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Humble question- Humidity/performance?

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Old 06-17-2002, 05:19 PM
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Default Humble question- Humidity/performance?

Forgive me for being unsure about this- we see lots of casual references to "faster" conditions.

I know cold air is good, cold water (for intercoolers) is good, sea level, salt water vs fresh, chop, headwinds for a cat etc.


I'm still a little fuzzy on humidity. I've seen references- without explanation that sounded as though higher humidity was slower? Off the cuff, I would expect it to help, act like water injection which if I remember correctly acts like an intercooler- lowers combustion temps, effectively raises compression etc. Can someone technically explain my confusion away??
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Old 06-17-2002, 06:52 PM
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Since down here the humidity is high 98% of the time I have been asking this question also. HP goes down with high humidity. The highter the humidity the less room you have for oxygen in the air. Air/fuel ratio would be close to the same so motor will have less oxygen, more fuel & end result is less HP. Blower motors will see a bigger % drop in HP that a natural aspriated motor will. In drag racing where a nitrous motor is racing a blower motor the nitrous guys like high humidy since is does not bother them a much as a blower motor will.
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Old 06-17-2002, 07:29 PM
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Turbojack is absolutely right!!! Even if it is cool if the humidity is very high HP will still be off compared to cool dry air.
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Old 06-17-2002, 07:38 PM
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It all comes back to DENSITY Hot and/or Moist air is less dense. I am also a private pilot and from time to time need to do a calculation to determie Density Altitude for takeoff/climb performance etc. On hot, humid, non standard days you'd be suprised on what the density altitude calculation comes out to. It can be 6,000 feet or more even close to sea level. Spoken differently, its like running your engine in the "thin air" of denver. Less dense, less power.
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Old 06-17-2002, 08:45 PM
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jdnca1

Do you use a chart to figure density? How much of a factor is humidy verse air temp? Hotter air can hold more water. Are these calculations for engine HP or for lift? I can see where the air temp has to do with the amount of lift but I can not see what humidity has to do with lift. I am not a pilot so forgive my ignorance if I am using wrong terms.
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