Sunday, January 2, 2022

Wind measurement - Observing earth boundary layer while landing

 With XCVario, several speeds are measured :

  • True AirSpeed (TAS) can be reconstructed from dynamic pressure & temperature measurements.
  • GPS measurement (from FLARM at this stage) gives direct access to Ground Speed (GS)
 --> Difference between both TAS & GS is then an estimate of instantaneous wind.

As an illustration for this, the difference between TAS & GS is plotted during final landing phase, representing earth boundary layer above the airfield.

A few observations can be made

  • On the 8th of may :
    • Both landings show a reclined boundary layer profile, with weaker wind at landing altitude than @ 20m above ground
    • On the 2nd landing, wind is stronger & deeper present on the ground
    • Gust content is rather low for both landings
  • On the 13th of september in St Auban :
    • Wind is present almost down to landing altitude, with little reduction of wind component before the last 5m of altitude
    • @t~10-12sec, a sensible gust can be observed ~70m above landing altitude, with a "gap" of TAS not visible on GS, and roll activity.
    • Another gust is visible @t~30sec, 10m above ground
    • A further gust is visible during ground roll -that has been filtered out of wind speed vertical profile

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Landing on the 8th of may 2021 against "vent d'Autan" with no lift

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Landing again on the 8th of may 2021 against "vent d'Autan" after a flight in weak distorded lift

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Landing on the 13th of september 2021 in St Auban

 

Friday, December 24, 2021

Observing temperature profile while flying thermals

Temperature as well as static pressure are measured by XC vario. As a results, it is possible to plot temperature as function of pressure altitude. 


Below are plotted a few time slices as recorded. Several observation can be made :

  • Flying straight in sink or neutral zone results in measuring a certain gradient of temperature versus altitude - generally steeper than -6.5deg standart atmosphere gradient.
  • Circling & climbing in a thermal shows a similar temperature gradient versus altitude compared to measured in straight flight, but with an offset corresponding to warmer air
  • While entering or exiting the thermal, a transition happens in the same order of magnitude : we end up drawing an hysteresis
  • The greater the climb, the greater the "warm offset"
  • Those observations seem to remain true for strong climb in mountain area as well as weak thermal over flat land on a poor day

Using temperature sensor as a "thermal sniffer" is not the objective here, nevertheless collecting this data could be worthwhile  in term of validating weather models - particularly if coming from a network of gliders flying the same area.

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 Strong thermal at Malaup montain on the 13th of september 2021

  • Transition
  • 3.95m/s mean value over 850m climb
  • Transition

 

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Good thermal at La Molière (north Vercors) on the 13th of september 2021

  • Transition in a uplift area, then sink
  • 2.1m/s mean value over 320m climb
  • Transition

 
 
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Soft climb at Gache mountain on the 13th of september 2021
  • Transition
  • 1.1m/s mean value over 370m climb
  • Transition

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Weak thermal over flat land on the 9th of october 2021

  • Transition
  • 0.6m/s mean value over 100m climb
  • Transition 






Recording with XC Vario

 As described in the former post, XCVario has onboard sensors of interest to analyse flight paths of a glider. With two other pilots, Jean-Luc & Guy-François, we are working on formulas & algorithms using those sensors to provide enhanced variometry measurement.

As a first step, Jean-Luc & Guy-François have created a fork from XCVario software, that is providing in particular the emission on Bluetooth for parameters of interest, that can be recorded by a smartphone. Over the season, I could record more than a ten of flight hour on my LS6 glider, that can be analysed on over the winter. A typical 5hrs flight results into ~30Mo of text file. For analysis purpose I use Scilab cripts (open source cousin for Matlab...), but Guy François has also developped his own post processing program.

Looking into this recorded material is providing interesting insight into the condition encountered while flying. Further post will be dedicated to observing what is measured

A Cross country flight over the alps (see the flight in Weglide)

Installing XC Vario

 At the begining of the season, I had dismantled the old C302 vario & have replaced it with a modern instrument : A XC Vario.

The old generation out...

... replaced by a modern tool !

XCVario is in the family of open source varios, with the interest that a very neat hardware can be purchased, while software is opened.


In the main features :

  • Basic sensors covers pressures (static, total & antenna) & temperatures informations for standart altitude & speeds parameter construction
  • Advanced sensors as options providing as well as 3axis acceleros & gyros (AHRS)
  • Full Wifi & Bluetooth connectivity is offered
  • It is compatible with XCsoar 
  • It is ready to receive FLARM information, with a contact display 
More info at :

https://xcvario.com/

https://github.com/iltis42/XCVario


This instrument has been used over 2021 flying season as a starting point for scientific investigations... 


The updated instrument panel


Sunday, September 19, 2021

Flying over Corrençon-en-Vercors

 A long dream come true : I did fly over the family house in Vercors mountains !

More at : https://www.weglide.org/flight/108138

"Eastern balcony" of Vercors Plateau, as flown staring from the south.

"Hauts plateaux" prairies in approach !

Flying over the village of Correncon, and the family house

Further north, city of Grenoble, were I was a pupil in the last century...



Tuesday, April 27, 2021

A day over the Pyrénées despite Covid19

 In this difficult sanitary period, it became legal to go out for sports as far as you stay in your department. And gliding was recorded as one of this sports !
After logging the day off at work, I took the trailer to Luchon-LFCB to have an out of the ordinary day.


This was really worth the logistic effort ! In the season, snow is still very much present, but not blocking convection too much.






Thursday, February 20, 2020

Flights from St Crepin

2019 was the opportunity to discover a new airfield, with the family onboard : nice mix of hiking & flying ! Thanks for the Bada tribe for the spot !



A few photos !

Classical view of the Ecrin
Outlanding in Aoste, Italy - Thanks to Boris for retrieval
Hiking toward Glacier Blanc
Evening welcome