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mzr36

Front riser straight-ins and line tension

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Blis

so if the weather is turbulent it's best to stay off the fronts (or rears for that matter)...



In my opinion, if the wind is so turbulent that you have to keep away from fronts or rears, you'd better off not jumping.

Besides that, normally pulling on your fronts increases airspeed and pressurization, both of which help to deal with turbulence. Of course, it deforms the airfoil as well, and if your wing when pulling on fronts is close to the tipping point where it is not really stable anymore, going through turbulence can make it worse. So at the end, it depends on the wing, I think.

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There's also a difference between steady state flight with fronts pulled down, and what happens when suddenly pulling fronts down.

When you suddenly pull down, the canopy hasn't yet had time to change its flight path and angle of attack to get to some new equilibrium.

I've had 'bad' canopies where a sharp pull on a front riser gets it close to zero force, which means near zero lift on the associated part of the canopy, which means the nose is close to getting to zero effective angle of attack and folding under.

This isn't what happens in practice on double fronts in typical situations on typical canopies, but shows the extremes. If one can move the front of the airfoil down too much too suddenly, one is just reducing the angle of attack. Combined with a turbulence induced change of angle of attack, yes one can get closer to having the canopy nose fold.

While the limits tend to be unknown, I tend to stay away from sudden big canopy inputs towards some aerodynamic limit, when in potential turbulence.

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>Does using double-front risers on final make a canopy more susceptible to turbulence? Say, by
>decreasing line tension or deforming the airfoil?

Yes - mainly by distorting the airfoil and increasing the severity of turbulence. Turbulence is effectively air moving in different directions along your flight path. The faster you go the worse the turbulence seems to be. The winds haven't changed, you are just passing through them more quickly.

In general full flight is the safest flight regime for moderate turbulence. If it's really bad (i.e. the canopy is starting to collapse) then 1/4 to 1/2 brakes will help reinflate the canopy if it does suffer a collapse.

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Quagmirian

***Canopy is most stable in full flight configuration

I'm not sure about that statement. I think it depends on the canopy. Mainly how it's trimmed.

I think biggest factor in canopy stability is how clean the airfoil is, in full flight configuration you should have zero (or very little) distortion in airfoil making it very stable. Obviously if it were trimmed to have very little internal pressure it will be very easy to collapse but I dont think it's a realistic scenario in a skydiving canopy.

Ofcourse I might be totally wrong, I'm not a expert canopy pilot or aerodynamics guru...

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Blis

Canopy is most stable in full flight configuration, so if the weather is turbulent it's best to stay off the fronts (or rears for that matter)...



Not exactly... the most stable configuration of most modern skydiving wings is a slow turn to keep airspeed up while maintaining small input and tension on the rears... it keeps the angle of attack up and should you tuck a tip, it aids in speedy reinflation. Brakes can have the opposite effect and move the center of lift back which can make tucks more likley.

The transition from brakes to fronts is the most susceptible time to collapse... you have low airspeed and then greatly decreasing your angle of attack while the wing is slightly depressurized...

If its that bumpy that youre worried about it, you shouldnt be jumping, but that being said, if you find yourself in bumpy conditions, rears and maintaining airspeed is your friend. Full flight is good due to the airspeed thing, but not the MOST stable...
I was that kid jumping out if his tree house with a bed sheet. My dad wouldn't let me use the ladder to try the roof...

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mzr36

Hey everyone,

Does using double-front risers on final make a canopy more susceptible to turbulence? Say, by decreasing line tension or deforming the airfoil?



IMHO, stability is only one factor in surviving heavy turbulence.
Another important one is the ability to react to what happens. Thats why I like a little extra airspeed. When needed, this gives me a lot more lift to stop my vertical speed. So my preferred solution is to gently put some pressure on the fronts, just enough to gain a little speed. Even that little bit of extra speed gives a lot more "flare power".

By the way this does not reduce the combined tension on the lines. The combined tension equals my weight, otherwise I would be accelerating or deccelerating (--> note the word "gently"). It may change the distribution between front and rear risers, but I don't think this this will cause any weird behaviour.

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Agreed.
The optimum configuration - for handling turbulence - depends upon the canopy.
For example, my Strato-Cloud handled turbulence best with 1/4 brakes because that improved pressurization.
My Nova was different because it was trimmed so steep that any front-riser input pulled the nose down so far that it promptly folded under. I quickly learned never to touch front rises on a Nova!

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mzr36

Hey everyone,

Does using double-front risers on final make a canopy more susceptible to turbulence? Say, by decreasing line tension or deforming the airfoil?



Hi,

Short answer - yes.

Long answer - pulling on fronts increases your wing's angle of attack, decreasing the resistance to collapses (wings collapse from a sudden increase in angle of attack). However, pulling on fronts eventually increases airspeed which produces more lift and internal pressurization making depressurization more difficult. So it's nuanced.

Here is a short document about dealing with turbulence under ram air canopies written by some Germans. https://www.dhv.de/web/fileadmin/user_upload/monatsordner/2004-06/Ausbildung/activ_flying_english_text.pdf

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lyosha

***Hey everyone,

Does using double-front risers on final make a canopy more susceptible to turbulence? Say, by decreasing line tension or deforming the airfoil?



Hi,

Short answer - yes.

Long answer - pulling on fronts increases your wing's angle of attack, decreasing the resistance to collapses (wings collapse from a sudden increase in angle of attack). However, pulling on fronts eventually increases airspeed which produces more lift and internal pressurization making depressurization more difficult. So it's nuanced.

Here is a short document about dealing with turbulence under ram air canopies written by some Germans. https://www.dhv.de/web/fileadmin/user_upload/monatsordner/2004-06/Ausbildung/activ_flying_english_text.pdf

Fronts decrease* the angle of attack, rears increase it.
I was that kid jumping out if his tree house with a bed sheet. My dad wouldn't let me use the ladder to try the roof...

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If you are talking about the angle of attack relative to the wind, pulling down in front risers decreases the angle between the bottom skin and the wind:
If you are talking about angle of incidence, then you are talking about the canopy's angle relative to the horizon.
Finally, greater speed may increase but I suspect that the "step" created by pulling front risers) adds more drag and disturbs airflow over both top and bottom skins. So pulling front-risers is primarily about increasing forward speed. When you release front risers the canopy smooths out and returns to an angle of attack close to is best glide ratio. The extra speed translates into extra lift and more forward momentum at the start of the flare.

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Alexg3265

Fronts decrease* the angle of attack, rears increase it.



You are correct and I'm dyslexic. However, the statement that fronts increase odds of a collapse is still true.

riggerrob

So pulling front-risers is primarily about increasing forward speed.



by aggressively decreasing angle of attack and exposing yourself to the risk of collapses. When you initially decrease your angle of attack you are more likely to suffer a collapse. Some time later, your canopy picks up speed and that risk once again decreases. When you release your fronts your angle of attack increases decreasing the odds of a collapse.

riggerrob

The extra speed translates into extra lift and more forward momentum at the start of the flare.



I haven't tried to intentionally collapse my skydiving wing (harder to accomplish), but I've intentionally collapsed my paraglider a bunch of times and the acceleration makes the turbulence worse and its effects on the canopy more dramatic. There is a definite point where you are not gaining stability, but are losing it but are just after the remainder of the speed you can milk from a wing.

I would expect my skydiving canopy to have similar dynamics. On the one hand the extra speed makes your wing more rigid making it harder to collapse your wing. On the other if it goes, it'll be more dramatic and recovery possibilities will be worse.

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lyosha



by aggressively decreasing angle of attack and exposing yourself to the risk of collapses.
.



Agreed, so don't do it agressively. Gently also works!


lyosha


When you initially decrease your angle of attack you are more likely to suffer a collapse.



I have never been able to collapse my canopy (Crossfire 2 129) with an agressive move, and I've tried pretty hard. Both from full flight and from flying in deep brakes at almost stall speed. I know the original Crossfire had a problem with collapses, so I thought it would be nice to try it up high.

Stalling it is much more likely, which is also a big risk in turbulence. IMO, increased airspeed helps to prevent this. Flying slow (in brakes) makes a stall more likely.

To be clear I'm not pulling my fronts as far as possible; just a little bit of tension is enough to gain some speed and add a lot of power to the flare.

lyosha


I haven't tried to intentionally collapse my skydiving wing (harder to accomplish), but I've intentionally collapsed my paraglider a bunch of times .....



A parachute is not a paraglider. Paragliders are scary!!!

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