What if the power grid fails?

[diablopilot 2]

No.

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

[Hooknswoop 19]

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No.

LOL! So, you feel you know the systems better than the designer. 'Well, there's your problem right there!' I guess I shouldn't be surprised. Well, since you are not willing to discuss how the system works and what happens if the power fails, and think you know more about the system than the designer, I am wasting my time. Good luck with that.

Derek

[RackJR 0]

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Never happened. And since Ben and I were the only two in the room when I had a meeting with him, we are the only two to know what was said. I think you're fishing.

man i love it. i'm not fishing for anything. i'm not the only one with this information. since i doubt you shared it with anyone, that means Ben did.

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Really? Who? I have never applied for work at SVNH. Again, you're fishing.

it's unfortuntate that i don't want to drag other people into this, who aren't talking on their own, because you know as well as i do that you did apply to work there, and were not given a job. i will say that one of my best friends is the reason you don't have a job there. that person was willing to say that you are nothing but a problem, and that they shouldn't hire you.

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As for "lead instructor" or "saftey supervisor" roles, well those are not worth discussing, since YOU were not priviy to the conversations had with owners of SVCO had both in LA and in Denver.

again JP, i'm not fishing for anything. you asked for those positions, and didn't get them. you then presented yourself as having that role, when you didn't. i'm the only one talking about it right now, but the whole staff knew you were signing your emails to customers as "lead instructor", and laughing at your tremendous ego that you were giving yourself a title that you would never have. i read the email JP. we passed it around. you called yourself the lead instructor, a position you never had.

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As amatter of fact I seem to remember you abandoning the company since you jumped into an agreement in which you couldn't keep your word.

I still work at SVCO. what agreement are you talking about? You, after hearing information from an explicity confidential meeting of instructors, went THE NEXT DAY to another staff member to share, in direct contradiction of those EXPLICIT instructions, that information. dude you were doomed from that moment on. you had the trust of no one. you deserved the trust of no one. had you not left, you would have been fired, not just for that, and you know that perfectly well.

I'm living up to my word. i still work there. i have a year left to go on my contract, and i'll be there long after that. You are saying in your profile that you are a tunnel instructor, when in fact you're not, and given that your reputation now precedes you, you probably won't be again. but keep up the facade. we love it. if you mean that i offered to quit, in response to your inability to maintain a level of trust, that's true, i did. i offered to pay back their investment in me, since i was working at the tunnel as a "fun" job, not my primary source of income. when i was ready to go to blows over you being untrustworthy, i thought it was probably time to leave. the owners decided to fire the other employee, and asked me to stay. unfortunately you left before you got fired. personally it would have been very gratifying to see you canned. i guess you're at least smart enough to see that you were on the way out.

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priviy

you mispelled privy. your spelling and grammar suck.

you're not bringing up anything else about experience, or my lack of it. that makes me smile. but keep talking. it gives me so many opportunities to point out the flaws, as you're clearly not clever enough to keep up with your own lies.

slander is a term that denotes a lie, a false statement that typically injures a person's reputation. i have done nothing of the kind. i have simply shared the truth. painful as that may be to you, it doesn't make it slander. you've made your own reputation. the great part is, you've done it at big drop zones. people know you. i'm positive that the silent majority is nodding it's head at everything i post. your actions in the past are the only piece of proof anyone needs to know exactly how you operate. also, slander is verbal. in print, it's called libel.

i never thought i'd have so much fun in a forum. the best part is, you took a thread talking about the power grid, and made it a personal insult against me and Derek. Was telling me to "try having a personality" the only thing you could come up with? fantastic. thank you for opening the door. i hope this has been as entertaining for anyone else as it has been for us. I'll continue to hope that you will KEEP IT COMING!!!!

I love the internet.

Say what you mean. Do what you say.

[RackJR 0]

sorry Kelli i'm having way, way too much fun.

Say what you mean. Do what you say.

[billvon 2,400]

>In order to actually "feel" this effect, the capacitors in the VFDs would have to be huge . . .

On power grids, much of the holdup comes from freewheeling motors. High voltage three phase power is often used industrially to drive very large motors (fans, mixers, conveyor belt drives) and when the source is disconnected, there's a significant amount of freewheeling that holds power up for a bit on the grid (depending on where power was cut, of course.)

[billvon 2,400]

Could all of you stop with the insults? It's a simple technical question; no need to get anyone's egos bruised.

[tunnelfly 0]

I was assuming that the power is converted to DC first and then converted back to AC with a variable frequency, depending on the requested speed of the motors.
That's how the VFDs work that I used to work with so far (for smaller motors, though).

No.1 reason NOT to be an astronaut: ...You can't drink beer at zero gravity...

[billvon 2,400]

>I was assuming that the power is converted to DC first and then
>converted back to AC with a variable frequency . . .

Yes. But the AC coming in to the tunnel is often "held up" for a short time by the large industrial motors that are likely on the same grid. Most large motors out there are still plain old AC three phase induction motors. Depends on what else is on that chunk of grid and where the power is disconnected, of course. If you just lose your own feed you go to zero almost immediately, as soon as your own capacitors (which likely have about 20 milliseconds of power storage) discharge.

[Hooknswoop 19]

So, just for fun, I hit the e-stop (which cuts all power to the motors instantly) while Jason was flying head down about 8 feet off the net. He held the head down for about a second, then transitioned to his belly. Taking his time he flew out the door. Flight did not stop immediately and it was a non-event. We accurately simulated a power grid failure with a head down flyer.

Derek

[sartre 0]

Thank God he's okay! I've been so worried about that!

Thanks for risking your lives to test it out.

[Vectracide 0]

Oh please don't say that his piece of information will solve this conundrum forever...... I was almost about to kiss off the BASE and swoop forum to hang out here........


Wheeeeeee..........

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Controlled and Deliberate.....

[Jewels 0]

I suppose I could claim to have done the same thing with very different results, just to keep the intensity up . . . but, of course, none of that would be true. It's the old "I could agree with you, but then we'd both be wrong" problem.

TPM Sister #102

[Vectracide 0]

After reading this whole thread, I have come up with a startling conclusion that I never expected to find. I might die in a tunnel. It's possible right? If the really good guys can break themselves doing it...I sure could. Now since JP has shown us the dangers out there, I began to wonder how he does it. How does someone that has spent so much time tunnel flying, be injury free? It's more dangerous that skydiving people!!!!!!

Well, after some research, I have found the secret that he has been keeping all to himself. Somehow Jason knew of the legend, perhaps it came to him in a dream...I dunno. Perhaps it was a faint sound he heard coming from JP's locker at SV in Co. every time he walked by. Now this is almost as good as finding that lightbulb that never burns out in the warehouse of inventions the government keeps from us. Somehow, JP has found the secret, the tunnel muse if you may, and we must hunt him down and take it from him for the benefit of everyone.

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Controlled and Deliberate.....

[mdrejhon 8]

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So, just for fun, I hit the e-stop (which cuts all power to the motors instantly) while Jason was flying head down about 8 feet off the net. He held the head down for about a second, then transitioned to his belly. Taking his time he flew out the door. Flight did not stop immediately and it was a non-event. We accurately simulated a power grid failure with a head down flyer.

Derek

Wow. That's a testament to the efficiency of a recirculating tunnel design.

Air has 1.29 kilograms of mass per cubic meter, and and guesstimating 100 cubic meters of air (there is probably more than that, but let's keep math simple) there's an amazing 129 kilograms in 100 cubic meters of moving, recirculated air -- which means plenty of momentum potential.

Imagine that: For every 1 cubic meter of air, there's 128 cubic meters behind it pushing the air forward. That applies to each and every air molecule in the windtunnel. So it keeps looping and looping -- gradually losing energy in resistance factors (i.e. motors, tunnel walls, tunnel flyer, etc).

Assuming an efficient-enough modern recirculating tunnel design, I am not surprised that momentum of the air keeps a tunnel flyer (in a modern, efficient recirculating design) flying for a quite a few more seconds, gradually tapering off. Assuming the fans are able to be loosely freely-spinning at relatively low resistance once the power is cut (i.e. fans are not put into braking mode as you say). Such as an automatic immediate e-stop upon power outage. (assuming this particualr motor freely and loosely spins with slowest taper-off in this situation)

A non-recirc tunnel would very obviously taper off much more abruptly -- there is far less "momentum" stored in a non-recirculating tunnel.

Either way, this is all very interesting to read.

I think both parties are right (albiet in very different ways). These are the variable factors:

Torque resistance of free-spinning powered-down motor
Newer motors often have lower resistance, slows down air less during a power outage

Whether the motor is put into braking mode (i.e. contacts shorted automatically - some electronics may do this)
It appears Skyventure Colorado's electronics avoid autobrake.

Recirculating versus nonrecirculating
The larger amount of momentum 'stored' in a the air in a recirc plays a major factor

Efficiency of a recirculating design
The amount of resistance the air encounters to go around the tunnel, including walls, turns, turn vanes, netting, etc. A more efficient recirc design means air tapers off less over time during outage.

Factors in a non-recirculating design
Things like mass of fans to keep momentum, amount of air in a tunnel to keep momentum, other efficiencies, etc.

How much the vents are opened up, in a recirc
The more open the vents are, the faster the air in a recirc will slow down. It's like "discharging" a capacitor or battery - the air equivalent of a power leak.

Etc. Other factors
There are obviously many other factors not listed.

The perfect recirc tunnel would have zero resistance, meaning air would recirculate infinitely much like a SMES (Super Conducting Magentic Energy Storage) which is simply electric current going in an infinite loop in a superconductor. That is what would happen to a recirculating tunnel if it had zero resistance. However, physics would dictate that zero resistance is impossible, and the floating human body is an obstacle of "resistance" itself to the airstream, but would only slow down the airstream gradually due to the amount of momentum charged into the air of a recirculating tunnel...

Eule probably could inject more engineer-related feedback, but Eule will agree with me about the mass of air -- empty air weighs a whopping 1.29 kilograms per cubic meter.

Some recircs may have stopped more abruptly in a power outage, so research is needed:

Differences in efficiency of the recirc construction, such as percentage of energy loss in the air, etc.

Inexperienced flyers vs experienced flyers - this can mean a difference in flying slow 110/100mph winds if the taper-off was approximately 10mph slower per second

Motor was put into autobrake mode. Verify whether or not this happened or not. The motor needs to be put into minimum resistance (spin freely)

Differences in motor designs and efficiencies, may mean different taper-down rates. As a rough example, possibly the difference between a 5mph-per-second taper-down versus a 10-mph-per-second taper-down. I suspect the difference can be bigger on this.

Whether the power outage was instant or gradual. This may affect motor braking behaviour and electronics.

What is happening to the motor during power outage. Power outage may have produced some resistance behaviour in the motor that mimicked braking behaviour (i.e. maybe electronics doesn't like brownout voltages, caused an autobrake, or caused reduced motor efficiency etc) Even a very minor autobrake could kill the air much more quickly than in the lowest-resistance free-spinning mode, as the motors are powerful enough to quickly stop the air

I can understand there can easily be unanticipated factors such as differences in motor behaviour responding to a power outage - as far as I know, not all motors go into their lowest-resistance free spinning mode immediately on a power outage, especially if the power outage cause a partial/brief autobrake behaviour bleeding some energy out of the tunnel's recirculating air faster. (Not all designs might automatically the motor completely from the grid when a power outage is detected. That way, there's infinite resistance between the motor terminals, and keeps the motor in its free-spinning mode longer -- assuming the motor is the type that is at its most efficient non-braking mode when completely disconnected. That way, the motor doesn't feed the air's momentum as electrical energy BACK into the electric grid. (motor = generator mode, if the electronics does not prevent that). Even how quickly the motor to be disconnected from the power grid, can have a big effect in the taper-down of the air -- a brownout situation might end up having a have a BRAKING effect on a windtunnel if the electronics does not compensate for that, so it is possible for different kinds of power outages to have different taper-down effects because of these little minor factors. Differences in firmware in electronics can MAKE A BIG DIFFERENCE in these behaviours -- you'd be amazed. According to you all, It appears these motors are the advanced types that uses electronics that contain firmware. Theoretically, a setting such as an adjustable disconnect delay could theoretically have a large effect, for example, or a different voltage regulator for different voltages (example: 120 vs. 240V) may cause different blackout-load-resistance behaviour, etc - there can be many little-known quirks that even the operator of the motors may not even know about. The point of this paragraph is, there are potentially lots of unanticipated factors that CAN explain why one nearly-identical recirc slowed down much faster than another recirc. -- for example Airkix stopping more abruptly than Skyventure Colorado may be easily explainable by an obscure factor...

Bottom line -- what matters is (1) low recirculating ressitance (low resistance of disconnected motor would be a major factor here), and (2) plenty of momentum stored in air in a recirc tunnel, in theory "guarantees" a human to float long enough, according to my mathematics. (Do the math yourself too -- the math actually works out)

While we all agree is that air has plenty of momentum, what many of us do not understand is all the little factors that can affect taper-down of a windtunnel.

Some of you are bigger experts than I am, and know terminology better, but someone here neglected to do some mathematics. But basic high school mathematics seem to show that both parties have a perfectly valid argument.

I feel that PaulIPod and Hooknswoop answers are both right (in different ways) -- they just are comparing apples to oranges -- because of very different variables and easily-unanticipated factors easily exist.

[RackJR 0]

unfortunately, two things happened. Billvon asked us to knock it off, which i'll try to respect. And JP has fallen strangely silent. hmmmm. But with 10000 posts, i'm sure i can find another point of engagement.

i guess i'll have to check out the base forum.

Say what you mean. Do what you say.

[Vectracide 0]

Shit....a day late and a post short....

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Controlled and Deliberate.....

[Jewels 0]

We should just ask the insurance companies. I'm sure they calculated this pretty precisely before settling on a premium.

TPM Sister #102

[PapaSmurf 1]

Howdy Folks,

How about reality, for a change ?

December 1, 2006
SVNH
Approx. 100 people at the tunnel for the Q Memorial tunnel boogie, including Q's mom - who flew great on her first flight !

We lost power during a massive thunderstorm.

A beginner flyer was in the tunnel about 5 feet off the net.
No problem, as the tunnel slowed gradually. ( 3 to 5 seconds of airflow seems about right).

Rob, Laurie, and staff did a fantastic job (as usual) !!!

Blueskys!!!

P. Smurf

[Stumpy 256]

Enough time and power to "hop in, pop up about 30 feet, come back down, stop, then back out the door"?

Never try to eat more than you can lift

[Hooknswoop 19]

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Enough time

"3 to 5 seconds of airflow seems about right)."

He answered that question.

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and power

"beginner flyer was in the tunnel about 5 feet off the net."

And that one too. You wouldn't give a beginner flyer enough power to pop up 30 feet.

***power to "hop in, pop up about 30 feet, come back down, stop, then back out the door"? [/quote

I'm sure they didn't have the power set so they could have done that, without the power failure. I do that from head down speeds with the throttle at zero, not from belly speeds and the throttle at zero. From belly speeds, you would have a couple of seconds before the wind slowed gradually and set you on the net. No freefall, no plummeting, etc.

Derek

[Eule 0]

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[....]and guesstimating 100 cubic meters of air (there is probably more than that, but let's keep math simple)

100 m^3 is in the right ballpark. If you model the enclosed volume of a tunnel as a cylinder with 3 m diameter, this gives you a height of about 14 m, which sounds reasonable.

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there's an amazing 129 kilograms in 100 cubic meters of moving, recirculated air

Well, for dry air at standard temperature and pressure (0 C and 101.325 kPA, or 32 F and 29.92 inHg), sure. [0] That's probably a beauty day up there in the Great White North, but it gets warmer down here. On a 25 C (77 F) day at standard pressure, dry air might be 1.18 kg/m^3, about 9% less. Humidity will lower the density of the air further.

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Imagine that: For every 1 cubic meter of air, there's 128 cubic meters behind it pushing the air forward.

If you assume the total volume is 100 m^3, then that one m^3 of air would have 99 m^3 behind it, wouldn't it?

Doing the math, Bosch [1] p. 46 says, "The velocity of fall approaches a limiting velocity v0 at which the air resistance Fl = 0.5 * rho * cw * A * v0^2 is as great as the weight G = m * g of the falling body." This is for falling, but I think it should apply to the tunnel as well. Let's say I'm (80 kg) in the tunnel and the density of air is 1.18 kg/m^3. I just used the platinum- iridium tiles on my kitchen floor (1 ft^2 each) to determine that my frontal area is about 9 ft^2 or 0.836 m^2. I also need a coefficient of drag. Page 47 says "disc, plate 1.1" so I'll use that; I suspect that it's actually a little higher with jumpsuit and everything. We have:

m * g = 0.5 * rho * cw * A * v0^2
80 kg * 9.81 m / s^2 = 0.5 * 1.18 kg / m^3 * 1.1 * 0.836 m^2 * v0^2
784.8 kg m / s^2 = 0.543 kg/m * v0^2
v0 = 38.0 m/s = 85 mph

which is, IMHO, in the ballpark. Interesting.

We could put people in the tunnels and do power-loss experiments. The correct way would probably involve personal protective equipment for arc flash, and a big fiberglass stick. The "hold my beer and watch this" way would involve something like a grounding rod, lots of heavy wire, a big rock, and a catapult. Maybe a backhoe if the lines are underground.

Eule

[0] Caution, Wikipedia link. Might be true, might not.
[1] Bosch "Automotive Handbook", 4th edition, ISBN 0-8376-0333-1

PLF does not stand for Please Land on Face.

[mdrejhon 8]

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[....]and guesstimating 100 cubic meters of air (there is probably more than that, but let's keep math simple)

Check my post in the other forum. My revised calculations show there's actually a lot more than 100 cubic meters of air:
Check My Newer Post

Very interesting discussion!

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If you assume the total volume is 100 m^3, then that one m^3 of air would have 99 m^3 behind it, wouldn't it?

Yes, you're right. I meant 128 kilograms of air behind every 1 cubic meter (0 degrees, which you are right about) Ooops.

In any case, I calculated Skyventure Colorado to have approximately 750 cubic meters of air when you also include all the ducting in the loop. This is a rough estimate. The bodyflight chamber alone contains more than 60 cubic meters of air! (See Newer Post)