What does dew point refer to when talking about flying planes?

Question

What does dew point refer to when talking about flying planes?

Answer 1

I suspect that with water vapor in the air, it becomes less dense and reduces the power out put of jet engines.

Answer 2

Dew point temperature is the temperature where condensation can occur.  It doesn't always occur then, but it might.

Condensation will bring on clouding.

If the surface temperature is near the dew point and it is getting colder, as around sunset, you might expect low clouds or even fog.

If the surface temperature is very near the dew point you might expect fog shortly after sunrise, too, because convection will bring more air in contact with the cold ground.

Answer 3

It's another way of stating how humid the air is.  Technically speaking it is the temperature to which the air must be cooled before condensation occurs.  Let's look at that a little more closely to see what it means.

Picture some dry air with relatively few water molecules bouncing around.  With only a few water molecules condensation is very unlikely.  As the temperature is cooled, the water molecules have less energy, move slower and are more likely to "stick together" (i.e. condense) if they bump into each other.  You're going to have to cool the air down a lot for this to happen (i.e. the dew point is very low = low humidity).

Now imagine some very humid air.  There is so much water vapor in the air that the temperature only needs to be lowered a little bit for them to start sticking together (condensing).  High humidity = high dewpoint.  If you see dewpoints above 70F that means the air is VERY humid and if the temp falls below 70F fog is going to form.

As far as what it means specifically to a pilot, when temp and dewpoint meet clouds/fog is going to form.  If the temp/dewpoint spread is very close at ground level you better have an instrument rating :)

As someone stated a high dewpoint (high humidity) can reduce engine performance (water doesn't burn very well).

Answer 4

Well in a nutshell, if the dew point is withing 2 degrees of the temperature there is a chance for fog

Answer 5

Dew point is that combination of air temperature and moisture (water vapor) in the air can causes the moisture to condense out (the dew on the grass is evidence of this phenonmonon) of the air. You have to be careful to make sure the dew point and temp do not conspire to form ice from this condensation as it will build up on the leading edge of the wing and distort the air flow over the wings. Enough distortion of the air flow coupled with the accumulation of ice on the wing can bring an aircraft down.

It is nice to know the dew point.

Answer 6

Jim had a good practical definition.  The other uses are cloud heights -- when the temperature and dew point are know, use the adiabatic laspe rate and you can figure out about where the clouds will form (condense out).

Answer 7

The dew point is an important statistic for general aviation pilots, as it is used to calculate the likelihood of carburetor icing and fog, and estimate the height of the cloud base.

To learn more, go to:

http://en.wikipedia.org/wiki/Dewpoint