Longer risers, longer openings??

[chuckakers 370]

I just put a new set of 21' risers on my rig, replacing an 18' set. I made two jumps on the new risers yesterday and had noticably slower openings on my Velocity. Coincidence?

Chuck Akers
D-10855
Houston, TX

[Bertt 0]

Did those risers change how far down the brake lines pull when the brakes are set?

You don't have to outrun the bear.

[chuckakers 370]

Hadn't thought about that . I guess if the brakeline rings are at a different position relative to the end of the riser, that could definitely affect the opening characteristics.

I'll measure that and post the results.

Chuck Akers
D-10855
Houston, TX

[davelepka 4]

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I guess if the brakeline rings are at a different position relative to the end of the riser, that could definitely affect the opening characteristics.

That's a fairly standard measurement. I'd bet they are going to be the same.

A more likely idea is that your old risers weren't 'square'. If they had worn and stretched at different rates, then you'd have a little funky-ness in the trim department. Your new risers may just be new and of the correct lengths (relative to each other).

Another thought is that the longer risers will allow the slider to spread a little more during deployment. If the distance between your 3-rings is less than the width of your slider, then the lines will be making a 'V' as they spread out to accomodate the slider. How they can spread depend on two things- the distance between the 3-rings, and how far up the 'V' the slider is. Longer risers will have the slider further up the 'V' where it can spread out a little more.

Keeping in mind that the Velo slider is huge, there's a fair chance that the distance between your 3-rings is less than the width of the slider.

I think the real quesiton is what were you doing with 18s on a Velo? The 21s will let you stretch the recovery arc out a little more, and go a little faster. A set of 24s would be even better, and provided you can still reach your slider after you open, I can vouch for 25s as being the way to go.

[riggerpaul 1]

The new Parachute Rigger Handbook (FAA-H-8083-17) has the following to say about the distance between the top of the riser and the ring:

"Check the distance from the end of the riser to the top of the ring. The industry
standard is 4", but there may be special dimensions for some applications."

This standardization would be specifically to ensure that deployment brake setting and steering line specs would not change from riser to riser.

[chuckakers 370]

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I think the real quesiton is what were you doing with 18s on a Velo? The 21s will let you stretch the recovery arc out a little more, and go a little faster. A set of 24s would be even better, and provided you can still reach your slider after you open, I can vouch for 25s as being the way to go.

I didn't mention the 18s were a three riser set-up. I could reach the slider on the 21s, but maybe not anything longer.

Thanks for the input on the openings.

Chuck Akers
D-10855
Houston, TX

[chuckakers 370]

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I guess if the brakeline rings are at a different position relative to the end of the riser, that could definitely affect the opening characteristics.

That's a fairly standard measurement. I'd bet they are going to be the same.

A more likely idea is that your old risers weren't 'square'. If they had worn and stretched at different rates, then you'd have a little funky-ness in the trim department. Your new risers may just be new and of the correct lengths (relative to each other).

I don't see how square or out of square would make much difference in deployment times.

Another thought is that the longer risers will allow the slider to spread a little more during deployment. If the distance between your 3-rings is less than the width of your slider, then the lines will be making a 'V' as they spread out to accomodate the slider. How they can spread depend on two things- the distance between the 3-rings, and how far up the 'V' the slider is. Longer risers will have the slider further up the 'V' where it can spread out a little more.

Keeping in mind that the Velo slider is huge, there's a fair chance that the distance between your 3-rings is less than the width of the slider.

The difference in opening time is primarily while it streamers. On these openings, the canopy just sniveled with the slider all the way up. I doubt the geometry change from longer risers would have much affect when everything is pretty much a straight line.

Chuck Akers
D-10855
Houston, TX

[davelepka 4]

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I don't see how square or out of square would make much difference in deployment times

The idea is the same as the idea that different guide ring placement would effect the deployment.

The guide ring would alter the brake setting - a higher guide ring would produce a slower opening. A lower guide ring, creating a deeper brake setting, would cause a faster opening.

You can replicate this phenomenon using the rear risers. Pull them both down a touch during the snivel, and the canopy will pop open. It's like using a deeper brake setting.

Lets say your 18" front risers had stretched 1/4 more than the rears. This would pitch the nose up, and cause a faster opening (pull down in the back or stretch out the front - same difference).

Add in a little asymetrical left/right wear on the old risers, and you get 'wonky' openings. Not horrible, but not like when everything is factory fresh.

New risers - new openings. Next year get a reline - it will reset your openings back to zero as well.

[chuckakers 370]

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I don't see how square or out of square would make much difference in deployment times

The idea is the same as the idea that different guide ring placement would effect the deployment.

The guide ring would alter the brake setting - a higher guide ring would produce a slower opening. A lower guide ring, creating a deeper brake setting, would cause a faster opening.

You can replicate this phenomenon using the rear risers. Pull them both down a touch during the snivel, and the canopy will pop open. It's like using a deeper brake setting.

I agree with your deeper brake setting statement, but I don't know that I would call it a phenomenon.

Lets say your 18" front risers had stretched 1/4 more than the rears. This would pitch the nose up, and cause a faster opening (pull down in the back or stretch out the front - same difference).

Not sure what would cause risers to stretch at different rates front vs rear.

Chuck Akers
D-10855
Houston, TX

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[davelepka 4]

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Not sure what would cause risers to stretch at different rates front vs rear

I'm pretty sure the front riser take more of the load on an opening. Ever notice that the front reserve risers are twice as thick as the rear reserve risers?

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I agree with your deeper brake setting statement, but I don't know that I would call it a phenomenon.

I'll stand behind my 'artistic license' in terms of word choice.

[councilman24 36]

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I'm pretty sure the front riser take more of the load on an opening. Ever notice that the front reserve risers are twice as thick as the rear reserve risers?

This is really just a function of the harness design. The front risers are a continuation of the main lift web. The rear risers are sewn into the junction at the three rings harness ring. Don't need the heavier webbing so not used.

Not all rigs are like this.

I'm old for my age.
Terry Urban
D-8631
FAA DPRE

[davelepka 4]

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This is really just a function of the harness design. The front risers are a continuation of the main lift web. The rear risers are sewn into the junction at the three rings harness ring. Don't need the heavier webbing so not used.

Not all rigs are like this.

While that may be true, I have to think that the front risers will take more load on opening.

I have used my rear risers during many openings, and they are generally easy to pull, with moderate pressure. I've never tried to pull a front riser during opening, but I would have to think that it would be tough, with very high pressure (aka load).

The amount of load my be well within the limits of the thinner reserve riser material, explaining the rigs with the thinner front reserve risers, but in a front-to-back comparison, I'm voting for the fronts as doing more of the 'heavy lifting'.

[pchapman 261]

In flight, due to airfoil aerodynamics, the fronts will tend to take more of the load.

But I'm not sure that riser loads on opening are higher on the fronts.

This is despite knowing that (at least towards the end of the inflation?) one can pull down on rear risers.

Some of the Parks College Parachute Research Group data show higher rear riser loading on opening. But that was just one paper with graphs for a Sabre 210 or similar and I haven't checked the rest of their data & conclusions.

Also, early in the inflation, the canopy is aerodynamically more like a flat plate, or maybe a cupped plate. The nose is gradually pulled down due to the trim angle the canopy was built with, and the outer tail is pulled down more sharply by brakes. I'm not sure all that biases strongly in favour of either front or rear loads.

Overall, I can't say for sure whether fronts or rears take more load on opening, but it isn't as clear cut as it is for flight under canopy.

[billvon 2,402]

>a higher guide ring would produce a slower opening.

I agree that moving the guide ring will change the opening, but it's hard to predict what will happen. On my Fox, shortening the brake lines definitely speeds up the openings. On my Safire1 129, lengthening the brake lines speeds up the openings as well, and using the shorter (original) stow points provides the softest openings.