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helldog

Wing loadings at High Alt DZ's

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The elevation at our DZ is 4100 MSL. When traveling to a sea level DZ the speed of the canopy is noticeably slower. What I was wondering was is it possible to compare wing loading and performance characteristics at these different altitudes. Right now I'm comfortable loading my canopy at 1.3 at my home dz. Does this mean that if I moved to a Sea level DZ that I would need to move to a smaller canopy to get similar performance? Or is the difference in the air density not that Great?
Just wondering out loud:|
Blues
Jim

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I jump regularly in the midweat and occasionally in Colorado - there is a HUGE difference between the two. My Sabre 135 in Colorado "seems" like my Stilletto 135 at sea level in the midwest for the first few jumps back...

-- (N.DG) "If all else fails – at least try and look under control." --

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Any pilot can help you calculate density altitude, which is also affected by temperature, humidity and barometric pressure.

The worst scenario is a hot, humid day in Colorado (5.000 + feet above sea level).

The best scenario is a cold, dry day in Death Valley, California (below sea level)

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I learned how to skydive @ 5003' MSL and made 1500 jumps there. I started on a PD 260 and when I was done my regular canopy was a Stiletto 120. I had jumps on FX 104 , Xfire 109 at that altitude. I moved to a new DZ to go to work and our elevation is 32' MSL. I have been here for 16 months and made about 750 jumps at near sea level. I made my first jump back home in over a year a couple of weeks ago and the difference in the air was amazing. I jumped a Sabre 170 and the forward speed on landing and the difference in the flare was impressive. This was in the wintertime with snow on the ground and "fat air". On a hot summer day in july there, the density altitude can be close to 10000'. You can tell the difference in the freefall, your openings, your canopy flight, and your landings.

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The elevation at our DZ is 4100 MSL. When traveling to a sea level DZ the speed of the canopy is noticeably slower. What I was wondering was is it possible to compare wing loading and performance characteristics at these different altitudes.



You go faster by about 2% for each 1000 feet of density altitude which corresponds to a canopy size decrease of about 4%. Traveling between sea level and mountain states can change your speed the same as 1-2 canopy sizes. There are also huge changes in your recovery arc - a disproportionate number of visiting flat landers who attempt high performance landings before they've figured that out do not fare well.

Control sensitivity seems more a function of canopy size than wing loading. A 105 up here may have the forward speed of an 87 at sea level, although the smaller canopy at sea level is still going to be twitchier to fly. You may find that this restricts your wing loading more than stall speed.

Interestingly enough this seems to be a good match for Brian Germain's WNE formula (-.1 / 2000 feet)

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... Or is the difference in the air density not that Great? ...



More dense or heavier air will slow down objects moving through it. Such air resistance is AKA drag and increases with air density.

Lower air density penalizes canopy pilots as the lifting force on the canopy decreases.

Temperature and air pressure at a particular time and place affects the air's density and therefore the canopy performance. In general, density altitude calculations don't take humidity into account since its affects are so much less than the others.

Density altitude is defined as the pressure altitude corrected for the effects of temperature and humidity.

Density altitude is a good way to relate air density to canopy performance.

Here is a good link about Density Altitude:

http://www.infodotinc.com/weather3/6-22.htm

And also a link for a Density Altitude Calculator:

http://www.wahiduddin.net/calc/calc_da.htm

Blue Skies! B|
-----------------------------
Mario Santos
Portugal

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I got to jump last weekend on a glacier in switzerland
where landing was at about 3000 Meter above see level (around 9'000 feet)... B|
Talk about fast landings... I felt like I was jumping a canopy much smaller. Plus the glide angle of my seven cell canpoy certainly did not help the flare!
lots of fun but could be really dangerous if not prepare for this kind of landing.

"We see the world just the way we are...

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I believe that the field elevation where I jump is 5,500. Our density altitude in the summer ranges from 8000 to 9500. I still jump a really conservative canopy, Spectre 190 at a wingloading of .78.

I have jumped in Ogden where the field elevation is only 700ft difference and with a density altitude of 6000, my Spectre felt like a 210. I have been told by my canopy coach that my 190 here is equivalent to jumping a 150 at sea level.

Hopefully that will give you a newbies prospective on the difference.

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