# Check this out: air cars!



## snoozy (May 10, 2002)

This is too cool!

http://www.youtube.com/v/QmqpGZv0YT4&hl=en&fs=1"

http://www.youtube.com/v/QmqpGZv0YT4&hl=en&fs=1"

http://news.bbc.co.uk/2/hi/science/nature/7241909.stm


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## watcher (Sep 4, 2006)

The problem is it takes a lot of energy just to compress a gas. And you lose a lot of energy while doing it. Two equations to remember are pv=nRT and P1V1/T1 = P2V2/T2. They show compressing a gas (increasing its pressure and decreasing its volume) causes a rise in temperature. This rise in temperature is wasted energy. So after you filled the air tanks they hold much less energy than you used to fill them. 

When you add in the inefficiencies in all big machines I hate to think how wasteful it is. But I'll try. Say you have an electric motor on your compressor that is 90% efficient running a compressor which is, being generous, 80% efficient putting air into a car which uses 80% of the energy from the tanks to move the car. That means you are losing 42% of the energy you had to begin with.

I don't have any numbers but I'd be willing to bet you'd use much less energy using the electricity to power an electric car via batteries.


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## tomjones (Dec 22, 2007)

But, compresssed air is a storage medium for energy that has a lot of otential for re. For instance, a decent sized carbon fibre tank could store the output from a small windmill driven air compressor to later charge your car. Or take that motor and adapt it to a generator to make electricity on demand for periods of low output from your solar. Heck I can even imgine air being moved from from a production windmill to a refueling station. This is extremely high pressure air, but it does make some sense.


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## Windy in Kansas (Jun 16, 2002)

As to compressing air or other gasses thereby creating heat----when will architects, scientists, and appliance manufacturers finally get together at get the most use out of consumed energy?

For example---why do we compress gasses with our refrigerators and freezers and air-conditioning units and not use the waste heat produced? Why not use it to pre-heat water prior to going into the water heater? At the least why not relocate the compressor away from the home interior so air-conditioning doesn't need to cool the waste heat. Yes, I do understand that in the winter it would be welcomed not unwanted. Perhaps homes should have mechanicals rooms where the compressor heat could be used in the winter and vented in the summer. I was once told by a HVAC man that some commercial compressor units are water cooled. Why not home units? Cost?

Why do we not recapture the heat from bath water, laundry, washing dishes, etc.? There are devices which do precisely that which preheat water going to the water heater. How many folk do you know that have such a device? 

We as peoples of the world do indeed need to think outside of the box to come up with workable solutions to energy needs.


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## wy_white_wolf (Oct 14, 2004)

So how many of you have seen a compressor capable of putting out 4500 psi? I have seen 1. It runs on 4160 VAC. No little windmill would be capable of running that.


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## tomjones (Dec 22, 2007)

It may not, but there is no reason that it couldnt. It is all a matter of machine design. Of course capacity is going to be affected. In fact, it has always seemed to me that air compression is a job wind was designed for. If a mll is turning a compressor, you dont have to worry about voltage regulation and such. I see a stright drive shaft going into a comressor that varies its output based on the power available. I think the technical challenges of that are minor compared to a wind electrical system.


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## Watcher48 (Aug 30, 2007)

Want to read some of my 1900-1960 pop mechanics and see what was available then. By all accounts were all suppose to be flying now. And there was one saucer looking thing that you used a lawnmower engine to power. I think I should dig that up and post it


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## OntarioMan (Feb 11, 2007)

I think cost is far more important than efficiency. Examples - electric heat is 100% efficient, but it may actually cost more than heating with a less efficient natural gas unit. If you had a mountain full of free wood, I'm guessing you'd be heating your home with wood, regardless of how efficient it is or isn't.

Hey, if "they" can build a 30% efficient air car which costs the consumer half as much as they'd pay for a gas powered car - why not. The air car has been around for awhile, and last I heard it was a dud due to an extremely limited range.



watcher said:


> The problem is it takes a lot of energy just to compress a gas. And you lose a lot of energy while doing it. Two equations to remember are pv=nRT and P1V1/T1 = P2V2/T2. They show compressing a gas (increasing its pressure and decreasing its volume) causes a rise in temperature. This rise in temperature is wasted energy. So after you filled the air tanks they hold much less energy than you used to fill them.
> 
> When you add in the inefficiencies in all big machines I hate to think how wasteful it is. But I'll try. Say you have an electric motor on your compressor that is 90% efficient running a compressor which is, being generous, 80% efficient putting air into a car which uses 80% of the energy from the tanks to move the car. That means you are losing 42% of the energy you had to begin with.
> 
> I don't have any numbers but I'd be willing to bet you'd use much less energy using the electricity to power an electric car via batteries.


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## Jim-mi (May 15, 2002)

Can't do your utube things on dial up. . . .so I haven't seen what ever..............

Being a 'Windy' guy for a few years now, all I can think of is your going to need one big mother of a wind unit to turn that big mother of a compressor.
With a big complicated clutch to kick in after a certain amount of run up.
Just thinking how my air compressor makes my 4500 watt inverter-grunt- on start up . . . . . . . . . .

Really need to know how much "Energy" would be needed to get the 'tank' up to a usable level.

Now if you wanna put in a big three phase compressor . . .

Ain't no free lunch......


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## Windy in Kansas (Jun 16, 2002)

Watcher48 said:


> Want to read some of my 1900-1960 pop mechanics and see what was available then. By all accounts were all suppose to be flying now. And there was one saucer looking thing that you used a lawnmower engine to power. I think I should dig that up and post it


I was always intrigued by the hovercraft idea but never had the inclination to build one.

Today we see giant hovercraft ferry boats used between ports so they really did come into their full use even if each of us doesn't have one parked in the backyard or garage.

On a PBS show some months ago I saw a bunch of kids building hovercraft in a school science project. They tried different modifications to see which worked better, etc. What fun. Expect I would have paid better attention in school if we would have had such a program.

There is an old song frequently sung by SPEBSQSA (Society for the preservation and encouragement of barbershop quartet singing in America.
It is entitled "Everything Old is New Again". How true.

One only has to study old automobiles to learn many modern options are simply old reruns. As an example our 1947 Pontiac had a rear window wiper. 
In the 1920 or 1930s front wheel drive came about. Turbo charged engines have been about perhaps 90 years.

Yup, everything old is new again.


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## MELOC (Sep 26, 2005)

i imagine you could build a compressor to handle a lower volume and still get a high psi. the ideal would be a commuter car that could travel 20-40 miles on a tank of air and a windmill/compressor that could fill the tank in 10-12 hours.


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## snoozy (May 10, 2002)

Well, whether or not it could be done with a windmill for a compressor is not the point. The point is a motor that runs on compressed air. YES, it would take some electricity to run a compressor, and I would think the idea is for there to be compressor stations like we have gas stations now. Did you see the size of the motor? The Australian design was not even as big as a breadbox. Let's say even our feeble brains cannot come up with a motor with sufficient range or speed or power to replace a car -- think of all the other gas engines it could replace: outboards and lawnmowers and that sort of thing. That in itself would big a good thing for the environment because (I have read) lawnmowers are nasty polluters.


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## watcher (Sep 4, 2006)

Windy in Kansas said:


> As to compressing air or other gasses thereby creating heat----when will architects, scientists, and appliance manufacturers finally get together at get the most use out of consumed energy?
> 
> For example---why do we compress gasses with our refrigerators and freezers and air-conditioning units and not use the waste heat produced? Why not use it to pre-heat water prior to going into the water heater? At the least why not relocate the compressor away from the home interior so air-conditioning doesn't need to cool the waste heat. Yes, I do understand that in the winter it would be welcomed not unwanted. Perhaps homes should have mechanicals rooms where the compressor heat could be used in the winter and vented in the summer. I was once told by a HVAC man that some commercial compressor units are water cooled. Why not home units? Cost?
> 
> ...


I wondered about this but I had an AC tech tell me you can only take so much heat from it before it starts interfering with the refrig cycle. I don't remember how.


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## watcher (Sep 4, 2006)

tomjones said:


> It may not, but there is no reason that it couldnt. It is all a matter of machine design. Of course capacity is going to be affected. In fact, it has always seemed to me that air compression is a job wind was designed for. If a mll is turning a compressor, you dont have to worry about voltage regulation and such. I see a stright drive shaft going into a comressor that varies its output based on the power available. I think the technical challenges of that are minor compared to a wind electrical system.


A major problem is the dangers of working with and storing air at that pressure. We've all seen SCUBA tanks so we have some idea how big they are. I found this on a website, I left off the math. FYI, 230 bar is about 3300 psi and 12L about 0.4 cu ft or 730 cu in or 3 gal.


_So for a 230 bar 12L tank we have 230*12*450 Joules. 1242000 joules!

You're not impressed? You don't have a feel for a joule perhaps?
A joule is one watt for one second. so 1242000 joules is 3 kilowatts for just under 7 minutes. That would boil 3.5 litres of water and so make coffee for everybody on the boat?

Still doesn't seem much does it? The trick is to release it in an instant.
In a previous life (see CV) I used a unit of energy that was 4.184x1012 joules representing the energy released by 1000 tons of TNT.
That works out at about 1866000 joules per pound.
In metric units the tank contains the energy in 300 grams of TNT. A normal hand grenade has about 150 grams. _

In British units that's about 10.5 oz of TNT. 

When you take efficiency of the system (mill-compressor-car) into account I'm willing to bet you'd be much better off using your mill to turn a genset to charge batteries to run the car.

Edited to add:

Do a google search for exploding SCUBA tanks if you want to see what can happen when you have a catastrophic failure. <shudder>


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## watcher (Sep 4, 2006)

OntarioMan said:


> I think cost is far more important than efficiency. Examples - electric heat is 100% efficient, but it may actually cost more than heating with a less efficient natural gas unit. If



True but if you can build an electric car which is 60% efficient you are using less energy therefore that 'saved' energy can be used to run other things.




OntarioMan said:


> you had a mountain full of free wood, I'm guessing you'd be heating your home with wood, regardless of how efficient it is or isn't.


True again but I'd still look at the most efficient way to use that wood. IOW, I wouldn't build huge open hearth fireplaces in each room when just because I had lots of wood. 




OntarioMan said:


> Hey, if "they" can build a 30% efficient air car which costs the consumer half as much as they'd pay for a gas powered car - why not. The air car has been around for awhile, and last I heard it was a dud due to an extremely limited range.


And it has a limited range due to the fact it is so inefficient.


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## watcher (Sep 4, 2006)

MELOC said:


> i imagine you could build a compressor to handle a lower volume and still get a high psi. the ideal would be a commuter car that could travel 20-40 miles on a tank of air and a windmill/compressor that could fill the tank in 10-12 hours.


Let's try some math. (I'm going to do the math in metric because its just easier) We have to make a few assumptions here. Say the gross weight of the car is 2000 pounds (907 kg) and the route is perfectly level and we'll ignore friction and drag.

First energy to move 2000 pounds (907 kg) 30 miles (48 km). A joule is the energy needed to move 1 kg 1 meter so.

907 kg * 48 km *1000 m/km = 43536000 j

Which works out to about 12 kW-hr to move our perfect car 30 miles.

Let's keep thinking this is a perfect system. You'd have to produce 1 KW for the 12 hours to charge your tanks. I've never done much research into wind power because I've never lived anywhere it made sense to use it but I doubt many people have enough wind each and every day to produce 1 kW/hr for 12 hr/day.

Now let's drop a little reality into the equation. I have no idea how efficient such a windmill-compressor-car system would be so I'll just post some numbers based on different ones. You have the efficiency, the number of kW-hr needed to move the car 30 miles and the number of kW per hour you'd need to charge the car in 12 hours:

80% 15 kW-hr 1.25 kW/hr
70% 17 kW-hr 1.43 kW/hr
50% 24 kW-hr 2.00 kW/hr
25% 48 kW-hr 4.00 kW/hr
10% 120 kW-hr 10.00 kW/hr

Can anyone with windmill experience tell us if these numbers are possible and/or practical?


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## mnn2501 (Apr 2, 2008)

OntarioMan said:


> The air car has been around for awhile, and last I heard it was a dud due to an extremely limited range.


For commuting, how much range do you need? I drive 3 miles to work and my wife drives 7. Now while this may be short range for many on this forum, I doubt many Americans commute more than 40 - 50 miles a day, which I believe is the range of the air car that I have researched. For the infrequent times we need more we could rent a regular car. I am sure most Americans (at least city folk) could do this and lets face it, theres a lot of 'city folk' sitting in traffic wasting a lot of gas.
Now I not talking about people that live out in the country where their regular drive is more than the range of these vehicles, this probably would not work for them.

Also when talking about the energey cost to produce energy (in this case compress air) people forget, its always more efficent to produce at big plants rather than small (individual) plants -- ie your local power company can produce electricity cheaper than you can.

Its just one more piece of the puzzle that many people (certainly not all) could use to both cut down on foreign oil we use and pollution at the same time.


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## mnn2501 (Apr 2, 2008)

You may want to check out "Energy storage" at this link to see one way to produce very cheap compressed air http://www.theaircar.com/acf/air-cars/energy-storage.html


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## watcher (Sep 4, 2006)

mnn2501 said:


> For commuting, how much range do you need? I drive 3 miles to work and my wife drives 7. Now while this may be short range for many on this forum, I doubt many Americans commute more than 50 miles a day,which I believe the range of teh air car is. For the infrequent times we need more we could rent a regular car.


The closest thing to me, other than a convince store, is about 30 miles one away.




mnn2501 said:


> Also when talking about the energey cost to produce energy (in this case compress air) people forget, its always more efficent to produce at big plants rather than small (individual) plants -- ie your local power company can produce electricity cheaper than you can.


Yes, but you are missing something; the transportation. Compressed gases are very difficult and expensive to move around. Which is why places which use them almost always produce them on site.

And when you are talking about pressures of 3000+ psi it is dangerous. 

Here's a couple of sites w/ pictures. Remember these are SCUBA tanks which aren't really that large.

http://www.scubaengineer.com/tank_servicingx.htm
http://www.thescubaguide.com/gear/tanks/safety.aspx

WARNING SLIGHTLY GRAPHIC PIC ON THIS SITE Nothing sickening but its not nice.

http://biobug.org/scuba/scubatank/


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## mnn2501 (Apr 2, 2008)

watcher said:


> The closest thing to me, other than a convince store, is about 30 miles one away.


 As I said, its not going to work for everyone, I thought I made that clear. The days with 1 energy solution is gone. different things MUST be used by different people to get us off of foreign oil. Being dependant on countries who - for the most part - hate us is holding us hostage just the same as if someone were holding a gun to our heads.



watcher said:


> Yes, but you are missing something; the transportation. Compressed gases are very difficult and expensive to move around. Which is why places which use them almost always produce them on site.


 See my link on my 2nd post and keep in mind, this is a solution for big cites and their suburbs. Probably wouldn't work where there was less than 100,000 people in a city, but at least a 1/4 of the American popluation lives within 25 miles of a city that size. Would cutting our oil usage by 1/4 help? I think it would.


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## watcher (Sep 4, 2006)

mnn2501 said:


> See my link on my 2nd post and keep in mind, this is a solution for big cites and their suburbs. Probably wouldn't work where there was less than 100,000 people in a city, but at least a 1/4 of the American popluation lives within 25 miles of a city that size. Would cutting our oil usage by 1/4 help? I think it would.


You are still missing my point. How do you supply high pressure air to the cars safely and cheaply?

I see very few options. Either each owner has a compressor, you have many 'compressor stations' around a city or you have few massive compressors and have recharge or tank exchange stations. Each has their own problem.

But again the biggest problem is compressed air is a very poor way to store energy because of the loses. Even the 150 year old lead acid battery is a better way to store energy. Why would you want to burn twice as much energy to power an air car than you would use to power an electric car?


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## MELOC (Sep 26, 2005)

the original intent was to create an environmentally friendly vehicle that could be used in huge cities in places like india where traffic is so congested that pollution from vehicles is a real concern. i am sure having vehicles that only expend energy when they actually move is a plus that helps offset any energy conversion loses. another offset is the amount of energy that is not expended to deliver the product physically. how much fuel is required to truck a tanker of fuel 100 miles or so?

many folks seem to be on a kick where if the alternative energy device of discussion is not the magic bullet, it must have no value. i doubt we see a magic bullet for quite some time if ever. that doesn't mean there is no niche for any given vehicle or device. i envision companies located in urban areas supplying short distance vehicle to commuters who can use them and to supply energy on site. having lots of businesses making small changes here and there can add up over time. every alternative method is worthy of research.


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## watcher (Sep 4, 2006)

MELOC said:


> the original intent was to create an environmentally friendly vehicle that could be used in huge cities in places like india where traffic is so congested that pollution from vehicles is a real concern. i am sure having vehicles that only expend energy when they actually move is a plus that helps offset any energy conversion loses. another offset is the amount of energy that is not expended to deliver the product physically. how much fuel is required to truck a tanker of fuel 100 miles or so?
> 
> many folks seem to be on a kick where if the alternative energy device of discussion is not the magic bullet, it must have no value. i doubt we see a magic bullet for quite some time if ever. that doesn't mean there is no niche for any given vehicle or device. i envision companies located in urban areas supplying short distance vehicle to commuters who can use them and to supply energy on site. having lots of businesses making small changes here and there can add up over time. every alternative method is worthy of research.


What I'm pointing out is there are things out there NOW that are better uses of energy. Why go out of your way to build something new which is worse than what is out there now?


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## mnn2501 (Apr 2, 2008)

watcher said:


> What I'm pointing out is there are things out there NOW that are better uses of energy. ?


What is better thats already out there?
As far as compressed air being dangerous, so is carrying 20 gallons of gasoline, so are the batteries in a hybrid, so is the fuel in a flex-fuel vehicle.


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## watcher (Sep 4, 2006)

mnn2501 said:


> What is better thats already out there?


1) Using batteries to store energy is many times better (i.e. more efficient) than using compressed air. 2) Electric motors are a proven technology. There's on need to spend money researching a new engine nor on new machines to build a new type of engine. 




mnn2501 said:


> As far as compressed air being dangerous, so is carrying 20 gallons of gasoline, so are the batteries in a hybrid, so is the fuel in a flex-fuel vehicle.


True but it takes quite a bit of work to make 20 gallons of gasoline to release all of its energy in a matter of milliseconds. It doesn't take that much for tank holding a gas at 3,000 to 5,000 psi to do the same thing. 

Let's crunch some more numbers. From googling I find a gallon of gasoline has about 125,000,000 j. So 20 gal of gas gives us 2,500,000,000 j. From the site www.onlineconversion.com we find out this is equal to 0.597 tons (which ranges from 1194 to 1337 pounds depending on which ton is used) of TNT.

Now think about two car tooling down the road. One is a gas powered car with 20 gal of gas and the other is an air car with an equal amount of compressed air. Each is involved in an accident. 

For the gasoline to release all of its energy quickly the gas must be vaporized, liquid gasoline will not burn. Then it must dispersed to the point there is enough O2 to burn it all (I couldn't find the exact ppm). Then it has to be ignited. The odds of this happening in an accident is very, very small. The proof to that is the fact you don't see it happening, outside the movies, even though there are million of accidents around the world. What usually happens if the fuel tank is damaged is the gasoline leaks out onto the ground.

But for the compressed air to release all of its energy in a matter of milliseconds all that has to happen is for the storage container to be cracked.

Therefore while both can be dangerous one is many factors more likely to cause harm. Think of dynamite and nitroglycerin. Both are dangerous but which would your rather carry in the back of your car?


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## MELOC (Sep 26, 2005)

doesn't gasoline explode at something like 40 psi?

since we are nit picking...at least compressed air won't burn you. you want to see damage from gasoline? try googling saddlebag gas tank explosion or static electricity gasoline ignition. something as simple as pantyhose rubbing a silk skirt can blow up an entire refueling station.


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## watcher (Sep 4, 2006)

MELOC said:


> doesn't gasoline explode at something like 40 psi?


HUH? 




MELOC said:


> since we are nit picking...at least compressed air won't burn you. you want to see damage from gasoline? try googling saddlebag gas tank explosion or static electricity gasoline ignition. something as simple as pantyhose rubbing a silk skirt can blow up an entire refueling station.


Just google "BLEVE" (Boiling Liquid Expanding Vapor Explosion) and "FAE" (Fuel-Air Explosives). But as I pointed out to have either you have to have a very specific set of circumstances to get these explosions. 

To get a compressed gas 'explosion' all you need is a container failure. You don't need to vaporise a liquid nor an ignition source.

I'd bet you, personally, could not make a 5 gallon container of gasoline explode with what you have around your house. But you could easily make the storage tank on a 150 psi compressor (like the ones sold for house hold use) fail catastrophically.

I have amidted each has a danger associated with it. My points are:

Storing super high compressed air is much more dangerous than storing gasoline.

Compressed air is a very inefficient energy storage medium.

There is a technology available today, electric cars, which is better (more efficient, with infrastructure already in place and safer) than compressed air cars.


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## MELOC (Sep 26, 2005)

watcher said:


> HUH?


just something i heard once somewhere. i thought maybe you would know, 40 lbs. does sound aweful low.


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## Jim-mi (May 15, 2002)

Thanks for that link watcher . . . . .

Would never have "thought much" about a tank letting loose.

wow . .all that from a tank of air........

You might think about changing your milli seconds to nano seconds.


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## watcher (Sep 4, 2006)

MELOC said:


> just something i heard once somewhere. i thought maybe you would know, 40 lbs. does sound aweful low.


I just don't understand what you are saying.


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## wy_white_wolf (Oct 14, 2004)

MELOC said:


> just something i heard once somewhere. i thought maybe you would know, 40 lbs. does sound aweful low.


If it was anywhere close to that gas engines wouldn't need spark plugs. Compression check on factory engines usually reveals 130 to 150 psi and high compression racing engines can run up to about 250 psi.

Desiel is a different story.


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## mightybooboo (Feb 10, 2004)

Out at the desert property there is a neighbor who is using a windmill to compress air and make electricity.

So he says,maybe he is yanking my chain,thats possible.

Anybody heard of that kind of system?


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