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Humid air versus Dry air

Brockrock

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Suppose that I fly my M2P on a day that is at the upper temperature limits of its operations specification, say 100 F. It is also a day associated with a high humidity level of 90% or so like we often see on the East Coast.

Then, suppose it is two days later. The temperature is still 100 F, but the humidity level is at a more comfortable 30%. This is also consistent with the East Coast, as we have a saying, "If you don't like the weather, wait a minute"...

My question is, would the higher humidity day provide better cooling for the copter's electronics due to the higher quantity of water particles in the air passing over and through it.

Intuitively, I would say that this would be the case. And the science is not new. After all, some race cars and even some aircraft use water injection systems into their intakes to more efficiently remove heat from the engine core via the exhaust, and combustion aside, the principal is still the same.

Also, I am purposely leaving the battery out of this equation, although I do realize that it is a significant factor as well in high - and low - temperature limit flying. It can be pre-cooled - or heated - in these cases - and I tend to do so as I near each extreme.
 
I live in New York along the coast and I know what you mean. However it has been my experience it is not that marginal and I'm not sure really if high humidity vs. Low humidity will play any significant factor. I really have not ran across problems with it being overly hot as I do when trying to fly in cold weather battery warnings that it's too cold.
it seems to me that the thing that you should probably worry about the most are the batteries as opposed to the craft. I would try to keep the batteries in a cool place to start with you should be fine.
 
The water injection systems utilize the latent heat of vaporization, going through a phase change from a liquid to a gas. Evaporative cooling... Huge amount of heat transfer in that case. That would not be happening in your scenario.

However, without looking things up, I believe that moist air has a larger sensible heat capacity and perhaps a larger net thermal conductivity than dry air. So moist air has a greater ability to cool your drone as opposed to dry air.

(It's been a long time since I've dealt with such matters. I retired 17 years ago.)
 
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I'm in Connecticut, so I know what you mean...

I think your biggest concern would be on humid days, if you landed and then put your drone or batteries into an air-conditioned space a short time after flying, condensation could be a problem
 
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Suppose that I fly my M2P on a day that is at the upper temperature limits of its operations specification, say 100 F. It is also a day associated with a high humidity level of 90% or so like we often see on the East Coast.

Then, suppose it is two days later. The temperature is still 100 F, but the humidity level is at a more comfortable 30%. This is also consistent with the East Coast, as we have a saying, "If you don't like the weather, wait a minute"...

My question is, would the higher humidity day provide better cooling for the copter's electronics due to the higher quantity of water particles in the air passing over and through it.

Intuitively, I would say that this would be the case. And the science is not new. After all, some race cars and even some aircraft use water injection systems into their intakes to more efficiently remove heat from the engine core via the exhaust, and combustion aside, the principal is still the same.

Also, I am purposely leaving the battery out of this equation, although I do realize that it is a significant factor as well in high - and low - temperature limit flying. It can be pre-cooled - or heated - in these cases - and I tend to do so as I near each extreme.

Unless the relative humidity reaches 100% there are no water particles in the air - just water vapor. As for the relative cooling effect, that depends on other factors, most notably specific heat capacity and molecular mass. Cooling is maximized by high specific heat capacity (for obvious reasons) and low molecular mass (higher root mean square speed). Water vapor is triatomic with 6 degrees of freedom, and so has a higher specific heat capacity than nitrogen and oxygen. It also has a lower molecular mass (18) vs oxygen (32) and nitrogen (28). As a result, adding more water vapor to the atmosphere should increase the cooling effect on surfaces, all other things (pressure and temperature) being equal.
 
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it is a false finding: high humidity has nothing to do with temperature change. Only evaporation leads to a cooling. At high humidity, there is no evaporation because the air is saturated with moisture.
 
it is a false finding: high humidity has nothing to do with temperature change. Only evaporation leads to a cooling. At high humidity, there is no evaporation because the air is saturated with moisture.

What's a false finding? Evaporative cooling is only one possible process, which isn't happening here, not because the air is saturated (which it is not until the RH is 100%) but because there is no liquid water involved. The relevant process here is convective cooling.
 
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i meant not your post... you are right, exactly your statement this is my mind...
 
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Don't forget that humid air is less dense than dry air. Presumably this means that your drone's motors have to work harder to achieve the same flight parameters (speed, altitude, starting, stopping, hovering). So, they may get warmer and certainly would use more battery in humid than dry.
 
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