My friend and I have a debate going about wind and temp. I understand that air gets less dence as it gets hotter, so a 10 mph wind at 110 degrees would exert less force than a 10 mph wind at 30 degrees. Heres the catch, Wind meters work by wind pushing a little fan or wheel and the speed of that rotation is translated into wind speed. I think unless your using dopler to check the wind speed 10 mph on a fan type wind meter equals X amount of force bieng exerted on the blades so 10 mph is the same strength at 30 or 110 degrees. Maybe the wind meters are calibrated to say 70 degrees, so in 30 degree weather with a reading of 10 mph the wind may be going say 9 mph or in 110 air with a reading of 10 mph the wind may actualy be moving at say 12 mph. Or maybe the wind meters take air temp into acount. If that is true then would a 30 degree wind be more powerful than a 110 degree wind?

What do you think?
:puzzled:
P.S.
I know I'm a kook

dont know.......whatever the temp,i need WIND,and i need it bad,man.........

I think your correct to say there is a difference. Between 30 and 70 degrees I would think there would be some noticeable difference.

I do know the speed of sound differs with temp for the same reason. But with the wind meter it would seem that it is showing the true speed in any temp now I guess the feeling on the kite would be stronger at 10mph in 30 degrees over 10 mph in 70 degrees.

Also water densities differ with temp. Cold water is denser than hot water. A boat will travel across cold water faster than it will hot water.

Just my 2 cents.

I think I see what you mean, and I agree.

IMHO, without any science, or too much thinking, the same wind at 30F feels 'stronger' than at 110F. Then again, there are too many other variables and time to compare snow-kiting winds to kitesurfing wind.

On the landboard, to me, the same wind, in the same field on the same surface, feels stronger in colder temps, but only a very little bit. (like less than 1/2 inch on the trim strap of my 12m or 7m Frenzy).

I could be totally wrong, about this, and am probably brain washed by 'common knowledge'...

Thanks for the map!! Thats the best one I have seen, it even has my spot on there.

Thanks again, Earl

Here is my theory ::

same wind speed more dense air because it's colder.

so more air molecules that move for the same speed.

more air so the force applied to the kite will be greater

First let me say that you have WAY too much time on your hands.
That being said, its an interesting debate. Air most certainly gets less dense as temperature rises. Aircraft are affected by this in the form of decreased lift and must use increased airspeed or shed weight to take off on a hot day. This is made even worse at higher elevations as air density decreases with altitude along with an increase in temp.
So, does this also affect the amount of "push" on a kite that any given wind speed has?
Does the sailing term "heavy air" refer to wind generated during denser air scenarios ie: colder or moisture laden?
Ananometers are not tied in or calibrated to temperature. Wind speed is simply that. A bubble floating along in 10 knot wind moves at 10 knots regardless of the temp.
What you are asking about is the amount of force generated by the moving mass of air.
Don't you love the way that I simply restated your question without contributing one iota to the answer? Brilliant!
Time for the science majors to chime in.

10 mph is 10 mph, regardless of the density. Dense air moving at 10 mph is the same as sparse air moving at 10 mph. The only way it would effect the kite differently is if it is very turbulent or gusty which would give you varying wind speeds, not constant 10 mph. Think of it this way, a vehicle traveling at 10 mph is going 10 mph, doesn't matter if it is a VW Bug or a semi tractor trailer.

Now the actual density of the air does effect the kite. Generally a kite will fly worse in cool or wet air than it will in dry air, the reason being is density. The thicker the air the more resistance the kite will have to move through it. Water replaces air so in a wetter climate, the kite will be more sluggish or hang back more than it would in a very dry climate just because the kite will have a harder time flying through the air because it is denser. Think of walking through clean water compared to walking through thick mud.

With power kites, max power comes from apparent wind, apparent wind comes from kite speed. The faster the kite will fly the more power the kite is capable of producing from the apparent wind. Denser air causes more restriction/resistance on the kite while it flies which could reduce apparent wind (max speed) and overall power. Dry air creates less resistance to the kite so it can reach maximum velocity and maximum apparent wind.

Denser air may give you more bottom end grunt because the kite will be dragging back in the power zone longer than normal, but overall power production would be lessened. Dry air would allow the kite to reach maximum speed and maximum apparent wind which should be maximum overall power. This is one of the reasons that land speed records are easier to achieve in the desert dry lake beds instead of other areas. Of course, skill has more to do with it than air density.

All of this is on the minimal scale and unless you were able to fly in both dense and dry air with the same wind conditions back to back, it would be very difficult to tell the difference.

Just my 2 cents anyways.....

whoops. Air Density is everything.

Reference: the following elementary kite buggy weather lesson:

Structure of the Atmosphere / Density Altitude as it relates to Ivanpah VS. Sunset and so on.....

"To understand the weather it helps to know a little about the air. Air is simply a gas comprised primarily

of nitrogen and oxygen and a variable amount of water vapor. Air has mass and weight. At sea level

where the air is most dense it exerts a pressure of 14.7 pounds per square inch.

Air density is affected by altitude, temperature, humidity and pressure. Air density alters wing

performance. The higher the altitude, temperature or humidity the less dense the air will be and the faster

you will have to move to generate lift.

For every 1000ft of altitude you gain, the air density drops approximately 4%.

For every 5ºF increase in temperature, the air density will drop 1%.



Water Vapor

The amount of water vapor a mass of air can hold depends on its temperature. As air heats up it is able to

hold more water. Low relative humidity means that the air at its current temperature could hold a lot more

water. When the temperature of an air mass drops, its relative humidity increases and when relative

humidity reaches 100%, water condenses and a cloud is formed.

Humid air is lighter then dry air and therefore has a tendency to rise just as when air is heated.



Solar Heating and Circulation

Solar heating and the resulting high and low pressure systems causes all atmospheric circulation. The sun

heats the ground, which heats the air above it. Different surfaces heat up at different rates. Some examples

of terrain that heat up slowly are water, snow, green grass, and forests. Examples of terrain that heat up

more quickly are asphalt, dry fields, dark soil and dark rocks.

As air warms up it expands, becomes less dense, and tends to rise. When warm air rises, cooler air moves

in from the surrounding areas to replace it."

When you are ready for the longest read in the world. Ask me for a copy of "understanding the sky" and you will beat yourself to kite making material raping your brain around this!


and...if you wonder why I go east of the beach in the fall...answer this for yourself...below

which do you prefer to kite in...hi or low pressure? and why?

then why can a 12 m kite at sea level go almost as fast as a 3m kite at 4,000 ft? Minus all the other components like line drag and wtfe.

Sunset-Jim witnessed cold air pushing hot air away last october when him and I drove 20 hrs for 1 day of riding...

ucky we didn't get stuck there for months...damn

:wee:

I've agreed with most everything said but will add one thing and question another.

Measuring wind speed with a propeller driven anemometer requires air molecules to strike the blades of the meter and give each individual blade "lift". Less dense air will have fewer of those molecules striking the blade and give you somewhat less of a reading. It could be that your measured speed will give an indication of force applied to the kite by the air. You could actually have a 12mph wind speed but it measures 10.5 and your kite would fly like it is a 10.5 mph wind.

Eli, I'll need more explanation about how air with higher moisture content is lighter than air with less moisture. That air will rise if it heats up but I don't understand when you say it rises just because it gets more moist.

it is a fact that you can fly a kite in say, 15mph summer winds and be comfortable with the power, but put the same kite up in 15mph winter winds and you will feel over powered.

Wow. I wake up with my first cup of coffee and see that it's really been a boring night.

Quote:

Originally posted by BeamerBob Eli, I'll need more explanation about how air with higher moisture content is lighter than air with less moisture. That air will rise if it heats up but I don't understand when you say it rises just because it gets more moist.

You have to back into this. Moisture content can be higher BECAUSE it is warmer and therefore lighter (less dense). It seems counter intuitive because water is heavier than air by volume, but it does not take a lot of molecules of water to be suspended in air for it to be "humid".

The original question is compelling. That airplane takes a lot more distance on one of Mel's runways to take off in warm humid air, so why is the impeller on an anemometer not affected? Hmmm.

wind velocity does not account for mass or rate of change . just time and distance

force contains elements that allow for the different FEEL ..the mass and accel.

Quote:

Originally posted by USA_Eli_A Humid air is lighter then dry air and therefore has a tendency to rise just as when air is heated.

Quote:

Originally posted by Acampbell You have to back into this. Moisture content can be higher BECAUSE it is warmer and therefore lighter (less dense). It seems counter intuitive because water is heavier than air by volume, but it does not take a lot of molecules of water to be suspended in air for it to be "humid".

I wouldn't argue about warm air rising moist or dry, but I'm not sure I get Eli's statement that moist air rises when all other things are equal. You can have warm air with the capacity for moisture that is however dry such as in the desert. Imagine a temp of 90 degrees and a dewpoint of 20 degrees giving a very low relative humidity. So in this scenario, Eli is saying that adding moisture to this air will cause it to rise, unless I misunderstood his intent. I say the air would be heavier with the added moisture and wouldn't tend to rise but would settle at a low spot.

Phew, I wish the wind would just blow and I could go outside!

there has to be a formula for this somewhere..... but....

with an anemometer, i would say that air density will not play a significant role.... air density does play a role with kites, though..... i have heard that while snowkiting in Colorado, a mmile high in altitude, that you must use a larger kitye, due to the fact that the air is less dense...

lets say that at 30 degrees, air is 75% as dense as it can get, while at 110 degrees, air is only 55% as dense as it can get.... (Ijust pulled these numbers out of nowhere)

lets also say that air at 100% density will push one square meter at 2 pounds of pressure per square meter, per mile an hour (5 squre meters.... 2pounds per square meter.... 10 pounds of pull on a 5 meter kite, per each mph that the wind blows... provided the wind is 100% dense)....

according to this, my blade would exert 75 pounds of pull in 10 mph winds at 30 degrees, and 55 pounds of pull at 10mph in 110 degrees.... (perfect density air being 100 pounds of pull... quite a difference....

back to the wind gauge on your anemometer... it is quite a bit less efficient at catching air, so it can only catch 1 pound of pressure over the same area that my blade is capable of catching... this is due to the moving nature of the fan, and the fact that the blades of the fan are at an angle, whereas the Blade has a much flatter profile.... there has already been extensive reasearch into the efficiency of those little fans.... i will spare you the details.... just trust that they are less efficient.... all you need to do is look at them...

so for the 10mph at 75% density (30 degrees), the blade will pull 75 pounds of pressure.... the fan will pull half that... 37.5 pounds.... but remember that this math was done to equal the size of the kite (the 37.5 pounds part).... so we need to divide 37.5 pounds of pull by 0.000129032... (this number is 5 square meters divided by one square inch).... the answer is .0048.... so the anemometer fan will pull .0048 pounds in the same breeze

and for the blade at 55% density (110 degrees), the blade will pull 55 pounds of pressure, and the fan will pull .0035 pounds.... a difference in pull of .0013 pounds in the fan, and 20 pounds in the kite....

the point behind all that is the difference in the fabn, really.... .0013 pounds at the varying densities of wind.... that translates to nearly half of a gram of pressure in the fan... what would it take for the fan to be half a gram off?? a slight move of the hand? a microscopic gust?

too many variables, and WAY TOO MUCH THOUGHT

put your wind gauge up, and get your reading, trust that it is right, and put your kite in the air... to be concerned with the difference in air density/ temperature (which, by the way will not fluctuate wildly between 30 degrees and 110 degrees while you are flying) at the level of the fan is a bit much. tyhe kite... sure, i can see that, but worrying about the fan is overkill.

****** the numbers in this post were made up by me simply to illustrate the point.... i have no idea about their sondness.... as a matter of fact, i would say they are complete BS.... DO NOT USE THIS INFORMATION TO PICK A KITE TO FLY IN ANY SITUATION...******

now.... less thinking, more playing

ok I have asked the weather channel for an answer on this. I'll post it if they reply.

It has more to do with Pressure. High Pressure doesn't allow air to move. High Pressure is ofter dryer. Low pressure systems allow the air to move.

What I said, is from years of studying the weather. And is very true.

High and Low pressure means everything.
Low = more stable
high = un stable

both can carry moisture, moisture is good it make the gas (air) more forceful. Low pressure is more predictable than High pressure which can change things dramatically. Moisture also has surface tension to the gas, so moisture in a gaseous state likes to hang on to air(gas) and they like to move together in low pressure.

At altitude, air has less molecules, so it is less dense, so wind feels strong but is less forceful compared to sea level..a sudden down draft/down pour, or 'Verga", can happen so always look upwind to see if something UNEXPECTED is about to occour.

Unfortunately there is no formula, but your expectations of Low pressure are likely to be met, at some point during high pressure, with all the extra pressure the air stops moving smoothly. It is capped, and released suddenly. It can cause Micro climates and sudden changes. Once low pressure moves in, things can smooth out. not saying it'll totally be stable, but way more predictable.

Inversions = High Pressure, once the Inversion cap is lifted the Inversion altitude suddenly climbs to dew point and that can cause clouds, once you figure out what the clouds are saying you will be able to know what to expect. sometimes the air can move upward at over 2,500 feet per minute. sort of like at Ivanpah when we see dust devils. And usually in the evening the winds smooth out, unless a scary front on the west side of the Mts at ivanpah fuel gust fronts. But in the evening the winds are smooth because the High pressure CAP lifts once heating turn to cooling.

If I had all of you in One room, I could draw this for you. It'll make tons of sense once you sit through the lecture with an extremely talented micro meteorologist. Unfortunately the weather channel employs low level clouds as meteorologis

don't fight it I will have the weather experts WE know visit this thread. If you want to know there is a sweet book you can read, it's not long, 100 pages, but it will be the most intense read!

this about Gases and how they are effected by solar heating, think about how thin the air gets and how unstable it gets when it doesn't have moisture.

I am very stoked that the group is trying to figure out WEATHER, it's my biggest pet peeve. I wish kiters would focus on weather more often, if all kites new something we'd never had idiots like the guy in Fl flying into building.

I AM SUPER PROUD YOU GUYS ARE DISCUSSING WEATHER!!!!

I've got my pencil sharp. Class is in session.

i think the title of the thread should be WEATHER DISCUSSION not so much a debate. It's a good chance to figure weather out..

if you know more, you'll be able to kite more and find when and where the good conditions are.

maybe we should check it out on
windmeterforum.com

WOW, just wow. You guys could of helped me out with my college physics exam last year.

Excellent map there thanks! A few spots in the J-land I didn't know about ... and I get to add one too

Quote:

Originally posted by william_rx7 I think I see what you mean, and I agree. IMHO, without any science, or too much thinking, the same wind at 30F feels 'stronger' than at 110F. Then again, there are too many other variables and time to compare snow-kiting winds to kitesurfing wind. On the landboard, to me, the same wind, in the same field on the same surface, feels stronger in colder temps, but only a very little bit. (like less than 1/2 inch on the trim strap of my 12m or 7m Frenzy). I could be totally wrong, about this, and am probably brain washed by 'common knowledge'...

Guess the weather channel is not going to respond

so when air gets water vapor in it, each different molecule takes up basically the same amount of space, so mooist air has H2O vapor molecules, which displace mainly Nitrogen and O2 molecules, both of which are heavier (more mass) than h20. So humid air has less mass than dry air since lighter molecules have replaced heavier.

I'm uncertain about the wind wheel ananometers. The blades of an anonometer are different than a "wing". I think that the little wheels are so light with no drag that a different density of wind doesn't affect the reading much, just the speed of the wind. How bout an experiment. We have a balsa wood stick pinned at its center on a table, so it can spin around if you hit the tip. Now lets say you roll a 1 lb marble at 1 mile an hour and hit the tip, the tip rotates at 1 mph basically, minus friction and the force needed to accelerate the stick. Now roll a 10lb ball at the tip at 1 mph, and i think the stick still rotates basically the same speed. Thats my thought anyway, haven't thought about the bubble meter yet. :puzzled:

Quote:

Originally posted by bourck so when air gets water vapor in it, each different molecule takes up basically the same amount of space, so mooist air has H2O vapor molecules, which displace mainly Nitrogen and O2 molecules, both of which are heavier (more mass) than h20. So humid air has less mass than dry air since lighter molecules have replaced heavier. I'm uncertain about the wind wheel ananometers. The blades of an anonometer are different than a "wing". I think that the little wheels are so light with no drag that a different density of wind doesn't affect the reading much, just the speed of the wind. How bout an experiment. We have a balsa wood stick pinned at its center on a table, so it can spin around if you hit the tip. Now lets say you roll a 1 lb marble at 1 mile an hour and hit the tip, the tip rotates at 1 mph basically, minus friction and the force needed to accelerate the stick. Now roll a 10lb ball at the tip at 1 mph, and i think the stick still rotates basically the same speed. Thats my thought anyway, haven't thought about the bubble meter yet. :puzzled:

Now throw feathers at the stick (in a vacuum) at 1 mph and see how fast the stick goes. At the air and space museum, there is a display showing the effectiveness of a propeller and either a jet or rocket (can't remember which :puzzled: ) It showed how the propeller became ineffective at higher altitudes because the air was thinner and didn't have enough air molecules to provide effective thrust from the backside of the propeller. The rocket/jet example was not hindered by the thinner air.

You might be right about the reading on an anemometer not being affected by moist air, since the differences are so small and the propeller spins so easily.

Agree that a propeller wind meter would not work in outerspace. I think though in the ranges we are talking about between sea level and say 10,000 feet, the air density my be %50 less at 10,000 feet, but the wind meter may only be affected a few percent from the decreased density. This little wheel has nearly no friction, and low mass, so its within its range.
I dunno, just some thoughts, but i think the wind meters are pretty accurate, and that in general, the same reading at sea level has much more power and lift than at elevation. I have a silver arrow that will fly well in 7 or 8 knots at sea level, but at 7000 ft elevation at a lake, i need 10 to 12 knots with same wind meter.

The simple answer is that, no, temperature will not affect an anemometer, but yes, it will affect a kite. The simple explanation for why that happens is because the anemometer measures wind speed, which doesn't change with temperature, while the kite uses energy from a moving mass of air, which does change with temperature. That's because temperature only affects density, and density only affects the kite. If simple was all you wanted, stop reading.

The actual reasoning gets a little more complicated, but it's not that bad. Air temperature won't affect the anemometer because it just measures wind speed, which is independent of temperature. The fan blades will match the speed of whatever air mass is moving past them regardless of density. True, as some of you guys have pointed out, a given volume of air will impart less power to each blade, but once the blades have gotten up to speed it's not going to matter. There's so little resistance on the blades that they'll match the wind speed regardless of density.

mgatc mentioned a soap bubble floating in the wind, which will float at the same speed regardless of air density for the same reasons. If it's traveling slower than the wind, air molecules behind it will knock into it and speed it up. If it's traveling faster than the wind, it will knock into air molecules ahead of it and slow down. If it travels at the same speed as the wind, no force will be exerted on it, and, as Newton's Laws tell us, an object in motion tends to remain in motion. The anemometer's fan blades work the same way; it just measures wind speed.

The kite is a different story. Unlike the anemometer, it's anchored and providing a significant amount of resistance. The amount of air that hits the kite is definitely going to affect it, and a lower temperature means that there's more air hitting the kite at a given wind speed than there would be at a higher temperature. More air means more mass and more mass means more push. Keep in mind that the volume of air caught by the kite doesn't change here, but only the density of that air. Higher density means more air molecules in a given area, and that's why there's more air hitting the kite in a lower temperature.

awindofchange posted that a VW Bug traveling at 10mph is the same as a semi-truck traveling 10mph, but that's only to the radar gun measuring them (analogous to the anemometer). When they hit a barrier at that speed (analogous to the kite), you can bet there's going to be a significant difference. Although the speed was the same, the semi-truck packs a ton more power. Heavier air will impart more power to the kite than lighter air - true, that added density will increase drag, like awindofchange says, but it will also increase lift. For any kite with higher lift than drag (read: any kite that flies), added density will give you more lift and more power. Boats move faster in cold water because their propellers push an extra amount of water that more than compensates for the increased resistance in front of them, and planes fly better because they generate an extra amount of lift that more than compensates for the added drag.

How do we know all this happens? Physics - namely, the Ideal Gas Law. The Ideal Gas Law states that pV=nRT, where p is the pressure of the gas, V is the volume of the gas, n is the amount of gas (i.e., number of molecules), R is the gas constant (for this, it's enough to just know that this number doesn't change), and T is temperature. The variables that won't change here are n and p. n doesn't change because we're not adding or removing air molecules, and p doesn't change because air pressure will remain more or less constant for a given altitude (the wind only blows to equalize pressure).

So what can change? T and V. When T rises, V rises to balance the equation. This spreads the same n over a larger V. In plain english, when the temperature rises, it spreads the same number of air molecules over a wider area. This means that a kite of a given sail size will catch more air molecules in a given period of time, meaning that the kite will generate more power.

Colder air is more dense, so a given volume of it will provide more power than the same volume of warmer air, which affects the kite but not the anemometer. Think about sticking both underwater in a river - same fluid dynamics, very different density. The anemometer will still measure the speed at which the water's moving, but the kite is going to catch all that water and pull way harder than it would in wind moving at the same speed. That's why acampbell's example plane takes off in a shorter distance during colder weather even though the anemometer reads the same, and why bourck needs a different anemometer reading at different altitudes in order to launch the same kite.

Here's hoping that all made sense...

Spot on PixelGuru. Way to back up your explanations with some solid facts. I've been taught to understand weather intimately from years of flying helicopters, where knowing the ins and outs of weather can be the difference between a safe flight and a life threatening situation. I understand how confusing weather can be but I really like the way you presented this, and I didn't see anything I would disagree with. ;-)

I am happy that this discussion was started because important parts of weather are often overlooked by the average kiter. None of us on PKF want to be the "average kiter," so this is essential.

What are some other areas of weather we have not covered? Lets start a thread for some other stuff on weather

PixelGuru, thanks for such an elegant essay.