Calculating Wind And Paraglider Speed

A fast and precise calculation of the wind speed is a clear advantage when paragliding as it helps in centering a thermal fast and provides relevant changes of wind with change in altitude or location. But there’s more to wind calculation in paragliding. It can be used to estimate the speed of your paraglider with respect to exactly your harness, specific adjustments and overall weight without any extra equipment.

With that said, there should be some notes on wind calculation and its use in paragliding. Rather than just referring to or relying on some wind directions and strengths provided by a vario app or dedicated varios, it is a good idea to understand what is going on in the vario app internally and know the preconditions that shall be met for trustworthy results.

But before that, let's recap the basic differences between air speed, ground speed and wind speed.

Ground Speed, Air Speed And Wind Speed

While ground speed and wind speed are directly related to each other, air speed relies (for a given setup) on other factors, especially air density

Ground Speed: The ground speed is basically what your vario or vario app reports as your speed when paragliding. It is taken from the GNSS readings and is your speed with regards to the ground below, how many meters you are making each second into your direction of flight. Which is not the (true) airspeed.

Air Speed: The air speed of your wing is the velocity your paraglider is traveling through the air. In total absence of any wind (which is rarely the case), this airspeed will match the ground speed. Meaning your ground speed into any direction [0, 360] will be the same. But most of the time there is some wind present.

Wind Speed: With wind present the air speed of your glider will not change. What will change is your ground speed, often referred to as speed above ground. A wind of 3 meters per second from e. g. the south will add 3 meters per second to the ground speed of the opposite direction.

Calculating The Wind Speed

Knowing the wind direction and speed at different altitudes assists in understanding conditions and decisions to maximize the distance flown.

Prerequisites

For calculating the wind without any extra gear like pivot tubes, two things are necessary which is the bearing and the speed of your paraglider at given point in time. Luckily, both are provided by the GNSS of your phone and this is also why it is important to have a high grade and ideally dual rate GNSS chipset as used in phones like the Pixel 6, 7, 8 or 9.

Well, actually there is a third requirement that must be met for the wind calculation in paragliding to work. You will have to be flying into different directions, not just straight.

Calculations And Fits

Once you take off, the wind calculation will be running continuously in the background. Each combination of bearing and speed is weighted and added to the calculation while the calculation is repeated with each new observation. If a bearing and speed combination has been used before, the newer one is weighted higher in the calculation. Old combinations are dropped at some point to not influence the wind calculation with outdated readings as are observations with low or no accuracy. The latter is also the reason why on phones with (outdated) limited GNSS chipsets the wind finder is not being displayed.

The objective itself is to come up with a prediction where predicted values are close (fitting) with observed values. But how do we know if a calculation actually fits? Well it needs to fit meaning, the differences between observed and the predicted values must be minimal AND the total of all deviations shall be below a certain threshold. While the calculation of differences is straightforward the thresholds are based with regards to the speeds involved in paragliding.

Applied statistics and math brought to purpose 🙂

Interpreting The Wind Finder

Using the wind finder while paragliding comes down to realizing that the windfinder is displayed at all and if it is blinking or not. The wind finder appears once calculations are successful. It blinks if the fit is questionable and it stops blinking if the fit is high enough.

Adjusting The Wind Finder

Wind calculation is actually quite stable with already a few combinations of speed and bearing given

the GNSS chipset of the phone is a newer one
the GNSS chipset is (ideally) dual rate capable
the bearing range is reaching to 180° or more

However you can tell the vario app to use any number of readings from 30 - 108. If there are only a few readings considered the vario app will adjust very quickly to changes in wind direction and speed but will only take a short range of readings which is fine while thermalling. If there are many readings taken into account the wind calculations will adjust slower to imediate changes in wind direction and speed but a long range of readings will be considered which can flatten out gusts and can provide readings without thermalling.

Other ways for estimating the wind direction and speed

Of course there are other ways for calculation of the aforementioned metrics. You can come up with all kinds of methodologies like checking the distance and direction of half or full circles flown with respect to time. But except for using extra external gear to come up with the true airspeed and incorporating that into the calculation there will be no faster one.

Calculating The Paraglider Speed

Calculating the speed of the paraglider is based on having determined the wind speeds over and over again. An overall average is being stored in the Pilot and Wing Preferences of the XC Vario after each flight (for now). There will be some more refinements.

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