Flying in Turbulence

[Hooknswoop 19]

Definition: A condition of fluid flow in which the flow is not smooth. The speed and the direction of the flow changes rapidly.

The best way to deal with turbulence is to avoid it. Become adept at predicting where turbulence is likely to be encountered and avoid those areas. Down wind of buildings and other obstacles is a prime area for turbulence. As the wind flows over the obstacles, it becomes turbulent, similar to water flowing over a rock. A rule of thumb is turbulence can be found up to 20 times downwind the height of an obstacle. If you fly behind another canopy, you can encounter the wingtip vortices coming off the wing tips and he disturbed air behind it. Behind a running aircraft, the propeler(s) create a tremendous amount of turbulence. Dark areas (asphalt, or any area darker than the surrounding area) on warm days soak up the heat from the sun and release it into the atmosphere, causing up drafts. Flying over a dark area and then a light area or vice versus it is possible to encounter turbulence. Thunderstorms will bring high, gusty, turbulent winds with them.

Before each jump, look at the landing area, check the winds and look for areas that will likely contain turbulence. Plan your approach to avoid these areas. Have a back up plan in case of traffic, long spot, etc. Be prepared to account for turbulence in a new landing approach if the wind changes.

If you find yourself in turbulence on final approach, fly through it at full flight (toggles all the way up), making small toggle inputs to keep the canopy flying into the wind. The more forward speed the canopy has, the more internal ram air pressure inside the canopy. The higher the internal pressure of the canopy, the more resistant to collapse it is. If you canopy buckles or folds, use the toggles to keep it flying straight, and prepare to PLF. Don’t ever give up.

Hook

[JJohnson 0]

Well put. Thanks.
JJ

JJ

"Call me Darth Balls"

[Michele 1]

Thanks for posting this, Derek. I appreciate it...am printing it out and saving it in my rainy day study book.

Ciels-
Michele

~Do Angels keep the dreams we seek
While our hearts lie bleeding?~

[Hallur 0]

Ditto, Thanks Derek

When I stop skydiving is the day that I die!!! Hallur

[rgoper 0]

Hook:

this is good, correct and useful information. i was wondering if i could impose upon you to post your thoughts on "proper body position" during deployment under an elipitacal main. i know this is more than likely what caused my severe line twists/cut-away, as i can find nothing else to blame it on, based on the severity of the twists. until i started jumping this Cobalt, i have experienced line twists now and then, but i know body position is more critical than ever under an elipitical main? i've read all of Atair's criteria on deployment during the "dual stage" deployment, but still have yet to have an opening that is uneventful. ie: end cell closure etc...i know some think you should arch symetrically and deploy, i do this, but i watch my canopy deploy, always looking up, until it's SSS, perhaps it's something i'm doing here that's killing me? i know this has nothing to do with you post topic, could you "shed some light" on this for me please? thanking you in advance for your time.

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

[Parrot 0]

Good info thx.
But there are exeptions on those situations i experienced, i flew over the landingzone ready to land up 30 feet, a rather large field, and somehow i got turbulence with nothing standing around me or flying around me.
Im still wondering where it came from.

Heh, thats funny .

[Hooknswoop 19]

***post your thoughts on "proper body position" during deployment under an elipitacal main.

iu used to try to steer through the openings, trying to keep the canopy on-heading. For quite a while now, I simply look at the horizone and keep my hips level w/ the ground through deployment. If you were sitting in a swing set and I turned you 90 degrees and let go of you, you would immediately turn back forward. i think it is the same w/ canopies, keeping your hips level will bring the canopy back on heading and if it doesn't, then just take the off heading opening.

I should have an article on line twists, prevntion and cures being printed in a magazine soon.

Hook

[steve1 5]

Hook,
Thanks again for the great info. Steve1

[franck102 0]

Quote

If you find yourself in turbulence on final approach, fly through it at full flight (toggles all the way up), making small toggle inputs to keep the canopy flying into the wind. The more forward speed the canopy has, the more internal ram air pressure inside the canopy. The higher the internal pressure of the canopy, the more resistant to collapse it is. If you canopy buckles or folds, use the toggles to keep it flying straight, and prepare to PLF. Don’t ever give up.

Hook

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

[Hooknswoop 19]

Quote

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

Internal pressure keeps the canopy more rigid, makes it more difficult for the canopy to collapse. Lift pulls against the canopy's lines keeping it from collapsing. Slowing down (brakes) reduces the internal pressure and the lift, making the canopy more susceptible to collapsing. If the canopy does collapse, brakes should help it re-inflate, but to avoid that, I recommend full flight.

Hook

[kallend 1,651]

Quote

Quote

If you find yourself in turbulence on final approach, fly through it at full flight (toggles all the way up), making small toggle inputs to keep the canopy flying into the wind. The more forward speed the canopy has, the more internal ram air pressure inside the canopy. The higher the internal pressure of the canopy, the more resistant to collapse it is. If you canopy buckles or folds, use the toggles to keep it flying straight, and prepare to PLF. Don’t ever give up.

Hook

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.
Franck

Your reply seems to ignore the pressure differences that are responsible for lift. That includes the pressure differences between the top and bottom surfaces and the stagnation point at the nose of the canopy.

[franck102 0]

Quote

Quote

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). 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

[cloud9 0]

This quote is directly from PD web site;

Quote

Contrary to what some people have been told, flying in brakes does not necessarily help keep the canopy pressurized. Aerodynamically, the canopy is actually more susceptible to turbulence in brakes. Years ago, flying in half brakes seemed to make some older ram-air canopy designs more stable in turbulence, though they were obviously very different from modern canopies. Flying in brakes is definitely not the best technique to use with the canopies we're flying today, although a lot of skydivers are still told to use this technique.

[Hallur 0]

Thank you for clarifying that cloud9

When I stop skydiving is the day that I die!!! Hallur

[quade 3]

Quote

This quote is directly from PD web site;

Could you post the URL for the document with that quote in it?

quade -
The World's Most Boring Skydiver

[Jimbo 0]

The quote is from the PD FAQ available here: http://www.performancedesigns.com/faq.htm

Specifically, the entry you're looking for is here: http://www.performancedesigns.com/faq.htm#turbulence

Hope that's helpful.

-
Jim

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

[crazy 0]

The PD FAQ about turbulence... I still don't understand their point.

Quote

Is it safer to be under a smaller or larger canopy when flying in turbulence?
[...]
Larger canopies tend to be affected by turbulence more easily. A jumper flying a large canopy may feel some significant bumps on days when people flying smaller, faster canopies feel hardly any turbulence at all. On the other hand, if turbulence causes a partial collapse on a small, fast canopy, it can result in a far more dramatic (and dangerous) turn and a greater loss of altitude. We've seen end cells fold under on larger canopies without having much effect at all on the canopy's flight path, while a similar situation has turned smaller canopies into Mister Toad's Wild Ride.This is basically the trade-off between flying a large or small canopy in turbulence.

Wing loading also has an effect on how a canopy handles turbulence. A heavy jumper might fly through some turbulence and only feel a few moderate bumps, but a very light jumper flying the same canopy through the same turbulence would probably feel a much greater effect.

So, what's PD's answer? Is the larger slower canopy (or lighter wing loading) less safe, as implied in the two 1st sentence and the second paragraph? Or is the smallest faster canopy less safe as implied in the last sentences of the 1st paragraph?

Are they really implying that the risk to have 3 cells collapsing is higher on a large canopy than on a small one? Or are they just mixing the comfort issue (bumpy ride) with the actual safety issue (collapse, loss of altitude. loss of controllability)?
--
Come

[bobsoutar 0]

Does sound as though PD don't want to commit to giving advice and want you to make your own decision.
In turbulence I would always rather go with a smaller canopy with a higher wingloading. I use either no brakes or just a touch (about 10%) and flare slightly higher than normal in case I get dumped a few feet.

[fool 0]

I think PD doesn't want to make a choice for you on this issue, just simply because they can't. They have presented the facts, and expect a person to define their own needs and acceptable risks. one COULD assume that if a larger canopy is more prone to being affected by turbulence, then if it were to fly through the same turbulence as a small canopy, where the small canopy actually was affected, that the larger canopy would be affected more, thus increasing the risk of possible collapse. I don't know, maybe I'm wrong.

S.E.X. party #1

"Life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways, totally worn out, shouting "f*#k, what a ride".

[bobsoutar 0]

I think you are completely right!

[franck102 0]

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

[Hooknswoop 19]

Quote

Today, all paraglider vendors still recommend using some brakes in turbulence. So this isn't a case of "old designs" vs "better, modern designs".

A paraglider is not the same as a skydiving canopy. You can't fly them the same way and they they don't react the same.

Hook

[cobaltdan 0]

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

many dhv1-2 paragliders do not even have a constant angle of attack across the planform.

atair recommendation for all our skydiving canopies: full flight in turbulence, no partial brakes.

sincerely,

dan<><>
www.extremefly.com

Daniel Preston <><>
atairaerodynamics.com (sport)
atairaerospace.com (military)

[quade 3]

Quote

many dhv1-2 paragliders do not even have a constant angle of attack across the planform.

Just as a point of reference, -most- aircraft do not have the same amount of angle of incidence across the wingspan. This is a common design feature called "washout" and it's purpose is to attempt to stall different parts of the wing at different times thereby giving the pilot a bit more of an indication of the incipient stall and a bit more control over the stall.

Generally speaking, the higher the aspect ratio, the more this design element can be put to use.

quade -
The World's Most Boring Skydiver

[franck102 0]

Quote

A paraglider is not the same as a skydiving canopy. You can't fly them the same way and they they don't react the same.

Hook

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