08:39 AM – Departure in the jump of Arbizon
With Louis, we arrived at around 07:30 AM and took off just before 08:00.
The Pyrenees were overcast on the Spanish side, but some rotor formed the waves and the lift spots well. My Taurus with self-launching engine is the key for big flights. Having a self-launching glider is a big advantage, as you can start at the precise position you want, and I usually don’t hesitate to climb up to 3200 meters or more, to be directly in the laminar air and to eliminate loss of time in the strong turbulence of the sub waves.
On that day we entered in the laminar air already at 2500 meters, so we turned off the engine and started to climb in the strong lift. Usually I prefer to start by climbing to the max authorized altitude 6000 meters (FL 195) but as we topped at 4200 meters, we decided to go westward to reach the jump of Arbizon and Pic du midi de Bigorre. We lost 1000 meters in only 20 km but because of that we directly reached the lift of Arbizon where we climbed to 5600 meters.
The wind was not very strong, 75km/h from the 200°, which is quite perfect for waves over the Pyrenees. The jump was nicely formed even though the cloudiness was quite strong. One of my big questions I often have on wave flights is at what speed I should fly in the waves with knowing the polar curve of the glider. The LX 9070 computer does an excellent job with the Mac Ready calculation, but it doesn’t integrate the wind speed component – but since the lift spots are fixed from the ground, it is essential to integrate the head wind component in the speed calculation.
I have worked on glider polar curve to find a simple rule to be used in flight, which would enable me to fly at the best speed depending on the lift, the vario netto and the headwind component. So I worked on quadratic equation of the polar curve (pure math) to find a rule (I call it “Waves rules”) to determine at which speed I have to fly depending on those 3 parameters. I discovered also that the Taurus has a quite good potential of speed, even with very strong head wind in waves condition. This is due to the very good medium speed characteristics of the Taurus (120 km/h to 160 km/h) and the altitude coefficient of speed (about 30% bonus at 5000 meters).
So we flew between 120 and 160 km/h indicated speed to west direction, and as the wind was quite orthogonal to our course, we had only 20-25 km/h head wind component which is not significant above 5000 meters. One big difficulty in southern waves over Pyrenees is to find a lift spot between Bagnères de Luchon (South of St Gaudens) and Pic d’Anie, 100 km west of Luchon. The lift spots are not always where they should be, so on the first leg you have to be careful. Here I would like to thank Mr. Michel Belaygues, who is usually flying his Apis, but who unfortunately couldn’t fly on that day. He had helped me a lot on all the flights we did together before, and he taught me how to find a good track to fly by on this difficult part of the mountains.
But on that day the lift was quite well materialized and the jump spots (Arbizon, Pic du Midi, Gourette and then Pic d’Anie) were located just as expected. The wave was very good and several times during the flight we nearly reached over-speed, so we used the airbrakes to keep below FL195 with netto sometimes at +6 m/s. Theoretically rotor cloud isn’t supposed to move away from the mountain, but I think this is quite false, since the rotor always moves as pushed by the wind, then disappears and a new one is generated a few kilometers ahead.
It is not easy to see if you are well-positioned on the rotor (staying always ahead of the small rotor, the furthest in front of the wind). So we tried to position ourselves correctly on the rotor every time, but we always checked to be at a good distance from the ridge of the mountain by applying the “Robert Prat” rule (a math equation which helps to calculate the distance of the jump spot from the mountain ridge according to the wind speed). His rule works perfectly and it is amazing to see how accurate it is. I took all the benefit of having a high resolution map on my LX9070, which gave me perfectly accurate positioning.
So on that day we glided quite fast to the first turn point at Santesteban, south of Biarritz. The glide was easy and we stayed high all the time, close to 5500 meters. We turned at 10:30, 2 hours after we started the circuit.