Image by Andrey Veselov
Stalling For Success: What You Don’t Know About Stalling Your Canopy Could Smack You. Hard.
This, suffice it to say, could end badly.
There was a balloon jump. (Whee!) The winds picked up at around 3,000’ and shoved your jolly crew rather far off-DZ. (Um…) You jumped anyway. (Whee!) You over-rotated your super-magnificent aerial and pulled a titch lower than you wanted to. (Um…) Your landing options are now -- well -- limited. And a little heavy on the obstacles. And kinda tiny. And now you’re on final. (Uh-oh.)
Do you know where your stall point is?
Probably not. Right about now, I bet you wish you did.
In this regard, skydiving is unusual. After all, stall training is a foundational part of the training process in other air sports (paragliding, specifically), and there’s no question it’s vital. Considering how important it is to know the exact point at which your equipment stops flying, it’s surprising how few skydivers – even advanced ones – have seriously investigated the stall point of their canopies.
Perhaps this is because the transition between the very-slow-flight and no-flight modes produces a stomach full of butterflies. It could also have something to do with the fact that skydiving canopy rides are much shorter than paragliding flights -- and, because the skydiving canopy is trimmed to fly down instead of up, comparatively easy to fast-forward. No matter what the root cause, the fact remains: knowing your stall point is an essential component of safe and skilled canopy flight. And there’s probably a lot that you probably don’t know -- yet. Here’s the skinny.
1. You aren’t really in control up there.
Sorry, buddy. Without understanding your system’s stall point, you are not in full control of your wing. Most notably, you’re at a significant disadvantage during the landing process, as the execution of a flare is the approach to a stall in very close proximity to the ground.
2. It’s not about slow flight. It’s about no-flight.
The lion’s share of ram-air canopy pilots believe that the definition of a stall is directly related to slow airspeed – that the “stall point” is when the canopy is flying too slowly to produce lift. Sound familiar? Yep. Unfortunately, while it often ends up being the case in practice, this isn’t actually true. The true “stall point” is defined as the moment when the parachute is no longer producing lift, no matter what the airspeed when you enter the maneuver. Bear with me here, because this has bearing on your jumping career.
When a ram-air airfoil reaches an excessive “angle of attack,”* a stall results. As relative wind moves over an airfoil, it “curls” over and downward to create lift. However, when the pilot adjusts the airfoil to a higher angle with respect to the relative wind – often, but not always, by pulling hard on the brakes – he or she is effectively building a nylon wall against that relative wind, making it harder for the relative wind to follow its usual path and create lift. Finally, it reaches a point where it can’t. At any point that the angle of attack reaches that point, no matter what the airspeed, the pilot has a stall on his or her hands. When you understand the stall as a function of AoA, you can easily see how a ram-air airfoil can stall at high speed as well as low speed.
This leads to an important fact: a higher-loaded wing will stall at a higher airspeed than its more lightly loaded counterpart. This is just another of the galaxy of reasons why it’s important to downsize your canopy thoughtfully and knowledgeably.
3. You can choose your own adventure.
Initiating a stall for the first time is not unscary. Don’t just stab the brakes and cross your fingers, though: manage the process. The rodeo quality of the stall depends on the type and sharpness of the inputs you use to get into it, and on your technique for stall recovery.
Stalls entered using slow inputs tend to initiate a stall from slow speed and slight sink, making the stall more docile than those entered using quick, brutal inputs. The more aggressive and uneven you are in your entry, the more likely you are to introduce a bank angle at the entrance of the stall. This will stall the lower wing first, which can often result in a spin (and, maybe, line twists) during recovery.
Another bit of advice: Don’t just reach for your brakes. Jumpers tend to initially experiment with stalls by monkeying around with their toggles – mostly, because they’re more familiar with those controls. That’s not really the best idea. Though rear-riser stalls “kick in” more suddenly than stalls initiated with the brakes (as they profoundly and quickly change the shape of the canopy using the C and D lines), recovering from them is smoother and easier.**
...and, of course, pull high. The “lab” is up at a nice, cushy altitude. Make sure to stop your experiments with a lot of margin between you and the dirt.
4. You don’t have to go it alone.
Look at your canopy’s manual to familiarize yourself with the stall dynamics you can expect from it. If there’s no information regarding stall behavior in the manual, contact the manufacturer and ask about it. They’re happy to help. So are canopy coaches.
Ask, ask, ask.
Then you might not have to ask the farmer to disentangle you from the fence, collect your scattered dignity and help you hobble to the road. That’s worth it, no?
Here’s a great little video by AXIS Flight School that demonstrates a rear-riser stall. In this video, you can closely inspect the canopy’s reaction to the stall input.
*The angle of attack, or AoA, is the angle between the cord line – visualized as a straight line between the leading edge and the trailing edge – and the relative wind that the airfoil is moving through.