The Unsteady Aerodynamics of Turbine Yaw and Over-Speed Protection - Small Wind Turbines: Analysis, Design, and Application - page 166

10. The picture shows the Vergnet 7-10 small wind turbine. The ''7'' refers to the
blade diameter in m and ''10'' to the rated power output in kW. The very
distinctive design ensures that the tail fin is not in the wake of the nacelle and
tower. Assuming that the tail boom angle is 45, estimate the difference in
natural frequency and damping ratio when compared a similar tail fin on a
horizontal boom of the same length.
11. Using the results of the previous exercise, would you use a rectangular tail fin
in preference to a delta wing of the same area? Assume the tail fin chord in
each case is much less than the tail boom.
12. It has been suggested that one way to get extra damping when needed is to
have the fin ''spring-loaded'' so it can slide along the tail boom and move
further away from the yaw axis as the centripetal force due to high yaw rates
overcome the spring tension. Comment on this suggestion.
13. Is it possible to design a furling tail fin that does not have a ''yaw error'' when
unfurled?
References
1. Leishman JG (2002) Challenges in modeling the unsteady aerodynamics of wind turbines.
Wind Energy 5:86-132
2. Leishman JG (2006) Principles of helicopter aerodynamics, 2nd edn. CUP, Cambridge
3. Ebert PR, Wood DH (1995) On the dynamics of tail fins and wind vanes. J Wind Eng Ind
Aerodyn 56:137-158
4. Bechly ME, Gutierrez H, Streiner S, Wood DH (2002) Modelling the yaw behaviour of small
wind turbines. Wind Eng 26:223-239
5. Wright AD, Wood DH (2004) The starting and low wind speed behaviour of a small
horizontal axis wind turbine. J Wind Eng Ind Aerodyn 92:1265-1279
6. Polhamus EC (1966) A concept of the vortex lift of sharp-edge delta wings based on a
leading-edge suction analogy. NASA TN D-3767, December 1966
7. Polhamus EC (1971) Predictions of vortex-lift characteristics by a leading-edge suction
analogy. J Aircraft 8:193-199
8. Bertin J, Cummings R (2009) Aerodynamics for engineers, 5th edn. Pearson Prentice Hall,
Upper Saddle River
9. Weiringa J (1967) Evaluation and design of wind vanes. J Appl Meteorol 6:1114-1122
10. Kristensen L (1994) Cups, props and vanes. Riso National Laboratory, Roskilde. http://www.
risoe.dk/rispubl/VEA/ris-r-766.htm . (accessed 21 Feb 2010)
11. Ackerman MC (1992) Yaw modelling of small wind turbines. J Wind Eng Ind Aerodyn
39:1-9
12. Davis D, Hansen C (2002) Operation and load measurements during extreme wind events for
a southwest windpower whisper H40. AWEA Windpower '02, Portland, Oregon
13. Katz J, Plotkin A (2001) Low speed aerodynamics, 2nd edn. Cambridge University Press,
Cambridge
14. Thomas ALR (1993) On the aerodynamics of birds tails. Philos Trans R Soc Biol Sci
340:361-380
15. Thomas ALR (1997) On the tails of birds. What are the aerodynamic functions of birds' tails,
with their incredible diversity of form? Bioscience 47:215-225