Everyone wants to stay up, which is why the audio vario is a pilot’s most essential piece of technology, explains Timothée Manaud
The main function of a vario is to indicate vertical speed – measured in metres a second (m/s) in Europe, and feet per minute (fpm) in other parts of the world and aviation. This information helps the pilot find thermals and better lock into the core, but also to have a better “buoyancy” and make better progress through the air.
Flying is not natural for human beings and we don’t have a sense dedicated to 3D motion. Once our visual reference to the ground is lost it’s very hard to figure out if we climb or sink.
You can of course feel when you enter or leave a thermal. Indeed, our brain uses three senses to know if we are in motion or not: the inner ear; proprioception (sense of movement and body position); and eyesight. The brain mixes these three elements to know how we are located in space.
Unfortunately, information about our absolute speed is missing: it’s impossible to tell the speed of a train if the window blind is down. Worse, our senses can fool us. When we are on a train at a platform, for example, and the train next to us leaves, our brain can have a hard time try-ing to figure out if we are moving or not until we visually check the plat-form outside.
In an established thermal we lose this sense of acceleration, although we are still climbing. If we don’t have a visual reference, then it’s hard to tell if we are in the thermal, let alone in the core.
A vario gives us this missing information: we immediately know if we are climbing or sinking, and the vertical speed of the climb (climb-rate).
The two types of vario
To determine our altitude we need a vertical ruler. That’s obviously impossible, but fortunately for us air pressure is directly correlated to altitude and it can act like a vertical ruler. A pressure sensor can quickly detect falling air pressure as altitude increases.
For us, the absolute altitude is not that interesting. Rather, it is altitude variation that matters. By recording air pressure very frequently (a minimum of 50 times a second, to 100 or 200 times a second in the fastest cases), it’s possible to determine the altitude variation, in other words the vertical speed. This is how a traditional vario works.
However, measuring just the air pressure also means the result is a bit late – there is always a time lag between the measurement and you hearing the audio signal telling you about the measurement. This is where an accelerometer sensor can come in. These measure acceleration in the thermal, and is to all intents and purposes an instant vario. Of course, the sensor is extremely sensitive and requires an absolute reference.
Acceleration, rotation and air pressure are measured more than 100 times a second with a specialist algorithm inside the device. The information is then passed to the pilot perfectly synchronised with their own senses (remember, you have an accelerometer inside your head.)
The result is the pilot gets a response from the vario as soon as they enter the thermal, not only after feeling the lift through the harness. There is no more one-second delay between feeling the lift, and the beep of your vario.
Why sound is so important
In flying we need to use 100% of our vision all the time. Not only for safety reasons (so we don’t crash) but so we are aware of what the environment is doing around us too.
Our sense of hearing is only used occasionally: the crumple of a wing as it collapses; the radio; the wind’s relative variations. That means we can use our hearing to listen to the vario and interpret what it is telling us. Using a note, sound, conveys information; no sound means no information.
By changing the sound it’s possible to convey an almost infinite array of information. In a vario beeps are made of three parameters:
1. Frequency. The pitch of the note, from deep to high-pitched
2. Duration. How long a note plays for and how long any pause is
3. Duty cycle. The relation between the note played and the duration of the pause. For example, a duty cycle of 50% means half the time the vario is silent.
All of the above is why an audio vario is so important to us. The correct vario sound will allow us to turn our sense of hearing into a sense of acceleration and speed. And that in turn totally complements the three senses mentioned above: the inner ear: proprioception; and eyesight.
Taken together, this then allows us instant access to very precise information about the range of our vertical motion.
Timothée Manaud runs Stodeus and makes le Bip Bip varios and other flying instruments
