First of all, thanks to everyone who’s posted comments to my first two uniBlogs – it’s nice to know someone’s out there! As for answers to your questions, some will be made apparent soon when uniLab goes live and Sigma darts hit the shops - hopefully those of you who have been waiting won’t be disappointed! An apology to Chris, though - I’m afraid I won’t be posting the full math (or maths, as we Brits say) behind them – I fear I’d wave goodbye to a large proportion of my audience if I start putting differential equations in these ramblings!
What I shall be trying to do instead, over a sort of mini-college-course of uniBlogs, is to explain in an understandable manner the key dart-related aspects of the complex subject of flight dynamics. Then Warren and Eric will get the full aerodynamic facts affecting the short dart/long dart choice they discussed in their comments and see why the matter is not quite as simple as it might seem. So, guys, you’ll just have to keep reading to find out which might fly straighter!
OK, on to business. Last time I explained that the flights of a dart stabilise it (meaning that it flies point-forward) because the aerodynamic lift on them acts behind the dart’s balance point - its Centre of Gravity or CG. What I didn’t mention was that smaller amounts of lift are also generated by other parts of the dart, particularly the barrel nose. The lift from this acts in front of the CG, thus tending to de-stabilise it a little.
One way to estimate the stability of a particular dart is to add up the lift components from the barrel, shaft and flights to get the total lift. The location of these lift components can then be averaged out (“taking moments” is the correct term, as Chris and other technically-minded ones amongst you may already know) to give a point along the axis of the dart where the total lift can be regarded as acting. This point is called the Centre of Pressure, or “CP” and a useful measure of the stability of the dart is the distance of the CP behind the CG. This is known as the “static margin”.
So much for theory. Now let’s see how understanding about the static margin can help astute dart players like Eric and Warren in real life.
Let’s say my imaginary pal Nigel the Novice wants to buy his first set of Unicorn steel tip darts. Now Nigel knows a bit about aerodynamics and realises he needs very stable darts because his throw is a bit wayward and his darts tend to hit the board at a variety of angles. This reduces his already dubious accuracy and also increases the chance of a previous dart blocking the target bed. Very stable darts – which means ones with a large static margin – will help him by flying straighter.
Nigel decides that the best way to ensure a large static margin is to buy “bomb” shaped barrels which have the weight - and thus the CG - biased toward the nose. A good example of this type of barrel is the Unicorn Dum Dum range, but Nigel decides he prefers the slightly more conventional Peter Manley Maestro Tungsten.
Unfortunately, these barrels do have a slight downside for Nigel – Peter Manley definitely isn’t a novice! The darts that bear his name thus don’t need to come with large “Plus” or “Big Wing” shape flights, but have the smaller, oval “Xtra” type, which produce less lift. Also, the supplied Maestro shafts are aluminium and the CG of the whole dart is hence a bit further back than if they were plastic. These factors reduce the static margin - no problem for Peter Manley, but maybe one for Nigel. But Nigel has the solution. He purchases a set of Big Wing flights and XL+ plastic shafts and customises the darts to be more stable.
As it happens, Nigel’s made a good choice. But a little knowledge is a dangerous thing and he has been a bit lucky. To find out why, join me next time!