Calculating your optimal wingloading

[Chris-Ottawa 0]

Ok, so I'm trying to figure out how PD or any swooper determines what size canopy is optimal for a given task. I’m trying to understand drag and skydiving at an advanced level. I know the knowledge is out there!

Eg #1: Distance swoopers obviously want as large a canopy as possible to generate lift, but without going too big where the drag nullifies any extra lift the larger canopy would allow. It seems like swoopers “generally” stay around 90-100, so I assume a loading of 2.4 on a 100ish canopy is roughly optimal, then it becomes pilot skill.

Eg #2: Me...115 lbs under a 105 sq ft canopy. Obviously I'm not making the canopy perform in it's optimal performance envelope. So, consider me, 1000 jumps from now competitive swooping. Disregard the fact that I’m still not interested in swooping. For me to have a wingloading at a "competition" (2.4ish) swoop level, I would need to be on a canopy smaller than 60 sqft. Obviously I know that a 60 sq foot canopy loaded at 2.4 will not even come close to swooping as far as a 100 loaded at 2.4 because the 100 has much more surface area to generate lift. As I understand, the 60 would be generating more lift simply due to the speed, but once that got to a certain level, it would just shut down. So if I was swooping the 100, I'd have to wear over 100 lbs of lead to load it to a competition level. Obviously if I was a competing swooper, I wouldn't be on a 100, nor a 60. I'm looking on how that "happy medium" is determined for any given canopy. I know canopy type has an effect on this too. Are lighter swoopers at a disadvantage because they cannot load a “large” canopy enough to generate the speed necessary to sustain flight and generate the required lift.

Now, I used those 2 examples because it's easier to explain what I'm looking for. I have no interest in swooping, but I'm kinda geeky in the fact that I want to know how things work and why. I like to know the physics behind things.

I guess I'm looking for 2 things:
A) What is the optimal canopy and jumper weight that will generate the best distance swoop. Would it be a 100 sq foot canopy, with a 280 lb jumper, or will it be a 120 with a 220 lb jumper or a 75 sq ft with a 190 lb jumper. Obviously there is an optimal configuration where theoretically someone with that config would be able to outswoop anyone no matter what.

B)Is there a way to figure out where a given wingloading under a given canopy is sitting in the canopy's performance envelope? Is there some sort of a scale that goes from 1 - 10, 1 being more lift, 5 being "optimal" and 10 being more drag. How can you figure out the point where drag overwhelms lift?

Hopefully I explained it clear enough, but feel free to ask for clarification. I'm pretty sure this just has to do with the drag coefficient and where the drag is minimal and loading is the highest. But I don't even know where to begin to look into that. This is just something that keeps me awake at night...random things I think about, but are way beyond my intellect level.

"When once you have tasted flight..."

[jakee 1,566]

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Eg #1: Distance swoopers obviously want as large a canopy as possible to generate lift, but without going too big where the drag nullifies any extra lift the larger canopy would allow.

That's a misunderstanding.

Do you want to have an ideagasm?

[Chris-Ottawa 0]

Care to elaborate? I'm curious why you think otherwise?

More surface area is capable of generating more lift and sustaining flight at a lower speed. A smaller canopy has less surface area, generating less lift and requires more speed to sustain the lift. So, on the smaller canopy, when your speed runs out...it shuts down quicker than the "large" canopy.

I could be completely wrong, but I generally know a fair amount about flight characteristics. Less surface area and/or less lift = more speed required to support the same payload.

"When once you have tasted flight..."

[piisfish 140]

are you sure about your 2.4 ?

scissors beat paper, paper beat rock, rock beat wingsuit - KarlM

[davelepka 4]

You are waaay over-thinking this. You're not making a split second decision here, canopy selection is a long, gradual process.

Jump a sensible wing loading based in your skill and experience. After an appropriate number of jumps, downsize to the next smaller size (no skipping sizes).

Eventually you'll find a canopy that scares the bejesus out of you. Some guys will stick with that size, others will back off a size. Either way, you've found your 'optimal' wing loading.


Also, 'optimal for competition' is not optimal for you. I prefer to jump at just under what most consider 'optimal' for a Velo. I tried 'optimal' for a season, and found it to be too much work under canopy. The pace of my canopy ride was faster than I wanted, so I dialed it back (two sizes actually), and have been very happy. What I lost in top speed, I more than made up for in distance, and my canopy ride is far more 'relaxing' than it used to be.

[obadz 0]

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Obviously I know that a 60 sq foot canopy loaded at 2.4 will not even come close to swooping as far as a 100 loaded at 2.4 because the 100 has much more surface area to generate lift.

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More surface area is capable of generating more lift and sustaining flight at a lower speed. A smaller canopy has less surface area, generating less lift and requires more speed to sustain the lift. So, on the smaller canopy, when your speed runs out...it shuts down quicker than the "large" canopy.

I could be completely wrong, but I generally know a fair amount about flight characteristics. Less surface area and/or less lift = more speed required to support the same payload.

You are right that a 60 sq ft loaded at 2.4 is not exactly the same as a 100 sq ft loaded at 2.4, but not for the reason invoked. You first say that the 100 sq ft has more surface area and therefore will generate more lift. But as you yourself point out in your second post, the payload isn't the same, so the 60 sq ft needs less lift to keep the jumper afloat.

They don't behave identically for reasons that are explained here: http://www.performancedesigns.com/docs/wingload.pdf

I once read somewhere on this forum that optimal wing sizes for swooping were in the order of 100 to 110 sq ft and a wingloading was also mentioned but I don't recall what it was. Light jumpers were supposed to carry lead to achieve that wingloading. I have no idea regarding the validity of that statement. From a pure physics perspective, a swoop is difficult to optimize as you fly at many different attitudes and speeds.

I submit however that the optimal glide performance of a given canopy is unaffected by suspended weight. To clarify: same canopy, same jumper (for drag), add/remove an arbitrary amount of lead; the jumper will cover the same distance over ground given 1000ft of altitude in the no-wind case if he trims his canopy optimally in each case (assuming we stay within a reasonable range where the trimming with risers does not significantly distort the wing)

Although it is unrelated to swooping, I find this to be an interesting fact.

[CanuckInUSA 0]

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You are waaay over-thinking this. You're not making a split second decision here, canopy selection is a long, gradual process.

Jump a sensible wing loading based in your skill and experience.

Good post Dave

Try not to worry about the things you have no control over

[morris 0]

I just would have liked to add that the opinion - about what the optimal wingloading is - changed over the years and in general went up and up and up.
The reason for this is very likely (besides the weight restriction rules) that the skills of the pilots got better and better as well.
I remember back in ~2001 the "perfect" wingloading for distance was about 2.05, with Shannon swooping far with a velo 103.
For speed it was about 2.2 back then.
Now at the 2007 WorldCup the top competitors chose loadings of about 2.7(!) for distance(!) in crosswind conditions.
Depending on the competitors weight this resulted in canopies choices form 79 to 90 to achieve those loadings.
If I remember correct, out of 57 competitors only ~3 flew a +100sqft canopy (Velo103) and those have been the heaviest guys in the field.

[punkd 0]

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You are waaay over-thinking this. You're not making a split second decision here, canopy selection is a long, gradual process.

Jump a sensible wing loading based in your skill and experience.

Good post Dave

I think Chris was trying to find out the theory behind these choices, not neccessarily saying hes gonna go get himself a sub 100 xbrace and strap on as much lead as he needs to achieve the correct WL.

From a physics and math perspective, there has to be away to figure out the drag vs the lift to calculate speed and distance. (Of course, eliminating variables like different canopies/pilots expereience level, wind etc..)

Im just not sure how to go about obtaining the neccessary formula's for such calculations.

[Chris-Ottawa 0]

That would be absolutely correct. If anyone thinks I'm trying to get to my optimal wingloading, that is far far far from my goal. Like I said in my post, I'm trying to figure out the math, if there is any behind it. From the posts so far, it seems as though people haven't really tried to figure this out and just use what they think works. There HAS to be math behind this.

I'm already jumping a 105 sq foot parachute which will last me many jumps to come.

"When once you have tasted flight..."

[SethInMI 174]

Yeah, Chris is just curious. I am too sometimes, its just as if I asked Peter Solberg how to slide a rally car down a gravel road at some ungodly speed. I am not going to do it, just want some idea of what is involved.

Dave said something that backs up what Chris said about larger swooping canopies being better for distance, he said he swoops a slightly larger canopy which is slower but flies farther. Why is that? And what would a 115lbs person have to do to be a competition swooper, and why?

Quote from Dave:

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...The pace of my canopy ride was faster than I wanted, so I dialed it back (two sizes actually), and have been very happy. What I lost in top speed, I more than made up for in distance, and my canopy ride is far more 'relaxing' than it used to be.

It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

[CanuckInUSA 0]

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I think Chris was trying to find out the theory behind these choices, not neccessarily saying hes gonna go get himself a sub 100 xbrace and strap on as much lead as he needs to achieve the correct WL.

Hmmm ... did I say anything about anyone jumping a specific canopy? No I just thought it was a good post by Dave and last night in my drunken stupor I felt like supporting what he wrote. Nothing more, nothing less. Carry on, there is nothing to see here.

Try not to worry about the things you have no control over

[davelepka 4]

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That would be absolutely correct. If anyone thinks I'm trying to get to my optimal wingloading, that is far far far from my goal. Like I said in my post, I'm trying to figure out the math, if there is any behind it. From the posts so far, it seems as though people haven't really tried to figure this out and just use what they think works. There HAS to be math behind this.

Look man, if I thought you were trying to figure out what canopy to order on Monday, I would have come at you with a much different attitude.

There is math behind all aspects of canopy flight, but there are no 'hard' numbers like you might see in a rigid wing craft. There are too many variables in canopy flight to come up with those figures.

The pilot is a big one, and I'm not talking about their skill level (yet). The size and co-efficient or drag of the pilot will have a huge effect on the canopy. A fat guy in a baggy suit will create all sorts of drag, and in steady state flight will be further behind the canopy, pitching the nose down slightly. A little guy with a big weight vest will provide the same wing loading, with less drag, and get a different level of performance.

Is the difference huge? Who knows, even if it's not, any difference at all will be very clear if you're looking at it in mathmatical terms.

Which brings me back to my earlier post, that there is no 'optimal' wing loading. Beyond your body type, your style of canopy flight may require a notch more loading than the next guy to yeild the best results. This something you'll discover as you mature as a canopy pilot, and learn what works for you.

[AggieDave 6]

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A fat guy in a baggy suit will create all sorts of drag, and in steady state flight will be further behind the canopy, pitching the nose down slightly.

And then a fat guy with a big wing and a high wingloading wearing tighter (but not scary tight, remember he's fat) clothing will haul ass and go a decent distance.

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

[morris 0]

I got another example showing how difficult it is to approach canopy flight with math.
A while ago I went pretty deep into the theory of line drag (at least for someone who hasn´t studied the topic), back then I also posted something about it here.
I don´t wanna write it all again, so here´s a short version of what happened.
The problem ahead was to calculate the difference in linedrag between HMA500 and HMA300 lines.
Finally we got all what it took to do this kind of calculation, at least for round lines (and as you know a lot of linetypes are not round and to calulate those is almost impossible cause they are moving all the time at least a little bit, even if they would be shaped like a teardrop - this has been tested on paragliders).
We found out about so called "reynolds number" (check it out yourself) and that (for example) half the diameter isn´t half the drag cause the thinner you go the more (percentage of) turbulent (high drag) airflow is created and less and less laminar (low drag) airflow goes around the line(s).
The final conclusions were that there is an advantage in drag using thinner lines (no surprise) but this advantage was supposed to be very very little (by the answers the math provided).
"Real" jumping proved the math being wrong!
The difference in drag was way more than it would have had to be!
How could that be?
The answer was that every line is creating turbulent airflow all the other lines that "travel behind" (B,C,D,...) have to fly through.
Therefore the calculations where useless except for the A-lines.
Now you can imagine that if you change just the location of the lineattachment points or the location of a linecascade this already affects the overall linedrag by changing the percentages of turbulent airflow in every "location"...