What if the power grid fails?

[cj1150gs 0]

And we are high up in the tunnel? The motor stops and we just fall off? Or is the inertia in the fan enough to slowly decelerate the air flow and bring us down gently?

Do tunnels have energy backup solutions like huge MW gensets??

I was this last weekend at Bedford where Paul was very nice answering some of our questions but I was busy being briefed/debriefed by my excelent coach Steven www.blincoe.org and getting amazed at Babylon activity, so I forgot to ask this one...

Carlos Martins
Portugal www.cj.smugmug.com

[Paulipod 0]

Hiya!

Hopefully managed not to bore you too much with the geek stuff!

Bottom line is - if the power goes off.... we all fall down!

As far as I am aware, a power outage in every tunnel built to date will result in almost instant air loss.

For this reason we make sure the net is more springy than not... and also that our power supply is as protected as possible.

Power backups of the size needed are not at all cost viable.

Bodyflight Bedford
www.bodyflight.co.uk

[skydiverek 54]

That would suck in a 160 mph head down...

[cj1150gs 0]

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Hopefully managed not to bore you too much with the geek stuff!

Not at all! I'm into geeking myself I am just sorry that I was rushing all over the place and couldn't chat more about the internals of the beautifull beast!

Thanks for your answer.

Carlos Martins
Portugal www.cj.smugmug.com

[MattM 0]

Thats why you sign a waiver.

Matt

[apoil 0]

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That would suck in a 160 mph head down...

In a wind tunnel that doesn't mean you will immediately plummet towards the net at 160mph. When the wind stops, your speed is ZERO relative to the earth and you will start to accelerate from there. It will be like falling from wherever you are onto the springy net. The only difference is the body position.
Hitting the net head first from 10-15 feet up carries a significant risk of serious injury but it isn't inevitable. A skilled flyer should be able to tuck up and land on their back.

[skydiverek 54]

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Hitting the net head first from 10-15 feet up carries a significant risk of serious injury

That's what I was referring to (maybe not clearly).

[tdog 0]

I have seen the instructors pull the throttle lever to zero quickly and the fans seem to take a while to slow down.

Now I know there is a computer between the lever and the fans that might smooth out this curve - but each time the wind does not just stop but gives some support for a few seconds. Granted, I have flown a lot more in a recirc tunnel than the others, which might add a bit more "inertia".

Just watching every fan in the world, from a ceiling fan in a house, to a prop on a plane, to a jet turbine - they all spin for a while after they are turned off - rotational inertia is a powerful force, especially with weight behind it.

So lets say the computers were removed from the shut down(like a power outage or someone throwing a main breaker) - how quickly will the air go from 120MPH to 0?

I just imagine that you would be "set down" on the net quickly but softly, especially if you are flying where you normally fly unless playing up high (0-10 feet off the net).

[Paulipod 0]

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how quickly will the air go from 120MPH to 0

Almost instantly... Having been in the situation a couple of times (in different facilities) the result is like going into instant freefall.

Although the fans still spin for a bit - there is a world of difference between just spinning down and the many hundreds of horses in normal flight....

Takes you by surpirse thats for sure! lol

Bodyflight Bedford
www.bodyflight.co.uk

[lauras 0]

Before SV Orlando upgraded the fans, I was flying with a friend when one of the fans shut down. We were well above the doors & both lost air instantly. Bounced onto the grate & she rebounded & landed on my back. It sucked, although the grid-shaped bruise on my front kinda looked cool.

[Hooknswoop 19]

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Almost instantly... Having been in the situation a couple of times (in different facilities) the result is like going into instant freefall.

At SVCO, I will have the controller cut the power. I can then hop in, pop up about 30 feet, come back down, stop, then back out the door. This is all after the power has been cut. Several of the Instructors will hop in after the power has been cut and back loop back out the door, run around the walls, etc. The wind will actually slow down slower if the power fails, since the braking system needs power to operate. A power falure at SVCO would be a non-event.

Derek

[DougH 270]

Why the difference in results?

"The restraining order says you're only allowed to touch me in freefall"
=P

[Jewels 0]

Good to know we're special! I know it's not going to happen, but now I want to get in there and try it.

What about the doors, though? I assume there's a manual override so we could get out. Not that I'd really complain about getting stuck in the tunnel, but eventually, I'd get hungry and I get grumpy when I'm hungry.

TPM Sister #102

[Eule 0]

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Paulipod: Almost instantly... Having been in the situation a couple of times (in different facilities) the result is like going into instant freefall.

Do any of the tunnels hold off on flying if, for instance, there is a thunderstorm and the lights have been flickering a bit? Also, for the amount of power a tunnel buys, I would think they might be able to negotiate a decent service level agreement with the electricity company. On the other hand, though, that kind of agreement might only say something like "if we need to shut off your power to work on the grid, we will give you X hours notice and only shut it off between 1 and 3 in the morning" and not say "you'll never get a glitch".

I agree that at tunnel power levels, having a backup probably wouldn't be cost effective. You probably wouldn't use a motor-generator set, as those take a few seconds to fire up and it sounds like those seconds could be critical. You'd probably have to make a giant UPS with batteries and static inverters. On the back of an envelope, the batteries wouldn't be super expensive - assuming a 1200 hp tunnel, you could probably buy enough car starting batteries to do it for US$15,000 or so. (This is the wrong battery for this application in every aspect except price.) You'd also get to build a battery room for four tons of batteries and deal with some hazmat issues, like the hydrogen that batteries make when charged. You'd also get to replace them every three to six years. The inverter would be the real killer - based on $/watt for "small" consumer-type inverters up to 7 kW, the inverter you need would cost at least US$250,000. Probably more since this is not the kind of thing that Acme Inverters can sell thousands of at Wal-Mart. I think I've seen a number thrown around in this forum of about US$1m for a SkyVenture tunnel, so the UPS would add 25% or so to the total (capital) cost. Alternatively, you could stick that much money in the bank and just hand it to somebody if they get injured in the tunnel due to a power cut, or use that money to pay for a few years' worth of a decent liability insurance policy.

You might be able to do it cheaper IF the first thing the VFD does is rectify the incoming AC power to DC. You'd still spend about the same amount of money on batteries, but hanging the batteries on that DC bus would eliminate the need for the inverter. You'd still have to add some charging and switching circuitry but it wouldn't be nearly as expensive as the inverter. Since this is "inside" the VFD, though, you'd probably have to involve the VFD manufacturer if you wanted to have any semblance of a warranty on it, and they'd probably have a non-trivial NRE charge, at least for the first one.

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At SVCO, I will have the controller cut the power. I can then hop in, pop up about 30 feet, come back down, stop, then back out the door. This is all after the power has been cut.

I think what you are talking about is having the operator turn the knob on the control panel down to zero. Go downstairs and trip the main breaker for the entire building and see what happens.

Eule

PLF does not stand for Please Land on Face.

[DougH 270]

Eule, do you drink a lot of coffee?

"The restraining order says you're only allowed to touch me in freefall"
=P

[Eule 0]

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Eule, do you drink a lot of coffee?

No, I don't like it that much. However the local Coca-Cola bottler has invited me for a ride on his new boat that was funded by my steady support of his business. :)

In reality, I am on the ground, looking at the sky, and waiting for some paperwork to come through before I get back in the air. If I go outside for too long in the daytime I'll get in the car and if I do that I'll drive to the DZ and if I'm at the DZ I'll probably put on a rig and get in the plane and if I'm in the plane I'll probably just fall out of it. So I stay inside and geek out instead. (At this point the good people of this forum tell me to go to a tunnel - the problem is that the tunnel is ~12 hours away but the DZ is only ~0.75 hour away, and I have to go past the DZ on the way to the tunnel...)

Eule

PLF does not stand for Please Land on Face.

[Paulipod 0]

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A power falure at SVCO would be a non-event.

Not sure this is correct - As Eule said... its not the same turning the speed down on a regulated controller to the VFD losing power.

Bottom line is - if you put zero power in.... you have zero lift.

Inertia of small turning blades is tiny... Inertia from our prop for example at 5m you think would give some lift - but with the power turned off would struggle to dry your hair.

Bodyflight Bedford
www.bodyflight.co.uk

[Bodyflight.Net 0]

Because the "source" of the air is located a few dozen feet away from the actual flight area, AND because the method of creating the column iteself involves first pressurizing a room (horizontally) before expelling the air vertically, a power failure or "fault" results in a gradual decrease of airspeed at Appalachian Amusement Center.

[davedlg 0]

The recirculating design at SVCO would probably buffer the effect somewhat compared to the open tunnels. There is alot of momentum in the air going around, so losing power would result in a continued airflow for longer then in an open tunnel.

[tdog 0]

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Also, for the amount of power a tunnel buys, I would think they might be able to negotiate a decent service level agreement with the electricity company.

I laughed at that... The power draw for a tunnel is often exaggerated to be huge.

Yes a tunnel uses a lot of power for one task, but in the big picture, it is a small customer... The retail mall next door to SVCO for an example draws orders of magnitude more power - heck just one department store with their HVAC systems draws many times more power. And - those customers have much more to lose when the cash register stops working - those stores definitely sell more than $1000 per hour in goods and services.

Heck - I do concert lighting for one of my jobs. The lighting rigs I install often can draw more power than a tunnel - and I have thousands of audience members who paid to see the show, and we can't get a service level agreement... (To pull 1600 amps or 192 KW on a concert rig is pretty normal - heck a college theatre often will pull that to light a stage, and these are not large rigs but middle of the road rigs.)

I actually read the Colorado tariff for Xcel energy, the local power company, cover to cover - (because the HOA I am president of is installing solar power, not because I am insane) - and I did not find a reference to quality of service, even for power sold to public companies like RTD (The Light Rail Public Transportation) or traffic signals. Hospitals buy the same class of power as the tunnel, and that class has no agreement in writing.

So all this is to say the power company expects amusement companies (roller coasters to wind tunnels) to fail safe if the power fails at any time.

[RossDagley 0]

the smaller SV tunnels (airkix for example) pull what? about 600KW on full chat? Bedford pulls almost 4MW (including cooling) on full chat. Thats a bill I'd rather you pay than me

And like was said above - there's a world of difference between a progressive turn to 0 pitch, and a power cut. I'd be mighty irritated if I was 15+ feet up and someone turned the power to idle, but you'd feel it coming and be able to ride it down. Kill the power (read: emergency stop, power cut etc) and I'd simply hope. Head down 25+ feet up and a power cut would probably kill you. Springy net or otherwise.

[diablopilot 2]

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Almost instantly... Having been in the situation a couple of times (in different facilities) the result is like going into instant freefall.

At SVCO, I will have the controller cut the power. I can then hop in, pop up about 30 feet, come back down, stop, then back out the door. This is all after the power has been cut. Several of the Instructors will hop in after the power has been cut and back loop back out the door, run around the walls, etc. The wind will actually slow down slower if the power fails, since the braking system needs power to operate. A power falure at SVCO would be a non-event.

Derek

I disagree. Knowing the systems as I do, neither the e-stop, or pulling the stick back to zero simulate a power outage. Having been an instructor and a flyer during power failures in tunnels I can say when the power stops, so does flight. Immediately.

----------------------------------------------
You're not as good as you think you are. Seriously.

[mdrejhon 8]

It would be interesting if someone built a 1 megawatt league wind turbine not too far from a wind tunnel, as a backup, and to resell back to the electric company.

Wind to generate wind.

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[SkymonkeyONE 3]

It sounds pretty clear to me that the resulting slow-down at different tunnel types varies greatly. I can tell you with absolute confidence that the big tunnel on Fort Bragg takes some time to spool down. We used to do two things at start-up and power-down: First, lay on the grate and see how fast we can get off the net as the fan spools up. Next, try to stay in the air as long as possible as it spools down. I guess that is a product of having one very-large fan and the fact that it's a recirculator.

Chuck

[Eule 0]

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The power draw for a tunnel is often exaggerated to be huge.

Probably it seems big to me, because I'm used to the amount of energy an "average" house in the US uses, and haven't worked with larger installations. In the summer my house might use 1.1 MWh over one month, whereas a tunnel cranked all the way up could probably burn through that in a couple of hours.

Another factor may be that even though some people realize it takes more power to turn a bigger motor, they don't realize that "1 horsepower" is just a funny way to write "746 watts". Take three-quarters of the claimed horsepower of the tunnel motors and that's the minimum load in kilowatts you would expect *IF* the tunnel was running full blast. In reality you can probably add 10-20% to that number for losses in the VFDs and motors, but you also have to take a large chunk off of that number for the fact that the tunnel doesn't run at full blast all the time.

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I actually read the Colorado tariff for Xcel energy, the local power company, cover o cover - (because the HOA I am president of is installing solar power, not because I am insane)

You probably already know this, but photovoltaic solar power is often a net energy loss - it takes more energy to make one solar panel than the panel will put out over its lifetime. The efficiency is improving all the time, but it still has a while to go before it can break even. Things like tax breaks and guerilla solar can make the money side look better. There are some applications where it's great - mostly places that are a long way from the nearest power line, like a geosynchronous orbit or halfway up a mountain. I think other solar applications, like solar hot water, actually do work out from an energy point of view.

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- and I did not find a reference to quality of service, even for power sold to public companies like RTD (The Light Rail Public Transportation) or traffic signals.

It probably varies by state. I know in some states, large customers can get power on an "as available" basis - it's really cheap but the power company can shut it down on relatively short notice. Some of the quality of service stuff is probably handled informally; if the substation for the baseball stadium craps out, there might be less of a sense of urgency than if the substation for the hospital craps out.

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So all this is to say the power company expects amusement companies (roller coasters to wind tunnels) to fail safe if the power fails at any time.

Sounds reasonable to me. Thanks for the informed reply!

Eule

PLF does not stand for Please Land on Face.