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VarioVoice

A flight instrument for paragliding and hang gliding that you listen to instead of looking at.

It runs on an iPhone that stays in a pocket with the screen off, and it talks into whatever earphones the pilot likes to fly with. Its job is safety and awareness: it tells you about traffic, airspace and weather while your eyes stay outside, and it makes you visible to the aircraft around you. There is nothing to read in the air and nothing to set on the ground.

It flies alongside the vario, the flight computer and the apps a pilot already uses. They keep the map, the task and the numbers on screen; VarioVoice adds the warnings, said aloud once and at the right moment, and a voice for the few figures that matter in the air.

What it warns you about

Traffic. When a glider, a tug, a helicopter, a powered aircraft or a drone is about to pass close, the voice says once what it is, where to look and whether it is higher or lower: "Glider, ahead right, high". The positions come from the Open Glider Network, the call comes about forty seconds before the pass, when the aircraft is close enough to find by eye, and the inconsistent data some transmitters send is rejected first. The positions travel over the internet, and where there is no coverage the warning is silent. Looking around remains the first instrument.

Controlled or active airspace ahead. The app projects your path a minute and a half forward, drift in a thermal included, and says how far away and on which side the boundary is, above, below or ahead. Active zones come from the day's activations published by XContest. It covers Italy, Switzerland, France, Austria, Slovenia and Germany. It speaks only when a boundary is really in your path, so that a warning is never something you learn to ignore.

A thunderstorm nearby. When a weather station within fifty kilometres reports a thunderstorm, or forecasts one if you want, the voice says so once per episode and names the station.

Föhn. The pressure difference between Lugano and Zurich is the gauge of föhn in the central Alps, and when it passes the threshold the voice says so, on launch if it is already there and then each time it crosses.

Weather and airspace data are downloaded while the phone is already connected for something else, so they cost little battery. Receiving traffic keeps the radio on for the whole flight and costs between half a point and two points of battery an hour.

Being seen

Your position goes to the Open Glider Network, the open network that follows gliders, paragliders and hang gliders across Europe, and from there to the traffic displays of those who fly faster than you: gliders, powered aircraft and drone pilots. The measured vertical speed and turn rate travel with each position, so whoever sees you also knows when you are circling in a thermal, instead of picturing you on a straight line.

The same position shows on the maps of whoever is coming to collect you, waiting for you on the ground or looking for you. Sending comes on when you decide, and it travels over the internet: where there is no coverage, the others cannot see you. With the switch off, nothing leaves the phone.

What it says

First of all it sounds a variometer, and in flight it has turned out more sensitive than the dedicated vario its author carries.

While you are circling, it tells you every so often how much height you have gained or lost over the last minute. That is the number a pilot works out in their head from any instrument, to decide whether the thermal is worth staying in.

When you leave a thermal, it says the course you have set off on and the wind relative to it, as a headwind and a crosswind from one side. On a long glide it says the altitude each time it has changed by fifty metres, so a flat glide stays quiet and a long sink is always announced.

And it answers a question. Two knocks on the phone, through the trouser or the harness, ask for altitude, course, ground speed and wind there and then. Every one of these phrases can be switched off, and the pilot chooses what the voice says.

Over a field where you have landed before it talks you through the approach: height above the field on entry, then at a hundred and at fifty metres, and the wind only if it has changed. It learns the fields from your own landings, with nothing to enter. When you touch down it says so in one sentence and then goes quiet, and the recording closes itself.

After the flight

Each flight gets a summary named after the launch: maximum altitude, height gained, best climb, distance, and the altitude profile coloured by how rough the air was. The debriefing detects turbulence, measuring how much of the flight was in strong or moderate air, and recognises collapses (in beta): each moment the wing unloaded is shown with its g-load, its duration and the climb before and after, and the pilot confirms whether it was one. With the flights of the beta testers it may learn to follow a pilot's progress in active piloting, flight after flight.

Every flight also becomes a signed IGC track, ready for XContest, and it can be printed as an A3 poster.

How it gets there

The variometer combines two sensors that complete each other. The barometer measures height to the centimetre and takes a few seconds to say so. The accelerometer feels the wing start to climb at the very moment it happens. A filter fuses the two, the accelerometer giving the signal and the barometer confirming it and keeping it anchored, and the beep comes a third of a second after the air, in time to tighten the turn onto the core.

The wind comes from four independent estimates: the drift of your circles in a thermal, the drift of the thermal itself, the difference between where the glider points and where it actually goes, and the ground speed on different headings. Each one does best in different conditions and reports how sure it is. The app weighs them by that confidence and sets aside the one that disagrees with the rest, so the wind is available for most of the flight, including the stretches where you are not turning.

The altitude calibrates itself on launch, so there is no QNH to enter, and corrects itself in flight for the temperature of the air, which it works out by comparing the climb the barometer measures with the climb the GPS measures and, when there is a network, from the temperature at the nearest weather station. In summer the air is warmer than the standard atmosphere every barometer assumes, and by the time you land the difference reaches twenty or thirty metres. With the correction, the error at the landing field on the test flights came down to a couple of metres.

Every rule was tuned by replaying dozens of recorded flights and then checked in real flight. During each flight the app records every sensor, the motion sensors at a hundred readings a second, so every second can be reconstructed afterwards at a desk. More than six hundred automated tests make sure a change breaks nothing that already works.

Later

English comes first, then other languages, with units of measure chosen separately, since a pilot may well want the climb in metres per second and the wind in kilometres an hour.

Then the Apple Watch. The flight logic has been written from the start so that it does not depend on how the device is oriented, which is what lets the same code run on a wrist.