Altitude changes

[bdbrown 0]

Quick question here.
Would a 1000 ft dz altitude change make a major effect on the landing performance of a canopy?

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[Canuck 0]

For sure, although it is likely more noticable with smaller wings at higher loadings. I definately notice it with my canopy if I'm somewhere 1000 ft. higher/lower than home.

It's good to find out the elevation before you jump at an unfamiliar DZ, that way you can adjust the visuals and your approach accordingly. As an estimate, I would say every 1000 ft. ASL adds about 100 ft. to my turn altitude.

Canuck

[quade 3]

As it so happens, there's a rule of thumb for this.

A 1000 foot increase in elevation equates to a 2% increase in airspeed.

See http://futurecam.com/densityAltitude.html

A +15° F change in temperature also changes the density-altitude by 1000 feet with a corresponding performance change.

quade -
The World's Most Boring Skydiver

[n23x 0]

Absolutely. My 2 primary dropzones are at 5050MSL and about 800MSL, and the difference is staggering!

.jim

"Don't touch my fucking Easter eggs, I'll be back monday." ~JTFC

[bdbrown 0]

Thanks for the info, thought I was going crazier. Stood up 15 straight landing sweet as can be at Z-Hills then came back to Atlanta and had to slide out the 1st landing...Does seem to come in a little faster here at home....

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[GQ_jumper 4]

after spending a year at a 6000' dz i went down to see level and felt like i was flying a tandem rig!!! the shortenedrecovery arc was incredible

History does not long entrust the care of freedom to the weak or the timid.
--Dwight D. Eisenhower

[Spizzzarko 0]

What a lot of you may not realize, is that your DZ's Density altitude may be changing 1000+ feet a day. No two jumps are the same. Are you done with your trip yet GQ? Weather here sucks.

[quade 3]

A single 1000 foot change in density-altitude over the course of the day isn't all that big of a deal. After all, we're only talking about a 15°F change for that which you'd sort of expect on any given day at a drop zone where the sun is shining. And that 1000 foot swing only changes your airspeed by about 2%.

Over the course of a year or when traveling though, it can be a significant factor.

For instance this morning at Perris it was about 45°F (yeah, I know, it's still warmer than a lot of the country) and in the hottest part of summer it can easily hit 110°F and that represents a swing of about 4500 feet in density-altitude. That's about a 10% change in airspeed, which might not sound like a lot, but it does matter.

quade -
The World's Most Boring Skydiver

[Spizzzarko 0]

Here in Colorado we have had DA close to 10500 at a 5500 field elevation. 10500 and no wind equals some fast landings.

[quade 3]

Yeah, that's an impressively high DA.

I can only imagine what it must be like for visiting jumpers from drop zones located near sea level.

My -guess- is that you guys usually purchase canopies at least a size or two larger than the folks that live at the beach. At least, that seems like it would be the smart thing to do.

quade -
The World's Most Boring Skydiver

[Spizzzarko 0]

I usually tell people that their canopy will act a size smaller up here. Going down to sea level the canopy acts a size bigger, when you are used to being up here. That's the easiest way to describe it.

[Harksaw 0]

I'm not sure how much of an issue it would be, but from a physics standpoint, the change in performance won't be linear. A change from 0 MSL to 1000' MSL should, from a physics standpoint, be less of an air density (performance) difference than a change from 5000 to 6000 MSL.

__________________________________________________
I started skydiving for the money and the chicks. Oh, wait.

[quade 3]

For most of the altitudes that skydivers use most of the time, a 1000 foot gain in density altitude at any altitude should "feel" pretty much the same. The rule of thumb being for each 1000 feet gained an increase of 2% airspeed holds pretty much true at all of these altitudes.

Above 20k feet msl they might notice a divergence in the rule, but rarely do skydivers land at those elevations.

quade -
The World's Most Boring Skydiver

[Tonto 1]

Quote

My -guess- is that you guys usually purchase canopies at least a size or two larger than the folks that live at the beach. At least, that seems like it would be the smart thing to do.

Spot on. Our DZ is 5500ft AMSL with summer DA over 10 000ft.

I'm jumping canopies in the 107 - 109 sq ft range.
If I were at Sea Level, they'd be down about 10 sq ft.

t

It's the year of the Pig.

[blu 0]

My dropzone is about 4500ft asl I don't think i would downsize if i lived @ the beach hehe

***Keep it fun, stay alive***
Safe swoops
Azul
Follow Orbita on Twitter @freeflyorbita

[proswooper 2]

hey spizzarko

are people able to shut down little cross braced canopies loaded at 2.0 + at that altitude where you are?

thanks

Paul

[Spizzzarko 0]

A little breeze helps, but sometimes there is a little sliding and running. It really depends on the pilot. I have a buddy who jumps a xaos 27 78 up here, and he loads closer to 3.0. His landings are extremely fast, and he runs his landings quite a bit, but he is a very skilled jumper. People jumping the little canopys are not the norm. People jumping cross braced canopys are not the norm either. There's probably only 10 people in the state that activley jump cross braced canopys here in Colorado.