Canopy for turbulence

[dorbie 0]

A faster canopy does not necessarily have the same stall speed as a slower one which has interesting implications for the fast vs slow canopy debate. By the same token any direct increase in the vertical air speed will affect the angle of attack on a faster canopy less. It's a head scratcher.

In a wind shear scenario it's not the size of turbulence that counts but the severity (unless you just punch through something really small) causing the sudden transition in air speed and this is a scenario where the delta between your air speed and the stall speed will be important to you.

You can fly and generate lift in any mass of air regardless of direction, eventually you'll reach equilibrium based on wing & loading, you can still flare in sink, and sinking air cannot sink through solid objects like the ground. You cannot flare when you have a stalled wing.

So in general IMHO it's encountering changes in air that affect your air speed or directly alter your angle of attack significantly are the most dangerous threats, OK that's pretty much the definition of turbulence at any level but I think it helps to visualize the problem in that domain to consider the canopy characteristics you might be interested in. Answering the question as to what's the best canopy under such circumstances seems like a question that's way too complex to give a simple answer. Canopies have performance envelopes not single metrics.

Valved canopies seem like an obvious benefit for mitigating the severity of the outcome if you hit bad turbulence, simply because airfoil integrity isn't compromised as much even when you stall, and lose the pressure maintaining flow into the nose. It doesn't necesarilly give you a smoother ride on an average flight (opinions vary), but that's not the only point of valves. The main safety feature is recovering with a flying wing sooner from a scenario that might otherwise have collapsed an unvalved wing, so don't be too swayed by those who claim a valved canopy never gave them a smoother ride, I don't think you can judge the usefulness of valved wings unless you're in REALLY rough air, and I wouldn't jump in air like that anyway because a valved wing is just as prone to stall as any other IMHO.

Jumping a valved canopy and observing it flies almost the same as unvalved and concluding there is no benefit is a bit like jumping with an AAD and concluding it's no use because it never fired on that jump (thank goodness it didn't). That's an extreme analogy but IMHO the biggest benefit of a valved canopy is in conditions where you shouldn't be jumping or in the not so unlikely event that those conditions find you anyway despite your better judgement.

[hugh 0]

Hi,

I agree about smaller canopies, but not for the reasons you're saying. Usually a collapse occurs when the angle of attack of ther canopy goes to a negative. This can be caused by turbulence. A higher loaded canopy is flying at a higher angle of attack (on the same glide path) so is less likly to encounter a collapse, however when it does collapse its likely to be more dynamic.

I had a couple of questions about airlocks. Bear in mind I'm coming at this with a number of years paragliding experience. Paraglider design experimented with an airlock type system and gave it up for two reasons.

Firstly, when an airlock does collapse, its likely to remain partially inflated potentially causing a more dynamic collaspe due to the additional drag on the collapsed wing section, and also meaning that section of the wing is more likely to get caught in lines.

Secondly, if an airlocked canopy does collapse and re-inflate that reinflation is likely to be in an uncontrolled manner. This 'shock reinflation' effect has caused issues with line and material damage, and problems with a further cascade of collapses due to the manner of re-inflation.

I'm not sure either of these would be an issue on a parachute canopy though?

Cheers

Hugh

[AggieDave 6]

Quote

The faster wing theory works if the turbulence is relatively smaller/ shorter in duration and you have some altitude to work with.

Slow down, I don't think you actually read what I wrote. The comment about the 747 was sarcasm and the entire point of my post is that no matter what kind of canopy your jumping turbulance is bad news, that there are advantages and disadvantages to every kind of wingloading and wing design out there for turbulance and at the end of the day the best way to make it through bad turbulance is to simply not jump in it. Get it?

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

[marinho 0]

Hi there,
Here are a few recommendations for you and for everybody that flies a wing.
1. Do some research and learn as much as you can about turbulence.
2. Also learn about aerodynamics and its concepts.
3. Watch Scott Miller canopy control classes.
Once you have all this basic information, it'll be much easier to understand that no matter which kind of canopy you have, you are under control to decide when you can be in the sky.
You are the pilot! Be smart and don't get trapped on wheather, but if you get in any problems, make decisions as higher as you can. Land away from fixed objects and fight until your canopy is on the ground.
Flying canopies are negleted for many reasons, but you are the one that can change that for yourself!
It's supposed to be fun, right?
Be safe and have fun,
Gus Marinho
Rigging Solutions

Gus Marinho

[riddler 0]

Quote

Airlocked canopies don't offer any protection whatsoever against the dangers of jumping in turbulent conditions.

I don't believe the airlocked canopy offers immunity from turbulence, but I do think it offers some advantages. Specifically, it doesn't drop as much in turbulence. It may only save you a few feet, or it may save a few hundred in a total collapse. Even a few feet of saved altitude makes a difference on landing. I do know one former jumper that is lucky to be alive after a turbulent landing and the lack of a PLF shattered his spine.

Trapped on the surface of a sphere. XKCD

[dorbie 0]

Good point, I too am a paraglider pilot, I think the dynamics are different because the wings are very different, particularly the aspect ratios. A skydiving canopy will pretty quickly recover from a collapse with no risk of a cravat, but altitude loss is the key concern in a low altitude scenario. There's a real risk of line twists and possible unrecoverable spin as a result so you can see that it's pretty different. The pendulum period is shorter and you don't need the same surge control to stay under your wing which has implications for inducing frontals.

I'm pretty sure a skydiving canopy can handle shock reinflation, but either way shock reinflation in a rare collapse event (unlike paragliders which collapse regularly in flight), is much better than a shock impact with the ground
I could speculate some more but don't really have objective information to base it on. There's no equivalent of DHV testing for parachutes, reinflation after a collapse and associated tendency to turn just isn't measured AFAIK.

[dorbie 0]

Quote

Quote

Airlocked canopies don't offer any protection whatsoever against the dangers of jumping in turbulent conditions.

I don't believe the airlocked canopy offers immunity from turbulence, but I do think it offers some advantages.

Yea, I think people need to be less absolutist in the absence of data. There's a difference between a canopy's tendency to stall in flight and it's potential to defalte. When you draw that distinction I think you get more agreement at least over where valves don't help so much and where the advantages if any start to kick in.

[isaiah85 0]

Turbulence is pretty complex, because there are more than one kind of turbulence, I would have to write a book here on the subject. So, I'm going to keep it pretty simple and only talk about the turbulence that we feel when we get to close to objects disturbing the wind on landing.

First off the easiest way to view turbulence is looking at water, try to picture air as if it was a fluid. Picture a river, now picture a fast moving river with a big rock in the middle. The water doesn't just happily flow around it and continue on, it's all stirred up. This is what the air looks like on a windy day in a field with a tree in it. Now picture a windy day with a bunch of trees on one end a building somewhere in there and you have most DZ's. On a really windy day the air looks more like white water rapids. I don't care what kind of boat your in you are going to be affected by the turbulence.

Now the topic of airlocks of not. Airlocks defiantly feel different in turbulence, are they safer....? The way I always explain airlock in turbulence vs. a open cell canopy is, an airlocked canopy is like riding a metal boat down a white water river and a open cell canopy is like riding in a rubber raft. The airlocked canopy is going to feel more ridged, but does it handle the turbulence better, I don't think so. The open cell canopy is going to appear to be breathing more but is it less safe in turbulence, I don't think so. What I do know is, you don't see too many white water enthusiasts taking on the river with aluminum boats, even though they are more ridged.

The best thing to do with turbulence is educate yourself, know what causes it and where you can expect it. Then avoid jumping in situations you don't want to be in.

My personal opinion, I agree with Breezy :-).

Later,
isaiah

[phoenixlpr 0]

Quote

I landed out on the weekend under a huge ass student canopy and had a pretty hard landing.

What is a pretty hard landing for you?

[kallend 1,625]

Quote

Quote

>The speed is also directly related to lift . . .

Nope. If a skydiver has a 190lb exit weight, their canopy generates 190lbs of lift over the course of their canopy flight, whether it's a 3:1 elliptical or a Manta.

I do not claim to have the knowledge to argue any skydiving related point with you, but this comment is in complete contrast to any thing I have read about wings, weather it be a ram-air wing or an airplane wing.

Lift is increased by the square of the speed. That is pretty much directly I thought

Gravity pulls an object towards the ground at 32ft\s\s with no consideration to drag/air resistance until said object reaches terminal velocity which is dertermined by density and air resistance. Now if a skydiver is falling feet first with a terminal velocity of about 180mi/hour then consider the drag of a parachute which would slow that terminal down to about (hell I dont know) lets say 40mi/hr then consider the lift generated by the air foil of the wing that causes a low pressure above the wing and high below the wing which would slow terminal down to about 20mi/hr. This lift would be acting on system during the intire canopy ride and total lift of the ride would have to be dependant apon the length of the ride since the lift is constant during the ride, that is with out considering change in wind and pressure ofcourse.(my explaination of lift with out walking to the bookshelf to get the physics book)

Again, I have no idea as to the answer to this thread as I do not have that kind of experience, nor do I offer my explanation of lift for any other reason than to get feed back from the more knowledeable

You're both right. In steady, unaccelerated flight the canopy provides exactly the lift that the load requires. Compare 2 canopies, one (big) flying at 10kt relative to the air, and one (small) at 40kt relative to the air. Both support the same load, say 200 pounds, which is therefore their lift.

Now you encounter a sudden increase in headwind of 5kts. The canopy cannot instantly adjust its airspeed (Newton). So the canopies are now flying, at least temporarily, at 15kt and 45kt.

The lift of the slower canopy increases to (15/10)^2 *200 = 450 pounds, a huge change that will jolt (accelerate) the skydiver a whole lot. The lift of the faster canopy increases to (45/40)^2 *200 pounds = 253 pounds, resulting in a much smaller jolt (acceleration) to the jumper.

Same applies to a sudden loss of airspeed - the % loss in lift will be smaller for the faster canopy.

Of course, the faster canopy will encounter such gusts more frequently.

...

The only sure way to survive a canopy collision is not to have one.

[kelpdiver 2]

Quote

Now the topic of airlocks of not. Airlocks defiantly feel different in turbulence, are they safer....? The way I always explain airlock in turbulence vs. a open cell canopy is, an airlocked canopy is like riding a metal boat down a white water river and a open cell canopy is like riding in a rubber raft. The airlocked canopy is going to feel more ridged, but does it handle the turbulence better, I don't think so. The open cell canopy is going to appear to be breathing more but is it less safe in turbulence, I don't think so. What I do know is, you don't see too many white water enthusiasts taking on the river with aluminum boats, even though they are more ridged.

I'm struggling a bit to see the relevence here. Airlocks are about avoiding canopy collapse. Rubber boats are about not bashing the occupants when it hits a rock. There may be a point in here, but I'm not getting past this mismatch.

[billvon 2,400]

>It wouldn't if the 747 had a more rigid wing or went faster, right?

Actually, it wouldn't if the 747 had a more rigid wing or went _slower_. Aircraft in turbulence slow to something called 'structural cruise' when they encounter turbulence; this helps ensure that the loads on the wings will not exceed design limits. If turbulence is severe they may slow even further to design manuevering speed. From an aviation website:

----------------
Va---Design Maneuvering Speed is lowest speed where full abrupt movement of the controls at gross weight will produce lift not exceeding the design load limit.

Vno is shown where the orange and green lines of the airspeed indicator meets. It is called the structural cruise speed at which speeds must be below to avoid damage in turbulence.

Vc is the speed range of the green arc or design cruising speed
It is used in turbulence that is different than Va; it is called structural cruise speed or Vno. Unlike Va this is shown on the airspeed indicator as the meeting point of the orange (yellow) and green. This is a speed below cruise that is recommended for rough air penetration. Vno does not offer the structural assurances offered by Va. At Vno the aircraft, as certified, should not be structurally damaged by a 35 knot vertical gust. This is not the same protection given by Va.
---------------

>Its like potholes in the road . . . .

It's really nothing like potholes in the road. Turbulence is one of the many places that our land-based intuition fails us.

[korvus 0]

Quote

Now the topic of airlocks of not. Airlocks defiantly feel different in turbulence, are they safer....? The way I always explain airlock in turbulence vs. a open cell canopy is, an airlocked canopy is like riding a metal boat down a white water river and a open cell canopy is like riding in a rubber raft. The airlocked canopy is going to feel more ridged, but does it handle the turbulence better, I don't think so. The open cell canopy is going to appear to be breathing more but is it less safe in turbulence, I don't think so. What I do know is, you don't see too many white water enthusiasts taking on the river with aluminum boats, even though they are more ridged.

Not a bad analogy, but flying and floating have some significantly different properties. The main factor that keeps a raft afloat is the relative density of (raft + passengers) versus water. It would be a better analogy if we were talking about flying hot air balloons.

I don't have any definite answers here because there are too many factors interacting, but an open cell canopy "breathing" is changing size (and shape). One way to think of it is that your wing loading is dynamically changing. Lift = [some coefficient] * density * velocity^2 * wing area. Shrink the wing and you lose lift. For a stalled canopy, the rate at which you fall is presumably relative to the amount of fabric area above you, which would also be decreasing if the canopy was doing an accordion impression. Flying or falling, it would seem to make sense that a wing that stays rigid makes you less likely to hit the ground hard. Of course, in turbulence, the density of the air is changing as well, so that messes with the equation. But I'd also think a rigid wing may maintain speed better, which would keep lift up.

Even if we aren't talking about hitting the ground, more lift means more tension on your lines, which helps you stay in control. I think most of us would want airlocks if we were flying in air likely to collapse a canopy. I think in other cases, you may not notice these effects, but if you do, I'd think it would be in favor of an airlocked wing relative to the same wing without airlocks.

[billvon 2,400]

>Lift is increased by the square of the speed. That is pretty much
> directly I thought.

Yes. And any stable aircraft or parachute will accelerate or decelerate to its "trim" speed, which is the speed it wants to fly at. In aircraft it's adjustable, in parachutes it's generally not unless you fly in brakes or something. And at that trim speed, the parachute is producing _exactly_ as much lift as there is weight. In other words, all the forces - lift, drag, weight - balance out perfectly. It's easy to see why this is; if that wasn't the case, we'd start to accelerate towards the ground (or straight up!) and would start going faster and faster. Unstable aircraft do this, but stable aircraft (and parachutes) always tweak themselves until all forces balance exactly.

That's why all canopies fly at different speeds but produce the same amount of lift (equal to exit weight.)

Now, you may be referring to the fact that some canopies have more lift _available_ when you flare, and that's definitely true. Smaller canopies go faster, and thus have more energy in their system. That can be translated into lift to either pop you up or give you a long surf on landing. Slower canopies are, well, slower, and thus have less energy to turn into lift when you land.

>consider the drag of a parachute which would slow that terminal
>down to about (hell I dont know) lets say 40mi/hr then consider the
> lift generated by the air foil of the wing that causes a low pressure
> above the wing and high below the wing which would slow terminal
> down to about 20mi/hr.

Well, you're talking about drag, not lift. An airplane that pulls out of a dive is using lift to alter its trajectory; it keeps most of the speed that it gained during the dive. Parachutes do the opposite. They open in a very high drag state, stop you, _then_ start flying.

[mnischalke 0]

Quote

The way I always explain airlock in turbulence vs. a open cell canopy is, an airlocked canopy is like riding a metal boat down a white water river and a open cell canopy is like riding in a rubber raft. The airlocked canopy is going to feel more ridged, but does it handle the turbulence better, I don't think so. The open cell canopy is going to appear to be breathing more but is it less safe in turbulence, I don't think so. What I do know is, you don't see too many white water enthusiasts taking on the river with aluminum boats, even though they are more ridged.

That analogy is completely irrelevant to this subject, unless you made big open holes in your rubber raft. Aluminum has been used extensively for canoes btw.

A better whitewater analogy might be a kayak. I use a neoprene sprayskirt on mine. It locks the air in. Hmmmmm. Ya know, I can't imagine taking on anything bigger than Class I--much less rolling--without one.

Let's do this: Let's take a Lotus 170 and a Sabre2 170 out and fly side by side. We can fly them backwards and see who's canopy deflates, who's retain's air, and who's recovers to stable forward flight more gently. I'll drop my money on the airlocked canopy for the latter two.

mike

Girls only want boyfriends who have great skills--You know, like nunchuk skills, bow-hunting skills, computer-hacking skills.

[alan 1]

Quote

The way I always explain airlock in turbulence vs. a open cell canopy is, an airlocked canopy is like riding a metal boat down a white water river and a open cell canopy is like riding in a rubber raft.

That analogy is so poor it begs me to question the validity of anything you have posted. That is a pitty because I thought you were doing pretty well with the rock in the water part.

An airlocked canopy is nothing at all like a metal boat in comparison to a rubber raft. A much better comparison would have been to a compartmentalized raft.

Quote

The best thing to do with turbulence is educate yourself, know what causes it and where you can expect it. Then avoid jumping in situations you don't want to be in.

Ahhh.....you have won me over again. Now I wonder if you are a parrot that got lucky or a thinker with a lapse in judgement.

alan

[alan 1]

Quote

im just a very unknowledgable newbie but im wondering what canopies are more resistant to turbulence?

The canopies that are on the ground and safely stored away for a better day. If you sift through the plethora of pointless crap that is posted in this thread, you will find a few genuine pearls. Educate yourself, understand the basic theory of flight and aerodynamics. You will then know how to avoid bad situations and on the occassions when you are simply thrust into them, you will better understand how to correctly assess and respond to a given situation.

alan

[alan 1]

Quote

A couple weeks ago I was watching people land in bumpy/choppy/gusty 30+mph winds.

"people" ??? That is being rather kind. At my DZ they are commonly referred to as fools, newbies, or any combination thereof.

alan

[alan 1]

Quote

Actually, it wouldn't if the 747 had a more rigid wing or went _slower_. Aircraft in turbulence slow to something called 'structural cruise' when they encounter turbulence; this helps ensure that the loads on the wings will not exceed design limits. If turbulence is severe they may slow even further to design manuevering speed. From an aviation website:

Good stuff. Does that same site offer any insights as to the proper procedure for flying in turbulent or gusty conditions near the ground in preparation to land, say like on final approach? Doesn't it recommend going _faster_ than the normal approach speed?

alan

[udder 0]

Well hard landing is relative. All I can say is that it hurt like fuck standing that thing up, Should have PLFed... So far in this thread I've heard alot about the dynamics of turbulence in extreme canopy collapses in really bad conditions. hope i'll never get that gung ho that i jump in that shit but in refernce to airlocks I think they may be the best option for where I jump. Consider there are dust devils and what not. On the other hand I dont have $2000 to spend on a new canopy and I dont see tons for sale. Billvon you said some canopies handle turbulence better? What canopies are these? Are 7 cells an advantage?(spectre, tri , omega?)

"In one way or the other, I'm a bad brother. Word to the motherf**ker." Eazy-E

[phoenixlpr 0]

I`d rather not jump in those condition I don't feel comfortable.

[crazydiver 0]

>The speed is also directly related to lift . . .

Nope. If a skydiver has a 190lb exit weight, their canopy generates 190lbs of lift over the course of their canopy flight, whether it's a 3:1 elliptical or a Manta.

[pilotdave 0]

Lift is related to speed (squared). But thinking backwards confuses people. They think a smaller canopy has more lift because it flies faster than a larger canopy (billvon responded to "the speed is also directly related to lift...").

Canopies want to find an equilibrium. Smaller canopies do fly faster in order to produce the same lift as a bigger canopy.

Forgetting the difference between lift and drag and just taking both to be the "upward" force created by a canopy, it's easy to see that a tandem drogue creates the same "lift" as a tandem main. When the rate of descent is constant (terminal velocity), both the drogue, in freefall, and the main, under canopy, are pulling up at exactly the weight of the jumpers. They just happen to be going very different vertical speeds to achieve the same lift.

Swooping is a dynamic situation. Lift does increase when the swooper comes out of a dive. When a canopy accelerates upward (ie levels off from a dive or actually goes up), lift no longer equals weight.

Dave

[billvon 2,400]

>Then why can a parachute while swooping or one that flies faster gain
> more altitude when coming into brakes/flaring quickly than a larger
> slower parachute?

Because it has more energy to turn into lift. Energy = 1/2MV^2, which means that if you double your speed, you have four times the energy. Small canopies have to fly faster to generate enough lift to keep you in the air, since all parachutes have to generate enough lift/drag to exactly balance your weight. With small canopies, you fly faster, so you have more energy to convert into lift at the end.

[crazydiver 0]

Quote

With small canopies, you fly faster, so you have more energy to convert into lift at the end.

So lift is created by speed.

Cheers,
Travis