kbell

I worked on this same problem a few years ago trying to analyze pro-track data on a non-PC platform. I remember it being much harder than I expected to find a formula to convert from pressure to altitude. Here's what I finally came up with, combining several formulas I found and solving for altitude. It seems to work pretty well (agrees within a few feet with the PC Jump-Track software) const float kDryAirGasConstant = 287.04; const float kGravity = 9.80665; const float kSeaLevelTemperatureK = 288.15; const float kSeaLevelPressure = 1013.250; const float kTempLapseRatePerMeter = -0.0065; const float kMetersToFeet = 3.28084; // calculate the height above sea level for test pressure float a = kDryAirGasConstant / kGravity * log(kSeaLevelPressure / testPressure); float meters = 2 * a * kSeaLevelTemperatureK / (2 - kTempLapseRatePerMeter * a); // optional: float feet = meters * kMetersToFeet; This calculates height above sea-level, so to get height above ground, you need to calculate the ground height above sea level and subtract that from all the altitudes you calculate. I find that the absolute altitudes vary a bit, especially in Texas on a hot day (100+ F), but the relative height above ground is pretty accurate.

From the data recorded by my Pro-Track, the ground level ranges between 993 and 1016 mbar with an average of 1002 mbar over the 87 jumps I have in my current database. The data is from DZs in southcentral Texas with ground level between 200-400 ft MSL. I've also attached a file showing a freefall profile with the pressures listed along with the altitudes. Hope this helps, Kevin

Dave, you need to learn how to spot. A few months ago I was doing a freefly jump with a friend when I saw one of his Tevas come off and go shooting upwards at about 8000ft. Later on, about 30 seconds after we landed, the missing shoe hit the ground less than 50 feet from where I was picking up my gear.

Aerial views taken during a glider ride showing my best guess of Dave's landing area.

I don't have my own machine handy to check, but I believe the Protrack transmits at n-8-1 19,200 bps Kevin

I demoed the yellow w/ blue diamonds 170 (loaded at 1.5) and it slammed me too. The good openings were the two that had 4-5 twists... at least it flew straight and level while I kicked out. I really liked the way it flew and landed, but couldn't get past the openings. Kevin

I went back and forth on color schemes for a while before ordering my new Samurai. I originally was going to get purple with neon green ribs/airlocks like the demo I had, then switched to yellow/blue, then yellow/black, and finally I went with yellow/purple (lemon/blackberry on the color charts) instead. I think it came out really well, but if I had to do it again, I think I'd just look at the stock list (if Big Air Sportz had a stock list) and just pick the least ugly one and get it the same week rather than waiting for a custom canopy.

You can see in the still that both brakes are unstowed, so this most likely started out as a packing error. After that, I'd guess that either uneven inflation or slight unevenness in the harness caused one side of the canopy to surge forward before the other.

Not sure what language we're coding in here, but the above solution is clever perhaps, but definitely the least efficient of the three, both in readability and execution speed. The division operation alone is probably enough to lose, then there's overhead of the 'trunc' function call (which is redundant if the language is 'C' like since both divisor and dividend are integers already). Finally, with so few cases in the switch statement, most compilers will turn it into a series of ifs anyway, possibly with more comparisons than the original since each case is represented rather than just the beginning and end points of each range of users. geekiness... it's a curse sometimes

I was having too much fun jumping so I didn't take that many pictures, and the ones I took are only so-so. But here's some of them: 1) Parked CASA early Friday morning 2) "California" Dave and Levin packing in the Hangar 3) Group photo setup: I don't know everyone, but on the wing, there's "Texan" Dave, and Zennie peeking out from behind the prop. On the cockpit is Levin, Todd (DZO), and Pablito. 4) Todd again, with Skygeek on the wing. It was great meeting all the DZ.commers in attendance, and look forward to meeting more of you next time. Also, thanks to Mike, Todd, Kathy, AggieDave, Pablo, and everyone else who worked their butts off to make this boogie a great success. Kevin

It's rain (stings at freefly speeds). I think the pics Andy attached are from the dive on Sunday. Not sure how many were on that one, but the list Ramon posted was from the Saturday sunset load.

Here's the link to the APF document. Also, The Big Air Sportz Owner's Manual has a good discussion of high performance flight and the risks involved.

In the latest news column on the front page, the link for 'Briefing structure' is broken Kevin

In the latest news column on the front page, the link for 'Briefing structure' is broken Kevin

We only have 12 months per year in our calendar over here

My first (and current) canopy was a Spectre 190 that I load at 1.3. I started jumping it on my 54th jump, so I rented student gear for a while. However, at my DZ, there was a wide range of sizes available and I was able to downsize gradually. Based on my experience, I don't think I'd recommend going directly from a 280 ft^2 student canopy to a Spectre 190 without jumping several sizes in-between (When you say run-out landings, are we talking an all-out sprint, or just a step or two?). My canopy progression was: PD 340: 4 jumps (practically a tandem main....) PD 300: 13 jumps PD 260: 8 jumps PD 230: 8 jumps Sabre 210: 20 jumps I remember going from the 340 to the 300 was barely noticeable, but on moving to the 260 things seemed to speed up drastically and I scared myself and went back and jumped the 300 for about five more jumps before trying the 260 again. Going to the 230 from the 260 wasn't too hard, but switching from the worn out student F-111 mains to the ZP Sabre was another challenge that took a few jumps to master. Moving from the Sabre to the Spectre wasn't too difficult once I got used to the steep approach and ground rush you get from a Spectre. BTW, I now have 300+ jumps on my Spectre, and still love flying it. Kevin

My last 280 or so jumps have been on a Spectre 190 that I load about 1.3. This afternoon, I had the opportunity to put two jumps on a friend's demo Sabre 2 170 before he returned it. Two jumps probably aren't enough to give a valid comparison, but I wasn't that impressed with the Sabre 2 vs the Spectre. I found the turns and flare to be very similar between the two and didn't have any problems with the switch, but the Spectre definitely dives more in turns and to me, it feels faster when landing (perhaps due to the ground rush from the steeper glide angle). I'm not saying that the Sabre 2 is a bad canopy, to me it just wasn't different enough from my Spectre, and I really love my Spectre. I'd definitely suggest a demo before trading in your Spectre for a Sabre 2.