Hybrid Canopy Question

[Dan1 0]

I did a couple searches and couldn't come up with anything that would answer my question.

I was wondering if a hybrid canopy has a higher sink rate over an all-ZP canopy? Not sure if I'm using "higher sink rate" in the proper manner...but basically if an all-ZP canopy and a hybrid canopy are side by side at 1,000 feet and are loaded at the exact same WL'ing, which will travel farther?

I feel kind of dumb for asking the question since I own a hybrid canopy (Silhouette) but am not sure of the answer

Edited to add: I know shape and design also play a factor, but for argument's sake let's just say their both the same canopy but one's constructed of all-ZP and the other is a hybrid

[LouDiamond 1]

If both are brand new, then they will both have an identical performance. Over time and use the non treated portions of fabric on a hybrid will become more porous while the full zp canopy will maintain it's lower level of porosity due to the fabric treatment. As the canopy fabric becomes more porous, it's performance and subsequent responsiveness will gradually decrease.

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[Dan1 0]

I assumed the hybrid would sink faster due to having a more porous material on the bottom skin/ribs, glad I asked since my assumption was incorrect.

Thanks for the quick response.

[antonija 0]

So F111 is actually just like ZP if both are new? After how many jumps does the difference between the two start to show?

I understand the need for conformity. Without a concise set of rules to follow we would probably all have to resort to common sense. -David Thorne

[jerolim 7]

No, 0-3 cfm low-porosity is “F-111” type fabric, 0cfm iz ZP (zero-porosity),....

[captain_stan 0]

Quote

they will both have an identical performance

Evidence to the contrary is the much-easier packing of a brand-new, all F-111 canopy as compared to a zero-P canopy. There is a measureable amount of air leakage through new F-111 fabric, whereas new zero-P will only leak air through the needle holes in the seams. Anyone who has flown a new, or nearly new, F-111 canopy will tell you it doesn't fly like zero-P. Maybe the accuracy community will weigh in on this one; they fly F-111 canopies for a reason.

BTW, the proper term for air leakage through fabric is "permeability."

[captain_stan 0]

Quote

which will travel farther?

Since PD is marketing the Silhouette as a canopy that is "easy to pack," I'm concluding that glide ratio was not the #1 priority in their design. It is popular with the people who own it, and obviously performs well enough to stay in the marketplace. But if the flattest-possible glide ratio was the goal in canopy design, I don't see how any part of such a canopy could be made out of a fabric that "leaked air." (OK--maybe the slider) The most important question is: are you satisfied with your canopy's performance? It's a fact that other canopies on the market will glide farther and I expect that most or all of these will be all Zero-P construction. Of course many other factors will also effect glide ratio. I suggest test-jumping some different canopies for comparison.

[LouDiamond 1]

I understand what you are saying and am not disputing what you said. However, from my personal experience and having seen it demonstrated in a real, controlled test situation,say that they perform the same.

I have seen an identical new non zp planform canopy flown with a new zp canopy in a side by side comparrison. The non zp canopy was able to match the descent rate and flight characteristics of the zp canopy. Both canopies where the same size, weighted the same and were the same planform. This was done as part of testing for a millitary project I was working on where the reserve was identical to the main except that it was not zp. This was later put to the test during a non planned cutaway on a HAHO jump and the jumper was able to continue flying with the group and make the DZ despite being under a non zp canopy.

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[captain_stan 0]

to continue flying with the group and make the DZ despite being under a non zp canopy.***

In a similar experience, I reached a different conclusion. I chopped my Stiletto, then flew my Raven reserve to the LZ and landed it right in front of the hangar. But I don't think it proved that both these canopies have the same glide ratio.

[davelepka 4]

Quote

I was working on where the reserve was identical to the main except that it was not zp. This was later put to the test during a non planned cutaway on a HAHO jump and the jumper was able to continue flying with the group and make the DZ despite being under a non zp canopy.

If you quoted the complete passage, you'd see that it is not similar.

The two canopies in question were identical, with one being F-111 for use in the reserve container. A Stiletto and Raven are not the same in any way.

Furhtermore, the example he gave proving his theory was a HAHO jump. High Altitude High Opening, where the LZ is a good distance from the exit point. The canopies are used to glide the distance into the LZ. A far cry from you chopping your Stiletto on a sport skydive where you were in close proximity to the LZ when you opened.

[captain_stan 0]

Quote

A far cry from

OK, I'll spell it out for you. Both these incidents are a far cry from a controlled test in which glide ratio is measured in an accurate manner.

[davelepka 4]

Quote

I have seen an identical new non zp planform canopy flown with a new zp canopy in a side by side comparrison. The non zp canopy was able to match the descent rate and flight characteristics of the zp canopy. Both canopies where the same size, weighted the same and were the same planform. This was done as part of testing for a millitary project I was working on where the reserve was identical to the main except that it was not zp.

Aside from building the same canopy from both materials, then loading them the same, and flying them side by side, what would else would you do to test this theory?

What sort of criteria would you have in place to produce results that you would consider valid?

[JohnRich 4]

Quote

I assumed the hybrid would sink faster due to having a more porous material on the bottom skin/ribs...

Good question there.

As you say, in a hybrid canopy the porous material is on the bottom skin, and the zp material is on the top skin. Since a canopy is descending, I would think that the natural air pressure inside the canopy would be trying to leak out through the top skin. But since that's zp, it can't escape the way it's being pushed. And since in order to sink you need leakage upwards, and that can't happen due to zp fabric, does a F111 bottom skin really cause the canopy to sink faster? And is there really much leakage through the bottom skin just from the pressure of the air inside the cells? If anything, I would think that air underneath the canopy would be seeping through to the inside?

[AggieDave 6]

Out of curiosity, are you asking just to learn or have you had some difficulty getting back from a long spot? If its just to learn, others are debating for you. If you're having trouble getting back from a long spot, the canopy you have is great for getting back, at this point its simply technique (unless you're against the winds and way out).

Let me know and we can address technique.

--"When I die, may I be surrounded by scattered chrome and burning gasoline."

[captain_stan 0]

Quote

Aside from building the same canopy from both materials, then loading them the same, and flying them side by side, what would else would you do to test this theory?

What sort of criteria would you have in place to produce results that you would consider valid?

The first thing I'd have to rule out would be any difference in pilot input. Both canopies would have to be flown in an identical manner with the exact same control input. As difficult as it might be to minimize or eliminate this human factor, it’s the only way to be absolutely objective.

Consider a sport cross-country canopy flight from 10,000 feet or higher. An assortment of canopies may all make it back. Some of these pilots might have preferred a longer spot and ended up bleeding off extra altitude by making more turns. Some may have to use more toggle or riser input to extend their glide. But they may all make it back. Because they all have the same glide ratio? No, because they are all canopy pilots and knew how to achieve the desired flight.

The second factor I would have to control would be to establish the objective for flying the greatest possible distance across the ground, instead of just trying to reach an intended target.

When two canopies, identical or not, are able to reach the same landing target from the same opening point, this does not mean that they have both covered their greatest achievable distance across the ground or have achieved their maximum glide ratio during the entire flight. What if one of these canopies was capable of flying farther but its pilot chose to land on the LZ instead of over-flying it? The only way to eliminate this variable is to have a big enough LZ that each canopy can fly its greatest possible distance across the ground and land at a point that is the farthest possible from the opening point. For test purposes, that means downwind landing w/o flying a standard (or any other) pattern.

Less significant requirements include:

(1) Identical wing loading. The suspended weight becomes lighter after the main is chopped and the reserve is deployed. Each jumper must also weigh the same and carry the same weight in equipment.

(2) Identical drag--body size, body position, clothing, equipment, etc. must be identical.

(3) Identical wind conditions. This was satisfied by flying both canopies simultaneously through the same airspace. No problem there.

[dgw 8]

The internal pressure in the cells should, in principle, act equally on the internal surfaces, top and bottom. If there was a significant difference in the pressure on the top and bottom surfaces, then the cells would collapse.

Consider, for example, a sealed balloon. The internal gas pressure acts equally around the internal surface.

[captain_stan 0]

Quote

The internal pressure in the cells should, in principle, act equally on the internal surfaces, top and bottom. If there was a significant difference in the pressure on the top and bottom surfaces, then the cells would collapse.

Although the internal pressure acts equally outward in all directions, the external pressure varies greatly. The top skin is exposed to the low-pressure above the wing, and the bottom skin is exposed to the high-pressure below the wing. That's what makes it fly. The result is a pressure differential that varies, in different areas of the wing. John's right. The highest potential for air leakage is through the top skin because that's where the greatest difference in pressure exists; it's less everywhere else. PD and others have proven that there is much performance to be gained even in making only the top skin from ZP.

edited to add: I'll let the engineers decide if air is leaking in or leaking out through the bottom skin. I can say with certainty that there is less pressure differential there than any other area. And our canopies are more rigid by design than your balloon, hence their ability to withstand these differences in air pressure without collapsing (usually).

[JohnRich 4]

Quote

The internal pressure in the cells should, in principle, act equally on the internal surfaces, top and bottom. If there was a significant difference in the pressure on the top and bottom surfaces, then the cells would collapse. Consider, for example, a sealed balloon. The internal gas pressure acts equally around the internal surface.

That's an instructive example, but the parachutes in question have a few differences. For one, the surfaces aren't impermeable like the balloon. In this case, the air can leak out the bottom. But the cells don't collapse, because new air is entering the front - that's why we call them "ram air" canopies. And when that air enters and has no place to go, it's pressurized. And since "nature abhors a vacuum" and always tries to equalize things, that positive pressure inside is going to try to leak out where it can, which in this case is through the F111 fabric on the bottom. That's the way my thinking is going...

And if all of that is true, I don't know if that means the canopy won't glide as efficiently as an all-zp canopy. My gut instinct is that any difference will be negligible.

Accuracy canopies are all F111 because they're used to sink straight down, making them behave more like a round canopy than a gliding canopy. To do that they need split stabilizers to allow air trapped underneath to vent out the sides. And the F111 probably helps them sink too, since air can seep out through the top skin fabric.

[CReW 0]

Don't some Hybrid canopies have the ZP on the bottom skin instead of the top?

Seems like a good way to make the ZP last a long time.

[Dan1 0]

Quote

The most important question is: are you satisfied with your canopy's performance?

Yes, I'm very satisfied with it's performance. I just had a kind of weird scenario play out, which is why I'm asking this question. (Story is below)

Quote

Out of curiosity, are you asking just to learn or have you had some difficulty getting back from a long spot? If its just to learn, others are debating for you. If you're having trouble getting back from a long spot, the canopy you have is great for getting back, at this point its simply technique (unless you're against the winds and way out).

Let me know and we can address technique.

I'm asking because last Saturday the winds were fairly strong and I didn't make it back to the usual landing area like most other jumpers did. I'm lightly WLing at 0.9:1, which at first I thought might be a problem on windy days, but even with the ground winds at 12+ knots and at 3,000 being at around 30 knots, I was able to penetrate into the wind easily.

So before jump run, with the winds having picked up since earlier in the morning, the DZO went over an aerial photo of the airport and showed us where a good area to start our downwind leg would be, since we would have a much long downwind leg than usual. This was only my 2nd jump at this particular DZ, so I wasn't too familiar yet with picking out landmarks as to what sets up a landing pattern to land right in front of the hanger.

Anyway, was under canopy a little above 3,000 and go to make my way over to where he mentioned a good idea was to setup for the downwind leg. On my way over there I noticed this was where the majority of people were starting to begin their downwind leg. So I made it over there at around 1,000 feet I notice I'm not drifting along nearly as fast as some of the other jumpers and my altitude was decreasing to the point where I knew I wasn't going to make it back to the hanger. I pulled down the rear risers a bit to maybe stretch out the length of my downwind leg but it didn't do a whole lot and at around 400 feet I just did a slow 180 to face into the wind and land.

Most of the other jumpers made it back to right in front of the hangar. I was around 1/3 mile or more away. If you've ever been to Skydive Carolina, the landing area is huge, so this only put me in the middle of the landing area with a longer than usual walk back to the hanger.

So I was kind of confused after this happened, which is why I'm asking this question. Most other jumpers there have a heavier wingloading than I do and smaller canopies, which added to me being confused.

So going off of what has been said above, the only thing that I can think of is that maybe my perception was off and the other jumpers were beginning their downwind leg farther away and closer to the hanger then where I thought they were?

[captain_stan 0]

Quote

Quote

Don't some Hybrid canopies have the ZP on the bottom skin instead of the top?

Let me know if you find one on the market. I'd be interested in studying it.

Quote

Seems like a good way to make the ZP last a long time.

Is that a joke? Silicone coating was invented to protect Nylon from UV. Not only will it outlast non-coated fabric, but it's superior performance properties were realized as soon as it was put to use. The shaded bottom skin is always gonna hold up better to UV weakening & long term permeability increase than the more-exposed top skin. So why waste a better material in an application where it's properties aren't needed nearly as much?

• Quote

[dgw 8]

Quote

In this case, the air can leak out the bottom. But the cells don't collapse, because new air is entering the front - that's why we call them "ram air" canopies. And when that air enters and has no place to go, it's pressurized. And since "nature abhors a vacuum" and always tries to equalize things, that positive pressure inside is going to try to leak out where it can, which in this case is through the F111 fabric on the bottom. That's the way my thinking is going...

Thanks for the considered reply. My thoughts are that, no matter where the air leaks out, the pressure is the same. The rate of 'refill' is not really important, because the 'ram air' effect keeps the pressure fairly constant. So, in princple, you have constant air pressure in the cells, regardless of where the air escapes from the cells.

Now, I'm no expert by any means. Parachutes have a touch of voodoo about them at the best of times (in my opinion
I think your comment about trim is important. I think Lou Diamonds observations, whilst limited to a test population on 1, are the best data.

As ever, YMMV....

[AggieDave 6]

Quote

So I was kind of confused after this happened, which is why I'm asking this question. Most other jumpers there have a heavier wingloading than I do and smaller canopies, which added to me being confused.

Smaller and faster canopies can be an advantage when bucking into a head wind, that's why you need to have a wind limit for yourself. That involves your wingloading and your ability level.

Now, have you seen the "accuracy spot" before? Under canopy if you look between your feet you'll see the ground going from front to back. If you look out towards the horizon, you will see the ground "going up." Look to where those two visuals meet. You'll find a spot that doesn't move. That is the "accuracy spot." If you did nothing and continued in the same winds, you would land on that spot that isn't moving.

Now, go out on a hop-n-pop some time, clear your airspace, point back towards the airport and find the accuracy spot. Now, go into 1/4 brakes and see what happens to the spot. Try it with 1/2 brakes and then 3/4 brakes. Try it while balling your body up and trying to have less drag. Try it with your rears. Try it into the wind and with the wind. See what happens.

Playing with your canopy at your wingloading with the accuracy spot will help teach you how to fly your canopy back from long spots.

Remember, though, if you need to land off, then land off. Its much much better to land off in a field of your choosing then to get caught with "get back-itis" and crash in hurting yourself.

--"When I die, may I be surrounded by scattered chrome and burning gasoline."

[Dan1 0]

Dave, thanks for all the suggestions and advice. I've only flown this canopy 4 times now so I've had barely any experience with it. I'd like to do a hop n pop from full altitude to really start playing with my canopy, but...I don't really feel like returning to the ground as a human popsicle in this weather

I guess I just need to jump it more to learn it's characteristics, so I will definitely play around and try the stuff you mentioned this weekend, thanks again!

[AggieDave 6]

No problem, enjoy your new canopy!

Remember to go through other important drills with your new canopy. Drills like the 9-flares, stalls and flat turns. If you don't have a local canopy mentor, then check the sticky in the Swooping forum. You're close enough to hook up with serious canopy teaching talent around the Georgia and Florida area!

--"When I die, may I be surrounded by scattered chrome and burning gasoline."