Flight plan

......My flight plan....

My blog is to inspire and motivate those who have a love for aviation. I will attempt to virtually open the flight deck door and allow a peek behind the scenes. And please help make this blog interactive by sending in comments. Don't be shy! :)))))

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Again, this blog is for aviation enthusiasts so welcome aboard!!!

CFM 56

CFM 56
Looking up the "butt" of my CFM56-5B

Saturday, April 23, 2011

Happy Hour and Evaporative Cooling?

Evaporative cooling at a local Phoenix emporium during my layover.
So how does two dollar beer tie into meteorology? Well let this pilot/meteorologist explain. :)

Many hot dry states like Arizona, Nevada, Southern California, New Mexico utilize water misters at restaurants. shops and pubs. Why? The process of evaporation requires heat.
Because energy is needed to overcome the molecular forces of attraction between water particles, the process from a parcel of water to a parcel of vapor requires the input of energy causing a drop in temperature in its surroundings. Translation...the air cools.

It's why you feel cool when you get out of a shower or pool even on a hot day. It's why you sweat. The sweat evaporates causing your body to cool. 

So the nearby air is cooled from the mist evaporating into the dry air. It also gets on your body and it causes cooling. As well, it also increases the relative humidity making you feel more comfortable. Remember we are talking near desert air with very low relative humidities. It's why aircraft are stowed in these desserts...it imposes less wear and tear on the aircraft. 

When I taught Weather 101 for new pilots, I asked the question....does rain reduce visibility? (I'd always ask smart ass questions knowing full well they would not get them.
Cruel....I know). Actually, rain refracts but it does not reduce visibility. It's the fog in between the rain droplets formed from evaporation which reduces the visibility. It's called rain induced or frontal fog. 

So while we capitalized on happy hour...meteorology was at play. Actually, I also asked my weather 101 class why a cloud forms in the neck of a freshly opened beer (coke if you don't drink) bottle? It's due to adiabatic expansion. You are releasing a compressed gas, expanding it and thus cooling it. Much like how clouds are formed. 

All of this meteorology talk is making me thirsty. 

So there you have it. Meteorology on my last layover. :))))


Daniel said...

I could have used some of that 5 years ago when my dad decided to go to Las Vegas in the summer. That was what you call hot, 121 degrees farenheit is what my uncles truck registered at 12:49 pm. No way could you walk the strip in that heat. Just weave in and out of Casino's.

From the Flight Deck said...

Yeah, Vegas can be HOT!!! Maybe that's why they put the casinos where they did? So you would have to go inside and gamble.

P.S Like your new avatar! :)

Daniel said...

It would be a good technique ! :D

Thanks, I got it a year? ago on the ramp after "riding the breaks" on the 767 to the maintenance hanger.

Cedarglen said...
This post has been removed by the author.
Cedarglen said...

And... As we all know, Density Altitude has a BIG temperature component. Very dry air, at high elevations and at miserably high temperatures is just not a great way fly airplanes, especially with 'jet' engines. While Lost Wages, NV has very long runways, I think Captain Doug will agree that on very hot summer afternoons, some flights/airplanes must be weight-limited to ensure a safe take-off. Not sure how else to describe it, but it is sort of like climbing stairs, but without the steps. The air is so darn thin that even those massive engines have nothing to grip to produce their thrust. There is little air and what little there is has no substance. If one wants to fly with vigor, try an empty plane, at Vancouver, BC, about 11 AM on a rainy day and about 38-F. YOu probably won't get any ice at that temp and the little bus will climb like a homesick angle. Humph! If it is a ferry flight, anyone who is not driving can Aisle Surf(*)during take off and even landing. (*Sorry. In honor of our host, you'll have to look it up elsewhere.) The science behind 'mist spraying' really is the same as a trying to fly to/from those places. The better the misting works, the worse your aiplane is going to work. Folks (pilots?) who really need to depart those high and dry airports, generally do it before 10 AM. If they are seriously heavy, very early morning departures are common. If you've ever been bumped from a flight out of Denver or Mexico City, with some obviously open seats, that's why. The airplane can and will fly, bit NOT with every seat filled. Our resident weatherman explains it even better... _C.

Bas said...

lol! Nice post Captain! I would've said 'Yes' on your reduced visibility question though! :P Meteorology remains a big mystery to me, but things like these are actually worth knowing.

If you have glasses, do they get foggy when sitting there?

Regards from across the Ocean,


fche said...

Cap'n Doug, if rain doesn't reduce visibility (due to mere refraction), by what mechanism would fog do so? Isn't fog just a mass of smaller water droplets, each of which merely refracts light?

Anonymous said...


Welcome back! :)

Chris Gardner said...

That photo of a rampie cleaning windows on the 747 reminds me from the movie "Airplane". Anyways wishing you and your family a happy Easter and lay low on the sweets I don,t want to see your blood sugers up to double digits,lol. Just the same take care, Chris.

From the Flight Deck said...


For many pilots, meteorology intimidates them. I quickly learned that when I flew as first officer.
Tell them you were an ex-meteorologist and usually the flight deck went quiet. LOL

It stems from how they learned weather...usually from a flight instructor who knew little about it as well.

However, the military, flight colleges and most universities have some very knowledgeable staff on board.

Yes, I guess your glasses would get foggy. :)
And sometimes it was difficult to see others.
The manager asked how things were going at one establishment, and I told him the misters were getting to be a bit of an overkill (the day was cooling) so he promptly turned them off. :))))

Happy Easter from Canada

From the Flight Deck said...


The larger rain drops would not reduce visibility per say. One can have a shower go through, but visibility remains unlimited.

I also ask the question..."if it starts to rain, what is the relative humidity?" Everyone says, "100 percent." Not so!

I also ask, "which is more dense...moist air or dry air?" Most would answer, "moist air" because they can see it. Not so. :)

I guess it would be like building a fence. The fence posts would not stop you from seeing your neighbour's house, but when you start
filling the fence in with tightly placed boards, there goes the neighbour. :)

Rain on a windscreen is a good refractor. So when a pilot flies next to a hill in rain, the hill will appear lower than what it is. Not a good thing!

Hope this suffices. :)))

Metman Doug

From the Flight Deck said...

Chris. That's exactly what it reminded me of.too!
The movie, "Airplane." That's why I said, "clean the windows and check the oil." :))))

No sweets in this house. The boss is in Halifax.

Looks like the computer based system snuck in a YYT layover in May.
Maybe I'll see ya there?

Happy Easter

Captain Doug in a "sweet free house." :))))

Anonymous said...

Happy Easter, Metman Morris. :)

Thanks for the weather talk. :))))

From the Flight Deck said...


I would say ten percent of pilots love meteorology.
Here in Canada nine out of ten initial conversations begin with the topic.

Sounds like you like weather too! :)))

Happy Easter to you and your family!

Metman Morris

fche said...

Cap'n Doug, thanks for the elaboration.

It sounds like there is no qualitative difference in terms of mechanism of visibility reduction between rain and fog. It sounds like the more drops light is made to pass through, the worse the visibility will be.

Are there situations where one sees pure rain, without much "fog in between the rain droplets", like perhaps halfway up a rain shaft?

Cedarglen said...
This post has been removed by the author.
From the Flight Deck said...


Pure rain. For sure. I was shocked to see rain in Victoria and Vancouver, yes Vancouver, with unlimited visibility. Coming from the Maritimes, rain means eventual poor visibility. I grew up in Nova Scotia thinking it was the only way to see rain.
I was wrong.

Here's something to ponder...and pilots see this phenomena sometimes. When it begins to rain why does poor visibility in fog improve? It can mean getting into an airport or not. :)


P.S It's because the rain droplets grow at the expense of the fog droplets. Hence improving visibility.

Man, this talk gets me thinking about my book I MUST write! :))))

From the Flight Deck said...

Cedarglen (Craig) One.

You're right the hotter the better to maximize efficiency. As well, the drier the better, think vapour pressure.

Weatherman/pilot Doug

From the Flight Deck said...

Cedargeln Craig. (TWO)

Excellent points about density altitude. The higher and the hotter it gets, the worse it is. And yes, many airlines (like Emirates in Dubai) have "wee hour" departures. Luckily they sit near sea level. Mexico city, "lost wages" (LAS), Denver and even Calgary, Alberta must weigh in these variables for take off.

One thing you alluded to was moisture.
Taking off in Vancouver is great at low temperatures but not in rain. The best scenario for any airplane is a cold, dry winter day at seal level into the wind than on a hot, HUMID, elevated airport with a slight tail wind...YUK!

Captain D

Anonymous said...

Captain Doug,

Thanks for the great discussion about weather, and you're right, you do need to get that book written!

Do you prefer a summer filled with thunderstorms to avoid, or dealing with winter ops? Which is easier to deal with from the flightdeck?

Happy Easter!
YYC Dispatcher

From the Flight Deck said...

Cedarglen Craig (Three)

You make a great point! For many pilots, things must be cut and dry and weather does not fit into that category...hence intimidation.
But this holds true for the general public and weather. It's just not that simple some times.

They want to read a passing cold front gives: shifting winds (they always veer - clockwise rotation in the northern hemisphere), dew point decreases, temperature decreases, barometer increases, pressure tendency increases, relative humidity decreases, visibility increases except in local showers, precipitation may change from rain to snow and clouds dissipate due a building
high pressure area that brings subsidence. Guess what? Not all cold fronts behave like the ones they ask about on transport weather exams. :)))

Life is not cut and dry nor is weather! It comes with curve balls, highs, lows and twists causing many, including well trained pilots, to ask...WTF?

End of rant! LOL

And yes....Happy Easter! :)))))

From the Flight Deck said...

YYC Dispatcher. You are SO right.....I must, I must, I must write that book!

I'm off for the next ten days. Maybe I should fly to Cuba like Ernest Hemingway did?
But then again, there may be too many distractions. I may be looking for happy hour but I know there won't be any "misters"...it's too humid there. :)

Good question about summer/winter operations. Really good question. :)

I think it's under the same guise as which is more crucial, a take off or landing?

Let's just say both offer unique challenges and if you are not on your game...you can end up
having a bad day. :)))

Always a pleasure!

Happy Easter!

Captain Doug

[email protected] said...

Totally unrelated to the post - the wing on your cover page ..

A300? .. the yellow wingtip fence has me scratching my head .. it seems too yellow for Lufthansa .. Merpati maybe .. I give up ..

From the Flight Deck said...

Chris. I would say it's an Airbus wing for sure. The "canoes" (housing for the flap hydraulic jacks) look Airbusish. Plus the static wicks look Airbus. It was a generic photo. I'm certain someone out there will tell us. :)))

At least my blog left you pondering. LOL


From the Flight Deck said...

Mark. Excellent about the C172! Doug

Anonymous said...

@ Chris and Doug,

After a bit of searching, I believe the wing is from a Monarch Airlines A300.


Looking at this photograph, it seems quite plausible that it is Monarch Airlines. However, just to confirm, I went through a list of A300 operators and found none of them have winglets painted in designs that match the one being displayed as your background image.


Finally, it cannot be Lufthansa because they have never painted any of their winglets. Furthermore, Merpati, to my knowledge, have not used an A300. Thus, it seems to me that the background image is in fact an image of a Monarch Airlines A300.


whywhyzed said...

Doug -- next time you have a layover in PHX (since you mentioned Tempe), a must stop is Four Peaks. make sure you put it on your list of "must do's". Great web page, too.

I've always had fun there.

From the Flight Deck said...

Whywhyzed. I checked out the website. What a site! For sure, I'll check out Four Peaks, but our summer flights to PHX are turns...no layovers...so I'm told.
But rumour has it...Scottsdale is where I should go next. Is there a Four Peaks there? lol


whywhyzed said...

Indeed there IS another Four Peaks in beautiful Scottsdale. I was once at the Scottsdale muni airport, and I never saw so many private jets with swanky looking people getting out of them..... a high end town to be sure!

From the Flight Deck said...

Whywhyzed. I must get checked out in "Four Peaks." Yes, I heard Scottsdale is the place to be.
I'll be certainly getting vectors there next time I'm in Phoenix.


From the Flight Deck said...

Nehal. WOW! You certainly did your homework! Thanks for finding the answer for both I and Chris.

Chris, you'll have to have Nehal on the TWN as another aviation expert. LOL

Again, thanks Nehal!

Captain Doug

Christer said...

Love that pic of the 767 and CRJ in SFO!

Are there any specific challenges flying into PHX in the summer? All I know from landing/taking off there as a passenger is that it seems to be excessively bumpy in the summer. Also, the sea of US A320-series tails is overwhelming at any time of the year:)

From the Flight Deck said...


Funny you should ask that. Our last landing had us floating down the runway a little. The temps were 28C, the airport sits about 1200 feet ASL
and we had a weak quarterly tail wind. After floating a bit, it's time to "put it on" and that's what the F/O did. :)

But yes, with high surface temps one is going to get bumps. Denver and Calgary also fall into the same category.


Chris Gardner said...

Capt Doug what would be the longest delayed layover for you due to bad weather.

Anonymous said...

Anon from Anon,

good find on the pic - I had just discounted Monarh as most of their A300's had blue wing end plates. Thought it could have been a Sudan Airways aircraft, but most of their A300 end plates were "base colour grey", or should that be "base color gray"?

Great post on evap cooling, Doug. I'll have to remember that bit about lowering vis in rain....... or not.

Also, what brand of beverage was used in the bottle opening experiment? I've done a few of those; bottle conditioned "ale" opened at slightly cooler than ambient provides a rather pleasing effect!


From the Flight Deck said...

Chris. One would think that's an easy one to answer, but when we show up for work the clock is ticking so a delay or cancellation may be more extensive because of duty time expiring.

For example, years ago we flew from London, England to New Delhi, India (I was a cruise pilot at the time). However, New Delhi was socked in with fog. We had to fly to our alternate airport, Bombay (Mumbai). Because of it, our duty time expired. We went to a hotel and got our minimum crew rest. Many of the passengers remained at the
airport and waited for us to return. So you tell me how long the delay was for? :))))))

And speaking of delays, your hometown used to take first prize for delays years ago. The overnighting crews knew if they could not see the hills across the harbour the inbound flight would not get in. Sometimes this would last for two to four days.
Because of it, a lot of "things" would happen on these layovers....ahem....

How's that for broad brushing your question?

Captain Doug

From the Flight Deck said...

Anon from Anon.

Matters not about the brand. But I am willing to conduct a few "adiabatic expansion" experiments to confirm this! LOL

JetAviator7 said...

Rather interesting - reminds me of the grocery store where they mist the fresh veggies!

See, all that aviation training came in handy after all!

By the way, Doug, just bought your book and when I get it I plan to read it and post a review on my website. Should be interesting!

From the Flight Deck said...

Jetaviator7. I guess "misters" are everywhere.

Thanks for buying my book and I look forward to your review!

Captain Doug