By Dennis Pagen
Originally published in USHPA Pilot, May/June 2020
Our forms of aviation make us extremely happy, except when they make us extremely terrified. In hang gliding, a tumble is perhaps the worst thing that can happen in the air. In paragliding, a total collapse and wrap-up of the canopy is perhaps the worst thing. For both of these disciplines, spins fall somewhere between the two extremes. We’ll look at the incidence of spins separately for the two sports because the consequences are entirely different.
The Anatomy of a Spin Cycle
Nearly all aircraft can spin, excluding balloons and rockets. If it has wings, it has at least a chance to spin. A paper airplane can be configured to spin, and some birds will use a spin maneuver to drop into a steep dive. Generally speaking, a spin occurs when one wing (only one) is stalled, so that wing loses lift while greatly increasing drag. As a result, the entire aircraft wants to rotate around the stalled wing with a circular path or radius well inside that of a normal turn as shown in Figure 1. The speed of the rotation greatly depends on the type of aircraft and the pilot reaction, as do other factors, such as pitch control position in the spin, G-forces, difficulty of recovery, initial resistance to spinning, and rate of descent.
Spins in an airplane can be deadly, so much so that decades ago the FAA stopped required spin training for a pilot’s license because too many students with instructors were augering in. Fortunately for free flight pilots, spins are a bit less severe, but they still have deadly potential.
There are two main problems with spins. First, spins can lead to a lot of altitude loss
in a short amount of time. A spin can occur with the nose pointed down or with it fairly flat. The latter is called a flat spin and is not as dangerous as a steeper spin. A downward pointed spin can lose altitude as rapidly as a spiral (a turning dive). In my experience, typically a hang glider spins fairly steeply, while a paraglider can spin flatter as we’ll see below. The second problem is that disorientation can occur rapidly after the onset of a spin, and the pilot can no longer recover. This is a common result of spins in airplanes and usually leads to severe consequences. More on this later.
Hang Gliding Spins
Here’s a blanket statement: You can’t easily spin most modern hang gliders. In fact, beginner and intermediate gliders may be un-spinnable without the pilot taking some extraordinary measures (like changing the glider’s sail tightness, twist, batten profile, etc.). Even a rogue robust thermal or vertical gust stalling one wing will not cause a spin. Rather that wing will be lifted, and the glider will slip to the opposite side and generally recover on its own, all while you manage your adrenaline overload.
Advanced hang gliders (and rigid wings) can be made to spin with much effort and the right technique, but they readily recover in most cases. To emphasize assurances, in flying the latest high-performance gliders since the late 70s, I have never inadvertently entered a spin. I have performed spins intentionally, but it takes effort.
There are two dangers related to hang glider spins. The first is really only related to rigid wings. A rigid wing performs better than flexies because the twist can be controlled all the way out on the wing, even with higher aspect ratios. But the penalty is a greater susceptibility to stalling one wingtip and thus spinning. And because a rigid wing tends to have less sweep than a flex wing and has no tail or fuse-age to slow the rotation, the wing can rotate fast in a spin. Because there is a large difference in the airspeed of the inner stalled wing and the outer wing, much greater lift develops on the (unstalled) outer wing. It rises rapidly and can roll the glider on its back. I witnessed this happen years ago and heard of it happening on modern rigid wings. This mishap may occur so suddenly that the pilot has no chance to react. The main way to avoid such a mishap is to not attempt a spin, to not push out too far in a thermal, and to keep your glider set
to the factory specs. I was with Felix Ruhle (designer of the Atos), and we were checking gliders for compliance in the World Meet in Annecy, France. He said the main thing to be concerned with is not turning the tips down too far and reducing washout. Some competition pilots did this adjustment in expectation of better performance, but several spun and went upside down. The manufacturer of your glider can provide tuning guidance.
As mentioned above, the second danger in
spins is disorientation. Without going into too much detail (the subject is covered much more in my book "Performance Flying"), after we have been turning for a short spell, our orientation system can get “wigged out” and totally confuse us. When we are confused, we may not be able to think or control properly. Original “standard” gliders would spin, and I once watched two incidences where the pilots spun in from over 100 feet. They were both
“wigged out” of control and disoriented and hit the ground in the spin. The descents were fairly slow, and they walked (limped) away. Both reported that they didn’t know which way was up once the spin began.
We all have different degrees of susceptibility to spatial confusion, but the average pilot is quite susceptible to it. However, with practice, we build up a tolerance. That’s why we start students out making turns of small heading changes, gradually building up to 360s and then spiral dives. In my experience, practicing high-G spirals helps build up a tolerance to spins and vice versa (spins are not typically high-G maneuvers on a hang glider, but they may involve faster rotation than in a spiral).
If I haven’t done either for a while, I notice that my tolerance is reduced. It is a matter
of staying current. But I don’t want to stay current on spins because they tend to load
up the sail outboard and stretch it more than normal flying.
Spin recovery on a flex hang glider is simply
a matter of lowering the nose and thus the angle of attack. This act may be counterintuitive because the nose may already be pointed downward. But we have to overcome our inclination to push out and let the glider reestablish proper airflow. This procedure is the same as the recovery when an outside wing
is lifted or an inside wing stalls in a thermal turn: pull in, let the airflow reattach, then roll back to the desired bank angle and resume the circle or straight flight with the appropriate airspeed.
In order to produce an intentional spin, a pilot must hold a strong roll control as well as hold the bar forward, so that merely relaxing will stop the spin and the glider will do the rest to recover. If the glider ends up in a steep dive, as is typical for spin recovery, you’ll have to pull in as it climbs to prevent another stall.
So in summary, spins are not a major concern in a current flex-wing hang glider. A rigid wing may have a more serious spin reaction, and I would not attempt one intentionally.
In all cases, spin recovery involves lowering the glider’s angle of attack and reestablishing normal flying mode.
I have witnessed four inadvertent spins on paragliders—-three were at world meets, and the pilots were advanced. One threw his reserve, two went to the hospital, and the fourth fared worse. However, these incidents were over 20 years ago, so today’s gliders may be a bit less susceptible to spins. Even still, a paraglider will spin more readily than a hang glider, so we need to pay them special attention.
In addition to the previously mentioned spins, I have seen hundreds of intentional spins when I was an official at several World Aerobatic Championships where pilots performed “helicopters.” This maneuver is essentially a flat spin. The pilot slows and intentionally stalls one wing with a sharp brake pull. Performing this maneuver takes lots of practice, patience, and willingness to toss a parachute. These semi-professional pilots build up to spin tolerance with many different high-G rotational maneuvers. Such practice is not for the faint of heart.
For the average pilot, inadvertent spins are usually a bit steeper than is the case with a
“helicopter.” Such a steep spin results in the pilot’s body rotating in a wide circle, pulling high G’s. The G forces can (and do) add to disorientation already present in a spin. In my observation, a spin in a paraglider isn’t too much different than a spiral (a spiral is a steep circling dive with no part of the wing stalled) in regard to the steepness, the altitude lost, the rate of rotation, and the disorientation effects. Remember, because you (the pilot) are far from the wing, your body will be making a fairly wide circle, resulting in high G forces.
In a paraglider, a spin occurs when one
wing stalls, as with every aircraft. Because
a pilot can easily pull one brake down to a great degree, it is not hard to stall one wing. That is why we learn to make turn controls smoothly, gradually, and in conjunction with weight shift. All these actions help prevent an inadvertent one-wing stall. In all four unintentional spins I witnessed, the pilots were thermaling. They were flying slowly with flat turns, and either a gust increased the angle of attack on the inside wing or they added a bit too much inside brake to change their circling path.
The last sentence brings up the first point of
defense against spins: make your turns with
a bit steeper bank, and you have a little more margin of error with respect to spins. The reason for this factor is that the steeper the bank, the less the differential in the airspeed of the inner and outer wing. Of course, the typical pilot likes to turn flat and slow, intending to eke out every scrap of lift, but most pilots find that by turning a bit tighter they can stay in smaller pieces of lift and do just as well. This point is most important when thermaling close to terrain with less recovery clearance.
The second point of spin defense is to constantly be aware of the wing’s position when flying slowly. If you feel a sudden reduction in brake force and/or a rotation of the wing in the direction of the turn, expect an incipient spin and immediately reduce the inside brake while maintaining weight shift. The final thing to prepare for in spin defense is
to be ready to toss silk (fling your reserve parachute). The one spin victim I witnessed who walked away did just that. They had been spinning a few rotations about 200 feet above the hill when they threw their reserve and came down gently. I expect they would have been seriously injured had they not deployed. The pilot told me that they were starting to get confused (disoriented) when they tossed. They were trained to do this and were prepared. In this regard, SIV courses can do a world of good preparing a pilot for the unexpected, even if spins are not addressed directly.
Taking a glider for a spin is not something we normally want to do. Since such an unexpected mishap only
occurs if we are making a control which leaves one wing at a high angle of attack and thus slowing much more than the opposite wing, we can generally avoid spins simply by being aware and somewhat careful with our controls. Though spins occur less frequently on modern gliders, we should be aware that they do happen but can be prevented with a bit of understanding and preparedness. Spins shouldn’t give you night terrors any more than certain politicians, but just recognize they are real and willing to threaten the careless.