Divecon, the Turbulator disrupts the air flow, which increases the pressure exerted by the air on the fletching. This increases the stabilizing effect of the fletching, which allows you to use a smaller amount of fletching to attain the same degree of stabilization in flight, but that is not the only purpose of the A&A fletching.
Using smaller fletching offers many benefits, and there's a pretty comprehensive thread about the A&A fletching. Here's the link.
http://tradgang.com/noncgi/ultimatebb.php?ubb=get_topic;f=1;t=057257#000000 On an arrow that is already well tuned (correctly bare shaft tuned), using the minimum fletching required to overcome the wind shear created by the broadhead gives a higher FOC. As one approaches the level of Ultra-EFOC reducing shaft weight at the arrow's rear becomes a major factor in the degree of FOC change you and attain.
Ultra-EFOC is (Study defined) as being 30% and above. The reason being, it's really difficult to reach 30% and above FOC without making a concentrated effort to attain FOC.
Just putting high tip weight on most light weight shafts will get you into the EFOC range, but the higher the FOC gets the more increase in tip weight it takes to make the same degree of FOC increase. As Ultra-EFOC is approached it is more 'productive' to be reducing weight at the shaft's rear than adding additional tip weight. That's because the rear leaver arm (the distance from the nock to the balance point) gets longer as the FOC increases, and the forward lever arm, from the arrow's front to the balance point) gets shorter. The longer the leaver arm the more force a given amount of weight will exert.
As for close shots, a well tuned Ultra-EFOC bare shaft will recover from paradox incredable rapidly; it will certainly be showing straight impact into the target within 3 yards, and usually at even closer ranges. By adding a broadhead and then the minimum fletching required to overcome the broadhead's wind shear effect equally rapid recovery from paradon is retained. That's one of the things I most like about EFOC and Ultra-EFOC arrows; they show faster paradox recovery than normal or high FOC arrows, giving greater penetration on close range shots.
As for longer range shots, because EFOC/Ultra-EFOC arrows recover from paradox much more rapidly than normal/high FOC arrows, and the smaller fletching required to stabalize the broadhead in flight has less surface area, they have less drag. The rapid paradox recovery means less of the bow-derived energy of the arrow is wasted by paradox. As the arrow proceeds downrange, the smaller fletching not only has less drag it drains less energy when any flight correction is required. Because the EFOC/Ultra-EFOC arrow has a longer 'rear leaver' (or rear stearing arm, if you prefer) the fletching requires less 'applied force' to overcome any flight instability required by such things as the broadhead's wind shear and changes in air flow/pressure caused by changes in wind direction. All this retained arrow energy is now used to produce 'productive work'; higher retained arrow velocity and arrow force.
If you take 2 broadhead-tipped arrows that are identical in all external dimensions (except for the fletching, as the lower FOC arrow will require more fletching to overcome the broadhead's wind shear), and of equal mass (weight) and equally well tuned but having a large difference in FOC and shoot them at longer ranges you will see a very noticable difference in trajectory. The arrow having very high FOC will shoot noticable flatter. This is because of the additional 'useful energy' the arrow has attained from the bow and retained as it traveled downrange. Make up 2 such arrows yourself; one at normal FOC and one at EFOC and try that simple test at 40 meters or so. The difference in trajectory is very noticable.
In the Study's testing, all test shots are conducted within 30 minutes of the animal expiring. That's because early testing showed a difference between the results from shots taken on very fresh tissues and those taken after the animal had been dead for a longer period of time. Starting in 1982 I began to keep a seperate detailed database of each big game, bow killed animal. This information is used as a cross reference between the results observed on the test shots and the outcomes observed on real hunting shots. While the bow killed database has only 629 animals, whereas the test shot database(s) contains thousands, there is excellent correlation between the shot outcomes between the test shots and the actual bow kills. I wish I had started that bow killed database 25 years sooner, with my first deer. It would be very interesting to have the performance of those early arrow setups to also compare against.
Hope that helps a bit,
Ed
Topic: Barely Above Heavy Bone Threshold Ultra-EFOC Arrow (Read 11282 times)
