Vacuum effect

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jmaas07
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Vacuum effect

Unread postby jmaas07 » Thu Jun 04, 2015 12:02 am

Couple questions on vacuum effect with wind coasting over timber and then hitting an opening...does the wind need to be coasting over a significant amount of timber before hitting an opening for the vacuum effect to be prevalent? Will you get the same effect if the wind is coasting across an open field and then hits timber where there is say roughly ten yards of timber and just inside that strip of timber there is an opening for say 20-30 yards and then the woods picks back up, will there be a vacuum in that opening as prevalent as when the wind is coasting over timber for a ways before hitting an opening? Have you guys noticed about how far out into an opening the vacuum effect goes in different situations? Is it just prevalent right at the transition or is the wind being pulled back the opposite direction for a little ways out into the opening?

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ihookem
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Re: Vacuum effect

Unread postby ihookem » Thu Jun 04, 2015 1:29 am

I think I know what you mean but not sure. This is what I noticed from hunting along a good size river. The river I hunt along goes east/west. If it is a west wind the wind blows in my face while Im looking at the river, then I cross the river and it still is blowing in my face while looking at the river Doesn't matter what side of the river Im on. I dont know for sure how far away from the river I have to be , never checked but I stay at least 50 yes from the river to make sure and theta is where the trail is that is parallel to the river. This might be why there are trails on both sides of the river that go for miles. Is this what you were asking , or am I scyco babbling?
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Stanley
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Re: Vacuum effect

Unread postby Stanley » Thu Jun 04, 2015 1:54 am

You have to really check with milk weed. There is no constant as wind velocity, terrain structure, ground cover, leaf density(leaves or no leaves) field size, timber size. Things like this.
You can fool some of the bucks, all of the time, and fool all of the bucks, some of the time, however you certainly can't fool all of the bucks, all of the time.
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jmaas07
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Re: Vacuum effect

Unread postby jmaas07 » Thu Jun 04, 2015 2:09 am

Ihookem I think what you are experiencing is the water thermal effect of the water being cooler than the air and pushing the thermals out towards the land. What I was asking was about the vacuum effect of wind blowing over timber and into an opening causing the wind to be sucked back towards where it was coming from

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jmaas07
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Re: Vacuum effect

Unread postby jmaas07 » Thu Jun 04, 2015 2:14 am

Stanley, I kind of figured that was what I would hear back, I have a stock pile of milkweed so I guess I need to play around with it a bit more in different situations. Was just seeing if maybe there was some generalizations on distance wind travels over a longer stretches of timber compared to a shorter distance over timber and the behavior of the vacuum effect once it hits the opening

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Re: Vacuum effect

Unread postby jmaas07 » Thu Jun 04, 2015 2:27 am

heres a scenario, and this might be a situation where milkweed is going to be what tells the tale but maybe there is a general rule of thumb that has been experienced. Lets say you are hunting a bed that is a little ways out into the cattails, maybe 70-80 yards off the transition line where the woods meets the cattails and to hunt the bed you need a just off wind blowing from the woods out into the cattails assuming movement is coming from the bed and into the timber...if I set up just inside the timber in the vacuum where my scent is being pulled back into the timber is it generally better to be lower in the tree so you are more in the zone where your scent is being pulled back in as opposed to being higher where your scent might be pushed out a bit before being sucked back in? Or does that not matter too much and just set up where ever in the tree your back cover is best?

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JoeRE
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Re: Vacuum effect

Unread postby JoeRE » Thu Jun 04, 2015 2:47 am

A word of warning - if you want to fully understand what is being called the vacuum effect we need to dig into fluid mechanics :lol:

To put it simply as possible, air and water act the same way as "fluids" so a very good way to see what is termed the vacuum effect is study a river or stream. When you have an air current or stream of water moving, the pressure actually drops in that stream or air current. That means when you move to the edge of that air current or stream of water (like right next to a stream bank or boulder or tree line for air) you have lower pressure in the moving flow than what is right next to it in pockets of air or water that are not moving. That results in vertical AND horizontal swirling and eddying because naturally some of that calmer air or water will try to move over to the moving flow that is lower pressure and sort of collides with it and you get a swirl. There is some other stuff going on too but I don't want to make it unnecessarily complex.

So, yea as Stanley said you really need to test out each spot. In general the deeper the "pocket" of still air (like from taller denser trees) the more vacuum effect and associated swirl you will see. Also like he said what was a pocket in full foliage woods that caused swirling can change or even disappear after leaf drop. Look at what the main flow of a stream does past boulders, that gives you a good handle on what air does behind a dense clump of trees - or an open pocket in a forest. Hope that helps...
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Re: Vacuum effect

Unread postby JoeRE » Thu Jun 04, 2015 2:51 am

jmaas07 wrote:heres a scenario, and this might be a situation where milkweed is going to be what tells the tale but maybe there is a general rule of thumb that has been experienced. Lets say you are hunting a bed that is a little ways out into the cattails, maybe 70-80 yards off the transition line where the woods meets the cattails and to hunt the bed you need a just off wind blowing from the woods out into the cattails assuming movement is coming from the bed and into the timber...if I set up just inside the timber in the vacuum where my scent is being pulled back into the timber is it generally better to be lower in the tree so you are more in the zone where your scent is being pulled back in as opposed to being higher where your scent might be pushed out a bit before being sucked back in? Or does that not matter too much and just set up where ever in the tree your back cover is best?

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Some of your scent would get sucked back in but keep in mind eventually it doesn't just stop there, it eventually blows off down wind of where ever that back draft current ends up. Its really hard to say what would be better high or low depending on the situation....drop a few milkweed as you are climbing up the tree and see what happens at different elevations. Its challenging because there is so much variability.
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Re: Vacuum effect

Unread postby jmaas07 » Thu Jun 04, 2015 4:18 am

Thanks guys, appreciate the responses.

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