Re: [robibird] Vectran Lines
Robibird,
I'm not saying that the Trango 3 is a bad canopy or that it will not work. Vectran will perform just perfectly if it's dimensioned correctly for slider up jumps. It’s an amazing fiber with outstanding properties.
What I am saying is only that for a lightweight 7 cells basejumping canopy, in my opinion, it doesn't bring anything that makes it better than spectra. But it will work fine for sure.
We can have different point of views, but this forum is an information exchange platform, so a bashing answer is just not relevant.
If you want to make your point, please take the time to explain this material choice and which characteristics of the Vectran lines you think are good enough for justifying this choice.
From what I know there is potentially two positive factors, the dimensional stability, and somehow the drag than can be very slightly reduced because Vectran lines can be made thinner for a given strength.
Now my opinion (and this is very personal and can indeed be different for every people) is that these factors are not really important for low performance parachutes - because the real effect will be marginal - if noticeable at all. But some people will for sure prefer it over other materials.
The rest of my post is just facts, not assumptions - and if they are wrong, please correct them. Saying that it’s incorrect whithout further details is just pointless.
Dimensional stability :
7 cells canopies tolerates well the dimensional changes that spectra has tendancy to get - it's proven by the precedent Trangos and - as you said - by the fact that most of the light base canopies are using spectra now. All these canopies are ageing very well and the small deformation in the lineset are not a big problem in the vast majority of the cases.
Now as a rule of thumb the consequences of a given trim change will get more severe as the performance of the canopy increase. Meaning that the same dimensional change that can be not noticeable on a low A/R canopy with poor L/D could greatly impact the behaviour of a high performing one.
To compare extreme cases, 2cm of deformation on some lines of a base canopy are generally no big deal and most of the people won’t even notice it in flight. If you have the same thing happening on a XC paraglider it will be flying like shit - if flying at all - and have very likely a dangerous behaviour.
Price & weight:
The price will depend on the manufacturer and his pricing scheme but if I take the small qty pricelist of Cousin Trestec lines for the parachute industry i get :
Vectraline 1500 - 1.15eu/m - 6g/m
Spectra 1500 - 0.74eu/m - 3.85g/m
Please note that the real breaking strength is about 25% higher for vectran lines than for the spectra lines - eventhough they are both named “1500” (just because Vectran is loosing slightly more strength than Spectra while being used)
So yes the 2x factor is too high in this case - it’s only 1.55x more expensive. About the same for the weight comparison. Well it’s still more expensive and more heavy - which was my point.
Strength :
Vectran looses strength all along it’s lifespan, more than spectra. One of the reasons is that the friction coefficient of spectra is lower, hence the effect of small abrasive particles getting inside of the braid has a smaller impact on spectra fibers.
However there’s been a lot of recent developement and this particular problem can be partially solved with different coatings or by using a blend of different fibers incorporated in the braid. Besides, Vectran is still one of the toughest polymer around - and good quality lines will easily last for the whole canopy life if chosen strong enough.
Lines failure chain reaction : you will have that effect with all low elasticity material, compared to more elastic lines. It's not specific to vectran and spectra will do the same (compared to for example nylon lines). It’s only more likely to happen with materials getting weaker over time - hence the need to size properly the lineset. Again, everything will work just fine if used properly.
The whole point is to know if the choice is coherent, and why. And the answer can be different for everyone. While i'm pretty confident in any spectra or polyester lines, i'm more conservative with vectran. The first ones tend to all have decent qualities because the technology is older. But i've seen and used very different qualities of vectran lines, hence my negative opinion about it.
To continue the thread for people who have an actual interest in the discussion here's some interesting general overviews of the different lines & their properties :
from
http://en.wikipedia.org/wiki/Sailcloth http://parachutistonline.com/...k_a_rigger/line-wear http://www.ojovolador.com/...orts/lines/index.htm
