1. Professor, Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano, Milano, Italy; and Chair of Wind Energy, Technische Univ. München, Boltzmannstraße 15, 85748 Garching b. München, Germany (corresponding author).
2. Engineer, iChrome, Maxet House, 28 Baldwin St., Bristol BS1 1NG, U.K.
3. Engineer, AWParc, AgustaWestland Politecnico Advanced Rotorcraft Center s.r.l., Via Durando 10, 20100 Milano, Italy.
4. Ph.D. Candidate, Beijing Univ. of Aeronautics and Astronautics, XueYuan Rd. No. 37, HaiDian District, Beijing, China.