Sagitar Posted October 11, 2010 Report Share Posted October 11, 2010 My photo of a friend shooting a "wheelie" bow in a County match last week. Quote Link to comment Share on other sites More sharing options...
phipck Posted October 11, 2010 Report Share Posted October 11, 2010 thats a rather snazzy compound bow, far far too posh for me i havent even managed to obtain a recurve bow yet! Quote Link to comment Share on other sites More sharing options...
Tony Posted October 11, 2010 Report Share Posted October 11, 2010 What's the deal with the wheels..... Is it so the wire can run freely? Quote Link to comment Share on other sites More sharing options...
phipck Posted October 11, 2010 Report Share Posted October 11, 2010 they are lobed in shape, so perform as a cam, this means that as you draw the string the resting point at full draw is lighter and easier to hold, but as the string is released the cams multiply the force and provide far superior power. the equivilent of punching above your weight bit of info http://en.wikipedia.org/wiki/Compound_bow Quote Link to comment Share on other sites More sharing options...
Tony Posted October 11, 2010 Report Share Posted October 11, 2010 More to this then meets the eye...... Stunning picture by the way. Quote Link to comment Share on other sites More sharing options...
phipck Posted October 11, 2010 Report Share Posted October 11, 2010 far far more, the way i discribe it is "if robocop had a bow this is what he would use". the picture is probably the exact moment the cams cut in. Impressive as always Sagitar Quote Link to comment Share on other sites More sharing options...
Tony Posted October 11, 2010 Report Share Posted October 11, 2010 Question for you..... As the flight passes the bow it must deform since it's running against a guide.... How much is this factored into the performance of the arrow. Quote Link to comment Share on other sites More sharing options...
Sagitar Posted October 11, 2010 Author Report Share Posted October 11, 2010 More to this then meets the eye...... Stunning picture by the way. Thanks Tony, it wasn't easy. It was a very dull, rainy day and the light was very flat. Taken with a monopod mounted Canon EOS-1DIII with a 50mm lens at a subject distance of 4.5 metres with subsequent cropping. Aperture value f/4.0; shutter speed 1/1000 sec; ISO 400. I deliberately underexposed by one stop in order to get some detail in the sky, then selectively lifted the foreground brightness and contrast in post processing. f/4.0 was chosen to give enough depth of field to cover the subject at the taking distance, but still give enough subject isolation from the background. I think the balance is OK on screen but there is probably not enough subject depth for a large print. 1/1000 sec is fast enough to catch the action, but doesn't stop everything dead, so there is a good impression of speed in the string, wheels and arrow. Quote Link to comment Share on other sites More sharing options...
Tony Posted October 11, 2010 Report Share Posted October 11, 2010 Reads like a very complicated but visually rewarding talent.... I'm talking photography by the way..... I dabbled at it some years back, well actually loads of years back but i had no experience or guidance so with poor results i focused on a different hobby "no pun intended". Quote Link to comment Share on other sites More sharing options...
Sagitar Posted October 11, 2010 Author Report Share Posted October 11, 2010 Question for you..... As the flight passes the bow it must deform since it's running against a guide.... How much is this factored into the performance of the arrow. There is more than one answer to this. The first, for a simple bow, is that there is a phenomenon know as "archers paradox" in which the arrow bends as a result of the force applied by the string and in which this bending of the arrow is used to get it to clear the bow. Part of the skill of setting up a bow (what we call tuning) is the selection of an arrow of appropriate stiffness and the slight angling of the arrow relative to the bow, in order to get it to clear the bow without touching anything as it goes past. The second, is that the arrow rest can be designed to touch only the shaft of the arrow, with discontinuities where the fletchings can pass through without touching. The third, for more complex bows, is that the arrow rest can be moved away from the arrow, once the arrow is in motion. In this case the rest stays in place as the shaft slides along it, but drops out of the way just before the fletchings get to it. Googling will show lots of high speed video pictures of what happens. Quote Link to comment Share on other sites More sharing options...
Tony Posted October 11, 2010 Report Share Posted October 11, 2010 This is bloody interesting stuff..... I'm going to Google all day tomorrow Quote Link to comment Share on other sites More sharing options...
Sagitar Posted October 11, 2010 Author Report Share Posted October 11, 2010 This is bloody interesting stuff..... I'm going to Google all day tomorrow An arrow has much in common with elements of the car structures that you know. It is either a long dowel of wood or plastics or a long tube of metal, or carbon fibre or a composite of the two. Its resistance to bending is a function of its length, its material strength and its polar moment of inertia. Its polar moment of inertia can be varied by changing the diameter or material of the arrow or, in the case of the tube type, by varying the wall thickness. Changing the material, length, diameter or wall thickness also changes the weight of the arrow. The arrow has a point at the front end, made of a material significantly heavier than the material of the arrow; brass, steel, or even tungsten. It has a nock and fletchings at the back, usually of very light materials. So an arrow with point, nock and fletchings fitted has a point of balance that is forward of the centre of the length of the arrow. Some arrows are tapered or even barrel shaped in order to improve their aerodynamics. The stiffness of the arrow is measured by placing it on knife edges that are a standard distance apart and suspending a standard weight from it at a point mid-way between the knife edges. The deflection produced is a measure of the stiffness of the arrow. When the bowstring is released by the archer it applies force to the back end of the arrow. This force is resisted by the inertia of the arrow and particularly by the mass of the point at the front end of the arrow. The effect is that crippling stresses are set up in the arrow which cause it to bend. You can get a sense of what happens by taking a flexible plastics foot-rule and pushing its ends together between your open palms - it bends. The arrow is unrestrained once the string is loosed and since, like any long column it has vibration nodes, it flexes to and fro about these nodes at a natural frequency that is a function of its weight and stiffness etc., while the amplitude of the flexure is affected by the force applied by the bowstring. The flexing about the nodes may take a shallow "U" shape or a shallow "S" shape and this can be seen in high speed videos of arrow release. If you can imagine a simple stick bow, the arrow touches the side of the bow and the string is centred behind the bow such that the arrow cannot line up with the centre of the bow; it is always angled off to one side. Nevertheless, by choosing the appropriate combination of weight and stiffness for the arrow it can be bent around the bow in such a way that it passes the bow without interference and flies on a course that is straight forward from the bow rather than off to one side. This is know as archers paradox. A heavy bow with a high draw weight needs a stiffer arrow than a light bow. Arrow manufacturers supply tables that enable the choice of suitable arrows, but it is still necessary to fine tune arrow to bow if you want arrows to fly well and strike the target in a tight group. Quote Link to comment Share on other sites More sharing options...
Tony Posted October 12, 2010 Report Share Posted October 12, 2010 Until reading this i would never have thought there was so much involved in archery, i'm truly gobsmacked..... Quote Link to comment Share on other sites More sharing options...
Rich Posted October 12, 2010 Report Share Posted October 12, 2010 Stunning photo as usual Quote Link to comment Share on other sites More sharing options...
phipck Posted October 12, 2010 Report Share Posted October 12, 2010 Until reading this i would never have thought there was so much involved in archery, i'm truly gobsmacked..... keep googling.....theres so much that can be involved! Quote Link to comment Share on other sites More sharing options...
Sagitar Posted October 12, 2010 Author Report Share Posted October 12, 2010 Until reading this i would never have thought there was so much involved in archery, i'm truly gobsmacked..... keep googling.....theres so much that can be involved! A typical high speed shot there are lots of others. Quote Link to comment Share on other sites More sharing options...
phipck Posted October 12, 2010 Report Share Posted October 12, 2010 as always i do a bit of searching from peoples links......kind of on topic but completely not at the same time he obviously cant be, but what a shot! Please wait a few moments for Video to Load! Quote Link to comment Share on other sites More sharing options...
Tony Posted October 12, 2010 Report Share Posted October 12, 2010 Until reading this i would never have thought there was so much involved in archery, i'm truly gobsmacked..... keep googling.....theres so much that can be involved! A typical high speed shot there are lots of others. Looking at that i'm surprised the arrow flies anywhere near straight.... Is it the case the modern bow exerts more force or has it always been the case the arrow distorts like that. Quote Link to comment Share on other sites More sharing options...
Sagitar Posted October 12, 2010 Author Report Share Posted October 12, 2010 Looking at that i'm surprised the arrow flies anywhere near straight.... Is it the case the modern bow exerts more force or has it always been the case the arrow distorts like that. It has always been like that. I am surprised that you are surprised. The centre of mass follows a predictable trajectory (on a windless day) and the system oscillates about that centre of mass. If everything is set up right, the whole flight follows a predictable and consistent pattern. It is quite like a motor car with good geometry. Did you see Nicky Hunt win her gold medal at the Commonwealth games last week? She hit the ten ring 12 times in 15 arrows. shooting at a distance of 70 metres. The ten ring is 12.2 cm diameter (that's about five inches diameter in old money). You can't group that tightly if the arrows are not flying consistently. Quote Link to comment Share on other sites More sharing options...
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