Wing Loading and High Performance

Canopy control today is a lot different than it used to be. Heavier jumpers under smaller canopies are filling the skies with zippy parachutes that are extremely sensitive to toggle input — especially on landing.

Getting safely to the ground becomes more complicated at higher wing loadings, even with all the improvements in technology.

Any freedom has its price, and the decision on what wing loading to fly is no exception. We may need to rethink our ideas about safe canopy flying if we are to avoid accidents.

What has changed?

Four general ideas come to mind about what has changed since I began jumping in the ’70s:

1. Advances in parachute aerodynamics have dramatically improved landing characteristics. The improved aerodynamics have given these jumpers new ways to test their limits by jumping smaller parachutes.
2. At novice or intermediate level, jumpers are often encouraged to transition to canopies that may seem large by today’s standards, but are actually smaller and faster than the hottest ram-airs used only a few years ago.
3. It has become easy to fall into the trap of thinking that a student or novice has grasped the basics of canopy control simply because he is observed to land softly every time so far.
4. When larger canopies were the norm, it was much easier for an expert to keep track of the canopy control environment. Today’s skydiver is faced with much more demanding piloting tasks that require much more concentration, attention and skill than even the ‘experts’ may have!

This means that we are all much more likely to find ourselves surrounded by a high concentration of jumpers flying at or beyond their skill threshold, even if they are highly experienced freefallers.

Now, tie these four factors together and what do we have? The accident reports answer that question.

Doesn’t it make sense that mistakes that go unnoticed under a large canopy are compounded under a smaller, less forgiving canopy, with dangerous results?

Higher wing loading

Let’s seek greater understanding of the changes created by going to a higher wing loading.

Wing Loading Defined: Wing loading is the ratio of how much weight is carried by how much parachute. To calculate wing loading, simply take the total exit weight (including the main, reserve and container), then divide this figure by the area of the canopy. (Wing Loading video here)

Why increase wing loading?

What’s the point of moving to a higher wing loading? Usually it’s one of six reasons:

1, Fun

We skydive for fun! The extra speed under canopy generated by increased wing loading can add to that fun.

2, More response

More nimble handling and crisp response; small movements of the controls produce notable changes inflight. This could be a double-edged sword; the canopy doesn’t care if your control input is correct or not!

3, Smaller rig

You may want a tiny rig like the one your friend has. Everybody gets the itch for a new toy once in a while, but remember, it must save your life and return your body unharmed to the ground.

Don’t be too quick to drop to another size simply because you landed well this time in an open field with no traffic

4, The ‘right’ wing loading

You may think you need to achieve the ‘right’ wing loading. But what exactly is correct? There is some confusion. The maximum recommended weight is often misinterpreted to mean a required weight, or even a minimum weight. PD’s canopy chart shows minimum weights frequently much lower than most would expect. (Example: Sabre3 Wing Loading chart)

Wing loading is a personal choice. If you feel a certain canopy might be a bit over your head in a tight situation, consider going one size bigger—or two. You’ll still get great performance and landings if the canopy is a good design.

5, Swooping

Long swooping landings are fun; the ability to achieve zero descent rate during flaring permits landing without injury at higher wing loadings. But don’t forget that the refined aerodynamics do not automatically provide good landings, only the potential for one. As wing loading goes up, there is less forgiveness.

6, No back-up

Higher wing loading can help you avoid backing up in winds. But, high winds often mean heavy turbulence. The increased ability to penetrate headwinds may give you a false sense of security in winds that should probably be waited out on the ground.

These are all valid reasons but can be taken too far, possibly with dangerous results.

What is the ‘best’ wing loading?

This question involves trade-offs that make a definite answer impossible. A number can’t be broken out for two reasons:

1, Different canopies are more capable of safe flight and landings at certain wing loadings than others. For example, if a jumper with 170 lbs exit weight finds the Sabre 150 flies and lands the way he wants, he should be careful to not assume the same applies to all 150-square foot parachutes.

2, People judge flight characteristics according to their own frame of reference, which varies greatly. Many get caught making too large a change in wing loading because some expert said their intended wing loading was ‘conservatively low.’ Well, by whose standards?!

We judge speed according to our own frame of reference, so what one jumper considers slow, another of the same weight and experience may consider lightning fast

Example

Consider two students:

A 100-pound jumper

This skydiver’s rig and clothing weigh 25 pounds, has been jumping a 260-square foot canopy as a student and is ready to buy his first set of gear. He has heard that 1.0 lb/sq ft is ‘correct,’ but a friend says to go bigger for the first canopy at a wing loading of 0.8. He chooses the more conservative guideline, and he runs the numbers: 125 pounds divided by 0.8 equals 156 square feet. What a huge change from the 260! While the 260 seemed to float all over the sky, the 156 just screams at the ground!

It would be better to try a 230 and see what it’s like, then a 210, and so on until a reasonable size feels right.

2, A 200-pound jumper

The second jumper has the same number of skydives but weighs 200lbs. He started on the PD-300, but transitioned to the 260 on the last few jumps. If he went to the same wing loading of 0.8, he would probably be disappointed. Why? 225 lbs exit weight, divided by 0.8 equals 281 square feet. He would be jumping a bigger canopy!

So the same wing loading might feel quite slow to one jumper but positively frightening to another.

What about experience level?

Defining experience level has become more complicated. These two jumpers may have the same number of jumps and similar freefall skills, but their experience under canopy is certainly different. The ‘type’ of experience, rather than the number of jumps, is most important when referring to canopy skills. Remember that it’s all relative to what you are used to. Don’t be too quick to drop to another size because you landed well this time in an open field with no traffic. You may be surprised how difficult it can then be to land accurately in a tight area.

Be careful talking about ‘high’ and ‘low’ wing loadings to others. If you happen to be comfortable with a wing loading of 1.6, then one jump on a friend’s new canopy at 1.2 lbs/sq ft will probably seem pretty docile. But don’t describe it as ‘docile’ to the new owner, or even to someone with twice as many jumps as you! You’ll likely mislead him.

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Changes in performance

It is important to become fully prepared for the changed flight characteristics of flying at a higher wing loading before you make an increase.

Speed

The most obvious change is more speed. However, the new feeling of greater speed will one day feel normal, and perhaps even slow, though it certainly isn’t. Many people then bring this additional experience to the next smaller size, and the rush is back. But at what cost? Clearly one can push this too far, too fast.

Descent rate

By going to a smaller size of a particular design, the small increase in speed comes mostly from a large increase in descent rate — which means less hang time, less time to collapse your slider and less time to play. At high wing loadings, the flight might be fun, but the time aloft is usually short.

Glide ratio

Glide ratio — the ratio of the forward movement compared to the downward movement in the air — reduces under increased wing loading. Glide ratio is the ratio of lift to drag. When we increase the parachute’s wing loading, we hang a bigger person out there, so the person’s body is a proportionally higher percentage of the drag. The result is a poorer glide.

Wind

Another change is how a jumper under canopy is affected by the wind. Keep in mind that glide ratio is not the same thing as the distance covered across the ground because the winds come into play. A higher wing loading makes it easier to penetrate headwinds. In a tailwind however, you might find that someone flying a big 7-cell may go further than you at full glide on your trusty 170, even though his glide ratio is lower. However, anyone can hold some brakes to slow the descent rate when flying back, and the exact amount of brakes helps considerably at high wing loadings.

Stall speed

When you go to a higher wing loading, the stall speed increases. A stall may happen more abruptly, with less warning, and at a higher airspeed. This means it is not possible to fly an approach into a tight area as slowly as you could with a lower wing loading.

Landings

The landing speed is also higher. Since we are descending much faster on final, the canopy must do more work in the flare to achieve zero rate of descent. With less canopy, it must also work more efficiently. To extract this efficiency, the flaring method must be more precise. Moving either toggle even a few inches may have a big effect on the resulting landing.

On the other hand, a large student canopy descends slowly on final. It doesn’t have to do much work to get to a zero rate of descent, and there is lots of surface area to work with. Therefore, a variety of rather crude flaring methods will all give reasonable landings. Toggle movements of as much as one foot will hardly affect the landings. Since poor technique can still produce soft landings under a big canopy, many students develop poor canopy control habits. In many cases, the student carries poor technique to smaller and faster canopies later, and eventually it causes problem landings.

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I think that the skydiving community has cleaned up its act a great deal since this article. Canopy control coaching was unheard of when this article was written, and many experienced skydivers would have been completely insulted at the thought that their technique could use some improvement. Now, people of all experience levels are getting canopy coaching, and thankfully most coaches are trying to learn more themselves. This is all great. The typical wing loading is higher now, even for novices, so avoiding accidents is still a challenge even with the greater skill level.

John LeBlanc

Note

• Look out for the second half of this article, coming soon, which discusses techniques for the canopy pilot learning to fly at higher wing loadings
• This article is an abridged version of one published almost 30 years ago in Skydiving Magazine, August 1995.
• To read the original article in its entirety visit Blog.Performance Designs
• Related article: 5 Wing Loading Misconceptions also by John LeBlanc