Jumping in humid air vs dry air

[jake95 0]

Hey guy, can anyone tell me the difference skydiving in humid air bs dry air, during freefall and under canopy. Thx

[BobMoore 0]

There was this guy many years ago who was featured in a video where he explained his high-speed landing was due to "rarefied air molecules". I think it might have been a tandem ....

"For you see, an airplane is an airplane. A landing area is a landing area. But a dropzone... a dropzone is the people."

[in2jumping 0]

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Hey guy, can anyone tell me the difference skydiving in humid air bs dry air, during freefall and under canopy. Thx

http://en.wikipedia.org/wiki/Density_of_air

"The addition of water vapor to air (making the air humid) reduces the density of the air, which may at first appear contrary to logic."

You will fall a bit faster and you canopy will fly a bit faster and have less lift on you flare.

[erdnarob 1]

Parachutes are like airplanes, their performances are sensitive to the air humidity and temperature as well.

When the air is warmed by the Sun, it expands therefore has less density than cold air. Amazingly, the humidity in the air is less dense than the air. This is how humid warm air goes up, expands, get cooler and forms a cloud. We can conclude that the lightest air is the hot and humid one.
For an airplane flying in hot and humid air, it get less lift from it and for instance will take quite a longer distance for taking off.

For a parachute, there will be also less lift in hot and humid air therefore less resistance, faster vertical speed and faster landing.

If it happens you jump your canopy at a Paraski over the snow, you will not get the same feeling at all than jumping the same parachute in the Summer.

Learn from others mistakes, you will never live long enough to make them all.

[chuckakers 425]

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There was this guy many years ago who was featured in a video where he explained his high-speed landing was due to "rarefied air molecules". I think it might have been a tandem ....

Bob, that was Lance Kirwin's tandem passenger face-thru-the-peas video and it was great!

Anyone have a link that somewhere??

Chuck Akers
D-10855
Houston, TX

[daremrc 0]

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There was this guy many years ago who was featured in a video where he explained his high-speed landing was due to "rarefied air molecules". I think it might have been a tandem ....

Bob, that was Lance Kirwin's tandem passenger face-thru-the-peas video and it was great!

Anyone have a link that somewhere??

No but it was shown at a film festival recently...

Good judgement comes from experience, and most of that comes from bad judgement.

[quade 4]

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Parachutes are like airplanes, their performances are sensitive to the air humidity and temperature as well

Parachutes are sensitive to temperature far more than humidity. Temperature can easily account for a 1000 foot difference in density altitude over the course of a day at certain locations.

On the other hand, humidity barely affects canopy performance at all. It can have a significant effect on aircraft engine performance since the water vapor is displacing oxygen molecules, but as a canopy pilot it's not something you need to worry too much about.

quade -
The World's Most Boring Skydiver

[erdnarob 1]

Thank you for the qualitative precisions added to my post. I guess I can get figures from my pilot books. For a piston airplane engine, for sure humidity affects the oxygen concentration. The temperature too since you can see a decrease of power when having the carburator heater on.

Learn from others mistakes, you will never live long enough to make them all.

[shropshire 0]

Beware of the 2 H's

Height

Heat
&

Humidity

And when all 3 co-exist you better be ready for a faster than normal landing.

It's all to do with Air Pressure ... Clicky

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Density Altitude

The conditions that you fly in will never be exactly the same from jump to jump. While we all appreciate the obvious changes in the wind there are less obvious changes taking place in the air all of the time.

Temperature: The hotter the air - the thinner the air. A temperature increase of 8?C is equivalent to an altitude change of approximately 1000 feet higher.

Pressure: Pressure changes with altitude; it also changes as weather patterns move around. Standard pressure at sea-level is 1013 mbar (millibars). Jumping while a low pressure system with a sea level pressure of 1000 mbar is passing through is equivalent to landing at about 400 feet higher.

Humidity: The amount of moisture in the air also changes its density. Strangely enough, the more humid the air, the thinner it is. (Yes, really.) So again the effect on a humid day is of jumping at a higher altitude.

All of these effects can be combined to produce an equivalent density altitude. These effects are cumulative and should also be added to the true altitude of your drop-zone (some Australian drop-zones are 2000 feet or more above sea-level).

What does all this mean and what does it do to your canopy's performance?

A 2000 feet increase in density altitude will alter your canopy performance by 3%. This means that since the air is 3% less dense, your true airspeed will be 3% higher (although it will not feel any different) so your landing distance required will increase, and you will lose 3% more height in a turn. (This may not sound very much but if you attempted a hook turn from 100 feet and were out by 3 feet then your leg straps would be scraping the ground!)

And the accumulated effect of hot, high and humid on the same drop-zone between summer and winter conditions could easily total 5000 feet and a change in your canopy's performance of around 8%.

(.)Y(.)
Chivalry is not dead; it only sleeps for want of work to do. - Jerome K Jerome

[jake95 0]

Thx for all great info guys, I'm new and I don't just want to do skydiving, I want to learn it. I will look for that video u were talking about. Thx again

[BobMoore 0]

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Thx for all great info guys, I'm new and I don't just want to do skydiving, I want to learn it. I will look for that video u were talking about. Thx again

I'm sorry, jake95, my comment about that video (post #2) was really a smartass remark. I was just trying to get a laugh from the folks here who have seen the video.

That video is more than 20 years old. The story is (the way I heard it anyway) that a tandem instructor had a less than stellar landing and surfed his passenger across the pea gravel pit. It was his bad luck to have it on video. A very clever skydiver/comedian made a 10 or 20 minute comedy video about the landing and the poor tandem master (who I will resist naming) was embarrassed nation-wide. The tandem instructor was also videoed explaining to the tandem passenger that the "high-speed" landing was because of "rarefied air molecules".

"For you see, an airplane is an airplane. A landing area is a landing area. But a dropzone... a dropzone is the people."

[jake95 0]

no worries bud

[shropshire 0]

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Thx for all great info guys, I'm new and I don't just want to do skydiving, I want to learn it. I will look for that video u were talking about. Thx again

Excellent attitude

Have fun.

(.)Y(.)
Chivalry is not dead; it only sleeps for want of work to do. - Jerome K Jerome

[shah269 0]

WOW!
So in higher temperatures turbulance should be less of an issue since the air lacks the density to throw you around?

Life through good thoughts, good words, and good deeds is necessary to ensure happiness and to keep chaos at bay.

The only thing that falls from the sky is birdshit and fools!

[quade 4]

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WOW!
So in higher temperatures turbulance should be less of an issue since the air lacks the density to throw you around?

It's the lower density of higher temperature air rising through slightly cooler and lower density air that causes convective turbulence and gives rise to things like dust devils.

But certainly you already knew that, so quit confusing the newbies. This isn't the forum for that.

quade -
The World's Most Boring Skydiver

[shah269 0]

Well kind of sort of....no.
I hit turbulance last year in the fall, a rotor off a building which started the sequence that led me to my hard landing.
But this summer I've hit the same rotor and it's been much softer and easier to deal with.
I'm sure it's mainly due to flying a functioning wing that's a solid 25sqft larger. But wasn't sure.

Life through good thoughts, good words, and good deeds is necessary to ensure happiness and to keep chaos at bay.

The only thing that falls from the sky is birdshit and fools!

[BobMoore 0]

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Well kind of sort of....no.
I hit turbulance last year in the fall, a rotor off a building which started the sequence that led me to my hard landing.
But this summer I've hit the same rotor and it's been much softer and easier to deal with.
I'm sure it's mainly due to flying a functioning wing that's a solid 25sqft larger. But wasn't sure.

You landed downwind of a building? Twice?

"For you see, an airplane is an airplane. A landing area is a landing area. But a dropzone... a dropzone is the people."

[quade 4]

I said convective, not mechcanical. Rotors don't have a lot to do with what's being talked about in this thead.

quade -
The World's Most Boring Skydiver

[shah269 0]

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I said convective, not mechcanical. Rotors don't have a lot to do with what's being talked about in this thead.

Ah yes! Ok.

And yes the way our DZ is set up just the way it is there is a section in the air that a rotor sets up when the wind comes from a given location. We are not sure if it's due to the buildings or the treet. But it's there at about 150ft. And with the old 265 it use to shake the hell out of me and toss me out a few feet off of my intended landing sight.
But with the 280 I'm using now I add some toggle pressure and pass through it but then hit the down wash at 100ft shich is not fun.

Life through good thoughts, good words, and good deeds is necessary to ensure happiness and to keep chaos at bay.

The only thing that falls from the sky is birdshit and fools!

[quade 4]

Ok, since you insist on going there.

Imagine wind moving around buildings and trees the same way you'd look at water flowing around rocks in a stream.

Ever notice how smooth the water is before it hits the rocks and how messed up it is afterward?

A reasonable rule of thumb if you're downwind of a building or trees is to stay away from them by at least five times their height. Under certain conditions this could be a lot more or a bit less, but it's a reasonable rule under normal conditions.

50 foot tall hanger? Try staying at least 250 feet away from it and most of your problems with mechanical turbulence from it will go away.

If the DZ is set up where that's not possible, maybe it's not a good idea to jump when the wind is blowing a certain way.

quade -
The World's Most Boring Skydiver

[shah269 0]

Roger i undestand the fluid dynamics.
But I never realized that fluid density effected things as much.
In the summer months....no problem cut through it like a knife.
Fall....hey now! This stuff has some weight!

Life through good thoughts, good words, and good deeds is necessary to ensure happiness and to keep chaos at bay.

The only thing that falls from the sky is birdshit and fools!

[billvon 2,998]

>In the summer months....no problem cut through it like a
>knife. Fall....hey now! This stuff has some weight!

It sounds like you might be thinking "turbulence in less dense air affects you less." That's not the case.

Turbulence is just moving air. A 20kt gust when the temperature is 20F will affect you just as much as a 20kt gust when the temperature is 100F.

Also, your airspeed doesn't change much when the air is less or more dense. The air is indeed less dense when it's hot, but your canopy just goes faster. It's like indicated airspeed in an airplane.

The big thing is how airspeed converts to groundspeed. When it's hot or humid, or the elevation is higher, a given airspeed will produce a higher groundspeed. Which is why it can be a problem for people when landing.

An additional issue is convective activity. Hot days generate more convection. (Actually the sun creating hotspots on the ground is what does that, but that happens more in summer than in winter, so it's generally associated with high temps.)

[Inspired 0]

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When it's hot or humid, or the elevation is higher, a given airspeed will produce a higher groundspeed. Which is why it can be a problem for people when landing.

Huh?