Skydive SAFETY – The CRUX
Dan's Dan's Thought for the Day...
Skydivers have a tendency to associate higher wing loading and smaller parachutes with pilot skill and proficiency. It has been baked into our learning progressions and DZ cultures. You buy a canopy, you get comfortable with it, and then you downsize.
Skydiving is not BASE jumping, and we treat canopy progression and wing loading very differently.
In BASE jumping wing loading is not typically correlated with experience and/or skill. An acceptable range of wing loadings has been established with different hazards coming into play as you get too far beyond that range on either side. In short, you should load your BASE canopy at (expressed in pounds per square foot):
.625 - .725
To calculate wing loading take your weight (in pounds) and divide it by canopy size. At Apex BASE we prefer to use body weight (without gear) as it provides the most consistent numerator.
For example: 180 lbs. / 260 square foot canopy = .69 lbs./sq. ft.
In skydiving we add gear weight because it is significant. Containers packed with a lot of hardware, AAD units, and reserve canopies add a material amount of exit weight. BASE gear weighs far less and we’ve found body weight to be the most consistently accurate way to determine an appropriate canopy size.*
*In some cases gear weight can be more substantial (if you're always jumping a large wingsuit, for example) and should be added into your w/l calculation. Apex BASE recommends using body weight simply because it's more consistent, especially for newer jumpers who are trying to determine an appropriate size for their “starter” canopy. Once you've gained some experience you can adjust your gear choices to account for added weight or desired performance changes. This is an individual decision which should be discussed with the manufacturer and/or your mentor.
This range of wing loadings has provided BASE jumpers with the best balance of:
Would loading a BASE canopy more heavily give you a better flare? Yes. But it would also increase your forward speed which is bad news after an off-heading opening. Wing loading in BASE isn’t a progression, it’s a range that we stay within because it gives us the best chance of remaining alive and uninjured.
Ideally we tell people to aim for the middle of the range when choosing their BASE canopy (.675 lbs./sq. ft.). But sometimes we may find ourselves on either the higher or lower end of this spectrum so it’s important to understand the pros and cons of approaching the ends of this range.
We are aware that some people jump canopies loaded outside of this range. We understand that there are special circumstances where loading a canopy outside of this range might be the safest, or most fun, option. This article is not intended to address special circumstances, but rather the most common circumstances that most average BASE jumpers find themselves in.
Lightly Loaded (.625 and under)
Sometimes we hear from jumpers that like to load their canopies very lightly in order to really slow down forward speed at opening, “soften their landings”, and generally feel more safe under canopy. While there are some benefits to under-loading your BASE canopy you should be aware of the following:
On the other end of the spectrum are jumpers who want more power in their controls, a stronger flare, and better range in windy conditions. All of that make sense, but make note:
Canopy performance does not scale in a perfectly linear fashion. Very large canopies tend to get quite docile. For this reason we will typically advise larger jumpers to load their canopies a little more heavily in order to maintain power in the control inputs. For example, we might suggest that someone who is 250 lbs. go with a 340 (for a wing loading of .735) instead of a 370 which would put them in the center of the range at .68 lbs./sq. ft.
Similarly very small jumpers often find themselves under wings which, while quite small, are under-loaded. We’re comfortable with this because we know that BASE canopies can start to feel “snappy” as they get smaller even if you keep the wing loading consistent. As with skydiving canopies, shorter lines make a difference in how a canopy behaves. So we’re comfortable recommending that smaller jumpers stick to the lower end of the range as opposed to getting a very small canopy. For example, we might suggest that a 110 pound jumper fly a 180 sq. ft. canopy (for a loading of .61) rather than go all the way down to a 160 in order to hit the center of the range at .69.
Ideally, start by aiming for the center of the range. As you get more experienced you’ll be able to better assess your skills, jumping style, jumping location, and canopy needs in order to determine which canopy and wing loading will allow you to have the most fun, and remain safe. But if you’re reading this article to think about what size canopy you need we can summarize it as follows:
If something seems off, chat with a local rigger or give your BASE manufacturer a call.
The above wing loadings are recommended by Apex but may not translate exactly to other manufacturers and their recommendations because:
If in doubt look up the recommended wing loading table in the relevant canopy manual, chat with a rigger or give your base manufacturer a call.