I hadn’t used the shooting machine for quite some time so I thought it best to set it up and do some test runs to line up the shooting machine and chronograph up with the backstop. The bow is mounted horizontally in the machine.
At 25% of draw length ok, 50% draw length ok, 85% disaster. Another try with a heavier arrow and I had a similar result. The arrows traveled too fast to see the arrow flight and were hitting high on the backstop and snapped in half at the front of the backstop.
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- 4 Archers Paradox Carnage.jpg (35.28 KiB) Viewed 5601 times
Finally the penny dropped, the bow was to be shot off the hand [no shelf] archer’s paradox and the backstop was placed too close, approximately 1.5 meters.
With the backstop moved to three meters and an arrow released from a 20 inch draw was slightly nock high. Moving the backstop to 5.5 meters solved the issue when releasing the arrow from a 26 inch DLPP.
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- 5 Setting Up Backstop.jpg (32.72 KiB) Viewed 5601 times
The whole setup must have been stable as the arrows were hitting the same hole. I released the fourth arrow and it disappeared from sight. It had entered through the same hole as the other three and was hanging out of the back of the backstop. A release aid is incorporated in the machine to eliminate the human factor.
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- 7 Four In One.jpg (66.93 KiB) Viewed 5601 times
The numbers are as follows;
Stored energy;
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- 1 Stored Energy.jpg (94.7 KiB) Viewed 5601 times
Draw force curve showed that the flatbow built up poundage earlier in the draw cycle and tapered off at a gentle rate to 26 inch DLPP with no sign of stacking.
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- 2 D F Curve 26 Inch DLPP.jpg (73.9 KiB) Viewed 5601 times
The static tip flatbow efficiency may suffer in some respect as does the Manchu and similar static tip styled bows which require much heavier draw weights as well as a longer draw.
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- 3 Flatbow Efficiency With Chrony.jpg (35.48 KiB) Viewed 5601 times
I have added some more details illustrating the performance differences between the two bows which were built on the same reflexed form and are 68 inches n to n.
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- 8 Stored Energy Compilation.jpg (162.26 KiB) Viewed 5601 times
Draw force curve comparison;
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- 9 Draw Force Curve Compilation.jpg (85.87 KiB) Viewed 5601 times
Longbow velocity / efficiency with chronograph;
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- 10 Longbow Efficiency With Chrony.jpg (74.66 KiB) Viewed 5601 times
Predicted longbow velocity using a 365grain arrow. Bow efficiency virtually remains the same however arrow velocity will vary.
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- 11 Predicted Values For 38 lb Longbow.jpg (39.19 KiB) Viewed 5601 times
Actual testing with the different mass arrows will either prove or disprove the above.
Daryl.