In his 1978 book Streckensegelflug (lit. "distance sail flight".
Cross-Country or Long-Distance Soaring), Helmut Reichmann describes a
flight made by Ingo Renner in a Libelle sailplane over Tocumwal in
Australia on 24 October 1974.

On that day there was no wind at the surface, but above an inversion at
300 metres there was a strong wind of about 70 km/h (40 knots). Renner
took a tow up to about 350 m from where he dived steeply downwind until
he entered the still air; he then pulled a sharp 180-degree turn (with
very high g) and climbed steeply back up again. On passing though the
inversion he re-encountered the 70 km/h wind, this time as a head-wind.
The additional air-speed that this provided enabled him to recover his
original height.

By repeating this manoeuver he successfully maintained his height for
around 20 minutes without the existence of ascending air, although he
was drifting rapidly downwind. In later flights in a Pik 20 sailplane,
he refined the technique so that he was able to eliminate the downwind
drift and even make headway into the wind.

Just amazing and fascinating!

Richard
ASW19 Phoenix