Flying in Turbulence

[franck102 0]

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for this discussion, there are strong differences between a very high aspect ratio canopy (paraglider) and a low aspect ratio canopy (skydiving).

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.

[Hooknswoop 19]

By the same token you could assume that canopy manufacturers are correct and para-glider manufacturers are not. I think they are both correct for their respective products.

I think the difference is paragliders are trimmed much flatter and have much higher aspect ratios than skydiving canopies and brakes is used more for recovery. Paragliders are much more prone to collapsing that skydiving canopies. With skydiving canopies we try to avoid the collapse in the first place, with speed, pressurization, and lift.. If it were to collapse, brakes is the best route to get it re-inflated.

I know from experience that the higher speeds and higher wing loadings of smaller canopies handle turbulence better than large, lightly loaded canopies. I can fly a tandem canopy and have end cells folding in and getting bounced around, then fly my VX-60 and barely feel a bump, and it sure doesn't fold up on me. Why don't airplane wings fold in turbulence?, Rigidity. The higher the difference between the internal pressure of a canopy and the surrounding air pressure, the less prone to collapsing a canopy is.

Hook

[eames 0]

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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 because skydiving canopy manufacturers don't give explanations in terms of paragliders, you won't listen? Find the evidence that a paraglider flies better with brakes in turbulence in terms of a skydiving canopy. Why should the entire skydiving industry cater its explainations to you because the foundation of your knowledge lies in paragliders?

Jason

[Jimbo 0]

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I know from experience that the higher speeds and higher wing loadings of smaller canopies handle turbulence better than large, lightly loaded canopies. I can fly a tandem canopy and have end cells folding in and getting bounced around, then fly my VX-60 and barely feel a bump, and it sure doesn't fold up on me. Why don't airplane wings fold in turbulence?, Rigidity. The higher the difference between the internal pressure of a canopy and the surrounding air pressure, the less prone to collapsing a canopy is.

Is it fair to compare a tandem canopy to a cross braced canopy? Given the cross bracing in your VX-60 they're two entirely different wings. A more fair and objective comparison might be if you flew your S189 and then a S149 or 129 through the same turbulance. Then there's the speed factor of this puzzle, do you not notice the turbulance because a higher loading really makes the canopy less succeptable to turbulance, or is it simply because you passed through the turbulance so quickly that you never really got the chance to notice it. Sorry for all the questions, I'm just trying to get a better understanding of all this. For whatever it's worth, and it sure ain't much, I think I'm a fan of the full flight through turbulance theory.

-
Jim

"Like" - The modern day comma
Good bye, my friends. You are missed.

[quade 4]

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Why don't airplane wings fold in turbulence?, Rigidity.

Not true on at least two counts.

First, airplane wings -can- separate from turbulence. One of the ways to avoid this is to fly the airplane through turbulence below a certain speed generally called Vno or "maximum structural cruising speed". There are variations of this for different airplanes (maximum turbulent air penatration speed, ect.), but the general concept is that if you fly the airplane below a certain speed, turbulence -should- slightly stall the airplane before structrual damage can be done.

Second, you'd almost never want to totally rigid wing. If the wing couldn't act a bit like a spring, then all of the forces would be transfered to the fuselage. Watch the wings of an airliner the next time you're in one and it takes off or is in turbulence and you'll see they flex quite a bit. On very large aircraft like the B-747, they may flex as much as six feet.

quade -
The World's Most Boring Skydiver

[quade 4]

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I know from experience that the higher speeds and higher wing loadings of smaller canopies handle turbulence better than large, lightly loaded canopies.

This is true of all aircraft, but has less to do with pressurization than it does with wingloading.

A very lightly wingloaded aircraft will feel the effects of turbulence more than a highly wingloaded one flying right beside it in the same turbulence.

If you think about it in terms of inertia of the aircraft and surface area of the wing that could be effected by the turbulence, this will all make sense.

The turbulent air that would be considered "light" in a B-747, might be considered "severe" in a Cessna 180.

quade -
The World's Most Boring Skydiver

[Hooknswoop 19]

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Is it fair to compare a tandem canopy to a cross braced canopy? Given the cross bracing in your VX-60 they're two entirely different wings. A more fair and objective comparison might be if you flew your S189 and then a S149 or 129 through the same turbulance.

No it itsn't probably fair, but I was going for two different extremes. I can feel a difference between a tandem and my Safire 189. I have had two types of canopies have the end cells fold in on me, a sabre 230 in heavy turbulence and a whole bunch of tandems. It hit turbulance so hard one day under an FX-70 that it was like hitting a speed bump in a car at 40 mph. No collapsing though.

I really think the higher internal pressures from higher wingloading and ZP fabric and more lift from the higher speeds makes it difficult for smaller high performance canopies to collaspe. Passing through turbulence faster just makes it "sharper". When under a tandem inturbulence I can feel the canopy "walffing", breathing, bending and sometimes, the end cells folding under. I stay out of braked approaches when doing tandems in turbulence.

Hook

[Hooknswoop 19]

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Why don't airplane wings fold in turbulence?, Rigidity.

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Not true on at least two counts.

First, airplane wings -can- separate from turbulence. One of the ways to avoid this is to fly the airplane through turbulence below a certain speed generally called Vno or "maximum structural cruising speed". There are variations of this for different airplanes (maximum turbulent air penatration speed, ect.), but the general concept is that if you fly the airplane below a certain speed, turbulence -should- slightly stall the airplane before structrual damage can be done.

Second, you'd almost never want to totally rigid wing. If the wing couldn't act a bit like a spring, then all of the forces would be transfered to the fuselage. Watch the wings of an airliner the next time you're in one and it takes off or is in turbulence and you'll see they flex quite a bit. On very large aircraft like the B-747, they may flex as much as six feet.

Right, but compared to a canopy, an aircraft's wing is rigid. I know they flex and bend and I understand Vno, but that doesn't apply to canopies. A canopy isn't going to break from turbulance. you don't want to canopy to stall and don't have to worry about structrual damage to a canopy.
My point ws you don't hear of aircraft wings folding under in turbulence because they are made of metal (or wood or composites) and much more rigid that the pressurized fabric of canopies.

Hook

[rgoper 0]

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On very large aircraft like the B-747, they may flex as much as six feet.

i witnessed this very thin on my voyage to the middle east, and back. i was glad they were flexing, and not breaking off! i flew a 747 series 400 aircraft, they flexed quite a bit, but not no six feet, but then again we were cruising at 42K at 565 mph and i didn't have a measuring tape, nor the inclination to get out and measure the span! just like the concord is designed to stretch, and straighten out at full speed, most aircraft are designed to stretch, and flex.

--Richard--
"We Will Not Be Shaken By Thugs, And Terroist"

[quade 4]

Understood. I just wanted to clarify the terms being used.

As you've pointed out already, even though they all fly using the same principles of lift, there may be significant differences in how different aircraft are flown due to structural design differences.

Nobody in his right mind would deploy a paraglider from terminal velocity and I'm thinking they -probably- behave a bit differently in a number of other flight regimes as well. Likewise, it's probably not entirely true that the way you'd fly one in turbulence applies to all types of canopies, both paraglider and parachute.

With that in mind it may also be true that what is valid for a highly loaded crossbraced canopy might not exactly apply to a lightly loaded 7-cell F-111 student canopy and we should -probably- be preaching appropriate controls rather than making blanket statements.

quade -
The World's Most Boring Skydiver

[quade 4]

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. . . they flexed quite a bit, but not no six feet . . .

Maybe the turb wasn't quite as bad as it can get.

Severe turb in a 747 is actually quite rare. You'll know it's severe when you can't read the instruments and the only ones that can keep their lunch down are the pilots.

quade -
The World's Most Boring Skydiver

[franck102 0]

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But because skydiving canopy manufacturers don't give explanations in terms of paragliders, you won't listen? Find the evidence that a paraglider flies better with brakes in turbulence in terms of a skydiving canopy. Why should the entire skydiving industry cater its explainations to you because the foundation of your knowledge lies in paragliders?

Jason

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

[kallend 2,026]

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internal pressure" doesn't keep your canopy inflated, lift does.

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).

But, as far as the airfoil is concerned, flying in turbulence is NOT constant speed steady flight.

It seems to me that the important thing to prevent a canopy collapse is to keep the stagnation point on the leading edge over the vent. This is the only way to ensure the internal pressure exceeds the dynamic pressure outside the airfoil.
How different designs maintain this situation in turbulence and at different trim settings clearly depends on the design of the leading edge and the placement of the vents, and will therefore be different from one design of canopy to another.
SO - I doubt there is a universal rule.

[crazy 0]

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It seems to me that the important thing to prevent a canopy collapse is to keep the stagnation point on the leading edge over the vent. This is the only way to ensure the internal pressure exceeds the dynamic pressure outside the airfoil.

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

[roq 0]

I think the big canopy is less danger for turbulence conditions, because lower speed in all conditions of the big canopys, and also the big canopy is better if the pilot have less experience.
But I think the um HP canopy is better for strong winds and turbulence conditions when driven for a good and experienced pilot and if the canopy is good and reliable.
I jump in demo jumps for tight places with accuracy Parafoil 252 light loaded and have no problems with turbulence conditions but I have problems with strong winds because the parafoil don't move forward.
With my HP canopys 75, 85 and 120 I don't have problems with strong winds and turbulences.
In my opinion the reasons because the HP canopys is more danger in turbulence conditions is:
Bad design of the canopy
Bad pilot control canopy technique and experience
Fast natural speed in all conditions of the HP canopys
Driving the HP canopy with lower horizontal speed in flying. It is good for student canopys, big old and classic 7 cell canopys (driving the canopy with 20 to 50 % brake in turbulence conditions) and paragliders, but definitively it is poor and danger technique for HP or intermediate canopys, because if you decrease horizontal speed with HP canopys you have low lift and low pressure in one small lift area. When it happen you have the danger to fall of the sky like one rock same with partial insuflate canopy. With big low load canopys, the lower wing load, lower permanent pressure in all platform of the canopy and big volume can't fly to high horizontal speed, and if the big canopy flew with same speed of a small canopy it was unmade in the air. In general big canopy low load have good behavior in low speed, small canopy high load have good behavior in high speed.

Here my opinions for don't collapse HP canopys:
Don't make radical or brutal inputs in your canopy in all conditions
Don't use canopy with bad design
Don't use new canopy without technical background or recognized technical quality
Don't use poor and inadequate technical pilot canopy control
Don't use HP canopys high loaded when you have low technique and or low experience
Keep the fast natural horizontal speed in all conditions of the HP canopys and intermediate canopys
Don't driving HP canopy with brakes for lower horizontal speed in flying.
Don't fly or landing to the crossed wind
Don't fly or landing close to natural or artificial obstacles, elevations or other canopys
Don't jump when have bad meteorological conditions

Roq

[franck102 0]

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It seems to me that the important thing to prevent a canopy collapse is to keep the stagnation point on the leading edge over the vent. This is the only way to ensure the internal pressure exceeds the dynamic pressure outside the airfoil.

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

[alan 1]

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With that in mind it may also be true that what is valid for a highly loaded crossbraced canopy might not exactly apply to a lightly loaded 7-cell F-111 student canopy and we should -probably- be preaching appropriate controls rather than making blanket statements.

Geez, that is exactly the point I was trying to make with billvon in that other thread that started all of this. I'll say it again here. The old advice of flying in 1/2 or 3/4 brakes in turbulence is not good on todays newer high performance designs. That may not be an exact quote, but I'm sure it is pretty close.

alan

[alan 1]

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But, as far as the airfoil is concerned, flying in turbulence is NOT constant speed steady flight.

It seems to me that the important thing to prevent a canopy collapse is to keep the stagnation point on the leading edge over the vent. This is the only way to ensure the internal pressure exceeds the dynamic pressure outside the airfoil.
How different designs maintain this situation in turbulence and at different trim settings clearly depends on the design of the leading edge and the placement of the vents, and will therefore be different from one design of canopy to another.
SO - I doubt there is a universal rule.

THANK YOU JOHN! I've been away for awhile, but is is nice to come back and see something intelligent from someone who understands what he is talking about. Well, that doesn't apply to only you here, but you did find a very simple, concise and accurate statement that conveys very clearly what I was trying to get across way back when I started this whole debate with billvon and Franck102.

alan

[darkwing 5]

It seems that there is very little concrete reasoning to this, with the exception of Franck102 and kallend (apologies to others I may have missed). I am disappointed that canopy manufacturers have so little logic to back up their assertions (or non-assertions) as to how to fly in turbulence.

On a related note, I fail to see how cross bracing has anything to do with the collapsability of a canopy in turbulence. To me it is mostly related to the stagnation point and the opening at the leading edge...

Serious students of airlocks will admit that they are far from fail-safe in turbulence. And that they suffer from inducing an unrealistic sense of security in turbulence.

-- Jeff
My Skydiving History