Effects of Humidity on Performance

[JHC Wilton]

Anybody any opinions/facts on the effects of humidity? I must have been asleep when they covered it on my pilots course. Rumour has it that its mentioned in a forthcoming accident report.

[Mice]

JHC,
More info please. Are we talking of the effect of humidity on a piston engine, a turbofan/turbojet, or on the wing airflow characteristics?

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When all else fails, read the manual!

[Old Dog]

Humid air is less dense than dry air. Effect of humidity is more pronounced in higher temperatures. At 20°C, 99% RH humid air is about 1% less dense than dry air. At 30°C about 1.5%, 40°C about 2.7%. A 3°C, 4.5°C and 8°C rise in air temperature has roughly the same effect respectively.

I remembered reading somewhere that those take-off performance charts (FAA) assumes 50% RH condition for temperature up to 30°C, reducing linearly for higher temperatures. (But I don't know the logical reasoning behind this)

Like you, I am also interested to know more.

[This message has been edited by Old Dog (edited 30 June 2000).]

[djliz]

Just to expand on HUMID AIR IS LESS DENSE THAN DRY AIR.This is because the relatively heavy oxy and hydro molecules are replaced by the somewhat lighter water molecules, hence the decrease in density.I think thats correct,any other views?I think this might be the reasoning behind this OLD DOG,im no expert i read it somewere recently.