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Effects Of Humidity On Perofrmance

Sun Nov 21, 1999 8:48 am

I'm trying to write a paper (10 pages minimum) on water in the atmosphere and how it relates to aviation for my ATMS 315 (Aviation Meteorology) class. Do any of you know where I might find concrete numbers regarding the effects of humidity on aircraft performance. Type specific performance numbers would work, as would general guidelines (i.e. xx% decrease in thrust for every yy% increase in relative humidity). If any of you know of a site where I can find this, can quote from a performance manual or book, or just know the answer, please help me out. If you just know off the top of your head, please also leave a title (i.e. 767 captain, etc.) so that I can quote you as a reputable source in the paper. I appreciate any help that y'all can provide. Thanks in advance.

Michael
 
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RE: Effects Of Humidity On Perofrmance

Wed Nov 24, 1999 5:34 pm

Hi Michael: I've been off line for the last 5 days doing recurrent sim, and got back to have computer problems. Hence the late response.

In direct answer to your question, here is a quotation from the Jeppesen publication entitled "Aircraft Gas Turbine Powerplants", one in a set of Sanderson Training Products (I'm not plugging the series, just want to attribute the following quote):

Chapter 2 - Jet Propulsion Theory
Section I - 5. Fan Engine Thrust
"Note that in the [given] examples no mention has been made of a humidity factor influencing thrust. The National Advisory Committee of Aeronautics (NACA) Standard Day conditions are 59 degrees Fahrenheit (15C), 14.7 psi (29.92" Hg), zero percent humidity at 40 degrees latitude. However an engine is seldom operated at zero percent humidity. The reason for not considering humidity in thrust calculations is that 65% to 75% of the mass airflow through a gas turbine engine is used for cooling the combustion mixture. The presence of moisture suspended in the atmosphere has a negligible effect on either the cooling process or the remaining 25% to 35% of mass airflow used for combustion. This situation holds true for all types of gas turbines."

I'm sure your aviation bookstore or flight school can point you in the direction of this and other reputable books. Hope it gets you started in the right direction.

Best Regards,

Buff
 
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RE: Effects Of Humidity On Perofrmance

Thu Nov 25, 1999 8:32 am

That's interesting. I knew that humidity was of almost no factor to engine performance but it does affect the take off performance of an aircraft. Humidiy will increase the required take off length as hot weather conditions do. I think so.

Ben Soriano
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RE: Effects Of Humidity On Performance

Fri Nov 26, 1999 6:24 am

I can't find any info in that regard, so it's quite possible. But probably negligible otherwise there'd be more info available. Now if the humidity is solid (rain, snow, standing water, frost, etc.), then there is lots of info available on effects on performance.

Hope someone else can add to this. I think this discussion took place here once before, long ago...

Best Regards,

Buff

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