https://matteocampagna.com/en/registry/equipment/arrow-shaft-boundary-layer-instability Changes to this claim in Matteo Campagna's evidence registry: its status, its year-by-year history, revisions of the page. en-gb https://matteocampagna.com/en/registry/equipment/arrow-shaft-boundary-layer-instabilityThe answer comes from a single calculation, from 2018, by a Japanese group working on a bare shaft without fletching at recurve speeds: around 60 metres per second, with a Reynolds number between ten and twenty thousand based on the diameter and a shaft about a hundred and twenty diameters long. In the layer of air next to the shaft only the non-symmetric disturbances grow: the two-lobed one, already in the front part, and the bending one, which keeps growing all the way to the nock, while the symmetric disturbance never grows. At lower speeds only the bending mode remains. The group velocity is always positive, so disturbances travel only towards the tail and whatever happens behind cannot destabilise the part of the arrow further forward. The amplification stays small all the same, with an N factor below 2.5 even at the highest speed, and the shape of the point matters only at the front: after about seventy radii the difference between a tapered point and a bulge point disappears. There is an exception right there, though: behind the bulge point, where the flow separates, all disturbances grow over about three radii, the symmetric one included, with a rough estimate of N around 4.5, in a region where the authors themselves say their method is not suited. It is all calculation, on a shaft without fletching, which means without the very part of the arrow that disturbs the air most at the tail; the authors describe it as consistent with their wind tunnel tests, where the boundary layer stayed laminar, but no measurement has checked the individual disturbances. On the state of the flow, an Australian water channel experiment from 2011 actually points elsewhere: with the standard bullet point the air turns turbulent at about 81 millimetres along the shaft for an arrow at 85 metres per second, and behind the short bulge point it stays turbulent along the whole shaft.claim:strato-limite-instabilita-asta:revision:2026-10-08:2Thu, 08 Oct 2026 08:00:00 GMT https://matteocampagna.com/en/registry/equipment/arrow-shaft-boundary-layer-instabilityclaim:strato-limite-instabilita-asta:new_claim:2026-09-14:trasferitoMon, 14 Sep 2026 08:00:00 GMT