The intent of this page is to explain how a barometric vario works, what you can expect from smartphone variometers and sensors and how you might benefit from an instant vario and why you will need a variometer for paragliding in general. 

Instant Vario

An instant variometer has virtually no delay or lag in calculating the vertical climb rate (vertical speed). What you feel is what you hear. And this makes for a much more intuitive flying... ¯\_(ツ)_/¯ 

Small bumps in the air can be felt and heard, lifts are easily identified and in weak conditions a zero delay indication of the vario can help you stay in the air much longer. It just flies different and thermals are much easier centered.

This instant feedback can be provided by most of the current middleclass smartphones using the FusionBoost algorithm of theFlightVario instant vario. theFlightVario takes readings from all motion sensors, especially the

and last but not least the barometer and calculates a fused climb rate. Combining all these readings at rate of up to 100 times each second straightens out individual errors of each sensor and make the fused signal non delayed.

How does a variometer work? 

A classical basic vario for paragliding works by taking continuous measurements of the air pressure. This is because the pressure is directly related to altitude, meaning with altitude increasing the pressure drops. One could also say, there is less air resting or pressing on you and the pressure sensor. And with decreasing altitude the pressure will pick up again. In other words: there is more air resting or simply pressing on you again. Take a look at some prominent European places for paragliding:

Now, finding out whether and how fast you are moving up or down (climb rate) is simply done by calculating the differences between the pressures which are being reported by the barometer (pressure sensor) inside that vario. Of course there is some more or less complex filtering and calculations going on, especially to separate noisy readings from readings due to vertical movement. But all in all this is how a basic variometer for paragliding works.

a vario reports a climb rate which is based on altitudes calculated from subsequent pressure readings

More simple, if you are at 1000 meters and the next second you are at 1001 meters than your climb rate is obviously one meter per second. With a vario, these measurements are being performed many, many times each second so you will get a continuous and smooth change of climb rates. Depending on the exact vario, information from other sensors  such as the accelerometer and gyroscope  might be processed. 

paragliding at 4000 meter in south tirol and heading south
thin air while paragliding at 4000m in south tyrol

Interesting fact, when calculating the climb rate the exact absolute altitude is irrelevant. It is the change in altitude that indicates your vertical speed and thus climb rate. The absolute altitude which is relevant especially for airspaces is being extracted from the GPS signal which includes the mean sea level (MSL) altitude.

What is an instant vario

Remember, a basic vario for paragliding uses the variation in pressure to calculate the difference in altitudes and from that difference the climb rate. However, that difference in altitudes will need to happen first which is why a barometric vario, one that is based on pressure alone, will be delayed, always! It can only indicate lifts or change in altitude that already happened ¯\_(ツ)_/¯ 

That said, there is another variation, more instant, that can be used to calculate the change of the climb rate. And again it is about relative change rather than absolute values.

Acceleration - the instant in the vario

To understand how an instant variometer works, imagine you just got into an elevator. (Thermals can actually be seen as our elevators to cloud base.) You pushed the very last button to get to the top (cloud base), closed your eyes and now you wait for the ride to begin. What will you be able to tell from your senses...?

Now, you naturally feel once the elevator starts accelerating. In this case you are experiencing a 

Positive G-Force: your climb rate is expected to increase!

which results in a higher vertical speed. The start is actually like entering a thermal.

Of course, you also feel once the elevator starts braking or more technically, decelerates. In this case you are experiencing a

Negative G-force  your climb rate is expected to decrease!

which results in lower vertical speeds and ultimately no speed.

So whenever you are accelerating (positive or negative) your climb rate will change. But what is more important, you are anticipating the change in climb rate before any barometric variometer could have made that calculation from altitudes and hence changes in pressure.

gravity changing is INSTANT

But what can you tell about the climb rate from the elevator going up at constant speed, once the acceleration (and deceleration phase to be correct) is finished. Can you tell how fast you are going up, your exact climb rate? No, you can’t! Without any visual clues it is impossible. Which is why we need the barometric climb rate calculated from changes in pressure due to changes in altitude.

change of altitudes is NOT INSTANT

Now, taking the instant part from gravity and fusing it with the not so instant part from pressure is the basic idea of an instant vario. Best of both worlds, plain simple. Fusing is the hard part!

How does an instant variometer work?

Changes in pressure need to be measured first meaning, the change in altitude must have have happened first, which is why any vario focusing on barometric sensors alone will be delayed. Still, this barometric calculation is important. You cannot have an instant vario without using the pressure sensor of your smartphone.

An up to date pressure sensor of a mid range smartphone currently provides a pressure reading around every 50ms. Some go down to around 25ms. Filtering out the noise, the pure change in altitude by comparing pressures is always a little delayed but provides already a climb rate and a decent variometer for paragliding, at least if your smartphone comes with a decent pressure sensor.

The change in gravity due to acceleration and deceleration is quasi instant. This is the non delayed information that can be used to make your barometric vario an instant one. For this you will need the accelerometer of your smartphone. However, there is one problem left. Depending on your phones orientation, the change of gravity will be associated with different directions. This is why an instant vario needs to also include information from the gyroscope to get the changes in acceleration calculated right.

Up to date accelerometer and gyroscopes of mid range smartphones currently read out easily at around 10ms. This is around 100 times each second and provides a continuous stream of information.

So, an instant vario is one that fuses all these sensor readings together. One could also say mixing but..., it is not just thrown together, shaked and magic happens. We call this complex algorithm fusing the accelerometer, gyroscope and barometer at  a rate of 10ms a FusionBoost.

The boost actually refers to the result: a boost in minimizing delay meaning instant. The fusion refers to how the sensor information is being synchronized continuously.

The instant vario for the paragliding pilot

Technology aside, the impact for the paragliding pilot is: The beeping starts when you are entering the thermal and the beeping stops when you leave the thermal. So what you hear is finally what you instantly feel and thus perfectly synchronized to your natural sense of flying. Once in a thermal centering and finding the core is easier due to the instant feedback  of the variometer.

Calibration algorithms included

Since no smartphone is identical to another with regards to its sensors, the Flight Vario App includes calibration algorithms to get the most out of your smartphones IMU and barometer. The algorithms are tested across Google, Nokia, Samsung, LG and Xiaomi devices with BMP280, BMP285, BMP380 and LPS22H barometer as well as accelerometer and gyroscope.

dialog to calibrate the imu and barometer sensors of a smartphone as  paragliding variometer
calibrating sensors of the smartphone

In case you're wondering what and IMU is or actually does: IMUs combine a gyroscope with an accelerometer in one chip and enable your smartphone for real-time motion detection which can be used to enhance the classic variometer based on pressure sensors as discussed in the previous lines.

Feedback on instant vario

Since the start of the instant vario feature we collected some feedback which can be summarized  as follows:

Beginners vs. experienced pilots

The feedback we got so far underlines an interesting but no unexpected fact that we also noticed when developing the instant vario algorithms. If you are used to flying with a classic vario and a delayed response, you might need a little retraining (learning curve) on getting what you feel working together with the instant varios output. As a beginner this (re)learning curve is not experienced, it feels natural from the beginning.

Feedback on smartphones

We also got some feedback regarding smartphones that seem to have the technical requirements in terms of barometer, accelerometer and gyroscope (IMU) to provide the instant vario feature. But please, keep in mind that we cannot guarantee for the general fit of a mentioned smartphone since it is not possible for us to test each phone.

Smartphones with barometer for instant vario

the following smartphones with integrated barometers were reported by pilots (exact model year not known):

Please get in contact with us if you have information on smartphones not listed here already.

Note: We restricted theFlightVario to smartphones running at least Android 8.0 aka OREO due to enhanced GNSS features.