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so i have a very technical question and if you dont have good information or experience please dont answer this. i dont want to sound like an arse, but this information could save my thousands and possibly my life if acurate.

does anyone know the rate that a parachutes deployment is affected by altitude. ie how much longer and how many more feet does a parachute take to open at lets say 20k-25k feet then it does at lets say for simplicity like 5-10k feet asl (above sea level) and is this rate constant or is there a magic celing which one cannot safely basejump off of. (like im on a mountain that is 25k feet high how much longer would it take for my parachute to deploy then it would normaly)

There are a ton of variables, and of course there is not way that all parachute openings are exactly the same. Even the same canopy packed in the exact same way, deployed the same way, same environment can have significant differences between openings.




at about 18k, literally half of the air mass per volume unit is gone. but this in no way translates directly into it taking twice as long to open, or twice as fast to create the same lift, but it is very significant.


It obviously is going to depend on the type of parachute and the factors involved in deployment.

Slider down? wingsuit?

there will be no wing suit i will have my climbing gear on and have oxygen mask on due to the extream altitude and weather. i will need the parachute to open as fast as possible, so no slider. i am currently looking at maps of the area to find a suitable location. it is remote enough that i will only get one shot at it. i will have lots of gear for the climb as well. i weigh about 200lb on my own but additional weight will force me to get a larger canopy im thinking around 350-400sq f

Why are you deploying the parachute? Do you need to freefall?

If it's just a way of getting down, it would make more sense to kite the canopy off a slope than search for a sheer face to freefall.

But since I'm pretty sure someone's already launched a paraglider from everest, that wouldn't be a 'world record'. Which is the vibe I'm getting here...

If you want to make it a world record, you just need to dress in drag. Pretty sure no one has launched a paraglider from Everest in drag yet.

and here i thought nick nitro did?

 
Marta and Jimmy are about the only people I know that might have any expeareance that high. But honestly I don't think they would have "numbers". I remember talking to them about it. They knew it would take longer but they aren't really that anilitical about it.

I'll throw out some thoughts. How big do you really need? What is the altitude of your expected landing area? Can you slide it in on a slope? A larger canopy will be heavier and will take longer to reach line streatch which will also be longer. It will take longer to fill and with a short delay the true airspeed will not be higher so you can froget about the commen knowlage of canopies opening harder/faster at higher altitudes do to higher volume fill rates. The internal force/preasure to inflate/spread the canopy will be lower and a larger canopies greater weight/inerta might agrovate that problem. The only place that a larger canopy might actually benifit you is once the canopy is spread there is a period where it is just pulled through the air as a square round before it is really inflated and leaned forward and flying. The extra drag there might decrease the hight lost during that time and the time that the canopy spends leaned forward trying to accelerate your body forwards to swing back under neath it to really beguin flying. In other word I don't think a tandom size canopy is the way to go. A lot of this shit happens so fast most of the time you would never notice but I think you'll find it to be an issue at those density altitudes.

If you had some good data/video you could try to extrapolate it up to those altitudes. Good video showing time/distance to bridal streatch on pc, t/d to line streatch on the canopy, t/d to full flight. maybe a string with flags every 10 feet for refrence off the bridge. With the known weight of the components you should be able to get a real world Cd for it and model it at 25k. It's a bit of a streatch on the renalds numbers but you could do a first cut.

Here's a thought. What's the celling on a hot air balloon? I know Burner has a really big envolope that he has used for records in the past. It wouldn't be a cheap jump but trips to the himalaias aren't cheap eather and you could get real measurements with a laser rangefinder to the inflation and flying points.

Lee