IJskonijn

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Everything posted by IJskonijn

  1. Haha! The way this topic turns out, it seems like it's been flipped over by turbulence! Me being the physicist that I am, I'll happily join the discussion. From an aerodynamic point of view, what really matters is the force per unit area on your wing (or strut, or control surface, or line, or whatever). Mass (in kg) is irrelevant insofar that you need a (non-fixed in both direction and magnitude) vector called acceleration to get the force from the mass (Newton's famous F = m*a). As mentioned, the mass of the system stays the same no matter how hard you whip around on front risers, but the force that your lines have to hold sure does change! So the technically correct (the best kind of correct) definition of wingloading would indeed be one of N/m^2 (because imperial schimperial), rather than kg/m^2. Which would be weight per unit area. And since weight is changed by a change in acceleration, wingloading does change when you give some sort of input under canopy. But in most cases we can simplify things by saying the acceleration is constant and equal to the local earth gravity. In that case, definitions of wingloading in kg/m^2 are equivalent to those in N/m^2, so under that simplification this entire discussion is completely pointless.
  2. In hot weather, it pays to think ahead about where the turbulence will be relative to the landing area. That type of turbulence is easy to predict, as surfaces like tarmac or gravel heats up more in the sun, and the air boils off those surfaces faster than off the (relatively) cool grass, causing turbulence. So in general for landing area, you want something smooth all around. With that I mean that it is way better to land in the middle of a large grassy field, rather than at the edges where the boiling air is likely more violent and can throw you around much more (not good when your altitude is measured in single digits...). Also, avoid the peas for the exact same reason.
  3. Last time I was in Florida, we hit the turbulence on hot days at altitudes up to 5.5kft. For me, flying through it with increased airspeed is impossible, since I won't have arms left if I have to frontriser for 5000ft. So I took the paraglider approach, to fly through it with a little brakes to keep a good feel for what my canopy was doing. The turbulence was never so bad though that I feared for a canopy collapse, flying on a Lightning 160 at 1.35 wingloaded. Then again, Lightnings tend to recover quickly from partial or full collapses, so ymmv. Another disadvantage of spiraling around is that you are more likely to lose sight of the other canopies in the air. An unplanned canopy collision is bad news with or without turbulence.
  4. Also take into account that the French have some crazy strict rules on canopy size... http://www.ffp.asso.fr/dt046-nouvelle-reglementation-relative-a-lutilisation-des-voilures-principales/. You may not be allowed to jump your own canopy, because they judge it to be too small. Then again, I've once been told by a French jumper to just fake a logbook with enough jumps if I was ever to go jump there... This is obviously not advice, just an anecdote on how some French view their own rules.
  5. The weird thing is indeed noticing my bedside alarm clock being behind all other clocks (phone, laptop etc) in my home. And yup, that's the only one keeping time by using the grid frequency. And I'm not really surprised. There is still a lot of tension in that part of Europe, so I think we're actually lucky it surfaces this way, rather than a repeat of the Kosovo war.
  6. Page 4 of the dual square report (found on the PD website: http://www.performancedesigns.com/docs/dualsq.pdf) says:
  7. Rise of the Zombie Thread! I'm too lazy to scroll back through the thread and see if this one has been posted yet, so I'll just post it. http://www.performancedesigns.com/docs/dualsq.pdf If ever I find myself in a stable flying two-out situation, I'd do minimum of inputs (as in, enough to ensure I land somewhere that is not high-voltage or will otherwise kill me), but keep it at that. Also keep in mind, the most likely way to get a two-out is if you burn through your altitude, deploy your main while your AAD also wakes up. In that case, there's not a lot of altitude left to mess around.
  8. Assuming that the pilot wants us to leave (I know most pilots at my home club will keep you inside, to avoid messing with cg during an already VERY busy time, and because less weight doesn't actually help them improve glide angle), I'd be happy to exit anywhere above ~600 feet. But in that case, I'm throwing my reserve ripcord back in the plane!
  9. That could very well be the problem with fabric. But the best way to find out is to test it. Easiest test would be to grab a piece of fabric, sew the reinforcements and handholds to it, write some gibberish on it with a permanent marker, and jump it with someone else filming it.
  10. One practical improvement brought along by the SKA is a boost to computing and algorithms. Once the SKA is up and running, it will produce a staggering amount of raw data, something like 160 Gbps per radio dish. At 3000 dishes, that's 480 Tbps of data generated, not including all the other detectors. This is about equal to the entire internet traffic as estimated in 2019 (note: the SKA website states it generates 10 times the internet traffic, I'm basing my stuff on Cisco's claim of 2 zettabytes per year in 2019). All this data needs to be filtered and transported from the middle of nowhere (Western Australia and somewhere in South Africa) to wherever the scientists are sitting comfortably doing their analysis. The necessary computing equipment does not exist yet, and needs to be developed. Of course, once developed for the SKA, it should quite quickly become generally available as well.
  11. That title is about 13.6 billion years wrong... But yeah, the science (and equipment) is sweet. And it's going to be even sweeter once the Square Kilometer Array is really up and running.
  12. Easy, make the sign out of old F111 fabric (find an old canopy with enough white in it as background, and sew on the letters or whatever on top. Make sure to sew reinforcement on the edges (fold in the edges with reinforcement tape in between for example), otherwise the fabric will rip itself to shreds in freefall. I would imagine it won't add that much drag in freefall that you can't compensate for it, but since my last freefall was half a year ago (a pure necessity because my main refused to open), someone else might want to pitch in on that. On pull time, maybe ask a freeflyer that has experience flying with tubes on how to best handle that.
  13. Pffffttt...flimsy details. Anyone can quit smoking and drinking. Height reduction surgery..... The plot sickens....... He jumped himself, and had such a hard opening that his height instantly reduced by 10 centimeters. From there on, he decided to make everyone else jump instead. Foolproof theory.
  14. Here's my take on the baglock vs linedump discussion. Linedumps (sometimes caused by not stowing properly) hurt as hell, and have been known to kill people. On the other hand, if you have a baglock, you look up, see a ball of shit that's obviously not going any place nice soon, and you chop. No pain, no death, just a difficult search for the canopy (been there, done that, still haven't found it). If I have the feeling that my stows, especially the locking stows, are too weak, I'll double-stow them without sparing a second thought. Also: clickyfied: https://www.youtube.com/watch?v=4Nsca5add8g
  15. Sweeping the cables is a solution to the wrong problem. The better solution is to take the time together with your rigger and adjust the cable length down to less than the travel length of your hand(s) when cutting away. Test that length, use whatever method of EPs you want (I personally have one hand on each handle, peel peel punch punch) and measure the maximum distance. For a two-hands-on-one-handle approach this distance will be shorter, since the reach of your opposite arm (left in case of the cutaway handle) will be shorter across your body. Then trim the cables down to where the length above the three-ring loop is less than that distance. That eliminates the need to waste precious seconds (and altitude) by sweeping the cables. On the original discussion, I'm in the don't throw away camp. I'll hang on to them unless I need to drop them, because they might fuck with my reserve deployment if I let go of them. For that reason I prefer the one-hand-per-handle EP procedure (also the one I learned from the beginning). The fact that I still have them when landing is a nice bonus.
  16. For that particular scenario, the wind is very important. You have a much lower airspeed than the small home-sick bowling balls the other guys were flying. I'm going to make two assumptions here: 1. you were all dropped quite a bit upwind from the DZ. 2. your glide angle is exactly the same as their glide angle, and airspeed is the only difference. Now, you all experienced exactly the same wind speed (the gods of weather hate us all equally), but with your lower airspeed (and thus lower downward speed) you stayed up in that wind much longer. If the bowling balls were down in a minute, and you took five minutes, and we assume 15kn winds up at altitude, the winds pushed you a whopping 1852 meters further downwind! Glide angle has nothing to do with it. Wind has everything to do with it. Generally, higher airspeed means you're less affected by wind, but also less able to use it to your advantage.
  17. Good on you for trying to find as much information as you can, but the internet can be a dangerous place in that regard. Much of the information randomly found is of rather poor quality, or from rather questionable sources. For some reasonably vetted material, check this thread in the Swooping & Canopy Control forum (don't let the Swooping discourage you, Canopy Control is vital for everyone with more than zero jumps in their logbook). A book I would especially recommend is The Parachute and its Pilot, by Brian Germain. As to your question regarding glide, that's not trivial to answer. Having the same exit weight will result in a higher wingloading for the 150 sqft canopy pilot, which will typically result in higher airspeed. However, that just means he's down faster, not necessarily further. Whether the glide is influenced is also dependent on the canopy designs and the actual wingloadings. Some canopies are of a design that doesn't really like high wingloading, and they really suffer in performance at very high wingloading. However, my gut feeling would be that due to reduced line drag on the 150 (smaller canopy = shorter lines), the 150 will have slightly better efficiency, and could glide a little bit further. However, these are second-order effects, and should NOT influence your canopy choice in whatever way. Pick a canopy that has handling characteristics (including forward speed, determined in large by your wingloading under the canopy), that you can handle when already deep in the shit (think low-pull, poor spot, crappy winds and landing in a tight field all at once). Also, your assumption of no winds is really limiting. There are almost always winds, and they always influence the options you have under canopy, both in terms of glide, and in terms of reachable area while flying upwind/downwind/crosswind/halfbraked/fullybraked/nobrake.
  18. Obligatory Friday Freakout CRW is a bit strange in that respect. It is prime Friday Freakout-territory (been there, done that, even with other experienced CRW-dogs), but when done right, the result is absolutely fantastic!
  19. There is no clear correlation between how elliptical a canopy is vs how it flies. For an interesting listen and view, check John LeBlanc's seminar on planforms: https://www.youtube.com/watch?v=f-mUyy1fhjE
  20. Ouch, that's like saying you don't need a parachute to jump because you've got a perfectly good helmet. The only excuse for flying CRW with such canopies is if both of them are already rock-solid CRWdogs with a proven history of flying millimeter-perfect next to eachother. But in that case they should know better than to think a trailing pilot chute is the only risk.
  21. That's going to cost a fortune to ship across the pond... =(
  22. Yup, but its easier to stall a canopy on rears, and that tends to reduce your glide ratio rather drastically. And for many canopies, half-brakes is not the most optimal for extending glide when flying with the wind. But figuring out the very best way to extend the glide for your specific canopy and wingload is something I don't really expect of a 20-jump student. It is also something that takes a few jumps on that canopy and in different weather conditions to dial in. So yeah, finding a good landing spot is more important than squeezing every bit of glide out of your wing. Only recently I saw someone make the main landing DZ, flying downwind at ~100ft, and pound the ground when still trying to land against the wind. Had that person picked a field upwind to land in when still at 2000ft, the ambulance could've stayed home...
  23. Although that works (as CRW-dog, I do it all the time if I need a bit more drive and forward speed relative to the formation), I would rather that a 20-jump student focusses on finding a good out-landing field, rather than try to make the main DZ no matter what. And the effect of toggles is indeed heavily dependent on the wind. If you are flying with the wind, flying half-brake will extend your glide relative to the ground by letting the wind carry you forward, while the exact same half-brake when flying against the wind will shorten your glide relative to the ground (and could easily push you backwards). If you use your brakes to let the wind push you back on final, be sure to let them up early enough. A parachute needs a bit of time to recover into full flight, and full flight gives you a good flare.
  24. A two-out can also realistically occur at normal pull time, if the reserve pin is almost out of the loop and the shock of the main opening takes care of the last little bit. I'll agree that will be a pincheck fail, but two-outs don't happen because everything went perfectly fine. Still, I agree that a two-out downplane burns through your altitude like crazy, so there's not much time to make decisions.
  25. Honestly, I fail to wrap my head around even the concept of a