The111 0 #26 March 29, 2004 Ok, you're right that forward speed is key. In my specific case, the forward speed of my reserve is less than the forward speed of the main, but not because it's larger (it's slightly smaller in fact, main=170, res=160). I'm guessing the forward speed of the reserve is less because it has a steeper glide angle than my Spectre. That is why I mentioned glide angle, but you are correct in that forward speed ultimately matters. But I think if the canopies are close to the same size then glide angle can be used to characterize penetration, since it will determine forward speed. Glide angle and forward speed are very closely related... for the sake of the following illustration assume a round canopy has no forward speed (I am not sure this is true, but I think it's close). Q: Why does a round canopy have no forward speed? A: Because its glide path is a vertical line! www.WingsuitPhotos.com Quote Share this post Link to post Share on other sites
VNugget 0 #27 March 29, 2004 QuoteQuoteWouldn't you stand a higher chance of making it back with a higher deployment? Generally speaking, winds aloft can be substantially higher than ground winds. Even if you exit with a perfect spot, if you chop high, you could be pushed back substantially. I once chopped at 10K and landed 2 miles off. Gah, thanks.. I didn't think of the case of the wind being so strong that it pushes you from a "long spot" back over the field, and then off in the "short" direction. It's just that billvon phrased it in a manner that posited "long spot" as the distinguishing factor in the situation, everything else being normal. Quote Share this post Link to post Share on other sites
billvon 2,421 #28 March 29, 2004 >Glide angle and forward speed are very closely related... Not really. The space shuttle glides like a brick; it has a glide ratio of about 6 to 1, but does about 220mph during short final. The Schweitzer 1-35 sailplane has a glide ratio of 36 to 1 but can't exceed about 160mph. But both of those are airplanes anyway. Parachutes are different; they have only one "trim speed" that cannot be adjusted the way an aircraft's can. (Front risers and brakes let you do this a bit, but it gives you a very limited range.) The two biggest factors that influence canopy speed are loading and trim angle. A canopy with a steep trim, like a Katana, will generally outspeed a canopy with a shallower trim like a Pilot even if they are loaded the same. Note that trim does not neccessarily equate to glide angle, although they are related. >I'm guessing the forward speed of the reserve is less because it >has a steeper glide angle than my Spectre. Generally a steeper glide angle means a faster canopy. The horizontal component (i.e. your forward speed) doesn't change that much even if you change the glide angle. Most canopies have a glide angle of about 15 degrees (which equates to an L/D of about 4.) Change that to 20 degrees, which would be a huge change, and an airspeed of 20 knots would go from a forward speed of 19.2 knots to 18.8 knots - about a .4 knot difference. The kicker is that if you do steepen the glide by 5 degrees you're going to get a much higher airspeed, such that you won't even notice the loss of the .4 knots caused by losing some horizontal component. Quote Share this post Link to post Share on other sites
The111 0 #29 March 29, 2004 So why do you think my PDR 160 was moving backwards at 1000 feet and coming straight down at ground level, in the same winds that my Spectre 170 was getting moderate penetration at both given altitudes? It's not larger. I would imagine and hope it doesn't have a steeper trim. ???www.WingsuitPhotos.com Quote Share this post Link to post Share on other sites
mr2mk1g 10 #30 March 29, 2004 According to Paragear its 4 sq foot bigger. Quote Share this post Link to post Share on other sites
The111 0 #31 March 29, 2004 Yeh yeh yeh, I was actually aware of that but didn't mention it because: 1) It's a very small difference 2) The difference in penetration was significant As far as I'm concerned the canopies are approximately the same size. But the main penetrates much better...www.WingsuitPhotos.com Quote Share this post Link to post Share on other sites
billvon 2,421 #32 March 29, 2004 Two reasons I would guess: 1) The winds changed a bit between jumps 2) Your Spectre has a higher trim speed than your reserve. Quote Share this post Link to post Share on other sites
ps5601 0 #33 March 30, 2004 The reason is that the reserve is made very differently to the main. Your reserve is much more of a square canopy, but more importantly the gap between the top and bottom skin on the reserve is much larger than on the main (ie your reserve is "deeper" than the main). This results in a much greater level of drag on the reserve, hence you fly slower. On top of that most reserves are F1-11 rather than ZP, I suspect that this also increases the drag on the reserve (though I an not 100% sure about this). Blue ones (they are today as I have to be at work) Paul Quote Share this post Link to post Share on other sites
Squeak 17 #34 March 30, 2004 QuoteQuoteI personally would not recommend that to anyone unless the person has practiced rear riser landings and feels comfortable with them. Personally I don't think anyone should be jumping a sport main that they cannot land on rear risers. Define "sport main", I jump a Hornet 150 that I have never tried to land on rears, and at my DZ I know of NO one who does land on rears.You are not now, nor will you ever be, good enough to not die in this sport (Sparky) My Life ROCKS! How's yours doing? Quote Share this post Link to post Share on other sites
Zeemax 0 #35 March 30, 2004 QuoteOne thing you should keep in mind. Reserve canopies are packed to open quick. The higher you are the quicker they will open. How does that work? why would it open noticably quicker at a higher altitude?Phoenix Fly - High performance wingsuits for skydiving and BASE Performance Designs - Simply brilliant canopies Quote Share this post Link to post Share on other sites
billvon 2,421 #36 March 30, 2004 >This results in a much greater level of drag on the reserve, hence you fly slower. The shuttle has far more drag than a sailplane; still, the shuttle glides much faster than a sailplane. A steeply trimmed draggy canopy will go faster than an efficient canopy trimmed flat. You can see this effect directly on a paraglider with a speed bar; the speed bar effectively changes the trim angle of the canopy and makes it go much faster (with some loss in glide performance.) Canopies are pretty complex flying things. Many simple rules that people come up with (like a 2:1 loaded canopy always turns at about X speed, lengthening the brake lines slows down openings, a bigger slider gives you softer openings) don't work, or don't work outside certain boundaries. There is much that is not intuitive about canopy aerodynamics, and the "drag always slows you down" idea is one such idea that seems intuitive but can lead you to the wrong conclusions. Quote Share this post Link to post Share on other sites
billvon 2,421 #37 March 30, 2004 > why would it open noticably quicker at a higher altitude? Reefing systems tend to force a canopy to open in a given amount of time (say, 2 seconds) at a given speed (say, terminal.) The problem is that if you are falling at terminal at 12,000 feet you are going 20% faster than terminal at 2000 feet. The same amount of time gives a harder opening to begin with at the higher speed, and many reefing systems don't work as well when the canopy is going faster to begin with. Quote Share this post Link to post Share on other sites
diablopilot 2 #38 March 30, 2004 QuoteDefine "sport main", I jump a Hornet 150 that I have never tried to land on rears, and at my DZ I know of NO one who does land on rears. Sport Main = The main you use for sport skydiving. Not a tandem Main. I did not say you have to land on rear risers every time, nor be good at it. You should think about your choice (it is an agressive main) if you a) are not willing to do it in an emergency, b) haven't tried it, and c) were not capable of doing it on your last main prior to downsizing/changing planform. Too many people are putting them selves under canopies they do not have complete control over. Scenario: you spiral down to 1000 ft agl, and flare to stop the turn. A brake line snaps. What are you going to do?---------------------------------------------- You're not as good as you think you are. Seriously. Quote Share this post Link to post Share on other sites
christelsabine 1 #39 March 30, 2004 FJC: what exactly does it mean? i'm German, you know. PLF: i learned the hard way. it's always in my mind within last seconds before touching the ground. PLF and EP are burned in my brain (BTW: i already hit something else than plain fields: a tree). my impression: somewhere is a lack. students already in the beginning should be trained to work on risers. it cannot be OK just to read about that, only by listening, watching videos, being capable to use risers. Holy Moses, probably i should stop reading all what is written on these pages. makes me completely confused and insecure. dudeist skydiver # 3105 Quote Share this post Link to post Share on other sites
cruzit 0 #40 March 30, 2004 QuoteFJC: what exactly does it mean? i'm German, you know. Acronym for the First Jump Course. Quote Share this post Link to post Share on other sites
