franck102

Thanks Lokie, exactly what I was looking for! Franck

Several people have mentioned a past thread discussing how to mount a dytter in a protec, however the search doesn't seem to work for me and I wasn't able to locate the thread. Would anyone have a URL to it? Thanks! Franck

Same problem here, in the last few weeks my searches started returning much less results. Also, are the old forum archives (http://www.dropzone.com/cgi-bin/dcforum/dcboard.cgi) searchable? There is a search there but it doesn't return any results, is this a known limitation? The "search forum" is incredibly useful for beginners like me, I sure hope it start working again! Thanks - Franck

This is an excellent view of the problem indeed. Hopefully, it will help to get rid of blunt (and dangerous) claims like: - faster is safer in turbulence - smaller is safer in turbulence -- Come True, and this is equivalent imho to saying that you need to keep the angle of attack in the flying range (which is something you can control as a pilot). More specifically, the best defensive strategy against turbulence is to find the flying regime where your angle of attack will stay in the flying range when faced with changes in the apparent wind. Of course once the turbulence starts playing havoc with your canopy you need to fly actively to keep the canopy flying. Franck

This isn't what I said... as I am sure you realize. I am just trying to say that a better understanding of why canopies collapse could save people from getting injured. Check this post, what is this pilot supposed to think after reading the present discussion? Should he get a more "modern design", try to fly even faster to "keep the internal pressure" up?? Only a better understanding of the aerodynamics involved can make flying in trubulence safer, and whether you like it or not the principles are the same for canopies, paragliders, or 747s (which of course isn't to say they require the same strategies). Franck

Sure there are. Which of those justify flying differently in turbulence? [reloy]many dhv1-2 paragliders do not even have a constant angle of attack across the planform. Again, how does this affect this discussion?? I'm sure this is good advice based on experience. BTW, would you have the polar curves available for any of your canopies? This would be very valuable to get some factual results. Franck

This was my point. If a canopy manufacturer could come up with a solid explanation of what is different with the trim or design of a skydiving canopy to warrant taking a different approach to flying in turbulence I'd be the first to listen... but blanket statements about "modern designs" or "cutting through turbulence" don't cut it. Franck

Hmmm, interesting quote. I guess they know what they are saying, although I find the argumentation questionable: > Aerodynamically, the canopy is actually more susceptible to turbulence in brakes. What does this mean? Flying at a higher speed means a given turbulence will affect your apparent wind less. Increasing the angle of attack requires flying at a slower speed. So the best speed is a compromise between those two factors. > Years ago, flying in half brakes seemed to make some older ram-air canopy designs more stable in turbulence Today, all paraglider vendors still recommend using some brakes in turbulence. So this isn't a case of "old designs" vs "better, modern designs". Also it didn't just "seem" to make them more stable. Hundreds of thousands of flight in severe turbulence have proven beyond doubt that this is the best strategy to keep a paraglider above your head; and there is a well understood aerodynamic explanation for it too. So while I must assume that PD knows what is best for their canopy, they definitely don't have the most convincing case... Franck

Slowing down (brakes) reduces the internal pressure and the lift, making the canopy more susceptible to collapsing. Hook Not so, please read this thread: http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=210136 No matter where your brakes are the lift always just balances drag + gravity (in straight, constant speed flight). The more interesting variable is the angle of attack, and the fact that if turbulence makes it too small your leading edge will fold under. Applying some brakes tries to prevent that by increasing the angle of attack. Franck

A better advice is to fly in with a small amount of brakes (ears / shoulder level). There was a looong thread recently about this in the safety & training forum (I think). "internal pressure" doesn't keep your canopy inflated, lift does. You need to keep the apparent wind at a working angle of attack and the best way to achive that is to apply some brakes. The previous thread contains references to several pilot manuals that recommend using a small amount of brakes in turbulence. Franck

I just received my new rig, it needs to be assembled and I can't get in touch with my DZ's rigger I'd really like to jump it next w.e., anyone knows a rigger living in the S.F. Bay Area who could put a new rig together? Thanks! Franck

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

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. 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. 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

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

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

We used to do that on early paragliders (which were very similar to today's high-performance 9 cell canopies). We added up to 5 french links (1+ inch each) on the rears to change the incidence and improve penetration. Later models had adjustable rears - you could pull them in several inches and keep them there. Another popular system is to have the linesesets go all the way down to the bottom of the harness seat (instead of being grouped above your shoulders), and you can adjust the incidence by sitting back or forward. Many paragliders today use foot-controlled "accelerator bars", which not only alter the incidence but also the camber of the canopy by pulling in different sets of lines by different amounts. Don't try any of this on your canopy of course, let the manufacturer try it first... Although I have toyed with the idea of asking my rigger to install adjusters on my rears, to make it easier to come back from long spots... Franck

Both essentially correct -) That angle is the angle of incidence (+90 degrees). And the CL moves along the chord as the angle of attack changes, so the angle of incidence changes with it. The CG is actually slightly behind the CP due to drag. Franck

Here are a few relevant articles & pilot manuals:

> ------------------------ > 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

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

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

You're right, he may have... though I wouldn't bet my life on it. My intuition (nothing to back this up but 2-3 rides with airlocks) is that if you are quick and make accurate and well-timed inputs you can probably get an airlocked canopy flying again earlier, but that less than perfect piloting could make for a pretty wild ride. With a non-airlocked canopy all you need to do is swear and the canopy will stay over your head and resume flying -) Franck

Probably not, see my other post. Unless there is a fundamental flaw with the canopy, it collapsed because it was out of its flying range, and an airlocked canopy while it would have reacted differently would not have helped. In fact I suspect that it may have made the problem worse by surging forward and causing a pendulum effect - but that's just a hunch. I have flown airlocked canopies in turbulence and I felt less safe that with a canopy that collapses but stays over your head. Franck

As a pilot you can forget about pressure in the cells, the canopy designer has (or should have -) ) taken care of making sure the canopy remains in shape across the range of useful angles of attack (AOA). If you get a perfectly airlocked canopy it will never collapse but it will kill you all the same if you allow the angle of attack to get our of control - so as a pilot it is more productive to think in terms of AOA. >What's the problem at low angles of attack? Your canopy is an airfoil that needs a positive angle of attack to generate lift (the force that keeps you in the air). If the AOA becomes too small, the canopy stops generating lift. It may collapse, or surge forward, one way or the other it will leave you at the mercy of gravity. >How about deep brakes? That would be a high angle of attack. I'd imagine flying slowly at a high angle of attack would lower the pressure inside the canopy so it would be less rigid Maybe but this isn't the problem. You're right, flying in deep brakes creates a high angle of attack. The problem is that airfoils don't like too high an angle of attack. At normal AOAs the air flies smoothly around your canopy (it is laminar and more or less follows the contour of the section), but if the AOA becomes too high (the wind starts hitting the canopy at a right angle) the flow suddenly becomes mostly turbulent - that's a stall. Again pressure in the cells has nothing to do with the problem, airplanes stall just the same as canopies do. Your canopy collapses because it stalled, not the opposite. Now how does turbulence affect youy cnaopy? The AOA is the angle between your canopy (its chord - the line between the tail and the leading edge) and the relative wind. Turbulence (or variations in the wind strength for that matter) can suddenly affect the direction and the strength of the relative wind, and thus play havoc with your angle of attack. Imagine you are flying in no wind with a glide ratio of 1/1, going 10 mph down and 10 mph forward. In a 10 mph gust from behind you are suddenly flying vertically at 10 mph down relatively to the air around you and your canopy's angle of attack is suddenly about 90 degrees ( not good -) ). A 10 mph vertical downward gust (unlikely) would leave you with just 10 mph forward speed relatively to the air around you, and your canopy at an AOA close to 0. It will stop generating lift and you will also fall from the sky. Note that only relative changes matter - a 5 mph wind that suddenly turns 180 degree will not affect you more that a 25 mph wind that suddenly drops to 15 mph without changing direction - and the latter is quite common on gusty days. Franck

I absolutely do not suggest that anyone try this at home of course. But I would guess that climbing harnesses do receive at least the same loads - people don't just hang in them, they sometimes fall quite a distance before being stopped by the rope. You don't get near terminal velocity, but you get stopped much more quickly - quickly enough to get killed by the shock. The buckles are different, they don't have any moving part. They would be much more of a pain to tighten or loosen though. Franck