Tag Archives: up- and downhill shots

Recurve Barebow Shots Up- and Downhill (Part 2)

This topic is burgeoning. I got an email from another Barebow Recurve archer on a similar topic while writing the last post and there are quite a few loose ends that still need to be tied up here. Also, since I pointed out that the cut chart I included in the last post was a “simplified one” somebody just had to see one that wasn’t simplified. So, let’s get that out of the way right now.

This chart includes the fact that on downhill shots, gravity is accelerating the arrows making their arcs flatter and on uphill shots gravity is decelerating the arrows making their arcs more pronounced. For example: a 50 m shot at an angle of 35° uphill would be shot as if it were a 42.3 m shot but if that angle were downhill it would shot as if it were 39.8 m. Note A 35 degree shot is quite extreme by American standards but not so much by European standards. (Europeans like shots you have to tie a rope around your waist so you don’t fall off of the cliff as you shoot from it.) The “simplified chart” has this shot at 41 m which would be a 1 m error either way, not a lot to worry about.

Note that the two charts are arranged differently: one has degrees vertically, the other horizontally. If you thought I would remake one of these for consistencies sake a blog that doesn’t make me a dime, you need to think again.

Onward and Upward
Stringwalking in Barebow makes things different, but the physics of gravity isn’t one of the differences. The simplified cut chart gives a reasonable number for the crawl setting for an “angled” shot. Using the example above, a 50 m shot at a 35° angle (uphill or downhill) should be attempted with whatever anchor and crawl you would use for a 41 m shot.

This is a starting point! You really need to check these things out. For one, when you take a crawl, you are detuning your bow substantially. Different crawls represent different tunes, in effect. This is why tuning for Barebow is different from tuning for Olympic recurve. Even using a “three fingers under” string grip requires a different tiller setting than the more typical Mediterranean string grip (one over, two under).

The more extensive chart is not needed unless your groups compare to those of Compound Unlimited archers, but those “cut distances” need to be checked. (Do I need to say it again?) The second reason they need to be checked carefully is anything greater than a very shallow angle for a shot can distort the archer’s form resulting in quite varied results (depending on the amount of distortion).

There are a number of compensations that Barebow Recurve archers make for these shots. One of those is to open their stance greatly for downhill shots and close them greatly for uphill shots. The open/downhill posture makes room for the bottom limb to go between the legs, instead of hitting the forward leg if a square stance were employed. Opening your stance shortens your draw length which actually helps with those downhill shots (shorter draws make arrows fall “short” which is what we want), but they also make shots more variable and, hence, more difficult. The ideal is keeping your upper body geometry consistent from shot to shot, but this is virtually impossible at higher angles of launch. The net effect of this distortion of the full draw position is to shorten the draw. By using a very closed stance on those difficult uphill shots, the closed stance lengthens the draw to compensate for the draw shortening described above, making the archer more consistent. (If you do not understand this effect, take a very light drawing bow and at full draw tilt up- and downhill and see what happens to your draw length. (You may need a helper to watch your arrow point or set up a video camera.) Hold the arrow level, again at full draw, and swing left and right (in effect changing to open and closed stances). (Go as far as you can.) Do these things, see what happens, they are more explicative than any thousand words you could read!


Filed under For All Coaches, Q & A

Recurve Barebow Shots Up- and Downhill (Part 1 … )

I got an email from a colleague regarding how to deal with shots that are up- and downhill whilst shooting Recurve Barebow. Here is the question:

“I have a question for you. The standard “cut charts” for distances and shot angles used in field archery are based on the mathematical computation of measuring the hypotenuse of a triangle but shooting a level distance (the long leg of the triangle).
“However, these charts don’t work for me because I shoot a wimpy bow with that produces very slow fps arrows (aka slow). Once I go beyond my POT distance (35m), I am shooting an arc, not a straight line. So I end up ADDING rather than cutting the distances.
“Can you or your stable of experts address this in Archery Focus? Is there a mathematical formula I can use? Trial and error (mostly errors) is costing me a lot of arrows…

And here is my convoluted answer and some of the “back and forth” conversation that followed:

* * *

Note The phrase “Once I go beyond my POT (point-on-target) distance (35m) … I end up adding rather than cutting the distances.” made me suspicious that the archer in question used a gap shooting technique beyond her “point on” which would hopelessly complicate the situation. But being fearless, I just plowed on!

Arrows never fly in a straight line; all arrows travel in an arc (technically it is a “decaying parabola”). Some arcs are just shallower than others in that higher arrow speeds produce flatter arcs. This is simply a manifestation of the fact that when you shoot on the level, gravity is acting only downwards (sideways) on your arrow and this fact forms part of the explanation regarding how to adjust for up- and downhill shots. When you shoot up- and down hill, only part of the force of gravity works as it does on the level, and part of it is applied to make the arrow go faster or slower. Think of arrows going straight up or down, Under those conditions gravity doesn’t bend the trajectory of the arrow into an arc at all. Since only part of the gravitational force is making the arrow bent on an angled shot, you need to plan on a sight setting for part of the distance being shot. Here is a standard “cut chart” used for figuring out the horizontal distances to the target (corresponds to the part that gravity is acting sideways to the trajectory).

This is a simplified chart that ignores the arrow slowing and speeding up effects of gravity. Angles are down the left side, distances across the top. A 50 m shot at 35 degrees is basically only a 41 m shot according to this chart.

If you were shooting with a sight, a program like Archer’s Advantage can calculate all of your sight marks for whatever angle you shoot. Since you aren’t using a sight, this gets complicated.

Have you ever seen a “sight tape”? Just in case, I attached a photo. The strips at the bottom of the printout are cut out and attached to the sight bar. You can see from the markings that the spacings get wider as you go to longer and longer distances. Look at the difference between 60 and 70 yards as compare to between 20 and 30 yards.

When one graphs out crawls, though, one gets a straight line relationship between distance and length of crawl. In other words, the difference between any two identical distances is the same amount of crawl.

Now, given that there is that built in distance, you are going to have to do a little gymnastics here.

Once you get to your POT distance, do you shoot off the shelf, aim high, or lower your anchor? (From your question I suspect that you just aim high for distances beyond your POT, a form of gap shooting. This makes things incredibly difficult, though. For the approach I am thinking of, it is better to go to a lower anchor.

The ideal situation (if using multiple anchors) is to have a low anchor (for long distances) and a high anchor (for shorter distances) and a set of crawls for each (actually the crawls for both anchors will be very similar in that the crawl for 5 m/yd less than POT will be roughly the same for both anchors). When you start to shoot up- and down hills, you would use the anchor for the target distance, but you would take a slightly greater crawl (taking a crawl for a closer target). What your cuts will be are roughly the distance calculated as the cosine of the angle of the shot. (This is straight physics and geometry.)

And, as you know, your bow isn’t gonna be anywhere near ideal for all of the assumptions made. So, you are going to have to do some experimentation. (Do you have an angle finder?)

* * *

To which the questioner responded:

“Wow, my head is spinning.

“Yes, I had already figured out through experience that there is a direct relationship between distance and length of crawl.
“This year, once I get to POT, I start using the plunger and rest plate for sighting points.  Last year I did different combinations of face walking and string walking and it was too much for me to remember on the FITA Barebow courses, which don’t allow written memoranda.  I also had a lot of trouble getting a replicable anchor once I dropped below my upper teeth, because how much tension I had in my lower jaw varied all over the place.
“The other thing I am wondering about is the arrow trajectory and its impact on crawls past POT or at least the zenith of the shot.  I don’t think my arrows travel in a nice curve, instead they go upwards most of the way and then drop steeply at the end.  I am planning to play around with walk-back shooting to see if I can figure this out, and whether or not it matters.
“What does the last column of your attachment mean? For less than 10m, because I don’t want to crawl anymore, I just aim off a little.

* * *

That’s for people with sights.

When you say “I am wondering about the arrow trajectory and its impact on crawls past POT” you are making me wonder because to go past your POT, there is no crawl. You either aim off (gap shoot) or switch to a lower anchor and crawl down from your new POT.

The system I recommend now is to use the most comfortable anchor you have (this is usually the finger in the corner of the mouth version of a “high anchor”) and figure out your POT(High Anchor) distance and then all of your crawls down (inward) from there. Then, to deal with distances past your POT(High Anchor), you adopt a different, lower anchor (usually the Olympic-style anchor) and find your new POT, the POT (Low Anchor), then you figure out your crawls down from there. If … if … those two series overlap, you are generally good to go.

This has the “feature” that the crawls for the two anchors are generally very close, so five yards inside both the POT(High Anchor) and the POT(Low Anchor) are about the same crawl (why I do not know), so this reduces the amount of memorization.

If there is a gap between the two sets of crawls, we try to bridge that by aiming high off of the POT(High Anchor). All this requires you to know, if there is say a five yard gap between the two series, is what a shot lands at five yard past your POT distance with a zero crawl. If your arrow lands five rings low under those circumstances, then you need to aim one ring high for every yard you are past your POT. (I picked those numbers for simplicity, of course, your situation will be much more complicated (much). ;o)

Every anchor has its own POT distance. And there are all kinds of anchors to chose (you have tried face walking you tell me). The FITA Field experts work like crazy to get a POT of 50 m which is their longest shot (for the unmarked). So they have one set of crawls for the entire course. So, your trepidation was certainly shared by others!

And we have yet to get to the crux of the aiming up and down hills issue.

PS When you shoot with a sight, there is a point in space where the arrow rises up from its position below the line of sight to the line of sight. Typically for me that was around 11 or 12 yards out. (If you check one of those sight tapes I sent you, the tape stops at that point as there are no more markings that mean anything.) When targets are inside of that distance, you have to set your sight for an even higher distance to work. For example, I often set my sight for 52 yards for a 4-yard shot. The arrow is still rising to the line of sight the aperture is in, so the aperture has to be set much higher to get the bow low enough to hit anything. That is what those boldface numbers are on the right side of the AA printout, shooting targets inside your crossover distance.

There is so much more to this discussion, I will follow-up with another post.







Filed under For All Coaches, Q & A