Over/Underloading a Canopy and "Efficiency"

[Elisha 1]

So, what do these terms mean?

For example, it seems that most squares are designed to be loaded less than around 1.3-1.4, semi-ellipticals (Sabre2s, Pilot, Fusion, Safire2, etc.) <1.6, regular ellipticals (Katana, Stilleto, Mamba, Crossfire2, etc.) <2.0 and something higher for crossbraces.

People have said that they have overloaded their semi's (1.6 or more) and still landed fine, loaded reserves at close to 2 and other stuff. I'm jumping a Sabre1-120, that I'm actually overloading according to the warning label at 1.25-1.3, but I guess PD revised the chart, and I'm still within range (up to 1.4 I guess). People say the wing becomes "less efficient". So, what does this mean? What if someone 200 or so OTD jumped my Sabre? Would it be difficult or near impossible to have an easy stand up landing?

I haven't come across much discussion on this topic. Thanks.

[DrewEckhardt 0]

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People have said that they have overloaded their semi's (1.6 or more) and still landed fine, loaded reserves at close to 2 and other stuff. I'm jumping a Sabre1-120, that I'm actually overloading according to the warning label at 1.25-1.3, but I guess PD revised the chart, and I'm still within range (up to 1.4 I guess). People say the wing becomes "less efficient". So, what does this mean?

Most significantly the stall speed goes up. You have to do more right to get a nice landing. Swoops get shorter. The glide ratio goes down.

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What if someone 200 or so OTD jumped my Sabre?

On a hot summer day at 5000' MSL they'd run like hell on landing. Or slide unless they were landing on asphalt/concrete where that isn't possible.

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Would it be difficult or near impossible to have an easy stand up landing?

Difficult is relative. It would be harder to get a nice landing than jumping a more efficient non-square wing. It would still be possible.

[phoenixlpr 0]

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Would it be difficult or near impossible to have an easy stand up landing?

Do you have problems with your landings?

[Elisha 1]

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Would it be difficult or near impossible to have an easy stand up landing?

Do you have problems with your landings?

Not at all (although I'm sure they'll get even better when the new lineset arrives) - I'm not talking about myself, but general questions. These are general questions to you experienced folk. Which of course leads to...why are people loading these canopies more than designed or intended by the manufacturer? What about loading these f-111 reserves so high and not getting a larger reserve?

[phoenixlpr 0]

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why are people loading these canopies more than designed or intended by the manufacturer?

They might perform good enough.

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What about loading these f-111 reserves so high and not getting a larger reserve?

Some reserves can be loaded, because they are certified.
Other reserves does not fly well if they are overloaded.

Can you fit 1 or 2 size bigger reserve in your container? Usually not. Changing reserve is major pain in the ass.

[DrewEckhardt 0]

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What about loading these f-111 reserves so high and not getting a larger reserve?

They don't land as nice or glide as flat as a more modern design at the same wing loading.

After putting 500 jumps and pack jobs on one as a main you wouldn't be able to get acceptable landings; although most of us aren't having more than 3 pack jobs done a year on our reserves,

According to George Galloway most of the wear occurs during the pack job and F111 reserves perform no different than a ZP canopy of the same shape.

[billvon 2,991]

>The glide ratio goes down.

Glide ratio stays exactly the same, actually, as loading goes up (everything else being equal.) However, if you increase drag as well (i.e. the heavier guy is 6" taller, or wears a floppy suit for fallrate purposes) then L/D goes down, which means glide goes down.

[bch7773 0]

these kind of questions are right up Brian Germain's alley.

MB 3528, RB 1182

[FrogNog 1]

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People say the wing becomes "less efficient". So, what does this mean?

I think this is a central question. I think we've lumped a lot of potential performance characteristics into one word here and said "more efficient is better" and then we look to optimize or envelope "efficiency".

And I see that as the logical falling-apart. Maximizing glide ratio or achieving the lowest possible minimum sink speed is good for some needs, but I don't see it necessarily having anything to do with landing characteristics. And I'm a big fan of landing.

Most people I know who load their canopies over 1.5 lbs/sf care a lot about how fast their canopy can be made to go level after a dive, and also about how it can be made to transition from the dive to the level part. Since I actually don't want my canopies to go really, really fast I can't take any of their advice on "efficiency".

-=-=-=-=-
Pull.

[Elisha 1]

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these kind of questions are right up Brian Germain's alley.

So I should just RTM (i.e. buy his book) and shut my piehole online here? Hey, I thought this could be an interesting discussion!

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[Martini 0]

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What if someone 200 or so OTD jumped my Sabre? Would it be difficult or near impossible to have an easy stand up landing?

I jump a Sabre-1 120 for most of my jumps (it's my wingsuit canopy). I'm around 190 OTD and wouldn't hesitate to jump the canopy with 10-20 lbs. extra weight. I usually spin a 360 hook but I've also used the canopy for a demo landing straight in on asphalt. The charts aren't literal.

Sometimes you eat the bear..............

[Ratty 0]

Everyone has mentioned the over loading, what about underloading? What is the minimum loading a canopy should be?
I'm currently doing my student progression and have to jump a 280 which gives me a wing loading of around 0.55. Means I descend VERY slowly even with doing lots of turns.
Only 3 more jumps and I get to convert to a 210 which will at least be a wing loading of 0.7

[DrewEckhardt 0]

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What if someone 200 or so OTD jumped my Sabre? Would it be difficult or near impossible to have an easy stand up landing?

I jump a Sabre-1 120 for most of my jumps (it's my wingsuit canopy). I'm around 190 OTD and wouldn't hesitate to jump the canopy with 10-20 lbs. extra weight. I usually spin a 360 hook but I've also used the canopy for a demo landing straight in on asphalt. The charts aren't literal.

You also jump at sea level in a temperate state. A 120 at 10K feet density altitude on a hot summer day in Colorado has the forward speed of a 97 at standard sea level conditions. Or you with 45 pounds of lead out the door.

While conservative for sea level jumpers, I don't think the PD numbers are too far out of line for jumpers at elevation.

[DrewEckhardt 0]

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>The glide ratio goes down.

Glide ratio stays exactly the same, actually, as loading goes up (everything else being equal.)

The problem is that everything else isn't equal when it comes to parachutes and skydivers.

Since the jumper is only adding drag without lift, the glide ratio can only stay the same if the jumper's frontal area is proportional to canopy size.

This obviously isn't the case for a single jumper increasing their wingloading by jumping a smaller canopy.

Lines also add drag without lift. Assuming line length increases linearly with the other canopy dimensions, thickness would need to be proportional to the square root of canopy size for lift/drag and glide ratio to not decrease with smaller canopies.

I assume that for a given body shape, surface area increases approximately with the square of height and weight with its cube which is to say human surface area increases with weight ^ 2/3.

Looking at skydivers' clothes and body position in both vertical and flat freefall positions, it appears that people only partially offset this by wearing more or less aerodynamic clothing and adding weight. The rest comes from body position differences. Small women seem to belly fly with harder arches. Big sit flyers often add drag with the insides of their calves. But the same skydivers adopt the same sort of position under canopy, meaning the smaller person + parachute will have a worse lift:drag ratio and glide at the same wing loading as a larger person.

Smaller parachutes mean decreased lift:drag for both individual parchutists and skydivers as an aggregate group.

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However, if you increase drag as well (i.e. the heavier guy is 6" taller, or wears a floppy suit for fallrate purposes) then L/D goes down, which means glide goes down.

Right, it's a L/D decrease.

[Martini 0]

I agree. But the original poster is a California jumper so likely jumps near sea level, temperature obviously isn't a constant. And having conservative charts is the only sensible thing to do. But they still aren't literal. While they might be too extreme for a few jumpers most experienced jumpers find manufacturer's w/l charts to be pretty conservative in average conditions. Again this is as it should be, if a jumper wants to exceed the reccommended loadings it is then the jumper must accept the result of his/her choice.

Sometimes you eat the bear..............

[billvon 2,991]

>The problem is that everything else isn't equal when it
>comes to parachutes and skydivers.

Sometimes it is, sometimes it isn't. If you increase loading by adding weight to your weight belt, then your L/D doesn't change, and your glide stays the same (although your forward speed may be faster.)

However, if you change your loading by going to a smaller canopy, the smaller canopy will likely NOT have the same L/D as the larger canopy. Aerodynamics doesn't scale like that.

[Elisha 1]

thanks guys...but I still can't believe there are so few replies to this thread. I thought it would get a lot more discussion. I thought of the Canopy Control forum, but thought that it was mostly just swoopers.

[phoenixlpr 0]

What do you expect? Most of us is not a canopy designer. Most of us use our canopy in its intended performance envelope.

[Elisha 1]

What do I expect? I expect answers, of course! There have been several posts saying, "I landed my Smart at 1.8:1 and it landed great!" or "My PDR113 loaded at 2:1 was a great ride and I stood up the landing easily." or " I jump my Sabre2 at 1.7:1 and it still performs great." (even though it may be only rated up to 1.6:1. There have also been discussions on jumping a lightly loaded elliptical (e.g. 1:1 or even less). I want to know why? How does the wing perform in these out of recommended ranges? Why do people jump them in these ranges? Etc., etc.?

[jheadley 0]

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Everyone has mentioned the over loading, what about underloading? What is the minimum loading a canopy should be?
I'm currently doing my student progression and have to jump a 280 which gives me a wing loading of around 0.55. Means I descend VERY slowly even with doing lots of turns.
Only 3 more jumps and I get to convert to a 210 which will at least be a wing loading of 0.7

I heard Scott Miller once say that in theory, there really is no such thing as "underloading". PD has no minimum wing loading for their canopies (except the velo). The chart says "VLC" which means Varies with Landing Conditions. In completely dead still air, evenly an extremely lightly loaded canopy would fly fine. It'd have very very slow airspeed, but it would work.

But the wind is almost never dead still. With an extremely lightly loaded parachute, it would have very little forward speed, so it would be harder to penetrate a headwind, making landing accuracy very difficult. Also, in turbulent conditions, it's "better" to have a higher wing loading, which would give more internal cell pressurization and it would be more resistant to collapse. Although some people will debate that.

So basically light wingloadings are perfectly fine, but you may want to stay on the ground more often than a person under a higher wingloading when winds get higher or bumpy. This is part of the reason why students (jumping lightly loaded canopies) have a wind limit.

[Ratty 0]

Thanks jheadley.

I agree about staying on the ground in windy conditions. A lot of people say that student canopy's don't collapse, I beg to differ. We were jumping at a new dropzone and the wind "limits" were unknown. The wind was very turbulent and I had a rather nasty canopy collapse, luckily high enough to recover before landing.

Its been an interesting thread for me as I will be looking into buying gear in the near future and want as much info as possible.

[phoenixlpr 0]

If you interested in highly loaded reserves you should read the manual of the PD reserves.

Overloaded main canopies? Some guys stated that front risers should be used for getting acceptable landing with some overloaded one.

[FrogNog 1]

I say with enough pilot experience, any extremely-lightly-loaded canopy can be hooked up backwards if the groundwind exceeds the steady-flight forward speed. Then you get to land moving forward.

Of course, when you flare, you'll pitch forward and your groundspeed will increase...

-=-=-=-=-
Pull.

[jerm 0]

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What do I expect? I expect answers, of course! There have been several posts saying, "I landed my Smart at 1.8:1 and it landed great!" or "My PDR113 loaded at 2:1 was a great ride and I stood up the landing easily." or " I jump my Sabre2 at 1.7:1 and it still performs great." (even though it may be only rated up to 1.6:1. There have also been discussions on jumping a lightly loaded elliptical (e.g. 1:1 or even less). I want to know why? How does the wing perform in these out of recommended ranges? Why do people jump them in these ranges? Etc., etc.?

These are some good questions, but i don't know that there are any concrete answers/whys what can be had. That being said, i'll give you my impressions fwtw.

re: highly loaded reserves - most reserves aren't recommended to be loaded at the ratios that you mentioned above, but that doesn't mean that they're suddenly unsafe to fly above some magic number. Even if that number does exist, i imagine the manufactures would pad it heavily because they know that skydivers are the type to push limits, break rules, and exceed stated tolerances for fashion sake. The numbers printed on the labels are there to define a relatively 'know quantity' with respect to canopy performance. Go outside of those boundaries and they don't make any promises.

As to why people would not only exceed those tolerances but do so in an egregious manner (2:1 reserve loading), that's likely a fashion issue -- small rig. Mind you, i have no doubt that i could land a PD reserve loaded at 2:1 just fine on a good day, but it's the bad days i'm worried about. The problem is that if you find yourself under your reserve, there's a good chance that it wasn't a good day that got you there. I don't want to be slumped to one side in my harness under s 2:1 reserve.


The same rules about magic numbers apply to main canopies as well. Jumping a sabre at 1.7 may fall outside of the 'ideal' performance envelope identified by the manufacturers, but 'ideal performance' is a very subjective thing. If someone loves their sabre at 1.7, great. Most people jumping that sort sort of loading are looking for the kind of flight characteristics that a fully elliptical canopy is better able to provide, and i'm sure that figures highly into the recommended loadings.

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

[JohanW 0]

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What do I expect? I expect answers, of course! There have been several posts saying, "I landed my Smart at 1.8:1 and it landed great!" or "My PDR113 loaded at 2:1 was a great ride and I stood up the landing easily." or " I jump my Sabre2 at 1.7:1 and it still performs great." (even though it may be only rated up to 1.6:1. There have also been discussions on jumping a lightly loaded elliptical (e.g. 1:1 or even less). I want to know why? How does the wing perform in these out of recommended ranges? Why do people jump them in these ranges? Etc., etc.?

If you want n=1 experiments, I have some for you.

I regularly fly a Triathlon 120 at a 1.8 wingload. Why? It opens on heading, flies straight in twists (up to 5 so far ), does not really react to harness input and it keeps diving nicely in an induced speed landing. I bought it for wingsuit jumps and I now use it for RW, CRW and HPPA, because it works and I like the way it flies (and lands). It is overloaded. It doesn't really maintain its speed after a turn, and its stallspeed is higher. Also, its glide ratio isn't amazing. It doesn't drop out of the sky like a brick, but it won't get you home if the spot sucks. Other designs work better at this wingloading. The Tri 135 I used to fly had better slow flight, but just wouldn't dive or turn as fast. To me, the 120 is more fun to fly. The 175 flew like a dog, the 160 flew like a nice docile canopy, the 135 flew like a nice advanced canopy, the 120 (at that wingload) is not for everybody, but I like it. Yes, I land it standing up.

I have also flown a PD 9Cell 150 @ 1.5 for wingsuiting. That one was seriously, don't try this at home overloaded. It didn't have a glide ratio, it had a ballistic index, speeding it up some for landing really helped the flare, and better have good timing on impact the flare. So why did I jump it anyway? Because it opened nice (it's completely square), and the price was right, i.e. free. And I got away with it. But that didn't make it a good idea. Comparing it to a differently sized square, 9-cell, non-ZP canopy is difficult, because the only one I've jumped was (almost) twice as big. A Manta. You know how those fly. Still, apart from the pack volume, I'd rather jump a Manta than a PD 150. The Manta flies. The Manta has a semblance of a flare.

The last comparison I can give you is a Katana 120 vs. a 107. Wingload 1.8 vs. 2.0. The 107 was not overloaded in the sense the other examples are, but the general "performance" of the 120 felt better (with my weight and skill) than that of the 107. The 107 was quite a handful for me, so I just couldn't make it perform the way I could the 120. Twitchy, extremely sensitive to inputs. With all that, I felt I could not get higher speed, sharper turns, longer dives, further swoops or more flare out of the 107 than I could out of the 120. This may be more of the pilot being overloaded than the canopy, but it definitely felt better flying the 120 than the 107.

So overloading your canopy design a little may be worth it. It might allow you to downsize a less aggressive design, at the cost of slow flight performance. This is not generally a good idea, but for a heavier wingsuiter (me), there are advantages to it. You do not want to overload the canopy to the point that is basically stops flying and starts dropping out of the sky, you do not want to downsize to the point of overloading the pilot, but if you can time and dose the flare, don't need the glide and don't care for swoop distance, you can fly a pig with a lot of thrust.

And that's why I do it. And why you should not (yet). Do as I say, not as I do. But I hope I have answered your question, at least with respect to (my) overloading canopies. And I can always be used as a bad example.

Johan.
I am. I think.