Noise measurements of flapping wings with tensed membrane

Micro air vehicles with flapping wings have the potential to be both more efficient and manoeuvrable than similar-sized fixed or rotary-wing aircraft. Reducing the noise produced by flapping wings without compromising or possibly enhancing their aerodynamic performance would be crucial in surveillance and military applications. To this aim we have designed and fabricated flapping wings whose supporting stiffeners tense the membrane material to which they are bonded. The sound produced by these wings at different flapping frequencies has been recorded in an anechoic chamber simultaneously to the thrust they produce. The results are compared with those of standard wings without tensed membranes. The tensed-membrane wings have lower noise per unit thrust and their characteristics and performance are discussed.