Frequently Asked Questions

The following sections handle some common questions found in paragliding. We hope to answer these as objective as possible.  Also, a good amount is spent clarifying the differences and expectations of using a smartphone as a variometer for paragliding. Needless to say, a smartphone is not designed and built with the requirements of a vario in mind firsthand. The pilot is responsible for choosing the appropriate equipment.

Contact us if you want to add or have improvements that you feel should be integrated.

Sensors - Barometer vs. IMU

A lot of questions often with overlapping interest but from different domains and technical understanding. The idea is to have a little documentation where interested pilots can check. All the following is written in the hope of being useful and informative for understanding how a barometer and vario works, especially in paragliding and what phones are potentially capable of.

Which sensors are used by the vario app?

Our vario app uses the combination of accelerometers, gyroscopes, magnetometers often referred to as IMU and the built in barometer as well as readings from the GNSS receiver.

What is a barometer

A barometer is a device that senses and indicates the current pressure. This pressure can be converted to an altitude with the help of the barometric formula.


Do I need a barometer?

For the vario app to function properly your phone needs to be equipped with a barometer. There cannot be a proper vario app without using a barometer. Using additional information from the IMU is optional and will boost the vario functionality of a phone. 

What is an IMU

An Inertial Measurement Unit (IMU) is a combination of sensors that provide information on orientation, velocity and gravitational forces. Nowadays IMUs are included in most phones and typically refer to a combination of accelerometers, gyroscopes and magnetometers. 

Does a vario benefit from using an IMU?

Combining multiple sensors, especially incorporating acceleration readings from the IMU on top of barometric readings, makes for two things: First the response is as instant as can be. Second, the response is more precise and robust. The more sources or sensors your information comes from the more reliable it is in terms of precision and robustness. This is simply statistics. Using the inertial measurement unit all degrees of freedom are observed to calculate the most likely true climb rate.


What is the difference between barometers and IMUs?

While a barometer is only capable of informing about vertical translation (up/down) using changes in pressure, IMUs provide information on all 6 degrees of freedom (6DOF). Thus additional information is available to determine the true state of motion including the vertical speed or climb rate.


How does an IMU relate to a barometer?

For the barometer a change in altitude needs to happen before it can be detected and reported. The barometer or  pressure sensor needs (more) time to actually integrate while the acceleration sensor reports the current acceleration right away or instant.


If you want to downtune your IMU Vario to match old fashioned barometric only varios, that can be easily done. An IMU vario can be delayed to feel like a barometric only vario, a barometric only vario however cannot match an IMU vario. In other words, if you are fast there's no problem in pretending to be slower. The other way around won't work.


Which Degrees Of Freedom exist?

Degrees of Freedom are distinguished into Translation and Rotation.


Translation covers three degrees of freedom (3DOF). As a pilot think of them like this:


Rotation covers three degrees of freedom (3DOF) that are familiar in paragliding:

9 DOF vs. 6 DOF 

Adding geomagnetic field sensor to reduce errors for edge case when working with gyroscopes and accelerometers.

GNSS vs. Magnetic  Compass

Practically all modern phones are equipped with a GNSS receiver and a digital magnetic compass. theFlightVario vario apps use both of them. 

What is the GNSS Compass?

Based on the locations, meaning latitude and longitude reported by the GNSS, a bearing between two locations can be calculated manually. The bearing represents the direction of movement, in this case the movement of the phone. The GNSS compass refers to this bearing. 

Note: This bearing is readily provided by the GNSS receiver using Doppler Shifts. There is no benefit and need for an extra calculation based on subsequent locations.


What is the difference between GNSS and Magnetic Compass?

In the context of paragliding, the bearing from the GNSS is the direction your glider moves towards while the heading from the compass is the direction your glider is pointing to. With wind present these two will be different.

For instance, with the magnetic compass showing south while an eastern wind is blowing, your GNSS bearing will be south with a little west.  If you do not correct your direction of  flight using the GNSS and the map, you will end up flying a curve rather than flying straight to the point of interest you are aiming for. The XC vario app displays a line from your current location using the bearing of the GNSS so you can correct. Additionally, the terrain view can be used to check with the underlying terrain.


Where in the vario app is the magnetic compass?

If your phone is equipped with a digital magnetic compass, the compass rose will rotate according to where the phone is pointing to while and only while a takeoff has not been detected. Also the magnetic compass needs to be activated in the Settings.

What about the geomagnetic field declination (GMF)?

Within the vario app, the magnetic compass is corrected for the geomagnetic field declination based on location and altitude. Note that this is based on a model. As for models, ‘all models are wrong, some are useful’ -> Use With Caution!


Metric vs. Imperial Units

The XC Vario and Classic Vario app support metric as well as non metric units alike. Units can be set individually for distances, speeds and altitudes reported by the vario apps. For instance, you can have altitudes reported in feet (non metric) while speeds are reported in kilometers per hour (metric), if you wish to do so. 

How to set metric or non metric units individually

Simply long click the field you are interested in. A pop up menu will open and you can choose between different units:

Vario Speeds

Speed can be set to different units like km/h, miles per hour or knots. The speed reported in the vario app is always speed above ground as reported by the GNSS.

In flight summaries a min, max and average speed is being reported. The average speed is calculated from a corrected flight track omitting the locations where time was spent thermalling.

Vario Altitudes

The vario apps provide mean sea level, flight level, QNH, QFE and manual altitudes by tapping the altitude field. More details can be found on the altitudes site.

Why is the altitude field blinking?

Upon startup the vario app will check how many satellites are in reach and if there is a valid GNSS fix. Once a regular GNSS fix has been established the vario app will try to come up with a 3D fix to also provide altitude information. This GNSS 3D fix contains a latitude, longitude and altitude. During this initialization the altitude field will blink.

Note: the altitude field will adjust further until a takeoff or start of flight is detected 

Which altitude information is fetched from GNSS

There are two altitudes available when parsing so called NMEA sentences from GNSS. MSL altitude refers to the mean sea level altitude while the WGS84 altitude refers to the WGS84 date.


What is an NMEA sentence

NMEA sentences are ASCI based messages with limited size that are amongst others used for communication between GNSS receivers like a phone and satellites. NMEA stands for National Marine Electronics Association.


Here is a sample NMEA sentence reporting latitude, longitude and WGS84 altitude


$GPGGA


Vario Troubleshooting - Bug Or Feature?

Why does the map occasionally turn black (XC Vario)? 

It's not a bug! Having the map turn black is an intended feature of the XC Vario that will reduce power consumption and focus on relevant information when paragliding. As soon as the vario app detects a flight style that indicates thermalling or soaring, the screen will turn black and only the thermal track will be displayed. Zooming into the map at that detailed resolution would provide only limited and rather distracting information.

When soaring this will help you anticipate the best time for turning, so you will not turn in the sinking but rather in rising air. When thermalling the colored thermal line will visualize how well you hit the core of a thermal, helping you to adjust if needed.

Do the vario apps have automatic start detection?

All vario apps have automatic start detection. The start detection is based on the GNSS speed and changes in pressure. There is no need to trigger a start manually unless you want to check some of the vario app’s behavior. A manual start can be triggered by clicking the Share Button on the main screen


Do the vario apps have automatic stop detection?

Sure equipped with automatic start detection, our vario apps also provide automatic stop detection. Upon stop the flight will be stored to the database,  distance and other metrics like xc distances and speeds will be calculated. A Flight Summary will be presented to the pilot.

Cloud Backup of flights

Cloud Backups of flights make it easier when switching phones. Upon signing in (again) flights from one vario app or phone will be synced to another. You must upload flights before by pressing the cloud button below each flight in the flight book. We do not upload flights automatically!

Sunset and Sunrise 

Sunset and Sunrise is calculated based on your location. See Settings -> Status. While this is nice to know it primarily serves the purpose of auto selecting the correct thermal hotspots by region and time of day.


IGC and G-Records

For rankings in preparation of competitions or competitions itself a mechanism is needed to verify the flight log of the pilots. This is being done with the help .igc files and a signature within these .igc files that can be verified by a third party.

What is an .igc file?

Basically it is a tracklog of a flight that adheres to the formatting and rules of the FA International Gliding Commission, in short IGC. The .igc file is stored as a text file and can be inspected with any editor. 

Which information is stored in an .igc file

Basic .igc files consist of three types of information:


Formal header information like pilot name, type of aircraft (including paragliders), the dates used like WGS84 and ICAO atmosphere and the manufacturer and model including information on the GNSS chipset use. Those are referred to as H-Records. A H-Record looks like this:


HFGTYGLIDERTYPE:Ozone Photon


The actual B-Records that contain the UTC time, the location in GNSS coordinates and a barometric/GPS altitude at equidistant points of time. For the XC Vario app each second a B-Record is logged. A B-Record looks like this:


B1306555039008N00122761WA0017500176007012003320242


A signature that is calculated from most of the information above to verify that especially the B-Records where not hampered with. This signature is called G-Record

What is the G-Record in an .igc file?

The G-Record is a small signature string at the end of the .igc file. It looks like this and varies based on the signature algorithms used


GdpxOWpTVjV3y0Frry5O8YQE3KJNunpsMgfao6ISUwsfr+Yr8dQR3T9l9U59RMd0A

GlevXXMbkhkqfLyhx4maSLC/Jp7Zu9qK4cAJy+Br/Ce7ZWh6OKOFh8iiaSa0uEhPV

Gh+laIKYW6AYrAPNvcnlqBeDH+pSoQN6dPdOPbt+NfIE=

When is a G-Record valid?

Technically, a G-Record is valid if the signature can be verified by a third party. For that case the low level solution is currently to provide a 32 Bit Portable Executable  (PE32) to these third parties that will fail to verify if the .igc file has been hampered with. These PE32s are referred to as valiXXX.exe for a specific three digit Manufacturer code issued by the FAI and integrated in services like the openvali. The three letter code for theFlightVario is XFV.

Does theFlightVario vario app provide valid G-Records?

Yes, in late 2023 our XC Vario App has been approved as supported software. 

How to validate the G-Record of an .igc file?

You can use the Online Validation Server of the FAI. Simply upload your .igc file to check. You can export your .igc file using the Share functionality of the Flightbook. Click the Share button and select for instance Google Drive.

Is there more on .igc files, structure and requirements?


(In case you have better references, let us know so we can link to it here)

Permissions

For the vario apps to function properly a couple of permissions is needed. Android will ask you from time to time whether these permissions are needed and deactivating can be done easily by accident. Always make sure these permissions are granted to ensure functionality of the vario.

What is the notification permission needed for?

To display in flight and feedback information to the pilot, notifications are used within the vario app. Also, if the vario app is pushed to the background, accidently or on purpose, a notification will allow you to jump back to the application, even after a longer period of time. Otherwise the vario app might run in the background with no way of accessing it despite stopping the app entirely.

What is the Precise Location Permission needed for?

Precise Location means that the vario app can access locations provided by GNSS only This is necessary to provide speed above ground, altitudes and bearings for navigation. GNSS only locations  is also a mandatory requirement for valid .igc files.

What is the Background Location Permission needed for?

With no interaction from the pilot, the vario app is technically running in the background. With screen turned off, for instance to save battery, or another app running on top for a while, locations from the GNSS cannot be accessed anymore and the vario including logging stops working, if not permitted via the Background Location Permission.

Battery Optimizations

Make sure to turn these off and whatever other optimizations your non native Android provider has installed on the phone.

Vario Audio and Tones

Our vario apps use our own low level synthesizer to generate customized tones, written in C++ for performance and fast audio. Audio and Tone is continuously generated and not using any playbacks, samples or such. This way any change in the climb rate will be directly audible.

Customized Vario Tone Curves?

We support custom vario tone curves like the XC Tracer or leGpsBip. You can import or choose from a set of predefined vario tones curves that will fit most pilots.

Which audio tone should I select?

Our vario app offers different tones to choose from. Currently the most preferred one is the smooth one “Smooth” which comes close to what you might be accustomed to from commercial varios. However we also have very loud or edgy ones. In case you are techie and have a very special tone we would need the different frequencies and amplitudes and can synthesize that one too. Just in case ;-)!

Sink Tones And Pre Lift

A continuous sink tone can be set for a user defined threshold. Same holds true for a pre lift zone.

Is there any audio delay

One of the reasons our vario apps are not running below Android 8.0 is the provisioning of non delay audio. Practically there is no delay in the generation of vario tones and sounds, limited to 10ms or one hundredth of a second (well below noticing threshold).  

When and where to use a variometer

Is this a bubble, already a steady thermal? Did I just fall out of the thermal? Did I reach an enhanced climb zone within this thermal?  What is this pull, is it just me feeling this or is it also indicated by the flight instrument, the vario that I’m using?


Often you hear things like:


"... as long as you are just learning to fly, a vario is not that important..."


Well, we think this is only half the truth. What is true, in the beginning you might or better simply cannot know which variometer is best. However you should go with a vario as early as possible. As soon as you fly it is important to consciously sense the movements of your wing and harness (up / down / pull / push) together with the output of the vario.


For your first flights it is not necessary to have a big display, information about airspaces or the exact speed over ground. Even the exact climbing rate is not that important and or how fast you are flying over ground. Most important is a vario tone that reflects the rate of climbing. It should get higher and beep more often if the climbing gets bigger and vice versa.


So, to learn fast and have long flights soon we recommend two things:


In case you are just soaring along a small ridge thinking, simply following the relief closely might be more relevant than flying with a vario...  Even while soaring, an instant vario can be extremely helpful to carefully select your turning points meaning the point where you turn your glider to get the most out of the local lift. Not getting that sweet spot makes you loose altitude twice.

Which variometer to choose?

In the beginning you might not know which variometer is best for your paragliding. Don’t just throw all your money into the very first vario. It will be very disappointing finding out you spend a lot of money on a flight instrument but your are actually more comfortable with another solution like a small bluetooth vario, a smartphone vario or a combination of both once you mastered your first flights.


Also, don’t invest too much money or time into (very) old variometers. These might be ok during flight but quite uncomfortable on the ground to use or connect to a computer (which will be your only way to reasonably analyze your flights). They might need special power plugs and or cables or drivers you might need to install. Using these as a backup vario or flight logger however will be fine.


So, while it is not possible to tell which flight equipment resembles the best variometer for paragliding, for different types of pilots different solutions exist.


(Note: This might be a biased opinion, but with smartphones nowadays having gyroscopes, accelerometers and barometers: Unless you are not going professional, your smartphone has a display, it logs the GPS coordinates of your flight, it already has an antenna in case live tracking is relevant, your flights are backed up with the cloud, you can analyze your flight directly on the phone and of course you carry it with you anyway.

We have never seen a pilot forget his smartphone. But we have seen many pilots that forgot their vario because they charged it and left it unintentionally at home or in the apartment or in the bus.

So in case you are going for a new smartphone you might want to consider getting a smartphone with instant vario capabilities to try this out.)


Where to attach the smartphone

Once using the smartphone as a vario the next question is where to attach it. Theoretically, once could strap it to the risers, put it into an arm wrist, attach to the leg or actually the best way and practiced by most pilots: Attach to the cockpit in front of you. This way you can also connect it to a powerbank or if relevant attach an external vario via usb or bluetooth. 

Can you fly without a vario?

Of course you can and it is fun and good practice to sharpen your senses for everything around your wing and harness. But after all your human senses are limited. Being human apart from visual and acoustic information you can sense changes in gravity which is why you can feel the initial lift when entering a thermal, the drag when you’re sucked into a thermal directly ahead or to the side of you but also being pushed away from a thermal or simply sliding down on the lee side of a thermal. 


However being inside a thermal with a constant climb rate it is impossible to tell how fast you are moving up without additional visual clues. Naturally the higher you get the less visual clues you have.


Better than training your senses without a vario, train your senses with a vario so that your (intuitive) judgement meets the objectivity of a flight instrument.


This is also the reason why good pilots can fly reasonably good without vario! All of their senses, visual, acoustic as well as regarding gravity have been aligned over time with the objectivity of a vario. On top of that, they either know the place or have been flying in comparable areas before having an implicit explanation of why the air is rising at certain spots and sinking at others. They either fly with an explicit understanding of the terrain and weather or intuitive (implicit understanding). They watch out for leaves whistling at the ridge, look for birds, dust moving into certain directions or trigger points for thermals, moving or fixed.

Using a phone as variometer

Now and then you can hear pilots talking about whether it is possible to use their phone as a standalone variometer for paragliding?


It depends! But lets break it down a little:



Displaying Information

Obviously a smartphone display is not engineered for paragliding needs! But, you won't stare at the display all the time. You will check your altitude now and then, direction of flight, direction of wind and distances. Of course, the climb rate, you need to know that but 90 percent of the time  you will listen to the vario tone in order to center the thermal.

If you are flying in areas with airspace restrictions, you should have prepared your flight before. So it is not like you are opening up your screen and look up all the information while flying. It is more about an indication whether you are close by or entering an (expected) airspace. For this, we think the visual indication is sufficient not to forget that this indication is accompanied with a warning sound or some kind of alert tone.

So, not having an optimal display, the upside is: Using your smartphone as a vario, it already comes with a screen!



Vario Tone

90 percent of your time flying you will be focusing on the audio feedback indicating an increase or decrease of the climb rate. So, whatever vario you are using it would be nice if the tone can adequately represent the (instant) changes in climb rate.

This means the frequency ot the tone, beep cycles, durations and duty times  need to be able to change instantly and simultaneously to provide continuous information on your lift within a thermal. It is also worth mentioning that different flight conditions might require different sound profiles. Think of  juicy spring thermals as opposed to weak flatland thermals.

Easier said: An Instant Vario should go along with an Instant Tone. For a  smartphone it is easy to provide a low latency instant  vario tone. The xc vario itself can be configured with different sound profiles using  xctracer or  leGPSBip config files and features a low latency due to optimized audio processing and synthesizing.



The Vario - Calculating Climb Rates

Ok, this one is often discussed first and with varying depths and arguments ranging from own experience up to pointing out by example why the smartphone sensors cannot be as good in providing a climb rate as some flight instrument sensor. These discussions are actually good as they show  that it is a good idea to again break it down a little.


Of course a smartphone is not built with the requirements of a vario in mind. Yet, some of them come equipped with the type of sensors also found in varios and in the end it is up to the pilot to decide.


So what are the key sensors in a vario and what does it take to calculate climb rates? 


Barometer:  the barometer measures the pressure at certain times. Modern mid range smartphones can do this at a rate of 25ms or 40 times per seconds. Using this barometer,  the vertical movement based on pressure differences at different altitudes can be calculated (how a vario works).


As for any sensor the question is  how do you know how good it is. And this leads to accuracy  and precision of a sensor.  Let's have a look at these terms using the barometer.


Accuracy would mean that if the  true pressure is 1013.25hpa, the barometer would report exactly these 1013.25hpa on average. Why on average, you might ask yourself. This is simply due to natural random errors happening when measuring continuous quantities. Unless you cannot count it exactly (like an amount of apples) you will always be a little off the accurate or true value.  So you might get a 



1013.2515 hpa as a fourth measurement.


So, is this accurate now? Generally speaking, yes! Taking the average of these values, you land at 1013.25hpa. Considering you can take 40 readings each second, you can be quite sure to have enough readings to average out at the true value.


So what are these little deviations then? These little deviations can be seen as a standard error imposed from any measurement device (in this case this is the sensor reporting back). This standard error is also called precision. The more precise your barometer, the more close to the average each single measurement will be.  Precision gives a clue as to what deviations can be expected and how likely a deviation would be.


Is accuracy important then? No, accuracy is not that important. At least not for calculating the climb rate (the vertical speed in the air) for a smartphone vario. If all pressure readings from the barometer inside your smartphone are off by a constant offset the differences between the readings  will be the same still.  In other words 100m - 90m = (100m + 10m) - (90m + 10m) This offset is also called bias and won't affect the calculation of the climb rate. For instance, a natural offset being introduced each day is the pressure of the airmass itself (low/high pressure).


Is precision important then? Yes, precision is important. Together with the rate at what the pressure measurements from the barometer are reported it will define the possible resolution of your smartphone vario.


Wait, wait resolution? Is that the magic 0.1 meter per second climb rate some pilots argue can only be reported with professional vario. Yes. And No, it can be done with smartphone barometer too. It is just that depending on the rate of readings it will take longer or shorter to detect such a pressure difference correctly.


Now, if accuracy is not that important. How do you know at which altitude you are flying? Sad but true, a vario will never know this accurate by barometric pressure readings alone unless it is calibrated on that very date and time on a location with know altitude. The altitude with respect to mean sea level is pulled from GPS - NMEA sentence information  such as the $GPGGA  sentence.


Finally: Professional devices do have professional barometer inside. These are very precise and can provide an extremely high rate of barometric measurements which in turn can be used to boost precision even further. Will these ever happen to be within a smartphone? Probably not

So. how much precision is needed? We think, this question is most interesting.


Inertial Measurement Unit: The IMU contains further sensors such as accelerometer and gyroscope in one chip and enables a smartphone to perform real time motion detection. These can be used to enhance the classical vario and calculation of climb rates based on barometric readings alone to provide an instant vario. Check theses details on how an instant vario works.



Current Location, Bearing And Speed Over Ground

Current Location, bearing, speed over ground and mean sea level altitude. All of this information relevant for paragliding is stripped from Global Positioning System (GPS) or nowadays more correctly speaking of Global Navigation Satellite Systems (GNSS) information. Even the wind direction will be calculated with the help of GPS.


Fears are that GPS/GNSS in a smartphone is not precise or accurate enough. Good thing, a smartphone can tell you how big the expected variation is at your current position. Another good thing, GPS itself is not alone nowadays. There is more than NAVSTAR GPS (USA). We also have GLONASS (Russia) , Galileo (European Union) and BeiDou/COMPASS (China) satellites to get the required information from.

How many different satellites your smartphone is using to determine the relevant information, simply depends on the GNSS chip itself. You can check this with GPSTest app if you are interested. For instance on a Pixel 4a we have around 30 satellites being reported from the 4 different GNSS.


Check this nice article on Mean Sea Level, GPS and the Geoid if you want to dig deeper.



Current Heading

Your heading will be different to your bearing. While the bearing is the direction your are flying to calculated from the GPS locations, your heading is the direction your are looking to.  The heading can be calculated from the magnetometer. The geomagnetic field declination has to be taken into account for this.




Battery Run Time

Standalone variometers are designed specifically for paragliding. So the battery should last more than a full paragliding day. This is seldom the case with smartphones. Being realistic you can expect up to 5 hours  depending on how intensively the display is being used.  Battery Packs do exist :-).

Charging and charging time is also a criteria. Using flight instruments you might need to carry extra cables and plugs to keep it operational. Although this is less relevant with new standalone variometers it might be worth mentioning when using legacy variometers.


Live Tracking

So what about live tracking when paragliding? Here we have to differentiate between two purposes.

One purpose is to stay safe while flying and exploring especially new routes and terrain that is beyond the boundaries of mobile service or cell phone coverage. This is the domain of GPS satellite messengers or tracking devices.

Another purpose is to  update your position to websites where other pilots can explore your history fo flights and current flights. For this to happen, you must have a mobile connection.

Setting Altitude with QNH / QFE 

We made it easier to fetch Metar information for a specific ICAO code. You can now fetch and set QNH pressure from weather stations on the main flight screen as shown in the screenshots below.


Upon starting the vario, markers for the ICAO stations will appear on the map. Click onto a marker to have the Metar fetched with QNH inside. In this case  Q1018 meaning 1018hpa being more than reference mean sea level of 1013.25hpa.

QNH of 1018hpa at EDVE

The QNH altitude is currently at 54 meters. Touch and hold QNH altitude field and a QNH pressure selection will appear. Setting to 1018 the QNH altitude changes to 95 meters.

Setting a QNH pressure of 1018hpa

Setting to 1018hpa the QNH altitude changes to 95 meters.

You can check with the mean sea level altitude fetched from GNSS and see that it is only slightly off. Pressure sensor of the Pixel 6 used here seems to be well calibrated and GNSS mean sea level altitude quite precisely. This of course depends on the number of satellites found and thus how well the region is covered.

Comparing QNH altitude to mean sea level from GNSS NMEA sentences