Field Elevation

[scott2002 0]

I've been skydiving for about a year now and have only had the chance to jump at two different dropzones in my area. Both of these dropzones are located 5100+ feet above sea level if memory serves me correctly. Well, I got to thinking about it and was wondering how big of a difference does field elevation make in canopy performance? For those of you that have jumped at both high and low field elevations, what did you notice different in your canopy flight characteristics? I would assume at lower altitudes you would get more lift at flare time but what about turn rate, forward speed, etc?

[BikerBabe 0]

Well, to put it bluntly, everything is faster!
When you compare 5000 feet to sea level, it's a helluva lot faster!
Basically, because the air is a lot less dense, you have less drag on your canopy, and it flies faster. This is especially noticeable on a high-performance canopy. For example, at Eloy(1,500 ft), my favorite thing is landing my Stiletto on a no-wind day. In Albuquerque (5,500 ft), it scares me a bit. I'm going faster, there's no grass to slide on, and a heck of a lot of crap out in the desert to trip over.
The best comparison I've heard is that the higher you get, the smaller and smaller your canopy performs (like you downsized). It's pretty much true. I've never jumped a Stiletto 107 or 97, but I can imagine landing it at sea level would feel a bit like landing my 120 in NM on a no-wind day.
However, because you've learned at high-altitude DZs, you'll have a distinct advantage in that regard over people who have only jumped at sea level. If you get visitors to your DZ, remind them of the speed.

[skycat 0]

Everything bikerbabe said, and I will add that little things are more noticable. Like in Houston I had a feeling my brake lines were to long, but it was no big deal I could work with it, came to Denver and ended up shortening them. You definately loose more altitude in a turn, and in normal flight. I would say coming from Houston to Mile-hi it definately felt like I downsized 2 sizes and that was on a weekend when it was in the 80s I've been told it will be even faster on weekends when it's in the upper 90s, instead of 5000MSL it will feel more like 9000MSL or one size smaller.
Now, I have opted to not upsize since my last landings were perfectly fine and flat turns and flare turns did not change from sea level, but I am dreading after jumping up here a few months and going down back to Houston to visit friends thinking my canopy is a dog.

[quade 4]

And temperature also plays a part in what is known as Density-Altitude.
Read about it HERE.
quade
http://futurecam.com

[Lindsey 0]

The thing I don't understand, though, is why does your canopy open faster at higher elevations. It seems with less density it would open slower? I can't figure that out (though haven't really tried).....
Please accept this question in the spirit of love in which it is presented.
Peace~
Lindsey
Ya' know Smack-water Jack he bought a shotgun
'cause he was in the mood for a little con-fron-ta-tion

[skycat 0]

I know it has something to do with the fact that you are falling faster, on my belly now without lead my fallrate is right around 125 vs. 114 in Houston. Also, I've noticed that the snivel which usually was, nice and smooth, is now very erratic and jumps around alot and causing wild off heading openings. I now have to harness steer through the openings when before I just kind of laid there enjoying the ride.

[polarbear 1]

I feel like I have a pretty good perspective.
In the fall-winter-spring, I jump in Illinois, at a field elevation of ~700 ft. (say on average at standard temperature). In the summer, I jump in New Mexico, at a field elevation of ~5000 ft (on average at 100 degrees). The difference? Between temperature and actual elevation, the difference is DRAMATIC. As mentioned earlier, a canopy seems to fly much smaller at the higher elevation...loses more altitude in a turn, flies faster, stalls at a higher speed, etc. It lends itself to good swoops. I find I have to start my final turn higher, start my flare higher, and be ready to run when I touch down.
If you are going from a "Normal" DZ to one at high altitude and/or high elevation, be ready for a difference. Take it easy for a jump or two (at least).

[billvon 2,990]

>The thing I don't understand, though, is why does your canopy open faster
>at higher elevations.
Because you are falling faster. Lower air density = higher terminal velocity.
-bill von

[Lindsey 0]

Doh! Yes....of course
Ya' know Smack-water Jack he bought a shotgun
'cause he was in the mood for a little con-fron-ta-tion

[SkydiveMonkey 0]

But if the air is thinner, wouldn't it be the equivalent of falling slower in denser air (same principle of TAS and SAS on a pro track).
Wynona's got herself a big brown beaver
and she shows it off to all her friends ....

[TomAiello 26]

Does that mean that with equal fall velocities, the canopy will open at the same speed at high and low altitudes?
Picture a go and throw deployment at sea level compared to the same deployment at 5500'. Will both canopies open in the same distance?
--Tom Aiello
tbaiello@mac.com

[billvon 2,990]

>But if the air is thinner, wouldn't it be the equivalent of falling slower in denser
>air (same principle of TAS and SAS on a pro track).
Well, no. Physics doesn't care about altitude, and even if your parachute opens in exactly the same amount of time, you're still going from 140mph to 5mph in the same time you used to go from 120mph to 5mph. Thus harder opening.
In addition, your parachute probably won't open at the same speed. Things don't scale linearly in aerodynamics. Larger parachutes loaded at 2:1 behave completely differently than a small parachute of exactly the same design loaded at 2:1, for example. A friend of mine did some research on HALO jumps, and tried opening at 30,000 feet with a "normal" MT1X. Almost tore his legs off. He eventually had to use a tandem setup with a huge drouge to slow down enough to get a reasonable opening.
-bill von

[billvon 2,990]

>Picture a go and throw deployment at sea level compared to the same
>deployment at 5500'. Will both canopies open in the same distance?
This is a complicated question. If the IAS of the aircraft is the same in both cases, its TAS will be higher at 5500 feet. If the parachute opens in the same distance, the 5500 foot deployment will be harder.
If the aircraft fly at the same TAS somehow? Then I _still_ suspect the opening would be harder, although I have no proof other than anecdotal.
(IAS = airspeed on aircraft airspeed indicator; TAS = actual speed aircraft is moving through the air.)
-bill von
-bill von

[TomAiello 26]

To simplify, what if it was a Balloon jump? Then the aircraft would be stationary.
Umm, to come clean, the real scenario I'm facing is a cliff at 11,000 ft exit elevation. Will the parachute still open at the same speeds I've experienced closer to sea level?
--Tom Aiello
tbaiello@mac.com

[skycat 0]

Well I don't know how this figures into Bill's equation, but the hop-n-pops that I’ve done the last few weeks including one from a helicopter, from 4k AGL, 9K MSL have taken longer to open, I was pumping on the rear risers to make it open. The jumps from altitude opened, I don’t want to say faster, cause I think even they were slower but they were harder, more of a snivel, snivel, snivel, pop, rather than snivel, snivel, ahhhh.
I’m sure what I just typed makes no sense what so ever.

• Quote

[TomAiello 26]

OK, I got a fairly good explanation from BASE 311 at:
http://www.blincmagazine.com/forum/board/3843.html
It sounds like the opening at altitude ought to take longer.
Thanks Bill, for trying to explain basic concepts to someone like me, who often just doesn't get it.
--Tom Aiello
tbaiello@mac.com

[billvon 2,990]

>It sounds like the opening at altitude ought to take longer.
I agree with what he said, that the initial phase of deployment (i.e. PC inflation and extraction) will take longer. Put another way, it will take a longer delay to get to, say, 40mph of indicated airspeed. On the other hand, the parachute itself, once exposed to the air, may open faster. If you plan on not using a slider this is probably immaterial, since 90% of your deployment time will be waiting for the PC to get the parachute to the end of the lines.
One difficulty here is that some parts of parachute inflation (like cell inflation) are dependent on the absolute speed of the air impinging on it, while some (like slider control) are dependent on the pressure on the slider, which has to do with density. When you change the relationship between those two you get odd effects.
-bill von

[AggieDave 6]

Would a larger PC or a ZP PC instead of F111 PC make a difference in cases like this? In other words, if someone consistantly jumps at higher field elevations (i.e. our displaced Texas Kitty), would it be worth while to change out PCs?
Or do I have a misunderstanding in openings and the role the PC plays?
Aerials
So up high
When you free your lives (the) eternal prize

[billvon 2,990]

>Would a larger PC or a ZP PC instead of F111 PC make a difference in cases like this? In other words, if someone consistantly
>jumps at higher field elevations (i.e. our displaced Texas Kitty), would it be worth while to change out PCs?
It might be worthwhile, but it is likely you'd want a _smaller_, not a larger, PC at altitude. Forces on the PC should be roughly the same, but a too-large PC can make openings harder - and at altitude you need all the help you can to soften the openings (usually.)
-bill von