Ground Effect

[raymod2 1]

I've been wondering if ground effect plays (or could play) a significant role in swoop distance. If so, some canopies may have an advantage in this area (wider planform and shorter lines). Also, it would be something to think about regarding technique during the swoop (ie. try to keep the wing as close to the ground as possible).

[superstu 0]

i asked this question either on dz.com or canopypiloting.com try a search

Slip Stream Air Sports
Do not go softly, do not go quietly, never back down

[quade 4]

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I've been wondering if ground effect plays (or could play) a significant role in swoop distance.

Ground effect is normally considered to "begin" at a height 1/2 that of the wing span.

For almost any skydiving canopy, it would not be considered a factor at all.

quade -
The World's Most Boring Skydiver

[diablopilot 2]

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For almost any skydiving canopy, it would not be considered a factor at all.

I don't agree.....I can't define it, nor really describe it, but sometimes it's there.....especialy when "bottom-ing out" from a turn into level flight.

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You're not as good as you think you are. Seriously.

[AggieDave 6]

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I don't agree.....I can't define it, nor really describe it, but sometimes it's there.....especialy when "bottom-ing out" from a turn into level flight.

That's just the lift produced from the added speed, its a normal component of the recovery arc. I honestly don't see how ground effect could become a factor in a canopy, due to the height they are off the ground, even during a "low and dirty" swoop.

That's why pilots talk about ground effect when talking about low wing aircraft.

--"When I die, may I be surrounded by scattered chrome and burning gasoline."

[diablopilot 2]

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That's just the lift produced from the added speed,

Naw, I'm pretty aware of that phenomena.....I'm talking about the "bubble I hit sometimes when I settle into the grove over a nice flat bit of water. Wher I tuck my knees to the side, dip the hip into the water and then get a bump back up about 6 inches, and feel like the canopy is rolling on marbles on a hard wood floor. Told ya it doesn't make any sense......

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You're not as good as you think you are. Seriously.

[AggieDave 6]

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eel like the canopy is rolling on marbles on a hard wood floor

Sure its not just the marbles in your head?

It could have to do with a slight change in density altitude over the water...who knows. But I really doubt its ground effect.

What we need is an areospace engineer, a pilot, Spectre230 and a chalkboard to figure this out.

--"When I die, may I be surrounded by scattered chrome and burning gasoline."

[diablopilot 2]

OR we cold kark all that and just swoop. I don't care how it works so much, I just love the "feel".


"Feel it."

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You're not as good as you think you are. Seriously.

[AggieDave 6]

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OR we cold kark all that and just swoop. I don't care how it works so much, I just love the "feel".

Sounds good to me. Now if the rain would let up so I could go swoop...atleast if it clears this weekend Aggieland will have a swoop pond or at the least a swoop swamp. Of course it used to be the landing area, but mother nature changed that.

--"When I die, may I be surrounded by scattered chrome and burning gasoline."

[skygod7777 0]

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OR we cold kark all that and just swoop. I don't care how it works so much, I just love the "feel".

great idea, thank you.

later

[diablopilot 2]

*gloat*



Shorts and a tshirt today Dave........6 jumps. Sorry man.

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You're not as good as you think you are. Seriously.

[quade 4]

I don't think you have a clear understanding of the term.

Ground effect isn't additional lift -- it's reduced drag.

It's not getting a cushion of air underneath the wing, but rather the ground reducing the induced drag of the wing tip vortices.

http://www.avweb.com/news/airman/185905-1.html

quade -
The World's Most Boring Skydiver

[diablopilot 2]

You are probably right.

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You're not as good as you think you are. Seriously.

[Spizzzarko 0]

I asked John Leblanc about this very issue about a year ago. The way he explained it to me is as follows. Air doesn't just flow from front to back of the wing. Air will flow from the center to the wingtips, too. This air rotating from the bottom of the wing to the top of the wing creates the vorticy. The addition of stabilizers on canopys really reduces this flow from the bottom to the top over the wingtips. It is these vorticees that allow for the increased lift in the "Ground Effect". As we slow down these vorticees are reduced quite a bit more. The speed required for the vorticees to create the added lift is usually only to be had on the smaller canopys. These smaller canopys have a smaller span, therefore they would have to be going at a very high airspeed very low to the ground (IE the pilot would have to be under the earth witch usually slows your swoop down quite a bit) for these vorticees to have effect on a skydiving wing. As far as the new JSX having no stabilizers, I don't know how that would effect the flight of the canopy. I would think that the reduced drag of not having the stabilizers would probably have more of an effect on the swoop than "Ground Effect" would ever have, but this is only speculation on my part about the JSX, as I havn't seen one fly or land. Things tend to get to Colorado about 5 years later than they hit the mainstream skydiving industry. Dual piggyback harnes systems are just now becoming popular here, but there are still a few die hards who will not give up their chest reserves!!! hahahahaha

[pilotdave 0]

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The speed required for the vorticees to create the added lift is usually only to be had on the smaller canopys.

All wings produce vortices. But as far as I know, only delta wings actually use vortices to create lift. Ground effect is basically what happens when a wing flies so close to the ground that the ground interferes with the vortices and the downwash coming off of it. Less downwash and weaker vortices means less induced drag.

Now the question is, how far around the canopy is the air affected as it flies by? Think any canopy moves the air under your feet (or a ways behind your feet actually)? I kinda doubt it... at least to any really significant degree.

Vortex strength is very much related to weight (along with planform, tip shape, etc). I just doubt a canopy produces very strong vortices or a whole lot of downwash. But it's possible.

Dave

[rsibbald 0]

What about during a wing-over? Would half the canopy enter ground-effect? Does the lower side of the canopy try to surge forwards at all for anyone who has tried this?

[larsrulz 0]

This is lots of fun...it's like an episode of kids say the darndest things. Quade (big surprise) and Pilotdave have it down. Vorticity is always made whenever a wing produces lift. In straight and level flight, vorticity doesn't change. It doesn't matter if you are 2 feet over the ground or 200, vorticity is the same. What vorticity does is induce downwash (little rotors off the wingtips). As a wing approaches the ground, the ground, in effect, imparts an upwash on the wing, which in total sees less downwash so hence, less drag.

I would imagine that the vast majority of the drag on a canopy is skin friction as opposed to induced drag, so ground effect would be negligible.

As for a wing-over, the canopy's orientation would produce the vorticies in a different way, so the ground effect would not hold. For instance, a vertical tail close to the ground would not actually be under ground effect, so the wing needs to be parallel (or the closer to parallel it is the better) to the ground.

I got a strong urge to fly, but I got no where to fly to. -PF