Is it Really Possible to Paper Tune a Bow?

    In my last post I described the design and construction of a shooting machine to evaluate bow and arrow performance.   Figure 1 shows my results for a set of well used Cabela's Stalker Extreeme arrows.  Arrows C,D, E, and F all shoot through the same hole.  In fact, the target takes a real beating if I repeat more than six shots in a row.   Arrow B, however, is consistently high and to the left.   What is causing this difference in arrow flight?   Would I get similar results with brand new arrows?   Does a particular brand of arrows fly better than others?   A shooting machine is one way to answer these questions, but for many archers this is overkill.  The archery discussion boards are full of debate over the benefits of paper tuning to optimize bow and arrow performance, and paper tuning is simple and inexpensive.  
    I decided to test the effectiveness of paper tuning using the shooting machine to remove the human element from the arrow flight.   WOW did this open up a can of worms.   This post details my results paper tuning three different types of arrows all shot from the same bow with a shooting machine.

    I started by building a simple paper tuning frame out of 1/2 PVC water pipe.   I made the top box of the frame twenty inches square so that it was one inch smaller than a full sheet of newspaper.   The legs were three feet long and could be pushed into the ground or clamped to stool to support the frame.  Newspaper was held onto the frame using simple spring clamps.  I shot from the bow in the shooting machine, through the paper, and into a target/backstop.   

    The paper tuning frame was moved forward/back to produce paper tear 
patterns for shooting distances from two to seven yards.    Figure 3 shows the "expected" tear pattern with the tuning frame seven yards from the bow shooting Beeman carbon arrows with four inch fletching.  The tip of the arrow punctured the paper in the center of the pattern with tears due the fletching radiating out symmetrically from the center.   When shooting from a shooting machine it is interesting to note that each tear pattern (produced with the same arrow) is identical in shape and orientation.   The paper tear is clearly capturing the orientation of the arrow as it passes through the plane of the paper.  

    So what happens if we move the tuning frame closer to the bow?   Most archers know that all arrows are designed with a specific spine to flex during launch.  The static spine on my arrows ranged from 350 to 400.   Static spine is defined as the deflection of the arrow in thousands of a inch when 1.9 pounds of force is applied to the middle of the arrow.  This is different than the actual flex (dynamic spine) of the arrow, but it is possible to say that the 400 spine arrows are more flexible the 340 spine arrows.  All arrows will flex back and forth (oscillate in a wavelike pattern) and rotate during flight in a hopefully reproducible way.   In fact, a paper tear pattern shot two yards from the bow clearly captures the oscillation of the arrow (Figure 4).  The tip of the arrow punctured the paper on the left side of the tear suggesting that the fletching of the arrow passed through the paper almost 1/2 inch to the right of the arrow tip.     

    Many proponents of paper tuning would argue that this tear pattern is due to a poorly tuned bow that is launching arrows with poor tip to nock alignment.  To test this possibility I shot six brand new Maxima Carbon-Express arrows from the bow in my shooting machine at a target 10 yards away.   All six arrows hit the target in the same place (Figure 5).   Based on this test the bow looks like it is pretty well tuned.  I next shot several different types of arrows at a 10 yard target and compared the point of impact to a bare shaft arrow.  Without fletching the bare shaft has much less chance to stabilize in flight and is a good indicator of string-rest alignment.   The bare shaft hit the target in perfect alignment with the fletched arrow.   Again, the bow tune looks very good.

    Are my "poor" my tuning results at close range due to the expected oscillation of the arrow.   How big are these oscillations?  The tear pattern in Figure 4 suggests that the arrow may be flexing with an amplitude of over 1/2 inch. The internet has several videos showing slow motion arrow flight with tremendous flex in the arrow shaft (http://www.youtube.com/watch?v=CO102jz8sFM), but it is hard to put these videos in context with real hunting arrows.

    To answer these questions I decided to try and capture the motion of my arrow shafts on video at a range of 4 to 7 yards.   Ideally, you would use a high end video camera shooting 1000 frames a second to capture the arrow flight.   I took a different approach and installed illuminated nocks on my arrows and recorded my shots at 60 frames a second using a Kodak PlaySport consumer video recorder.   At this recording speed the camera records an image every 10 milliseconds.  At my bow speed of 240 ft/second the camera will capture about 30 inches of arrow flight per video frame.  This will result in an image of the arrow as an illuminated blur. 

    Figures 7 through 9 show arrows captured in flight and the green trace of the illuminated arrow nock.   For all arrows the video clearly captures the oscillation of the arrow at a distance of seven yards from the bow.   The amplitude of the motion is similar for all arrows and seems to be on the order of one arrow shaft diameter.  This is not that unexpected since all of the arrows have close to the same spine.  All arrows are moving back and forth by at least 1/4 of an inch and if you squint at the image you might convince yourself that the oscillation is becoming less with distance.  At least one full oscillation is visible in each image suggesting one oscillation every 30 inches and an oscillation frequency of 100 oscillations per second.   For a shooting distance of 10 yards the arrow would oscillate about 12 times from launch to the target.   These calculations are only approximate because the frequency and amplitude of arrow motion will decease with flight time.   The bottom line is that real hunting arrows do have significant horizontal motion for flight distances out to ten yards and this can make paper tuning tricky.   My two yard paper tune results are likely due to the flex of my arrows, not poor bow alignment.  Because the flex of the arrow oscillates in a wave pattern we also expect nodes in the oscillation.  Nodes would occur every 30 inches where the horizontal arrow motion is zero or very small.   Depending on where you place the paper tuning frame you may or may not be at a node.

    To test the idea that nodes in arrow oscillation influence paper tear results, I shot through the paper at increasing distances from 4 to 21 feet (Figure 10).   The tear patterns change dramatically with distance!  However, I get good tear patterns at 3, 7, 11, and longer than 14 feet.  This experiment has captured the oscillation of the arrow.    The nodes in arrow flight, the position where the tip and fletch are in alignment,  occur at intervals of every four feet.  This distance is consistent with my pictures of arrow flight (Figures 7-9).   If you pick the wrong distance to paper tune you will get very wrong results.  Paper tuning does not seem particularly helpful?

    In my opinion, a better approach to tuning a bow is walk-back shooting.   Shoot two or more arrows at close range at a vertical line on a target.   Now walk back at least 10 yards and shoot another group of arrows at the same line.   A bow in good horizontal tune should produce groups that align in the vertical.   Figure 11 shows my results with the arrow rest too far left, too far right, and in the well tuned position.   In my hands, this is an equivocal and easy test to perform.   It is currently winter in Maine so I am shooting indoors and am limited to a 12 yard shooting distance.   When tuning outdoors I like to walk back forty or more yards.

    Just for fun, I repeated the paper tuning distance experiment with my arrow rest too far right (Figure 12) and too far left (Figure 13).  These conditions resulted in very poor shooting results as shown in Figure 11.  The paper tune results are not bad at 7 and 10 meters, poor at most other distances, and not particularly helpful in correcting alignment problems with the bow.

    As I tune other bows I am going to skip paper tuning in preference for bare shaft and walk-back tuning.  Paper tuning may help identify substantial problems with bow alignment, but it certainly isn't a substitute for group testing arrows at multiple distances.












Figure 1.  Shooting Machine Results.

Figure 2.   Paper tuning frame made of PVC pipe.

Fig. 3. Typical Paper Tune 

Figure 4.  Paper tear at 2 yards shooting distance.



Figure 5. Shot group for six arrows.   The arrow is in the hole hit by all six arrows!











Figure 6.  Bare shaft and fletched shaft group.  Notice that the bare shaft flies a bit higher due to less drag.


Figure 7.  Beeman ICS Hunter Arrow, 340 spine.  The 
green trail is due to the 10 millisecond exposure of the 
illuminated nock.  The yellow line was added as a straight
line references.  The arrow is also rotating during flight.



Figure 8. Cabela's Stalker Extreme Arrow, 400 spine.


Figure 9. Carbon-Express Maxima Arrow, 400 spine.   Noticethat the 400 spine arrows due show more oscillation in flight.


Figure 10. Paper tune tears as a function of shooting distance in feet.  The yellow stars shows the tip puncture.  The numbers next to each tear is the shooting distance to the tuning frame.

Figure 11.   Walk back tuning results for arrows shot at 2 yards (blue line) and 12 yards (red line).

Figure 12. Paper tune tears as a function of shooting distance with the rest too far right.  The yellow stars shows the tip puncture.  The numbers next to each tear is the shooting distance to the tuning frame.

Figure 13. Paper tune tears as a function of shooting distance with the rest too far left.  The yellow stars shows the tip puncture.  The numbers next to each tear is the shooting distance to the tuning frame.


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