Canopy Buffeting

[pBASEtobe 0]

Anybody have any experience with flying skydiving canopies with no slider and using the line-mod?

I d-bagged a Sabre 170 from a paraglider yesterday and had an interesting ride to say the least. I loaded it slightly less than 1.1:1 and delployment was done at around 900' AGL / 2600' MSL. I had a bit of a strange opening. I got center cell inflation first then the outer cells and then the 3 center cells deflated, surged a bit and then inflated properly. This didn’t surprise me much because it’s a 9-cell and not meant for such slow airspeed deployments. What surprised me is that I flew it straight and had some major buffeting of the entire wing. I had an end cell have a little frontal collapse which re-inflated instantly but sent a wave/collapse from the nose to the tail. It also got worse when I started to pull front risers. I would just chock this all up to very turbulent conditions but the fact is it wasn’t turbulent. I d-bagged off a tandem paraglider and there were other PG’s in the air around as well. The paraglider I left from (now a tandem lightly loaded with only one person on it) landed without incident. No collapses and no trouble getting down. Also, some of the other paragliders in the air were having trouble staying up which means there weren’t many thermals and/or they weren’t very strong. I talked to some of the PG pilots afterwards and they said it wasn’t very punchy.
I’m wondering if the problem was the fact that I was flying the canopy with no slider and the line-mod or maybe there are some trim problems with the canopy. I also checked for tension knots when I got down and didn’t see any.

Anyone have any other ideas?

I can attach some video of the flight later tonight so it’ll show the buffeting.

edited for spelling

[TomAiello 26]

Were you using the standard deployment brakes (i.e. the skydiving setting)?

I'd guess that some of the issues could have started with the very shallow (since there was no slider to bring them to the point they'd be on a skydive) deployment brakes.

-- Tom Aiello

Tom@SnakeRiverBASE.com
SnakeRiverBASE.com

[pBASEtobe 0]

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Were you using the standard deployment brakes (i.e. the skydiving setting)?

Yes, I was using the skydiving brake settings. That could account for the funky opening but what about the rest of the flight?

I'm going to try it again but jump slider down (not off) with the brakes routed through the grommets and keeper rings and see how it goes.

[TomAiello 26]

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I'm going to try it again but jump slider down (not off) with the brakes routed through the grommets and keeper rings and see how it goes.

Bringing the slider down should leave you with the same (effective) brake setting as removing the slider. What advantage do you see from keeping the slider on there?

Are you using a tailgate? And some kind of line release toggles, I hope?

-- Tom Aiello

Tom@SnakeRiverBASE.com
SnakeRiverBASE.com

[pBASEtobe 0]

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What advantage do you see from keeping the slider on there?

Nothing for the opening but wouldn't it make a difference with the line length for flight?

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Are you using a tailgate? And some kind of line release toggles, I hope?

Masking tape but that's it. I do these jumps with a PG round throw out reserve so I do have a back-up. Not that I really trust it that much though. And I've been cutting away at around 750' AGL if not higher so I do have a bit of time.

Edit to add: I do have that cool hook knife Kate Cooper gave me. I think I'll bring that along next time.

[nicknitro71 0]

Russel,

How many jumps on the current line set?

Memento Audere Semper

903

[pBASEtobe 0]

If I remember correctly there are 300-400 jumps on the canopy and around 100 on the line set.

[JaapSuter 0]

Actually, it's over 900 on the canopy and close to 400 on the lineset. Last time that canopy was jumped, over five months ago by me, it was flying really well. Since then, it's been in a little box, packaged up and stored in a dry place. I can't explain the fluttering, but I do recall talking to my rigger about a new lineset.

I won't need it anymore though; these days canopies that small scare me. Anybody want to buy a Sabre 170? Flutters great!

I'll be back... soon.

[RayLosli 11]

Anyone have any other ideas?
-

Maybe the cross-ports are much to small for positive inflation you are seeking.@ those low air speeds ?
.

[CanuckInUSA 0]

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these days canopies that small scare me. Anybody want to buy a Sabre 170?

They don't scare me when they're flown the way they're supposed to be flown (I'm jumping a Velo 103 and loading it up with weight and it's tons of fun). Of course I also jump a FLiK 293 and a Rock Draggon 303. Use the right tools for the right job and the job will get done. But hey your Sabre 170 could be used as a ground launching canopy depending on your size and where you plan to launch from.

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

[cornishe 0]

ill through out another idea here because

a) you werent pulling on any lines
b) this happened way after inflation and during flight

...This canopy is attached at about your hips, not the shoulders. You are also sitting in a trike. In the video the bullshit starts happening after you intiate some turns. I think you may have unloaded that side for a moment while rocking around. Does this make sense to anybody with an understanding of the systems involved?


.

Abbie Mashaal
Skydive Idaho
Snake River Skydiving
TandemBASE

[CanuckInUSA 0]

Is there video somewhere? I bet you Dwayne H and Jim S out in CA would help with their experience flying harnesses attached at the hips.

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

[pBASEtobe 0]

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Is there video somewhere?

Here it is.

[pBASEtobe 0]

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the bullshit starts happening after you intiate some turns.

Part of it does look like that but why then was I still getting somuch commotion going on during straight flight? Also I did this exact jump with a PD 190 and had absolutely no problems what-so-ever.

What are people's thought about me actually unloading the canopy during flight. I'm not so sure that's happenening, not enough to get slack in the lines. With that kind of decent rate and weight under the canopy leaning in the harness shouldn't slack or unload the lines enough to cause that. You think? Why when I fly my paraglider with the same harness, worse conditions, and a wing that is more suseptable to collapses I have no problems.

This is very puzzling to me. I'm really looking forward to jumping this Sabre again to see if I get the same results.

[CanuckInUSA 0]

Were you on your fronts when this buffeting occurred? Often people may be applying too much front riser pressure which causes the wing to buckle. But I have to admit that the last slow-mo portion of your video is puzzling if you're just in full flight or have light toggle inputs applied. But I am no expert in this area.

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

[nicknitro71 0]

By the way Russel,

We gotta find a way to throw you off airplanes with that trike

Maybe adding couple of wings so you can do trike-WS jumps and trike BASE WS too, now that would be fucking cool

Do you know where the center of mass is located with you on it wearing your rig?

Memento Audere Semper

903

[pBASEtobe 0]

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Were you on your fronts when this buffeting occurred?

The first bit of buffeting I think I was on my front risers but very slightly. I started to slowly pull them down when it started, then I said to my self, forget that idea, and I let up on them. I think I only pulled a couple inches of fronts.

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the last slow-mo portion of your video is puzzling if you're just in full flight or have light toggle inputs applied.

It looks like I had just started a slight turn to the left when that happened. I actually felt quite comfortable in turns under the canopy. It felt stable then but straight flight felt the worst.

[hookitt 1]

It sure appears that you hit the edge of a thermal or dust devil, sans dust. I'd bet on it.

Lengthen the brake lines a couple inches so the tail isn't deflected during front riser.

How much shorter are the outside lines compared to the inside lines?

As for the opening. It sounds like a fairly normal opening for that type of canopy. Take a good frame by frame look at a regular slider down deployment on a BASE canopy. It inflates nose first, then as it finishes slamming open, the center of it is compressed. It's very noticeable on the top skin but it happens very quick.

When I did an ultra low speed deployment on my slydiving canopy, the center cells closed back up briefly. It sounds exactly like the deployment you described.

My grammar sometimes resembles that of magnetic refrigerator poetry... Ghetto

[pBASEtobe 0]

There are many things that influence this flight. I think the only way to really tell if it was the canopy or conditions is to just jump it again. I think I'll be jumping it in 2 weeks. I'll post how it goes.

[base311 0]

Looks like a trim problem to me. I've experienced this (more than I'd like to admit) behavior in kites that are not properly trimmed and/or the airfoil/overall design was flawed. It can be due to a number of environmental issues, but in the absence of severe turbulence I think mainly: trim and airfoil type (which you won't be able to change at this point).

Since your canopy attachment points are at your hips, I would assume the tow point (for lack of better nomenclature) spacing now relative to a normal skydiving arrangement has changed to become significantly wider... add to that the removal of the slider (which would bring the line groups back together - thus maintaining the design's dihedral) and you're probably pretty severly out of trim.

As to which direction to tell you to go? you're on your own. I will say this, though... you're a test pilot: proceed with extreme caution and maybe consider doing some of this stuff with a little more altitude and a lot more reserve fabric close at hand.

Not sure what the rib x-section looks like on that sabre or how much it is reflexed (if at all), but that nose-diving behavior is exactly what a reflexed airfoil is supposed to prevent. Read THIS for interesting info on reflexed airfoils for tailless designs.

Talk to some of your paraglider design gurus for advice... you don't want that sumbitch bowtying on you at 100' agl... it'd ruin your day.

Gardner

[pBASEtobe 0]

You think I didn't have this same problem when I jumped the PD-190 because it wasn't loaded as high?

[base311 0]

possibly... possibly not. It's also possible that the same issues were present but just not nearly as pronounced at the lower W/L, therefore you might not have noticed them. Was that pd190 a 9 or 7 cell (2.5:1 aspect vs. 2.1:1 aspect)? and what is the difference in aspect ratio for either canopy and the sabre (2.5:1)). I'm just trying to collect more info.

I'd say more than anything the changes in the towpoints have affected the outboard cells' trim relative to the inboard cells' trim and the whole thing is out of whack <--- scientific canopy-engineering terminology.

Gardner

[pBASEtobe 0]

The PD-190 was a 9-cell so I think it has the same aspect ratio as the Sabre 170, 2.5:1.

[Treejumps 0]

I don't think that having the attachement point at the hips will have any negative effect. Nearly all canopies benefit from opening the chest strap as it allows the canopy to expand to its proper shape. In swooping it is mandatory to open up the chest strap as the canopies perform noticably poorer without opening it.

Form the video I would say that your brake lines are too short. Their should be a couple inches of slack in them when you are at full flight. You can tell if they are correct if there is a curve in them at full flight, as opposed to your's which are pulled stright and taunt.

I'm fairly certain that your buffeting was caused by a change in air pressure by a thermal or downdraft. Canopies seldomly buckle like that without oustside input, and if they had something built in that caused that it would keep doing it.

Either way, your nuts. Keep up the good work.