Jack Harrison wrote:
"Michael Mcneil" wrote in message
news:9009dc8b5fe10d00759c8646af9396ec.45219@mygate .mailgate.org...
No, it's not about the mess a £4 like Spencer Hines is making on
s.m.n.

Does anyone on here know the diameter of condensation trails of
aircraft?

How do they vary with size of plane, height, humidity and speed? If
a
rough correspondence to the wing diameter could be given, that
would be
enough for me to gauge it.


I am a retired airline pilot. I do have to say that I could never of
course
see my own contrails. The nearest I got to seeing my own was as
shadows on
the ground or on cloud below me. But I did plenty of contrails made
by
other aircraft.



The trail is initially produced some distance (circa a few tens to a
hundred
metres) behind the engines. It is the engines that provides the
hygroscopic
nuclei on which the condensation can occur.



Then other factors come into play. All aircraft produces vortices
from the
wing tips. These affect the contrail and result in the swirling
pattern
that can often be seen when close. From the ground, this rotation is
hard
to observe (try binoculars) so tends to show itself as a serrated
pattern.

I've noticed when sitting in a windowseat by the wing on a plane, that
what look like mini-contrails emanate backwards from the wing. Smoke
from the engines, or is this the "vortices"?

Often on a clear day, when looking up at a plane with a contrail from
the ground, I can spot the gap between the plane and the start of the
trail.






The next step depends on numerous factors. Often in very dry air,
the trail
quickly dissipates - it appears as a very short trail, often looking
like a
needle with an eye (the eye being the divided trail from the pair or
the
four engines). But when conditions are just right, the injection of
these
condensation nuclei can be the trigger for yet more condensation to
occur
and the trail spreads laterally and becomes persistent. It can be
many
times wider than the aircraft that initially produced it and can last
for a
very long time.

I've noticed at least 3 types of contrail from the ground. One the
"needle" you mention, another a longer, wider version of it where you
can see the division in the middle, this persists and widens for
several minutes then vanishes, and one that refuses to dissipate, just
spreads out and ends up turning into what looks like cirrostratus. I've
seen a lot of the latter type just lately- this is the type I think
might be meddling with the weather (though I shan't go into that here).


Edmund