Humidity

[Ringbark]

Hi.
Forty percent humidity, same Gyro, ninety percent humidity, same temp, same general conditions, sea level.
Does the performance drop off with the higher humidity ?
If so, would the optional 27ft rotor as opposed to the standard 26ft, restore the performance at the higher humidity.

Over.

Bob.

[choppergabor]

Originally Posted by Ringbark

Hi.
Forty percent humidity, same Gyro, ninety percent humidity, same temp, same general conditions, sea level.
Does the performance drop off with the higher humidity ?
If so, would the optional 27ft rotor as opposed to the standard 26ft, restore the performance at the higher humidity.

Over.

Bob.

But of course. Think of how much of the water molecules will occupy the precious space the air molecules would occupy in the case of lower humidity! Big big difference!!!!

[Redbaron]

good question mate! more humidity equals less lift. you will get your best performance in cold, dry air.

[kolibri282]

40% humidity reduces air density (and rotor lift) by 0.3%, 90% by 0.75% at 20° Celsius and 1040 hPa. I think that a couple of bugs smashed on the leading edge of your rotor will be more detrimental to your lift than some water vapour (a couple of double cheesburgers you had before flight by the way give the same result in terms of thrust coefficient...;-). The next question is what the humid air does to your engine power. An air density calculator including humidity can be found here:
https://www.brisbanehotairballooning...r-density.html

[birdy]

Yeh, humidity saps more from your powerplant than rotor.
But, i woulda thought there woulda been a much bigger difference than .75%.
I know that ona 45c day its all good, till you get a scud of rain that shoots the humidity through the roof, then it feels like sumone cut 3' off each blade.

[ckurz7000]

I get 18% difference on a day with 30 C and standard pressure, once dry air and once 100% humidity. Thats very noticable when you are flying.

-- Chris.

[kolibri282]

That's odd Chris, could you please check your values on the site I have posted the link for? Should there be a bug in the program or is it a user error?

[PTKay]

You all talk RH (relative humidity) in %.

This is not g/kg water in the air.
RH is temperature dependent.

High temperature AND high RH make the difference.
High temperature and high RH mean high g/kg water in the air.

[kolibri282]

My idea was that rotor lift depends on specific density of humid air (i.e. air & water vapour mixture), what do I do wrong here?