say I don’t know the height of the plane, nor how much sky is visible, but perhaps someone could do the trig if needed.
There was absolutely no breeze at ground level, and it was a cool dry day. (My friend said that it’s always calmer at altitude than at ground. This sounds like baloney to me.)
What’s the longest possible contrail given those conditions? My friend and I have a bet.
And, what’s the longest contrail possible at all, no matter what kind of jet? In what atmospheric conditions?
Contrails are high altitude phenomena. For all practical purposes, they only form in cruise flight. But … there are really three questions here:
A) “For how much distance could an airplane produce a contrail?”
and
B) “How long could the stripe in the sky be?”
and
C) “How long a stripe could I possibly see from a fixed spot on the ground?”
For A) it could be from near top of climb to near top of descent, potentially over 10 thousand miles for a very long range flight. But practically speaking the conditions for formation are common, but not universal. An airplane going thousands of miles would be all but certain to move through an area where contrails don’t form.
For B) we need to consider that if conditions are poor for contrail survival, the trail would dissipate shortly behind the aircraft. You often see a dot dragging a 1/2 mile long streamer across the sky. He might be *making *a contrail for thousands of miles, but it’s dissipating 4 seconds later 1/2 mile behind him. Is that a thousand mile contrail or a 1/2 mile contrail? Either interpretation is plausible.
I don’t have the quick trig handy to answer question C, but I’m going to SWAG that if you had perfecty clear air and an unobstructed horizon all around you and a contrail that extended from horizon to overhead to the opposite horizon it’d be about 300 miles long.
Other than immediately after takeoff, airliners ascend at more like 3-10 degrees than 30. 15 would be an absolute max, and only achieved in the first mile or two after liftoff.
Winds at airliner cruise altitudes are almost always stronger than winds on the surface. 30-80 knots are 100% typical, and 100-130 knots are not rare. But … as you ascend into the stratosphere the winds eventually drop to near zero worldwide. That altitude is above about 95% of airliner traffic though. So your friend may have gotten the right idea applied to the wrong situation.
Weather conditions at the ground have essentially no effect on contrail formation. They do have an effect on how well you can see them. i.e. there could be horizon-to-horizon contrails up there but if you’re sitting under a drizzling overcast you won’t see a thing.
I bet the OP will need to clarify with his friend what they’re really betting over.
I did a quick crude calc for an airplane at 7 miles = 37,000 ft altitude. Got that the contrail intercepts the visible horizon at ~235 miles distance. So from horizon to overhead to horizon that’s about 470 miles total. If you were on a mountain peak or in another airplane that number gets bigger.
From orbit you could conceivably see one that encompasses just shy of a complete hemisphere; about 12,000 miles.