How does wing loading affect altitude loss in a turn?
How can we manage this to keep ourselves safe?
Note: This is part 2 of John LeBlanc’s article – Part 1 looks at general affects of higher wing loadings here.
Wing loading and turns
High wing loading changes the flight characteristics of turns. The aerodynamic relationship between bank angle, turn radius and rate make the turns different at high wing loadings. Misunderstanding of this often leads to the dangerous low turn accidents all too common today, even with conservative people who never want to do hook turns.
Obviously as the canopy gets smaller, the turns get quicker, right? Well, yes and no. To explain, think of two motorcycles going around the same curve but at different speeds. The faster bike must be leaned over much more to make the turn, while the slower rider leans much less.
For turns that have a constant radius, more bank angle is required as the speed increases
If the slower rider now chose to lean exactly the same amount as the faster one, he would go off the inside of the road and make a much tighter turn. The slower bike would turn a complete circle much quicker than the faster one.
For turns that have a constant bank angle, the slower the speed, the tighter and quicker the turn.
These two observations are also true for airplanes and parachutes.
For a given bank angle, the slower parachute will make a 360° turn more quickly, and in a smaller area. So in some ways, the canopy at the lower wing loading has better turn performance, especially if you start looking at how much space a certain turn occupies!
In this description, we are referring to a turn where the flight path is still somewhat flat, and turning at a full glide rather than a vertical spiral straight toward the ground. At full glide, an attempt to turn faster results in a spiral dive with a rapid increase in descent rate. When flying a smaller canopy, this spiralling dive rotates much faster. As the wing loading goes up, the spiraling rate gets quicker. Since more speed requires greater bank angle for a given turn rate, the altitude loss builds up much faster at high wing loadings.
A large student canopy might double its rather low rate of descent in a hard spiral. A modern canopy flown at high a wing loading, however, may quadruple its already high rate of descent in the same turn! At extreme wing loadings, the increase in rate of descent can be astronomical, with a 180-degree turn consuming as much as 500 feet of altitude!
Underestimating the amount of altitude lost in a turn can easily get you into trouble when flying at higher wing loadings than you’re used to. Planning your landing pattern becomes much more challenging. Many conservative jumpers are often caught off guard by this when trying a smaller canopy. The typical experienced yet conservative jumper flying his own canopy becomes accustomed to judging how much time and altitude he needs to fly a conventional downwind, base and final approach, where the final turn is moderate.
When this conservative jumper tries a smaller canopy, the turns cover more ground than he expects. Since the turns run wide, he turns a little sharper. As he does this, the flight path becomes very steep, resembling a diving spiral, eating up altitude very quickly. After a turn like this onto downwind, then another onto base, the unfortunate jumper may have insufficient altitude to complete his last turn to final. But often the extra speed taxes his perceptual skills, throws his judgment slightly behind, and he finds himself doing an unwanted low hook turn. Yes, his first hook turn, on the fastest canopy he’s ever jumped—and an unfamiliar one too!
How do we manage this rapid altitude loss in turns at higher wing loading?
1, Downsize progressively
Make only a small change to the next size down and, if you’re not sure, wait!
2, Plan further ahead
Plan further ahead. Enter your downwind leg much higher, and fly a larger pattern with larger radius turns. Use brakes to adjust flight path and descent rate.
3, Learn flat turns
Really experiment and learn all about flying braked [flat] turns. By using braked turns early in the pattern, you can leave lots of altitude for a safe turn to final. Doing the opposite (making full-glide turns early and a low, braked hook turn at the last second) shows poor planning skills and lack of judgment. It is also somewhat suicidal.
Accidents occur when swoop landings are done incorrectly. The higher risks of such landings cannot be ignored. I don’t wish to encourage the uninterested to experiment with swoops, but some safety hints may help those presently involved:-
1, Evaluate the traffic
There is no real reason for a swoop landing — except for pure enjoyment. This does not dominate over the obligation to fly in a manner that enhances the safety of all the jumpers in your vicinity. Don’t even think of swooping if traffic is even a little heavy. It’s not even close to permissible just because you didn’t hit anybody. If your fancy landing startles some novice jumper or causes others to become preoccupied with your actions, then your fancy landing was dangerous and rude.
2, Improve efficiency
An efficient swoop is made with a smooth but conservative approach. You’ll swoop farther than the guy making the radical snapping turn with the coarse control movements. If you make turning approaches, do so much higher and smoother, with less bank angle. You’ll be amazed at how much speed can build up using this technique.
If you think a turning approach is needed to build up enough speed to get a good landing, you probably need to work on perfecting your technique. A conventional landing approach should work well, even at high wing loadings. But if you insist on experimenting with turning approaches, do so only on a canopy you are very familiar with, not some new canopy that you have only one or two hundred jumps on. It can take thousands of jumps on a single canopy to become consistent with turning approaches. The accident reports are littered with those who seemed to be consistent until that last jump.
3, Build in excess altitude
When the decision is made to attempt a turning approach, do so with lots of excess altitude. This will give more time to correct errors in judgment, or even to change the plan entirely. For example, if you set up very high and notice previously unseen traffic halfway through your turn, you should have the speed, altitude and skill to quickly abort the diving approach and change to a rapid gain of altitude, even continuing the turn if necessary. Make a braked approach to a straight-in landing, then walk over to the other jumper and apologize for your lack of vigilance for other traffic. None of this is possible from a “low hook turn.” If you can’t visualize the methods needed for this set of maneuvers, then don’t even think about doing a turning approach—especially when I’m in the air with you.
Learn how little altitude can be lost in a turn while at higher altitudes, but only use this method as an emergency salvage maneuver to abort the normal turn that seems a little too close. Never intentionally attempt a turn so close to the ground that the salvage method is the only possibility of pulling it out. Your judgment is probably off, so you might smack the ground. You don’t think your judgment will be off? Then how did you get into the position of needing this low turn anyway?!
4, Don’t become a ‘digger’!
If you find yourself needing to pull the toggles down hard to avoid hitting the ground [digging yourself out], of course do so. Try hard to keep the wings exactly level, all the way through touch down, until all movement stops. Don’t give up! Then, assuming you have survived, get up (if you can) and kick yourself hard for exhibiting such poor planning and judgment. It’s critical to understand that an intentional ‘low turn’ has no value for swoop landings. It doesn’t allow enough altitude:-
- for salvage if you misjudge
- for a more efficient, gentle pullout
- to build up lots of speed.
Therefore, little energy is left after the pullout, resulting in little ground skim, if any. Every weekend, people foolishly impress themselves with these low hook turns with sharp pullouts, actually believing that they have it all figured out. They should stop kidding themselves.
5, Stay alert
Canopy collisions are more frequent now than ever before. As jumpers continue to buy smaller and faster parachutes, it’s everyone’s job to stay alert. If experienced jumpers, especially swoopers, are concerned enough about your approaches to talk to you, listen well! Carefully evaluate what is said, and determine whether the information is helpful or dangerous. There is always more to be learned — no matter who you are or how many jumps you have.
6, Be considerate
Never underestimate how much your approach decisions affect traffic that is very far away. Don’t be selfish or stupid. If somebody seems angry because of an approach you made, listen and think carefully about what he says.
Advancements in canopy design have created better landing qualities, permitting jumpers to experience the challenge of higher speeds and swoop landings. Unfortunately, our decision-making skills don’t speed up just because the canopy flies and descends faster. Our workload under canopy has greatly increased, whether we fly a fast canopy or not. The accident reports show us that we are having growing pains.
Margin for Error
Our bodies are fragile. Since we occasionally make mistakes, we must be very careful to choose a parachute size and model that allows for some reasonable margin of error consistent with the type of canopy flying experiences each person has. We must also choose a flying style that allows for the same margin of error. We need to realize that as wing loading becomes extreme, the options for safe flight in traffic can become so limited they restrict the canopy flying experience too much to be really enjoyed. A slightly larger canopy will allow experimentation with more aggressive techniques and provide more fun, freedom and safety. As more and more jumpers become highly skilled and more courteous to each other in the air, our sport will become safer and more enjoyable.
One result would be a decline in today’s high accident rate under canopy. Our wonderful flying machines have been made possible not only by extensive research into aerodynamics, but also by the general improvement in canopy flying skills. Getting a parachute through development and onto the market depends as much on the public’s skills and readiness as it does the manufacturer’s research. Parachute manufacturers feel uneasy knowing that some people will fly their new products improperly. This will delay introduction of new, totally different parachutes with undreamed of capabilities. In my place of work, these parachutes of the future sometimes feel like decades away, but who knows? If we all move toward more courteous piloting, higher canopy control skills and better judgment, perhaps these ‘super canopies’ may come sooner than we think.
This article is the second part of a summary of an article published almost 30 years ago in Skydiving Magazine, August 1995.
We asked John LeBlanc for his thoughts on re-reading his original article:
In the last paragraph, I tried to challenge the reader to do better with their canopy flying skills, as I saw this as being key to our company’s willingness to release new models capable of even greater performance. I think the community bought into this challenge, and is part of the reason for our ability to bring our such capable wings. We know that a larger group of skydivers can handle these new wings, and that an even greater portion of the community has the sense to wait until they gain more skill. I am very happy about that.John LeBlanc
Further Reading – Related articles
When Less is More by Brian Vacher, explains how to do Flat Turns
Advanced Wing Loading Concepts by John LeBlanc, 2021, tests your knowledge and understanding of Wing Loading
5 Wing Loading Misconceptions by John LeBlanc in 2021, highlights a number of myths
- Advanced Wing Loading Concepts - 12th May 2021
- 5 Wing Loading Misconceptions - 29th April 2021
- Wing Loading and High Performance - 26th April 2018
- Wing Loading and Turns - 23rd July 2014