Vapour trails

"Ash Wyllie" wrote in message
...

Add a touch of quinine to your CO2 + DHMO + ethanol mix, and you have a
good
anti-malarial compound. Now, what did I do with that mosquito...

Hmmmm, first I think you need to compound a small amount of liquidus DHMO
and ethanol with the steam distillate of Dipterocarpus cornutus. The result
is less volatile and enhances the effect of the quinine. The result, when
ingested after having been passed over "en solidus" DHMO will cause
impairment of vision in persons with low tolerance. Supporting your claim
above, I have not found one case history of malaria involved with this
treatment. Hyperingestion, on the other hand, has led to nausea and
vomiting, combined with disorentation and cardiovascular depression.

So, lets look at this factually...

In recent history, atmospheric CO2 levels have been at their lowest levels
in the entire history of the planet. It has been as low as about 150 ppm.
In recent history, it has been steadily climbing toward 300 ppm, presumably
due to human activity, but there has been a fair amount of volcanic activity
in recent years which also contributes large amounts of CO2.

Given the fact that during the age of the dinosaurs, CO2 levels were up
around 1,000 to 2,000 ppm, this recent CO2 rise is rather insignificant by
comparison.

Also, historical global temperature data shows that the earth has a
bi-stable average temperature (bouncing between 12C and 22C). The average
temperature of the earth is currently at the low bi-stable point, but
throughout most of the earths history, the temperature was at the high
bistable point. The last time that the earth had the current combination of
low CO2 and low average temperature was about 300 million years ago.

There is a nice historical summary graph that shows both atmospheric CO2
levels and average temperature that is available at
http://www.clearlight.com/~mhieb/WVF...s/image277.gif

Dean

Dean Wilkinson wrote:
So, lets look at this factually...

In recent history, atmospheric CO2 levels have been at their lowest levels
in the entire history of the planet.

You have no way of knowing that. I can just see the caveman out there
with his CO2 test kit.....


It has been as low as about 150 ppm.
In recent history, it has been steadily climbing toward 300 ppm, presumably
due to human activity, but there has been a fair amount of volcanic activity
in recent years which also contributes large amounts of CO2.

It's a guess. We only have maybe 150 years of temp data and much less
years of other data. In the history of the planet that is zip.



Also, historical global temperature data shows that the earth has a
bi-stable average temperature (bouncing between 12C and 22C). The average
temperature of the earth is currently at the low bi-stable point, but
throughout most of the earths history, the temperature was at the high
bistable point. The last time that the earth had the current combination of
low CO2 and low average temperature was about 300 million years ago.

The earth has cooled and warmed constantly. Glaciers come and go.
Humans couldn't change that if they wanted.

"Newps" wrote in message
...


Dean Wilkinson wrote:
So, lets look at this factually...

In recent history, atmospheric CO2 levels have been at their lowest
levels
in the entire history of the planet.

You have no way of knowing that. I can just see the caveman out there
with his CO2 test kit.....


Actually, we do know this with a fair degree of confidence. Antarctica has
trapped bubbles of air going way back in its ice that has been core sampled.
There are other geologic indicators that they use to determine the levels as
well for prehistoric data.

It has been as low as about 150 ppm.
In recent history, it has been steadily climbing toward 300 ppm,
presumably
due to human activity, but there has been a fair amount of volcanic
activity
in recent years which also contributes large amounts of CO2.

It's a guess. We only have maybe 150 years of temp data and much less
years of other data. In the history of the planet that is zip.

There are other geological records that are used to determine temperature
besides direct measurements.



Also, historical global temperature data shows that the earth has a
bi-stable average temperature (bouncing between 12C and 22C). The
average
temperature of the earth is currently at the low bi-stable point, but
throughout most of the earths history, the temperature was at the high
bistable point. The last time that the earth had the current
combination of
low CO2 and low average temperature was about 300 million years ago.

The earth has cooled and warmed constantly. Glaciers come and go.
Humans couldn't change that if they wanted.

On Mon, 13 Dec 2004 at 03:20:38 in message
, Capt.Doug
wrote:

No, less air, because the density of the ambient air is less as altitude
rises. Less air in the front means less air out the back (though the
pressure ratio can be the same). Jet engines produce less thrust at
altitude. There is less cooling air which means that maximum exhaust
temperature is reached at a lower thrust. The efficiency gains come from the
forward speed of the engine (sort of a ram effect) and the lower aerodynamic
drag at altitude (higher true airspeed).

This interests me as it is often said, the idea of less drag at
altitude presumably comes from the idea that drag depends on air
density? Which of course it does. However if you fly for maximum range
than you fly close to maximum lift/drag ratio which depends only on
getting the correct alpha (ignoring compressibility effects).

So since lift = weight, drag depends on weight and it reduces as fuel is
burned. The aircraft flies faster to create the lift at altitude but the
drag is presumably almost the same?

Am I wrong?
--
David CL Francis

Dean Wilkinson wrote:


You have no way of knowing that. I can just see the caveman out there
with his CO2 test kit.....



Actually, we do know this with a fair degree of confidence. Antarctica has
trapped bubbles of air going way back in its ice that has been core sampled.

Would that be before, during or after the volcanic eruption? While
interesting, trapped air doesn't tell us much of anything. We can't
even affix a date to within a reasonable amount of time.




There are other geological records that are used to determine temperature
besides direct measurements.


Yes, but today we know what the temp is every hour of every day.
Looking at rocks we only have generalities. It was hot during this
period of years, cold during this period, etc. Now we're trying to say
that because the temp has gone up 1 degree in the last 50 years we have
a problem.

"David CL Francis" wrote in message
...
[...]
So since lift = weight, drag depends on weight and it reduces as fuel is
burned. The aircraft flies faster to create the lift at altitude but the
drag is presumably almost the same?

Am I wrong?

Yes.

The drag is actually less. The indicated airspeed is a good way of seeing
how the airframe is currently being affected by the ambient air at whatever
density it is. Regardless of the air's actual density, the 1G stall speed
is always the same, and for constant engine power, cruise speed remains
remarkably constant (I'm not sure whether it is actually constant, but
having flown a turbocharged engine at altitudes up to 18,000' and noting an
airspeed drop only higher than 16,000', the turbocharger's "critical
altitude", I am confident in saying that, when measured by indicated
airspeed, there's practically no change as long as power is kept constant).

As altitude goes up and indicated airspeed remains constant, TRUE airspeed,
on the other hand, goes up. Same lift (equal to weight, as you note), but
you're going faster for the same power. Obviously thrust didn't increase
(and in fact, decreased, since you get less thrust from the prop due to the
less dense air...though with a constant speed prop, much if not all of the
lost thrust can be regained using coarser prop pitch), so the only way to go
faster is for drag to have decreased.

Since lift is constant, maximum lift/drag ratio still occurs at the
particular angle of attack where drag is minimized. But the ratio is
higher, because drag is lower. It's the angle of attack that's constant,
not the ratio itself.

Pete

Air is pretty heavy, which is why we can fly. It weighs .078
lb/cubic foot at standard sea level pressure and temperature. What's
that, about 13 cubic feet for a pound? The air in a room can easily
outweigh the occupants.

Dan

In article .com,
wrote:

Air is pretty heavy, which is why we can fly. It weighs .078
lb/cubic foot at standard sea level pressure and temperature. What's
that, about 13 cubic feet for a pound? The air in a room can easily
outweigh the occupants.

Dan

I seem to recall .002378 #m/ft3 as air density at STP.

Air is mostly (70%) Nitrogen, most of the rest is Oxygen.

The atomic mass of Nitrogen is 14, of Oxygen is 16. Both occur as
molecules (N2, O2) so the mass of each molecule is twice the above
figures.

Now, at STP, there are 22.4 liters in a mole, and a mole is the amount
of stuff that would weigh (in grams) what its molecular mass is. So,
22.4 liters of nitrogen would weigh 28 grams. Of Oxygen, it would be
32 grams. So we have a little over a gram per liter. Ok, more than
just a little, but less than a gram and a half per, and it's in the
ballpark. Lets use one gram per liter.

A liter is 1000 cubic centimeters, which is the volume of a cube 10
centimeters on a side. (or equivealently, 1/10 meter on a side).
1000 liters would be a cube one meter on a side, and air would weigh
"a little" over one Kg per cubic meter. A meter is "a little" over
three feet, so a cubic meter is "a little more" over 27 cubic feet.
One Kg is "a little" over two pounds, divide by 27, or even 30, and I
get something less than a tenth of a pound per cubic foot.

Air is pretty heavy, which is why we can fly. It weighs .078
lb/cubic foot at standard sea level pressure and temperature. What's
that, about 13 cubic feet for a pound?

Yep. That's just about right.

Now, take a typical room that's three meters tall, three meters wide,
and four meters deep. Not a very big room, but it has a high ceiling.
This gives us 36 cubic meters, and the air would weigh "a little"
over 36 Kg. Well, I weigh more than a little over 36 Kg, but it's
close enough to show that a smallish room will hold less than a
person's mass in air, but a largish roomfull of air can easily
outweigh a person.

The air in a room can easily
outweigh the occupants.

Yep again.

Now, how big is the White House?

Jose
--
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