Tunnel chambers with 1 exit versus 2 exits -- Comments?

[mdrejhon 8]

Hello,

I'd like to hear from some experienced tunnelflyers as well as tunnel engineers to understand this better.

Some tunnels have 2 exits from the chamber, while others only have 1 exit. The recent trend has been to reduce the number of exits to 1. This ever so slightly reduces enter/exit efficiency as everyone has to exit before the next tunnelflyers can go into position to enter the tunnel, but much LESS annoying turbulence when flying 4 or more people in the tunnel at the same time, correct?

Most people who has flown in 4-ways love the 1-exit configuration, flying multiple people in a tunnel inevitably pushes some flyers towards the exit, whereupon they sometimes lose control or need to temporarily slow down the formation point-scoring to quickly regain bearings (recovery delay)

It is observed (and agreed among between many of us) that even the turbulence of 1-exit tunnels (i.e. Skyventure Montreal, Paraclete XP) have much LESS turbulence in front of the exit, than in front of either 1 of the 2 exits of 2-exit tunnel chamber. It doesn't even matter if this tunnel is recirculating or non-recirculating; having 2 exits seem to affect turbulence significantly.

I have always observed "wind" going through the waiting area of a 2-exit tunnel, but never a 1-exit tunnel. This is often caused by flyers near the exit deflecting the air into one exit, which gets blown into the waiting area, and then out of the other exit. As a result, the air around a 2-exit tunnel feels "softer" (because the air easily defflects into the exit and out of the other exit, air always follows the path of least resistance). The air next to a 1-exit tunnel chamber is more 'solid' and has a very predictable transition of softness -- making it easier to enter/exit too, and more predictable in flying near. (it's never randomly 'too soft' or 'too hard' depending on whether flyers are near the other exit, as air can flow bidirectionally through the waiting area between the two exits, depending on who's deflecting air near the exit.

I have even noticed flying near Exit 1 always feels slightly different if somebody is flying near Exit 2 than when nobody is flying near Exit 2). It's the "air mattress" effect -- if one sits on one end of the air mattress, the other end of the air mattress is firmer. Roughly, approximately the same thing happens with 2-exit tunnel chambers. When you do frequent 4-ways or bigger in a tunnel, you get many opportunities to observe this air mattress effect. If a bellyflyer is very, very, near the other exit, I feel a difference in the airflow at the other exit -- it's definitely slightly firmer. (Perhaps, it may probably also contribute slightly to why you almost never see two skydivers fall into two separate exits at the same time. When someone in a 4-way-plus falls into an exit, it's usually when nobody else is near the other exit -- that's when the air near the exit is the softest and more easily deflectible from one exit to the other. Even as a spectator in the waiting area feeling the 'wind', I can tell by the direction the wind is blowing in through the waiting area, which clearly tells me air is being deflected from one exit to the other)

I think this, apparently, is now why Skyventure now prefers to design tunnels with only 1 exit -- the airflow around the exit is always smoother and more predictable -- an additional benefit above and beyond fewer exits to worry about falling into in tunnel RW training.

Anyone think I'm on-base or off-base?

[punkd 0]

Having flown in Montreal and Paraclete XP (both 1 door) and the 2 door configuration at New Hampshire. I must say that the 2 door is much more noticeable in terms of turbulence around the door. I think I've fell out of the exit door more times than I've entered that tunnel.

[Kimsdu 0]

I wish they would close one of the doors in Orlando too, It makes us coaches constantly think about positioning our students so they dont get the burble or drop out of the door whilst trying to keep them on camera..
One door would eliminate this and would in turn make the airflow faster and smoother.
Because orlando is a big tourist tunnel its nice to have 2 doors, one for entry one for exit but for skydivers 1 is better... In my opinion..

[LloydDobbler 2]

I agree with all Michael's comments on the burble advantages/disadvantages. I prefer the airflow in the single-door tunnels.

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Because orlando is a big tourist tunnel its nice to have 2 doors, one for entry one for exit but for skydivers 1 is better... In my opinion..

Interesting. From my experience, I'd say exactly the opposite. For the more touristy tunnels, I've noticed that entrances/exits are easier/quicker with only one door, because the TI doesn't have to finish with exiting customer, then slide back through the airflow to get to the next customer. They're right there, ready to go.

On the flipside, for 4-way, entrances/exits are always faster in a 2-door tunnel, because (provided the other people in the chamber are aware) we can shoot 2 out one door and 2 out the other (same goes for entrances).

Makes getting in/out much faster.

(But to each their own).

If given the choice, I definitely agree, though - much prefer the single-door tunnels for flying.

Signatures are the new black.

[mdrejhon 8]

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I agree with all Michael's comments on the burble advantages/disadvantages.

Just a heads up. My name is Mark Rejhon.

[LloydDobbler 2]

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I agree with all Michael's comments on the burble advantages/disadvantages.

Just a heads up. My name is Mark Rejhon.

That's what I get for making a quick post, Mark. I even thought twice about it, but just hit 'Post' anyway.

Signatures are the new black.

[MikeJD 0]

I don't really have enough tunnel experience to comment, but Bodyflight Bedford used to have two doors and now has only one. They must have had a reason for changing the configuration, and there must be plenty of people who've flown in there a lot both before and after the change.

Maybe you should try contacting Bodyflight direct - they can probably advise you.

[Sandro29 0]

I believe one of the main reasons for having a single entrance as opposed to two....insurance premiums.

I believe the rates are considerably lower when having only 1 entrance...and a tunnel is all about making $$.

If at first you don't succeed....then Skydiving is not for you!

[mdrejhon 8]

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I believe one of the main reasons for having a single entrance as opposed to two....insurance premiums.

Interesting. I guess the insurance companies figured out a tunnel is safer with just one entrance/exit, after noticing some past injuries involved the doors.

[Morrison79 0]

I think it was at Eloy the tunnel instructor told me they sealed off the second door so they didn't have to guard it from ppl flying out of it. Not sure if they used to have 2 instructors in the tunnel, one for each door, but if that was the case then it could be to save money on instructors.

[mdrejhon 8]

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I think it was at Eloy the tunnel instructor told me they sealed off the second door so they didn't have to guard it from ppl flying out of it.

That should also stabilize and smooth airflow around the only exit too -- have any Eloy tunnelflyers noticed improvements in airflow smoothness flying adjacent to the exit?

[Paulipod 0]

Well.. I can only speak for ourselves at Bedford in this subject... but our reasoning was :-

. We opened with two doors originally as we figured that and 'in-out' flow for customers would be quickest and make for a sensible operation
. After a couple of years and listening to customer feedback etc decided that two doors actually made for a slower operation. (ie the instructor had to move from one door to the other prior to customers getting in)

So we closed off one door and made the area around the remaining door larger to make the transition for flyers smoother.

From a safety point of view it definitely makes it safer only having one door to guard. Makes no difference to insurance premiums - however cuts down potential blame issues if someone did fall out an unguarded door.

From an air quality point of view - any door loses pressure slightly in the chamber however in our system this is very minimal. In fact we have removed all our windows (for the Bond filming) and still flown with no noticable issues.

Bodyflight Bedford
www.bodyflight.co.uk