Wingloading Big vs. small

[RichardWeed 0]

Heres a general question hopefully someone who has gained or lost alot of weight in their career can answer. PD talks about higher wingloading having less affect on a larger canopy vs. obviously the smaller. My question is how much of a difference is there? Lets say you had a Safire2 189 at 1.3 and a 149 at 1.3 how drastic would the performance be based on canopy size alone? Not many people have had the oppurtunity to fly both scenarios at the same wing loading. There must be Jenny Craig skydiving team somewhere. LOL

[Andrewwhyte 1]

The performance in turns will be similar; the big difference is that the smaller canopy is going faster.

[billvon 2,874]

>The performance in turns will be similar . . .

Not really true. The smaller canopy will turn faster; it has shorter lines, a shorter wingspan and the same toggle deflection will produce a faster turn since it will deflect the tail more. That's one reason some smaller women are quite happy at a 1:1 loading.

[RichardWeed 0]

Would it be safe to say then that the big (athletic) boys would typically run a slightly higher WL based on the same experience levels.

[KrisFlyZ 0]

Read the articles on the PD website
here.

Especially this one. You will need acrobat reader.

[RichardWeed 0]

I read those articles and the concept is a no brainer, but my question was to anyone with the experience of flying two very different sized wings (same model)at the SAME wing loading HOW MUCH of a performance difference there was. There are probably very few if any people that have flown the same canopy model at the same wing loading, like I said you would have to either gain a ton of weight and upsize or lose a ton and downsize. Thats the perspective I am looking for. Thanks for the input though.

[billvon 2,874]

>Would it be safe to say then that the big (athletic) boys would
>typically run a slightly higher WL based on the same experience
> levels.

Often, yes - although it's hard to make any hard-and-fast rules on what changes with scaling. John LeBlanc gives a good talk on these effects.

[thelem 0]

Quote

>The performance in turns will be similar . . .

the same toggle deflection will produce a faster turn since it will deflect the tail more.

Yes, but if you are lighter, then you may well be shorter and have shorter arms, which would affect your toggle deflection.

[billvon 2,874]

>Yes, but if you are lighter, then you may well be shorter and have
>shorter arms, which would affect your toggle deflection.

Length increases linearly, strength increases by the square of size, and weight increases by the cube of size (very roughly.) That's why a 6 foot tall guy may only be 20% taller than a 5 foot tall woman, but can weigh more than twice as much. So if your weight decreases by 50% your arms (on average) won't get anywhere near 50% shorter. But you're right that it might be a factor - I know some short women who have to take wraps on their brake lines to flare even smaller canopies well.

Interesting fact of the day - that's also why you can't just scale up an ant until he's the size of an elephant. The square-cubed law will get you every time.

[Andrewwhyte 1]

Quote

Interesting fact of the day - that's also why you can't just scale up an ant until he's the size of an elephant. The square-cubed law will get you every time.

Which is why poodles are smart and miniature poodles are stupid like a flat tire. The scale just does not work.

[wushidaoist 0]

I'm a low number jumper - 107. I haven't posted in a while, but always read the advice.

You guys have no idea how much your expertise helps.

I'm in the hospital right now with a knee injury from one of my other extreme sports. I was sure hoping to skydive this weekend.

[crazy 0]

Quote

my question was to anyone with the experience of flying two very different sized wings (same model)at the SAME wing loading HOW MUCH of a performance difference there was.

II didn't try, but it's quite easy to figure out what would change and to quantify it. Check this older thread to get an idea.

Since you consider the same pilot at different weight, the most significant change would be the reactivity to the input: the length of the arms is the same, but the lines on a 149 are 13% shorter than on a 189. This roughly means that you would need 13% less input on the 149 to get the same reaction than on the 189.

With the convenient assumption that the total drag on the 149 is 60% from the canopy surface, 20% from the pilot, and 20% of parasitic drag (lines, seams, etc), then the lift/drag is 7% better with the same pilot+lead under a 189. This should make the 189 glide better, pick up speed faster (counteracting the need for 13% more input), and swoop longer.

I let you make your own computation for the opening (the terminal velocity would be higher with lead, which would counteract the effect of the bigger volume) and other performance factor.

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Come
Skydive Asia

[DrewEckhardt 0]

I put about 20 jumps on a Samurai 120 with an exit weight of 195 pounds, and 150-200 on a Samurai 105 at 170 pounds out the door. I also have 600 jumps on a Stiletto 120 at exit weights from 170-205 pounds.

Toggle and harness control senstivity varies more noticeably with size than wing loading, with up to 35 pounds less weight at the same size having a minimal effect. Speed varies noticeably with wing loading. The actual magnitude isn't important.

Stall speed could limit the canopy size you jump (I wouldn't want to own a conventional elliptical loaded beyond 1.7-1.8 pounds/square foot at 5000 feet MSL for this reason).

Control sensitivity could - when I changed from a Batwing 134 to a Stiletto 120 I had problems flying straight after planeout.

[jerm 0]

Quote

Since you consider the same pilot at different weight, the most significant change would be the reactivity to the input: the length of the arms is the same, but the lines on a 149 are 13% shorter than on a 189. This roughly means that you would need 13% less input on the 149 to get the same reaction than on the 189.

With the convenient assumption that the total drag on the 149 is 60% from the canopy surface, 20% from the pilot, and 20% of parasitic drag (lines, seams, etc), then the lift/drag is 7% better with the same pilot+lead under a 189. This should make the 189 glide better, pick up speed faster (counteracting the need for 13% more input), and swoop longer.

the problem is that there's SO much more to it than that... jsut a few off the the top of my head

-inertia of the txtra air inside the larger wing will make it react slower

-extra drag of the bigger surface area of the larger wing will affect it differently (it's a square thing not a linear thing IIRC)

-how much air the deflected portion of the tail actually moves

-13% shorter lines does not necessarily correspond to how much less input one needs to give the canopy, it will be different, but i don't beleive it's as relative as you're making it out to be

bottom line is that the two different sizes are really 2 different wings, just ask kallend about how well the laws of aerodynamics scale... they don't.

Landing without injury is not necessarily evidence that you didn't fuck up... it just means you got away with it this time

[crazy 0]

Quote

the problem is that there's SO much more to it than that... jsut a few off the the top of my head

-inertia of the txtra air inside the larger wing will make it react slower

-extra drag of the bigger surface area of the larger wing will affect it differently (it's a square thing not a linear thing IIRC)

-how much air the deflected portion of the tail actually moves

-13% shorter lines does not necessarily correspond to how much less input one needs to give the canopy, it will be different, but i don't beleive it's as relative as you're making it out to be

bottom line is that the two different sizes are really 2 different wings, just ask kallend about how well the laws of aerodynamics scale... they don't.

You are right, i didn't spend much time thinking about the inertia of the extra air inside the bigger canopy. I just assumed, maybe presumptuously, that it was an appropriate and useful answer to the question, even if it's just approximations. Since you disagree, let's stick to your bottom line. Laws of aerodynamics don't scale; different canopies under different conditions have different performances. Better?

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Come
Skydive Asia

[WeakMindedFool 0]

Ok...the disclaimer is that I only have 150 Skydives, very little experience and no advice to give. I can give you my qualified impressions. Take them for what they are...the voice of inexperience:
170 Saber 2 @ 1.5
149 Safire @ 1.54

I lost 25 to 30 lbs from my first jump on my Saber 2 till now. Just jumped a friends Safire 149. The difference I found was dramatic. It turns/dives faster, flies faster is more twitchy all around. Found myself saying WOW alot. Took lots of self control not to just say "Fuckit" and get a 150! While it was fun, I figure a got quite a bit more to learn before I jump a 150 on regular basis. I found the difference to be...profound.

Faith in a holy cause is to a considerable extent a substitute for lost faith in ourselves.
-Eric Hoffer -
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