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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!

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.

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.

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.

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.

Yah, that's why I said old

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.

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?

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

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)]

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.

I've seen that video at your house

That was a tail wind?

all the tech has been said..

niiice avatar

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.

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

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)?

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

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.

 
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.

Standard Disclaimer: The following are my opinions only. 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 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).






In general, I'd say that the vents aren't necessary 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.




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

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.

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?

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?

Wow!
Now that's a pretty complete reply.
This thread is nice!

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!

Probably what you saw is the point at which they popped their brakes. Most canopies with a well tuned DBS seem to hang motionless until the brakes are popped. This has nothing to do with vented vs. non-vented.

The inflation time you saw is due to the venting. A vented canopy tends to pop into shape almost instantly. A non-vented canopy actually looks like you say where it is taking a breath. I would expect this to be more so when the DBS is well tuned, because it wouldn't have the forward movement to help keep the wing pressurized. The vented canopy has two inlets for air so the forward movement isn't as necessary to keep the wing inflated.

They could be, but I don't think you could say for certain. To check if brake settings are too deep, grab a riser and initiate a turn immediately after opening (with the brakes set). If the canopy turns, the brakes are either too shallow or just right. If the canopy stalls straight down without turning, the brakes are too deep.

Thanks. I went back and fixed it.

Sure. As long as you understand what you're doing, then whatever you want to do is what makes sense.

In terms of getting used to the canopy, there's not a whole lot of difference (some in steep approaches, I think, but overall very little) between a vented and unvented canopy of the same model.

I'm not sure. I think you've captured the essence of it, but I also think that the "gust induced stall" phenomenon that Pete referenced is pretty relevant. Once the wing takes shape as an airfoil it could still be experiencing a gust induced stall.

Let us not forget two very important things:

-Different canopy designs benefit from vents more than others (Flik vs. Ace for instance).

-Larger canopy size (260+) and underloaded canopies (.65 and lower) also benefit more.

IMO, an Ace 220 loaded @ .75 will benefit much, much less than a Flik 322 @ .6.

The only system on the market that I would consider putting holes in the bottom skin is the Troll MDV.

I am also fortunate to jump smaller canopies (220 and 240) but depending on the landing area I would not mind a 200 or 180.

I'd not jump anything bigger than 240 vented or not.

Another 0.02...IMO vented canopies suffer from off-headings more than convetional ones. And I am not the only one thinking so...there is a saying...with a vented your chances of hitting a wall are greater, with a non-vented the chances of more severe injuries when you do hit the wall are greater.

For the type and size of canopies I jump I do not see myself going down the vented route...If I was 200LBS plus I bet I would think much differently.

Vent or no-vent PLEASE set your DBS!!! Ask tfelber about it...just to rub it in...

Where do you get that from?
How many jumps have you done on vented vs un-vented?

I bought my Flick 322 unvented (non V-TEC) and PCA'd it off a popular pre-bridge day object. I ened up cracking my tailbone because the canopy didn't have enough time to get flying and I landed hard on my ass. I got it vented and then did the same jump next year. There was a world of difference. Check out a video comparison on skydivingmovies.com

I didn't put enough jumps on the non-vented version to notice a difference in forward speed. However, I think because the vented canopy starts flying faster, you would also start flying foward quicker.

I wouldn't consider buying a non-vented canopy ever again - unless it was only going to be in a terminal rig. Because I fly a large canopy - I need it open and flying as fast as possible. The vents allow for this.

Hey Thanks! I have actually already seen this video, it does a good job showing the diff between vented vs non-vented. I actually got to see quite a few examples in person off that bridge this year, that was one of the reasons why I am looking into vented for my next canopy. We were standing at the bottom watching jumpers and you could tell every time which were vented and which were not. Most of the non-vented canopies were just scary to watch! It definitely got my mind going!

The Troll MDV already has vents. (forgive me if I'm wrong!)

I'm not sure I understand the statement, would you mind clarifying/explaining it? Thanks!

MDV is an acronym for Mono Directional Valve, so no forgiveness is necessary.

That's what I thought, which is why base_rigger's statement doesn't seem to make much sense to me.

Reading it back, yes is does not!

What I meant is that if I had a gun pointed at my head given the choice of either fire or a valved canopy, well the only valved canopy I would get at the point in time would be the Troll MDV as its valved design is superior.

And Lonnie please read my "IMO" and "0.02" used in the same sentence. Everyone is entitled to opinions and mine is give me a Mojo or an Ace anytime, no holes for me thanks.

Yes, everyone is entitled to their opinion.

We are also entitled to ask what you are basing that opinion on.

I know Lonnie has a few hundred jumps on both Aces and Blackjacks of the same size and therefore a very valid statistical sample to make conclusions on heading performance of the two types of canopies.

I would like to know how what experience you based your statement on, as I am sure do many others who read this thread.

thanks
sam

Thanks for clarifying

Now Tom, do you see any reason not to "buy once" and stick with a particular canopy? Getting valves on one's first canopy may cost a little more initially, but it'll still be cheaper than a new canopy when the jumper moves to lower or underhung objects.

Am I missing something essential? Some reason that something like a BlackJack may not be appropriate for most objects at all delays?

I agree with you here. I would buy (and did) a vented canopy first time around so that I wouldn´t need to replace it later on.

Because it will wear out?

From my perspective, it's "not worth it" because of the number of canopies I've gone through. My first canopy became vented (I sent it back to Basic Research when the original vtec [no valves] became available, at which time it had around 300 jumps) well into it's (and my) career. I've owned probably close to 20 canopies now, so I don't really see them as something you can reasonably "stick with". In my mind, they're more of a consumable product.

Another thought about "sticking with" your canopy. Does that mean that when you buy your first canopy, you already know exactly what canopy will suit you best, and will never shop around again, look at newer designs, or swap manufacturers?

I think it is likely that a new jumper buying their first canopy will probably hang onto it for a while, probably around a year at least. In that year, they will probably have advanced to the point where they are able to jump lower objects (which is what many jumpers in the US are limited to in their area)

I think it's pretty reasonable for a new jumper to spend the extra money on a vented canopy when they know that they may soon progress to low slider-down strikeable objects.

In addition, I think newer jumpers are less likely to be picky about which canopy they fly because they have less experience flying different designs. While a more experienced jumper may experiment heavily with trying new canopies; buying, trading, selling them; I think most new jumpers are out to purchase a conservative canopy that they can become comfortable with and grow into (edit: for a while).

Just my 0.02

Of course not! It's why I asked. Thanks for clarifying.

Oh great, so you want me to buy a 'scary' canopy. I see how it is..

Come out to the Perrine in March so you can jump with me!!

One good reason to get a vented canopy is the canopy is more likely to stay inflated during a cliff strike

A quote from This thread

That would suggest it will last plenty long to have legitimate use for the vents. My suggestion would be to get the vents. My preference would be a Black Jack of proper size.

Good luck.

It sounds like some of the problems related to back-surge on vented/valved canopies could perhaps be counteracted by some Airlock-esque design features on the nose. In effect dampening the effects of relative wind on DBS settings?

I'd be curious to see what that would do to heading performance, as cell inflation and pressurization would be almost entirely accomplished via the vents (since the nose airlocks might tend to be closed during opening). I would also think it would pressurize much more slowly, cancelling out the effect of the vents.

In my limted jumping career my blackjack 280 has been awesome. About 20 jumps slider up at Kjerag, the openings were nice and 3 or 4 were more than 30 degrees off heading. Perhaps my body position? Slider down on objects 350' and below with manufacturers DBS and the openings have been on heading every time and seem to burn minimal altitude. Canopy response is crisp as soon as I pop the toggles. I have nothing to really compare it to but I have total confidence in my kit. Manufacturers advice on canopy size and loading seems to work well for brake setings. (You'd hope so!) I'd recomend my blackjack to any beginner.

How can you "recomend" a canopy to any "beginner" when you your self have limited experience on it?

This is madness...... you may as well say "I have done this a few times so I think you can do it"


So what? You have confidence in your kit with nothing to compare to it, but you have NO PROBLEM advising newbies on what they should jump.....

another great quote:


Seriously, how can you recommend something you have such limited experience on?

 To play devil's advocate for a second:
Canopy experience numbers are relative. What used to be alot isnt as much these days. In order to be qualified to be a base newbie, that person should have the ability (to think for themself) to qualify to varying degrees the opinions of each person giving recommendations based on how they feel about the recommendor's experience. In other words, who are you or anybody else to decide who can or cannot give recommendations, shouldn't the listener decide for themself who they want to heed and what they want for themselves?

yet another great quote:


Why did you all assume that what Tom posted was the way it happens? Why did none of you question anything he had to say, there were NO QUESTIONS!!!! Just because someone sounds like they know what they are talking about, does not mean they do...... (no disrespect TA, just trying to make a point)....

any BASE jumper that advises to use/do something that they have limited experience in themselves (especially to newbies) is out of order..... thats my thought


sadly the new breed of BASE jumpers (In my opinion) are not the people that make decent choices

Has it occured to you that possibly there were no questions because Tom's explanation made sense to them?

Rather than slacking others for their alledged ignorance, you would do better to invest that energy into proving their ignorance.

E.g., show them what kind of questions they could have asked.

I guess that goes for me to, rather than slacking the slacker, I should be drinking beers while listening to Dire Straits. Come on Mac, it's time you come visit in Vancouver so we can flick something. Stop breaking your head over the dying noobs around you. As Ray Losli said: "...we're just paying back an overdue loan, who cares about a beginner here and there."

Mono Directional? that suggests only one way? that is completly against the design of what the MDV actually is????

I thought MDV is a Multi directional valve and not mono. This is from the fact that the valve closes in various directions.... compared to the "flaps" that most valves have...

According to the advertisement on Page 12 of this months Skydiving, it stands for Mono Directional Valve (P-MDV is explained parenthetically as Penta-Mono Directional Valve).

I believe that mono directional is meant to refer to the fact that air can flow into the canopy through the bottom skin, but not out. Hence, the valve is mono-directional, where the previous Vtec (no covers) system that had dominated the market initially was a bi-directional (air could flow in and out) system.

See also the Morpheus Web Site which gives this explanation (under the Products: Canopies heading):

touché



I will fuck off and get my coat now.....

 
Quote: sadly the new breed of BASE jumpers (In my opinion) are not the people that make decent choices
Hey Mac just a question here but who are you to say that I don't make decent decisions? Just because I'm new to BASE? You don't know much about me or my abilities to make such a statement.
I have been doing a lot or research reading talking with jumpers local and non local jumpers as well as my post here to help me decide what I'm going to get for my new canopy. I chose to get all of the information I could get from many different places to be sure I got the best information I could get and to ensure it is not bias to say jumpers who have jumps on only one canopy. I wanted to make decisions based on many circumstances and view points and not because some jumper with 1000 or 1500 BASE jumps says so. I want to self educate myself. Is that such a bad thing? Should I just do as I'm told and let more experienced jumpers think for me? I agree with tr027here I will and I have decided who's advice am willing to take.
As far as no one questioning Tom's post, I was questioning Toms previous posts on backsurge because from what I read in his old posts didn't make much sense to me and I have never seen it personally during the past year that I have been doing ground crew. He did a great job in explaining where he was coming from in his own eyes. What he said made sense to me and I saw no reason to question him.
Now am I going to make my decision because of one post? No, nor am I going to make my decision based on quifmiester's post. My final decision will be based on my comfort level and knowledge of what is what. I'm not saying I agree that newbees should be giving each other advise I'm certainly going to take comments from more experienced jumpers far more seriously then those from newbees, but I'm not going to discount their post at all I see his advice only as his preference but just because it his preference I'm not going to go out and by myself a blackjack I'm just going to keep in mind there are some who enjoy tat specific canopy. But like I said the people who replied to me giving me concrete explanations on their view point are going to hold more weight when it comes time to pull out my "Credit Card"! Yes sadly I must be another skydiver with a credit card (insert sarcasm warning here).

Thank you again to all who responded to my thread, although the initial thread was not to ask what canopy I should get it was merely to clear up some confusion about new jumpers and dangers of vented canopies it was none the less helpful in many ways.

Hey look at it this way it could be worse I could go out buy all brand new gear top of the line which I could let the factory decide for me what canopy container ect.. to get. Buy myself a FJC and when I'm done take my proclaimed base jumping self (cause I will know everything) up the local A and throw myself off, but don't worry my accuracy will suck too so I will make sure I only do a go and throw so I'm open high enough to set up a great skydiving like right hand pattern and land right on the big X I'm going to painting in the middle of the landing area! Ok so who's with me come on it will be fun. We can even dayblaze it so we get cool video . Hopefully you don't take me to seriously on that last part

remember:
"The individual is always the exception.
'Everybody can't...' but anybody can."
- Richard Bach

i.e. Mac may be correct in general, but wrong in regards to you.

I got one jump on a Unit, best damn canopy I have ever flown, however vented people are right, jumping conventional canopies will kill you and it's just madness, should not be done, you will die, they will open all fucked up and off heading, you will strike things left and right, and you won't be able to free fall anything lower than 150'. All the mojos and aces should be burnt to the ground now, please go and burn those canopies now before you die.

I am hotknifing a the bottom skin of a cruiselight as we speak so I won't die.

Thanks for those helpful words Mac. Perhaps my 'recommendation' was inappropriate. Just trying to share my experiences as a newby jumper on a vented canopy. I qualified my comments by trying to be humble and stating the limited nature of my experience. I think confidence in your kit is very important. If you have are worried about opening with brake settings set too deep and stalling whilst peering over the edge, your mind is not where it should be.

Should I refrain from passing comment until I have a minium level of experience? Jump numbers? You tell me.

Shelley, I'd suggest having a look at poster's details when reviewing the advice given. There are some low key posters who have close to a 1000 jumps and others who are critical, frequently passing comment and have very little practical experience (and they are crap jumpers to boot).

With a notable exceptions there seems to be an inverse relationship between the number of posts a person makes and the number of jumps they have.

Good luck

Standard disclaimer , etc.

Just trying to clarify :

As I understand the phenomenon the prime motivation of the canopy filling is the depression zone created over the canopy because of the vertical speed (relative to air) towards the ground. This depression expands the upperskin, just like inflating a chewing-gum outside-in (inside your mouth) by sucking air from outside. There would be three steps in an ideal canopy inflation :

*POC = air Pressure Over Canopy
PIC = air Pressure Inside Canopy
PUC = air Pressure Under Canopy


1) The canopy (after expansion) is deflated and act as an aerodynamic deccelerator just like said above. The trajectory is vertical. A depression is created over the canopy, thus sucking the upperskin up, making the canopy suck the air from outside. During this phase, POV < PIC < PUC so any vent will let the air inside the canopy fill the cells quicker but the canopy will inflate even if there's no forward motion and no vents.

2) The canopy is inflated, but the bottom skin is curved inside or just flappy. POC < PIC = PUC. The shape is ready to act as a wing as soon as any horizontal component will occur.

3) As the canopy begins to move forward (because of the "deflection" explained by Tom), a minimal amount of air goes dynamically in the cells from the nose (due to the relative wind). POV < PUD < PIC. As the pressure inside the canopy is greater than the pressure under the canopy the bottom skin inflates towards the outside, making a clean inflated shape of each cells.

so pretty much the same conclusions
head wind -> quicker inflation in 3) and quicker transition to flight mode (less forward speed to build before flying)
vents (any) -> really quicker inflation in phase 1) reducing the loss of altitude during this phase. the inflation also begins earlier when the canopy is still expanding
open vents (no valves) -> maybe slowing down last inflation phase in 3) but probably not noticeable


Anyone could try to evaluate the relative duration of each phase? (probably they arent practically clearly separated, mostly because the forward motion depends on when you pop the brakes and how you set them)

any comment or stupid joke appreciated : )


L.

To verify the theory of bottom skin expansion, one could make the following experiments on a windy day:

1. Pinch the nose cells and try to kite the canopy. Does it expand?

2. Fold the overhung tops of the nose cells inside and fix with tape to make the nose "straight", with no overhang. Present the canopy perpendicularly to the wind (so that it passes parallel to nose openings). Does it expand?

I think even without doing the above, it's clear that the canopy will just bunch up and flap like an old rag.