morris

I would recommend to place your set up further away (than you would expect)...

Are you using a liner for your pond or is this one without?

hope you like this one...

I´d really like to see a different, additional type of distance runs where you`r not allowed to pop up. We could call the existing format "distance unlimited" and the other one whatever...

Thanks for the information, it matches with "PD-Opinion", they put 300s only on by themselves/at the factory due to the difficulty of bartacking those lines... I just received 500s from them (not round, "ellipse-style") very nice, about half the seize of vectran 500s....

Sorry guys, I might have been wrong with my statement "the perfect line is for sure a round one", cause if you take two HMA 500 lines (for example) one round and one shaped like an ellipse (for example), the ellipse one is going to be thinner (at least from the "airflow point of view"). That means, that even if its drag coefficient might be higher (and it`s only higher if the line vibrates, otherwise drag coefficient is even lower) the resulting overall drag is less...

Is there anyone outthere who has experience with HMA 280lb?

puh, difficult question... I´d say that if you`r able to go for more than 500ft on the good ones, it´s gonna be more than 400ft on most landings (with the same conditions),something like 80%, but once again, difficult question...

spizzzarko, teardropshaped lines have been tested on paragliders in Europe (they used kind of a tape to make em shaped like that) and it didn`t work! It`s not like a falling raindrop where you just have gravity, the relative wind and nothing else. the wind isn´t coming always from the same direction (turn, dive, whatever) and any "second row line" is in the turbulences of the line(s) in front. Therefore the line(s) start moving, and once it has started, it`s not gonna stop again,... once again - round is better - not in general but for lines on a chute...

Dear Mel, as a matter of fact it`s NOT simple math! First thing is that if you go from vectran to HMA this really makes sens cause every line that isn`t round (even if it would be shaped like raindrop! that´s been tested on paragliders in Europe) has a tendency to move its wide side into the wind. On a chute the lines aren`t able to do so, but nevertheless they are "trying" and hereby they create vibrations, drag and noise. So the perfect line is for sure a round one. (There`s a dissertation out there about the physics of paragliders, coming to the same result.) Now to HMA: If you go for thinner and thinner lines, this becomes more and more ineffective! (Why this is, see "point 3") This does not mean, that it doesn`t make sense, it`s just way less advantage than you would imagine. First thing is that if you go from let´s say 500 all the way down to 300 (the extremes?!) this is NOT reducing the diameter by 40%, it´s way less (about half that much ~20%, simple circle surfacearea calculation). Second thing is that even though the surfacearea of the line exposed to the airflow is reduced, the turbulences created by the line are still the same (actually they are even more, see "point 3") so they advantage isn`t 20% it`s less once more, let´s say ~15%. Now to the real "bad thing": If you reduce the diameter you`ll need something called "Reynolds number" for the calculation. This number is used to be able to compare the drag of objects of the same shape but different seizes (to the experts: I´m just trying to keep it simple). The result will tell you that even though "Reynolds number" is going down if you reduce the diameter, the drag coefficient goes up, while you go thinner and thinner. That`s the reason why it becomes more and more ineffective to go thinner and thinner.... and therefore the overall advantage in linedrag is less once more... in the range of ~10%. If you now keep in mind that the parasite drag created by the pilot (in a "normal" body position) is about ten times as high as the one created by the lines (on a seven cell), the advantage in parasite drag is down to ~1%! (and you`ll realise how important the bodyposition is) and if you finally look at the overall drag of the system (profile drag, induced drag and parasite drag) you`r down to an advantage of about 0,??%!!! Talking to Jonathan Tagle at the 1st WorldParachutingChampionships in Vienna about this topic (that was before I did the calculations), he kind of felt this facts, saying "give me vectran, I don`t care!" I wouldn`t go this far (and I think he wouldn`t as well), - to go from vectran to HMA really makes sense due to the shape AND the reduction in diameter. The advantage of ultrathin HMA is very little. If you`ll be the first to break the 700ft-barrier - you might get an extra 2ft.... but we`re seekers for perfection - MEL, I´ve written you an email yesterday, didn´t receive an answer yet - I need thinner lines!!! And I need `em soon, please get back to me asap :-) Cheers and speed to everyone, Morris

The difference in drag in between (for example) HMA 340 and HMA 500 is very little, way less than most (me included) would expect, more on this if your interested...

Till yesterday I would have answered you that the 1 has an even longer (too long) way for opening and that it (the 1) dives longer. I thought that they made the 2 because the openings of the 1 were a little too long and that they though the 1 would have been a little too aggressive for the average crossfire pilot. But yesterday a friend of mine who isn`t that experienced (at least from my point of view) jumped a 1 the same seize as his 2 and the 1 was definitly slower and didn´t dive as much. I expected it to be opposite (maybe something is wrong with the canopy or I`m wrong) but I`m not a crossfire expert. Nevertheless I´m gonna contact a guy from the german association who`s the one to clear every chute for the german market, he will know, I`ll let you know...

winglets definitly reduce wingtip vorticies and don`t use them to produce a positive effect, they just make a bad effect a little better...

Maybe the stabilizers don`t need to be pushed outwards cause watch this http://www.b737.org.uk/737winglets.jpg maybe they create this effect just by being there?

So far so good, but how about Z-brace? The centercells in between linegroups on our chutes now are "supported" by X-braces from BOTH sides. This is not the case with the additional cells of a Z-brace (the ones right next to the center), right? On those you got "bracesupport" just from one side...

Here comes the picture once more in higher resolution...

To start with I`d like you to have a look at the attached picture. It shows a Velocity96, loaded at 2.4, after a 450degree turn from 1100ft, just before the entrygate. Viewing the canopy from behind and below (almost invisible from the front), you can see that the bottomskin of the centercells in between linegroups are "out of shape", meaning "too high" (of course mostly in the middle of the canopy). The X-braces hold the topskin in place, but can`t do that to the bottomskin. So on a "traditionalbraced" canopy 3/3 of the topskin and 2/3 of the bottomskin are "where they belong". Does anybody agree so far? Now lets have a look at a Z-brace: The next, additional X-brace(s) - the "Z-brace(s)" - are fastened at a place that is already "too high" this will result in the centercell topskin being "too high" as well (don´t even wanna think about the bottomskin of the centercell!). This problem can´t be solved by just making the brace shorter cause the cell has a given width as well. So on a Z-brace just 2/5 of the topskin is in place, same goes for bottomskin, centercell(s) being even "second floor". This will create kind of a curve of the profil in between line groups, not the way the perfect profil should look like... (and if you look at the picture of the PD prototype on their Z-brace informationsheet from the PIA two years ago, it really looks a bit like that, even though it doesn´t look like being in full flight/full speed) Now please tell me that I´m totally wrong (and how things are for real), cause otherwise a Z-brace would just be more expensive, more packing volume, but most likely not more performance. Thanks, Morris

rhys,I haven`t been talking to Jim but Jyro...

And this one goes to "polarbaer", you`r right with what you`r saying about the difference between stabilizers and "modern winglets", but just kind of... The way a modern winglet reduces induced drag with "vectored forward lift" is of course way more advanced. But that doesn´t mean they aren´t both doing the same, they do, a winglet is just more effective, but both (stabilizers and winglets) reduce the induced drag by reducing wingtip vorticies...

One more for Superstu, the induced drag is a function of the inverse(!) of the square of the airspeed - it is smallest at high speeds and increases as you slow down. This explains why stabilizers make more and more sense as you slow down, at the bottom end of the swoop, where you "feel" (good perception!) that the velo has more bottom end lift.

Hi "superstu", You`r saying "I feel I have more bottom end lift in my velo then I did in my JVX." This matches with what Jyro(!) told me at the WorldParachutingChampionships in Germany. He said that HAVING stabilizers would help/be useful at the bottom end of the swoop! Morris

Thanks a lot for your link "Lou", Para-Flite says its "reducing wingtip vortices", just what I thought, just was winglets do...

Sorry Alex, I think you`r not right. Most (but not all!)winglets point upwards, that`s correct. But the reason for that is just that they want the wingtips to have as much clearance from the ground as possible... the principle is working both ways! Morris

Hi again, it has been said that the fact that the JVX has no stabilizers would reduce drag. Even though that seems to make sense, I dare to doubt it, I even think the opposite might be possible (but I don`t know for sure). Reason: Winglets help to reduce the induced drag! A stabilizers might be kind of a winglet. Any thoughts on that? Morris

Hi outthere, I´m wondering if the "665ft-information" is really correct, cause if you check out the results of that competition at the website of the DZ where it took place www.skydive-leipzig.de it´s telling you just about a missed entrygate (or at least zero points) in distance round 1 and of 129,81meters (=425ft) in distance round 2... any information on it? Morris