Effects of wing-loading on glide angles...?

[LloydDobbler 2]

Okay, folks. I know I've grasped this concept before, but for some reason my mind isn't zipped up right today and it's eluding me here at the office as I ponder some things...(and where I don't have a copy of Brian Germain's book lying around for reference...). So, specifically, here's the Q:

Say I weigh 170 out the door, flying a Sabre2-170 at 1:1.

Then I downsize to a Sabre2-150 (or any canopy, really...key being, it's the same canopy model, so as to remain constant). Still weighing the same, I'm now at a W/L of 1.13:1.

What effect is the different w/l going to have on the glide angle of the canopy? Better penetration? Steeper descent? In my mind right now it seems to make sense that a higher-loaded canopy would sink more...but then again, it also seems to make sense that you'd get better penetration and airspeed would increase.

Can someone give me a quick, easy answer to this question so I can free up my mind from thinking about it today? For some reason it's just not coming to me right now.

Maybe it's that I've spent 4 hours staring at Excel. Ugh. I need to be in the sky....

Signatures are the new black.

[phoenixlpr 0]

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What effect is the different w/l going to have on the glide angle of the canopy? Better penetration? Steeper descent? In my mind right now it seems to make sense that a higher-loaded canopy would sink more...but then again, it also seems to make sense that you'd get better penetration and airspeed would increase.

If you compare your body would have more resistance, due to the wing is smaller, but the difference is small.

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In my mind right now it seems to make sense that a higher-loaded canopy would sink more...

What is sink more? Do you mean sink steeper? No, but you'll spend less time under it, because if will sink faster in full glide.

So your glide ratio will remain about the same, but you will come down faster.

Is that good for you? Who knows? Are you ready for that?

[BMFin 0]

Im no expert but what I understand, glide angle remains the same with any wingloading on the same canopy. Only the speed will increase as WL goes higher.

Also I think you have misunderstood the word penetration. It is used on talking about ground speed, not air speed.

When a high WL canopy is having a fast airspeed it will "penetrate" the upwind better

[DrewEckhardt 0]

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Okay, folks. I know I've grasped this concept before, but for some reason my mind isn't zipped up right today and it's eluding me here at the office as I ponder some things...(and where I don't have a copy of Brian Germain's book lying around for reference...). So, specifically, here's the Q:

Say I weigh 170 out the door, flying a Sabre2-170 at 1:1.

Then I downsize to a Sabre2-150 (or any canopy, really...key being, it's the same canopy model, so as to remain constant). Still weighing the same, I'm now at a W/L of 1.13:1.

What effect is the different w/l going to have on the glide angle of the canopy? Better penetration? Steeper descent? In my mind right now it seems to make sense that a higher-loaded canopy would sink more...but then again, it also seems to make sense that you'd get better penetration and airspeed would increase.

Can someone give me a quick, easy answer to this question so I can free up my mind from thinking about it today? For some reason it's just not coming to me right now.

Maybe it's that I've spent 4 hours staring at Excel. Ugh. I need to be in the sky....

If you reduced your frontal area in proportion to the canopy size decrease and line diameter with its square root, glide angle (disregarding wind) would theoretically not change.

Since you stay the same size and line area only decreases with the square root of canopy size, you have a worse lift/drag ratio than you would at the same wing loading under the larger parachute and therefore your glide angle goes down.

This has been measured.

Some one on dz.com also hypothesized that with drag increasing with the square of velocity, at higher speeds the wind moves you farther back relative to the canopy thus trimming it more nose down.

Note that this assumes no-wind conditions. With enough head-wind you'll be able to achieve a higher glide ratio since you have more air speed (for example, in a 25 MPH wind a canop ywith that forward speed comes straight down, while one that goes 30 MPH will be going 5 MPH relative to the ground). With enough tail wind your glide ratio will go down because it becomes about staying up as long as possible and your sink rate will be necessarily higher (if you have 45 MPH air speed and a minute under canopy versus 15 MPH and two minutes with a larger parachute, with a 60 MPH tail wind you cover 1.75 miles versus 2 miles).

In practice it usually doesn't matter. With similar suspended weights a conventional 105 square foot Samurai (in brakes) will stay up with a 170 square foot Spectre (in full flight)

[LloydDobbler 2]

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Im no expert but what I understand, glide angle remains the same with any wingloading on the same canopy. Only the speed will increase as WL goes higher.

Also I think you have misunderstood the word penetration. It is used on talking about ground speed, not air speed.

When a high WL canopy is having a fast airspeed it will "penetrate" the upwind better

Ah-ha! Yes, I think you hit on it. That distinction is what's been giving me the headache.
Ground speed was the missing link.

I was just pondering the notion of CRW, and how I've heard people say they want someone with w/l between X & Y to fly with comfortably. It was just puzzling the heck out of me, trying to figure out how it would affect the dynamic.

Thanks for the responses, y'all!

Signatures are the new black.

[blackj 0]

downsizing the canopy will change glide angle. Canopys are design to have the same characterists over all there sizes but they do vary. A better analogy would be to keep the canopy the same i.e. a saber2 170 and increase the weight under it. Ideally without increasing the surface area of the weight. In this case "from my understanding" the glide angle will remain the same but the forward speed will increase.

[riggerrob 643]

Glide angle will remain the same ,as long as you stay within the manufacturer's wing-loading recommendations, both horizontal speed and vertical speed (rate of descent) with increase.

In other words, it will just slide down that imaginary "rope in the sky" faster.

Yes, jumper size does not scale exactly, but as long as you wear a similar jumpsuit, the difference will be negligible.

It is only when you get outside manufacturer's recommended wing-loading that glide performance suffers. For example, a seriously under-loaded sport canopy ( less than 0.6 pounds per square foot) canopy will mush along, too slow to glide properly.
Similarly, a seriously overloaded sport canopy ( more than 2.5 pounds per square foot) will be going so fast, that drag will increase faster than lift, also deteriorating glide angle.

Flamers: yes I know that some professional pond swoopers fly canopies specifically designed to be loaded more than 2.2 pounds per square foot, but that is outside the realm of most casual, weekend skydivers.

[riggerrob 643]

Note that this assumes no-wind conditions. With enough head-wind you'll be able to achieve a higher glide ratio since you have more air speed (for example, in a 25 MPH wind a canop ywith that forward speed comes straight down, while one that goes 30 MPH will be going 5 MPH relative to the ground). With enough tail wind your glide ratio will go down because it becomes about staying up as long as possible and your sink rate will be necessarily higher (if you have 45 MPH air speed and a minute under canopy versus 15 MPH and two minutes with a larger parachute, with a 60 MPH tail wind you cover 1.75 miles versus 2 miles).

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>.

You were doing great until this paragraph.
Try to picture a canopy wandering around in a block of air. The canopy does not have a clue that a planet is drifting around, below its block of air.

[billvon 3,090]

1) If you change ONLY the loading on a given wing the glide angle will not change. i.e. if you add weight to yourself, your canopy will glide faster but will not change its glide angle; descent speed and forward speed will change at the same ratio. You will get better wind penetration. You will have more speed for landing, which (managed well) will give you longer planeouts.

2) A Sabre2-170 is not the same wing as a Sabre2-150. Wings don't scale like that. A Sabre2-170 loaded at 1:1 does not fly exactly like a Sabre2-150 loaded at 1:1. In general, the smaller canopy at the same loading (and with the same jumper) will have a slightly worse glide due to scaling effects. It will also turn faster due to its shorter lines and feel more responsive to toggles. This is why many lighter women are happy at lighter loadings.

[reinhart36 0]

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In other words, it will just slide down that imaginary "rope in the sky" faster.

Rob, I need some newby clarification related to this comment;

Does that mean that the "penetration" of a canopy is basically a function of the canopy itself, and not so much related to how heavily it's loaded (within reason of course)?

thanks!

[darkwing 5]

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...Does that mean that the "penetration" of a canopy is basically a function of the canopy itself, and not so much related to how heavily it's loaded (within reason of course)?

"Penetration" is usually considered the horizontal component of the velocity vector, so that if two otherwise identical canopies have different loadings, the higher loaded one will fly down the same glide slope faster, and thus have a higher horizontal component to its velocity. Thus it has more penetration.

As has been mentioned, the first, rough, estimate is that changing loading only changes speed down the same glide slope. A first adjustment to that rule of thumb is that higher loadings will result in a steeper descent angle, thus (on a no-wind day) landing shorter than the less loaded canopy, due to increased drag losses that arise because of the higher speed.

-- Jeff
My Skydiving History

[riggerrob 643]

Au contraire!

Let's try again.

Glide ratio (angle of descent) is set at the factory when they cut the lines.
Assuming that you do not touch toggles or risers ...
Simply increasing wing-loading (within manufacturers' guidelines) increases horizontal velocity (penetration) and vertical velocity (rate of descent).
The angle of descent (glide ratio) only deteriorates slightly as you increase wing-loading.
The angle of descent (glide ratio) will change (deteriorate) a little faster because drag increases faster than lift.

So wing-loading is the dominant variable in determining how fast the canopy "penetrates."

For example, if you hang identical twins (dressed in identical jumpsuits, helmet, etc.) under canopies with consecutive serial numbers, but hang a 20 pound weight belt on one of them. The heavier-loaded canopy will "penetrate" (forward speed) faster and descend faster, so that it lands first, but the glide angle (lift to drag ratio) will only change a tiny amount.

"Penetration" measures how fast the canopy flies forward, relative to the wind.

[LloydDobbler 2]

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For example, if you hang identical twins (dressed in identical jumpsuits, helmet, etc.) under canopies with consecutive serial numbers, but hang a 20 pound weight belt on one of them. The heavier-loaded canopy will "penetrate" (forward speed) faster and descend faster, so that it lands first, but the glide angle (lift to drag ratio) will only change a tiny amount.

Great example, Rob - thanks for providing a concrete illustration.

To complete the analogy (so I'll be able to better discuss it when the question arises), back to my original question - what if you hung those two identical twins under the exact same model canopy, except one was a 150, and the other was a 135 (or a 210 and a 190 - basically, one size smaller)?

In theory, the glide ratio would stay close to the same on a no-wind day, but the twin under the smaller canopy would get down faster, correct? (And, as discussed earlier, if it was a windy day, they'd have more penetration into the wind due to increased forward speed)?

Signatures are the new black.

[Squeak 17]

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In theory, the glide ratio would stay close to the same on a no-wind day, but the twin under the smaller canopy would get down faster, correct? (And, as discussed earlier, if it was a windy day, they'd have more penetration into the wind due to increased forward speed)?

This is the anaolgy i like to use,
if you have a steep slope and two cars of different horse power (WL) the car with a higher HP (WL) will reach the bottom faster, but the slope does not change for either car
(is this 100% technically correct probably not, but it does serve to illustrate a concept)

You are not now, nor will you ever be, good enough to not die in this sport (Sparky)
My Life ROCKS!
How's yours doing?

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[billvon 3,090]

>In theory, the glide ratio would stay close to the same on a no-wind day . . .

Well, no. The 150 is not the same "aircraft" as the 135. For one thing, the canopy is smaller on a percentage basis, but the lines are not. So drag does not change linearly; it would be like thickening the lines on the 150. The pilot chute will likely be the same size, as will the jumper - which means you're not scaling them, either.

So in _general_ the 135 will not get the same glide ratio; it will be worse.

[reinhart36 0]

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So wing-loading is the dominant variable in determining how fast the canopy "penetrates."

"Penetration" measures how fast the canopy flies forward, relative to the wind.

I see. I was under the impression that what was being refered to as "penetration" was horizontal distance that could be achieved, not airspeed.

If your forward airspeed was faster at a higher wing loading, but your descent rate was increased in the same proportions, then the reduced duration of flight due to the higher wing loading would result in slightly less distance covered across the ground for a fixed begining altitude, because of increased drag losses.

Am I understanding this correctly?

thanks!

[riggerrob 643]

Basically you are correct.
A Sabre 150 and 135 will cover almost the same distance across the ground, the 135 will just do it faster.

[BMFin 0]

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A Sabre 150 and 135 will cover almost the same distance across the ground, the 135 will just do it faster.

This is only in theory since there is always the wind factor wich will have much effect on the ground distance covered.

Things like increased drag are true ofcourse, but relatively insignificant compared to wind conditions.

In a nutshell higher WL is more efficient on flying upwind and lower WL is more efficient on flying downwind.

[popsjumper 2]

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Basically you are correct.
A Sabre 150 and 135 will cover almost the same distance across the ground, the 135 will just do it faster.

Which implies that the 135 loses more altitude...which implies that the glide angle is steepened on the 135?

or,

Which implies that both canopies will get to the same altitude in the same distance with only the time factor involved...which implies no change in glide ratio, only horizontal ground speed?

Just needing clarification....

My reality and yours are quite different.
I think we're all Bozos on this bus.
Falcon5232, SCS8170, SCSA353, POPS9398, DS239

[riggerrob 643]

or,

Which implies that both canopies will get to the same altitude in the same distance with only the time factor involved...which implies no change in glide ratio, only horizontal ground speed?

Just needing clarification....

[riggerrob 643]

In a nutshell higher WL is more efficient on flying upwind and lower WL is more efficient on flying downwind.

[phoenixlpr 0]

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In a nutshell higher WL is more efficient on flying upwind and lower WL is more efficient on flying downwind.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

That is because the heavier-loaded canopy is exposed to winds aloft for fewer minutes.
On the other end of the scale, a lightly-loaded canopy will travel farther downwind because it is exposed to the winds aloft for more minutes.

[JerryBaumchen 1,451]

Back in the '60's Dan Poynter did some testing on glide angle of round canopies. He rigged up some Rube Goldberg device to determine the glide angle. Then he started jumping canopies with various mods; double L's, TU's, blow holes, etc. I think everything that he tested were 1.1's. He found that all of the canopies had the same glide angle, some just got to the ground faster (ouch ).

Jerry

[billvon 3,090]

>Think again! Does a boat knows if the water is still or moving?

Nope. But a boat doing 5 knots into a 6 knot current will still never be able to go upstream - but will be able to go downstream quite quickly. Likewise, a canopy's _groundspeed_ (which is what you care about, since you will only be in the air for X minutes under a given canopy after opening at 3000 feet) is affected by windspeed - even if it the canopy itself is just happily flying along.

>So canopy with the higher wing load covers more ground both ways.

Not really. A slow canopy in a strong wind (flying downwind) will have a more horizontal velocity vector, since you are adding a small downward vector (canopy glide angle) to a large horizontal vector (wind.)

Take an extreme. Assume a big round canopy that has ZERO drive but will take 10 minutes to descend 2000 feet in a 20fps wind. It will cover over 2 miles before reaching the ground. Now consider a 2.5:1 loaded canopy that will be on the ground in under a minute from 2000 feet. Is it going to be able to cover two miles? Probably not; it is descending too steeply, even in the strong wind.

A wise pilot will try to go to minimum sink rate if he wants to extend the glide on the heavily loaded canopy, because that way the wind contributes more to his total speed vector.

[phoenixlpr 0]

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Take an extreme. Assume a big round canopy that has ZERO drive but will take 10 minutes to descend 2000 feet in a 20fps wind. It will cover over 2 miles before reaching the ground. Now consider a 2.5:1 loaded canopy that will be on the ground in under a minute from 2000 feet. Is it going to be able to cover two miles? Probably not; it is descending too steeply, even in the strong wind.

Apples to oranges? Big round canopy is not an airfoil, those two does not have the same trim. How do you want to compare glide if those canopies has nothing in common?

I was flying a formation with a Cobalt loaded 1.6. My wing man used a Sabre loaded <1.3. And we kept the formation for several hundred meters....