What size HMA do you fly?

[Cacophony 0]

I just got my Velo 96 back from the factory and I had 500 HMA put on. I probalby won't get to jump it for a while, but out of curiosity: What do you all jump for competition? I have about 1000 jumps on Velocities, but none with HMA. Next step is an RDS but that will be a bit since I make my living with my Velocity.

[CanuckInUSA 0]

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Next step is an RDS but that will be a bit since I make my living with my Velocity.

Save the full RDS for competition and practice. But get yourself a removable slider. You won't look back. I can take my slider off faster than I could stow it and it's so nice not to have it hanging around your head. Plus it only takes an extra one minute (maybe two) to put it back on.

Try not to worry about the things you have no control over

[marks 0]

the 500 HMA is the thicker HMA.

[SkymonkeyONE 3]

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Next step is an RDS but that will be a bit since I make my living with my Velocity.

Save the full RDS for competition and practice. But get yourself a removable slider. You won't look back. I can take my slider off faster than I could stow it and it's so nice not to have it hanging around your head. Plus it only takes an extra one minute (maybe two) to put it back on.

I second everything written in that post.

Chuck

[kamalasound 0]

I have both kinds of HMA. PD's and Mel's but the latter IMHO is much better; Mel's is thinner, almos hals the size.

[SkymonkeyONE 3]

The stuff most competitors get from MEL is 340

[kamalasound 0]

HMA 340 VS 500.......it makes a difference!!

[ntacfreefly 0]

300

Blues,
Ian

To the mind that is still, the whole universe surrenders. ~ Lao-Tzu

It's all good, they're my brothers ~ Mariann Kramer

[Cacophony 0]

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Next step is an RDS but that will be a bit since I make my living with my Velocity.

Save the full RDS for competition and practice. But get yourself a removable slider. You won't look back. I can take my slider off faster than I could stow it and it's so nice not to have it hanging around your head. Plus it only takes an extra one minute (maybe two) to put it back on.

I'll definately look into it. I agree, even when its stowed its annoying! The only problem still is that I don't always pack for myself because I don't have time and i know I would just be asking for trouble having someone else do it. Thanks for the response. 350 range answers the question.

[dharma1976 0]

and it make sa cool whistling sound as you come screaming through...

http://www.skyjunky.com

CSpenceFLY - I can't believe the number of people willing to bet their life on someone else doing the right thing.

[morris 0]

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...

[masterrigger1 2]

Morris,
Simple math puts it at 38% less drag.
DxWxL

MEL

Skyworks Parachute Service, LLC
www.Skyworksparachuteservice.com

[tetra316 0]

So what size hma are people flying on katana 120s?

[superstu 0]

i believe 500# is what PD is putting on them.

Slip Stream Air Sports
Do not go softly, do not go quietly, never back down

[tetra316 0]

Just got my new lineset in the mail and it's 675, according to their website. I was expecting 500, should have asked before ordering
Although I can't imagine it would make much difference at my level. Mel's post about the 38% difference between 340 and 500 seems like a big difference though.

[RMURRAY 1]

2 linesets of 350 HMA came with my JVX. the blue HMA from skyworks for my VX seemed smaller although I think it's rated strength is the same. I had skyworks use dacron for the LCLs - I really liked that option....

rm

[Widgeon 0]

500HMA is installed now on Katanas up to a 107. 675 comes on the 120, 135, 150, and the 170.

[Cacophony 0]

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Morris,
Simple math puts it at 38% less drag.
DxWxL

MEL

So then what is the simple math to figure out the difference from other line types and sizes? For example what is the difference in drag from 750 Vectran to 500 HMA?

[morris 0]

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

[icevideot 0]

I think morris pulled a muscle in my head.

Flying a lot of tandem video, I expect my UV exposure to be greater than most jumpers so I ordered the heavy stuff for my Stiletto 89. I hope that doesn't make a huge difference but having jumped a small Viper with Dacron lines, I think it will be fine. I just have to get used to covering my lines in the landing area.

"... this ain't a Nerf world."

[davelepka 4]

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the overall advantage in linedrag is less once more... in the range of ~10%

10%? I'll take it. You wouldn't want a 10% reduction in line drag on your canopy?

If Cessna could make a Citation 10% faster or more fuel efficient with only a nominal increase in production cost, they'd be all over that shit.

[flow 1]

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the overall advantage in linedrag is less once more... in the range of ~10%

10%? I'll take it. You wouldn't want a 10% reduction in line drag on your canopy?

If Cessna could make a Citation 10% faster or more fuel efficient with only a nominal increase in production cost, they'd be all over that shit.

But how large portion of the overall drag is caused by lines?

[Spizzzarko 0]

I have heard it said that next to jump suit choice and body position that line type is the next biggest drag cause or reduction.

[davelepka 4]

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But how large portion of the overall drag is caused by lines?

Who really cares? We know the lines create drag, and reducing it by 10% is a good thing.

There's no real down side to reducing line drag. It's not a trade off. You could say that you need more frequent relines due to smaller lines that may wear faster, but most higher level swoopers are relining their canopies well before the lines are breaking, and would see the marginal cost increase as worth the extra speed under canopy.

If all it cost was money to reduce drag even further, I'd be spending waaay too much money on canopy mods.

[flow 1]

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Who really cares? We know the lines create drag, and reducing it by 10% is a good thing.

Sure it's a good thing. I just have never heard any estimations how large part of the overall drag is coming from the lines.

But, Spizzarko already gave an answer, thanks.