Spin rate and spin characteristics are significant for most sports projectiles. The infamous Adidas Jabulani 2010 World Cup ball has been replaced by the Brazuca ball for Brazil. Although the Jabulani ball was felt to be too light, the main problem was the unpredictability of its flight. Although goalkeepers were confused, mostly it affected accuracy on long shots. No word from Adidas but I expect the pattern on the eight panel construction adversely affected the laminar flow across the surface and hence the spin rate, and/or there was less grip on the boot. Whatever it will be replaced by the Brazuca ball with a new crazily patterned six panel design which Adidas says has a more consistent flight.
The performance of a golf ball is affected by spin more than any other projectile. The first golf balls were made of various materials with a rough surface and when they started to mould them with a smooth surface they didn't fly so far. A golf ball climbs up in the air and therefore carries further due the back spin imparted by the slight downward path of the club and the angle of the clubface. The rough surface helped reduce the drag on the ball so the first moulded balls were made with small raised squares which evolved into the familiar dimples as they were more durable and easier to clean.
The spin of a cricket ball affects the flight but more important for swing is the seam. The trick is to deliver the ball without spin such that the seam causes much greater drag on one side of the ball compared with the other. One is allowed to clean the ball which means one side can be polished although it is illegal to rough up the other side, although this is common practice. I was taught that the smooth side should go through the air more quickly; I suspect the opposite is true, anyone tested this?
Picking at the seam of a cricket ball is illegal as is tampering with the feathers on a shuttlecock. However, in both cases cleaning or smoothing is allowed and this makes it difficult to be sure what is going on. Consistency of performance such that people know that a particular action will have a predictable result is all important as skill levels increase. Consistency in the flight of a shuttle is paramount at a high level where centimetres can be crucial and, as good as feathers feel, people do get frustrated when their perfectly weighted clear drifts out for the umpteenth time.
Badminton is the only sport that uses a handed projectile. The anticlockwise rotation of a feather shuttlecock causes it to veer to the right. This means that a high clear will be drifting slightly out on the left side (when you are the receiver) and vice versa. In match play analysis we see twice as many errors on leaves made on the right side because of this. I have not spoken to any coaches who take account of this.
This off-set feature of feather shuttles makes the game slightly more difficult for left-handers. A right handed out-to-in slice shot is hit in the same direction as the lay of the feathers. This increases the spin in the normal direction, opening up the feathers which improves the drop shot and helps accuracy. Left-handers hit into the lay of the feathers (often causing damage) and puts reverse spin on the shuttle which fights the natural direction of spin, thus losing a degree of control.
Tests have shown that Bird2 has a good spin rate and gets more grip on the strings than conventional nylons without opening up or getting damaged like feathers.
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.
Bird2 may be seen as just ‘another nylon’ shuttle so I explain below some of the conceptual thoughts that went into the design of what is a more radical design than might be at first perceived.
Most of the design work done over the last few decades has gone into trying to make a synthetic feather to replace the16 individual feathers that make up the traditional shuttlecock. A close look at a feather reveals the amazing intricacies of the ‘design’ which have evolved over 150 million years. The stems are hollow and uniquely strong and the feathery bits act as a complete baffle to air but weigh virtually nothing. The chances of replicating the performance of a feather to any degree at a reasonable manufacturing cost are zero.
If one did manage then one still has to stick 16 individual ‘feathers’ into a piece of tree bark, bind them altogether somehow and stop them from moving and breaking readily. A moulded one piece flight gives the integrity and resilience to make a durable shuttlecock, but the moulding process is very limiting when trying to make an effective baffle or a rigid structure. After hundreds of different ideas to prevent the collapse of the body of the skirt, the current 2 piece design was conceived.
Splitting the form into 2 mouldings retains the concentric integrity and shortens the length of flow path to the vital lightweight section of the flight. This speeds up the moulding cycle and gives a more durable moulding. The undercut feature gives three times the rigidity as compared with standard nylon shuttles and cannot be formed in a one piece mould tool. It is not formed in the conventional way and gives perfect shape recovery; the processes involved cannot be seen in the finished design.
In the next blog I will go into the design in more detail and then explain some of the tests and trialing procedures we developed to prove the design.
Gordon Willis, Bird Design
Hi, I'm the designer of the revolutionary Bird2 shuttlecock. Let's change Badminton for the better, together; all comments and feedback are essential to perfecting our products.