Angle of attack vs collapse of a canopy?

[rhino 0]

o.k. I have a couple questions?
#1 - Is a canopy that glides say 30 degrees downward flying into the wind more apt to collapse that a canopy with a flatter glide of say 15 degrees?
It just seems that If I were flying into a 20mph wind and my canopies angle of attack was 30 degrees for example that the wind would be actually pushing against the top of the canopy instead of flowing around the canopy like air flowing over a wing?
Does anyone get what I am saying? I am wondering if maybe a canopy with a flatter glide angle is safer than one that drops quicker in high winds?
#2 - Is light front riser pressure conducive to any drawbacks as far as risks? Is light front riser pressure a good, bad or indifferent issue aside from personal preference?
Just wondering?
Rhino
Semper Fi .....
http:// www.aahit.com

[diverdriver 7]

I get exactly what you are saying. Everyone should pay attention to this next statement. ANY wing can stall in ANY ATTITUDE and airspeed. You are refering to attitude of flight. (30 degrees down) But that may not be what its' ANGLE OF ATTACK is. That the angle the wing makes with the direction of flight. Do I have you so far? If I don't the rest of what I have to say won't make sense.
Draw a line from the trailing edge to the leading edge of the wing. The compare that line to the DIRECTION of flight. This is the angle of attack and a wing will ALWAYS stall at the same angle of attack. No matter what ATTITUDE it is in or airspeed. This is called the "Critical Angle of Attack".
During a rotor encounter that critical angle of attack can be reached on part of the canopy and cause a partial stall.
Chris Schindler
ATP/CFII
D-19012
www.DiverDriver.com

[rhino 0]

Direction of flight yes.. Say you look directly forward and the wind is blowing 20+ in your face yet you are flying forward and 30 degrees down..
Semper Fi .....
http:// www.aahit.com

[diverdriver 7]

Nah, you're missing my point. Sorry. The wind speed has nothing to do with a wing in flight. It is your speed through the air that counts. Called Airspeed. Now, 30 degrees down is your attitude. But, you angle of attack might be only 5 degrees. This refers to "Relative Wind". That is the wind direction (refering to wing in flight) opposite the direction of flight. Does this help?
I'm trying to teach basic aerodynamics without aid of drawings and much time. Hope I can clarify this for you.
Chris

[rhino 0]

Naw.. I got your point I was just trying to say what I meant.
I know airspeed still counts but what about the relative wind coming straight at the top of your canopy?
Attached...
Semper Fi .....
http:// www.aahit.com

[diverdriver 7]

That's what I'm talking about. In your picture you show the wind as it flows over the ground. That is NOT relative wind. The relative wind is coming opposite the flight path of the canopy. In your picture you would have about a 5-10 degree POSITIVE angle of attack. You are thinking it is a negative angle of attack. Now, you can induce a negative angle of attack by pulling the front riser.
Just because the nose of the canopy is pointed down from the horizon doesn't mean it has a negative angle of attack. If you had a negative angle of attack the canopy would dive forward trying to recover normal flight. When this happens on part of the canopy it can cause partial collapses and line twists.
Chris

[rhino 0]

Now we are getting somewhere...
Did you like the art work Semper Fi .....
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[billvon 3,090]

>#1 - Is a canopy that glides say 30 degrees downward flying into the wind more
>apt to collapse that a canopy with a flatter glide of say 15 degrees?
No, in fact it is the opposite. Very flat ram-airs (like paragliders) have horrendous problems with collapses.
>It just seems that If I were flying into a 20mph wind and my canopies angle of
> attack was 30 degrees for example that the wind would be actually pushing
> against the top of the canopy instead of flowing around the canopy like air
> flowing over a wing?
No, your canopy does not care how fast the wind is blowing relative to the ground - it just cares how fast the wind is blowing relative to _it._ A canopy sees exactly the same airspeed when you are gliding hands-off whether you're in still air, in a 10kt tailwind, or a 40kt headwind. You can prove this to yourself when you do a cross-country in a 40kt wind. Even though your groundspeed might be -20kts, the canopy doesn't care.
>#2 - Is light front riser pressure conducive to any drawbacks as far as risks? Is
> light front riser pressure a good, bad or indifferent issue aside from personal
> preference?
In _general_, light front riser pressure indicates that the primary stabilizing force on the canopy (i.e. the restraining effect of the lines vs the higher pressure below) is shifted towards the rear. This means the nose is somewhat more vulnerable to collapse. However, this can also be because the canopy is rigged oddly (i.e. A/B/C line groups near the nose, D near the tail) so it doesn't necessarily mean it's unstable.
-bill von

[rhino 0]

Good input.. more.. more.. M U S T H A V E M O R E Semper Fi .....
http:// www.aahit.com

[psw097 0]

There still seams to be some confusion about angle of attack vs. angle of incidence.
Angle of attack is the angle at which the canopy strikes the perceived wind. Angle of incidence is the angle of the canopy to the horizon.
Until a canopy reaches the critical angle of attack it produces more lift, determined by the coefficient of lift (Cl). After that point it will stall. At the same time it produces more drag and slows down. Lift looks something like this:
Lift = 1/2pV(sq) * Gl * A
If the angle of attack is too high there will not be enough pressurization to maintain cell shape. The canopy will react poorly in turbulence and may deflate. If the angle of attack become too low or worse negative the stagnation point may/will migrate to the top skin of the canopy. This will cause a venturi effect and suck the air from the cell and again cause the nose to roll under.
Under a canopy the only way to significantly change your angle of attack is with your brake lines. Your risers will change the angle of attack some, but mostly they change the angle of incidence.
Turbulence can cause a partial, or full, canopy collapse because of an AOA change. It really has nothing to do with AOI.
This is a quick and dirty explanation and may not be 100% accurate since I did no research before throwing it together.
Paul Webster
D-24223

[quade 4]

Quote

Angle of incidence is the angle of the canopy to the horizon.

Uh, sort of, but let's rephrase that so it's a bit more understandable.
The angle of incidence is created by the hands-off line trim of the parachute in it's normal static state.
The angles relative to the horizon we'll call pitch and bank angle. We can also call it attitude.
BTW, love the fact that you actually know the formula for lift! Too many folks around hear seem to think lift is created by airspeed alone.
quade
http://futurecam.com

[diverdriver 7]

Looks like pretty solid aerodynamics to me.
Chris

[psw097 0]

"The angle of incidence is created by the hands-off line trim of the parachute in it's normal static state."
I agree, but that brings up a whole new concept of riggers angle of incidence or trim angle vs. true angle of incidence or pitch. It starts getting confusing, I'll stick with your definition.
The basic lift formula would be a great predictor of performance. You just never see Cl data out of the manufactures so the only thing you can quantify is velocity. Plus, its difficult to change AOA for more than a few seconds, the Cl value stays rather constant.
Makes it more fun that way I guess.

[Billy 0]

OK guys,,
in laymans terms,, so what would be the best approach on a turbulent day so as not to induce a collapsed canopy at an altitude ya couldn't recover from??
Don't read this shit down here,, it's nonsense,,,

[Remster 30]

Quote

so what would be the best approach on a turbulent day

From safest to not as safe
1- not jump
2- stay away from turbulance
3- fly in full glide
and be ready to PLF for 2 and 3
Remster
Muff 914

[diverdriver 7]

Quote

OK guys,,
in laymans terms,, so what would be the best approach on a turbulent day so as not to induce a collapsed canopy at an altitude ya couldn't recover from??

Straight in. FULL FLIGHT hands UP. That's on Zero-P material canopies. You need to do what aircraft do in turbulent air: INCREASE SPEED. You can only do that by letting it fly at FULL FLIGHT. Second, don't jump in conditions that require your full skill to survive.
Is that in layman's terms enough?
Chris

[rhino 0]

I wonder what the IDEAL turbulence busting canopy is?
Semper Fi .....
http:// www.aahit.com

[Remster 30]

Quote

IDEAL turbulence busting canopy

The one still in the pack tray
Remster
Muff 914

[diverdriver 7]

Quote

The one still in the pack tray.

Oh, touche.

[psw097 0]

"2- stay away from turbulance"
This one is great. Knowing where turbulence hides is as important as knowing how to fly in it. Stay away from buildings, treelines, hot tarmac, cool water, dropoffs, rises.....Thermals and/or obstructions are what cause the turbulence in the first place.
Paul Webster

[rhino 0]

Seriously.. If you were in the air and the shit hit the fan, what would you like to be flying over your head??
diver don't say a 747 damnit.. Semper Fi .....
http:// www.aahit.com

[diverdriver 7]

A 777?
From everything I've heard, since I haven't flown it myself, it's the Jedei. That's just opinions I've heard over the years. Personally, I fly a Stilleto 107 and think it does just fine. But I am also pretty picky on the conditions I jump in. I also avoid obstacle turbulence like the plague. Set up early or land out to land away from obstacle turbulence. "Land safe, not close". Golden Rule of Skydiving.
Chris

[Remster 30]

With all due repsect to Brian,
if turbulance is bad enough to collapse a [inset non airlock canopy name here] I am not sure any airlock canopy (jedei, vengence, lotus, samurai) would fly through it. I havent flown one, but at best, i think thet would help in slightly marginal condition, but not in "shit hitting the fan" conditions.
Remster
Muff 914

[n2skdvn 0]

i have jumped the samuri and in turbulant conditions (not
severe) the canopy's shape was solid you could feel the shaking but not a s much and the canopy did not distort
kept its shape! i believe that the conditions that caused
that one canopy pilots demise would of been the same under
an airlocked canopy. The canopy retains shape but the conditions for lift are gone.
in all the air locked canopy is rock solid!!!! smooth and the samuri has a great flare.
i personaly do not jump in high winds15+ because of wing loading and hate turbulent days!!!
if ya can't dodge it RAM IT !!!!!!
click me

[rhino 0]

My vote is for the Triathlon..
Semper Fi .....
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