Now if I were a sensitive soul I could be fretting that the great darting public’s initially fairly active curiosity concerning the admittedly occasionally tedious subject of flight dynamics is waning somewhat. That is certainly one sadly poignant interpretation of the undeniable fact that, as I write, only Lonnie has posted a comment to my last blog.
Luckily, however, it befits a dedicated scientist to be blithely oblivious to any widespread indifference concerning their pet subject. I shall hence press on regardless and focus this little dissertation on Lonnie’s question about spin, as well as answering his previous one on soft-tip darts (posted too late for me to address last time). To the victor the spoils! (OK, if you want to be pedantic, to the only contestant the spoils!)
So, is spinning a dart when you throw it a good thing? Well, yes-ish. First of all, even a small amount of spin during flight (say just half-a-turn) will help to even out the intrinsic directional bias (non-axisymmetry is the technical term) in the aerodynamics of the flights. By this I mean that, even if the flights are perfectly set in the shaft with all the surfaces at right-angles, the amount of lift they provide will be slightly different (around 10%) depending on whether they’re in an “x” or a “+” configuration. If the dart didn’t spin at all, it would then make a noticeable difference to its yawing motion which way up it was held – and not many players would want to worry about that.
This evening out (that’s “evening out” as in “levelling”, not as in a couple of beers during a few games of 501 down the club and a dodgy burger on the way home) effect is yet more important given that, in the real world, (a) the flights’ surfaces won’t be precisely at right-angles to each other (b) the flights won’t precisely line-up with the shaft and (c) the shaft won’t be precisely straight and co-axial with the barrel.
Of course, these factors can be minimised by using top-quality darts and components, maintaining them properly, and changing them when they get a bit tatty, but they will still exist to some extent, even if this extent is almost unnoticeable to the human eye. Without spin, such asymmetries could still cause enough lift to throw a dart off-target. But, as I said, even a small amount of spin will mitigate these effects and not only will many players impart this automatically, without making a conscious effort, but some of the very flight lift asymmetries which can cause deviation can also help to reduce it by inducing an “aerodynamic rolling moment” which will make the dart (or just the flights assembly if a “spinner” type shaft is used) start to spin after it has left the hand.
However, if a player wants to minimise not only the lift deviation caused by, say, slightly bent flights, but also any consequent in-flight yaw angles and off-line impact of the point, spinning the dart deliberately as it is thrown can certainly help – and will be especially useful when using darts with high-lift flights. Which is why, Lonnie, you found that uniLab takes deliberate spin into account when recommending a set-up.
We can now also answer Lonnie’s further question on whether Sigma darts are suitable for players who impart deliberate spin. The short answer is yes, but with provisos.
In the One configuration, Sigmas have relatively high-lift flights and, as I’ve explained, could thus work even better for players who spin their darts. Even the performance of the much lower lift Pro set-up can slightly benefit from any deliberate spin, but not so much as conventional darts and hence one aspect of its accuracy advantages would be somewhat reduced.
Now for some rather more academic points about dart spin. Skip the next two paragraphs if you’re not feeling that technically-minded!
Despite what one might think, it should be noted that the advantages of spinning a dart are really nothing whatsoever to do with stabilising it. The spin rates involved and a dart’s “axial moment of inertia” (see my earlier “A Matter of Some Moment” blog) are both much too low to create the gyroscope effect which keeps a bullet (which is a “statically unstable, spin-stabilised projectile”) pointing the right way. Indeed, if dart spin rates were higher, they might actually start to have a de-stabilising effect as they would induce aerodynamic forces on the flights which could turn the normal “yaw damping” into yaw excitation, an effect known as “dynamic instability”.
To get really esoteric, it is also true that, even at low spin, these aerodynamic forces can create other dynamic problems such as “spin-yaw resonance”, which occurs when the spin rate is too close to the yawing rate. Fortunately, however, the flight path of a dart is too short for this to be much of a worry.
So, after that brief excursion into vaguely purposeless erudition, back to some rather more practical darting issues and the remaining answers to Lonnie’s questions – and also an apology. Yes, the 19gm Sigma soft-tip is indeed too heavy for some leagues, especially in the US – just blame the limey designer (sorry!). As to what would be the best 18gm substitute, can I suggest Lonnie bides his time for a while – say no more!
Finally, back on the topic of deliberately imparting spin, a word of warning: unless your darts are bent like bananas, it won’t really make that much difference and I wouldn’t recommend trying it (usually achieved using opposing vertical motions of the thumb and gripping fingers during release, Lonnie) unless it comes naturally to you – doing so could easily interfere with achieving that all-important clean release.
And talking about darts bent like bananas, let me sign off with a slight misquotation of Groucho Marx:
“Darts fly like an arrow, fruit flies like a banana”.
Hopefully see at least one of you again next time!