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Wind Tunnel is not the same as Skydiving

 

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skrovi  (D 29976)

Apr 10, 2006, 9:04 AM
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Wind Tunnel is not the same as Skydiving Can't Post

hello:
I'm a new jumper with 32 jumps and was heading up to Orlando on some work and figured I could use the trip to sharpen my freefall skills in the tunnel there. What I experienced is completely different. Firstly, I was disappointed with my performance. I found it hard to fly stable maintaining heading in the Tunnel Vs in freefall. It seemed more turbulent in the tunnel than it is in freefall. And needless to say, I looked like I'm fighting to remaining stable. My instructor at the tunnel told me that he sees lots of skydivers perform poorly when introduced to tunnel with my experience level. I've not jumped after the tunnel time and would liek to see if it improved my skills.
So I would like to get responses from anyone who can comment on what I saw is normal and any further comments on how I can take what I learnt in the tunnel to improve the freefall skills.
thanks,


TrickyDicky  (C 103196)

Apr 10, 2006, 9:25 AM
Post #2 of 73 (3841 views)
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Re: [skrovi] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

I think its fairly normal.

Basically, in the tunnel, the air is forced around your body
In the sky, the air flows around your body.

So you have to put more effort in to fly in the tunnel, but tunnels skills will translate to air skills.


AMax

Apr 10, 2006, 10:05 AM
Post #3 of 73 (3786 views)
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Re: [skrovi] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

The speed does change sometimes but that's not the major cause or your 'problem' Wink. Unlike actual freefall, in a tunnel you have to fly in restricted column of air. The tunnel is less forgiving to any inperfection in your flying (like sliding around) which is pretty normal for you experience level. I would bet that you experience the same problems in freefall but you cannot really identify them because of lack of stable reference (like the walls in a tunnel). Don't get frustrated - the tunnel is amazing tool that teaches you how to skydive better. It is a lot of fun too. Wink


Premier billvon  (D 16479)
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Apr 10, 2006, 10:16 AM
Post #4 of 73 (3777 views)
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Re: [TrickyDicky] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

>Basically, in the tunnel, the air is forced around your body
>In the sky, the air flows around your body.

Air in the tunnel is basically identical to air in freefall. There's more interference from flying close to someone in 'real' freefall than in the center of the tunnel by yourself.

>So you have to put more effort in to fly in the tunnel . . .

That's true, but it's not because the air is different. It's because you have to not backslide, change your fallrate or sideslide. When you do any of those things in the air, you may not notice them, and think you're not doing them. In the tunnel you will definitely notice them.


Hooknswoop  (D License)

Apr 10, 2006, 11:01 AM
Post #5 of 73 (3727 views)
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Re: [skrovi] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

Quote:
I'm fighting to remaining stable.

Which is why you aren't stable. You had a reference that you were moving in the tunnel and were trying to correct for that movement. In free-fall, you would have just moved without knowing it.

Moving makes you move, holding still makes you hold still.

Look at good tunnel flyers, they don't move because they don't move.

Skydivers think they fall straight down, until they get in the tunnel and realize how much they actually move around the sky. The tunnel is almost the same as free-fall.

Derek


(This post was edited by Hooknswoop on Apr 10, 2006, 11:03 AM)


mattjw916  (D License)

Apr 10, 2006, 2:34 PM
Post #6 of 73 (3583 views)
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Re: [skrovi] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

Sounds like just about the same experience as most skydivers the first time they try out the tunnel. Laugh

How much time did you fly?

I recently reviewed my first tunnel flights (on VHS Crazy) from a couple years ago when I had about 50 jumps and I didn't do much better than you described... so don't feel bad. Like anything worth doing, practice will increase your proficiency.

Relax and arch works in the tunnel too... don't "fight" it. Wink


CMiller  (B 30864)

Apr 10, 2006, 2:49 PM
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Re: [billvon] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

Quote:
Air in the tunnel is basically identical to air in freefall. There's more interference from flying close to someone in 'real' freefall than in the center of the tunnel by yourself.

That's odd, because the first thing I was told when I got into the tunnel was the air is thicker than in the sky, since it's at ground level. Therefore, smaller movements produce the same results. This might explain why initially, it might seem hard to control.


Premier billvon  (D 16479)
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Apr 10, 2006, 3:14 PM
Post #8 of 73 (3545 views)
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Re: [CMiller] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

>because the first thing I was told when I got into the tunnel was the air
>is thicker than in the sky, since it's at ground level. Therefore, smaller
>movements produce the same results.

If that was true, then we would have had a very hard time doing the 400 way world record - at 25,000 feet, the air is less than half as dense as it is at the surface! And the tunnel in Denver would be even easier to fly in than regular freefall. But in both cases it feels pretty much like any other freefall.

The reason you don't notice much difference is that your indicated airspeed stays the same. In Denver, the true airspeed of the air in the tunnel (i.e. the airspeed you would measure if you let a dandelion seed go in the tunnel and measured how fast it went) is higher than the true airspeed in the Perris tunnel. And our true airspeed on the 400-way shortly after exit was close to 200mph. But skydivers don't care about true airspeed - they care about indicated airspeed, which is how much air flows past you each second. (It's also what airplanes care about.) As long as your indicated airspeed is the same, you don't really care what the true airspeed is.


skrovi  (D 29976)

Apr 10, 2006, 6:07 PM
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Re: [mattjw916] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

I did 10 minute tunnel time with four 2.5 minute session with 2 minutes break after each session. I had an objective for each session


mattjw916  (D License)

Apr 10, 2006, 7:47 PM
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Re: [skrovi] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

WHAT!!? You mean you didn't totally nail belly-flying in only 10 whole minutes in the tunnel?!! WinkLaugh

Seriously though, those people that you see flying in the tunnel who are totally smooth and effortless usually have dozens of _hours_ in the tunnel and typically hundreds to thousands of skydives on top of that!

Don't let your expectations get set too high as to what you feel like you "should" have accomplished in the short time you flew. Chances are you did make some progress whether you realize it or not. The best way to tell is to get videos of your flights and review them. I know I am my own harshest critic of how I fly in the sky and in the tunnel.

oh yeah... and don't forget to have fun! Wink


Ron

Apr 10, 2006, 9:06 PM
Post #11 of 73 (3448 views)
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Re: [CMiller] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

In reply to:
Therefore, smaller movements produce the same results. This might explain why initially, it might seem hard to control.

I find that it takes LARGER movments to get the same result.

That is due to a slower fall rate (hover rate?Tongue) due to a lighter jumper. In freefall you are going to be wearing close to 20 pounds more than in a tunnel. Less weight is going to equal a slower fall rate. A slower fall rate is going to require more input to get the same speed result.

I think that what you experienced was the simple fact that in the tunnel you have references all around you. So any small move will result in you SEEING you are moving faster.

It is a common problem when a jumper goes to the tunnel for the first time.

To limit this, my team last year wore rigs that were almost the same weight as our freefall rigs. This allowed us to fall at close to the same rate, and gave us restricted movement like a rig would give us.


Premier billvon  (D 16479)
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Apr 11, 2006, 8:50 AM
Post #12 of 73 (3369 views)
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Re: [Ron] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

>That is due to a slower fall rate (hover rate?) due to a lighter jumper.

That's a good point. A jumper with the same configuration of weight/jumpsuit/rig will fly the same in a tunnel as in freefall. However, most jumpers do NOT use rigs in a wind tunnel; that makes them fly a bit differently. It's hard to predict exactly how they will fly differently because, for many people, rig parasitic drag is an issue; their rig interferes with how wind flows over their bodies. (People with tiny rigs and large bodies may be an exception.) And although weight can be increased to deal with the loss of the rig's weight, most people don't do this.


djd  (D 10759)

Apr 11, 2006, 2:41 PM
Post #13 of 73 (3313 views)
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Re: [TrickyDicky] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

In reply to:
I think its fairly normal.

I second that. i was the same and have seen many there too. my mate had 3 n a half thousand skydives and never been in the tunnel, i went with him for his first session and could see the look of fear in his face at the thought of being crap. .. well guess what...He was..the look of dispare on his face after the first 2 mins was awfull,,,,however his second was much better and by the end of his 15 mins was pretty much flying well, but that could be down to the 3.5 thousand jumps under his belt me thinks...
dont be to hard on yrself with yr level of experiance i dought if you will have a lot of the bad habbits skydivers can have in the tunnel so you will pick things up mega fast....
i have bounced of more walls than i care to remember and woke up with bruises that i have had no idea how i got all i know is every time i go in the tunnel i come out with the biggest grin on my face...

keep trying keep banging them walls its the only way to learn and it scares the crap out the tunnel rats....lol...Wink


4wayFly  (D License)

Apr 11, 2006, 5:32 PM
Post #14 of 73 (3285 views)
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Re: [Ron] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

In reply to:
In freefall you are going to be wearing close to 20 pounds more than in a tunnel.

Why? Did you just pull that out your butt? Surely it depends on how fast you fall in the first place? I know plenty of skydivers who wear a lot MORE in the tunnel than in freefall. And the venturi effect (of some tunnels eg the SV ones) creates additional pressure within the chamber that does not exactly replicate freefall (not so in Bedford for example, no Venturi effect). So, many skydivers find that even if they jump with the same team in the tunnel that they jump with in the sky, the lightest person sometimes has to add extra lead in the tunnel. So ner Tongue

In reply to:
Less weight is going to equal a slower fall rate. A slower fall rate is going to require more input to get the same speed result.
Yes indeed. The input required is just about the speed you are travelling through the air and nothing to do with the tunnel or the sky.


Ron

Apr 11, 2006, 6:19 PM
Post #15 of 73 (3274 views)
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Re: [4wayFly] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

In reply to:
Why? Did you just pull that out your butt?

Can't disagree without being rude?

In reply to:
Surely it depends on how fast you fall in the first place?

Sure, but MOST people weigh less in the tunnel than in freefall since MOST do not wear rigs in the tunnel (avg weight 20 pounds). Even more so for the first time they are in the tunnel.

In reply to:
So, many skydivers find that even if they jump with the same team in the tunnel that they jump with in the sky, the lightest person sometimes has to add extra lead in the tunnel.

Ah, but ever think that might be due to how much time they spend in the tunnel vs in freefall? People wear out after several two min rotations in the tunnel. They don't have the rest of a 12 min plane ride.

In reply to:
Yes indeed. The input required is just about the speed you are travelling through the air and nothing to do with the tunnel or the sky.

So if a person weighs less in the tunnel (due to not having a rig) than in freefall, which most do, then what I said would be true, so why the insulting?

BTW ever flown a rig in the tunnel? I base my guess off of over 100+ hours of flying in tunnels, about 15 hours with a rig.

BIG difference with the rig. Also, I have strapped about 30 pounds on to see how that worked as well. I found that with the extra 30 pounds, the higher airspeed made me SO much more powerful.

In reply to:
And the venturi effect (of some tunnels eg the SV ones) creates additional pressure within the chamber that does not exactly replicate freefall (not so in Bedford for example, no Venturi effect)

That makes no sense. Your body is not going to be able to tell the difference between Venturi created speed and any other type of created speed.


(This post was edited by Ron on Apr 11, 2006, 9:04 PM)


pilotdave  (D License)

Apr 11, 2006, 6:29 PM
Post #16 of 73 (3268 views)
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Re: [4wayFly] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

Quote:
And the venturi effect (of some tunnels eg the SV ones) creates additional pressure within the chamber that does not exactly replicate freefall (not so in Bedford for example, no Venturi effect).

Can you explain what you mean by that?

Dave


Ron

Apr 11, 2006, 6:38 PM
Post #17 of 73 (3267 views)
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Re: [billvon] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

In reply to:
It's hard to predict exactly how they will fly differently because, for many people, rig parasitic drag is an issue; their rig interferes with how wind flows over their bodies.

Yes.

I will say the differences *I* noticed with a rig on in the tunnel.

1. The biggest difference was I felt the weight on my upper body. I was unable to get a over exagerated mantis like most fly in the tunnel. This wore my arms/chest out really fast. I have done 6 hours in one day before, and I can honestly say that 30 mins with the rig smoked me worse than those 6 hours.

2. The weight made it so the tunnel needed to be cranked up. This made it so I felt I had more power....But here is the rub, I also felt I needed more power to get my body to move.

3. The cool and groovy "snap" turns I can do in the tunnel where I turn almost on my side....Well they didn't work as well since the rig caught air like you commented on. And the rig limited my ability to torque my body into positions that let me move faster.

4. My back flying really sucked Tongue. We let Joey and I think Thomas play in the tunnel with our rigs...They still were very good, but it was a big difference. When I tried, I had to fight just to stay in control.

In reply to:
And although weight can be increased to deal with the loss of the rig's weight, most people don't do this.

I am a BIG fan of training 4way with rigs. I think that was a major reason my team did so well at the nats last year (Phugoid). We only made 170 jumps, but almost ALL of our tunnel that year was with rigs.


(This post was edited by Ron on Apr 11, 2006, 6:41 PM)


diablopilot  (D License)

Apr 11, 2006, 7:49 PM
Post #18 of 73 (3262 views)
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Re: [4wayFly] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

Quote:
And the venturi effect (of some tunnels eg the SV ones) creates additional pressure within the chamber that does not exactly replicate freefall (not so in Bedford for example, no Venturi effect).

What?


Again what?Crazy


mattjw916  (D License)

Apr 11, 2006, 9:26 PM
Post #19 of 73 (3242 views)
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Re: [4wayFly] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

Actually the "venturi effect" _reduces_ the pressure in the tunnel making the air flow _faster_ through the constricted area (i.e. the flight chamber) reducing the sheer power the motors need to have in order to make the tunnel useable for our purposes.

Whether the "venturi effect", or just raw power, is making the air flow at a given speed through the flight chamber doesn't matter in the least to us as flyers. What it really means is that your electric bill will always be higher than a Skyventure-style tunnel (or any other tunnel with a venturi air-inlet for that matter) and consequently you will have a higher operating cost.

Now that we've got that out of the way... I totally agree with Ron's assessment of flying in the lower airspeeds of the tunnel. MUCH bigger movements are required at the low-limit of my flying range in order to produce the desired result. And my back-flying is still pretty average in the sky... but in the tunnel, without a rig, I totally rock. TongueLaugh


djd  (D 10759)

Apr 12, 2006, 1:19 AM
Post #20 of 73 (3219 views)
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Re: [diablopilot] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

In reply to:
Quote:
And the venturi effect (of some tunnels eg the SV ones) creates additional pressure within the chamber that does not exactly replicate freefall (not so in Bedford for example, no Venturi effect).

What?


Again what?Crazy

it was explained to me as dynamic air presure...Crazy

if you imagine a small straw with a pea in that is only a little smaller than the straw you dont need a lot of air to hold up the pea...hence go up in a sv tunnel its harder to stay up there unless you weigh 100ib and can fly with yr pants on fire (not jelous at allWink )
however double the size of the straw and keeping the same pea up in the air you are going to need more wind speed.

Well it made sense to me at the time but now im typing Crazy lol...lol...if this makes sense to you let me know or if im completely wide of the mark, tell me so too..


Paulipod  (B 1234)

Apr 12, 2006, 4:59 AM
Post #21 of 73 (3199 views)
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Re: [diablopilot] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

 
In reply to:
Quote
And the venturi effect (of some tunnels eg the SV ones) creates additional pressure within the chamber that does not exactly replicate freefall (not so in Bedford for example, no Venturi effect).

What?


Again what?Crazy
In reply to:

Without getting into any kind of which you prefer type debate here is the technical difference between the two :-

In a tunnel with contraction before the test section you are setting a different atmospheric pressure level in the flight chamber. This pressure difference is why for example you have to keep the doors shut.

If the air is 'squeezing' for want of a better word into a smaller area then the effect is slightly different - which most people can feel.

In our tunnel we move the air through the fans without this fan/chamber size difference - hence we have the flight chamber at the same atmospheric pressure as outside (hence no need for doors shut etc)

Air has many qualities to it... Density / Speed / Temperature all make a difference.

Smile


Ron

Apr 12, 2006, 9:51 AM
Post #22 of 73 (3158 views)
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Re: [Paulipod] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

In reply to:
If the air is 'squeezing' for want of a better word into a smaller area then the effect is slightly different - which most people can feel.

I can't understand HOW people can "feel" the difference.

Anyone care to explain how it "feels" different?

I would think that a tunnel with "X" as an airspeed would feel the same no matter how that airspeed was created. And I would also think that any difference would be too small for most (maybe all?) to tell. I mean there is a different pressure altitude at 13.5 vs 2 grand, but I would bet most could not "feel" a difference.

Question: How many fans do you have?


pilotdave  (D License)

Apr 12, 2006, 10:22 AM
Post #23 of 73 (3150 views)
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Re: [Ron] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

I agree with you... I think all that talk about the air feeling different due to the venturi effect (or really bernoulli's principle) doesn't make much sense. Air pressure isn't constant on a skydive, so we're used to flying at different atmospheric pressures.

In research wind tunnels, there are 3 things that you need to have in order to properly simulate the air flow around the object you're testing... The shape of the model has to be the same as the shape of the real object... no problem there for us, since we are the model and the real object, minus the rig usually. Second, the mach number must be the same. We're using "full scale" wind speed, which is completely subsonic, so no issue there. Third is the reynolds numbers need to be equal. That's dependent on the size and shape of the objects and the air velocity, density and viscosity, which does vary with altitude. When testing a scale model in a wind tunnel, the air density can be adjusted in some tunnels to adjust the reynolds number to match the real flow you're trying to simulate. For a vertical tunnel, all the important numbers are really damn close to the real things. Objects in the tunnel will therefore behave the same as they will in "real life." That is, as long as you stay away from walls.

Now if you're really big in a small wind tunnel, the walls will have an effect. I'm sure a 4-way in a skyventure tunnel blocks enough of the cross sectional area of the tunnel to make a difference. You start to choke off the flow at some point.

Dave


diablopilot  (D License)

Apr 12, 2006, 10:48 AM
Post #24 of 73 (3144 views)
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Re: [Paulipod] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

Quote:
If the air is 'squeezing' for want of a better word into a smaller area then the effect is slightly different - which most people can feel.

I'll have to diagree with that.


rehmwa  (D 12816)

Apr 12, 2006, 11:23 AM
Post #25 of 73 (3134 views)
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Re: [diablopilot] Wind Tunnel is not the same as Skydiving [In reply to] Can't Post

In reply to:
Quote:
If the air is 'squeezing' for want of a better word into a smaller area then the effect is slightly different - which most people can feel.

I'll have to diagree with that.

Ditto - I'd wonder if a non-venturi design might be less subject to flow choking and edge effects, which can be felt. But I doubt if the improvement would be any better than just having powerful enough fans and good circulation features. I'd think the benefits to avoiding choking off flow or poor edge effects for the Bedford tunnel is most likely supported by the bigger size rather than the flow scheme. But, then again, It's been 15+ years since I've studied wind tunnels and airflow.

All I do think now is, if I get too many bodies on one side of a tunnel, especially right at a wall, then the air will route around on the other surface, and if the fans are too close, it could even stall our the blocked side. That's when I have to climb off of my teammates or vice versa. So I'd think there is a 'theoretical' benefit to a recirc or push flow of air rather than a drawing flow. Hoever, in subsonic flow, it's greatly mitigated regardless of whether it's a blower or a sucker. Because pressure information travels through the flow in either case much faster than the flow itself travels.

In practice, I'd agree with Ron - having a rig on makes a ton of difference - I have more power (it seems) in the sky and it's likely the faster airflow. But I also need that extra power especially in sideways movements (which I wonder if it is due to the extra area presented by the rig). And the rig makes it harder for me to get really 'tall' in my mantis too. I'd love to practice in the tunnel frequently and with tunnel "rigs" of the correct weight and shape.

Just because it 'looks' like a chocolate egg, doesn't mean you want to take a bite of it.


(This post was edited by rehmwa on Apr 12, 2006, 11:25 AM)


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