Ernie
Joined: 11 Jan 2006
Posts: 513
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 Posted: Sat Mar 14, 2015 9:00 am Post subject: Emergency Air Tank. |
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Sorry if this arrives multiple times.
This was in response to DaBears post earlier, it never made it up.
Nothing I've done here is of my own invention, all I'm doing is leveraging what the paintball community has been doing for years.
For example, I have another idea for the emergency system that I'm contemplating. Firefighters use a much smaller Carbon Fiber bottle (98 Cu/In) for emergencies in case their main breathing apparatus fails. It is sometimes referred to as an "Oh Shit" bottle. It is meant to supply 5 min of breathing air. It weighs about 2 lbs and fits in the palm of your hand.
These bottles have a working pressure of 4500 Lbs. Total volume of air in a cylinder is the result of initial volume multiplied by the pressure. For example our stock spherical bottle in our CJ has a water capacity of 3 liters, or about .1Cu/Ft. At 750 PSI that equates to about 5 Cu/Ft of air.
The storage volume for a compressed gas can be calculated using Boyle's Law: | Quote: |
pa Va = pc Vc (1)
where
pa = atmospheric pressure (14.7 psia, 101.325 kPa)
Va = volume of the gas at atmospheric pressure (cubic feet, cubic meter)
pc = compressed pressure (psi, kPa)
Vc = volume of the gas at compressed pressure (cubic feet, cubic meter)
e.g. 750 psi x .1Cu/Ft / 14.7 = 5.1 Cu/Ft |
5.1 Cu/Ft is the total volume of air that is required to blow down the gear and have some left for flaps and brakes.
Now take the same equation and apply it to the mini bottle. .057 x 4500 / 14.7 = 17.4 Cu/Ft !
This means that the tiny little bottle has the potential to hold 3 times the amount of air as our stock system.
But wait you say....I can't use 4500 PSI in my system.......Well yes you're right whoever you are.. But the paintballers come to the rescue again. Their guns can't handle 4500 PSI either, but coincidentally they work at around 800 PSI. The paintballers have developed small regulators that screw into the bottle and reduce the pressure to the lower pressure usable in our airplanes.
In order to use this you would give up charging the emergency system from the on board air system however. This would be a system where you would need to recharge after an emergency deployment. The bottle would be deployed in the cockpit replacing the emergency air valve and plumbed directly to the emergency circuit. Total loss systems were common in many airplanes, The Mig15 comes to mind.
This setup however would eliminate several sources of problems/leaks including:
The Air Valve (Can't hold emergency air?)
The Check Valve (Can't get your gear up????)
It would also eliminate the Tee from the main air system, and all the tubing and weight from the tail. So basically it is a much simpler system, albeit 1 shot, actually 3 shots.
The bottle can be easily unscrewed for recharging at your local firehouse or paintball or scuba store (Yes 3000 PSI would work but not as many blows).
During annual inspections when you're doing multiple blows you can just recharge from your own Scuba bottle to 3000 PSI a butt load of times.
And best of all A brand new bottle and regulator is about $200, available on Amazon, and all it takes is a few adapters to fit in our airplane.
The Main Air tank at 750 PSI contains 20 Cu/Ft of air. As a bonus you could carry a spare mini bottle in your luggage, which you could use to replace the emergency bottle after a blow, or in a pinch, you could fill your main air tank enough to get you started! It would be about 3 Cu/Ft short, but we've all started with less than full tanks.
Now here are some caveats.
Both solutions use the Carbon Fiber wrapped aluminum cylinders. The Carbon fiber is what allows the higher pressures. They have a DOT requirement for Hydro checking every 5 years. Steel cylinders are every 3 years.
Carbon Fiber wrapped cylinders have a life limit of 15 years, but this is for commercial use at 4500 PSI. The main air bottle will never be pressurized beyond 750 PSI so it should last indefinitely. The emergency system would be fully pressurized, but I can spring for $200 bucks every 15 years.
Ernie
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