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Lift enhancement by self actuating flaps (Artificial bird feathers)

Flow condition on an airfoil with self actuating flaps . Motor glider Stemme S 10 with installed self actuating flaps . Closed self actuating flaps in normal cruise . Open self actuating flaps in flight stall condition

The covering feathers on bird wings affect the flight behaviour in the range of high lift. They limit flow separation on the wing and thereby avoid or delay a sudden lift breakdown by obstructing the back flow.

Nature’s example is technically realised by the so-called self actuating flaps. After the proof of positive influence of self actuating flaps had been shown, the technical realisation on the motor glider Stemme S10 has been worked out in excessive tests and optimisations in the wind tunnel, up to the performance of free-flight tests with self actuating flaps. Flight tests showed, the tested self actuating flaps are working reliable at all speeds. An improvement in flight performance as well as a reduction of the stall speed (i.e. lift increase) has been confimed.