Working out the efficiency of the concentric strengthening ring in the center of Bird2's flight was exciting but was tempered when early prototypes failed to spin. One wouldn't expect a feature on the inside of the shuttle to have such an effect on the turning moment of laminar flow. It took a while to work out why this happens. Many months of work went into designing features to get the spin rate up to an adequate level and the work continues and will be seen in the enhanced Bird3 due out in early 2015. In all six different features were conceived, some of them working together to emulate the turbine effect given by offset feathers.
The spin rate is fundamental to the flight of a shuttlecock. I first visited the Carlton factory in Saffron Walden nearly 20 years ago. I was there to discuss thin wall moulding to used on the first LNB's on satellite TV dishes. When the engineers (all made redundant when Dunlop/Slazenger took over) showed me the nylon shuttle production lines they explained that spin was difficult to engender and models often didn't spin or even spun the wrong way. They joked about it and admitted they didn't really understand the dynamics involved. This didn't sound right to me and started me on a quest to resolve this and all the other problems I later discovered about the performance of shuttlecocks.
The obvious function of spin is to true up the flight through the air and reduce the drag effect of any wobble. Also, through centripetal release, it improves the efficiency of air displacement thus reducing air density close to the surface of the shuttle. Both these effects reduce drag thus increasing speed. This is why a feather shuttle of the same shape and weight as a nylon one will fly further (contrary to popular wisdom). However, the most important effect of spin is to improve the 'peak and drop' parabola. Although light, there is sufficient weight in a shuttlecock, particularly the base, to develop sufficient centripetal force to keep the heavier base from tipping downwards as soon as the air speed reduces. This is the gyroscopic effect and leads to another interesting characteristic, most notably seen on feather shuttles. I will discuss this and why the asymmetrical design of the flutes on a shuttlecock favour right handed players in another blog.
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