[cliveanne]

Found this in my files, don't know if it of any use to you, but a friend of mine sent it into another archery forum (Forget which one) some time ago. It is a copy of his own work.

Although this is not strickly about arrow stiffness it may be of some interest to those who advocate the use of bare shaft tuning. In 2000 I was supervising 2 PhD students, who, finding themselves with a little time on their hands, were involved in a discussion regarding the flight and mechanical characteristics of bare and fletched arrows. We decided to test a hypothesis that there was no difference between the two arrow types or the difference was minimal as advocated by coaches at the time. We mounted a Yamaha Alpha X riser with Super Ceramic Carbon Limbs to a modified steel frame previously used for testing balance recovery in subjects with long term head injury. The frame was a triangular construction of 75mm dia steel pipe , 5mm wall thickness secured to 1 cubic meter of isolated (mechanical and acoustic) concrete The frame was secured at 12 locations using 12mm bolts. The draw was achieved by the use of a linea displaced actuator secured to a free motion gimble mechanism The release mechanism for the arrow was a cartel release aid attached to a Z beam load cell (range 100 - 999 N) with a small servo motor activating the release cam. .The load cell activated the release at 18kg load (+/- 0.003 kg) with a draw speed of 0.2 meter/ sec. In order to dertmin the position of the arrow after firing a custom target was printed . The target had 72 radial lines (5 degree increments) and 30 concentric circles at 5mm intervals. This recording system would provide a two co-ordinate location system i.e. distance from the centre in mm and deviation in degrees. The entire mechanism was mounted on micrometer adjustments giving adjustment in all three cardinal planes. We began by shooting a single fletched Easton A.C.E. and aligning the mechanism untill the shot was consistantly in the centre 5mm ring (n= 50 arrows). We then carefully removed the fletchings and repeated the test shots recording the location of the unfletched arrow The unfletched arrow was consistantly 35 - 40mm at 285 degrees away from the centre. We repeated the testing again changing a single perameter on each occasion of a) button stiffness, b) botton position,c) nocking point . At each set of tests, we could not find a configureation that would put the bare shaft and the fletched shaft in the same location. We concluded that fletching an arrow changes the flight characteristics in such a way that setting up a bow with a bare shaft gave dissimular location results. If a bow was to be setup witha bare shaft, then using fletched arrows would give different results.