Forums: Skydiving Disciplines: Swooping and Canopy Control:
Jumping at high altitude DZ

 

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DocPop  (C License)

Nov 22, 2010, 5:18 PM
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Jumping at high altitude DZ Can't Post

I am planning a trip to South Africa and hope to spend a few days at JSC which I believe is about 5,000' MSL. I currently jump at a DZ at about 700' MSL.

Is there a rule of thumb that would enable me to get some idea of how my canopy will behave given this increase in altitude (assume all other density parameters stay the same). Is this going to make my 135 feel like a 120 would at my home DZ? Or would the difference be bigger or smaller than that?

I realize that these are some very vague questions. Just trying to get a feel for what to expect.


JamMasterJay

Nov 22, 2010, 6:28 PM
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Re: [DocPop] Jumping at high altitude DZ [In reply to] Can't Post

That's a good question...but you're kind of missing another whole side of it. You're not just concerned with altitude in itself, what you're real concern is "density altitude". Density Altitude is Pressure Altitude corrected for non-standard temperature variations. This means, the hotter it is, the higher it feels.

I'm not sure what DZ or area you're from but you mentioned it was around 700' MSL. If this DZ is in Florida, on a HOT summer day, your density altitude could easily change to 3K or maybe even 4K.

It's all about air density. The higher you are, the more humid and hotter the air, the less dense it is. While, the lower you are, cooler air and less humid, the more dense it is.

Just about everything performs better in cooler, more dense air; parachutes aren't any different.

Back to you. Figure out what the average pressure density is at you DZ in the summer; compare that to where you're going. Maybe it will turn out to not be as big of a difference as you originally thought. Then again, maybe it will be even worse.

It's summer in the southern hemisphere; that means with a field elevation of 5K and a hot summer day, it could be 6K or even 7K density altitude.

Just my $.02


AggieDave  (D License)

Nov 23, 2010, 6:00 AM
Post #3 of 28 (2629 views)
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Re: [DocPop] Jumping at high altitude DZ [In reply to] Can't Post

A lot of people will tell you that going to a near sea level DZ to a 5,000msl DZ that it will like downsizing. That isn't a bad description, but the changes in flight characteristics go a bit further than that.

You canopy will "feel" faster, but that also means that the canopy's recovery arc will be longer and that the canopy won't respond as fast to toggle input. So that means your canopy will turn faster, dive faster and will take longer to respond to arrest those dives and turns.

In short, you can get in trouble faster and it will take longer to get out of it!

That is the "layman's" explanation.


JohanW  (D 86318)

Nov 23, 2010, 6:03 AM
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Re: [DocPop] Jumping at high altitude DZ [In reply to] Can't Post

More than 4000' plus the temperature difference - I think you're looking at about two sizes smaller. Call it a 107. You want to be careful. Smile

There is, or used to be, a calculator online for canopy size (or suspended weight, or wingloading) vs. density altitude. Unfortunately, last time I looked, I couldn't find it. Maybe somebody else has a link.


craigbey  (C 31991)

Nov 23, 2010, 6:20 AM
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Re: [JohanW] Jumping at high altitude DZ [In reply to] Can't Post

http://www.divemaker.com/trajectory/da.php

http://www.pilotoutlook.com/...-altitude-calculator


DocPop  (C License)

Nov 23, 2010, 8:01 AM
Post #6 of 28 (2595 views)
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Re: Jumping at high altitude DZ [In reply to] Can't Post

Thank you to all of you. The comments and calculators were very interesting.

I understood about speed and recovery arc being greater but I had no idea that the canopy won't respond as fast to toggle input. I am guessing this catches people out.

I feel better (and worse!) about my first jump there now!


moonjumpster  (D 858)

Nov 23, 2010, 8:35 AM
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Re: [DocPop] Jumping at high altitude DZ [In reply to] Can't Post

When you get to JSC, have a chat to Rob Kruger & get a DZ briefing from him...

If you get to jump at PSC, speak to Selwyn,James or Mike,and likewise get DZ briefings from any of them...

Jumping here in Gauteng is fun to say the least...density altitude last week-end at PSC was 7500ft...& we're at 4k....38deg C ...not the norm but we still had fun!

Pull high for your first few(5k+) (don't forget to let the load know...) & have fun!

JSC & PSC have pre-manifest systems in place...prudent to book before traveling out to either DZ's...

http://www.jsc.co.za/

http://www.iloveskydiving.co.za/


Have fun!


DocPop  (C License)

Nov 23, 2010, 10:03 AM
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Re: [moonjumpster] Jumping at high altitude DZ [In reply to] Can't Post

Baie dankie, meneer.

I appreciate your advice. The other DZ I will probably end up at is Skydive Central in Bloem.


Premier ianmdrennan  (D 25821)
Moderator
Nov 23, 2010, 10:35 AM
Post #9 of 28 (2557 views)
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Re: [DocPop] Jumping at high altitude DZ [In reply to] Can't Post

In reply to:
Baie dankie, meneer.

I appreciate your advice. The other DZ I will probably end up at is Skydive Central in Bloem.

If you get a chance, stop by my old home DZ in Grahamstown, Eastern Cape. EP Skydivers.

Have fun, and talk to the names mentioned above - above all, take it easy on the first few jumps.

Blues,
Ian


DocPop  (C License)

Feb 13, 2011, 10:59 PM
Post #10 of 28 (2307 views)
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Re: Jumping at high altitude DZ [In reply to] Can't Post

Just finished the trip and I had an excellent time. I jumped at Rustenburg and Skydive Central (Bloemfontein). Got weathered out at Mossel Bay and JSC saw fit to crash their PAC into a fuel bowser on Saturday so I never got to jump there.

Many thanks to all the great people who advised me on jumping in SA, esp. Rob Kruger, Hein Geldenhuys and Glen Vermeulen.

As to my initial question, my canopy did feel fast, but not to the point where I felt out of control. I did take things very easy due to the altitude, heat, my uncurrency (4 months off) and the fact that I am already over the recommendations for downsizing. I also felt that coming straight in, my Katana seemed to have a very steep descent, but that may be because I usually do some kind of HP landing and am used to experiencing plane-out on most jumps. The most I did was 90 turn and the additional altitude loss was quite noticeable, and I have to say - a lot of fun! I can't say I noticed much difference in the flare (I was expecting it to be "weaker").

I hope this thread might be helpful to other new jumpers going to a high altitude DZ.

I would now be interested to see how a 120 or a 107 feels at my own dropzone......but that is just asking for trouble and I'll be waiting another couple of hundred jumps for that!


deathwish603  (B License)

Mar 5, 2011, 12:03 PM
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Re: [DocPop] Jumping at high altitude DZ [In reply to] Can't Post

IDK much about DZs specs, but I learned that every time you go to a new DZ, just open up higher and get used to Canopy Flight in this place, when you got used to it, feel free to do it your way...


Doing crazy shit in a smart wayCool


SRI85  (D License)

Mar 7, 2011, 11:49 PM
Post #12 of 28 (2069 views)
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Re: [DocPop] Jumping at high altitude DZ [In reply to] Can't Post

i dont think theres much of a big deal to be made about the altitude. I downsized to a 119 and my first jump on it was at a DZ located 5500ft ASL. i usually jump at a dz thats 240ft above.

i dont think theres much to worry about going to a higher altitude dz. i think saying its like downsizing is a little overstepping it.


stayhigh  (F 111)

Mar 8, 2011, 7:15 AM
Post #13 of 28 (2039 views)
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Re: [SRI85] Jumping at high altitude DZ [In reply to] Can't Post

5000 ft diffrence should feel like downsize and half atleast.


Premier ianmdrennan  (D 25821)
Moderator
Mar 8, 2011, 7:48 AM
Post #14 of 28 (2030 views)
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Re: [SRI85] Jumping at high altitude DZ [In reply to] Can't Post

In reply to:
i dont think theres much of a big deal to be made about the altitude. I downsized to a 119 and my first jump on it was at a DZ located 5500ft ASL. i usually jump at a dz thats 240ft above.

i dont think theres much to worry about going to a higher altitude dz. i think saying its like downsizing is a little overstepping it.

I totally disagree.

It's been, in my experience, at LEAST 1 downsize in my turn altitudes and flying style.

Ian


DocPop  (C License)

Mar 8, 2011, 8:00 AM
Post #15 of 28 (2026 views)
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Re: [SRI85] Jumping at high altitude DZ [In reply to] Can't Post

In reply to:
i dont think theres much to worry about going to a higher altitude dz.

I think anyone going to a high altitude DZ should definitely take it easy for the first few jumps - in the same way one would when jumping an unfamiliar canopy.


matt002

Mar 8, 2011, 8:10 AM
Post #16 of 28 (2025 views)
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Jumping at high altitude DZ [In reply to] Can't Post

I usually jump at approx sea level.
I have to put 150' - 200' on my turn height at mile high colorado, the difference is huge in all respects, height lost during the turn and especially during the recovery arc, horizontal speed over the water even straight in landings things happen much quicker.
You can clearly see the effect in the distance and speed results of competitions held at very high elevation.


SRI85  (D License)

Mar 8, 2011, 8:34 AM
Post #17 of 28 (2014 views)
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Re: [ianmdrennan] Jumping at high altitude DZ [In reply to] Can't Post

In reply to:
In reply to:
i dont think theres much of a big deal to be made about the altitude. I downsized to a 119 and my first jump on it was at a DZ located 5500ft ASL. i usually jump at a dz thats 240ft above.

i dont think theres much to worry about going to a higher altitude dz. i think saying its like downsizing is a little overstepping it.

I totally disagree.

It's been, in my experience, at LEAST 1 downsize in my turn altitudes and flying style.

Ian

perhaps the colder temperature made it not that noticable. guess ill just have to visit out here in the summer time.


DrewEckhardt  (D 28461)

Mar 8, 2011, 3:31 PM
Post #18 of 28 (1958 views)
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Re: [SRI85] Jumping at high altitude DZ [In reply to] Can't Post

In reply to:
i dont think theres much of a big deal to be made about the altitude. I downsized to a 119 and my first jump on it was at a DZ located 5500ft ASL. i usually jump at a dz thats 240ft above.

i dont think theres much to worry about going to a higher altitude dz. i think saying its like downsizing is a little overstepping it.

It's a huge deal. It's like going 1-2 sizes smaller depending on temperature. When my home DZ was over 5000 feet MSL (with density altitudes to 8000-9000 feet MSL in the summer) we'd tell people things were different, that their turns needed to start higher, not to go big until they figured it out and a disproportionate number went away in ambulances.


polarbear  (D 25673)

Mar 8, 2011, 5:13 PM
Post #19 of 28 (1940 views)
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Re: [DrewEckhardt] Jumping at high altitude DZ [In reply to] Can't Post

My home DZ and the DZ I travel to most often are both at 5100'. Going down to sea level changes things dramatically...as others have already stated, it's at least like changing a full size in terms of the speed of the canopy and the altitude necessary for completing a turn. Another way of looking at it is I find it takes maybe 15 or 20 lbs of lead when I am at sea level to get the same speed and dive.

While it's perfectly possible to fly at higher altitudes, it is definitely not something to take lightly. Remember a year or two ago when there were several serious injuries and a fatality at the world cup in South Africa? I gaurantee you altitude was factor.


DocPop  (C License)

Mar 8, 2011, 5:31 PM
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Re: [polarbear] Jumping at high altitude DZ [In reply to] Can't Post

I jumped regularly with one of the guys who got badly hurt in SA during that competition and the was one of the reasons why I started this thread.

I wanted to get some advice because if it can happen to a competitive swooper, it sure as hell can happen to me.


chuteless  (D 41)

Mar 9, 2011, 7:56 AM
Post #21 of 28 (1859 views)
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Re: [DocPop] Jumping at high altitude DZ [In reply to] Can't Post

I spent two periods of time jumping in Ecuador. The first time the DZ was 9500 above sea level, so we had to climb to over 16000 ft for a 30 sec delay.

It was extremely hard on breathing, as we had no supplementary oxygen. I would put my rig on my back and gasp for air for about three minutes, and then I could do up the snap hooks. Once out of the aircraft everything was just like back home, flying was not noticably different, nor was canopy flying.

Once on the ground is was gasp fr air again, and you learned quickly to move slowly and breathe steady .

The 2nd time I went there, we were jumping at sea level, and no problems except putting chunks of ice in your cold drink, bacteria and all. That was cause for terrible sickness and dehydration, and a four day stay in hospital when I got home.


Bill Cole D 41 , aka chuteless


SRI85  (D License)

Mar 9, 2011, 10:20 AM
Post #22 of 28 (1835 views)
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Re: [DrewEckhardt] Jumping at high altitude DZ [In reply to] Can't Post

In reply to:
In reply to:
i dont think theres much of a big deal to be made about the altitude. I downsized to a 119 and my first jump on it was at a DZ located 5500ft ASL. i usually jump at a dz thats 240ft above.

i dont think theres much to worry about going to a higher altitude dz. i think saying its like downsizing is a little overstepping it.

It's a huge deal. It's like going 1-2 sizes smaller depending on temperature. When my home DZ was over 5000 feet MSL (with density altitudes to 8000-9000 feet MSL in the summer) we'd tell people things were different, that their turns needed to start higher, not to go big until they figured it out and a disproportionate number went away in ambulances.


for swooping i can see it being a big deal, regular landings really didnt seem that different.


RichLees

Mar 9, 2011, 12:40 PM
Post #23 of 28 (1825 views)
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Re: [DocPop] Jumping at high altitude DZ [In reply to] Can't Post

Airtec kindly lent me a Cypres datalogger and sent me the traces from some jumps. My Viso often records 95mph+ at about 200-250 feet and I wanted to understand the margin of safety for my AAD.

At sea-level on my 450 degree turn, I peaked at 41.7m/s vertical at 220 feet. The parameters for the Speed Cypres mean it will fire at over 43m/s between 750 and 330 feet. (Expert Cypres, its 37m/s between 750 and 180 feet.)

I also did a couple of 450s at 5000' and exceeded 47m/s from which I conclude I should turn off my AAD at a high DZ. Having taken a down-winder into the thistles and prairie dog holes, I'm too chicken to go back to Mile Hi.


Premier billvon  (D 16479)
Moderator
Mar 9, 2011, 1:09 PM
Post #24 of 28 (1822 views)
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Re: [SRI85] Jumping at high altitude DZ [In reply to] Can't Post

>for swooping i can see it being a big deal, regular landings really didnt seem
>that different.

Your groundspeed is guaranteed to be significantly higher. Your decision making has to change when winds are squirrely. A downwind landing that you can shrug off at sea level can (quite literally) kill you at 5000 feet.

A lot of people jump at higher altitudes only in stronger winds and conclude "hey, my canopy doesn't fly all that differently!" Which is certainly true - it flies the same way at 5000 feet whether or not you are at a sea level DZ or in Denver. It even flies at the same indicated airspeed (IAS in pilot terms.)

However, IAS is very different than ground speed at 5000 feet - and your legs don't get stronger to compensate for the higher speeds. Which is why injuries are common when sea level jumpers go to high altitude DZ's.


AggieDave  (D License)

Mar 9, 2011, 4:09 PM
Post #25 of 28 (1799 views)
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Re: [SRI85] Jumping at high altitude DZ [In reply to] Can't Post

In reply to:
In reply to:
In reply to:
i dont think theres much of a big deal to be made about the altitude. I downsized to a 119 and my first jump on it was at a DZ located 5500ft ASL. i usually jump at a dz thats 240ft above.

i dont think theres much to worry about going to a higher altitude dz. i think saying its like downsizing is a little overstepping it.

It's a huge deal. It's like going 1-2 sizes smaller depending on temperature. When my home DZ was over 5000 feet MSL (with density altitudes to 8000-9000 feet MSL in the summer) we'd tell people things were different, that their turns needed to start higher, not to go big until they figured it out and a disproportionate number went away in ambulances.


for swooping i can see it being a big deal, regular landings really didnt seem that different.

It IS a big deal for an every day jumper. When you turn, your recovery arc will be longer, your canopy will take longer to respond, the flare won't be as "powerful." Basically, any mistake will be amplified. Any standard movement will be faster and the canopy will recover slower.

On the upside, you'll be going faster when you hit the ground...maybe that's not the upside you're looking for.

Are there any canopy coaches in your area you could consult for some coaching?


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