Vapour trails

Hello,

Question from a complete landlubber.

I work outdoors beneath the flightpath to Edinburgh Airport.

I take it that vapour trails are the condensed water contained in the
air ingested by the engines. My question is, how much air does an engine
ingest at cruise? How would you visualise that amount of air?

Yours in amazement at how you stay aloft,

Michael

In article ,
Michael Calwell wrote:

Hello,

Question from a complete landlubber.

I work outdoors beneath the flightpath to Edinburgh Airport.

I take it that vapour trails are the condensed water contained in the
air ingested by the engines. My question is, how much air does an engine
ingest at cruise? How would you visualise that amount of air?

Yours in amazement at how you stay aloft,

Michael


Vapor trails are also the condensed ice crystals resulting from just the
movement of the plane through the air. On a humid day, I can pull
contrails off my prop tips.

"Michael Calwell" wrote in message
...
Hello,

Question from a complete landlubber.

I work outdoors beneath the flightpath to Edinburgh Airport.

I take it that vapour trails are the condensed water contained in the
air ingested by the engines. My question is, how much air does an engine
ingest at cruise? How would you visualise that amount of air?

Yours in amazement at how you stay aloft,

Michael

It is not the vapor from the air you are seeing, it is the water that is
produced as a byproduct of burning hydrocarbons.

Ever see water dripping from your car tailpipe, especially in the morning
when you start it up? Water is being produced, and being condensed on the
cold sides of the tailpipe, then it drips out. When the tailpipe gets
warm, the water stays invisible, so you don't see clouds unless the outside
temperature gets very very cold, then you get clouds coming from the back of
the car, as the result of the exhaust cooling rapidly, and the vapor in
exhaust condenses to become visible.

This is similar to what is happening when you see contrails. They almost
always are very high, so the water vapor condenses and then freezes into ice
crystals almost instantly, so then it is harder for the water to
re-evaporate into the surrounding air. This is the reason con trails are
visible for a long time after the aircraft passes by.

The vapor that you see off the tips of props, or from the topside of fighter
jet wings when they are pulling high G-forces are from the pressure in the
air being reduced very quickly, which causes the water vapor to become
visible for an instant, then disappearing just as quickly when the pressure
is returned back to normal.

As far as the amount of air being passed through an engine, for a
reciprocating engine, the amount is much smaller than a jet engine. Gallons
per second for a piston engine, and hundreds of gallons for a jet engine?
Something like that.

I hope this has helped.
--
Jim in NC

On Sat, 11 Dec 2004 20:42:05 +0000, Michael Calwell
wrote in
::

I work outdoors beneath the flightpath to Edinburgh Airport.

I take it that vapour trails are the condensed water contained in the
air ingested by the engines. My question is, how much air does an engine
ingest at cruise? How would you visualise that amount of air?

If I recall correctly, as a result of the ban on flight over the US
following the 9/11 terrorist attack, there was a measurable
temperature rise attributed to the reduction in airliner contrails.

Yahoo yielded this:
http://p211.ezboard.com/fchemtrailss...picID=75.topic

"Larry Dighera" wrote

If I recall correctly, as a result of the ban on flight over the US
following the 9/11 terrorist attack, there was a measurable
temperature rise attributed to the reduction in airliner contrails.

Yahoo yielded this:

http://p211.ezboard.com/fchemtrailss...picID=75.topic

I was unable to find where the link talked about that in a reasonable amount
of time, but I gotta say.....

Yeah, right!!! :-)
--
Jim in NC

As far as the amount of air being passed through an engine, for a
reciprocating engine, the amount is much smaller than a jet engine. Gallons
per second for a piston engine, and hundreds of gallons for a jet engine?
Something like that.

Let me see..... The fuel-air mixture for a piston engine is about 14
pounds of air per pound of avgas, is it not? Would it be about the
same for jet fuel?

How "big" a pound of air is depends on pressure and temperature
(Boyles' and Charles' Laws, if I recall correctly), but I can't even
guess how big a box it would take to hold a pound of air at STP.
Perhaps someone else can. I guess any good chemist could do it.

vince norris

"vincent p. norris" wrote in message
The fuel-air mixture for a piston engine is about 14
pounds of air per pound of avgas, is it not? Would it be about the
same for jet fuel?

Jet fuel averages 6.7 pounds per gallon with more BTUs, so the
stoichiometric ratio is slightly different. Much of the air ingested by a
jet engine is used for cooling, not for burning. Do we include this air as
being ingested? Do we include the fan's cold stream as being ingested?

D.

"Michael Calwell" wrote in message
My question is, how much air does an engine
ingest at cruise? How would you visualise that amount of air?

The smaller jet engines are rated for 2000 pounds of thrust. The largest are
rated around 100,000 pounds of thrust. For every action (forcing air through
a jet engine), there is a reaction (thrust). The best visual I know of for
this is to watch, hear, and feel a B-777 do a full-power engine run. It's
awesome.

D.

Jets use something like 100% "excess air" in their combustion process,
unlike piston engines. Much of this air is used for internal engine cooling
and some is used as "bleed air" for cabin pressurization, de-icing, etc.

Rod
"vincent p. norris" wrote in message
...
As far as the amount of air being passed through an engine, for a
reciprocating engine, the amount is much smaller than a jet engine.
Gallons
per second for a piston engine, and hundreds of gallons for a jet engine?
Something like that.

Let me see..... The fuel-air mixture for a piston engine is about 14
pounds of air per pound of avgas, is it not? Would it be about the
same for jet fuel?

How "big" a pound of air is depends on pressure and temperature
(Boyles' and Charles' Laws, if I recall correctly), but I can't even
guess how big a box it would take to hold a pound of air at STP.
Perhaps someone else can. I guess any good chemist could do it.

vince norris

On Sat, 11 Dec 2004 19:01:04 -0500, "Morgans"
wrote in ::

I was unable to find where the link talked about that...


Absence of contrails increases diurnal temperature range

Clouds formed by the water vapor in the exhaust from jet planes have a
small but significant effect on daily temperatures, a new study
confirms. The grounding of commercial flights for three days after
last September's terrorist attacks in the United States gave David
Travis at the University of Wisconsin-Whitewater and colleagues a
chance they never thought they'd have: to study the true impact that
contrails from jet engines have on our climate1

Despite a wealth of experiments, it had been virtually impossible to
gauge the effect of contrails because air traffic, particularly over
regions such as Europe and North America, never stopped. Until 11
September 2001, that is. Contrails left high in the atmosphere spread
out into cirrus-like clouds under the right atmospheric conditions.
Natural cirrus clouds - thin layers of wispy water vapor that often
resemble fish scales - trap heat being reflected from the ground and,
to a lesser extent, reflect some of the Sun's rays.

Travis's team compared the average daily high and low temperatures
over North America from 11 to 14 September 2001, with climatic records
from 1977 to 2000, matching the weather over those three days with
similar weather in September from historical records.
They found that the difference between daily high and nightly low
temperatures in the absence of contrails was more than 1 oC greater
than in the presence of contrails. Comparing the three-day grounding
period with the three days immediately before and after, the impact
was even larger - about 1.8 oC.

The researchers suggest that in regions with crowded skies, contrails
work just like artificial cirrus clouds, preventing days from getting
too hot by reflecting the Sun's rays, and keeping nights warmer by
trapping the Earth's heat. Averaged over the globe, which is largely
free of air traffic, the effect is negligible. "But locally, contrails
are equally as significant as greenhouse gases," says Carleton.

The discovery is important, "especially when you consider that air
traffic is expected to increase at about five per cent a year". But
making use of the information by incorporating it into climate models,
for example, will be difficult. Little is known about what conditions
lead to contrail formation, how long they last, and whether they
affect more than just temperature.

References

1Travis, D. J., Carleton, A. M & Lauritsen, R. G. Contrails reduce
daily temperature range. Nature, 418, 601, (2002).