Why Your Vario Can't Predict Collapses — And What Can

If you fly with a variometer — and most paraglider pilots do — you've probably wondered why it can tell you exactly how fast you're climbing or sinking, but gives you zero warning before a wing collapse. The reason comes down to what a vario actually measures, and what it doesn't.

This is not a limitation of current technology. It's a limitation of the measurement location. Your vario sits at your chest. Collapses happen inside your wing. These are separated by metres of air, and the physics at those two locations are fundamentally different.

What Your Vario Measures

A variometer measures barometric pressure changes over time. As you climb, the ambient air pressure decreases; as you sink, it increases. The vario converts this pressure change into a vertical speed reading and translates it into audio tones — the familiar beeping that tells you when you've found a thermal.

Modern varios are remarkably precise. Using complementary filters that fuse barometric altitude with accelerometer data, they can detect climb rates with a resolution of around 0.1 m/s and a response time under half a second. For thermal flying and cross-country navigation, this is exactly what you need.

But here's the fundamental limitation: your vario measures the air around your instrument. It tells you about the airmass you're flying through. It tells you nothing about what's happening inside your wing.

The Physics Gap

Wing collapses are caused by a localised loss of internal canopy pressure. This happens when the angle of attack on part of the wing drops below a critical threshold — usually because of wind shear, rotor turbulence, or an abrupt thermal boundary. The air stops entering the leading edge on the affected side, the cells deflate, and the fabric folds.

The important point is that this is a local, asymmetric event. It happens on one side of the wing before (and sometimes without) affecting the other side. Your vario, sitting in the instrument pod at your chest, measures the bulk atmospheric pressure at a single point. It cannot distinguish between "the whole airmass is sinking" and "the left side of my wing is about to fold."

Why GPS and Accelerometers Aren't Enough

Modern flight instruments combine GPS position, barometric altitude, and inertial measurement (accelerometer + gyroscope). Together, these sensors can detect the consequences of a collapse — the sudden altitude loss, the asymmetric loading, the rotation. But by the time these sensors register the event, the collapse has already happened. They detect the result, not the cause.

There's a second problem: normal flying produces similar sensor signatures. A sharp thermal entry, an aggressive weight-shift turn, or moderate turbulence can all produce acceleration spikes and altitude changes that overlap with the signature of a collapse. Without knowing what the wing itself is doing, any prediction system based purely on external sensors will produce too many false alarms to be useful.

Consider the sensor signatures in isolation:

The Physics of Why Collapses Are Local Events

Understanding why collapses are asymmetric is crucial to understanding why differential pressure sensing is the only reliable detection method.

Thermal boundaries, wind shear, and rotor turbulence don't hit your entire wing simultaneously. Your paraglider is 12 metres wide. A gust cell that affects your left wing tip may not reach your right wing tip for 0.3–0.5 seconds. During that window, you have asymmetric exposure — one side of the wing is in stronger wind or a more aggressive thermal boundary than the other.

When this happens, the exposed side experiences an increase in angle of attack and internal canopy pressure, while the sheltered side may see a decrease. If that decrease crosses the critical threshold where the leading edge closes, collapse happens locally first. It shows up as a massive asymmetry in internal pressure before it becomes a visible deformation of the wing.

This is the crucial insight: internal pressure loss is local before it becomes global. The wing doesn't collapse all at once. One side goes first. If you can measure that asymmetry with dedicated internal pressure sensors, you can detect the collapse before it develops into a full deformation that affects your entire flight path.

Measuring What Matters: Internal Wing Pressure

This is the insight that led to ParaBaro. If collapses are caused by internal pressure loss, the most direct way to predict them is to measure internal pressure directly.

ParaBaro uses differential pressure sensors positioned inside the canopy — measuring the pressure difference between the interior of the wing cells and the ambient air. By placing sensors on both the left and right sides, we can detect the asymmetric pressure signature that precedes a collapse.

The physics is straightforward. When a thermal boundary crosses the wing, the side that enters the thermal first experiences an increase in angle of attack and internal pressure, while the other side may see a decrease. This creates a pressure differential — a measurable gradient across the wingspan. Our sensor data shows this gradient appearing 0.5 to 1.5 seconds before any visible deformation of the wing.

Two-Stage Detection: Speed and Reliability

ParaBaro uses a two-stage approach that combines the strengths of both technologies — pressure sensing for speed, and conventional flight instruments for false alarm filtering:

The result is a system that can alert a pilot to a developing collapse before it becomes visible, while keeping false alarm rates low enough to be trusted in real flying conditions.

What This Means in Practice

We're not suggesting you replace your vario. It remains the essential tool for thermal flying and navigation. What we're building is a complementary instrument — one that fills the gap your vario can't cover.

The technology is currently in beta testing with 50 pilots. Every hour of flight data they upload helps train the machine learning models that make collapse prediction more accurate. If you're interested in being part of this, visit the beta programme page.