It's Boyle's Law I believe - to do with gases, volumes, pressures and
temperatures. As a gas reduces in temperature for a given pressure, it is
less able to hold the same mass of water. However, I failed my Physics 'O'
Level at school (taken at 15 years old for our non-Brit friends) so all I
know is from Aerodynamics and Principles of Flight classes for pilot
training.
Therefore, if you reduce the temperature of saturated air, it will condense
some of its moisture (that's why cloud starts at a certain altitude for a
given air mass). Also if you reduce the pressure of a gas, it will reduce
in temperature (that's why cloud forms as well, since air reduces in
temperature with altitude/pressure - "adiabatic lapse in temperature".
The air flowing over a wing is reduced in pressure because it speeds up to
get to the trailing edge of the wing at the same time as the air flowing
under the wing - which has less distance to travel. This is how lift forms.
Since the air has reduced in pressure, it also cools. If that air is
saturated it will condense some of its moisture in a visible form. Wing tip
vortices are formed in humid conditions because the airflow is out towards
the wingtip. The greater the lift (drop in pressure over the wing) for a
given air condition, the greater the likelihood of visible moisture
appearing.
However, the "anomaly" over the wing at altitude was probably to do with the
formation of a Mach wave, since the air is much drier (holds less moisture)
at cruising altitudes.
The Tornado would give off wingtip vortices in many different conditions.
The most interesting air phenomenon for me while flying was in a Hawker
Hunter in training from Brawdy in South Wales. Traditionally the last trip
on the weapons conversion course ended in an (illegal) flyby at the home
airfield at high speed (up to 600 knots). I chickened out at 525 knots
(perhaps just as well, since I managed to stay in the RAF for the next 17
years), but there was still a little wisp of vapur dancing about a small
imperfection in the canopy above my head. It quite distracted me for a few
minutes until I realised what it was ;-).
Regards
Chris
--
><> Chris Barker
mailto:cmib@xxxxxxxxxxxxxxx
----------
>From: Acer V <siddim01@xxxxxxxxxxxxxxx>
>To: "'olympus@xxxxxxxxxxxxxxx'" <olympus@xxxxxxxxxxxxxxx>
>Subject: Re: OT!! RE: [OM] Notes on the road
>Date: Wed29 Dec 1999 21:25
>
> Could it also be water vaporization? Above the wing, air pressure is
> lower, so water "boils" at a lower temp, etc. Did that make sense? I've
> seen these "trails" lots of time and enjoyed the sight as well. If I
> recall, most of them ocurred when descending thru cloud layers for landing
> approach. Anyone?
>
> /AV
> --
> email access may be spotty as Student is upgraded/debugged over holidays;
> webpage under re-organization;
> "We apologize for the inconvenience."
> --Douglas Adams in _The Hitch Hiker's Guide To The Galaxy_
>
>
> < This message was delivered via the Olympus Mailing List >
> < For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
> < Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
>
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|