Testing a flight bow and a new arrow. The first couple of shots went well, and the new arrow was good (more about that later).
Next shot BANG and the bow disintegrated spectacularly. The entire flight bow build is on my Youtube channel and this first video shows the defect in the otherwise gorgeous log
Inspecting the debris and sawing through where the belly defect had been filled with a V shaped patch, showed a bit of a cavity at one end of the patch. Maybe that was the weakpoint where the break initiated. Studying the grain pattern in that cross section picture it looks as if the trunk may have originally been two limbs that grew together, it couldn't be seen from the outside. We never did find the nocks!
Back to the flight arrow!
This was the first flight arrow I'd made with the balance point slightly behind the geometric centre. Turkish flight arrows are like that and other accounts say it's a good thing. However I'd been put off trying it as I'd seen a wild arrow with the balance point behind centre fly extremely eratically, turning at right angles, diving and climbing and finally settling as it lost speed.
The new arrow had the balance point about 5mm behind centre and it flew fine. I think the difference between this and the wild arrow was the taper in the shaft (the wild one being virtually parallel).
My arrows are much thinner for about 1/3 of the length from the front. There are several ways of viewing what this does aerodynamically for stability. You can say the extra width at the back end is effectively like extra fletching, or the extra diameter increases drag at the back. Either way it helps stop the back end trying to go sideways. My thoughts about flight arrows are more qualitative that quantitative and are just my attempt to explain what and why makes a good arrow... you may dissagree and I'm not going to argue or attempt to defend my views. BUT, if someone finds them useful or though provoking, that's good.
I think the first 1/3 of a flight arrow (at the pointy end) is mostly there to stop the arrow falling off your hand or arrow shelf! Obviously that's a slight over simplification, but the bending forces early in the loose are relatively small as the arrow path is still fairly straight. The arrow only needs to bend round the bow as the string starts to get closer to the belly. You can test this youself by watching the sideways movement of the poit as you slowly let the arrow down from full draw. Or you can draw it out to scale and see how the angle of the arrow changes (All this assumes a bow that has the arrow pass about 1/2" off centre, ELBs etc).
Anyhow, the result of this is that you can have a nice stiff back end, a thin front end footed with a stiff heavy wood, a tiny point, small fletchings (say 2mm long 6mm high) and a balance point just behind centre. It should still fly well. It is virtually impossible to make an arrow that is sufficiently stiff but is too light. People will shout "Heresy", but you'll struggle to get below about 400 grains. People go on about 10 grains per pound (gpp) but that's nonsense other than for hunting arrows. 5gpp is no problem and I've gone much lower. Note bow poundage is no reliable indicator of accelleration on the arrow of launch speed. A 50# flight bow can out perform a 100# warbow and enven with "normal" bows a 70# doesn't shoot twice as fast as a 35#
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