Another Gear Question--Canopies

[imported_Tom Aiello]

Cheerful Greetings:

I posted this earlier today, but I think it may have gotten lost. Apologies in advance if I've double posted. If I have, can somebody point it out to me and I'll erase this one? Thanks.

I have a question about canopies. I'm wondering if anybody has any commentary on it.

I own and jump both a Fox and a Mojo. I'm very happy with both.

However, I have also jumped an old Australian canopy called a Pooster. The Pooster is a BASE specific canopy, not a skydiving canopy.

I noticed that the Pooster flares from half brakes significantly better than either my Fox or Mojo. I think that this is because the Pooster has five control lines in the toggle cascade, rather than the four on my canopies. I am also told that using spectra, rather than dacron, control lines will give a better flare from half brakes.

Why don't our canopies do these things?

1) Spectra lines: I can see the trade off here--dacron lines are better shock absorbers, since spectra is completely static. But would it matter if just the control lines were spectra, while the others were dacron? Would that throw off the flying trim of the canopy? What about openings?

2) Five control lines: I know that some riggers modify Triathlons to have five lines, rather than four, to help them flare better. Why are BASE canopies not built this way? Is there more chance of line over with the extra line? Or is there some other reason I'm ignorant of?

If anyone has any idea, I'd love to know what's going on here (especially the four v. five lines thing).

--Tom Aiello

[guest]

We have tried different variations in placement and also number of control lines. And it's been well known for some time that the addition of an extra control line on each side will, on some canopies, increase both turning and flaring ability.

The Cruislite is an example. ParaFlite added an extra control lines to the canopy shortly before the end of it's production run. And people liked it. At the time, however, the new popularity of nine cells, spelled doom for the popular 7-cell.

So, you are correct in saying this modification might inhance the landing phase, but you must get to the landing phase in order for that to be of any importance.

With that in mind, we discarded the idea of adding the extra lines simply because the "more traditional" method has a long and exceptional track record behind it. It exhibits no inherent, or hidden, problems that can't be controlled.

A new method, would be exactly that, a new method.
We do experiment with these types of modifications in house, but we realize our customers are jumping single parachute systems and this demands we only give them what we know works.

We are a bit more conservative then we should be sometimes, and it causes what I'll term "discussions" here at BASIC RESEARCH from time to time. But in the end we know it's always better to come down on the side of sticking with what has a good track record, or something we have tested to our own satisfaction.

Here's another point;

We see people sometimes getting themselves into trouble by over-controlling a BASE canopy, especially during or right after deployment. We (all BASE jumpers) thought at one time that an immediate pull on the rear risers is the first response to an off heading opening. What's wrong with that, however, is the simple fact that a fully open canopy responds better to toggle inputs than a canopy that's not fully pressurized.

So making the toggles even more responsive may increase these types of problems.

Since we bias the design of the FOX canopy towards opening more than landing, we recommend larger size canopies than some people at first think is appropriate, especially when they are just starting BASE jumping and coming straight from the DZ.
Buying the right size canopy, gives you the best of both worlds, good openings and good landings.

Is the present control line configuration on the FOX set in stone? No, of course not, but any changes will come slowly. Our products are used by people with a wide range of experience levels, and that is always on our minds.

Nick
BR

[bps]

Hi Tom -

I was just thinking about your question and came across something that never dawned on me...the Pooster was a 220 whereas your Mojo and Fox are 260/265 respectively. When you jumped the Pooster, could the higher wing-loading provide the higher lift that you experienced?

I know this doesn't address the 5-line configuration...and I'm curious to see if anyone comes up with some more thought on the effects of an extra upper steering line.

Bryan
Tom - if you read this message prior to 4:00, give me a call at work.

[guest]

Tom Here is my posting from earlier today that got blasted into cyberspace some how.

Hi Tom,
Why you got the type of flare that you did from your pooster and not your other canopies is probably not a function of the steering system. I would tend to believe that it was more circumstance than design. From full-flight the steering system you described does give a more dynamic flare as it would more effectively chamber the airfoil and generate drag. On the other hand from 1/2 brakes, getting a good flare is more about keeping flow attached than it is generating a dynamic motion. In other words the extra trailing edge deflection will not help much when the canopy is already slowed.
Infact we have a Mojo in the field configured as such (4 upper control lines positioned at seams #1,2,5 and 6 - effectively like your pooster) Our initial testing and all reports (100 jumps)don't indicate any better flare pereformance form 1/2 brakes.
One of the reasons that BASE style canopies aren't built using this extra line is that it requires different length uppers to keep the steering geometry the same. This creates a packing scenerio that is not popular. (Remember the Cruiselite). Not to say that it couldn't be done but in our experience the benefits haven't been demonstrated yet. Another consideration is opening performance. It is better to leave a portion of the tail unsupported during deployment. As this unsupported tail deflects, it forms a monorail on which the canopy rides. Very stable. The other extreme would be to support the entire tail. The result would be miserable heading performance. Just how much support is ideal? We haven't pushed those limits yet. The extra line is not a bad idea. I'm just not convinced it was responsible for the flare you got.

Perhaps Aerodyne Research (Bill Hazlet)can give you some feedback on the Triathalon Mod. I know it was not originally done with their consent - maybe that has changed.

Hope that helps.



Adam
Consolidated Rigging, Inc.
<http://www.crmojo.com|CR Home Page>

[guest]

Hi there,

I have been thinking about something for a little while now, and now that I saw this thread I think my question fits in neatly with Tom's questions.

While gathering info on BASE the question of what canopy would be best for me to begin with came to my mind. It will be a base-specific canopy, that's for sure, but what size?

After I read about wingloading and canopies I was setting my mind on something in the 0.75 lbs/ft2 range and I also thought "the bigger the better".

I thought that something in the 280 range would be best for me. I weigh about 90 kg and I have met a few jumpers who weigh about the same. A few have chosen to jump 260 while others jump 240. They advised me to not go bigger than a 260 because of the increased packing volume and because it would just be big enough.

Now this is not about who is right, but more about the factors that play a role.

One thing I know is that the smaller the canopy, the faster things go, and IF ##### happens (180 or so), ##### happens faster as well.

The second thing is landing. The bigger the canopy, the less a fucked up landing will hurt...

And now my question: How about stalling?
Imagine a 180-off-heading opening, facing the object. I immediately pull the rear riser down; what is more likely to stall? A bigger or smaller canopy?

Another thing that comes to my mind only now: How about center cell stripping? A 190 canopy weighs less than a 280 canopy and will therefore be accelerated easier than than the big canopy. Is the center cell less likely to be pulled out of the packjob?

I know that all this might be a bit to theoretical and that in reality it will all do the job, but I was just wondering...

Cheers,
Robert

[bps]

Hi Robert -

You've asked some good questions. By no means am I an expert, but I would like to share my thoughts and maybe some people with more experience (maybe Adam from CR or Todd from BR) can provide some answers that are even more in-depth.

"How about stalling? Imagine a 180-off-heading opening, facing the object. I immediately pull the rear riser down; what is more likely to stall? A bigger or smaller canopy?"

Your brake setting will greatly influence the ability to stall your canopy. If you are "in-between" sizes, say between a 260 and a 280, I don't think that the size will be as important as your brake settings will be.

I feel that it is *very* important to dial-in a brake setting and become very familar with it. There are general formulas for deep-brake settings, but preferences run far and wide.

Too deep of a setting, and the canopy will have little forward airspeed on opening, but it will also turn slowly with riser input and have the tendency to stall while you are trying to turn. Keep in mind that you will lose alot of altitude trying to turn the canopy around.

A brake setting that is on the shallow side will provide you with more forward airspeed on opening. Yes, this will move you towards an object faster, but the canopy will respond faster to riser input and lose less altitude in a turn.

Finding the proper balance is important and is something that takes many jumps (with lots of experimentation) to figure out a setting that is right for you.

Your next question was about center-cell stripping and whether or not a smaller canopy will "strip less" due to its lighter weight.

With today's equipment, the amount of center-cell stripping is greatly influenced by the amount of "snatch-force" generated by the pilot-chute.

Let's say you use a 46"PC on a 1 second delay. The pilot chute will generate moderate snatch force. But now take a 4 second delay with a 46"PC and you will generate an incredible amount of snatch force (enough to cause severe stripping).

I'm sure in theory that the weight of a pack job will influence the amount of strip given the same amount of snatch-force, but I'm pretty sure that the difference is minimal. Practically speaking, I would be more concerned with proper pilot-chute sizing for your planned delay.

Center-cell stripping is a problem with any canopy that is free-packed and many people are trying to address that issue today with various inventions, but that is an issue for another post.

And in my humble opinion....if you are in-between sizes on a canopy - go with the larger one. Your comments were right on track - a larger canopy will provide you with better landings when the landings get tight, and beleive me, they will!

C-ya,

Bryan