  A flexible sheet clamped at both ends and submitted to a permanent wind is
unstable and propagates waves. Here, we experimentally study the selection of
frequency and wavenumber as a function of the wind velocity. These quantities
obey simple scaling laws, which are analytically derived from a linear
stability analysis of the problem, and which also involve a gravity-induced
velocity scale. This approach allows us to collapse data obtained with sheets
whose flexible rigidity is varied by two orders of magnitude. This principle
may be applied in the future for energy harvesting.
