Airlocks & Turb.

[ramon 0]

I'm still skeptical that is all.

In time maybe... my vX is pretty unforgiving the way it is.

I heard recovery arc is shortened also

"Revolution is an abrupt change in the form of misgovernment.", Ambrose Bierce.

[bobsoutar 0]

Works for me too although I try to glide in a touch higher just in case I do get bumped down a couple of feet. Probably worth mentioning that we are still talking about x-braced and tri-braced canopies.

[alan 1]

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The benefit of using a bit of brake in turbulence is to put your angle of attack in the middle of the range that is acceptable for your canopy.

Presumably we are talking about turbulence at low altitudes, such as during landing, at least my post indicated such. At higher altitudesyou can do what ever you choose and bounce around a little and go on. Also, I was specific about todays designs, which except for s few specialty canopies, are designed to be flown with front risers as a significant source of control input. Front or rear riser input will have the effect of changing the trim angle and change the angle of attack as a result. Brakes will slow your forward speed, reducing pressurization and distort the airfoil, making it less efficient and more prone to abrupt changes in altitude as a result of turbulence. Increasing the angle of attack with brakes won't necessarily put it closer to the middle of the accpetable range of the canopy, it may actually put it nearer the critical angle for a stall. You have to know your canopy.

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With a canopy designed to keep flying when you pull hard on both front risers you may not need any brakes, but if the leading edge tends to tuck under when you do this you should really consider applying some brakes in strong turbulence.

I think most of the recent canopy designs that are most commonly in use today are designed for front riser use and are not prone to collapsing, as the older designs were. Especially the 7 cells. As I said in my previous post, there may have been some merrit to the old advice of brakes and some of those canopies are certainly still flying today.

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Turbulence is really good at creating large shifts in the angle of attack and if you happen to already be at one of the extremes things will get interesting real fast...

Yes it is, but during most landing approaches we are not at or near the extremes of the canopy's design limits. An exception would be a high performance landing approach.....which most of us know better than to attempt in turbulent conditions. A few of us exercise poor judgement and we generally read about them.

alan

[alan 1]

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Flying in 1/4 to 1/2 brakes does three things. It reduces the forward speed of the canopy, which reduces pressurization.

Reduced pressurization results in amore distorted and much less efficient canopy. One that is much more prone to significant reaction to turbulence. Up high, no big deal, close to the ground and you might eat some of it.

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It puts the canopy in a better position to recover if it does collapse.

It also puts the canopy in a better position to collapse in the first place. So again, altitude should affect the decision here.

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It reduces your speed so that if you do have a collapse near the ground, your impact speed is less.

That is true and all very nice but it also increases the likelyhood of impact with the ground. So, we can choose to reduce our energy and minimize injuries or we can choose to conserve energy and avoid the injury in the first place.

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Larger canopies can be more prone to turbulence than smaller canopies, yet people tend to get injured far more often under small canopies in turbulence. This is because, when you're landing a 2:1 canopy, everything has to work perfectly. A 2 foot dip at 30mph and you have two broken legs, whereas the same dip on a Triathalon 190 will just get you a bit dusty.

Agreed. But, I think the chances of the two foot dip are higher under the Tri. in brakes than the canopy at 2:1 in full flight. BTW, what would be the assumed wing loading of the Tri? 1:1, 1.2:1, 1.4:1? It does matter.

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Another way to look at this is that, if you can fly your approach a little more slowly (i.e. in slight brakes) the odds of bad turbulence causing you serious injury may be reduced.

Another way to look at it is any time you are moving slower, you have less energy to transfer into injury. But, and this is a big but, I still maintain that with the majority of todays newer designs, you are increasing the likelyhood of turbulkence dropping you into the ground by flying in brakes on landing approach. A light aircraft pilot, say a C152 or C172, does not add flaps and reduce airspeed when making a landing approach. The common practice is to add airspeed (1/2 the gust) and use no flaps. Why is that so hard to understand and apply to todays canopies. Of course we could argue that if we reduced airspeed and used flaps, the crash would be less severe. Most pilots choose to follow the flight manual and avoid the crash all together.

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Nothing can keep turbulence from collapsing your canopy if it's strong enough.

Absolutely agreed.

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Flying at full speed through turbulence may help keep it inflated if the turbulence is weak enough

True, but I'll add that flying at full speed will keep it inflated in turbulence that would collapse it at slower speeds in brakes.

flying in 1/4 to 1/2 brakes may help you survive a bad incidence of turbulence. ***

I think it will reduce the amount of energy with which you might impact the ground, but I also think you are more likely to impact the gound.

alan

[alan 1]

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I heard recovery arc is shortened also

Yes, in my opinion it is. But you know that it has a very long recovery arc to begin with, so it is still very long compared to other canopies.

alan

[alan 1]

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Works for me too although I try to glide in a touch higher just in case I do get bumped down a couple of feet. Probably worth mentioning that we are still talking about x-braced and tri-braced canopies

Yes, good point. I do come in (surf) a little higher as well and yes we are talking primarily about x-braced canopies although I don't exclude canopies such as the Crossfire, Stiletto, Vengeance and such.

alan

[alan 1]

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The pressure in the cells isn't the issue here, the angle of attack is.

They kinda go hand in hand. Increase the angle of attack too much or decrease it too much and the stagnation point moves above or below the nose inlet. Either way, it has a venturi effect and will depressurize the canopy. Any wing that exceeds its' critical angle of attack will stall and a stall should not be confused with a collapse.

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but a perfectly airlocked canopy in the same situation would simply stop generating lift, surge forward and probably slam you into the ground even harder than the collapsed canopy.

Yes and inducing a secondary stall by stabbing the brakes in a panicked attempt to recover from a stall caused by turbulence can cause you to impact with less energy than just letting the stalled canopy surge and recover. But, a smooth controlled application after the surge may allow the canopy to recover before impact and therby no injury results. None is better than reduced. We have to bear in mind that some situatiuons are simply not recoverable. So yes, letting the canopy surge and applying smooth, aggressive brakes won't always save you and you may hit the ground with more energy than if you go to full brakes and just "parachute" it in. But, letting the canopy fly or even using a little careful front riser may let you avoid the entire situation. I would generally choose prevention over cure or treatment.

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By applying some brakes, you indeed slow down which makes you angle of attack more sensitive to a given variation in the relative wind, but you also increase you angle of attack (on a typical canopy that is), taking it farther away from the extreme at which you canopy will stop flying, and this is I think by far the overriding factor on most canopies.

I believe that on most modern canopies, increasing the angle of attack does not take it farther away from the angle at which it stops flying, but actually moves it closer and makes it more susceptable to turbulence induced stalls. I think this is the point at which we fundamentally are not in agreement.

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As a practical hint if you can apply a bit of brake and you don't feel you significantly slowed down, but you fell your glide ratio increased significantly, your angle of attack probably just increased as well. At some point the slowing down becomes obvious and the glide ratio starts degrading, this is when you are getting closer to the other end of the spectrum, your angle of attack is high and any turbulence may suddenly increase it enough to stall the canopy.

You can get hints at what your angle of attack is doing by watching the top front of you canopy's leading edge, but this is subtle and varies from canopy to canopy.

Sounds like good advice and leads me to believe you are approaching this more from an at altitude point of view rather than on landing approach. You can also "see" your gide ratio improve as well as feel it. I use the old "accuracy trick". Find the point in front of you that doesn't appear to move as you approach it, then as you apply brakes it appears to sink as you approach it. You are improving your glide ratio as long as that happens. As soon as it appears to sink, you have gone into too much brake and the glide starts to drop off.

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Disclaimer: I used to fly paragliders, not canopies designed to keep flying even if you hang your whole weight on both front risers. Those canopies may fly at a safely high angle of attack even without brakes; but be sure of one thing, if turbulence collapses it, that is because the change in relative wind moved the angle the attack out of the flying range, and you may have prevented it by flying differently to start with.

Agreed and as a side point, I have never flown a paraglider, just a wide variety of canopies.

alan

[franck102 0]

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A light aircraft pilot, say a C152 or C172, does not add flaps and reduce airspeed when making a landing approach. The common practice is to add airspeed (1/2 the gust) and use no flaps. Why is that so hard to understand and apply to todays canopies.

Because they don't have engines maybe? Thrust radically changes the aerodynamic picture.
On a given canopy speed and angle of attack are directly related (the relationship is a property of the airfoil). To fly faster under a given canopy you must reduce the angle of attack.
That being said I agree with you that it all depends on the canopy - namely on where the "no brakes" angle of attack is located with respect to the extremes, "stalling" AOA and "no meaningful lift" AOA.
Franck

[billvon 2,989]

>Reduced pressurization results in amore distorted and much less
>efficient canopy.

Agreed.

>One that is much more prone to significant reaction to turbulence.

This does not follow. Efficient airfoils react more violently to stalls; recall the function of turbulators on an aircraft wing.

>That is true and all very nice but it also increases the likelyhood of
>impact with the ground. So, we can choose to reduce our energy and
> minimize injuries or we can choose to conserve energy and avoid
> the injury in the first place.

If by "conserving energy" you mean to hold as much enegy in your body as possible before landing, that simply makes no sense. Your landing is not a ballistic event; your energy must be dissipated, not conserved, to land safely. I agree that you should maintain enough airspeed to flare safely, whatever that airspeed on your canopy is.

Flying in 1/4 to 1/2 brakes slows you. It makes you slightly more susceptible to turbulence, due to reduction of internal pressure. It makes you slightly less susceptible to turbulence to begin with, since you are moving through the area of changing winds more slowly. It's been my observation that these two effects pretty much cancel out. It reduces your speed so a collapse, if it does happen, will not injure you as badly. It puts your canopy in a position so that it will recover much more quickly if it is affected by turbulence.

> . . .say a C152 or C172, does not add flaps and reduce airspeed
> when making a landing approach. The common practice is to add
> airspeed (1/2 the gust) and use no flaps. Why is that so hard to
> understand and apply to todays canopies.

If parachutes were as rigid as Cessna wings I would agree. Unfortunately, they are not, and the pressure inside them gives them a structural strength many orders of magnitude less than a 152's wing.

OTOH, if Cessnas regularly crashed when their wings collapsed on final, you would see pilots reducing their airspeed to reduce the speed at which they penetrate turbulence (and to reduce structural loads as a result of that turbulence.) Since Cessna wings are stronger than that, they only have to reduce speed (to structural cruise) at high speeds when they encounter turbulence.

>True, but I'll add that flying at full speed will keep it inflated in
>turbulence that would collapse it at slower speeds in brakes.

If the only effect were the greater stability that pressurization affords I would agree. However, turbulence is effectively a change in wind direction in a short time. If you go faster, the changes happen faster, and the canopy will experience more turbulence.

[franck102 0]

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It makes you slightly more susceptible to turbulence, due to reduction of internal pressure. It makes you slightly less susceptible to turbulence to begin with, since you are moving through the area of changing winds more slowly.

Bill, flying slower means the same gust will have more of an effect on the speed and direction of your relative wind, so it will definitely make you more sensitive to turbulence.
And a reduced internal pressure (most of which is actually suction lift pulling the top skin up) doesn't make you more sensitive to turbulence (neglecting the marginal benefit of a slightly degraded airfoil section). It means that you canopy may react differently (collapse instead of surge forward) when the angle of attack reaches an extreme, but it won't change the fact that the airfoil just stopped generating lift (although it will affect the recovery as mentioned earlier).
In other terms, as I mentioned earlier, you don't fall from the sky because your canopy collapses. You fall from the sky because the relative wind became such that your canopy stopped generating lift.
Franck

[billvon 2,989]

>Bill, flying slower means the same gust will have more of an effect
> on the speed and direction of your relative wind, so it will definitely
> make you more sensitive to turbulence.

Actually, it will make the turbulence seem less severe for the reasons outlined above. Rather than repeat those reasons I'll quote from an excellent book on micrometeorology by Dennis Pagen, intended for paraglider, hangglider and sailplane pilots:

------------------------
Turbulence creates two problems for aviators, loss of control and stress on the aircraft. Strong turbulence can nose you over or lift a wing wildly or even stall you by rapidly changing your angle of attack. When this happens close to the ground it is disconcerting at best. Such turbulence can also produce gust loads that can break up or fold certain types of aircraft. To combat the first problem we need to speed up for quicker control. To combat the second problem we need to slow down so as to reduce the suddenness of the gusts.
----------------------

So if your problem is that you do not have control over the attitude of the parachute, speeding up is the answer. If collapse (folding) of the wing is the worry, then slowing down is the answer. I don't know of any skydiver who has been turned downwind uncontrollably by turbulence, but I know several who have been injured by canopy collapse. Given that, I will stand by my advice that some amount of brakes (say, 1/4 to 1/2) can increase survivability in turbulence.

>In other terms, as I mentioned earlier, you don't fall from the sky
> because your canopy collapses. You fall from the sky because the
> relative wind became such that your canopy stopped generating lift.

From my own observations, most injuries are the result of both occurring - a loss of lift following a canopy collapse.

[franck102 0]

> ------------------------
> Turbulence creates two problems for aviators, loss of control and stress
> on the aircraft. Strong turbulence can nose you over or lift a wing wildly
> or even stall you by rapidly changing your angle of attack. When this
> happens close to the ground it is disconcerting at best. Such turbulence
> can also produce gust loads that can break up or fold certain types of
> aircraft. To combat the first problem we need to speed up for quicker
> control. To combat the second problem we need to slow down so as to
> reduce the suddenness of the gusts.
>----------------------
>
> So if your problem is that you do not have control over the attitude
> of the parachute, speeding up is the answer. If collapse (folding) of
> the wing is the worry, then slowing down is the answer.
I maintain that a non-airlocked canopy collapses because of "the first problem" (nosing you over or stalling, none of which a canopy can't do without collapsing), not because of the second one.
Common sense corroborates this, if you were flying at 200 mph that 5mph gust would be a non-event. If you have flown in turbulence a lot you also the the feeling is that your canopy collapses because of one major event, not because you hit two events in too quick a succession. Basically you are flying stable and the next thing you know you have a mess over your head.
> I don't know of any skydiver who has been turned downwind
> uncontrollably by turbulence,
I have, under an airlocked canopy, in a fraction of a second. I have also seen it surge forward far enough to be able to see the landing above the canopy. A non airlocked doesn't do that because it collapses first - same cause, different effects...
I guess we'll just have to agree to disagree on this one -)
Franck

[franck102 0]

Here are a few relevant articles & pilot manuals:


To reiterate, maintaining a POSITIVE ANGLE OF ATTACK is what keeps the wing inflated overhead.
"
[url "http://www.shgc.demon.co.uk/b_more2.htm">http://www.shgc.demon.co.uk/b_more2.htm

"So what makes the glider collapse? Simply, too low an angle of attack. The Angle of Attack is the angle between the Apparent Airflow and the Chord Line of the wing. Provided we always have a positive angle of attack, (apparent wind hitting the underneath of the chord line) the wing will generate some lift and keep tension on the lines. If the apparent wind is ever allowed to make an angle above the chord line then the wing will try to generate lift downwards (very briefly), unload the lines and promptly collapse."

http://www.swing.de/_eng/_downloads/mistral2_gb.pdf"

"Flying in TurbulenceWhen flying in turbulent conditions you should apply slight brake pressure to both sides - around 20 % - to maintain a good angle of attack, thus reducing any tendency to collapse."

"You need to practice using the foot-operated speed bar. To be able to control your glider with your feet as well as with your hands is especially important when flying in turbulence. When changing from lift to sink it is essential to take your feet off the accelerator in order to reduce the risk of collapses
Remember: Flying accelerated the canopy has a lower angle of attack this means a collapse may occur much easier !"

[url "http://www.solsports.com.br/downloads/manuais/PDF/impulse%20ingles.pdf"[/url]

"Thermaling and soaring :
In turbulent conditions the canopy should be flown with a small amount of brake applied. This improves stability by increasing the angle of attack of the canopy." "The angle of attack is lowered with the increase in speed and the canopy may tuck easier than in normal flight."

Franck

[billvon 2,989]

>You have no doubt heard of the COLLAPSE. There have been many
> articles written about it's causes etc. Mostly these have talked about
> pressure inside the wing. This description of collapses is TOTALLY
> WRONG.

This is my view as well, but it seems to be an unpopular one in skydiving. Most jumpers see internal pressure as the primary (and indeed sometimes the only) thing between them and a collapse. However, imagine doing CRW and pushing down on the front corner of a canopy with even 30 pounds of force - the corner WILL fold under, no matter what your internal pressure is. Turbulence can exert a lot more force than that. If the turbulence acts to increase your AOA, then you're in good shape. Your lines can withstand literally thousands of pound of force trying to lift the wing up. If the turbulence is such that it causes air to impinge on the top of the wing (i.e. AOA goes negative) then all the internal pressure in the world won't keep the canopy inflated.

Of course, under marginal conditions (i.e. a zero AOA) internal pressure can help _a_little_, which is one reason airlocked canopies seem a bit more stable. (The other reason is that they're effectively cross-braced.)

>Flying in TurbulenceWhen flying in turbulent conditions you should
> apply slight brake pressure to both sides - around 20 % - to
> maintain a good angle of attack, thus reducing any tendency to
> collapse.

This is my advice as well.

>Flying accelerated the canopy has a lower angle of attack this means
> a collapse may occur much easier !

Fortunately (or unfortunately) skydiving canopies do not have speedbars. All they have are front risers, which are not nearly as efficient. Still, it's good advice to not use front risers in turbulence as well, but I think most skydivers understand that.

[alan 1]

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Because they don't have engines maybe? Thrust radically changes the aerodynamic picture.

Really? How so? Are you implying that a C172 pilot with his engine out would land with flaps down and a reduced airspeed in turbulence as compared to what he would do in calm conditions? Engine or no, that pilot is not going to add flaps and reduce his airspeed when landing in turbulence.

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On a given canopy speed and angle of attack are directly related (the relationship is a property of the airfoil). To fly faster under a given canopy you must reduce the angle of attack.

That being said I agree with you that it all depends on the canopy - namely on where the "no brakes" angle of attack is located with respect to the extremes, "stalling" AOA and "no meaningful lift" AOA.

Franck, I think we are on the same page. That is pretty much a summary of what I said in the original post about brakes being bad advice on todays newer canopy designs and expanded on in my subsequent posts.

alan

[alan 1]

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>Reduced pressurization results in amore distorted and much less
>efficient canopy.

Agreed.

>One that is much more prone to significant reaction to turbulence.

This does not follow. Efficient airfoils react more violently to stalls; recall the function of turbulators on an aircraft wing.

Odd, a less efficient airfoil would stall at a higher airspeed with less AOA. Turbulence will more easily cause that threshold to be crossed on an airfoil flying closer to it, ie. a canopy in brakes or a C172 in flaps at a reduced airspeed. Additionally, the discussion was not about the realtive violence of the stall, but the the occurance of the stall.

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If by "conserving energy" you mean to hold as much enegy in your body as possible before landing, that simply makes no sense.

I don't know what you mean by holding as much energy in your body as possible before landing. I meant to not dissipate it in turbulence during the landing approach by prematurely using the brakes to buffer out the effects of the turbulence. I meant to use the mass of the canopy combined with the jumper and the speed of that mass to counter effect the energy imposed on the system by turbulence. Once the turbulence has been dealt with, then dissipate that energy as we normally would with the flare technique that works best for the particular jumper/canopy.

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I agree that you should maintain enough airspeed to flare safely, whatever that airspeed on your canopy is.

That has kinda been my point all along. I don't think that the majority of the newer canopies at the wing loadings that seem to be popular with todays pilots can be safely flared in 1/4 or 1/2 brakes in turbulent conditions. Hell, for that matter, most of the pilots I see can't land well in good conditions in 1/2 brakes.

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Flying in 1/4 to 1/2 brakes slows you. It makes you slightly more susceptible to turbulence, due to reduction of internal pressure.

Definitely slows you. I think it makes you greatly more susceptable to turbulence, but not just because of reduced internal pressure of the canopy. An increased AOA and external pressure changes can effect a stall and/or a collapse. Applying brakes squeezes air out and allows relatively smaller forces outside the canopy to exaggerate the effect.

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It makes you slightly less susceptible to turbulence to begin with, since you are moving through the area of changing winds more slowly.

It's not just about how fast you are going. It is a combination of the design parameters of the particular canopy, AOA, internal pressure and external pressure (turbulence). Going slow buffers the perception of the turbulence and is a factor that by itself can reduce the effects, but the whole picture results in a greater probability of an impact with the ground. You might also consider that at a higher speed, one might feel a sharper, more abrupt bump from the turbulence, but you pass through it before it moves you very far. In other words, by going slower you allow it to act on you longer and move you farther.

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It reduces your speed so a collapse, if it does happen, will not injure you as badly. It puts your canopy in a position so that it will recover much more quickly if it is affected by turbulence.

Again, it makes the collapse or stall more likely to happen in the first place. I would rather avoid the injury all together than minimize an unnecessary one. And don't confuse a stall with a collapse. Yes, being in brakes may help a collapsed canopy reinflate more quickly, but it won't necessarily help it recver from a stall, it may actually inhibit stall recovery as in a secondary stall. Again, old advice from the old days, with big old canopies that in brakes acted more like a "parachute" than a non-rigid ramair wing.

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If parachutes were as rigid as Cessna wings I would agree. Unfortunately, they are not, and the pressure inside them gives them a structural strength many orders of magnitude less than a 152's wing.

OTOH, if Cessnas regularly crashed when their wings collapsed on final, you would see pilots reducing their airspeed to reduce the speed at which they penetrate turbulence (and to reduce structural loads as a result of that turbulence.) Since Cessna wings are stronger than that, they only have to reduce speed (to structural cruise) at high speeds when they encounter turbulence.

We're not talking about structural failure here. We're talking about turbulence near the ground causing a wing to abruptly stop flying or change altitude. A wing stalling or collapsing is a symptom of the effects of turbulence. Skydivers as a general rule don't jump in conditions that would cause a Cessna's wing to fold. And, if fewer canopy pilots followed the advice to fly in brakes on landing approach in turbulence, you would see fewer crashing with their wings collapsed.

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If the only effect were the greater stability that pressurization affords I would agree. However, turbulence is effectively a change in wind direction in a short time. If you go faster, the changes happen faster, and the canopy will experience more turbulence.

If you go faster,t he changes happen faster and you are exposed to the forces for less time, so they will move you less but more abruptly. The turbulence is the same. You don't create more or less of it, you can control how much you let it affect you.

alan

[billvon 2,989]

>That has kinda been my point all along. I don't think that the
> majority of the newer canopies at the wing loadings that seem to be
> popular with todays pilots can be safely flared in 1/4 or 1/2 brakes
> in turbulent conditions. Hell, for that matter, most of the pilots I see
> can't land well in good conditions in 1/2 brakes.

I agree. Many pilots can't flat turn either. That does not mean that flat turns are bad. Similarly, most pilots cannot land _slower_ than normal because they all want to land as fast as possible. That does not mean you can't do it; I can land in 1/4 brakes under a 1.7 to 1 canopy with no problem. It is worth practicing.; even HP canopy pilots have to land in trees sometimes.

>An increased AOA and external pressure changes can effect a stall
> and/or a collapse.

Increased AOA _prevents_ collapses. A high AOA means that air is coming from beneath your canopy, as happens during opening. Canopies very much want to open (and remain open) under those conditions.

Increasing AOA can indeed stall you; but as you are then going UP (i.e. you have a very strong updraft beneath you, which caused the high AOA) that's not as dangerous a situation as a canopy collapse, which is caused by a transient negative AOA.

>Applying brakes squeezes air out and allows relatively smaller forces
> outside the canopy to exaggerate the effect.

Again, I do not believe in the "pressurization is the primary driver of stability" theory.

>It's not just about how fast you are going. It is a combination of the
> design parameters of the particular canopy, AOA, internal pressure
> and external pressure (turbulence). Going slow buffers the
> perception of the turbulence . . .

Agreed, and how the canopy perceives the turbulence is the critical issue here.

>and is a factor that by itself can reduce the effects, but the whole
>picture results in a greater probability of an impact with the ground.

At some point in the canopy ride you WILL impact the ground. The issue is - how hard? I argue that to get a good surf, but a higher chance of an impact hard enough to hurt, keep normal speed or slightly higher. To get a less powerful flare, shorter surf etc but also minimize your chances of an impact that will injure you, some small amount of brake can help.

> You might also consider that at a higher speed, one might feel a
> sharper, more abrupt bump from the turbulence, but you pass
> through it before it moves you very far.

This is also correct - but if you hit that turbulence fast enough to collapse your canopy, and then leave it just as quickly, you are now doing 20mph towards the ground under a collapsed canopy that must now reinflate before you can use it to slow you down. Preventing that collapse is important to increase your odds of landing without injury.

>Again, it makes the collapse or stall more likely to happen in the
> first place. I would rather avoid the injury all together than minimize
> an unnecessary one.

Agreed; see above.

>And don't confuse a stall with a collapse. Yes, being in brakes may
> help a collapsed canopy reinflate more quickly, but it won't
> necessarily help it recver from a stall, it may actually inhibit stall
> recovery as in a secondary stall.

If you stall a HP canopy, the WORST thing you can do is go to full flight. You MUST hold a little bit of brake to prevent a potentially dangerous surge as it recovers - which could be fatal if you are 30 feet up. If your canopy stalls, adding a bit of brake is absolutely critical (or holding the brake you have.)

>We're not talking about structural failure here.

Yes we are; you can get hurt when your canopy collapses and is no longer airfoil-shaped. When that happens, you can no longer slow yourself for landing.

>Skydivers as a general rule don't jump in conditions that would cause
> a Cessna's wing to fold.

Correct, but since we have no metal in our wings, they collapse a lot more easily under much milder conditions.

>And, if fewer canopy pilots followed the
> advice to fly in brakes on landing approach in turbulence, you would
> see fewer crashing with their wings collapsed.

I believe the opposite is true, for the reasons I've listed.

>If you go faster,t he changes happen faster and you are exposed to
> the forces for less time, so they will move you less but more
> abruptly. The turbulence is the same.

That is 100% true. It is also true that if you stand in a 10mph wind for 10 hours or a 100mph wind for 1 hour, the total wind passing you is the same. Which one would you rather see at your house? Although they are the same, the 100mph wind is more destructive since it moves past you more quickly.

Our goal is not to eliminate turbulence. We can choose to jump when it's not so turbulent, but sometimes we end up in turbulent air anyway. When that happens, we can't reduce the turbulence. But by flying in brakes, we can reduce the turbulence experienced by our canopies and increase the odds of making it to the ground safely.

[alan 1]

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I agree. Many pilots can't flat turn either. That does not mean that flat turns are bad. Similarly, most pilots cannot land _slower_ than normal because they all want to land as fast as possible. That does not mean you can't do it; I can land in 1/4 brakes under a 1.7 to 1 canopy with no problem. It is worth practicing.; even HP canopy pilots have to land in trees sometimes.

We're talking about flying in brakes during turbulent conditions near the ground. A flat turn in turbulence near the ground implies you are in brakes, maybe not 1/4 or 1/2. but maybe you are. Then it would be bad. BTW, I can land my VX nicely in 1/4 brakes. 1/2 brakes, well maybe there are better pilots than me out there, any of you care to comment? I've tried the 1/4 brake thing you advocate in mild to strong turbulence. you can come up with as many theories as you want to. Actual life real practice has demonstrate dto me that you have great arguements but they don't work in the real world. I've jumped a wide variety of the new higher performance canopies in bith calm and turbulent conditions. I can land any of them nicely in 1/4 brakes on a calm day. When I attempt to do it in turbulence, the canopy becomes very difficult to control and I often(usually) have a less than glamorous landing with a canopy that is stalled or very near it.

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Increased AOA _prevents_ collapses. A high AOA means that air is coming from beneath your canopy, as happens during opening. Canopies very much want to open (and remain open) under those conditions.

Increased AOA, when it exceeds the critical angle, willcause the canopy to stall. If the AOA is not immediately reduced (let up a little on the toggles), the canopy will collapse or fortune cooky. That is the problem, the stall occurs before the collapse, except possible in extreme cases of violently turbulent conditions. In that case, neither brakes nor full air speed will be of much help.

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Increasing AOA can indeed stall you; but as you are then going UP (i.e. you have a very strong updraft beneath you, which caused the high AOA) that's not as dangerous a situation as a canopy collapse, which is caused by a transient negative AOA.

See my comments above. In my experience, rarely does turbulence alone cause a collapse. A collapse is usually after a stall has occured while someone was flying in 1/2 brakes during turbulence. My experience has mostly been in the last 10 to 12 years. Yours goes back much further to older canopy designs. Maybe that has had some carry over effect.

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Again, I do not believe in the "pressurization is the primary driver of stability" theory.

Neither do I, but then I don't dismiss as much as you do either. It is an important factor and your arguements seem to dismiss it on the basis of extreme cases of turbulence, not the kind we ordinarily find ourselves jumping in and when we see the crash and burns.

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At some point in the canopy ride you WILL impact the ground. The issue is - how hard? I argue that to get a good surf, but a higher chance of an impact hard enough to hurt, keep normal speed or slightly higher. To get a less powerful flare, shorter surf etc but also minimize your chances of an impact that will injure you, some small amount of brake can help.

Here is where we have to agree to disagree. I do note that you have gone from 1/4 or 1/2 brakes to "some small amount." You know Bill, after I plane out and am surfing, I always have "some small amount" of brakes in (well, except for rear riser landings, but those I finish with brakes). It is normal on every canopy I jump, from a Manta 288 to a VX 89. I just don't like to use the brakes on the approach....as in before the rovery arc. Maybe semantics has been our problem.

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This is also correct - but if you hit that turbulence fast enough to collapse your canopy, and then leave it just as quickly,

Again, that is a really rare case....like a dust devil. We just don't usually jump in conditions that are that turbulent. I would argue that if it is that turbulent that it will collapse a full flight canopy, then it will do the same to one in brakes, perhaps not in the same manner but the end result is the same. I've hit strong mechanical turbulence (rotors from buildings and trees in 20 mph winds) at full flight (60+mph) and felt some sudden bumps but no collapse. The only brakes I use are a bump in the recovery arc to plane out and then the normal smooth application to surf and flare. Not much surf BTW. So bill, just how fast are we talking about here and what kind of turbulence?

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If you stall a HP canopy, the WORST thing you can do is go to full flight.

Agreed.

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You MUST hold a little bit of brake to prevent a potentially dangerous surge as it recovers - (or holding the brake you have.)

Actually, for the stall to have ocurred, you would already be in brakes and usually pretty deep brakes. What you do is let up a little to let the canopy recover and build up speed with minimal surge.

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which could be fatal if you are 30 feet up. If your canopy stalls, adding a bit of brake is absolutely critical

Exactly my point all along. Riding in brakes 30 feet up in turbulance is a very good way to find yourself in a stall that you won't be able to recover from. Adding brakes in a stall is absurd and I doubt you teach that in your FJC. As the canopy rocks back just prior to a stall, you can prevent the stall by letting up a few inches. Once the canopy stalls, don't let the brakes all the way up, just ease aup a few inches and hold them there until the canopy recovers, then smoothly return to full flight. Does any of that sound familiar? The old C172 stalls, the drops over as the wing tries to build speed and recover. The pilot pulls back on the yoke. It won't recover. I wonder what flight manual recommends adding flaps in a stall. Oh yeah, those old rigid airfoils are different. Funny, Quade says a wing is a wing and the aerodynamic principals are the same. Maybe he is wrong.

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>We're not talking about structural failure here.

Yes we are; you can get hurt when your canopy collapses and is no longer airfoil-shaped. When that happens, you can no longer slow yourself for landing.

I could go back in the archives and dig up a post by you where you argued the opposite, that our canopies can't go fast enough to experience
"structural failure". I guess you define that however it is most beneficial to your current arguement.

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>And, if fewer canopy pilots followed the
> advice to fly in brakes on landing approach in turbulence, you would
> see fewer crashing with their wings collapsed.

I believe the opposite is true, for the reasons I've listed.

Yeah, agree to disagree. My advice is anyone reading this has seen good arguements both ways. Go out on your canopy in see for yourselves. Start in calm conditions and try landing in 1/4 or 1/2 brakes and no brakes, then work progressively into more turbulent conditions until it makes you uncomfortable. Then quit. You have found your limit and what works best for your on that canopy. As you get more experience you may find that your comfort level has expanded and you have a bigger envelope. The real trick is knowing when to quit, when you are out of the envelope. Many of us find this several times over the years and it is usually punctuated with a cast (or worse) for 6 or 8 weeks.

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That is 100% true. It is also true that if you stand in a 10mph wind for 10 hours or a 100mph wind for 1 hour, the total wind passing you is the same. Which one would you rather see at your house? Although they are the same, the 100mph wind is more destructive since it moves past you more quickly.

Neat story, except we are not standing in a wind, we are flying in it and are not a fixed object, we are part over that ocean of air that the turbulence occurs in. We are also not exposing ourselves to those extremes and the house is not an aerodynamic structure.

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Our goal is not to eliminate turbulence. We can choose to jump when it's not so turbulent, but sometimes we end up in turbulent air anyway. When that happens, we can't reduce the turbulence. But by flying in brakes, we can reduce the turbulence experienced by our canopies and increase the odds of making it to the ground safely.

OK, if you say so, I don't agree though. My grandmother fell and broke her hip. At 94 that is pretty serious so I'm off to NJ to tend to her. Hate to break off the debate, but I'll be gone for awhile. Time to end it anyway. I wonder why Quade, Chuck, Hook and few others didn't offer an opinion, they certainly have a knowledge of the aerodynamics combined with practical experience.

alan

[franck102 0]

If you are still following this thread and getting confused, please check your pilot's manual or contact the manufacturer to find out what the safest way to fly your canopy in turbulence is.
There has been a lot of conflicting advice in the previous posts, so some of it has to be wrong...
Franck

[JJohnson 0]

Well you both make your points, but I have to tend to agree that speed through turbulence feels a lot safer to me.

Both of you have said that going from a stall to full flight is a bad idea, due to potentially dangerous forward surge, close to the ground. Or words to that effect, I'm not direct quoting. Well, by my perverse logic, let's suppose you are landing into the wind. A wind which is inconsistent, gusting and varying it's direction. If you are in part brakes and the wind decides to lull on you, your canopy is going to surge forward, correct? I would also think that at that moment your descent rate is going to pick up a bit as well. But as you are already into the brakes, you are giving up control range of the canopy. I could be wrong in my assesment here.

I have been slammed into the ground trying to ease into a landing during choppy wind, while riding a small amount of brakes. It feels like someone just takes the floor out from under you. It even seems that you lose forward drive, like you almost drop straight down.

Due to those close calls, I prefer to build up some speed when landing into anything I consider turbulent. I haven't been biffed yet with that method.
However as I would not classify myself as any sort top gun canopy pilot or an aeronautical engineer, I am open to clarification.
Lacking that particular technical educational background, I am forced to pilot my canopy by what I feel and percieve and understand.

As the original post was on airlocks, I will also say I did like the feel of the Samurai at Lost Prairie during some bumpy air. I can't say it was safer, but it sure felt solid going through the chop. More so than my Cobalt.
MHO

JJ

JJ

"Call me Darth Balls"

[jerm 0]

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"Flying in TurbulenceWhen flying in turbulent conditions you should apply slight brake pressure to both sides - around 20 % - to maintain a good angle of attack, thus reducing any tendency to collapse."

"You need to practice using the foot-operated speed bar. To be able to control your glider with your feet as well as with your hands is especially important when flying in turbulence. When changing from lift to sink it is essential to take your feet off the accelerator in order to reduce the risk of collapses
Remember: Flying accelerated the canopy has a lower angle of attack this means a collapse may occur much easier !"



"Thermaling and soaring :
In turbulent conditions the canopy should be flown with a small amount of brake applied. This improves stability by increasing the angle of attack of the canopy." "The angle of attack is lowered with the increase in speed and the canopy may tuck easier than in normal flight."

ummm... didn't you just make bill's point for him with these paragraphs???

Landing without injury is not necessarily evidence that you didn't fuck up... it just means you got away with it this time

[markbaur 0]

Recent posts assume that soaring ram-airs are sufficiently like skydiving ram-airs that techniques used for one type can be used for the other.

I am not so sure, but I have no experience with soaring ram-airs.

What are the significant design differences between the two, and especially, how do their angles of attack compare?

Mark

[franck102 0]

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ummm... didn't you just make bill's point for him with these paragraphs???

I fully agree with Bill that you should apply a small amount of brakes in turbulence, we just disagreed on the reason for doing so.

Applying a bit of brakes slows you down which makes you more susceptible to turbulence (because your angle of attack will shift more for a given gust/updraft/downdraft). But it also increases your angle of attack, and the consensus among the canopy vendors I quoted is that this is the overriding factor.

Another few random thoughts:

- don't get tricked into thinking that because you can pull on your fronts, increasing your angle of incidence by 15 degrees, without collapsing means your angle of attack in no brakes is safely high. When you pull on your fronts your glide ratio deteriorates (you dive) and your angle of attack only goes down by a few degrees. A gust on the other hand can quickly reduce your angle of attack to the point where your canopy collapses.

- the discussion didn't take into account the speed you may need for an efficient flare - you have to do what's right for your wing loading in that respect.

Franck

[franck102 0]

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Well you both make your points, but I have to tend to agree that speed
through turbulence feels a lot safer to me.

Same for crossroads - dangerous places, better get through them as
fast as possible... just kidding -)
Faster is better, *but* not if it requires your canopy to be at the
limit of its flying range.

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I would also think that at that moment your descent rate is going to
pick up a bit as well. But as you are already into the brakes, you are
giving up control range of the canopy. I could be wrong in my
assesment here.

You are right, in a lull or an updraft, your angle of attack suddenly
increases and your canopy gets closer to its stall point.
But the other side of the coin is that in a downdraft or a gust,
having a bit of brakes keeps your angle of attack from becoming 0.

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I have been slammed into the ground trying to ease into a
landing during choppy wind, while riding a small amount of brakes. It
feels like someone just takes the floor out from under you. It even
seems that you lose forward drive, like you almost drop straight
down.

If it makes you feel better, be aware that if your angle of incidence
goes to 0 and the leading edge or your canopy folds, it will feel more
like if the ceiling fell on your head -) The small amount of brakes we
are discussing is usually at or above your ears. With the ground
approaching it is easy to use too much. If you feel that the apparent
wind is markedly reduced you probably have too much brakes.

Franck

[franck102 0]

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Recent posts assume that soaring ram-airs are sufficiently like skydiving ram-airs that techniques used for one type can be used for the other.

I am not so sure, but I have no experience with soaring ram-airs.

What are the significant design differences between the two, and especially, how do their angles of attack compare?

Mark

The first paragliders were skydiving canopies. About 8 years ago they
were very much like today's high performance nine cells. Today they
have a much much higher aspect ratio (up to 30 or 40 cells, aspect
ratio up to 6). Check those pictures:
http://www.windtech.co.uk/paragliding/intro.htm

In terms of angle of attack, paragliders have a similar control range
in both directions - stall with brakes between waist and full brakes,
and the ability to increase the incidence significantly (10 degrees?)
using foot controlled "accelerators" (similar to pulling on your
fronts).
This would indicate that the range of usable angle of attacks around the
AOA in no brakes is similar to the one on skydiving canopies.

Here is an excerpt from Flight Concept's 9 cell main (http://www.flightconcepts.com/pdf/9cell2002.pdf):

"It is considered good practice to fly your
canopy at quarter-brakes if you expect to encounter turbulence."

Franck