BFGC Soaring & Cross Country

Transcription

1 Lecture 2 Meteorology: Basic Weather Forecasting: Websites to use Pressure Charts Fronts Cloudbase Forecast Hidden Meanings Thermal Strength Trigger Temperature Advantageous Route Planning Principles of Thermal Centering

2 What ever is presented here. Gaining soaring skills means: Thinking for yourself Asking questions Practice, Practice and more practice. It does not mean someone will do it all for you.

3 Meteorology - Helpful Websites: RASP UK- rasp.inn.leedsmet.ac.uk/ - Thermal strength etc Click above link for example Sat24: Cloud cover, rain etc Click above link for example Weather online: - Everything! Click above link for example XC Weather: Met Office BBC and Local Weather sites

4 WHERE IS THE WEATHER COMING FROM? PRESSURE CHARTS & FRONTS: Normal Low Pressure systems from the Atlantic what we are looking for is when will we NOT be troubled by these? Front Free Periods What is the air mass like? Warm = Moderate Thermals Humid = Lots of cloud Cooler, drier = Stronger Thermals Look for Cold Front passing through with classic Cu following with good thermals Building High Pressure can provide good thermal conditions For how many days will it build? Longer than a couple of days then inversion builds, poor vis and blue days

5 WHERE IS THE WEATHER COMING FROM? PRESSURE CHARTS & FRONTS: Isobars Direction of Curvature, does the air belong to: High Pressure = Drier/Sunnier weather Low Pressure = Cloudier/Showery Windspeed More than 15 kts then becomes hard work, thermals fragmented but there can be helpful streeting. Very Light Static thermals, large clouds with areas of large sink in between kts Moderate sized Cu with good thermals Look for the Isobars to be 4mb apart ( miles)

6 (EXAMPLE - Met Office view of 0000 UTC surface analysis ) A cold front lies near far southwest of the UK, marking a band of rain moving northeastwards into the country. A number of occlusions sit over the UK, and these show areas of showery rain. There is also a line near the east coast and Belgium, marking a heavy thunderstorm here.

7 Cloudbase Ideally feet Here s a formula for working it out.. Find the overnight min temp Find the daytime max temp Formula: Max-Min x 400 = CB EG - 20 o C 11 o C x 400 = 3600

8 Forecast Hidden meanings & whether to go or not? Scattered Showers What sort? Unlucky to get one Risk of Everyone will see one Each will help decide whether the conditions will be useable or just too much cloud and showers. The following.. Fairweather clouds, Clouds bubbling up & ridge of high pressure are all likely to produce promising thermal conditions.

9 Thermal Strength? Again, look at the isobars and see where the air has originated from, strong thermals are often associated with cold air masses. Rule of thumb for anticipated thermal strength is: Thermal Strength (kt) = Cloudbase(ft)/1,000 x 1.2 EG CB/1000 x1.2 = 3.6 kt

10 Thermal Strength? So, off you romp looking for 3.6kt thermals What will change en-route? Cloudbase could have changed for better or worse Topography? What do you notice time and time again at Chipping when tracking out towards the coast? Yes, the cloudbase lowers. (Moister, cooler air?) So, re-estimate thermal strength as you go and either speed up or slow down accordingly

11 Trigger Temperature? What is it? Roughly It s when the surface temperature is equal to the FORECAST temperature at cloudbase (better known as the dew point temp ) PLUS three times the cloudbase (in thousands of feet). So, with a cloudbase of 3000 and the temperature there of 9 o C then: Trigger temp = 9 + (3 x 3) = 18 o C

12 Advantageous route planning Airspace! Topography: E.G. Higher = drier and therefore produces better thermals? Wind direction/strength Head - Tail - Cross Landable sites?

13 On days with a distinct trigger temperature, hotter ground sources become more important. Think about towns and villages, sun facing slopes, rocks vs forests etc. Trigger may be a point heat source, eg fire; a small hill or peak (or steeple!), some disturbance, eg tractor in field, another glider landing, a winch launch; a sharp temperature gradient, eg lake edge or cloud shadow edge. The lumpier the terrain, the more pronounced terrain effects. In hilly areas, thermals often only trigger off ridges and peaks make sure you do not fall into valleys and stay above the lowest peaks and ridges. Use lower peaks and ridges to work way up onto main peaks and ridges.

14 Choosing a route up to ±30 o off track does not significantly reduce speed to destination. Larger diversions rapidly increase flight kms required and cost valuable time. Try to restrict large track diversions to survival flying, unless conditions are so variable that it is obviously a much quicker route (eg unusual strong convergences). If given a choice, try to make track deviations into wind you will drift back when you thermal.

15 Principles of Thermal Centering

16 Before we consider, lets think about thermals in general? Areas that have been in cloud shadow for some time are unlikely to produce thermals, haze & dust will do the same thing. At what angle is the sun to the ground? (Strength) What is the strength and direction of the wind? (Shape) Lower down the thermal will be thinner. (Higher bank angle) Higher up the thermal will be wider (Reduced bank angle)

17 Bank angle, airspeed and diameter of circle The aim is to fly in as small a circle as possible. Most pilots do not use enough bank in the thermal. You should use as much bank as you can whilst remaining in control and keeping the speed as low as possible. If you use too much bank you will either stall and lose lift, or start to spiral dive and build up speed and fly a larger circle. Constant speed allows you to map the lift mentally with less confusion as to where the core is. Many gliders thermal best right back near the stall (eg K21, LS8). Some modern gliders climb better if flown a few knots faster than this (eg Discus 2, ASW24). (Sarah Kelman)

18 Centering: We are feeling and hearing for better climb conditions all the time. Try and mentally visualise the thermal and where the strongest lift is in an attempt to center on it. We will do this many times during the climb.

19 Methods: 1. Level out in lift (B-C) - fly straight for a short period of time, then circle again. B C D

20 Method 1 Right wing raised due to rising air Pilot turns right

21 Method 1 Continues for short period then circles once more Better lift encountered straightens Right wing up raised due to rising air Pilot turns right

22 Method 1 Straigten up again

23 2. Heinz Huth technique: As soon as the lift becomes weaker fly a half circle as tight as possible (A-B) until climb begins to increase, then assume original bank angle. Heinz Huth 2 times world champion B D A

24 Method 2 Resume original bank angle Resume original bank angle Encounter weaker lift, turn tightly Encounter weaker lift, turn tightly

25 3. Helmut Reichman: Combination of both As climb deteriorates steepen the circle (A-B) approx 50 o As climb improves, flatten the circle (B-C) o If climb remains constant, keep constant bank (approx o ) D B A C Helmut Reichman 3 times world champion

26 Method 3

27 4. Tighten on the Surge Jay Rebbeck When the vario indicates the greatest climb rate (B) you should increase the angle of bank and dig your wing into the thermal. A B Jay Rebbeck Junior world champion 2001

28 What ever works for you use it But remember: If you fly poorly you will not climb. The Yaw String is unrelenting in showing slip and skid, BUT center on the thermal first and then fly accurately in a coordinated manner. And remember. Look Out, Look Out, Look Out!

29 Questions?

30 Example of RASP CLICK BUTTON TO RETURN

31 Example of SAT24.COM CLICK BUTTON TO RETURN

32 Example of WEATHER ONLINE.CO.UK CLICK BUTTON TO RETURN