0
sillie1111

Vented Canopies?

Recommended Posts

I have looked back in previous threads and I read tom a's first base rig recommendations but I am still a little confused about a few things concerning vented canopies. As I was reading I saw a lot of threads talking about "backsurge" when the brake settings are to deep, as well as "surging forward" when they are to shallow. I know you want your brakes set so your canopy has very little forward speed. From what I understand a vented canopy is not good for a beginner because the canopy is more likely to surge either forward or backward upon opening? Is it not possible to use an ideal brake setting on a vented canopy? Or is it just vented canopies are more susceptible to this behavior then a non vented canopy therefore shouldn't be used by beginners?

Another question I had was regarding forward speed of a vented vs non vented canopy initially after opening. If a vented canopy is designed to pressurize faster then an un vented canopy does this also mean in the event of a 180 you will begin flying towards the object you just jumped from sooner giving you less time to react?

Thanks!
~Shelly

Share this post


Link to post
Share on other sites
I only have 25 BASE jumps on my BlackJack and 6 skydives, but I would recommend it to any BASE jumper. I've never heard of vented canopies having a higher forward surge or forward speed. If you're worried about backsliding, make sure your deep break settings are good. I'm assuming with good deep break settings a head wind wouldn't cause anymore backslide than it would on a non-vented canopy, but I'm not sure about that.

It's definitely possible to have good break settings on them. I have jumped bridges in headwinds, and not had any noticable stall or backslide.

They do pressurize sooner, but flying sooner doesn't give you less time to react unless the object was more overhung the lower you were.

Forward speed obviously effects your time to react, so good DBS give you more time to react. I have heard the argument that DBS slows the riser turn. I played with this on skydives and it's true. If you do a riser turn with your toggles stowed, then riser turn with them all the way up, you turn faster with them up. I figure the increase in forward speed compared to increase in turning speed probably makes DBS a safer and horizontally faster solution though. Just my theory.

Another great thing about the BlackJack is flare power from deep breaks. You can sink all the way to landing at 50% breaks and still have a nice flare. Other than the blackjack I have only flown an old Ace and a Mojo, and neither had as nice of a flare as my BlackJack.

Hopefully someone with a lot of canopy experience comments about the forward surge/forward speed of vented vs. non-vented. If there is any noticable difference. I think that would probably be more of a canopy brand to brand type of difference than a vented to non-vented.

Share this post


Link to post
Share on other sites
The vents help the canopy to become a flying wing in a shorter time (and vertical distance) then an unvented canopy. Once fully pressurised the canopy will behave in exactly the same way as an unvented version of the same wing (assuming values on vents).

So if you have an offheading and are facing something, yes you will start to move towards it sooner under a vented canopy (all other things being equal) and therefore you have a shorter time to react to the offheading.

However an inflated canopy will respond to control inputs better and I'd rather have one if I hit something.

Another potential drawback of an unvented canopy that I have heard from a much more experienced jumper than I is that they MAY be more more prone to offheadings. I believe his thinking was if a canopy can inflate quicker via the vents, there is more POTENTIAL for uneven inflation too. I'm not so sure I buy that, and feel that the issue he is worried would be compensated by achieving full pressurasiation in a short time.

Share this post


Link to post
Share on other sites
Quote


Another great thing about the BlackJack is flare power from deep breaks. You can sink all the way to landing at 50% breaks and still have a nice flare. Other than the blackjack I have only flown an old Ace and a Mojo, and neither had as nice of a flare as my BlackJack.



Once pressurised you shouldn't notice a great differece between the flare on a Blackjack and Ace assuming they are the same size, configuration and condition.
Your observation probably has something to do with the fact that it was an "Old Ace". It does have an identical airfoil to the Blackjack after all.

Share this post


Link to post
Share on other sites
Dont forget vented is different then valved which is what a blackjack is. If you have a vented canopy all you should have is a mesh opening, but with a valve the canopies pressure closes off the vent which allows for a good flare.

Share this post


Link to post
Share on other sites
Quote

Once pressurised you shouldn't notice a great differece between the flare on a Blackjack and Ace assuming they are the same size, configuration and condition.
Your observation probably has something to do with the fact that it was an "Old Ace". It does have an identical airfoil to the Blackjack after all.



Yah, that's why I said old :D

Share this post


Link to post
Share on other sites
I jump a FLik 322 Vtec and I screwed up at BD when I forgot and tried to sink it in like my Triathalon. I picked up a little tailwind and was going long so I got too deep in the brakes, my legs swung out a little to far and I landed on my ass.

I like the way the vented canopy flies and with the extra brakelines (5 on each steering line instead of 4) it flares faster than my Triathalon. Just don't forget (like I did) that a vented BASE canopy isn't going to fly the same as a non-vented skydivng canopy.
"I'm not a gynecologist but I will take a look at it"
RB #1295, Smokey Sister #1, HellFish #658, Dirty Sanchez #194, Muff Brothers #3834, POPS #9614, Orfun Foster-Parent?"

Share this post


Link to post
Share on other sites
Quote

vented is different then valved


What fo you mean valved? Is there a mechanism to close of the vents after the canopy is inflated? How do you activate these so called Valves?

Share this post


Link to post
Share on other sites
Vented canopies do not surge more then non vented canopies. They do pressurize faster which is a good thing in all cases. Wether you have an on heading or a 180. If you get a 180 it means the canopy will be pressurized quicker making it possible to turn from the object faster. I jumped non vented canopies for years because vented canopies didn't exist. But once I started jumping vented canopies it didn't take long for me to realize the difference the venting makes. I don't know how I lived for as long as I did without them. My life has been saved by them more times then I can count. I will not jump a canopy slider down that isn't vented ever again. I would never let a person i was training to jump a canopy slider down that wasn't vented. Venting was one of the most important innovations sense the tailgate...

Jeb Corliss

Share this post


Link to post
Share on other sites
Quote

Quote

vented is different then valved


What fo you mean valved? Is there a mechanism to close of the vents after the canopy is inflated? How do you activate these so called Valves?



There is an (often red) valve activation handle near the top of your right main lift web, on the inside. It is typically a cloth loop connected to two yellow cables... ;)

[edit: just in case there are any 15-yr-old base-jumping wonders who just acquired a rig off of ebay reading this... i'm only kidding. (okay my conscience is clear now)]
-Ghetto
"The reason death cannot frighten me, is because life has cured me of fear."
Web Design
Cleveland Skydiving

Share this post


Link to post
Share on other sites
Quote

I have jumped bridges in headwinds, and not had any noticable stall or backslide.



In my experience backsurge is much more common in tailwinds. Check out the video of (I believe it's Liv) jumping the fire lookout on the ABA 2003 (? might be 2004) video and you can see what I mean--the canopy backsurges hard enough to strike the tower tailfirst and hang up on it.
-- Tom Aiello

[email protected]
SnakeRiverBASE.com

Share this post


Link to post
Share on other sites
all the tech has been said..

niiice avatar:P

Stay safe
Stefan Faber

Share this post


Link to post
Share on other sites
Hey guys thanks for the responses! So am I correct in understanding back surge can still happen even if you have good deep brake settings? Or was this because when vents frist came out there was not alot of research done and people were messing with their brake settings too much?

Currently im jumping a non vented fox which I do like the way it flys and lands. I do recognize though I am only jumping easier objects now I do know at some point I will be jumping more advanced objects (when im ready of course) and will want a vented canopy. I was thinking it would be good to train myself on a vented canopy so when I am ready for more advanced object I am also under a familiar wing. I will be buying a new canopy soon as I am underloading my 225 so the winds that make it good for me to jump in also make it tough to not be blown backwards under canopy! I am trying to explore all options for a canopy. I think a vented is the way to go.

It makes sense that a vented canopy will pressurize faster therefore become a flying wing faster but the reason I asked is because I have a friend with a vented fox but when he opens it appears from the ground anyways that it takes the same amount of time then a non vented canopy to start flying forward. Almost seems as it just hangs there for a half of a second or so exactly the same as the non vented canopies I have seen. My friend has also complained about the landings with the vents so he sent his canopy back to have valves installed which improved his landings considerably. B|
~Shelly

Share this post


Link to post
Share on other sites
Quote

So am I correct in understanding back surge can still happen even if you have good deep brake settings?



Yes, but it's pretty condition dependent. A "good" brake setting in zero winds can result in backsurge in significant tailwind.
-- Tom Aiello

[email protected]
SnakeRiverBASE.com

Share this post


Link to post
Share on other sites
Quote

...I have a friend with a vented fox but when he opens it appears from the ground anyways that it takes the same amount of time then a non vented canopy to start flying forward. Almost seems as it just hangs there for a half of a second or so exactly the same as the non vented canopies I have seen.



Slider up or down? Any wind? Freefall or static line? Deep or shallow brakes? Were the brakes customized to each jumpers body weight? Are the canopies the same size? Are all the canopies you are comparing the same kind (i.e. all FOXes)?
-- Tom Aiello

[email protected]
SnakeRiverBASE.com

Share this post


Link to post
Share on other sites
I'm just comparing his canopy to other canopies on the same jump with similar wingloadings. One jump I can remember well was a SL slider down very little tail wind, both deep brake settings, a vented fox compared to a mojo. My observations very well could have been because of the different types of canopies. But it appeared that the mojo and the fox both hung for second before moving forward. The only difference I observed was the mojo took quite a few breaths and was pressurized significantly lower:S
~Shelly

Share this post


Link to post
Share on other sites
It sounds like a "backsurge" is a relative of a gust induced stall. Gravity constantly working and downward velocity being arrested, but the wing getting hit with an influence (tail wind) and and needing more vertical velocity to overcome it. Being unable to "Fly", it must "Stall" and pick up more speed/pressure to become a semi ridgid wing.

Share this post


Link to post
Share on other sites
Yes, but it's pretty condition dependent. A "good" brake setting in zero winds can result in backsurge in significant tailwind.



So do you have two different vented canopies you use? One for no wind E or B's and one for tail winds, both with different brake settings? Or do you adjust your deep brake settings for each jump? Please note im not going to be messing my brake settings in any way i'm a long way from jumping in zero winds and my current canopy is not vented and the brake settings are fine. I'm just trying to find out what other jumpers do for these types of situations.
~Shelly

Share this post


Link to post
Share on other sites
Standard Disclaimer: The following are [I]my opinions only[/I]. Ask lots of different people, read everything you can, and then decide for yourself what you think.


A modern ram air canopy has two functions, which it performs in sequence.

First, it acts as an aerodynamic decelerator (a big air brake) to stop the jumper's fall. In this it performs the same function as a round parachute (this is pretty much the only function of a round parachute, although drive vents complicate things a little).

Second, it acts as a wing. Once it has finished decelerating the jumper, it transitions into an airfoil, which flies the jumper to the landing area, and allows a nice flared (and soft) landing.

For purposes of this discussion, the interesting stuff all happens during the transition from the first point to the second--while the parachute is changing from a pure aerodynamic decelerator into a flying wing.



Unvented Slider Down:

First lets talk about the opening sequence of an unvented slider down canopy. I'll start at line stretch (because that's where the difference between vented and unvented starts to matter).

Bottom Skin Expansion: After the canopy reaches line stretch, air hits the bottom skin and causes it to expand. [The tailgate promotes a nose first expansion, but let's leave that aside for now, because it's going to work in a roughly similar fashion on vented and unvented canopies.] The bottom skin expands until it's roughly rectangular (something approximately the shape it will be once the canopy is inflated).

Cell Inflation: After the bottom skin expands, the cells fill with air. This happens for many reasons, but a prime motivator is that the canopy will slide or hop forward (almost in the same fashion as an old style tracking jumper--by deflecting air off the bottom skin). This forward motion is not strictly "flight" (the cells are not yet inflated and the canopy is not yet formed into an airfoil shape), but rather more "deflection." This motion results in air rushing in through the nose of the canopy, pressurizing the cells (and creating the "wing" that you will fly to the landing area).

Flight: The now inflated wing begins to fly.


Vented Slider Down:

So, what do the vents do? Basically, they synchronize[/I] the Bottom Skin Expansion with the Cell Inflation, so the process looks more like this:

Bottom Skin Expansion and Cell Inflation: As the bottom skin expands, air passes through the vents and pressurizes the cells almost simultaneously. The canopy moves directly into the "flight" stage without needing to "hop" or "slide" forward to pressurize the cells.

Flight: The now inflated wing begins to fly.


Slider up:

Interestingly, the slider works in a different fashion, to the same end. The slider also synchronizes bottom skin expansion with cell inflation. However, instead of accelerating the cell inflation to match the bottom skin expansion, it operates more by slowing the bottom skin expansion down to the rate of cell inflation. So, with a slider, the process looks like this:

Bottom Skin Expansion and Cell Inflation: As the bottom skin begins to expand, air rushes into the cells. The slider slows the bottom skin expansion such that the cell inflation is almost synchronized with the bottom skin expansion.

Flight: The now inflated wing begins to fly.

It's been my observation that the slider basically overrides the vents (or they work together, if you prefer) such that there is virtually no difference between vented and unvented cell inflation slider up.


So, what about the brakes?

With properly set deep brakes, the canopy should transition into a wing with the minimum possible forward speed. Some forward speed is necessary for the wing to fly (otherwise it's stalled, and it will drop the jumper out of the sky very quickly). The goal of setting your deep brakes (which ought to be done custom to your body weight) is to find the ideal point where the wing has the absolute minimum forward speed to still function as a wing (flying forward) and to be controlled (respond to riser input). [If you are a "toggles first" kind of jumper, you can pretty much ignore that second part, because you'll give the canopy more forward speed by popping the brakes, pulling it back off the stall point as you initiate your turn.]


What happens if your brakes are too deep (on an unvented canopy slider down)?

If they are way too deep, you'll find the wing opens in a stall, and never gets flying. The canopy will simply drop out of the sky until you pop the toggles. This may be because the pulled down tail (from the brakes) is essentially counteracting the forward "slide" necessary to inflate the cells, and the cells are never inflating. It might also be because the cells do inflate, but the resulting wing never begins to fly, and instead stalls and drops (or slides backward). For ease of reference, let's refer to this phenomenon (stall during initial inflation, or failure to inflate at all, followed by backsliding or straight dropping) as Deployment Stall.


What happens if your brakes are too deep (on a vented canopy slider down)?

This is where you can see opening backsurge start to develop. As the air rushes in through the bottom skin vents, it surges upward, strikes the topskin of the canopy (inside the cells) and then is deflected (both forward and backward). Some of the deflected air is expelled through the nose of the canopy, pushing it backward. This creates a noticeable backward movement of the canopy. I've seen this backward movement stop (and the canopy stabilize in a nearly parked flight mode, sinking almost straight down), and I've also seen it turn into a full on stall (with the canopy losing altitude fast until the jumper pops the toggles and the canopy recovers by diving forward to gain speed).


What does the wind do?

In general, during the transition phase when the canopy is changing from its aerodynamic decelerator mode to its flying wing mode, it is still susceptible to wind effects. However, the effects of the wind on this transition may seem counter intuitive.

Tailwind: As the canopy starts to transition, the tailwind essentially blows wind up the canopy from tail to nose. The canopy "perceives" this wind (in combination with the inflation forces) as "slowing" the rate at which the wind blows into the nose (or if you prefer, the rate at which the canopy moves forward). This means that the back surge air (the air that is flowing in through the vents and striking the topskin) is "stronger" by comparison, and hence more likely to cause a backsurge. The tailwind effectively deepens the brake setting during this step, and also results in a slightly slower inflation (i.e. a greater time from PC pitch to flying wing overhead).

Headwind: During the transition phase, a headwind pretty much acts in the opposite way of a tailwind. The canopy "perceives" the headwind as increasing the force into the nose, and hence reducing backsurge (and effectively making the brakes more shallow for this step). The headwind effectively makes the brakes shallower, and also results in slightly faster inflation (i.e. less time from PC pitch to flying wing overhead).





Quote

From what I understand a vented canopy is not good for a beginner because the canopy is more likely to surge either forward or backward upon opening? Is it not possible to use an ideal brake setting on a vented canopy? Or is it just vented canopies are more susceptible to this behavior then a non vented canopy therefore shouldn't be used by beginners?



In general, I'd say that the vents aren't [I]necessary[/I] for a beginner, because the vents are most noticeable on lowish slider down, and especially underhung (where you want the wing flying to avoid the object coming out below you), solid objects. Beginners shouldn't really be jumping those types of objects, so why waste the money buying a (pricey) bit of technology that won't help you on the objects you are jumping? I think it's better to wait and get them on your next canopy, which you're more likely to be taking to such sites.



Quote

Another question I had was regarding forward speed of a vented vs non vented canopy initially after opening. If a vented canopy is designed to pressurize faster then an un vented canopy does this also mean in the event of a 180 you will begin flying towards the object you just jumped from sooner giving you less time to react?



No. Faster cell pressurization does not automatically yield more forward speed at opening.
-- Tom Aiello

[email protected]
SnakeRiverBASE.com

Share this post


Link to post
Share on other sites
Quote

Or do you adjust your deep brake settings for each jump?



That one. Some of my canopies have as many as 4 brake settings which I'll use in different situations. It can be tough to predict conditions while packing, though, so it's something of a crapshoot.
-- Tom Aiello

[email protected]
SnakeRiverBASE.com

Share this post


Link to post
Share on other sites
Wow Tom, Thank you I found this post to be very helpful in understanding the backsurge phenomenon you are referring to. It is also very helpful in understanding the opening sequence in better depth. I did mention before my friend with a vented fox almost seems to have his canopy hang when it initially opens. You mentioned "This creates a noticeable backward movement of the canopy. I've seen this backward movement stop (and the canopy stabilize in a nearly parked flight mode, sinking almost straight down), and I've also seen it turn into a full on stall (with the canopy losing altitude fast until the jumper pops the toggles and the canopy recovers by diving forward to gain speed)." Could my observations be because his brake settings are too deep? Each and every opening (slider down) looks exactly the same on his canopy pressurized then it just hangs for a second, he is very quick on his toggles so once he pops them the canopy goes right into forward flight by the time he gets to his toggles.

Asfar as not wasting my money on new gear, I need a new canopy anyhow, I would like to make a trip to the prine this spring to further practice object avoidance as there are no suitable objects to intentionally practice on in the North East. I would like to stay consistent on one canopy and if I plan on jumping more experienced objects when my skills are at par, then wouldn't it make sense to buy a vented canopy now so I am consistent with my canopy?
~Shelly

Share this post


Link to post
Share on other sites
Found a typo:
Where you say "Unvented Slider Up:" you go on to explain Vented slider down.

Nicely written. At first I had trouble understanding " The canopy "perceives" this wind (in combination with the inflation forces) as "slowing" the rate at which the wind blows into the nose"

Then I thought of it picturing the canopy from the side with the nose facing left, and imagining the wind moving left, so the air that would be going into the nose is actually moving away from the nose. Do you think there's more to it than that?

Share this post


Link to post
Share on other sites
Wow!
Now that's a pretty complete reply.
This thread is nice!
The bums will never win Lebowski, the bums will never win!
Enfin j'ai trouvé:
Bieeeen

Share this post


Link to post
Share on other sites
get the vented canopy - period!
Make sure you get proper canopy size for your weight too.
Brake settings is all about your personal preferences, and can be adjusted in few jumps from the bridge.
All discussion about four or five brake line set up is easy to solve too - personal preference + type of the canopy will say to you what is better.

Learning on the field w good mentor is essential!
Robert Pecnik
[email protected]
www.phoenix-fly.com

Share this post


Link to post
Share on other sites
0