wing loading

[ArmitageShanks 0]

Question:
If .75 is the ideal "mid-range" wingloading, and .7 to .8 work for gnarly / forgiving respectively, at what point does a wingloading become dangerously low, if at all? Would a .65 be problematic? .6? Is there a point you shouldn't go beyond?
Cheers.

[Faber 0]

you dont want a tandem chute for different reassons

for an example too big a canopy could give you less/no forward speed under windy conditions,but a small one could fly too fast(indeed if your facing the object just after the opening).

just some thourghts..but i guess it depends on the pilot.Im sure some really experienced will tell more about this

Stay safe
Stefan Faber

[TomAiello 26]

I actually think your best bet is to go with Shotgun Ray's Rule of Thumb, which is explained by Dwain in this thread.

Quote

Many years ago I used to be a dealer for BASE gear and so the "what canopy size should I get" question is something I've been asked many times. From my experiences the .75 textbook wingloading is outdated, oversimplified and often results in people using the wrong sized canopy for their needs.

Two people with the same wingloading will have very different results if, for example, one person is flying a 200 sqr foot canopy and the other a 320 sqr foot canopy. Wingloading is not a constant formula which can be applied to all canopy sizes. Many years ago I developed a rather detailed and complex table for customers to determine their ideal sized canopy given a number of variants.

However about a year ago Ray from Portland told me his formula for working out your ideal canopy size. His formula is so idiotically simple on the outset that it continues to annoy me to no end. However in my opinion, when you apply it, it provides the best results of anything I've heard so far.

Basically it goes like this:
Take your naked body weight in pounds and add 100 to it. This is your ideal mid-range canopy size. Add 20 if you are going to be doing lots of objects where you land in really bad landing areas or if you prefer landing in deep brake approaches. Subtract 20 if you are going to be doing lots of jumping in high winds (eg. antennas or big walls) with good landing areas.

I've asked many experienced BASE jumpers what their preferred canopy size is and this formula seems to apply the best.

Kudos to Shotgun Ray - an unsung BASE legend of the Pacific NorthWest.

-- Tom Aiello

Tom@SnakeRiverBASE.com
SnakeRiverBASE.com

[TomAiello 26]

Quote

...at what point does a wingloading become dangerously low, if at all? Would a .65 be problematic? .6? Is there a point you shouldn't go beyond?

I have jumped canopies as highly loaded as .92 and as lightly loaded as .58. Note that the .75 wingloading is a general guideline, which can be innaccurate at the high and low ends of the scale (because canopies do not scale precisely, hence neither does wingloading).

The answer to this question will vary, depending on several things, such as:

1) What kind of object you are jumping

On a solid object, it is more important to have (a) a docile canopy on opening (hence, a bigger canopy) and (b) a quicker, cleaner opening (hence a smaller canopy). When I have taken my wingloading below about .65 (no vents) or .6 (vents) I've found the openings become unacceptably unpredictable. In my experience, this is not a gradual progression. It's more of a bright line. At some point, as you drop your wingloading lower and lower, you hit a size where the canopy just doesn't open right. Adding some weights (or downsizing) pretty much fixes the problem immediately. I suspect that this point occurs at different places on different canopies, generally following the rule that canopies with cleaner openings experience it at lighter wingloadings (so, if you are jumping an unvented Troll or FOX, you will hit it sooner than on an Ace or Mojo, with the vented canopies--Blackjack, FOX and Flik Vtec, Troll MDV--allowing the lightest wingloadings of all).

2) What the landing area is like

If your landing area is wide open, you don't need a giant canopy (especially on a wind-through object, where you won't need docility at opening either) and can get away with a smaller, lighter, cheaper canopy that performs just fine for wide open landing areas and non-solid object openings. (This may help explain why historically, Aussies have jumped the largest canopies and Floridians have jumped the smallest.)

3) How high the wind is

With lots of wind, you'll need a higher wingloading to achieve penetration (cue Beavis). If you habitually jump in high winds, you'll want a smaller canopy (and you're probably jumping mostly towers or bridges). If you jump in light or zero winds, you can get away with a larger canopy (lighter wingloading), and hence you can take worse landing areas, and higher strike potential objects.

4) How high the object is

On a very high object, you will have very little strike potential, so a relatively undocile canopy (i.e. higher wingloading) will be acceptable. If your object is lower, you will need a more docile (i.e. lighter wingloading) canopy on opening. If you are free falling ultra low objects (i.e. sub 200') you may consider downsizing again, as the difference in opening time between sizes becomes noticeable at these altitudes.

5) What your experience level is

Obviously, your ability to control the canopy is the most important factor. If you can stand up a .9 wingloading on jagged talus, then you may be able to load higher. If you can maximize all your control inputs to fight a 20 knot wind at .6 wingloading, you may be able to load lighter.

Your experience and skill are going to be the most important factors--far more important than your choice of canopy size or wingloading.

Hope this helps.

-- Tom Aiello

Tom@SnakeRiverBASE.com
SnakeRiverBASE.com

[DexterBase 1]

Wow, well written Tom.